BISPECIFIC T CELL MOLECULES ACTIVATED BY A PROTEASE

Description

Field of the Invention

[0001] The present invention generally relates to novel protease-activatable antigen-binding molecules that comprise an anti-idiotype-binding moiety which reversibly masks antigen binding of the molecule. Specifically, the invention relates to T cell binding molecules having an anti-idiotype-binding moiety that masks the CD3-binding moiety until cleaved by a protease. This allows the CD3-binding moiety to be inaccessible or "masked" until it is in proximity to a target tissue, such as a tumor, e.g., tumor-infiltrating T cells. In addition, the present invention relates to polynucleotides encoding such protease-activated T cell binding molecules and idiotype-specific polypeptides, and vectors and host cells comprising such polynucleotides. The invention further relates to methods for producing the protease-activated T cell binding molecules of the invention, and to methods of using the same, e.g., in the treatment of disease.Background

[0002] The selective destruction of an individual target cell or a specific target cell type is often desirable in a variety of clinical settings. For example, it is a primary goal of cancer therapy to specifically destroy tumor cells, while leaving healthy cells and tissues intact and undamaged.

[0003] An attractive way of achieving this is by inducing an immune response against the tumor, to make immune effector cells such as natural killer (NK) cells or cytotoxic T lymphocytes (CTLs) attack and destroy tumor cells. In this regard, bispecific antibodies designed to bind with one "arm" to a surface antigen on target cells, and with the second "arm" to an activating, invariant component of the T cell receptor (TCR) complex, have become of interest in recent years. The simultaneous binding of such an antibody to both of its targets will force a temporary interaction between target cell and T cell, causing activation of any cytotoxic T cell and subsequent lysis of the target cell. Hence, the immune response is re-directed to the target cells and is independent of peptide antigen presentation by the target cell or the specificity of the T cell as would be relevant for normal MHC-restricted activation of CTLs.

[0004] In this context it is crucial that CTLs are activated only when in close proximity to a target cell, i.e., the immunological synapse is mimicked. Particularly desirable are T cell activating bispecific molecules that do not require lymphocyte preconditioning or co-stimulation in order to elicit efficient lysis of target cells. Several bispecific antibody formats have been developed and their suitability for T cell mediated immunotherapy investigated. These include BiTE (bispecific T cell engager) molecules (Nagorsen and Bäuerle, Exp Cell Res 317, 1255-1260 (2011)), diabodies (Holliger et al., Prot Eng 9, 299-305 (1996)) and derivatives thereof, such as tandem diabodies (Kipriyanov et al., J Mol Biol 293, 41-66 (1999)), DART (dual affinity retargeting) molecules, (Moore et al., Blood 117, 4542-51 (2011)), and triomabs (Seimetz et al., Cancer Treat Rev 36, 458-467 (2010)). WO2016014974 describes activatable anti-CD3 antibodies and methods of using the same. Carreno et al 1991 Hum Immunol 33(4):249-58 (1992) describe cross-species reactivity of the anti-idiotype anti-OKT3 cascade.

[0005] The task of generating bispecific molecules suitable for treatment provides several technical challenges related to efficacy, toxicity, applicability and produceability that have to be met. In instances where the bispecific molecule targets an antigen on a target cell, e.g., a cancer cell, that is also expressed in non-target tissue, toxicity can occur. There is thus a need for efficacious T cell activating bispecific molecules that unleash full T cell activation in the presence of target cells but not in the presence of normal cells or tissue.SUMMARY OF THE INVENTION

[0006] The invention generally relates to T cell activating bispecific molecules that are activated selectively in the presence of a target cell.

[0007] In one aspect, the invention relates to a protease-activatable T cell activating bispecific molecule comprising (a) a first antigen binding moiety capable of specific binding to CD3, wherein the first antigen binding moiety is an antibody or fragment thereof; (b) a second antigen binding moiety capable of specific binding to a target cell antigen, wherein the second antigen binding moiety is an antibody or fragment thereof; and (c) a masking moiety covalently attached to the T cell bispecific binding molecule through a protease-cleavable linker, wherein the masking moiety is capable of specific binding to the idiotype of the first or the second antigen binding moiety thereby reversibly concealing the first or second antigen binding moiety, wherein the masking moiety is an anti-idiotypic scFv.

[0008] In one embodiment, the masking moiety of the protease-activatable T cell activating bispecific molecule is covalently attached to the first antigen binding moiety. In one embodiment the masking moiety is covalently attached to the heavy chain variable region of the first antigen binding moiety. In one embodiment the masking moiety is covalently attached to the light chain variable region of the first antigen binding moiety. In one embodiment the masking moiety is an anti-idiotype scFv.

[0009] In one embodiment the protease-activatable T cell activating bispecific molecule comprises a second masking moiety reversibly concealing the second antigen binding moiety.

[0010] In one embodiment the protease capable of cleaving the protease-cleavable linker is expressed by the target cell. In one embodiment the second antigen binding moiety is a crossover Fab molecule wherein either the variable or the constant regions of the Fab light chain and the Fab heavy chain are exchanged. In one embodiment the second antigen binding moiety is a crossover Fab molecule wherein the constant regions of the Fab light chain and the Fab heavy chain are exchanged. In one embodiment the first antigen binding moiety is a conventional Fab molecule. In one embodiment the protease-activatable T cell activating bispecific molecule comprises not more than one antigen binding moiety capable of specific binding to CD3. In one embodiment the protease-activatable T cell activating bispecific molecule comprises a third antigen binding moiety which is a Fab molecule capable of specific binding to a target cell antigen. In one particular embodiment the third antigen binding moiety is identical to the second antigen binding moiety. In one particular embodiment the third antigen binding moiety is not identical to the second antigen binding moiety. In one embodiment the second antigen binding moiety is capable of specific binding to FolR1 or HER1. In one embodiment the second antigen binding moiety is capable of specific binding to FolR1, HER1 or Mesothelin. In one embodiment the second antigen binding moiety is capable of specific binding to FolR1, HER1, HER2 or Mesothelin.

[0011] In one embodiment the first and the second antigen binding moiety are fused to each other, optionally via a peptide linker. In one particular embodiment the second antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the Fab heavy chain of the first antigen binding moiety. In one particular embodiment the first antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the Fab heavy chain of the second antigen binding moiety. In one particular embodiment the Fab light chain of the first antigen binding moiety and the Fab light chain of the second antigen binding moiety are fused to each other, optionally via a peptide linker.

[0012] In one embodiment the protease-activatable T cell activating bispecific molecule additionally comprises an Fc domain composed of a first and a second subunit capable of stable association.

[0013] In one embodiment the Fc domain is an IgG, specifically an IgG 1 or IgG 4 , Fc domain. In one embodiment the Fc domain is a human Fc domain. In one embodiment the Fc domain exhibits reduced binding affinity to an Fc receptor and / or reduced effector function, as compared to a native IgG 1 Fc domain. In one embodiment the Fc domain comprises one or more amino acid substitution that reduces binding to an Fc receptor and / or effector function. In one particular embodiment the one or more amino acid substitution is at one or more position selected from the group of L234, L235, and P329 (Kabat numbering). In one particular embodiment each subunit of the Fc domain comprises three amino acid substitutions that reduce binding to an activating Fc receptor and / or effector function wherein said amino acid substitutions are L234A, L235A and P329G. In one particular embodiment the Fc receptor is an Fcy receptor. In one embodiment the effector function is antibody-dependent cell-mediated cytotoxicity (ADCC). In one embodiment, the target cell is a human cell.

[0014] In one embodiment the masking moiety comprises a heavy chain variable region comprising at least one of: (a) a heavy chain complementarity determining region (CDR H) 1 amino acid sequence of DYSIH (SEQ ID NO:20); (b) a CDR H2 amino acid sequence of WINTETGEPAYADDFKG (SEQ ID NO:21); and (c) a CDR H3 amino acid sequence of PYDYDVLDY (SEQ ID NO:22).

[0015] In one embodiment the masking moiety comprises a light chain variable region comprising at least one of: (a) a light chain (CDR L)1 amino acid sequence of RASKSVSTSNYSYIH (SEQ ID NO:23); (b) a CDR L2 amino acid sequence of YVSYLES (SEQ ID NO:24); and (c) a CDR L3 amino acid sequence of QHSREFPWT (SEQ ID NO:25).

[0016] In one embodiment the masking moiety comprises a heavy chain variable region comprising: (a) a heavy chain complementarity determining region (CDR H) 1 amino acid sequence of DYSIH (SEQ ID NO:20); (b) a CDR H2 amino acid sequence of WINTETGEPAYADDFKG (SEQ ID NO:21); (c) a CDR H3 amino acid sequence of PYDYDVLDY (SEQ ID NO:22); and a light chain variable region comprising: (d) a light chain (CDR L)1 amino acid sequence of RASKSVSTSNYSYIH (SEQ ID NO:23); (e) a CDR L2 amino acid sequence of YVSYLES (SEQ ID NO:24); and (f) a CDR L3 amino acid sequence of QHSREFPWT (SEQ ID NO:25).

[0017] In one embodiment the masking moiety comprises a heavy chain variable region comprising at least one of: (a) a heavy chain complementarity determining region (CDR H) 1 amino acid sequence of SYGVS (SEQ ID NO:26); (b) a CDR H2 amino acid sequence of IIWGDGSTNYHSALIS (SEQ ID NO:27); and (c) a CDR H3 amino acid sequence of GITTVVDDYYAMDY (SEQ ID NO:28).

[0018] In one embodiment the masking moiety comprises a light chain variable region comprising at least one of: (a) a light chain (CDR L)1 amino acid sequence of RASENIDSYLA (SEQ ID NO:29); (b) a CDR L2 amino acid sequence of AATFLAD (SEQ ID NO:30); and (c) a CDR L3 amino acid sequence of QHYYSTPYT (SEQ ID NO:31).

[0019] In one embodiment the masking moiety comprises a heavy chain variable region comprising: (a) a heavy chain complementarity determining region (CDR H) 1 amino acid sequence of SYGVS (SEQ ID NO:26); (b) a CDR H2 amino acid sequence of IIWGDGSTNYHSALIS (SEQ ID NO:27); (c) a CDR H3 amino acid sequence of GITTVVDDYYAMDY (SEQ ID NO:28); and a light chain variable region comprising: (d) a light chain (CDR L)1 amino acid sequence of RASENIDSYLA (SEQ ID NO:29); (e) a CDR L2 amino acid sequence of AATFLAD (SEQ ID NO:30); and (f) a CDR L3 amino acid sequence of QHYYSTPYT (SEQ ID NO:31).

[0020] In one embodiment the protease cleavable linker comprises at least one protease recognition sequence. In one embodiment the protease cleavable linker comprises a protease recognition sequence. In one embodiment the protease recognition sequence is selected from the group consisting of: (a) RQARVVNG (SEQ ID NO:36); (b) VHMPLGFLGPGRSRGSFP (SEQ ID NO:37); (c) RQARVVNGXXXXXVPLSLYSG (SEQ ID NO:38); and (d) RQARVVNGVPLSLYSG (SEQ ID NO:39) (e) PLGLWSQ (SEQ ID NO:40), wherein X is any amino acid.

[0021] In one embodiment the protease cleavable linker comprises a protease recognition sequence. In one embodiment the protease recognition sequence is selected from the group consisting of: (a) RQARVVNG (SEQ ID NO:36); (b) VHMPLGFLGPGRSRGSFP (SEQ ID NO:37); (c) RQARVVNGXXXXXVPLSLYSG (SEQ ID NO:38); (d) RQARVVNGVPLSLYSG (SEQ ID NO:39); (e) PLGLWSQ (SEQ ID NO:40); (f) VHMPLGFLGPRQARVVNG (SEQ ID NO:97); (g) FVGGTG (SEQ ID NO:98); (h) KKAAPVNG (SEQ ID NO:99); (i) PMAKKVNG (SEQ ID NO:100); (j) QARAKVNG (SEQ ID NO:101); (k) VHMPLGFLGP (SEQ ID NO:102); (l) QARAK (SEQ ID NO:103); (m) VHMPLGFLGPPMAKK (SEQ ID NO:104); (n) KKAAP (SEQ ID NO:105); and (o) PMAKK (SEQ ID NO:106), wherein X is any amino acid.

[0022] In one embodiment the protease capable of cleaving the protease-cleavable linker is selected from the group consisting of metalloproteinase, e.g., matrix metalloproteinase (MMP) 1-28 and A Disintegrin And Metalloproteinase (ADAM) 2, 7-12, 15, 17-23, 28-30 and 33, serine protease, e.g., urokinase-type plasminogen activator and Matriptase, cysteine protease, aspartic protease, and cathepsin protease. In one specific embodiment the protease is MMP9 or MMP2. In a further specific embodiment, the protease is Matriptase. In one embodiment the protease cleavable linker comprises the protease recognition sequence RQARVVNG (SEQ ID NO:36).

[0023] In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the first antigen binding moiety comprises at least one heavy chain complementarity determining region (CDR) comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to an amino acid sequence selected from the group consisting of SEQ ID NO: 44, SEQ ID NO: 45 and SEQ ID NO: 46 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18 and SEQ ID NO: 19.

[0024] In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the first antigen binding moiety comprises the heavy chain complementarity determining region (CDRs) of SEQ ID NO: 44, SEQ ID NO: 45 and SEQ ID NO: 46 and the light chain CDRs of SEQ ID NO: 17, SEQ ID NO: 18 and SEQ ID NO: 19.

[0025] In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the first antigen binding moiety comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 43 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55.

[0026] In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the first antigen binding moiety comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 43 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 55.

[0027] In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the second antigen binding moiety is capable of specific binding to FolR1 and comprises at least one heavy chain complementarity determining region (CDR) comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to an amino acid sequence selected from the group consisting of SEQ ID NO: 14, SEQ ID NO: 15 and SEQ ID NO: 16 and at least one light chain CDR comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to an amino acid sequence selected from the group consisting of SEQ ID NO: 17, SEQ ID NO: 18 and SEQ ID NO: 19.

[0028] In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the second antigen binding moiety is capable of specific binding to FolR1 and comprises at least one heavy chain complementarity determining region (CDR) comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to an amino acid sequence selected from the group consisting of SEQ ID NO: 151, SEQ ID NO: 152 and SEQ ID NO: 153 and at least one light chain CDR comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to an amino acid sequence selected from the group consisting of SEQ ID NO: 154, SEQ ID NO: 155 and SEQ ID NO: 156.

[0029] In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the second antigen binding moiety is capable of specific binding to FolR1 and comprises at least one heavy chain complementarity determining region (CDR) comprising an amino acid sequence selected from the group consisting of SEQ ID NO: 14, SEQ ID NO: 15 and SEQ ID NO: 16 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18 and SEQ ID NO: 19.

[0030] In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the second antigen binding moiety is capable of specific binding to FolR1 and comprises at least one heavy chain complementarity determining region (CDR) comprising an amino acid sequence selected from the group consisting of SEQ ID NO: 151, SEQ ID NO: 152 and SEQ ID NO: 153 and at least one light chain CDR selected from the group of SEQ ID NO: 154, SEQ ID NO: 155 and SEQ ID NO: 156.

[0031] In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the second antigen binding moiety comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 47 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55.

[0032] In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the second antigen binding moiety comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 157 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 158.

[0033] In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the second antigen binding moiety comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 47 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 55.

[0034] In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the second antigen binding moiety comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 157 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 158.

[0035] In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the second antigen binding moiety is capable of specific binding to Mesothelin and comprises at least one heavy chain complementarity determining region (CDR) comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to an amino acid sequence selected from the group consisting of SEQ ID NO: 107, SEQ ID NO: 108 and SEQ ID NO: 109 and at least one light chain CDR comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to an amino acid sequence selected from the group consisting of SEQ ID NO: 110, SEQ ID NO: 111 and SEQ ID NO: 112. In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the second antigen binding moiety is capable of specific binding to Mesothelin and comprises at least one heavy chain complementarity determining region (CDR) comprising an amino acid sequence selected from the group consisting of SEQ ID NO: 107, SEQ ID NO: 108 and SEQ ID NO: 109 and at least one light chain CDR selected from the group of SEQ ID NO: 110, SEQ ID NO: 111 and SEQ ID NO: 112.

[0036] In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the second antigen binding moiety comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 113 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 114.

[0037] In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the second antigen binding moiety comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 113 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 114.

[0038] In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the second antigen binding moiety is capable of specific binding to HER1 and comprises at least one heavy chain complementarity determining region (CDR) of any one of the antibodies disclosed in WO / 2006 / 082515.

[0039] In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the second antigen binding moiety is capable of specific binding to HER1 and comprises at least one heavy chain complementarity determining region (CDR) comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to an amino acid sequence selected from the group consisting of SEQ ID NO: 56, SEQ ID NO: 57 and SEQ ID NO: 58 and at least one light chain CDR comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to an amino acid sequence selected from the group consisting of SEQ ID NO: 59, SEQ ID NO: 60 and SEQ ID NO: 61.

[0040] In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the second antigen binding moiety is capable of specific binding to HER1 and comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 56, SEQ ID NO: 57 and SEQ ID NO: 58 and at least one light chain CDR selected from the group of SEQ ID NO: 59, SEQ ID NO: 60 and SEQ ID NO: 61.

[0041] In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the second antigen binding moiety comprises a heavy chain comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 32 and a light chain comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 33. In one embodiment of the protease-activatable T cell activating bispecific molecule described herein the second antigen binding moiety comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 32 and a light chain comprising the amino acid sequence of SEQ ID NO: 33.

[0042] In one embodiment, the first antigen binding moiety is capable of specific binding to CD3, and comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 43 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55, and the second and third antigen binding moieties are capable of specific binding to HER2, wherein the second antigen binding moiety comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 160 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 161, wherein the third antigen binding moiety comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 159 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 161.

[0043] In one particular embodiment the protease-activatable T cell activating bispecific molecule described herein comprises (a) a first heavy chain comprising the amino acid sequence of SEQ ID NO:2; (b) a second heavy chain comprising the amino acid sequence of SEQ ID NO:3; and (c) a light chain comprising the amino acid sequence of SEQ ID NO: 1.

[0044] In one particular embodiment the protease-activatable T cell activating bispecific molecule described herein comprises (a) a first heavy chain comprising the amino acid sequence of SEQ ID NO:4; (b) a second heavy chain comprising the amino acid sequence of SEQ ID NO:3; and (c) a light chain comprising the amino acid sequence of SEQ ID NO:1.

[0045] In one particular embodiment the protease-activatable T cell activating bispecific molecule described herein comprises (a) at least one heavy chain comprising the amino acid sequence of SEQ ID NO:32; (b) at least one light chain comprising the amino acid sequence of SEQ ID NO:34.

[0046] In one particular embodiment the protease-activatable T cell activating bispecific molecule described herein comprises (a) a first heavy chain comprising the amino acid sequence of SEQ ID NO:72; (b) a second heavy chain comprising the amino acid sequence of SEQ ID NO:3; and (c) a light chain comprising an amino acid sequence of SEQ ID NO:1.

[0047] In one particular embodiment the protease-activatable T cell activating bispecific molecule described herein comprises (a) a first heavy chain comprising the amino acid sequence of SEQ ID NO:85; (b) a second heavy chain comprising the amino acid sequence of SEQ ID NO:3; and (c) a light chain comprising an amino acid sequence of SEQ ID NO:1.

[0048] In one particular embodiment the protease-activatable T cell activating bispecific molecule described herein comprises (a) a first heavy chain comprising the amino acid sequence of SEQ ID NO:73; (b) a second heavy chain comprising the amino acid sequence of SEQ ID NO:3; (c) a first light chain comprising an amino acid sequence of SEQ ID NO: 1; and (d) a second light chain comprising an amino acid sequence of SEQ ID NO: 74.

[0049] In one particular embodiment the protease-activatable T cell activating bispecific molecule described herein comprises (a) a first heavy chain comprising the amino acid sequence of SEQ ID NO:77; (b) a second heavy chain comprising the amino acid sequence of SEQ ID NO:82; (c) a first light chain comprising an amino acid sequence of SEQ ID NO:78; and (d) a second light chain comprising an amino acid sequence of SEQ ID NO:81.

[0050] In one particular embodiment the protease-activatable T cell activating bispecific molecule described herein comprises (a) a first heavy chain comprising the amino acid sequence of SEQ ID NO:76; (b) a second heavy chain comprising the amino acid sequence of SEQ ID NO:77; (c) a first light chain comprising an amino acid sequence of SEQ ID NO:78; and (d) a second light chain comprising an amino acid sequence of SEQ ID NO:79.

[0051] In one particular embodiment the protease-activatable T cell activating bispecific molecule described herein comprises (a) a first heavy chain comprising the amino acid sequence of SEQ ID NO: 132; (b) a second heavy chain comprising the amino acid sequence of SEQ ID NO: 136; (c) a first light chain comprising an amino acid sequence of SEQ ID NO:81; and (d) a second light chain comprising an amino acid sequence of SEQ ID NO: 133.

[0052] In one particular embodiment the protease-activatable T cell activating bispecific molecule described herein comprises (a) a first heavy chain comprising the amino acid sequence of SEQ ID NO: 137; (b) a second heavy chain comprising the amino acid sequence of SEQ ID NO: 139; (c) a first light chain comprising an amino acid sequence of SEQ ID NO:81; and (d) a second light chain comprising an amino acid sequence of SEQ ID NO: 138.

[0053] In one aspect, the invention relates to an idiotype-specific polypeptide for reversibly concealing an anti-CD3 antigen binding site of a molecule, wherein the idiotype-specific polypeptide is an anti-idiotype scFv, and wherein the idiotype-specific polypeptide is covalently attached to the molecule through a peptide linker. In one embodiment the linker is a protease-cleavable linker. In one embodiment the peptide linker comprises at least one protease recognition site. In one embodiment the protease is selected from the group consisting of metalloproteinase, e.g., matrix metalloproteinase (MMP) 1-28 and A Disintegrin And Metalloproteinase (ADAM) 2, 7-12, 15, 17-23, 28-30 and 33, serine protease, e.g., urokinase-type plasminogen activator and Matriptase, cysteine protease, aspartic protease, and cathepsin protease. In one specific embodiment the protease is MMP9 or MMP2. In a further specific embodiment, the protease is Matriptase. In one embodiment the idiotype-specific polypeptide is covalently attached to the molecule through more than one linker. In one embodiment the idiotype-specific polypeptide is covalently attached to the molecule through two linkers.

[0054] In one embodiment the molecule which comprises the anti-CD3 antigen binding site is a T-cell activating bispecific molecule. In one particular embodiment the idiotype-specific polypeptide comprises a heavy chain variable region comprising at least one of: (a) a heavy chain complementarity determining region (CDR H) 1 amino acid sequence of DYSIH (SEQ ID NO:20); (b) a CDR H2 amino acid sequence of WINTETGEPAYADDFKG (SEQ ID NO:21); and (c) a CDR H3 amino acid sequence of PYDYDVLDY (SEQ ID NO:22).

[0055] In one particular embodiment the idiotype-specific polypeptide comprises a light chain variable region comprising at least one of (a) a light chain (CDR L)1 amino acid sequence of RASKSVSTSNYSYIH (SEQ ID NO:23); (b) a CDR L2 amino acid sequence of YVSYLES (SEQ ID NO:24); and (c) a CDR L3 amino acid sequence of QHSREFPWT (SEQ ID NO:25).

[0056] In one particular embodiment the idiotype-specific polypeptide comprises: (a) a heavy chain complementarity determining region (CDR H) 1 amino acid sequence of DYSIH (SEQ ID NO:20); (b) a CDR H2 amino acid sequence of WINTETGEPAYADDFKG (SEQ ID NO:21); (c) a CDR H3 amino acid sequence of PYDYDVLDY (SEQ ID NO:22); and a light chain variable region comprising: (d) a light chain (CDR L)1 amino acid sequence of RASKSVSTSNYSYIH (SEQ ID NO:23); (e) a CDR L2 amino acid sequence of YVSYLES (SEQ ID NO:24); and (f) a CDR L3 amino acid sequence of QHSREFPWT (SEQ ID NO:25).

[0057] In one particular embodiment the idiotype-specific polypeptide comprises a heavy chain variable region comprising at least one of: (a) a heavy chain complementarity determining region (CDR H) 1 amino acid sequence of SYGVS (SEQ ID NO:26); (b) a CDR H2 amino acid sequence of IIWGDGSTNYHSALIS (SEQ ID NO:27); and (c) a CDR H3 amino acid sequence of GITTVVDDYYAMDY (SEQ ID NO:28).

[0058] In one particular embodiment the idiotype-specific polypeptide comprises a light chain variable region comprising at least one of: (a) a light chain (CDR L)1 amino acid sequence of RASENIDSYLA (SEQ ID NO:29); (b) a CDR L2 amino acid sequence of AATFLAD (SEQ ID NO:30); and (c) a CDR L3 amino acid sequence of QHYYSTPYT (SEQ ID NO:31).

[0059] In one particular embodiment the idiotype-specific polypeptide comprises a heavy chain variable region comprising: (a) a heavy chain complementarity determining region (CDR H) 1 amino acid sequence of SYGVS (SEQ ID NO:26); (b) a CDR H2 amino acid sequence of IIWGDGSTNYHSALIS (SEQ ID NO:27); (c) a CDR H3 amino acid sequence of GITTVVDDYYAMDY (SEQ ID NO:28); and a light chain variable region comprising: (d) a light chain (CDR L)1 amino acid sequence of RASENIDSYLA (SEQ ID NO:29); (e) a CDR L2 amino acid sequence of AATFLAD (SEQ ID NO:30); and (f) a CDR L3 amino acid sequence of QHYYSTPYT (SEQ ID NO:31).

[0060] According to another aspect of the invention, an isolated polynucleotide encoding a protease-activatable T cell activating bispecific molecule of the invention. The invention further provides an expression vector comprising the isolated polynucleotide of the invention, and a host cell comprising the isolated polynucleotide or the expression vector of the invention. In some embodiments the host cell is a eukaryotic cell, particularly a mammalian cell.

[0061] In another aspect is provided a method of producing the protease-activated T cell molecule of the invention, comprising the steps of a) culturing the host cell of the invention under conditions suitable for the expression of the protease-activated T cell molecule and b) recovering the protease-activated T cell molecule.

[0062] In another aspect there is provided for reference only a method of producing the idiotype-specific polypeptide as described herein above, comprising the steps of a) culturing the host cell of the invention under conditions suitable for the expression of the protease-activated T cell molecule and b) recovering the idiotype-specific polypeptide.

[0063] The invention further provides a pharmaceutical composition comprising the protease-activatable T cell activating bispecific molecule of the invention and a pharmaceutically acceptable carrier. Also encompassed are methods of using the protease-activated T cell molecule and pharmaceutical composition as herein before described. In one aspect the invention provides a protease-activated T cell molecule or a pharmaceutical composition of the invention for use as a medicament. In one aspect is provided a protease-activated T cell molecule or a pharmaceutical composition according to the invention for use in the treatment of a disease in an individual in need thereof. In a specific embodiment the disease is cancer.

[0064] In a specific embodiment the disease is cancer. In any of the above embodiments the individual preferably is a mammal, particularly a human.

[0065] In another aspect the invention also provides a composition comprising a protease-activatable T cell activating bispecific molecule described herein and a pharmaceutically acceptable carrier.

[0066] In another aspect there is provided for reference only a composition comprising an idiotype-specific polypeptide as described herein above and a pharmaceutically acceptable carrier.

[0067] In another aspect provided is a protease-activatable T cell activating bispecific molecule as described herein above, or the composition described herein above, for use as a medicament.

[0068] In another aspect the invention also provides a protease-activatable T cell activating bispecific molecule as described herein above for use in the treatment of a disease in an individual in need thereof. In one embodiment, the disease is a proliferative disorder, particularly cancer.

[0069] In another aspect the invention also provides an anti-idiotype CD3 antibody or antigen-binding fragment thereof specific for an idiotype of an anti-CD3 antigen-binding molecule, wherein the anti-idiotype CD3 antibody or fragment thereof when bound to the anti-CD3 antigen-binding molecule specifically blocks binding of the anti-CD3 antigen-binding molecule to CD3, wherein the anti-idiotype CD3 antibody or antigen-binding fragment thereof is reversibly associated with the anti-CD3 antigen-binding molecule through a peptide linker comprising a protease recognition site. In one embodiment, the CD3 is a mouse, monkey or human CD3.SHORT DESCRIPTION OF THE FIGURES

[0070] Figures 1A-Edepict schematics of different CD3 binders with masking moieties. FIG. 1A: 7859 anti-ID CH2527 scFv 4.15.64 MK062 Matriptase site CD3 Fc. FIG. 1B: 7860 anti-ID CH2527 scFv 4.32.63 MK062 Matriptase site CD3 Fc. FIG. 1C: 7857 anti-ID CH2527 scFv 4.15.64 non-cleavable linker CD3 Fc. FIG. 1D: ID 7858 anti-ID CH2527 scFv 4.32.63 non-cleavable linker CD3 Fc. FIG. 1E: 7861 monovalent CD3 Fc. Figure 2 shows a table summarizing the affinities of the anti-idiotypic masking moieties to the CD3 binder (CH2527). Figure 3A-Dshows Capillary Electrophoresis-SDS analysis of the molecules depicted in Figures 1A and B. FIGs. 3A-BCapillary Electrophoresis-SDS analysis of the molecule depicted in FIG. 1A under non reducing (FIG. 3A) and reducing conditions (FIG. 3B). Comparison of the untreated (I) and treated molecule (III) shows complete cleavage of the anti-ID scFv after rhMatriptase / ST14 treatment for 48 h at 37°C. One sample (II) was untreated but incubated at 37°C for 48 h. FIGs. 3C-D Capillary Electrophoresis-SDS analysis of the molecule depicted in FIG. 1B under non-reducing (FIG. 3C) and reducing conditions (FIG. 3D). Comparison of the untreated (I) and treated molecule (III) shows complete cleavage of the anti-ID scFv after rhMatriptase / ST14 treatment for 48 h at 37°C. One sample (II) was untreated but incubated at 37°C for 48 h. Figure 4A-Cshow the effect of anti-idiotypic masking of CD3 binding. FIGs. 4A and B depict results of Jurkat NFAT reporter assays to show the masking effect of anti-idiotypic CD3 scFv 4.15.64 (FIG. 4A) or anti-idiotypic CD3 scFv 4.32.63 (FIG. 4B). Monovalent CD3 IgGs were crosslinked via an anti-human Fc antibody (coated on assay plate) before Jurkat NFAT (acute lymphatic leukemia reporter cell line with a NFAT promoter, expressing human CD3ε) were added. The Jurkat-NFAT reporter cell line (Promega) is a human acute lymphatic leukemia reporter cell line with a NFAT promoter, expressing human CD3ε. If CD3 binder binds CD3ε Luciferase is expressed and this can be measured in Luminescence after addition of One-Glo substrate (Promega). FIG. 4C shows a comparison of EC50 values of CD3ε binding for masked and unmasked monovalent CD3 binder. Figure 5A-Hdepict schematics of different T cell bispecific molecules with masking moieties. FIG. 5A: 7344 anti-ID CH2527 scFv 4.15.64 MK062 Matriptase site CD3 16D5 Fc. FIG. 5B: 7676 anti-ID CH2527 scFv 4.15.64 non-cleavable linker CD3 16D5 Fc. FIG. 5C: 7496 anti-ID CH2527 scFv 4.32.63 MK062 Matriptase site CD3 16D5 Fc. FIG. 5D: 7611 anti-ID CH2527 scFv 4.32.63 non-cleavable linker CD3 16D5 Fc. FIG. 5E: 6298 GA916-D-16D5-02 sf W(1). FolR1 16D5 classic 2+1 TCB with common light chain. FIG. 5F: 6100 GA916-D-16D5 sf W(3a). FolR1 16D5 inverted 2+1 TCB with common light chain. FIG. 5G: ID 6182 DP47GS TCB sf CHO W(9a). DP47 inverted 2+1 TCB. FIG. 5H: 7494 anti-ID CH2527 Fab 4.15.64 MK062 Matriptase site CD3 16D5 Fc. Figure 6 shows a first plasmid ratios used for transfection by size exclusion chromatography (1(hole): 1 (knob): 3 (CLC)). Figure 7 shows a second plasmid ratios used for transfection by size exclusion chromatography. (1(hole): 2 (knob): 3 (CLC)). Figure 8 shows CE-SDS analysis of the TCB molecule depicted in FIG. 5A (ID 7344) (final purified preparation): Lane A = non-reduced, lane B = reduced, lane C = Protein standard. Figure 9 shows CE-SDS analysis of the TCB molecule depicted in FIG. 5B (ID 7676) (final purified preparation): Lane A = non-reduced, lane B = reduced, lane C = Protein standard. Figure 10 shows CE-SDS analysis of the TCB molecule depicted in FIG. 5C (ID 7496) (final purified preparation): Lane A = non-reduced, lane B = reduced, lane C = Protein standard. Figure 11 shows CE-SDS analysis of the TCB molecule depicted in FIG. 5D (ID 7611) (final purified preparation): Lane A = non-reduced, lane B = reduced, lane C = Protein standard. Figures 12A-Dshow shows Capillary Electrophoresis-SDS analysis of the molecules depicted in Figures 5A and C. FIGs. 12A and B shows Capillary Electrophoresis of the molecules depicted in Figures 5A (ID 7344) anti-ID CH2527 scFv 4.15.64 MK062 CD3 16D6 Fc under non reducing (FIGs. 12A) and reducing conditions (FIGs. 12B). Comparison of the untreated (I) and treated molecule (III) shows complete cleavage of the anti-ID scFv after rhMatriptase / ST14 treatment for 48 h at 37°C. One sample (II) was untreated but incubated at 37°C for 48 h. Pre-stained protein Marker (IV) Mark 12 (Invitrogen) was used for estimation of correct molecule weight. FIGs. 12C and D dhows Capillary Electrophoresis of the molecule depicted in FIG. 5C (ID 7496) anti-ID CH2527 scFv 4.32.63 MK062 CD3 16D6 Fc under non reducing (FIGs. 12C) and reducing conditions (FIGs. 12D). Comparison of the untreated (I) and treated molecule (III) shows complete cleavage of the anti-ID scFv after rhMatriptase / ST14 treatment for 48 h at 37°C. One sample (II) was untreated but incubated at 37°C for 48 h. Pre-stained protein Marker (IV) Mark 12 (Invitrogen) was used for estimation of correct molecule weight. Figure 13 shows FolR1 expression level quantification done by Qifikit (Dako). Antibody for FolR1: #LS-C125620-100 (LifeSpan BioSciences Inc); used at 20 µg / ml; mouse IgG1 isotype: #554121 (BD). Figures 14A and Bshow T cell activation by protease activated TCBs. FIG. 14A shows killing of Skov3 cells induced by protease-activated TCB molecules at a concentration of 10nM (TCBs with different anti-idiotypic CD3 masks, cleavable and non-cleavable linker, molecules pretreated with purified rhMatriptase / ST14) and human PBMCs after 48 h of incubation (E:T = 7:1, effectors are human PBMCs). Pre-treatment with rhMatriptase / ST14 (R&D Systems) was done for 24 h at 37°C. FIG. 14B shows T cell activation of human PBMCs induced by protease activated TCB binding of 10nM (TCBs with different anti-idiotypic CD3 masks, cleavable and non-cleavable linker, treated molecules) on Skov3 cells after 48 h of incubation (E:T = 7:1, effectors are human PBMCs). T cell activation markers CD25 (left panels) and CD69 (right panels). CD4+ and CD8+ T cells as indicated. Figures 15A and Bshow T cell activation by protease activated TCBs. FIG. 15A shows killing of Mkn-45 cells induced by protease activated TCB molecules at a concentration of 100nM (TCBs with different anti-idiotypic CD3 masks, cleavable and non-cleavable linker, treated molecules) and human PBMCs after 48 h of incubation (E:T = 7:1, effectors are human PBMCs). Pre-treatment with rhMatriptase / ST14 (R&D Systems) was done for 24 h at 37°C. FIG. 15B shows T cell activation of human PBMCs induced by protease activated TCB binding of 100nM (TCBs with different anti-idiotypic CD3 masks, cleavable and non-cleavable linker, treated molecules) on Mkn-45 cells after 48 h of incubation (E:T = 7:1, effectors are human PBMCs). T cell activation markers CD25 (left panels) and CD69 (right panels). CD4+ and CD8+ T cells as indicated. Figure 16 shows killing of HT29 cells induced by protease activated TCB molecules at a concentration of 10nM (TCBs with different anti-idiotypic CD3 masks, cleavable and non-cleavable linker, treated molecules) and human PBMCs after 48 h of incubation (E:T = 10:1, effectors are human PBMCs). Pre-treatment with rhMatriptase / ST14 (R&D Systems) was done for 24 h at 37°C. Bars from left to right are 7344: anti-ID CH2527 scFv 4.15.64 MK062 CD3 16D6Fc; 7344: anti-ID CH2527 scFv 4.15.64 MK062 CD3 16D6Fc_treated; 7676: anti-ID CH2527 scFv 4.15.64 non-cleavable CD3 16D6Fc; 7496 anti-ID CH2527 scFv 4.32.63 MK062 CD3 16D6 Fc; 7496 anti-ID CH2527 scFv 4.32.63 MK062 CD3 16D6 Fc_treated; 7611: ID anti CH2527 scFv 4.32.63 non-cleavable linker CD3 16D6 Fc; 6298 GA916-D-16D5-02 sf W(1); 6182 DP47GS TCB sf CHO W(9a). Figure 17 shows killing of Skov3 cells induced by protease activated TCB molecules at a concentration of 10nM (TCBs with different anti-idiotypic CD3 masks, cleavable and non-cleavable linker, treated molecules) and human PBMCs (from a different donor than PBMCs used for FIG. 14A) after 48 h of incubation (E:T = 10:1, effectors are human PBMCs). Pre-treatment with rhMatriptase / ST14 (R&D Systems) was done for 24 h at 37°C. Bars from left to right are 7344: anti-ID CH2527 scFv 4.15.64 MK062 CD3 16D6Fc; 7344: anti-ID CH2527 scFv 4.15.64 MK062 CD3 16D6Fc_treated; 7676: anti-ID CH2527 scFv 4.15.64 non-cleavable CD3 16D6Fc; 7496 anti-ID CH2527 scFv 4.32.63 MK062 CD3 16D6 Fc; 7496 anti-ID CH2527 scFv 4.32.63 MK062 CD3 16D6 Fc_treated; 7611: ID anti CH2527 scFv 4.32.63 non-cleavable linker CD3 16D6 Fc; 6298 GA916-D-16D5-02 sf W(1); 6182 DP47GS TCB sf CHO W(9a). Figures 18A and Bshow T cell activation by protease activated TCBs. FIG. 18A shows dose-dependent killing of HeLa cells induced by protease activated TCB molecules (TCB with anti-idiotypic CD3 4.15.64 mask, cleavable and non-cleavable linker, treated molecule) and human PBMCs (isolated from buffy coat) after 48 h of incubation (E:T = 10:1, effectors are human PBMCs). Pre-treatment with rhMatriptase / ST14 (R&D Systems) was done for 24 h at 37°C. FIG. 18B shows dose-dependent T cell activation of human PBMCs induced by protease activated TCB binding (TCB with anti-idiotypic CD3 4.15.64 mask, cleavable and non-cleavable linker, treated molecule) on HeLa cells after 48 h of incubation (E:T = 10:1, effectors are human PBMCs). T cell activation markers CD25 (left panels) and CD69 (right panels). CD4+ and CD8+ T cells as indicated. Figures 19A and Bshow T cell activation by protease activated TCBs. FIG. 19A shows dose-dependent killing of HeLa cells induced by protease activated TCB molecules (TCB with anti-idiotypic CD3 4.32.63 mask, cleavable and non-cleavable linker, treated molecule) and human PBMCs (isolated from buffy coat) after 48 h of incubation (E:T = 10:1, effectors are human PBMCs). Pre-treatment with rhMatriptase / ST14 (R&D Systems) was done for 24 h at 37°C. Fig. 19B shows dose-dependent T cell activation of human PBMCs induced by protease activated TCB binding (TCB with anti-idiotypic CD3 4.32.63 mask, cleavable and non-cleavable linker, treated molecule) on HeLa cells after 48 h of incubation (E:T = 10:1, effectors are human PBMCs). T cell activation markers CD25 (left panels) and CD69 (right panels). CD4+ and CD8+ T cells as indicated. Figures 20A and B show T cell activation by protease activated TCBs. FIG. 20A shows dose-dependent killing of Skov3 cells induced by protease activated TCB molecules (TCB with anti-idiotypic CD3 4.15.64 mask, cleavable and non-cleavable linker, treated molecule) and human PBMCs (isolated from buffy coat) after 48 h of incubation (E:T = 10:1, effectors are human PBMCs). Pre-treatment with rhMatriptase / ST14 (R&D Systems) was done for 24 h at 37°C. FIG. 20B shows dose-dependent T cell activation of human PBMCs induced by protease activated TCB binding (TCB with anti-idiotypic CD3 4.15.64 mask, cleavable and non-cleavable linker, treated molecule) on Skov3 cells after 48 h of incubation (E:T = 10:1, effectors are human PBMCs). T cell activation markers CD25 (left panels) and CD69 (right panels). CD4+ and CD8+ T cells as indicated. Figures 21A and Bshow T cell activation by protease activated TCBs. FIG. 21A shows dose-dependent killing of Skov3 cells induced by protease activated TCB molecules (TCB with anti-idiotypic CD3 4.32.63 mask, cleavable and non-cleavable linker, treated molecule) and human PBMCs (isolated from buffy coat) after 48 h of incubation (E:T = 10:1, effectors are human PBMCs). Pre-treatment with rhMatriptase / ST14 (R&D Systems) was done for 24 h at 37°C. FIG. 21B shows dose-dependent T cell activation of human PBMCs induced by protease activated TCB binding (TCB with anti-idiotypic CD3 4.32.63 mask, cleavable and non-cleavable linker, treated molecule) on Skov3 cells after 48 h of incubation (E:T = 10:1, effectors are human PBMCs). T cell activation markers CD25 (left panels) and CD69 (right panels). CD4+ and CD8+ T cells as indicated. Figures 22A and Bshow T cell activation by protease activated TCBs. FIG. 22A shows dose-dependent T cell activation of human PBMCs (different donor than in experiments described above) induced by protease activated TCB binding (TCB with anti-idiotypic CD3 4.15.64 mask, cleavable and non-cleavable linker, treated molecule) on HT29 cells after 48 h of incubation (E:T = 10:1, effectors are human PBMCs). T cell activation markers CD25 (left panels) and CD69 (right panels). CD4+ and CD8+ T cells as indicated. FIG. 22B shows dose-dependent T cell activation of human PBMCs (different donor than in Figure 16) induced by protease activated TCB binding (TCB with anti-idiotypic CD3 4.32.63 mask, cleavable and non-cleavable linker, treated molecule) on HT29 cells after 48 h of incubation (E:T = 10:1, effectors are human PBMCs). T cell activation markers CD25 (left panels) and CD69 (right panels). CD4+ and CD8+ T cells as indicated. Figure 23 shows dose-dependent T cell activation of human PBMCs (different donor than in experiments described above) induced by protease activated TCB binding (TCB with anti-idiotypic CD3 4.15.64 mask, cleavable and non-cleavable linker, treated molecule) on HRCEpiC cells after 48 h of incubation (E:T = 10:1, effectors are human PBMCs). T cell activation markers CD25 (left panels) and CD69 (right panels). CD4+ and CD8+ T cells as indicated. Figure 24 shows killing of Ovcar3 cells induced by protease activated TCB molecules at a concentration of 50nM (TCBs with different anti-idiotypic CD3 masks, cleavable and non-cleavable linker, treated molecules) and human PBMCs after 48 h of incubation (E:T = 10:1, effectors are human PBMCs). Pre-treatment with rhMatriptase / ST14 (R&D Systems) was done for 10 min at 37°C (not fully cleaved). Figure 25 shows killing of Skov3 cells induced by 10nM of protease activated TCB molecules (TCB with anti-idiotypic CD3 4.15.64 mask, cleavable and non-cleavable linker, treated molecule) and human PBMCs (isolated from buffy coat) after 48 h of incubation (E:T = 10:1, effectors are three different Donors for human PBMCs). Pre-treatment with rhMatriptase / ST14 (R&D Systems) was done for 24 h at 37°C. Figure 26 shows killing of Skov3 cells induced by 10nM of protease activated TCB molecules (TCB with anti-idiotypic CD3 4.32.63 mask, cleavable and non-cleavable linker, treated molecule) and human PBMCs (isolated from buffy coat) after 48 h of incubation (E:T = 10:1, effectors are three different Donors for human PBMCs). Pre-treatment with rhMatriptase / ST14 (R&D Systems) was done for 24 h at 37°C. Figure 27 shows killing of HeLa cells induced by 100 pM of protease activated TCB molecules (TCB with anti-idiotypic CD3 4.32.63 mask, cleavable and non-cleavable linker, treated molecule) and human PBMCs (isolated from buffy coat) after 48 h of incubation (E:T = 10:1, effectors are three different Donors for human PBMCs). Pre-treatment with rhMatriptase / ST14 (R&D Systems) was done for 24 h at 37°C. Figure 28 depicts a schematic of anti-ID GA201 scFv Matrix Metalloprotease site GA201 Fc (GA201-anti-GA201-scFv). Figure 29 depicts a schematics of the anti HER1 antibody GA201. Figures 30A and Bshow capillary Electrophoresis-SDS analysis of the molecule depicted in FIG. 28 under non-reducing (FIG. 30A) and reducing conditions (FIG. 30B). The molecule depicted in FIG. 28 was purified to homogeneity by Protein A and Size Exclusion chromatography and subjected to Capillary electrophoresis-SDS analysis. Figure 31 shows FACS analysis of GA201-anti-GA201-scFv and GA201 binding to HER1 expressed on H322M cells to confirm masking effect of anti-idiotypic GA201 scFv. GA201-anti-GA201-scFv was incubated overnight with the Matrix Metalloprotease MMP-2 and binding to H322M cells was compared to uncleaved GA201-anti-GA201-scFv, GA201 and an isotype IgG1 control antibody. Binding to HER1 on H322M cells was detected with a F(ab')2-goat anti-human IgG Fc secondary antibody FITC conjugate and analyzed by FACS using the BD FACS Canto II. The median fluorescence intensity (MFI) was used for analysis. Figure 32 shows surface plasmon resonance analysis of HER1 binding of masked and unmasked GA201, before and after MMP2 cleavage. Figures 33A-Jdepict schematics of different T cell bispecific molecules with masking moieties. FIG. 33A: ID 8364. 16D5 TCB, classic format, anti ID CH2527 scFv 4.32.63 MMP9-MK062 Matriptase site N-terminally fused to CD3. FIG. 33B: ID 8363. 16D5 TCB, classic format, anti ID CH2527 scFv 4.32.63 Cathepsin S / B site N-terminally fused to CD3. FIG. 33C: ID 8365. 16D5 TCB, inverted format, anti ID CH2527 scFv 4.32.63 MK062 Matriptase site N-terminally fused to common light chain. FIG. 33D: ID 8366. 16D5 TCB, inverted format, anti ID CH2527 scFv 4.32.63 non-cleavable linker N-terminally fused to common light chain. FIG. 33E: ID 8672. aMesothelin RG7787 charged residues TCB, classic format, anti ID CH2527 scFv 4.32.63 MMP9-MK062 Matriptase site N-terminally fused to CD3 X Fab. FIG. 33F: ID 8673. aMesothelin RG7787 charged residues TCB, classic format, anti ID CH2527 scFv 4.32.63 non-cleavable linker N-terminally fused to CD3 X Fab. FIG. 33G: ID 8674. aMesothelin RG7787 charged residues TCB, inverted format, anti ID CH2527 scFv 4.32.63 MMP9-MK062 Matriptase site N-terminally fused to CD3 XFab. FIG. 33H: 8675. aMesothelin RG7787 charged residues TCB, inverted format, anti ID CH2527 scFv 4.32.63 non-cleavable linker N-terminally fused to CD3 XFab. FIG. 33I: ID 8505. aMesothelin RG7787 charged residues CD3 XFab TCB, inverted format. FIG. 33J: ID 8676. CD3 XFab aMesothelin RG7787 charged residues TCB, classic format. Figure 34 depicts CE-SDS analysis of the TCB ID 8365 and TCB ID 8366 (final purified preparation): Lane A = Protein standard, lane B = protein stored at 4 °C, lane C = protein pretreated with rhMatriptase / ST14 (R&D Systems), lane D = protein incubated for 72 h at 37 °C and lane E = molecule 3. Figures 35A and B.depicts CE-SDS analysis of the TCB depicted in FIG. 33A (ID 8364) and the TCB depicted in FIG. 33B (ID 8363). FIG. 35A: CE-SDS analysis of the TCB 8364 (final purified preparation): Lane A = Protein standard, lane B = protein stored at 4 °C, lane C = protein pretreated with rhMatriptase / ST14 (R&D Systems), lane D = protein incubated for 72 h at 37 °C and lane E = non-cleavable linker construct. FIG. 35B: CE-SDS analysis of the TCB 8363 (final purified preparation): Lane A = Protein standard, lane B = protein stored at 4 °C, lane C = protein pretreated with rhCathepsin B (R&D Systems), lane D = protein pretreated with rhCathepsin S (R&D Systems), lane E = protein incubated for 72 h at 37 °C and lane F = non-cleavable linker construct. Figures 36A and B.depicts Jurkat NFAT activation assay using HeLa and Skov-3 cells as target cells. Each point represents the mean value of triplicates. Standard deviation is indicated by error bars. Jurkat-NFAT reporter cell line (Promega) is a human acute lymphatic leukemia reporter cell line with a NFAT promoter, expressing human CD3ε. If the CD3 binder of the TCB binds the tumor target and the CD3 (cross-linkage is necessary) binds CD3ε the Luciferase expression can be measured in Luminescence after addition of One-Glo substrate (Promega). The FolR1 TCB (black triangles pointing down) and the pretreated protease activated TCB (8364, grey filled squares) with N-terminally fused anti ID CD3 4.32.63 scFv and MMP9-Matriptase MK062 site were compared. The molecule was treated with rhMatriptase / ST14 (R&D Systems) for about 20 h at 37 °C. The masked TCB (containing a GS non-cleavable linker, grey triangles pointing up) and the non-targeted TCB control (empty triangle pointing down) are shown as well. The dotted line shows the Luminescence of target cells and effector cells without any TCB. FIG. 36A shows a Jurkat NFAT activation assay using HeLa cells as target cells. FIG. 36B shows a Jurkat NFAT activation assay using Skov-3 cells as target cells. Figures 37A-Ddepicts tumor cell cytotoxicity mediated by FolR1 TCBs and human PBMCs (Effector : Target = 10 : 1). Each point represents the mean value of triplicates. Standard deviation is indicated by error bars. FIG. 37A: HeLa target cell cytotoxicity. Comparison of two different formats of the Protease activated TCBs both containing an anti idiotypic CD3 scFv linked with a MK062 Matriptase linker. FIG. 37B: Skov-3 target cell cytotoxicity. Comparison of two different formats of the Protease activated TCBs both containing an anti idiotypic CD3 scFv linked with a MK062 Matriptase linker. FIG. 37C: HeLa target cell cytotoxicity. Comparison of classic Protease activated TCB containing an anti idiotypic CD3 scFv and GS linkers with different protease sites. Protease activated TCB containing the MMP9-Matriptase MK062 linker (8364, grey squares), FolR1 TCB (light grey triangles pointing down), protease activated TCB containing only Matriptase MK062 (light grey rhomb) / Cathepsin site (grey circles) or non-cleavable linker (black triangles pointing down). FIG 37D: Skov-3 target cell cytotoxicity. Comparison of classic Protease activated TCB containing an anti idiotypic CD3 scFv and GS linkers with different protease sites. Protease activated TCB containing the MMP9-Matriptase MK062 linker (8364, grey squares), FolR1 TCB (light grey triangles pointing down), protease activated TCB containing only Matriptase MK062 (light grey rhomb) / Cathepsin site (grey circles) or non-cleavable linker (black triangles pointing down). Figures 38A and Bdepicts quantification of CD69 of CD8 positive cells after co-incubation of primary human renal epithelial cortical cells (FIG. 38A) or human bronchial epithelial cells (FIG. 38B) with 200 nM of the different TCBs and three different donors of human PBMCs. T cells were stained after 48 h of incubation. (E:T = 10:1, effectors are human PBMCs). Median fluorescence intensity of T cell activation marker CD69 for CD8 +< T cells is shown. Each point represents the mean value of triplicates of three different human PBMC donors. Standard deviation is indicated in error bars. Unpaired t test was used for statistical analysis. Figures 39A and Bdepicts tumor cell cytotoxicity mediated by MSLN TCBs and human PBMCs (Effector : Target = 10 : 1). Maximal lysis of the target cells (= 100%) was achieved by incubation of target cells with 1% Triton X-100 20 h before LDH readout. Minimal lysis (= 0%) refers to target cells co-incubated with effector cells without any TCB. Each point represents the mean value of triplicates. Standard deviation is indicated by error bars. FIG.39A: NCI H596 target cell cytotoxicity. Protease activated MSLN TCB containing an anti idiotypic CD3 scFv linked with a MMP9-MK062 Matriptase linker. The protease activated TCB (8672, light grey circles), the MSLN TCB (dark grey triangles pointing down) and the protease activated TCB containing a non-cleavable linker (8673, grey triangles pointing up) are compared. FIG. 39B: AsPC-1 target cell cytotoxicity. Protease activated MSLN TCB containing an anti idiotypic CD3 scFv linked with a MMP9-MK062 Matriptase linker. The protease activated TCB (8672, light grey circles), the MSLN TCB (dark grey triangles pointing down) and the protease activated TCB containing a non-cleavable linker (8673, grey triangles pointing up) are compared. Figure 40 depicts a Jurkat-NFAT activation assay with primary tumor samples and Protease activated FolR1 TCBs. Jurkat NFAT reporter cells are activated after co-incubation with FolR1 TCB (6298) and Protease activated FolR1 TCB containing MMP9-Matriptase cleavage site (8364). Protease activated FolR1 TCBs (8363, 8408) and control TCBs (8409, 7235) do not induce Luciferase expression. The dotted line indicates the baseline Luminescence for Jurkat NFAT cells co-incubated with tumor. Figures 41A-C: Capillary electrophoresis of protease activated TCBs after incubation in human serum. Molecules were incubated for 0 or 14 days in human IgG depleted serum at 37 °C in a humidified incubator (5 % CO 2 ). All molecules were purified by affinity chromatography (ProteinA) and then analyzed by Capillary electrophoresis. FIG. 41A: CE-SDS analysis of serum, FolR1 TCB (6298) in serum at day 0 and day 14. FIG. 41B: CE-SDS analysis of serum, Protease activated FolR1 TCB with MMP9-Matriptase linker (8364) in serum at day 0 and day 14. FIG. 41C: CE-SDS analysis of serum, Protease activated FolR1 TCB with Matriptase linker (8408) in serum at day 0 and day 14 and the precleaved molecule in serum. Figures 42A-Fdepict schematics of different T cell bispecific molecules with masking moieties. FIG. 42A: ID 8955. Herceptarg TCB, classic format, anti ID CH2527 scFv 4.32.63 MK062 MMP9 linker N-terminally fused to VH. FIG. 42B: ID 8957. Herceptarg TCB, classic format, anti ID CH2527 scFv 4.32.63 non cleavable linker N-terminally fused to VH. FIG. 42C: ID 8959. Herceptarg TCB, classic format. FIG. 42D: ID 8997. FolR1 36F2 TCB, classic format, anti ID CH2527 scFv 4.32.63 MK062 MMP9 linker N-terminally fused to VH. FIG. 42E: ID 8998. FolR1 36F2 TCB, classic format, anti ID CH2527 scFv 4.32.63 non cleavable linker N-terminally fused to VH. FIG. 42F: ID 8996. FolR1 36F2 TCB, classic format. Figure 43 depicts Human Bronchial Epithelial Cell toxicity mediated by human PBMCs and 100 nM or 10 nM of TCBs. Maximal lysis of the target cells (= 100%) was achieved by incubation of target cells with 1% Triton X-100 20 h before LDH readout. Minimal lysis (= 0%) refers to target cells co-incubated with effector cells without any TCB. Each point represents the mean value of triplicates. Standard deviation is indicated by error bars. Figure 44 depicts FolR1 negative target cell (Mkn-45) cytotoxicity mediated by 100 nM of FolR1 TCBs and human PBMCs. Maximal lysis of the target cells (= 100%) was achieved by incubation of target cells with 1% Triton X-100 20 h before LDH readout. Minimal lysis (= 0%) refers to target cells co-incubated with effector cells without any TCB. Each point represents the mean value of triplicates. Standard deviation is indicated by error bars. DETAILED DESCRIPTION Definitions

[0071] Terms are used herein as generally used in the art, unless otherwise defined in the following.

[0072] As used herein, the term "antigen binding molecule" refers in its broadest sense to a molecule that specifically binds an antigenic determinant. Examples of antigen binding molecules are immunoglobulins and derivatives, e.g., fragments, thereof.

[0073] The term "bispecific" means that the antigen binding molecule is able to specifically bind to at least two distinct antigenic determinants. Typically, a bispecific antigen binding molecule comprises two antigen binding sites, each of which is specific for a different antigenic determinant. In certain embodiments the bispecific antigen binding molecule is capable of simultaneously binding two antigenic determinants, particularly two antigenic determinants expressed on two distinct cells.

[0074] The term "valent" as used herein denotes the presence of a specified number of antigen binding sites in an antigen binding molecule. As such, the term "monovalent binding to an antigen" denotes the presence of one (and not more than one) antigen binding site specific for the antigen in the antigen binding molecule.

[0075] An "antigen binding site" refers to the site, i.e. one or more amino acid residues, of an antigen binding molecule which provides interaction with the antigen. For example, the antigen binding site of an antibody comprises amino acid residues from the complementarity determining regions (CDRs). A native immunoglobulin molecule typically has two antigen binding sites, a Fab molecule typically has a single antigen binding site.

[0076] As used herein, the term "antigen binding moiety" refers to a polypeptide molecule that specifically binds to an antigenic determinant. In one embodiment, an antigen binding moiety is able to direct the entity to which it is attached (e.g., a second antigen binding moiety) to a target site, for example to a specific type of tumor cell or tumor stroma bearing the antigenic determinant. In another embodiment an antigen binding moiety is able to activate signaling through its target antigen, for example a T cell receptor complex antigen. Antigen binding moieties include antibodies and fragments thereof as further defined herein. Particular antigen binding moieties include an antigen binding domain of an antibody, comprising an antibody heavy chain variable region and an antibody light chain variable region. In certain embodiments, the antigen binding moieties may comprise antibody constant regions as further defined herein and known in the art. Useful heavy chain constant regions include any of the five isotypes: α, δ, ε, γ, or µ. Useful light chain constant regions include any of the two isotypes: κ and λ.

[0077] As used herein, the term "antigenic determinant" is synonymous with "antigen" and "epitope," and refers to a site (e.g., a contiguous stretch of amino acids or a conformational configuration made up of different regions of non-contiguous amino acids) on a polypeptide macromolecule to which an antigen binding moiety binds, forming an antigen binding moiety-antigen complex. Useful antigenic determinants can be found, for example, on the surfaces of tumor cells, on the surfaces of virus-infected cells, on the surfaces of other diseased cells, on the surface of immune cells, free in blood serum, and / or in the extracellular matrix (ECM). The proteins referred to as antigens herein (e.g., FolR1, HER1, HER2, CD3, Mesothelin) can be any native form of the proteins from any vertebrate source, including mammals such as primates (e.g., humans) and rodents (e.g., mice and rats), unless otherwise indicated. In a particular embodiment the antigen is a human protein. Where reference is made to a specific protein herein, the term encompasses the "full-length", unprocessed protein as well as any form of the protein that results from processing in the cell. The term also encompasses naturally occurring variants of the protein, e.g., splice variants or allelic variants. Exemplary human proteins useful as antigens include, but are not limited to: FolR1, HER1 and CD3, particularly the epsilon subunit of CD3 (see UniProt no. P07766 (version 130), NCBI RefSeq no. NP_000724.1, SEQ ID NO: 54 for the human sequence; or UniProt no. Q95LI5 (version 49), NCBI GenBank no. BAB71849.1 for the cynomolgus [Macaca fascicularis] sequence). In certain embodiments the protease-activatable T cell activating bispecific molecule of the invention binds to an epitope of CD3 or a target cell antigen that is conserved among the CD3 or target antigen from different species. In certain embodiments the protease-activatable T cell activating bispecific molecule of the invention binds to CD3 and FolR1, but does not bind to FolR2 or FolR3. In certain embodiments the protease-activatable T cell activating bispecific molecule of the invention binds to CD3 and HER1. In certain embodiments the protease-activatable T cell activating bispecific molecule of the invention binds to CD3 and Mesothelin. In certain embodiments the protease-activatable T cell activating bispecific molecule of the invention binds to CD3 and HER2. By "specific binding" is meant that the binding is selective for the antigen and can be discriminated from unwanted or non-specific interactions. The ability of an antigen binding moiety to bind to a specific antigenic determinant can be measured either through an enzyme-linked immunosorbent assay (ELISA) or other techniques familiar to one of skill in the art, e.g., surface plasmon resonance (SPR) technique (analyzed on a BIAcore instrument) (Liljeblad et al., Glyco J 17, 323-329 (2000)), and traditional binding assays (Heeley, Endocr Res 28, 217-229 (2002)). In one embodiment, the extent of binding of an antigen binding moiety to an unrelated protein is less than about 10% of the binding of the antigen binding moiety to the antigen as measured, e.g., by SPR. In certain embodiments, an antigen binding moiety that binds to the antigen, or an antigen binding molecule comprising that antigen binding moiety, has a dissociation constant (K D ) of ≤ 1 µM, ≤ 100 nM, ≤ 10 nM, ≤ 1 nM, ≤ 0.1 nM, ≤ 0.01 nM, or ≤ 0.001 nM (e.g., 10 -8< M or less, e.g., from 10 -8< M to 10 -13< M, e.g., from 10 -9< M to 10 -13< M).

[0078] "Affinity" refers to the strength of the sum total of non-covalent interactions between a single binding site of a molecule (e.g., a receptor) and its binding partner (e.g., a ligand). Unless indicated otherwise, as used herein, "binding affinity" refers to intrinsic binding affinity which reflects a 1:1 interaction between members of a binding pair (e.g., an antigen binding moiety and an antigen, or a receptor and its ligand). The affinity of a molecule X for its partner Y can generally be represented by the dissociation constant (K D ), which is the ratio of dissociation and association rate constants (k off and k on , respectively). Thus, equivalent affinities may comprise different rate constants, as long as the ratio of the rate constants remains the same. Affinity can be measured by well-established methods known in the art, including those described herein. A particular method for measuring affinity is Surface Plasmon Resonance (SPR).

[0079] "Reduced binding", for example reduced binding to an Fc receptor, refers to a decrease in affinity for the respective interaction, as measured for example by SPR. For clarity the term includes also reduction of the affinity to zero (or below the detection limit of the analytic method), i.e. complete abolishment of the interaction. Conversely, "increased binding" refers to an increase in binding affinity for the respective interaction.

[0080] "T cell activation" as used herein refers to one or more cellular response of a T lymphocyte, particularly a cytotoxic T lymphocyte, selected from: proliferation, differentiation, cytokine secretion, cytotoxic effector molecule release, cytotoxic activity, and expression of activation markers. The protease-activatable T cell activating bispecific molecules of the invention are capable of inducing T cell activation. Suitable assays to measure T cell activation are known in the art described herein.

[0081] A "target cell antigen" as used herein refers to an antigenic determinant presented on the surface of a target cell, for example a cell in a tumor such as a cancer cell or a cell of the tumor stroma.

[0082] As used herein, the terms "first" and "second" with respect to antigen binding moieties etc., are used for convenience of distinguishing when there is more than one of each type of moiety. Use of these terms is not intended to confer a specific order or orientation of the protease-activatable T cell activating bispecific molecule unless explicitly so stated.

[0083] A "Fab molecule" refers to a protein consisting of the VH and CH1 domain of the heavy chain (the "Fab heavy chain") and the VL and CL domain of the light chain (the "Fab light chain") of an immunoglobulin.

[0084] By "fused" is meant that the components (e.g., a Fab molecule and an Fc domain subunit) are linked by peptide bonds, either directly or via one or more peptide linkers.

[0085] As used herein, the term "single-chain" refers to a molecule comprising amino acid monomers linearly linked by peptide bonds. In certain embodiments, one of the antigen binding moieties is a single-chain Fab molecule, i.e. a Fab molecule wherein the Fab light chain and the Fab heavy chain are connected by a peptide linker to form a single peptide chain. In a particular such embodiment, the C-terminus of the Fab light chain is connected to the N-terminus of the Fab heavy chain in the single-chain Fab molecule.

[0086] By a "crossover" Fab molecule (also termed "Crossfab") is meant a Fab molecule wherein either the variable regions or the constant regions of the Fab heavy and light chain are exchanged, i.e. the crossover Fab molecule comprises a peptide chain composed of the light chain variable region and the heavy chain constant region, and a peptide chain composed of the heavy chain variable region and the light chain constant region. For clarity, in a crossover Fab molecule wherein the variable regions of the Fab light chain and the Fab heavy chain are exchanged, the peptide chain comprising the heavy chain constant region is referred to herein as the "heavy chain" of the crossover Fab molecule. Conversely, in a crossover Fab molecule wherein the constant regions of the Fab light chain and the Fab heavy chain are exchanged, the peptide chain comprising the heavy chain variable region is referred to herein as the "heavy chain" of the crossover Fab molecule.

[0087] In contrast thereto, by a "conventional" Fab molecule is meant a Fab molecule in its natural format, i.e. comprising a heavy chain composed of the heavy chain variable and constant regions (VH-CH1), and a light chain composed of the light chain variable and constant regions (VL-CL).

[0088] The term "immunoglobulin molecule" refers to a protein having the structure of a naturally occurring antibody. For example, immunoglobulins of the IgG class are heterotetrameric glycoproteins of about 150,000 daltons, composed of two light chains and two heavy chains that are disulfide-bonded. From N- to C-terminus, each heavy chain has a variable region (VH), also called a variable heavy domain or a heavy chain variable domain, followed by three constant domains (CH1, CH2, and CH3), also called a heavy chain constant region. Similarly, from N- to C-terminus, each light chain has a variable region (VL), also called a variable light domain or a light chain variable domain, followed by a constant light (CL) domain, also called a light chain constant region. The heavy chain of an immunoglobulin may be assigned to one of five types, called α (IgA), δ (IgD), ε (IgE), γ (IgG), or µ (IgM), some of which may be further divided into subtypes, e.g., γ 1 (IgG 1 ), γ 2 (IgG 2 ), γ 3 (IgG 3 ), γ 4 (IgG 4 ), α1 (IgA 1 ) and α 2 (IgA 2 ). The light chain of an immunoglobulin may be assigned to one of two types, called kappa (κ) and lambda (λ), based on the amino acid sequence of its constant domain. An immunoglobulin essentially consists of two Fab molecules and an Fc domain, linked via the immunoglobulin hinge region. The term "antibody" herein is used in the broadest sense and encompasses various antibody structures, including but not limited to monoclonal antibodies, polyclonal antibodies, and antibody fragments so long as they exhibit the desired antigen-binding activity.

[0089] An "antibody fragment" refers to a molecule other than an intact antibody that comprises a portion of an intact antibody that binds the antigen to which the intact antibody binds. Examples of antibody fragments include but are not limited to Fv, Fab, Fab', Fab'-SH, F(ab') 2 , diabodies, linear antibodies, single-chain antibody molecules (e.g., scFv), and single-domain antibodies. For a review of certain antibody fragments, see Hudson et al., Nat Med 9, 129-134 (2003). For a review of scFv fragments, see e.g., Plückthun, in The Pharmacology of Monoclonal Antibodies, vol. 113, Rosenburg and Moore eds., Springer-Verlag, New York, pp. 269-315 (1994); see also WO 93 / 16185; and U.S. Patent Nos. 5,571,894 and 5,587,458. For discussion of Fab and F(ab') 2 fragments comprising salvage receptor binding epitope residues and having increased in vivo half-life, see U.S. Patent No. 5,869,046. Diabodies are antibody fragments with two antigen-binding sites that may be bivalent or bispecific. See, for example, EP 404,097; WO 1993 / 01161; Hudson et al., Nat Med 9, 129-134 (2003); and Hollinger et al., Proc Natl Acad Sci USA 90, 6444-6448 (1993). Triabodies and tetrabodies are also described in Hudson et al., Nat Med 9, 129-134 (2003). Single-domain antibodies are antibody fragments comprising all or a portion of the heavy chain variable domain or all or a portion of the light chain variable domain of an antibody. In certain embodiments, a single-domain antibody is a human single-domain antibody (Domantis, Inc., Waltham, MA; see e.g., U.S. Patent No. 6,248,516 B1). Antibody fragments can be made by various techniques, including but not limited to proteolytic digestion of an intact antibody as well as production by recombinant host cells (e.g., E. coli or phage), as described herein.

[0090] The term "antigen binding domain" refers to the part of an antibody that comprises the area which specifically binds to and is complementary to part or all of an antigen. An antigen binding domain may be provided by, for example, one or more antibody variable domains (also called antibody variable regions). Particularly, an antigen binding domain comprises an antibody light chain variable region (VL) and an antibody heavy chain variable region (VH).

[0091] The term "variable region" or "variable domain" refers to the domain of an antibody heavy or light chain that is involved in binding the antibody to antigen. The variable domains of the heavy chain and light chain (VH and VL, respectively) of a native antibody generally have similar structures, with each domain comprising four conserved framework regions (FRs) and three hypervariable regions (HVRs). See, e.g., Kindt et al., Kuby Immunology, 6th ed., W.H. Freeman and Co., page 91 (2007). A single VH or VL domain may be sufficient to confer antigen-binding specificity.

[0092] The term "hypervariable region" or "HVR", as used herein, refers to each of the regions of an antibody variable domain which are hypervariable in sequence and / or form structurally defined loops ("hypervariable loops"). Generally, native four-chain antibodies comprise six HVRs; three in the VH (H1, H2, H3), and three in the VL (L1, L2, L3). HVRs generally comprise amino acid residues from the hypervariable loops and / or from the complementarity determining regions (CDRs), the latter being of highest sequence variability and / or involved in antigen recognition. With the exception of CDR1 in VH, CDRs generally comprise the amino acid residues that form the hypervariable loops. Hypervariable regions (HVRs) are also referred to as "complementarity determining regions" (CDRs), and these terms are used herein interchangeably in reference to portions of the variable region that form the antigen binding regions. This particular region has been described by Kabat et al., U.S. Dept. of Health and Human Services, Sequences of Proteins of Immunological Interest (1983) and by Chothia et al., J Mol Biol 196:901-917 (1987), where the definitions include overlapping or subsets of amino acid residues when compared against each other. Nevertheless, application of either definition to refer to a CDR of an antibody or variants thereof is intended to be within the scope of the term as defined and used herein. The appropriate amino acid residues which encompass the CDRs as defined by each of the above cited references are set forth below in Table 1 as a comparison. The exact residue numbers which encompass a particular CDR will vary depending on the sequence and size of the CDR. Those skilled in the art can routinely determine which residues comprise a particular CDR given the variable region amino acid sequence of the antibody. TABLE 1. CDR Definitions 1< CDR Kabat Chothia AbM 2< V H CDR131-3526-3226-35V H CDR250-6552-5850-58V H CDR395-10295-10295-102V L CDR124-3426-3224-34V L CDR250-5650-5250-56V L CDR389-9791-9689-97 1< Numbering of all CDR definitions in Table 1 is according to the numbering conventions set forth by Kabat et al. (see below). 2< "AbM" with a lowercase "b" as used in Table 1 refers to the CDRs as defined by Oxford Molecular's "AbM" antibody modeling software.

[0093] Kabat et al. also defined a numbering system for variable region sequences that is applicable to any antibody. One of ordinary skill in the art can unambiguously assign this system of "Kabat numbering" to any variable region sequence, without reliance on any experimental data beyond the sequence itself. As used herein, "Kabat numbering" refers to the numbering system set forth by Kabat et al., U.S. Dept. of Health and Human Services, "Sequence of Proteins of Immunological Interest" (1983). Unless otherwise specified, references to the numbering of specific amino acid residue positions in an antibody variable region are according to the Kabat numbering system.

[0094] The polypeptide sequences of the sequence listing are not numbered according to the Kabat numbering system. However, it is well within the ordinary skill of one in the art to convert the numbering of the sequences of the Sequence Listing to Kabat numbering.

[0095] "Framework" or "FR" refers to variable domain residues other than hypervariable region (HVR) residues. The FR of a variable domain generally consists of four FR domains: FR1, FR2, FR3, and FR4. Accordingly, the HVR and FR sequences generally appear in the following sequence in VH (or VL): FR1-H1(L1)-FR2-H2(L2)-FR3-H3(L3)-FR4.

[0096] The "class" of an antibody or immunoglobulin refers to the type of constant domain or constant region possessed by its heavy chain. There are five major classes of antibodies: IgA, IgD, IgE, IgG, and IgM, and several of these may be further divided into subclasses (isotypes), e.g., IgG 1 , IgG 2 , IgG 3 , IgG 4 , IgA 1 , and IgA 2 . The heavy chain constant domains that correspond to the different classes of immunoglobulins are called α, δ, ε, γ, and µ, respectively.

[0097] The term "Fc domain" or "Fc region" herein is used to define a C-terminal region of an immunoglobulin heavy chain that contains at least a portion of the constant region. The term includes native sequence Fc regions and variant Fc regions. Although the boundaries of the Fc region of an IgG heavy chain might vary slightly, the human IgG heavy chain Fc region is usually defined to extend from Cys226, or from Pro230, to the carboxyl-terminus of the heavy chain. However, the C-terminal lysine (Lys447) of the Fc region may or may not be present. Unless otherwise specified herein, numbering of amino acid residues in the Fc region or constant region is according to the EU numbering system, also called the EU index, as described in Kabat et al., Sequences of Proteins of Immunological Interest, 5th Ed. Public Health Service, National Institutes of Health, Bethesda, MD, 1991. A "subunit" of an Fc domain as used herein refers to one of the two polypeptides forming the dimeric Fc domain, i.e. a polypeptide comprising C-terminal constant regions of an immunoglobulin heavy chain, capable of stable self-association. For example, a subunit of an IgG Fc domain comprises an IgG CH2 and an IgG CH3 constant domain.

[0098] A "modification promoting the association of the first and the second subunit of the Fc domain" is a manipulation of the peptide backbone or the post-translational modifications of an Fc domain subunit that reduces or prevents the association of a polypeptide comprising the Fc domain subunit with an identical polypeptide to form a homodimer. A modification promoting association as used herein particularly includes separate modifications made to each of the two Fc domain subunits desired to associate (i.e. the first and the second subunit of the Fc domain), wherein the modifications are complementary to each other so as to promote association of the two Fc domain subunits. For example, a modification promoting association may alter the structure or charge of one or both of the Fc domain subunits so as to make their association sterically or electrostatically favorable, respectively. Thus, (hetero)dimerization occurs between a polypeptide comprising the first Fc domain subunit and a polypeptide comprising the second Fc domain subunit, which might be non-identical in the sense that further components fused to each of the subunits (e.g., antigen binding moieties) are not the same. In some embodiments the modification promoting association comprises an amino acid mutation in the Fc domain, specifically an amino acid substitution. In a particular embodiment, the modification promoting association comprises a separate amino acid mutation, specifically an amino acid substitution, in each of the two subunits of the Fc domain.

[0099] The term "effector functions" refers to those biological activities attributable to the Fc region of an antibody, which vary with the antibody isotype. Examples of antibody effector functions include: C1q binding and complement dependent cytotoxicity (CDC), Fc receptor binding, antibody-dependent cell-mediated cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), cytokine secretion, immune complex-mediated antigen uptake by antigen presenting cells, down regulation of cell surface receptors (e.g., B cell receptor), and B cell activation.

[0100] As used herein, the terms "engineer, engineered, engineering", are considered to include any manipulation of the peptide backbone or the post-translational modifications of a naturally occurring or recombinant polypeptide or fragment thereof. Engineering includes modifications of the amino acid sequence, of the glycosylation pattern, or of the side chain group of individual amino acids, as well as combinations of these approaches.

[0101] The term "amino acid mutation" as used herein is meant to encompass amino acid substitutions, deletions, insertions, and modifications. Any combination of substitution, deletion, insertion, and modification can be made to arrive at the final construct, provided that the final construct possesses the desired characteristics, e.g., reduced binding to an Fc receptor, or increased association with another peptide. Amino acid sequence deletions and insertions include amino- and / or carboxy-terminal deletions and insertions of amino acids. Particular amino acid mutations are amino acid substitutions. For the purpose of altering e.g., the binding characteristics of an Fc region, non-conservative amino acid substitutions, i.e. replacing one amino acid with another amino acid having different structural and / or chemical properties, are particularly preferred. Amino acid substitutions include replacement by non-naturally occurring amino acids or by naturally occurring amino acid derivatives of the twenty standard amino acids (e.g., 4-hydroxyproline, 3-methylhistidine, ornithine, homoserine, 5-hydroxylysine). Amino acid mutations can be generated using genetic or chemical methods well known in the art. Genetic methods may include site-directed mutagenesis, PCR, gene synthesis and the like. It is contemplated that methods of altering the side chain group of an amino acid by methods other than genetic engineering, such as chemical modification, may also be useful. Various designations may be used herein to indicate the same amino acid mutation. For example, a substitution from proline at position 329 of the Fc domain to glycine can be indicated as 329G, G329, G 329 , P329G, or Pro329Gly.

[0102] As used herein, term "polypeptide" refers to a molecule composed of monomers (amino acids) linearly linked by amide bonds (also known as peptide bonds). The term "polypeptide" refers to any chain of two or more amino acids, and does not refer to a specific length of the product. Thus, peptides, dipeptides, tripeptides, oligopeptides, "protein," "amino acid chain," or any other term used to refer to a chain of two or more amino acids, are included within the definition of "polypeptide," and the term "polypeptide" may be used instead of, or interchangeably with any of these terms. The term "polypeptide" is also intended to refer to the products of post-expression modifications of the polypeptide, including without limitation glycosylation, acetylation, phosphorylation, amidation, derivatization by known protecting / blocking groups, proteolytic cleavage, or modification by non-naturally occurring amino acids. A polypeptide may be derived from a natural biological source or produced by recombinant technology, but is not necessarily translated from a designated nucleic acid sequence. It may be generated in any manner, including by chemical synthesis. A polypeptide of the invention may be of a size of about 3 or more, 5 or more, 10 or more, 20 or more, 25 or more, 50 or more, 75 or more, 100 or more, 200 or more, 500 or more, 1,000 or more, or 2,000 or more amino acids. Polypeptides may have a defined three-dimensional structure, although they do not necessarily have such structure. Polypeptides with a defined three-dimensional structure are referred to as folded, and polypeptides which do not possess a defined three-dimensional structure, but rather can adopt a large number of different conformations, and are referred to as unfolded.

[0103] By an "isolated" polypeptide or a variant, or derivative thereof is intended a polypeptide that is not in its natural milieu. No particular level of purification is required. For example, an isolated polypeptide can be removed from its native or natural environment. Recombinantly produced polypeptides and proteins expressed in host cells are considered isolated for the purpose of the invention, as are native or recombinant polypeptides which have been separated, fractionated, or partially or substantially purified by any suitable technique.

[0104] "Percent (%) amino acid sequence identity" with respect to a reference polypeptide sequence is defined as the percentage of amino acid residues in a candidate sequence that are identical with the amino acid residues in the reference polypeptide sequence, after aligning the sequences and introducing gaps, if necessary, to achieve the maximum percent sequence identity, and not considering any conservative substitutions as part of the sequence identity. Alignment for purposes of determining percent amino acid sequence identity can be achieved in various ways that are within the skill in the art, for instance, using publicly available computer software such as BLAST, BLAST-2, ALIGN or Megalign (DNASTAR) software. Those skilled in the art can determine appropriate parameters for aligning sequences, including any algorithms needed to achieve maximal alignment over the full length of the sequences being compared. For purposes herein, however, % amino acid sequence identity values are generated using the sequence comparison computer program ALIGN-2. The ALIGN-2 sequence comparison computer program was authored by Genentech, Inc., and the source code has been filed with user documentation in the U.S. Copyright Office, Washington D.C., 20559, where it is registered under U.S. Copyright Registration No. TXU510087. The ALIGN-2 program is publicly available from Genentech, Inc., South San Francisco, California, or may be compiled from the source code. The ALIGN-2 program should be compiled for use on a UNIX operating system, including digital UNIX V4.0D. All sequence comparison parameters are set by the ALIGN-2 program and do not vary. In situations where ALIGN-2 is employed for amino acid sequence comparisons, the % amino acid sequence identity of a given amino acid sequence A to, with, or against a given amino acid sequence B (which can alternatively be phrased as a given amino acid sequence A that has or comprises a certain % amino acid sequence identity to, with, or against a given amino acid sequence B) is calculated as follows: 100 times the fraction X / Y where X is the number of amino acid residues scored as identical matches by the sequence alignment program ALIGN-2 in that program's alignment of A and B, and where Y is the total number of amino acid residues in B. It will be appreciated that where the length of amino acid sequence A is not equal to the length of amino acid sequence B, the % amino acid sequence identity of A to B will not equal the % amino acid sequence identity of B to A. Unless specifically stated otherwise, all % amino acid sequence identity values used herein are obtained as described in the immediately preceding paragraph using the ALIGN-2 computer program.

[0105] The term "polynucleotide" refers to an isolated nucleic acid molecule or construct, e.g., messenger RNA (mRNA), virally-derived RNA, or plasmid DNA (pDNA). A polynucleotide may comprise a conventional phosphodiester bond or a non-conventional bond (e.g., an amide bond, such as found in peptide nucleic acids (PNA). The term "nucleic acid molecule" refers to any one or more nucleic acid segments, e.g., DNA or RNA fragments, present in a polynucleotide.

[0106] By "isolated" nucleic acid molecule or polynucleotide is intended a nucleic acid molecule, DNA or RNA, which has been removed from its native environment. For example, a recombinant polynucleotide encoding a polypeptide contained in a vector is considered isolated for the purposes of the present invention. Further examples of an isolated polynucleotide include recombinant polynucleotides maintained in heterologous host cells or purified (partially or substantially) polynucleotides in solution. An isolated polynucleotide includes a polynucleotide molecule contained in cells that ordinarily contain the polynucleotide molecule, but the polynucleotide molecule is present extrachromosomally or at a chromosomal location that is different from its natural chromosomal location. Isolated RNA molecules include in vivo or in vitro RNA transcripts of the present invention, as well as positive and negative strand forms, and double-stranded forms. Isolated polynucleotides or nucleic acids according to the present invention further include such molecules produced synthetically. In addition, a polynucleotide or a nucleic acid may be or may include a regulatory element such as a promoter, ribosome binding site, or a transcription terminator.

[0107] By a nucleic acid or polynucleotide having a nucleotide sequence at least, for example, 95% "identical" to a reference nucleotide sequence of the present invention, it is intended that the nucleotide sequence of the polynucleotide is identical to the reference sequence except that the polynucleotide sequence may include up to five point mutations per each 100 nucleotides of the reference nucleotide sequence. In other words, to obtain a polynucleotide having a nucleotide sequence at least 95% identical to a reference nucleotide sequence, up to 5% of the nucleotides in the reference sequence may be deleted or substituted with another nucleotide, or a number of nucleotides up to 5% of the total nucleotides in the reference sequence may be inserted into the reference sequence. These alterations of the reference sequence may occur at the 5' or 3' terminal positions of the reference nucleotide sequence or anywhere between those terminal positions, interspersed either individually among residues in the reference sequence or in one or more contiguous groups within the reference sequence. As a practical matter, whether any particular polynucleotide sequence is at least 80%, 85%, 90%, 95%, 96%, 97%, 98% or 99% identical to a nucleotide sequence of the present invention can be determined conventionally using known computer programs, such as the ones discussed above for polypeptides (e.g., ALIGN-2).

[0108] The term "expression cassette" refers to a polynucleotide generated recombinantly or synthetically, with a series of specified nucleic acid elements that permit transcription of a particular nucleic acid in a target cell. The recombinant expression cassette can be incorporated into a plasmid, chromosome, mitochondrial DNA, plastid DNA, virus, or nucleic acid fragment. Typically, the recombinant expression cassette portion of an expression vector includes, among other sequences, a nucleic acid sequence to be transcribed and a promoter. In certain embodiments, the expression cassette of the invention comprises polynucleotide sequences that encode bispecific antigen binding molecules of the invention or fragments thereof.

[0109] The term "vector" or "expression vector" is synonymous with "expression construct" and refers to a DNA molecule that is used to introduce and direct the expression of a specific gene to which it is operably associated in a target cell. The term includes the vector as a self-replicating nucleic acid structure as well as the vector incorporated into the genome of a host cell into which it has been introduced. The expression vector of the present invention comprises an expression cassette. Expression vectors allow transcription of large amounts of stable mRNA. Once the expression vector is inside the target cell, the ribonucleic acid molecule or protein that is encoded by the gene is produced by the cellular transcription and / or translation machinery. In one embodiment, the expression vector of the invention comprises an expression cassette that comprises polynucleotide sequences that encode bispecific antigen binding molecules of the invention or fragments thereof.

[0110] The terms "host cell", "host cell line," and "host cell culture" are used interchangeably and refer to cells into which exogenous nucleic acid has been introduced, including the progeny of such cells. Host cells include "transformants" and "transformed cells," which include the primary transformed cell and progeny derived therefrom without regard to the number of passages. Progeny may not be completely identical in nucleic acid content to a parent cell, but may contain mutations. Mutant progeny that have the same function or biological activity as screened or selected for in the originally transformed cell are included herein. A host cell is any type of cellular system that can be used to generate the bispecific antigen binding molecules of the present invention. Host cells include cultured cells, e.g., mammalian cultured cells, such as CHO cells, BHK cells, NS0 cells, SP2 / 0 cells, YO myeloma cells, P3X63 mouse myeloma cells, PER cells, PER.C6 cells or hybridoma cells, yeast cells, insect cells, and plant cells, to name only a few, but also cells comprised within a transgenic animal, transgenic plant or cultured plant or animal tissue.

[0111] An "activating Fc receptor" is an Fc receptor that following engagement by an Fc domain of an antibody elicits signaling events that stimulate the receptor-bearing cell to perform effector functions. Human activating Fc receptors include FcyRIIIa (CD16a), FcyRI (CD64), FcyRIIa (CD32), and FcαRI (CD89).

[0112] Antibody-dependent cell-mediated cytotoxicity (ADCC) is an immune mechanism leading to the lysis of antibody-coated target cells by immune effector cells. The target cells are cells to which antibodies or derivatives thereof comprising an Fc region specifically bind, generally via the protein part that is N-terminal to the Fc region. As used herein, the term "reduced ADCC" is defined as either a reduction in the number of target cells that are lysed in a given time, at a given concentration of antibody in the medium surrounding the target cells, by the mechanism of ADCC defined above, and / or an increase in the concentration of antibody in the medium surrounding the target cells, required to achieve the lysis of a given number of target cells in a given time, by the mechanism of ADCC. The reduction in ADCC is relative to the ADCC mediated by the same antibody produced by the same type of host cells, using the same standard production, purification, formulation and storage methods (which are known to those skilled in the art), but that has not been engineered. For example the reduction in ADCC mediated by an antibody comprising in its Fc domain an amino acid substitution that reduces ADCC, is relative to the ADCC mediated by the same antibody without this amino acid substitution in the Fc domain. Suitable assays to measure ADCC are well known in the art (see e.g., PCT publication no. WO 2006 / 082515 or PCT publication no. WO 2012 / 130831).

[0113] An "effective amount" of an agent refers to the amount that is necessary to result in a physiological change in the cell or tissue to which it is administered.

[0114] A "therapeutically effective amount" of an agent, e.g., a pharmaceutical composition, refers to an amount effective, at dosages and for periods of time necessary, to achieve the desired therapeutic or prophylactic result. A therapeutically effective amount of an agent for example eliminates, decreases, delays, minimizes or prevents adverse effects of a disease.

[0115] An "individual" or "subject" is a mammal. Mammals include, but are not limited to, domesticated animals (e.g., cows, sheep, cats, dogs, and horses), primates (e.g., humans and non-human primates such as monkeys), rabbits, and rodents (e.g., mice and rats). Particularly, the individual or subject is a human.

[0116] The term "pharmaceutical composition" refers to a preparation which is in such form as to permit the biological activity of an active ingredient contained therein to be effective, and which contains no additional components which are unacceptably toxic to a subject to which the formulation would be administered.

[0117] A "pharmaceutically acceptable carrier" refers to an ingredient in a pharmaceutical composition, other than an active ingredient, which is nontoxic to a subject. A pharmaceutically acceptable carrier includes, but is not limited to, a buffer, excipient, stabilizer, or preservative.

[0118] As used herein, "treatment" (and grammatical variations thereof such as "treat" or "treating") refers to clinical intervention in an attempt to alter the natural course of a disease in the individual being treated, and can be performed either for prophylaxis or during the course of clinical pathology. Desirable effects of treatment include, but are not limited to, preventing occurrence or recurrence of disease, alleviation of symptoms, diminishment of any direct or indirect pathological consequences of the disease, preventing metastasis, decreasing the rate of disease progression, amelioration or palliation of the disease state, and remission or improved prognosis. In some embodiments, protease-activatable T cell activating bispecific molecules of the invention are used to delay development of a disease or to slow the progression of a disease. The term "package insert" is used to refer to instructions customarily included in commercial packages of therapeutic products, that contain information about the indications, usage, dosage, administration, combination therapy, contraindications and / or warnings concerning the use of such therapeutic products.

[0119] An "idiotype-specific polypeptide" as used herein refers to a polypeptide that recognizes the idiotype of an antigen-binding moiety, e.g., an antigen-binding moiety specific for CD3. The idiotype-specific polypeptide is capable of specifically binding to the variable region of the antigen-binding moiety and thereby reducing or preventing specific binding of the antigen-binding moiety to its cognate antigen. When associated with a molecule that comprises the antigen-binding moiety, the idiotype-specific polypeptide can function as a masking moiety of the molecule. Specifically disclosed herein are anti-idiotype antibodies or anti-idiotype-binding antibody fragments specific for the idiotype of anti-CD3 binding molecules.

[0120] "Protease" or "proteolytic enzyme" as used herein refers to any proteolytic enzyme that cleaves the linker at a recognition site and that is expressed by a target cell. Such proteases might be secreted by the target cell or remain associated with the target cell, e.g., on the target cell surface. Examples of proteases include but are not limited to metalloproteinases, e.g., matrix metalloproteinase 1-28 and A Disintegrin And Metalloproteinase (ADAM) 2, 7-12, 15, 17-23, 28-30 and 33, serine proteases, e.g., urokinase-type plasminogen activator and Matriptase, cysteine protease, aspartic proteases, and members of the cathepsin family.

[0121] "Protease activatable" as used herein, with respect to the T cell activating bispecific molecule, refers to a T cell activating bispecific molecule having reduced or abrogated ability to activate T cells due to a masking moiety that reduces or abrogates the T cell activating bispecific molecule's ability to bind to CD3. Upon dissociation of the masking moiety by proteolytic cleavage, e.g., by proteolytic cleavage of a linker connecting the masking moiety to the T cell activating bispecific molecule, binding to CD3 is restored and the T cell activating bispecific molecule is thereby activated.

[0122] "Reversibly concealing" as used herein refers to the binding of a masking moiety or idiotype-specific polypeptide to an antigen-binding moiety or molecule such as to prevent the antigen-binding moiety or molecule from its antigen, e.g., CD3. This concealing is reversible in that the idiotype-specific polypeptide can be released from the antigen-binding moiety or molecule, e.g., by protease cleavage, and thereby freeing the antigen-binding moiety or molecule to bind to its antigen.Detailed Description

[0123] In one aspect, the invention relates to a protease-activatable T cell activating bispecific molecule comprising (a) a first antigen binding moiety capable of specific binding to CD3, wherein the first antigen binding moiety is an antibody or fragment thereof; (b) a second antigen binding moiety capable of specific binding to a target cell antigen, wherein the second antigen binding moiety is an antibody or fragment thereof; and (c) a masking moiety covalently attached to the T cell bispecific binding molecule through a protease-cleavable linker, wherein the masking moiety is capable of specific binding to the idiotype of the first or the second antigen binding moiety thereby reversibly concealing the first or second antigen binding moiety, wherein the masking moiety is an anti-idiotypic scFv.

[0124] The first antigen binding moiety capable of specific binding to CD3 comprises an idiotype. In one embodiment, the masking moiety of the protease-activatable T cell activating bispecific molecule is covalently attached to the first antigen binding moiety. In one embodiment the masking moiety is covalently attached to the heavy chain variable region of the first antigen binding moiety. In one embodiment the masking moiety is covalently attached to the light chain variable region of the first antigen binding moiety. This covalent bond is separate from the specific binding, which is preferably non-covalent, of the masking moiety to the idiotype first antigen binding site. The idiotype of the first antigen binding moiety comprises its variable region. In one embodiment the masking moiety binds to amino acid residues that make contact with CD3 when the first antigen biding moiety is bound to CD3. In a preferred embodiment, the masking moiety is not the cognate antigen or fragments thereof of the first antigen binding moiety, i.e., the masking moiety is not a CD3 or fragments thereof. In one embodiment the masking moiety is an anti-idiotypic antibody or fragment thereof. In one embodiment, the masking moiety is an anti-idiotypic scFv. Exemplary embodiments of masking moieties which are anti-idiotypic scFv, and protease activatable T cell activating molecules comprising such masking moieties, are described in detail in the examples.

[0125] In one embodiment the protease-activatable T cell activating bispecific molecule comprises a second masking moiety reversibly concealing the second antigen binding moiety.

[0126] In one embodiment the protease-activatable T cell activating bispecific molecule comprises (i) a first antigen binding moiety which is a Fab molecule capable of specific binding to CD3, and which comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 44, SEQ ID NO: 45 and SEQ ID NO: 46 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19; (ii) a second antigen binding moiety which is a Fab molecule capable of specific binding to a target cell antigen.

[0127] In one embodiment the first antigen binding moiety comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to an amino acid sequence of SEQ ID NO: 43 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to an amino acid sequence of SEQ ID NO: 55.

[0128] In one embodiment the first antigen binding moiety comprises the heavy chain variable region comprising an amino acid sequence of SEQ ID NO: 43 and the light chain variable region comprising an amino acid sequence of SEQ ID NO: 55.

[0129] In a specific embodiment the second antigen binding moiety is capable of specific binding to FolR1 and comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 14, SEQ ID NO: 15 and SEQ ID NO: 16 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18 and SEQ ID NO: 19.

[0130] In another specific embodiment, the second antigen binding moiety is capable of specific binding to FolR1 and comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 47 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55.

[0131] In a specific embodiment the second antigen binding moiety is capable of specific binding to FolR1 and comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 151, SEQ ID NO: 152 and SEQ ID NO: 153 and at least one light chain CDR selected from the group of SEQ ID NO: 154, SEQ ID NO: 155 and SEQ ID NO: 156.

[0132] In another specific embodiment, the second antigen binding moiety is capable of specific binding to FolR1 and comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 157 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 158.

[0133] In another specific embodiment, the second antigen binding moiety is capable of specific binding to HER1 and comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 56, SEQ ID NO: 57 and SEQ ID NO: 58 and at least one light chain CDR selected from the group of SEQ ID NO: 59, SEQ ID NO: 60 and SEQ ID NO: 61.

[0134] In another specific embodiment, the second antigen binding moiety is capable of specific binding to HER1 and comprises a heavy chain comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to an amino acid sequence of SEQ ID NO: 32, and a light chain comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to an amino acid sequence of SEQ ID NO: 33.

[0135] In another specific embodiment, the second antigen binding moiety is capable of specific binding to HER1 and comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 115 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 116.

[0136] In a specific embodiment the second antigen binding moiety is capable of specific binding to Mesothelin and comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 107, SEQ ID NO: 108 and SEQ ID NO: 109 and at least one light chain CDR selected from the group of SEQ ID NO: 110, SEQ ID NO: 111 and SEQ ID NO: 112.

[0137] In another specific embodiment, the second antigen binding moiety is capable of specific binding Mesothelin and comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 113 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 114.

[0138] In one embodiment the present invention provides a protease-activatable T cell activating bispecific molecule comprising (i) a first antigen binding moiety which is a Fab molecule capable of specific binding to CD3, comprising at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 44, SEQ ID NO: 45 and SEQ ID NO: 46 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19; (ii) a second antigen binding moiety which is a Fab molecule capable of specific binding to FolR1 comprising at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 14, SEQ ID NO: 15 and SEQ ID NO: 16 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18 and SEQ ID NO: 19.

[0139] In one embodiment the present invention provides a protease-activatable T cell activating bispecific molecule comprising (i) a first antigen binding moiety which is a Fab molecule capable of specific binding to CD3 comprising a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 43 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55, (ii) a second antigen binding moiety which is a Fab molecule capable of specific binding to FolR1 comprising heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 47 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55.

[0140] In one embodiment the present invention provides a protease-activatable T cell activating bispecific molecule comprising (i) a first antigen binding moiety which is a Fab molecule capable of specific binding to CD3, comprising at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 44, SEQ ID NO: 45 and SEQ ID NO: 46 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19; (ii) a second antigen binding moiety which is a Fab molecule capable of specific binding to FolR1 comprising at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 151, SEQ ID NO: 152 and SEQ ID NO: 153 and at least one light chain CDR selected from the group of SEQ ID NO: 154, SEQ ID NO: 155 and SEQ ID NO: 156.

[0141] In one embodiment the present invention provides a protease-activatable T cell activating bispecific molecule comprising (i) a first antigen binding moiety which is a Fab molecule capable of specific binding to CD3 comprising a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 43 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55, (ii) a second antigen binding moiety which is a Fab molecule capable of specific binding to FolR1 comprising heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 157 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 158. In one embodiment the present invention provides a protease-activatable T cell activating bispecific molecule comprising (i) a first antigen binding moiety which is a Fab molecule capable of specific binding to CD3, comprising at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 44, SEQ ID NO: 45 and SEQ ID NO: 46 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19; (ii) a second antigen binding moiety which is a Fab molecule capable of specific binding to HER1 comprising at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 56, SEQ ID NO: 57 and SEQ ID NO: 58 and at least one light chain CDR selected from the group of SEQ ID NO: 59, SEQ ID NO: 60 and SEQ ID NO: 61.

[0142] In one embodiment the present invention provides a protease-activatable T cell activating bispecific molecule comprising (i) a first antigen binding moiety which is a Fab molecule capable of specific binding to CD3 comprising a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 43 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55. (ii) a second antigen binding moiety which is a Fab molecule capable of specific binding to HER1 comprising a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 115 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 116.

[0143] In a particular embodiment, the first antigen binding moiety is a crossover Fab molecule wherein either the variable or the constant regions of the Fab light chain and the Fab heavy chain are exchanged.

[0144] In one embodiment the present invention provides a protease-activatable T cell activating bispecific molecule comprising (i) a first antigen binding moiety which is a Fab molecule capable of specific binding to CD3, comprising at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 44, SEQ ID NO: 45 and SEQ ID NO: 46 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19; (ii) a second antigen binding moiety which is a Fab molecule capable of specific binding to Mesothelin comprising at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 107, SEQ ID NO: 108 and SEQ ID NO: 109 and at least one light chain CDR selected from the group of SEQ ID NO: 110, SEQ ID NO: 111 and SEQ ID NO: 112.

[0145] In one embodiment the present invention provides a protease-activatable T cell activating bispecific molecule comprising (i) a first antigen binding moiety which is a Fab molecule capable of specific binding to CD3 comprising a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 43 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55, (ii) a second antigen binding moiety which is a Fab molecule capable of specific binding to Mesothelin comprising heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 113 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 114.

[0146] In one embodiment, the second antigen binding moiety is a conventional Fab molecule.

[0147] In a particular embodiment, the first antigen binding moiety is a crossover Fab molecule wherein the constant regions of the Fab light chain and the Fab heavy chain are exchanged, and the second antigen binding moiety is a conventional Fab molecule. In a further particular embodiment, the first and the second antigen binding moiety are fused to each other, optionally through a peptide linker.

[0148] In particular embodiments, the protease-activatable T cell activating bispecific molecule further comprises an Fc domain composed of a first and a second subunit capable of stable association.

[0149] In a further particular embodiment, not more than one antigen binding moiety capable of specific binding to CD3 is present in the protease-activatable T cell activating bispecific molecule (i.e. the protease-activatable T cell activating bispecific molecule provides monovalent binding to CD3).Protease-activatable T cell activating bispecific molecule formats

[0150] The components of the protease-activatable T cell activating bispecific molecule can be fused to each other in a variety of configurations. Exemplary configurations are depicted in Figures 1A-E and 5A-H. Further exemplary configurations are depicted in Figures 33A-K.

[0151] In particular embodiments, the protease-activatable T cell activating bispecific molecule comprises an Fc domain composed of a first and a second subunit capable of stable association. In some embodiments, the second antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the first or the second subunit of the Fc domain.

[0152] In one such embodiment, the first antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the Fab heavy chain of the second antigen binding moiety. In a specific such embodiment, the protease-activatable T cell activating bispecific molecule essentially consists of a first and a second antigen binding moiety, an Fc domain composed of a first and a second subunit, and optionally one or more peptide linkers, wherein the first antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the Fab heavy chain of the second antigen binding moiety, and the second antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the first or the second subunit of the Fc domain. Optionally, the Fab light chain of the first antigen binding moiety and the Fab light chain of the second antigen binding moiety may additionally be fused to each other. In another such embodiment, the first antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the first or second subunit of the Fc domain. In a specific such embodiment, the protease-activatable T cell activating bispecific molecule essentially consists of a first and a second antigen binding moiety, an Fc domain composed of a first and a second subunit, and optionally one or more peptide linkers, wherein the first and the second antigen binding moiety are each fused at the C-terminus of the Fab heavy chain to the N-terminus of one of the subunits of the Fc domain.

[0153] In other embodiments, the first antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the first or second subunit of the Fc domain.

[0154] In a particular such embodiment, the second antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the Fab heavy chain of the first antigen binding moiety. In a specific such embodiment, the protease-activatable T cell activating bispecific molecule essentially consists of a first and a second antigen binding moiety, an Fc domain composed of a first and a second subunit, and optionally one or more peptide linkers, wherein the second antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the Fab heavy chain of the first antigen binding moiety, and the first antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the first or the second subunit of the Fc domain. Optionally, the Fab light chain of the first antigen binding moiety and the Fab light chain of the second antigen binding moiety may additionally be fused to each other. The antigen binding moieties may be fused to the Fc domain or to each other directly or through a peptide linker, comprising one or more amino acids, typically about 2-20 amino acids. Peptide linkers are known in the art and are described herein. Suitable, non-immunogenic peptide linkers include, for example, (G 4 S) n , (SG 4 ) n , (G 4 S) n or G 4 (SG 4 ) n peptide linkers. "n" is generally a number between 1 and 10, typically between 2 and 4. A particularly suitable peptide linker for fusing the Fab light chains of the first and the second antigen binding moiety to each other is (G 4 S) 2 . An exemplary peptide linker suitable for connecting the Fab heavy chains of the first and the second antigen binding moiety is EPKSC(D)-(G 4 S) 2 (SEQ ID NOs 105 and 106). Additionally, linkers may comprise (a portion of) an immunoglobulin hinge region. Particularly where an antigen binding moiety is fused to the N-terminus of an Fc domain subunit, it may be fused via an immunoglobulin hinge region or a portion thereof, with or without an additional peptide linker.

[0155] A protease-activatable T cell activating bispecific molecule with a single antigen binding moiety capable of specific binding to a target cell antigen is useful, particularly in cases where internalization of the target cell antigen is to be expected following binding of a high affinity antigen binding moiety. In such cases, the presence of more than one antigen binding moiety specific for the target cell antigen may enhance internalization of the target cell antigen, thereby reducing its availability.

[0156] In many other cases, however, it will be advantageous to have a protease-activatable T cell activating bispecific molecule comprising two or more antigen binding moieties specific for a target cell antigen (see examples in shown in Figure 5A-H), for example to optimize targeting to the target site or to allow crosslinking of target cell antigens.

[0157] Accordingly, in certain embodiments, the protease-activatable T cell activating bispecific molecule of the invention further comprises a third antigen binding moiety which is a Fab molecule capable of specific binding to a target cell antigen. In one embodiment, the third antigen binding moiety is a conventional Fab molecule. In one embodiment, the third antigen binding moiety is capable of specific binding to the same target cell antigen as the second antigen binding moiety. In a particular embodiment, the first antigen binding moiety is capable of specific binding to CD3, and the second and third antigen binding moieties are capable of specific binding to a target cell antigen. In a particular embodiment, the second and the third antigen binding moiety are identical (i.e. they comprise the same amino acid sequences).

[0158] In a particular embodiment, the first antigen binding moiety is capable of specific binding to CD3, and the second and third antigen binding moieties are capable of specific binding to FolR1, wherein the second and third antigen binding moieties comprise at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 14, SEQ ID NO: 15 and SEQ ID NO: 16 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18 and SEQ ID NO: 19.

[0159] In a particular embodiment, the first antigen binding moiety is capable of specific binding to CD3, and comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 44, SEQ ID NO: 45 and SEQ ID NO: 46 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19; and the second and third antigen binding moieties are capable of specific binding to FolR1, wherein the second and third antigen binding moieties comprise at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 14, SEQ ID NO: 15 and SEQ ID NO: 16 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18 and SEQ ID NO: 19.

[0160] In a particular embodiment, the first antigen binding moiety is capable of specific binding to CD3, and comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 44, SEQ ID NO: 45 and SEQ ID NO: 46 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19; and the second and third antigen binding moieties are capable of specific binding to FolR1, wherein the second and third antigen binding moieties comprise at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 14, SEQ ID NO: 15 and SEQ ID NO: 16 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18 and SEQ ID NO: 19.

[0161] In a particular embodiment, the first antigen binding moiety is capable of specific binding to CD3, and comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 43 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55, and the second and third antigen binding moieties are capable of specific binding to FolR1, wherein the second and third antigen binding moieties comprise a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 47 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55.

[0162] In one embodiment, the first antigen binding moiety is capable of specific binding to CD3, and the second and third antigen binding moieties are capable of specific binding to HER1, wherein the second and third antigen binding moieties comprise at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 56, SEQ ID NO: 57 and SEQ ID NO: 58 and at least one light chain CDR selected from the group of SEQ ID NO: 59, SEQ ID NO: 60 and SEQ ID NO: 61.

[0163] In one embodiment, the first antigen binding moiety is capable of specific binding to CD3, and comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 44, SEQ ID NO: 45 and SEQ ID NO: 46 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19; and the second and third antigen binding moieties are capable of specific binding to HER1, wherein the second and third antigen binding moieties comprise at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 56, SEQ ID NO: 57 and SEQ ID NO: 58 and at least one light chain CDR selected from the group of SEQ ID NO: 59, SEQ ID NO: 60 and SEQ ID NO: 61.

[0164] In one embodiment, the first antigen binding moiety is capable of specific binding to CD3, and comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 44, SEQ ID NO: 45 and SEQ ID NO: 46 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18 and SEQ ID NO: 19; and the second and third antigen binding moieties are capable of specific binding to HER1, wherein the second and third antigen binding moieties comprise at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 56, SEQ ID NO: 57 and SEQ ID NO: 58 and at least one light chain CDR selected from the group of SEQ ID NO: 59, SEQ ID NO: 60 and SEQ ID NO: 61.

[0165] In one embodiment, the first antigen binding moiety is capable of specific binding to CD3, and comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 43 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55, and the second and third antigen binding moieties are capable of specific binding to HER1, wherein the second and third antigen binding moieties comprise a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 115 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 116.

[0166] In one embodiment, the first antigen binding moiety is capable of specific binding to CD3, and the second and third antigen binding moieties are capable of specific binding to HER2, wherein the second antigen binding moiety comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 142, SEQ ID NO: 143 and SEQ ID NO: 144 and at least one light chain CDR selected from the group of SEQ ID NO: 148, SEQ ID NO: 149 and SEQ ID NO: 150, and wherein the third antigen binding moiety comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 145, SEQ ID NO: 146 and SEQ ID NO: 147 and at least one light chain CDR selected from the group of SEQ ID NO: 148, SEQ ID NO: 149 and SEQ ID NO: 150.

[0167] In a particular embodiment, the first antigen binding moiety is capable of specific binding to CD3, and comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 44, SEQ ID NO: 45 and SEQ ID NO: 46 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19; and the second and third antigen binding moieties are capable of specific binding to HER2, wherein the second antigen binding moiety comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 142, SEQ ID NO: 143 and SEQ ID NO: 144 and at least one light chain CDR selected from the group of SEQ ID NO: 148, SEQ ID NO: 149 and SEQ ID NO: 150, and wherein the third antigen binding moiety comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 145, SEQ ID NO: 146 and SEQ ID NO: 147 and at least one light chain CDR selected from the group of SEQ ID NO: 148, SEQ ID NO: 149 and SEQ ID NO: 150.

[0168] In one embodiment, the first antigen binding moiety is capable of specific binding to CD3, and comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 43 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55, and the second and third antigen binding moieties are capable of specific binding to HER2, wherein the second antigen binding moiety comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 160 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 161, wherein the third antigen binding moiety comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 159 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 161.

[0169] In a particular embodiment, the first antigen binding moiety is capable of specific binding to CD3, and the second and third antigen binding moieties are capable of specific binding to Mesothelin, wherein the second and third antigen binding moieties comprise at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 107, SEQ ID NO: 108 and SEQ ID NO: 109 and at least one light chain CDR selected from the group of SEQ ID NO: 110, SEQ ID NO: 111 and SEQ ID NO: 112.

[0170] In a particular embodiment, the first antigen binding moiety is capable of specific binding to CD3, and comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 44, SEQ ID NO: 45 and SEQ ID NO: 46 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19; and the second and third antigen binding moieties are capable of specific binding to Mesothelin, wherein the second and third antigen binding moieties comprise at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 107, SEQ ID NO: 108 and SEQ ID NO: 109 and at least one light chain CDR selected from the group of SEQ ID NO: 110, SEQ ID NO: 111 and SEQ ID NO: 112.

[0171] In a particular embodiment, the first antigen binding moiety is capable of specific binding to CD3, and comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 43, and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55, and the second and third antigen binding moieties are capable of specific binding to Mesothelin, wherein the second and third antigen binding moieties comprise a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 113 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 114.

[0172] In one embodiment, the first antigen binding moiety is capable of specific binding to CD3, and the second and third antigen binding moieties are capable of specific binding to HER1, wherein the second and third antigen binding moieties comprise at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 56, SEQ ID NO: 57 and SEQ ID NO: 58 and at least one light chain CDR selected from the group consisting of SEQ ID NO: 59, SEQ ID NO: 60 and SEQ ID NO: 61.

[0173] In a particular embodiment, the first antigen binding moiety is capable of specific binding to CD3, and comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 44, SEQ ID NO: 45 and SEQ ID NO: 46 and at least one light chain CDR selected from the group consisting of SEQ ID NO: 17, SEQ ID NO: 18 and SEQ ID NO: 19; and the second and third antigen binding moieties are capable of specific binding to HER1, wherein the second and third antigen binding moieties comprise at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 56, SEQ ID NO: 57 and SEQ ID NO: 58 and at least one light chain CDR selected from the group consisting of SEQ ID NO: 59, SEQ ID NO: 60 and SEQ ID NO: 61.

[0174] In one embodiment, the third antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the first or second subunit of the Fc domain. In a more specific embodiment, the second and the third antigen binding moiety are each fused at the C-terminus of the Fab heavy chain to the N-terminus of one of the subunits of the Fc domain, and the first antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the Fab heavy chain of the second antigen binding moiety. Optionally, the Fab light chain of the first antigen binding moiety and the Fab light chain of the second antigen binding moiety may additionally be fused to each other.

[0175] The second and the third antigen binding moiety may be fused to the Fc domain directly or through a peptide linker. In a particular embodiment the second and the third antigen binding moiety are each fused to the Fc domain through an immunoglobulin hinge region. In a specific embodiment, the immunoglobulin hinge region is a human IgG 1 hinge region. In one embodiment the second and the third antigen binding moiety and the Fc domain are part of an immunoglobulin molecule. In a particular embodiment the immunoglobulin molecule is an IgG class immunoglobulin. In an even more particular embodiment the immunoglobulin is an IgG 1 subclass immunoglobulin. In another embodiment the immunoglobulin is an IgG 4 subclass immunoglobulin. In a further particular embodiment the immunoglobulin is a human immunoglobulin. In other embodiments the immunoglobulin is a chimeric immunoglobulin or a humanized immunoglobulin. In one embodiment, the protease-activatable T cell activating bispecific molecule essentially consists of an immunoglobulin molecule capable of specific binding to a target cell antigen, and an antigen binding moiety capable of specific binding to CD3 wherein the antigen binding moiety is a Fab molecule, particularly a crossover Fab molecule, fused to the N-terminus of one of the immunoglobulin heavy chains, optionally via a peptide linker.

[0176] In a particular embodiment, the first and the third antigen binding moiety are each fused at the C-terminus of the Fab heavy chain to the N-terminus of one of the subunits of the Fc domain, and the second antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the Fab heavy chain of the first antigen binding moiety. In a specific such embodiment, the protease-activatable T cell activating bispecific molecule essentially consists of a first, a second and a third antigen binding moiety, an Fc domain composed of a first and a second subunit, and optionally one or more peptide linkers, wherein the second antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the Fab heavy chain of the first antigen binding moiety, and the first antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the first subunit of the Fc domain, and wherein the third antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the second subunit of the Fc domain. Optionally, the Fab light chain of the first antigen binding moiety and the Fab light chain of the second antigen binding moiety may additionally be fused to each other.

[0177] In one embodiment the present invention provides a protease-activatable T cell activating bispecific molecule comprising (i) a first antigen binding moiety which is a Fab molecule capable of specific binding to CD3, comprising the heavy chain complementarity determining region (CDR) 1 of SEQ ID NO: 44, the heavy chain CDR 2 of SEQ ID NO: 45, the heavy chain CDR 3 of SEQ ID NO: 46, the light chain CDR 1 of SEQ ID NO: 17, the light chain CDR 2 of SEQ ID NO: 18 and the light chain CDR 3 of SEQ ID NO: 19, wherein the first antigen binding moiety is a crossover Fab molecule wherein either the variable or the constant regions, particularly the constant regions, of the Fab light chain and the Fab heavy chain are exchanged; (ii) a second and a third antigen binding moiety each of which is a Fab molecule capable of specific binding to FolR1 comprising the heavy chain CDR 1 of SEQ ID NO: 14, the heavy chain CDR 2 of SEQ ID NO: 15, the heavy chain CDR 3 of SEQ ID NO: 16, the light chain CDR 1 of SEQ ID NO: 17, the light chain CDR 2 of SEQ ID NO: 18 and the light chain CDR3 of SEQ ID NO: 19.

[0178] In one embodiment the present invention provides a protease-activatable T cell activating bispecific molecule comprising (i) a first antigen binding moiety which is a Fab molecule capable of specific binding to CD3 comprising a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 43 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55, wherein the first antigen binding moiety is a crossover Fab molecule wherein either the variable or the constant regions, particularly the constant regions, of the Fab light chain and the Fab heavy chain are exchanged; (ii) a second and a third antigen binding moiety each of which is a Fab molecule capable of specific binding to FolR1 comprising heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 47 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55.

[0179] In one embodiment the present invention provides a protease-activatable T cell activating bispecific molecule comprising (i) a first antigen binding moiety which is a Fab molecule capable of specific binding to CD3, comprising the heavy chain complementarity determining region (CDR) 1 of SEQ ID NO: 44, the heavy chain CDR 2 of SEQ ID NO: 45, the heavy chain CDR 3 of SEQ ID NO: 46, the light chain CDR 1 of SEQ ID NO: 17, the light chain CDR 2 of SEQ ID NO: 18 and the light chain CDR 3 of SEQ ID NO: 19, wherein the first antigen binding moiety is a crossover Fab molecule wherein either the variable or the constant regions, particularly the constant regions, of the Fab light chain and the Fab heavy chain are exchanged; (ii) a second and a third antigen binding moiety each of which is a Fab molecule capable of specific binding to FolR1 comprising the heavy chain CDR 1 of SEQ ID NO: 151, the heavy chain CDR 2 of SEQ ID NO: 152, the heavy chain CDR 3 of SEQ ID NO: 153, the light chain CDR 1 of SEQ ID NO: 154, the light chain CDR 2 of SEQ ID NO: 155 and the light chain CDR3 of SEQ ID NO: 156.

[0180] In one embodiment the present invention provides a protease-activatable T cell activating bispecific molecule comprising (i) a first antigen binding moiety which is a Fab molecule capable of specific binding to CD3 comprising a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 43 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55, wherein the first antigen binding moiety is a crossover Fab molecule wherein either the variable or the constant regions, particularly the constant regions, of the Fab light chain and the Fab heavy chain are exchanged; (ii) a second and a third antigen binding moiety each of which is a Fab molecule capable of specific binding to FolR1 comprising heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 157 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 158.

[0181] In one embodiment the present invention provides a protease-activatable T cell activating bispecific molecule comprising (i) a first antigen binding moiety which is a Fab molecule capable of specific binding to CD3, comprising the heavy chain complementarity determining region (CDR) 1 of SEQ ID NO: 44, the heavy chain CDR 2 of SEQ ID NO: 45, the heavy chain CDR 3 of SEQ ID NO: 46, the light chain CDR 1 of SEQ ID NO: 17, the light chain CDR 2 of SEQ ID NO: 18 and the light chain CDR 3 of SEQ ID NO: 19, wherein the first antigen binding moiety is a crossover Fab molecule wherein either the variable or the constant regions, particularly the constant regions, of the Fab light chain and the Fab heavy chain are exchanged; (ii) a second and a third antigen binding moiety each of which is a Fab molecule capable of specific binding to HER1 comprising the heavy chain CDR 1 of SEQ ID NO: 56, the heavy chain CDR 2 of SEQ ID NO: 57, the heavy chain CDR 3 of SEQ ID NO: 58, the light chain CDR 1 of SEQ ID NO: 59, the light chain CDR 2 of SEQ ID NO: 60 and the light chain CDR3 of SEQ ID NO: 61.

[0182] In one embodiment the present invention provides a protease-activatable T cell activating bispecific molecule comprising (i) a first antigen binding moiety which is a Fab molecule capable of specific binding to CD3 comprising a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 43 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55, wherein the first antigen binding moiety is a crossover Fab molecule wherein either the variable or the constant regions, particularly the constant regions, of the Fab light chain and the Fab heavy chain are exchanged; (ii) a second and a third antigen binding moiety each of which is a Fab molecule capable of specific binding to HER1 comprising a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 115 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 116.

[0183] In one embodiment the present invention provides a protease-activatable T cell activating bispecific molecule comprising (i) a first antigen binding moiety which is a Fab molecule capable of specific binding to CD3, comprising the heavy chain complementarity determining region (CDR) 1 of SEQ ID NO: 44, the heavy chain CDR 2 of SEQ ID NO: 45, the heavy chain CDR 3 of SEQ ID NO: 46, the light chain CDR 1 of SEQ ID NO: 17, the light chain CDR 2 of SEQ ID NO: 18 and the light chain CDR 3 of SEQ ID NO: 19, wherein the first antigen binding moiety is a crossover Fab molecule wherein either the variable or the constant regions, particularly the constant regions, of the Fab light chain and the Fab heavy chain are exchanged; (ii) a second and a third antigen binding moiety each of which is a Fab molecule capable of specific binding to HER2, wherein the second antigen binding moiety comprises the heavy chain CDR 1 of SEQ ID NO: 142, the heavy chain CDR 2 of SEQ ID NO: 143, the heavy chain CDR 3 of SEQ ID NO: 144, the light chain CDR 1 of SEQ ID NO: 148, the light chain CDR 2 of SEQ ID NO: 149 and the light chain CDR3 of SEQ ID NO: 150, and wherein the third antigen binding moiety comprises the heavy chain CDR 1 of SEQ ID NO: 145, the heavy chain CDR 2 of SEQ ID NO: 146, the heavy chain CDR 3 of SEQ ID NO: 148, the light chain CDR 1 of SEQ ID NO: 148, the light chain CDR 2 of SEQ ID NO: 149 and the light chain CDR3 of SEQ ID NO: 150.

[0184] In one embodiment the present invention provides a protease-activatable T cell activating bispecific molecule comprising (i) a first antigen binding moiety which is a Fab molecule capable of specific binding to CD3 comprising a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 43 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55, wherein the first antigen binding moiety is a crossover Fab molecule wherein either the variable or the constant regions, particularly the constant regions, of the Fab light chain and the Fab heavy chain are exchanged; (ii) a second and a third antigen binding moiety each of which is a Fab molecule capable of specific binding to HER2, wherein the second antigen binding moiety comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 160 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 161, and wherein the third antigen binding moiety comprises a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 159 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 161.

[0185] In one embodiment the present invention provides a protease-activatable T cell activating bispecific molecule comprising (i) a first antigen binding moiety which is a Fab molecule capable of specific binding to CD3, comprising the heavy chain complementarity determining region (CDR) 1 of SEQ ID NO: 44, the heavy chain CDR 2 of SEQ ID NO: 45, the heavy chain CDR 3 of SEQ ID NO: 46, the light chain CDR 1 of SEQ ID NO: 17, the light chain CDR 2 of SEQ ID NO: 18 and the light chain CDR 3 of SEQ ID NO: 19, wherein the first antigen binding moiety is a crossover Fab molecule wherein either the variable or the constant regions, particularly the constant regions, of the Fab light chain and the Fab heavy chain are exchanged; (ii) a second and a third antigen binding moiety each of which is a Fab molecule capable of specific binding to Mesothelin comprising the heavy chain CDR 1 of SEQ ID NO: 107, the heavy chain CDR 2 of SEQ ID NO: 108, the heavy chain CDR 3 of SEQ ID NO: 109, the light chain CDR 1 of SEQ ID NO: 110, the light chain CDR 2 of SEQ ID NO: 111 and the light chain CDR3 of SEQ ID NO: 112.

[0186] In one embodiment the present invention provides a protease-activatable T cell activating bispecific molecule comprising (i) a first antigen binding moiety which is a Fab molecule capable of specific binding to CD3 comprising a heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 43 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55, wherein the first antigen binding moiety is a crossover Fab molecule wherein either the variable or the constant regions, particularly the constant regions, of the Fab light chain and the Fab heavy chain are exchanged; (ii) a second and a third antigen binding moiety each of which is a Fab molecule capable of specific binding to Mesothelin comprising heavy chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 113 and a light chain variable region comprising an amino acid sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 114.

[0187] The protease-activatable T cell activating bispecific molecule according to any of the ten above embodiments may further comprise (iii) an Fc domain composed of a first and a second subunit capable of stable association, wherein the second antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the Fab heavy chain of the first antigen binding moiety, and the first antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the first subunit of the Fc domain, and wherein the third antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the second subunit of the Fc domain.

[0188] In some of the protease-activatable T cell activating bispecific molecule of the invention, the Fab light chain of the first antigen binding moiety and the Fab light chain of the second antigen binding moiety are fused to each other, optionally via a linker peptide. Depending on the configuration of the first and the second antigen binding moiety, the Fab light chain of the first antigen binding moiety may be fused at its C-terminus to the N-terminus of the Fab light chain of the second antigen binding moiety, or the Fab light chain of the second antigen binding moiety may be fused at its C-terminus to the N-terminus of the Fab light chain of the first antigen binding moiety. Fusion of the Fab light chains of the first and the second antigen binding moiety further reduces mispairing of unmatched Fab heavy and light chains, and also reduces the number of plasmids needed for expression of some of the protease-activatable T cell activating bispecific molecule of the invention.

[0189] In certain embodiments the protease-activatable T cell activating bispecific molecule comprises a polypeptide wherein the Fab light chain variable region of the first antigen binding moiety shares a carboxy-terminal peptide bond with the Fab heavy chain constant region of the first antigen binding moiety (i.e. a the first antigen binding moiety comprises a crossover Fab heavy chain, wherein the heavy chain variable region is replaced by a light chain variable region), which in turn shares a carboxy-terminal peptide bond with an Fc domain subunit (VL (1) -CH1 (1) -CH2-CH3(-CH4)), and a polypeptide wherein a the Fab heavy chain of the second antigen binding moiety shares a carboxy-terminal peptide bond with an Fc domain subunit (VH (2) -CH1 (2) -CH2-CH3(-CH4)). In some embodiments the protease-activatable T cell activating bispecific molecule further comprises a polypeptide wherein the Fab heavy chain variable region of the first antigen binding moiety shares a carboxy-terminal peptide bond with the Fab light chain constant region of the first antigen binding moiety (VH (1) -CL (1) ) and the Fab light chain polypeptide of the second antigen binding moiety (VL (2) -CL (2) ). In certain embodiments the polypeptides are covalently linked, e.g., by a disulfide bond.

[0190] In alternative embodiments the protease-activatable T cell activating bispecific molecule comprises a polypeptide wherein the Fab heavy chain variable region of the first antigen binding moiety shares a carboxy-terminal peptide bond with the Fab light chain constant region of the first antigen binding moiety (i.e. the first antigen binding moiety comprises a crossover Fab heavy chain, wherein the heavy chain constant region is replaced by a light chain constant region), which in turn shares a carboxy-terminal peptide bond with an Fc domain subunit (VH(i)-CL(i)-CH2-CH3(-CH4)), and a polypeptide wherein the Fab heavy chain of the second antigen binding moiety shares a carboxy-terminal peptide bond with an Fc domain subunit (VH (2) -CH1 (2) -CH2-CH3(-CH4)). In some embodiments the protease-activatable T cell activating bispecific molecule further comprises a polypeptide wherein the Fab light chain variable region of the first antigen binding moiety shares a carboxy-terminal peptide bond with the Fab heavy chain constant region of the first antigen binding moiety (VL (1) -CH1 (1) ) and the Fab light chain polypeptide of the second antigen binding moiety (VL (2) -CL (2) ). In certain embodiments the polypeptides are covalently linked, e.g., by a disulfide bond.

[0191] In some embodiments, the protease-activatable T cell activating bispecific molecule comprises a polypeptide wherein the Fab light chain variable region of the first antigen binding moiety shares a carboxy-terminal peptide bond with the Fab heavy chain constant region of the first antigen binding moiety (i.e. the first antigen binding moiety comprises a crossover Fab heavy chain, wherein the heavy chain variable region is replaced by a light chain variable region), which in turn shares a carboxy-terminal peptide bond with the Fab heavy chain of the second antigen binding moiety, which in turn shares a carboxy-terminal peptide bond with an Fc domain subunit (VL (1) -CH1 (1) -VH (2) -CH1 (2) -CH2-CH3(-CH4)). In other embodiments, the protease-activatable T cell activating bispecific molecule comprises a polypeptide wherein the Fab heavy chain variable region of the first antigen binding moiety shares a carboxy-terminal peptide bond with the Fab light chain constant region of the first antigen binding moiety (i.e. the first antigen binding moiety comprises a crossover Fab heavy chain, wherein the heavy chain constant region is replaced by a light chain constant region), which in turn shares a carboxy-terminal peptide bond with the Fab heavy chain of the second antigen binding moiety, which in turn shares a carboxy-terminal peptide bond with an Fc domain subunit (VH (1) -CL (1) -VH (2) -CH1 (2) -CH2-CH3(-CH4)). In still other embodiments, the protease-activatable T cell activating bispecific molecule comprises a polypeptide wherein the Fab heavy chain of the second antigen binding moiety shares a carboxy-terminal peptide bond with the Fab light chain variable region of the first antigen binding moiety which in turn shares a carboxy-terminal peptide bond with the Fab heavy chain constant region of the first antigen binding moiety (i.e. the first antigen binding moiety comprises a crossover Fab heavy chain, wherein the heavy chain variable region is replaced by a light chain variable region), which in turn shares a carboxy-terminal peptide bond with an Fc domain subunit (VH (2) -CH1 (2) -VL (1) -CH1 (1) -CH2-CH3(-CH4)). In other embodiments, the protease-activatable T cell activating bispecific molecule comprises a polypeptide wherein the Fab heavy chain of the second antigen binding moiety shares a carboxy-terminal peptide bond with the Fab heavy chain variable region of the first antigen binding moiety which in turn shares a carboxy-terminal peptide bond with the Fab light chain constant region of the first antigen binding moiety (i.e. the first antigen binding moiety comprises a crossover Fab heavy chain, wherein the heavy chain constant region is replaced by a light chain constant region), which in turn shares a carboxy-terminal peptide bond with an Fc domain subunit (VH (2) -CH1 (2) -VH (1) -CL (1) -CH2-CH3(-CH4)).

[0192] In some of these embodiments the protease-activatable T cell activating bispecific molecule further comprises a crossover Fab light chain polypeptide of the first antigen binding moiety, wherein the Fab heavy chain variable region of the first antigen binding moiety shares a carboxy-terminal peptide bond with the Fab light chain constant region of the first antigen binding moiety (VH(i)-CL(i)), and the Fab light chain polypeptide of the second antigen binding moiety (VL (2) -CL (2) ). In others of these embodiments the protease-activatable T cell activating bispecific molecule further comprises a crossover Fab light chain polypeptide, wherein the Fab light chain variable region of the first antigen binding moiety shares a carboxy-terminal peptide bond with the Fab heavy chain constant region of the first antigen binding moiety (VL (1) -CH1 (1) ), and the Fab light chain polypeptide of the second antigen binding moiety (VL (2) -CL (2) ). In still others of these embodiments the protease-activatable T cell activating bispecific molecule further comprises a polypeptide wherein the Fab light chain variable region of the first antigen binding moiety shares a carboxy-terminal peptide bond with the Fab heavy chain constant region of the first antigen binding moiety which in turn shares a carboxy-terminal peptide bond with the Fab light chain polypeptide of the second antigen binding moiety (VL (1) -CH1 (1) -VL (2) -CL (2) ), a polypeptide wherein the Fab heavy chain variable region of the first antigen binding moiety shares a carboxy-terminal peptide bond with the Fab light chain constant region of the first antigen binding moiety which in turn shares a carboxy-terminal peptide bond with the Fab light chain polypeptide of the second antigen binding moiety (VH (1) -CL (1) -VL (2) -CL (2) ), a polypeptide wherein the Fab light chain polypeptide of the second antigen binding moiety shares a carboxy-terminal peptide bond with the Fab light chain variable region of the first antigen binding moiety which in turn shares a carboxy-terminal peptide bond with the Fab heavy chain constant region of the first antigen binding moiety (VL (2) -CL (2) -VL (1) -CH1 (1) ), or a polypeptide wherein the Fab light chain polypeptide of the second antigen binding moiety shares a carboxy-terminal peptide bond with the Fab heavy chain variable region of the first antigen binding moiety which in turn shares a carboxy-terminal peptide bond with the Fab light chain constant region of the first antigen binding moiety (VL (2) -CL (2) -VH (1) -CL (1) ).

[0193] The protease-activatable T cell activating bispecific molecule according to these embodiments may further comprise (i) an Fc domain subunit polypeptide (CH2-CH3(-CH4)), or (ii) a polypeptide wherein the Fab heavy chain of a third antigen binding moiety shares a carboxy-terminal peptide bond with an Fc domain subunit (VH (3) -CH1 (3) -CH2-CH3(-CH4)) and the Fab light chain polypeptide of a third antigen binding moiety (VL (3) -CL (3) ). In certain embodiments the polypeptides are covalently linked, e.g., by a disulfide bond.

[0194] According to any of the above embodiments, components of the protease-activatable T cell activating bispecific molecule (e.g., antigen binding moiety, Fc domain) may be fused directly or through various linkers, particularly peptide linkers comprising one or more amino acids, typically about 2-20 amino acids, that are described herein or are known in the art. Suitable, non-immunogenic peptide linkers include, for example, (G 4 S) n , (SG 4 ) n , (G 4 S) n or G 4 (SG 4 ) n peptide linkers, wherein n is generally a number between 1 and 10, typically between 2 and 4.Fc domain

[0195] The Fc domain of the protease-activatable T cell activating bispecific molecule consists of a pair of polypeptide chains comprising heavy chain domains of an immunoglobulin molecule. For example, the Fc domain of an immunoglobulin G (IgG) molecule is a dimer, each subunit of which comprises the CH2 and CH3 IgG heavy chain constant domains. The two subunits of the Fc domain are capable of stable association with each other. In one embodiment the protease-activatable T cell activating bispecific molecule of the invention comprises not more than one Fc domain.

[0196] In one embodiment according the invention the Fc domain of the protease-activatable T cell activating bispecific molecule is an IgG Fc domain. In a particular embodiment the Fc domain is an IgG 1 Fc domain. In another embodiment the Fc domain is an IgG 4 Fc domain. In a more specific embodiment, the Fc domain is an IgG 4 Fc domain comprising an amino acid substitution at position S228 (Kabat numbering), particularly the amino acid substitution S228P. This amino acid substitution reduces in vivo Fab arm exchange of IgG 4 antibodies (see Stubenrauch et al., Drug Metabolism and Disposition 38, 84-91 (2010)). In a further particular embodiment the Fc domain is human.Fc domain modifications promoting heterodimerization

[0197] Protease-activatable T cell activating bispecific molecules according to the invention comprise different antigen binding moieties, fused to one or the other of the two subunits of the Fc domain, thus the two subunits of the Fc domain are typically comprised in two non-identical polypeptide chains. Recombinant co-expression of these polypeptides and subsequent dimerization leads to several possible combinations of the two polypeptides. To improve the yield and purity of protease-activatable T cell activating bispecific molecules in recombinant production, it will thus be advantageous to introduce in the Fc domain of the protease-activatable T cell activating bispecific molecule a modification promoting the association of the desired polypeptides. Accordingly, in particular embodiments the Fc domain of the protease-activatable T cell activating bispecific molecule according to the invention comprises a modification promoting the association of the first and the second subunit of the Fc domain. The site of most extensive protein-protein interaction between the two subunits of a human IgG Fc domain is in the CH3 domain of the Fc domain. Thus, in one embodiment said modification is in the CH3 domain of the Fc domain.

[0198] In a specific embodiment said modification is a so-called "knob-into-hole" modification, comprising a "knob" modification in one of the two subunits of the Fc domain and a "hole" modification in the other one of the two subunits of the Fc domain.

[0199] The knob-into-hole technology is described e.g., in US 5,731,168; US 7,695,936; Ridgway et al., Prot Eng 9, 617-621 (1996) and Carter, J Immunol Meth 248, 7-15 (2001). Generally, the method involves introducing a protuberance ("knob") at the interface of a first polypeptide and a corresponding cavity ("hole") in the interface of a second polypeptide, such that the protuberance can be positioned in the cavity so as to promote heterodimer formation and hinder homodimer formation. Protuberances are constructed by replacing small amino acid side chains from the interface of the first polypeptide with larger side chains (e.g., tyrosine or tryptophan). Compensatory cavities of identical or similar size to the protuberances are created in the interface of the second polypeptide by replacing large amino acid side chains with smaller ones (e.g., alanine or threonine).

[0200] Accordingly, in a particular embodiment, in the CH3 domain of the first subunit of the Fc domain of the protease-activatable T cell activating bispecific molecule an amino acid residue is replaced with an amino acid residue having a larger side chain volume, thereby generating a protuberance within the CH3 domain of the first subunit which is positionable in a cavity within the CH3 domain of the second subunit, and in the CH3 domain of the second subunit of the Fc domain an amino acid residue is replaced with an amino acid residue having a smaller side chain volume, thereby generating a cavity within the CH3 domain of the second subunit within which the protuberance within the CH3 domain of the first subunit is positionable.

[0201] The protuberance and cavity can be made by altering the nucleic acid encoding the polypeptides, e.g., by site-specific mutagenesis, or by peptide synthesis.

[0202] In a specific embodiment, in the CH3 domain of the first subunit of the Fc domain the threonine residue at position 366 is replaced with a tryptophan residue (T366W), and in the CH3 domain of the second subunit of the Fc domain the tyrosine residue at position 407 is replaced with a valine residue (Y407V). In one embodiment, in the second subunit of the Fc domain additionally the threonine residue at position 366 is replaced with a serine residue (T366S) and the leucine residue at position 368 is replaced with an alanine residue (L368A).

[0203] In yet a further embodiment, in the first subunit of the Fc domain additionally the serine residue at position 354 is replaced with a cysteine residue (S354C), and in the second subunit of the Fc domain additionally the tyrosine residue at position 349 is replaced by a cysteine residue (Y349C). Introduction of these two cysteine residues results in formation of a disulfide bridge between the two subunits of the Fc domain, further stabilizing the dimer (Carter, J Immunol Methods 248, 7-15 (2001)).

[0204] In a particular embodiment the antigen binding moiety capable of binding to CD3 is fused (optionally via the antigen binding moiety capable of binding to a target cell antigen) to the first subunit of the Fc domain (comprising the "knob" modification). Without wishing to be bound by theory, fusion of the antigen binding moiety capable of binding to CD3 to the knob-containing subunit of the Fc domain will (further) minimize the generation of antigen binding molecules comprising two antigen binding moieties capable of binding to CD3 (steric clash of two knob-containing polypeptides).

[0205] In an alternative embodiment a modification promoting association of the first and the second subunit of the Fc domain comprises a modification mediating electrostatic steering effects, e.g., as described in PCT publication WO 2009 / 089004. Generally, this method involves replacement of one or more amino acid residues at the interface of the two Fc domain subunits by charged amino acid residues so that homodimer formation becomes electrostatically unfavorable but heterodimerization electrostatically favorable.Fc domain modifications reducing Fc receptor binding and / or effector function

[0206] The Fc domain confers to the protease-activatable T cell activating bispecific molecule favorable pharmacokinetic properties, including a long serum half-life which contributes to good accumulation in the target tissue and a favorable tissue-blood distribution ratio. At the same time it may, however, lead to undesirable targeting of the protease-activatable T cell activating bispecific molecule to cells expressing Fc receptors rather than to the preferred antigen-bearing cells. Moreover, the co-activation of Fc receptor signaling pathways may lead to cytokine release which, in combination with the T cell activating properties and the long half-life of the antigen binding molecule, results in excessive activation of cytokine receptors and severe side effects upon systemic administration. Activation of (Fc receptor-bearing) immune cells other than T cells may even reduce efficacy of the protease-activatable T cell activating bispecific molecule due to the potential destruction of T cells e.g., by NK cells.

[0207] Accordingly, in particular embodiments the Fc domain of the protease-activatable T cell activating bispecific molecules according to the invention exhibits reduced binding affinity to an Fc receptor and / or reduced effector function, as compared to a native IgG 1 Fc domain. In one such embodiment the Fc domain (or the protease-activatable T cell activating bispecific molecule comprising said Fc domain) exhibits less than 50%, preferably less than 20%, more preferably less than 10% and most preferably less than 5% of the binding affinity to an Fc receptor, as compared to a native IgG 1 Fc domain (or a protease-activatable T cell activating bispecific molecule comprising a native IgG 1 Fc domain), and / or less than 50%, preferably less than 20%, more preferably less than 10% and most preferably less than 5% of the effector function, as compared to a native IgG 1 Fc domain domain (or a protease-activatable T cell activating bispecific molecule comprising a native IgG 1 Fc domain). In one embodiment, the Fc domain domain (or the protease-activatable T cell activating bispecific molecule comprising said Fc domain) does not substantially bind to an Fc receptor and / or induce effector function. In a particular embodiment the Fc receptor is an Fcγ receptor. In one embodiment the Fc receptor is a human Fc receptor. In one embodiment the Fc receptor is an activating Fc receptor. In a specific embodiment the Fc receptor is an activating human Fcγ receptor, more specifically human FcyRIIIa, FcyRI or FcyRIIa, most specifically human FcyRIIIa. In one embodiment the effector function is one or more selected from the group of CDC, ADCC, ADCP, and cytokine secretion. In a particular embodiment the effector function is ADCC. In one embodiment the Fc domain domain exhibits substantially similar binding affinity to neonatal Fc receptor (FcRn), as compared to a native IgG 1 Fc domain domain. Substantially similar binding to FcRn is achieved when the Fc domain (or the protease-activatable T cell activating bispecific molecule comprising said Fc domain) exhibits greater than about 70%, particularly greater than about 80%, more particularly greater than about 90% of the binding affinity of a native IgG 1 Fc domain (or the protease-activatable T cell activating bispecific molecule comprising a native IgG 1 Fc domain) to FcRn.

[0208] In certain embodiments the Fc domain is engineered to have reduced binding affinity to an Fc receptor and / or reduced effector function, as compared to a non-engineered Fc domain. In particular embodiments, the Fc domain of the protease-activatable T cell activating bispecific molecule comprises one or more amino acid mutation that reduces the binding affinity of the Fc domain to an Fc receptor and / or effector function. Typically, the same one or more amino acid mutation is present in each of the two subunits of the Fc domain. In one embodiment the amino acid mutation reduces the binding affinity of the Fc domain to an Fc receptor. In one embodiment the amino acid mutation reduces the binding affinity of the Fc domain to an Fc receptor by at least 2-fold, at least 5-fold, or at least 10-fold. In embodiments where there is more than one amino acid mutation that reduces the binding affinity of the Fc domain to the Fc receptor, the combination of these amino acid mutations may reduce the binding affinity of the Fc domain to an Fc receptor by at least 10-fold, at least 20-fold, or even at least 50-fold. In one embodiment the protease-activatable T cell activating bispecific molecule comprising an engineered Fc domain exhibits less than 20%, particularly less than 10%, more particularly less than 5% of the binding affinity to an Fc receptor as compared to a protease-activatable T cell activating bispecific molecule comprising a non-engineered Fc domain. In a particular embodiment the Fc receptor is an Fcγ receptor. In some embodiments the Fc receptor is a human Fc receptor. In some embodiments the Fc receptor is an activating Fc receptor. In a specific embodiment the Fc receptor is an activating human Fcγ receptor, more specifically human FcyRIIIa, FcyRI or FcyRIIa, most specifically human FcyRIIIa. Preferably, binding to each of these receptors is reduced. In some embodiments binding affinity to a complement component, specifically binding affinity to C1q, is also reduced. In one embodiment binding affinity to neonatal Fc receptor (FcRn) is not reduced. Substantially similar binding to FcRn, i.e. preservation of the binding affinity of the Fc domain to said receptor, is achieved when the Fc domain (or the protease-activatable T cell activating bispecific molecule comprising said Fc domain) exhibits greater than about 70% of the binding affinity of a non-engineered form of the Fc domain (or the protease-activatable T cell activating bispecific molecule comprising said non-engineered form of the Fc domain) to FcRn. The Fc domain, or protease-activatable T cell activating bispecific molecules of the invention comprising said Fc domain, may exhibit greater than about 80% and even greater than about 90% of such affinity. In certain embodiments the Fc domain of the protease-activatable T cell activating bispecific molecule is engineered to have reduced effector function, as compared to a non-engineered Fc domain. The reduced effector function can include, but is not limited to, one or more of the following: reduced complement dependent cytotoxicity (CDC), reduced antibody-dependent cell-mediated cytotoxicity (ADCC), reduced antibody-dependent cellular phagocytosis (ADCP), reduced cytokine secretion, reduced immune complex-mediated antigen uptake by antigen-presenting cells, reduced binding to NK cells, reduced binding to macrophages, reduced binding to monocytes, reduced binding to polymorphonuclear cells, reduced direct signaling inducing apoptosis, reduced crosslinking of target-bound antibodies, reduced dendritic cell maturation, or reduced T cell priming. In one embodiment the reduced effector function is one or more selected from the group of reduced CDC, reduced ADCC, reduced ADCP, and reduced cytokine secretion. In a particular embodiment the reduced effector function is reduced ADCC. In one embodiment the reduced ADCC is less than 20% of the ADCC induced by a non-engineered Fc domain (or a protease-activatable T cell activating bispecific molecule comprising a non-engineered Fc domain).

[0209] In one embodiment the amino acid mutation that reduces the binding affinity of the Fc domain to an Fc receptor and / or effector function is an amino acid substitution. In one embodiment the Fc domain comprises an amino acid substitution at a position selected from the group of E233, L234, L235, N297, P331 and P329. In a more specific embodiment the Fc domain comprises an amino acid substitution at a position selected from the group of L234, L235 and P329. In some embodiments the Fc domain comprises the amino acid substitutions L234A and L235A. In one such embodiment, the Fc domain is an IgG 1 Fc domain, particularly a human IgG 1 Fc domain. In one embodiment the Fc domain comprises an amino acid substitution at position P329. In a more specific embodiment the amino acid substitution is P329A or P329G, particularly P329G. In one embodiment the Fc domain comprises an amino acid substitution at position P329 and a further amino acid substitution at a position selected from E233, L234, L235, N297 and P331. In a more specific embodiment the further amino acid substitution is E233P, L234A, L235A, L235E, N297A, N297D or P331S. In particular embodiments the Fc domain comprises amino acid substitutions at positions P329, L234 and L235. In more particular embodiments the Fc domain comprises the amino acid mutations L234A, L235A and P329G ("P329G LALA"). In one such embodiment, the Fc domain is an IgG 1 Fc domain, particularly a human IgG 1 Fc domain. The "P329G LALA" combination of amino acid substitutions almost completely abolishes Fcγ receptor (as well as complement) binding of a human IgG 1 Fc domain, as described in PCT publication no. WO 2012 / 130831. WO 2012 / 130831 also describes methods of preparing such mutant Fc domains and methods for determining its properties such as Fc receptor binding or effector functions.

[0210] IgG 4 antibodies exhibit reduced binding affinity to Fc receptors and reduced effector functions as compared to IgG 1 antibodies. Hence, in some embodiments the Fc domain of the protease-activatable T cell activating bispecific molecules of the invention is an IgG 4 Fc domain, particularly a human IgG 4 Fc domain. In one embodiment the IgG 4 Fc domain comprises amino acid substitutions at position S228, specifically the amino acid substitution S228P. To further reduce its binding affinity to an Fc receptor and / or its effector function, in one embodiment the IgG 4 Fc domain comprises an amino acid substitution at position L235, specifically the amino acid substitution L235E. In another embodiment, the IgG 4 Fc domain comprises an amino acid substitution at position P329, specifically the amino acid substitution P329G. In a particular embodiment, the IgG 4 Fc domain comprises amino acid substitutions at positions S228, L235 and P329, specifically amino acid substitutions S228P, L235E and P329G. Such IgG 4 Fc domain mutants and their Fcγ receptor binding properties are described in PCT publication no. WO 2012 / 130831.

[0211] In a particular embodiment the Fc domain exhibiting reduced binding affinity to an Fc receptor and / or reduced effector function, as compared to a native IgG 1 Fc domain, is a human IgG 1 Fc domain comprising the amino acid substitutions L234A, L235A and optionally P329G, or a human IgG 4 Fc domain comprising the amino acid substitutions S228P, L235E and optionally P329G.

[0212] In certain embodiments N-glycosylation of the Fc domain has been eliminated. In one such embodiment the Fc domain comprises an amino acid mutation at position N297, particularly an amino acid substitution replacing asparagine by alanine (N297A) or aspartic acid (N297D).

[0213] In addition to the Fc domains described hereinabove and in PCT publication no. WO 2012 / 130831, Fc domains with reduced Fc receptor binding and / or effector function also include those with substitution of one or more of Fc domain residues 238, 265, 269, 270, 297, 327 and 329 (U.S. Patent No. 6,737,056). Such Fc mutants include Fc mutants with substitutions at two or more of amino acid positions 265, 269, 270, 297 and 327, including the so-called "DANA" Fc mutant with substitution of residues 265 and 297 to alanine (US Patent No. 7,332,581).

[0214] Mutant Fc domains can be prepared by amino acid deletion, substitution, insertion or modification using genetic or chemical methods well known in the art. Genetic methods may include site-specific mutagenesis of the encoding DNA sequence, PCR, gene synthesis, and the like. The correct nucleotide changes can be verified for example by sequencing.

[0215] Binding to Fc receptors can be easily determined e.g., by ELISA, or by Surface Plasmon Resonance (SPR) using standard instrumentation such as a BIAcore instrument (GE Healthcare), and Fc receptors such as may be obtained by recombinant expression. A suitable such binding assay is described herein. Alternatively, binding affinity of Fc domains or cell activating bispecific antigen binding molecules comprising an Fc domain for Fc receptors may be evaluated using cell lines known to express particular Fc receptors, such as human NK cells expressing FcyIIIa receptor.

[0216] Effector function of an Fc domain, or a protease-activatable T cell activating bispecific molecule comprising an Fc domain, can be measured by methods known in the art. A suitable assay for measuring ADCC is described herein. Other examples of in vitro assays to assess ADCC activity of a molecule of interest are described in U.S. Patent No. 5,500,362; Hellstrom et al. Proc Natl Acad Sci USA 83, 7059-7063 (1986) and Hellstrom et al., Proc Natl Acad Sci USA 82, 1499-1502 (1985); U.S. Patent No. 5,821,337; Bruggemann et al., J Exp Med 166, 1351-1361 (1987). Alternatively, non-radioactive assays methods may be employed (see, for example, ACTI ™< non-radioactive cytotoxicity assay for flow cytometry (CellTechnology, Inc. Mountain View, CA); and CytoTox 96 ®< non-radioactive cytotoxicity assay (Promega, Madison, WI)). Useful effector cells for such assays include peripheral blood mononuclear cells (PBMC) and Natural Killer (NK) cells. Alternatively, or additionally, ADCC activity of the molecule of interest may be assessed in vivo, e.g., in a animal model such as that disclosed in Clynes et al., Proc Natl Acad Sci USA 95, 652-656 (1998).

[0217] In some embodiments, binding of the Fc domain to a complement component, specifically to C1q, is reduced. Accordingly, in some embodiments wherein the Fc domain is engineered to have reduced effector function, said reduced effector function includes reduced CDC. C1q binding assays may be carried out to determine whether the protease-activatable T cell activating bispecific molecule is able to bind C1q and hence has CDC activity. See e.g., C1q and C3c binding ELISA in WO 2006 / 029879 and WO 2005 / 100402. To assess complement activation, a CDC assay may be performed (see, for example, Gazzano-Santoro et al., J Immunol Methods 202, 163 (1996); Cragg et al., Blood 101, 1045-1052 (2003); and Cragg and Glennie, Blood 103, 2738-2743 (2004)).Antigen Binding Moieties

[0218] The antigen binding molecule of the invention is bispecific, i.e. it comprises at least two antigen binding moieties capable of specific binding to two distinct antigenic determinants. According to the invention, the antigen binding moieties are Fab molecules (i.e. antigen binding domains composed of a heavy and a light chain, each comprising a variable and a constant region). In one embodiment said Fab molecules are human. In another embodiment said Fab molecules are humanized. In yet another embodiment said Fab molecules comprise human heavy and light chain constant regions.

[0219] At least one of the antigen binding moieties is a crossover Fab molecule. Such modification prevent mispairing of heavy and light chains from different Fab molecules, thereby improving the yield and purity of the protease-activatable T cell activating bispecific molecule of the invention in recombinant production. In a particular crossover Fab molecule useful for the protease-activatable T cell activating bispecific molecule of the invention, the constant regions of the Fab light chain and the Fab heavy chain are exchanged. In another crossover Fab molecule useful for the protease-activatable T cell activating bispecific molecule of the invention, the variable regions of the Fab light chain and the Fab heavy chain are exchanged.

[0220] In a particular embodiment according to the invention, the protease-activatable T cell activating bispecific molecule is capable of simultaneous binding to a target cell antigen, particularly a tumor cell antigen, and CD3. In one embodiment, the protease-activatable T cell activating bispecific molecule is capable of crosslinking a T cell and a target cell by simultaneous binding to a target cell antigen and CD3. In an even more particular embodiment, such simultaneous binding results in lysis of the target cell, particularly a tumor cell. In one embodiment, such simultaneous binding results in activation of the T cell. In other embodiments, such simultaneous binding results in a cellular response of a T lymphocyte, particularly a cytotoxic T lymphocyte, selected from the group of proliferation, differentiation, cytokine secretion, cytotoxic effector molecule release, cytotoxic activity, and expression of activation markers. In one embodiment, binding of the protease-activatable T cell activating bispecific molecule to CD3 without simultaneous binding to the target cell antigen does not result in T cell activation.

[0221] In one embodiment, the protease-activatable T cell activating bispecific molecule is capable of re-directing cytotoxic activity of a T cell to a target cell. In a particular embodiment, said redirection is independent of MHC-mediated peptide antigen presentation by the target cell and and / or specificity of the T cell.

[0222] Particularly, a T cell according to any of the embodiments of the invention is a cytotoxic T cell. In some embodiments the T cell is a CD4 +< or a CD8 +< T cell, particularly a CD8 +< T cell.CD3 binding moiety

[0223] The protease-activatable T cell activating bispecific molecule of the invention comprises at least one antigen binding moiety capable of binding to CD3 (also referred to herein as an "CD3 antigen binding moiety" or "first antigen binding moiety"). In a particular embodiment, the protease-activatable T cell activating bispecific molecule comprises not more than one antigen binding moiety capable of specific binding to CD3. In one embodiment the protease-activatable T cell activating bispecific molecule provides monovalent binding to CD3. The CD3 antigen binding is a crossover Fab molecule, i.e. a Fab molecule wherein either the variable or the constant regions of the Fab heavy and light chains are exchanged. In embodiments where there is more than one antigen binding moiety capable of specific binding to a target cell antigen comprised in the protease-activatable T cell activating bispecific molecule, the antigen binding moiety capable of specific binding to CD3 preferably is a crossover Fab molecule and the antigen binding moieties capable of specific binding to a target cell antigen are conventional Fab molecules.

[0224] In a particular embodiment CD3 is human CD3 or cynomolgus CD3, most particularly human CD3. In a particular embodiment the CD3 antigen binding moiety is cross-reactive for (i.e. specifically binds to) human and cynomolgus CD3. In some embodiments, the first antigen binding moiety is capable of specific binding to the epsilon subunit of CD3.

[0225] The CD3 antigen binding moiety comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 11, SEQ ID NO: 12 and SEQ ID NO: 13 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19.

[0226] In one embodiment the CD3 antigen binding moiety comprises the heavy chain CDR1 of SEQ ID NO: 11, the heavy chain CDR2 of SEQ ID NO: 12, the heavy chain CDR3 of SEQ ID NO: 13, the light chain CDR1 of SEQ ID NO: 17, the light chain CDR2 of SEQ ID NO: 18, and the light chain CDR3 of SEQ ID NO: 19.

[0227] In one embodiment the CD3 antigen binding moiety comprises the heavy chain CDR1 of SEQ ID NO: 44, the heavy chain CDR2 of SEQ ID NO: 45, the heavy chain CDR3 of SEQ ID NO: 46, the light chain CDR1 of SEQ ID NO: 17, the light chain CDR2 of SEQ ID NO: 18, and the light chain CDR3 of SEQ ID NO: 19.

[0228] In one embodiment the CD3 antigen binding moiety comprises a heavy chain variable region sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 43, and a light chain variable region sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to the amino acid sequence of SEQ ID NO: 55.

[0229] In one embodiment the CD3 antigen binding moiety comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 43 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 55.

[0230] In one embodiment the CD3 antigen binding moiety comprises the heavy chain variable region sequence of SEQ ID NO: 43 and the light chain variable region sequence of SEQ ID NO: 55.Target cell antigen binding moiety

[0231] The protease-activatable T cell activating bispecific molecule of the invention comprises at least one antigen binding moiety capable of binding to a target cell antigen (also referred to herein as an "target cell antigen binding moiety" or "second" or "third" antigen binding moiety). In certain embodiments, the protease-activatable T cell activating bispecific molecule comprises two antigen binding moieties capable of binding to a target cell antigen. In a particular such embodiment, each of these antigen binding moieties specifically binds to the same antigenic determinant. In an even more particular embodiment, all of these antigen binding moieties are identical. In one embodiment, the protease-activatable T cell activating bispecific molecule comprises an immunoglobulin molecule capable of specific binding to a target cell antigen. In one embodiment the protease-activatable T cell activating bispecific molecule comprises not more than two antigen binding moieties capable of binding to a target cell antigen.

[0232] In a preferred embodiment, the target cell antigen binding moiety is a Fab molecule, particularly a conventional Fab molecule that binds to a specific antigenic determinant and is able to direct the Protease-activatable T cell activating bispecific molecule to a target site, for example to a specific type of tumor cell that bears the antigenic determinant.

[0233] In certain embodiments the target cell antigen binding moiety specifically binds to a cell surface antigen. In a particular embodiment the target cell antigen binding moiety specifically binds to a Folate Receptor 1 (FolR1) on the surface of a target cell. In another specific such embodiment the target cell antigen binding moiety specifically binds to an epidermal growth factor receptor (EGFR), specifically, a human EGFR, e.g., HER1. In another specific such embodiment the target cell antigen binding moiety specifically binds to HER2. In another specific such embodiment the target cell antigen binding moiety specifically binds to Mesothelin, specifically, to human Mesothelin.

[0234] In certain embodiments the target cell antigen binding moiety is directed to an antigen associated with a pathological condition, such as an antigen presented on a tumor cell or on a virus-infected cell. Suitable antigens are cell surface antigens, for example, but not limited to, cell surface receptors. In particular embodiments the antigen is a human antigen. In a specific embodiment the target cell antigen is selected from Folate Receptor 1 (FolR1) and epidermal growth factor receptor (EGFR), specifically, a human EGFR, e.g., HER1. In a further specific embodiment the target cell antigen is HER2. In a further specific embodiment the target cell antigen is Mesothelin.

[0235] In some embodiments the protease-activatable T cell activating bispecific molecule comprises at least one antigen binding moiety that is specific for HER1. In one embodiment, the antigen binding moiety that is specific for HER1 comprises at least one heavy chain complementarity determining region (CDR) of selected from the group consisting of SEQ ID NO: 56, SEQ ID NO: 57 and SEQ ID NO: 58 and at least one light chain CDR selected from the group of SEQ ID NO: 59, SEQ ID NO: 60, and SEQ ID NO: 61.

[0236] In one embodiment, the antigen binding moiety that is specific for HER1 comprises the heavy chain CDR1 of SEQ ID NO: 56, the heavy chain CDR2 of SEQ ID NO: 57, the heavy chain CDR3 of SEQ ID NO: 58, the light chain CDR1 of SEQ ID NO: 59, the light chain CDR2 of SEQ ID NO: 60, and the light chain CDR3 of SEQ ID NO: 61.

[0237] In one embodiment, the antigen binding moiety that is specific for HER1 comprises the heavy chain and light chain CDR sequences of an anti-HER1 antibody disclosed in PCT Application Publication Number WO2006 / 082515.

[0238] In one embodiment the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for HER1 comprises at least one of a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 32, a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 33, a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 34. In one embodiment the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for HER1 comprises the polypeptide sequence of SEQ ID NO: 32, the polypeptide sequence of SEQ ID NO: 33, and the polypeptide sequence of SEQ ID NO: 34.

[0239] In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for HER1 further comprises an anti-idiotypic CD3 scFv comprising at least one of the heavy chain CDR1 of SEQ ID NO: 20, the heavy chain CDR2 of SEQ ID NO: 21, the heavy chain CDR3 of SEQ ID NO: 22, the light chain CDR1 of SEQ ID NO: 23, the light chain CDR2 of SEQ ID NO: 24, and the light chain CDR3 of SEQ ID NO: 25. In one embodiment, the anti-idiotypic scFv comprises the heavy chain CDR1 of SEQ ID NO: 20, the heavy chain CDR2 of SEQ ID NO: 21, the heavy chain CDR3 of SEQ ID NO: 22, the light chain CDR1 of SEQ ID NO: 23, the light chain CDR2 of SEQ ID NO: 24, and the light chain CDR3 of SEQ ID NO: 25.

[0240] In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for HER1 further comprises an anti-idiotypic CD3 scFv comprising at least one of the heavy chain CDR1 of SEQ ID NO: 26, the heavy chain CDR2 of SEQ ID NO: 27, the heavy chain CDR3 of SEQ ID NO: 28, the light chain CDR1 of SEQ ID NO: 29, the light chain CDR2 of SEQ ID NO: 30, and the light chain CDR3 of SEQ ID NO: 31. In one embodiment, the anti-idiotypic scFv comprises the heavy chain CDR1 of SEQ ID NO: 26, the heavy chain CDR2 of SEQ ID NO: 27, the heavy chain CDR3 of SEQ ID NO: 28, the light chain CDR1 of SEQ ID NO: 29, the light chain CDR2 of SEQ ID NO: 30, and the light chain CDR3 of SEQ ID NO: 31.

[0241] In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for HER1 further comprises an anti-idiotypic CD3 scFv comprising a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 41 or 42. In one embodiment, the anti-idiotypic scFv comprises the polypeptide sequence of SEQ ID NO: 41 or 42.

[0242] In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for HER1 further comprises an anti-idiotypic HER1 scFv comprising at least one of the heavy chain CDR1 of SEQ ID NO: 48, the heavy chain CDR2 of SEQ ID NO: 49, the heavy chain CDR3 of SEQ ID NO: 50, the light chain CDR1 of SEQ ID NO: 51, the light chain CDR2 of SEQ ID NO: 52, and the light chain CDR3 of SEQ ID NO: 53. In one embodiment, the anti-idiotypic scFv comprises the heavy chain CDR1 of SEQ ID NO: 48, the heavy chain CDR2 of SEQ ID NO: 49, the heavy chain CDR3 of SEQ ID NO: 50, the light chain CDR1 of SEQ ID NO: 51, the light chain CDR2 of SEQ ID NO: 52, and the light chain CDR3 of SEQ ID NO: 53.

[0243] In one embodiments the protease-activatable T cell activating bispecific molecule that comprises at least one antigen binding moiety that is specific for HER1 further comprises a linker comprising a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 35.

[0244] In one embodiment the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for HER1 further comprises a linker having a protease recognition site comprising a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 36, 37, 38, 39, 40, 97, 98, 99, 100, 101, 102, 103, 104, 105 or 106. In one embodiment, the protease recognition site comprises the polypeptide sequence of SEQ ID NO: 36, 37, 38, 39, 40, 97, 98, 99, 100, 101, 102, 103, 104, 105 or 106. In one embodiment, the protease recognition site comprises the polypeptide sequence of SEQ ID NO: 36. In one embodiment, the protease recognition site comprises the polypeptide sequence of SEQ ID NO: 97. In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for HER1 further comprises a linker comprising a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 7, 8, 9, 10, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95 or 96. In one embodiment, the linker comprises the polypeptide sequence of SEQ ID NO: 7, 8, 9, 10, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95 or 96. In one embodiment, the linker comprises the polypeptide sequence of SEQ ID NO: 7. In one embodiment, the linker comprises the polypeptide sequence of SEQ ID NO: 86.

[0245] In some embodiments the protease-activatable T cell activating bispecific molecule comprises at least one antigen binding moiety that is specific for HER2. In one embodiment, the antigen binding moiety that is specific for HER2 comprises at least one heavy chain complementarity determining region (CDR) of selected from the group consisting of SEQ ID NO: 142, SEQ ID NO: 143 and SEQ ID NO: 144 and at least one light chain CDR selected from the group of SEQ ID NO: 148, SEQ ID NO: 149, and SEQ ID NO: 150. In a further one embodiment, the antigen binding moiety that is specific for HER2 comprises at least one heavy chain complementarity determining region (CDR) of selected from the group consisting of SEQ ID NO: 145, SEQ ID NO: 146 and SEQ ID NO: 147 and at least one light chain CDR selected from the group of SEQ ID NO: 148, SEQ ID NO: 149, and SEQ ID NO: 150.

[0246] In one embodiment, the antigen binding moiety that is specific for HER2 comprises the heavy chain CDR1 of SEQ ID NO: 142, the heavy chain CDR2 of SEQ ID NO: 143, the heavy chain CDR3 of SEQ ID NO: 144, the light chain CDR1 of SEQ ID NO: 148, the light chain CDR2 of SEQ ID NO: 149, and the light chain CDR3 of SEQ ID NO: 150. In a further embodiment, the antigen binding moiety that is specific for HER2 comprises the heavy chain CDR1 of SEQ ID NO: 145, the heavy chain CDR2 of SEQ ID NO: 146, the heavy chain CDR3 of SEQ ID NO: 147, the light chain CDR1 of SEQ ID NO: 148, the light chain CDR2 of SEQ ID NO: 149, and the light chain CDR3 of SEQ ID NO: 150.

[0247] In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for HER2 further comprises an anti-idiotypic CD3 scFv comprising at least one of the heavy chain CDR1 of SEQ ID NO: 20, the heavy chain CDR2 of SEQ ID NO: 21, the heavy chain CDR3 of SEQ ID NO: 22, the light chain CDR1 of SEQ ID NO: 23, the light chain CDR2 of SEQ ID NO: 24, and the light chain CDR3 of SEQ ID NO: 25. In one embodiment, the anti-idiotypic scFv comprises the heavy chain CDR1 of SEQ ID NO: 20, the heavy chain CDR2 of SEQ ID NO: 21, the heavy chain CDR3 of SEQ ID NO: 22, the light chain CDR1 of SEQ ID NO: 23, the light chain CDR2 of SEQ ID NO: 24, and the light chain CDR3 of SEQ ID NO: 25.

[0248] In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for HER2 further comprises an anti-idiotypic CD3 scFv comprising at least one of the heavy chain CDR1 of SEQ ID NO: 26, the heavy chain CDR2 of SEQ ID NO: 27, the heavy chain CDR3 of SEQ ID NO: 28, the light chain CDR1 of SEQ ID NO: 29, the light chain CDR2 of SEQ ID NO: 30, and the light chain CDR3 of SEQ ID NO: 31. In one embodiment, the anti-idiotypic scFv comprises the heavy chain CDR1 of SEQ ID NO: 26, the heavy chain CDR2 of SEQ ID NO: 27, the heavy chain CDR3 of SEQ ID NO: 28, the light chain CDR1 of SEQ ID NO: 29, the light chain CDR2 of SEQ ID NO: 30, and the light chain CDR3 of SEQ ID NO: 31.

[0249] In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for HER2 further comprises an anti-idiotypic CD3 scFv comprising a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 41 or 42. In one embodiment, the anti-idiotypic scFv comprises the polypeptide sequence of SEQ ID NO: 41 or 42.

[0250] In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for HER2 further comprises an anti-idiotypic HER2 scFv comprising at least one of the heavy chain CDR1 of SEQ ID NO: 48, the heavy chain CDR2 of SEQ ID NO: 49, the heavy chain CDR3 of SEQ ID NO: 50, the light chain CDR1 of SEQ ID NO: 51, the light chain CDR2 of SEQ ID NO: 52, and the light chain CDR3 of SEQ ID NO: 53. In one embodiment, the anti-idiotypic scFv comprises the heavy chain CDR1 of SEQ ID NO: 48, the heavy chain CDR2 of SEQ ID NO: 49, the heavy chain CDR3 of SEQ ID NO: 50, the light chain CDR1 of SEQ ID NO: 51, the light chain CDR2 of SEQ ID NO: 52, and the light chain CDR3 of SEQ ID NO: 53.

[0251] In one embodiments the protease-activatable T cell activating bispecific molecule that comprises at least one antigen binding moiety that is specific for HER2 further comprises a linker comprising a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 35.

[0252] In one embodiment the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for HER2 further comprises a linker having a protease recognition site comprising a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 36, 37, 38, 39, 40, 97, 98, 99, 100, 101, 102, 103, 104, 105 or 106. In one embodiment, the protease recognition site comprises the polypeptide sequence of SEQ ID NO: 36, 37, 38, 39, 40, 97, 98, 99, 100, 101, 102, 103, 104, 105 or 106. In one embodiment, the protease recognition site comprises the polypeptide sequence of SEQ ID NO: 36. In one embodiment, the protease recognition site comprises the polypeptide sequence of SEQ ID NO: 97. In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for HER2 further comprises a linker comprising a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 7, 8, 9, 10, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95 or 96. In one embodiment, the linker comprises the polypeptide sequence of SEQ ID NO: 7, 8, 9, 10, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95 or 96. In one embodiment, the linker comprises the polypeptide sequence of SEQ ID NO: 7. In one embodiment, the linker comprises the polypeptide sequence of SEQ ID NO: 86.

[0253] In one embodiment the protease-activatable T cell activating bispecific molecule comprises a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 132, a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 136, a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 81 and a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 133.

[0254] In one embodiment the protease-activatable T cell activating bispecific molecule comprises the polypeptide sequence of SEQ ID NO: 132, the polypeptide sequence of SEQ ID NO: 136, the polypeptide sequence of SEQ ID NO: 81 and the polypeptide sequence of SEQ ID NO: 133.

[0255] In particular embodiments the protease-activatable T cell activating bispecific molecule comprises at least one antigen binding moiety that is specific for FolR1. In one embodiment the FolR1 is a human FolR1. In one embodiment, the protease-activatable T cell activating bispecific molecule comprises at least one antigen binding moiety that is specific for human FolR1 and does not bind to human FolR2 or human FolR3. In one embodiment, the antigen binding moiety that is specific for FolR1 comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 14, SEQ ID NO: 15 and SEQ ID NO: 16 and at least one light chain CDR selected from the group of SEQ ID NO: 17, SEQ ID NO: 18 and SEQ ID NO: 19.

[0256] In one embodiment, the antigen binding moiety that is specific for FolR1 comprises the heavy chain CDR1 of SEQ ID NO: 14, the heavy chain CDR2 of SEQ ID NO: 15, the heavy chain CDR3 of SEQ ID NO: 16, the light chain CDR1 of SEQ ID NO: 17, the light chain CDR2 of SEQ ID NO: 18, and the light chain CDR3 of SEQ ID NO: 19.

[0257] In a further embodiment, the antigen binding moiety that is specific for FolR1 comprises a heavy chain variable region sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 47 and a light chain variable region sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 55, or variants thereof that retain functionality.

[0258] In one embodiment, the antigen binding moiety that is specific for FolR1 comprises the heavy chain variable region comprising an amino acid sequence of SEQ ID NO: 47 and the light chain variable region comprising an amino acid sequence of SEQ ID NO: 55.

[0259] In one embodiment, the antigen binding moiety that is specific for FolR1 comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 151, SEQ ID NO: 152 and SEQ ID NO: 153 and at least one light chain CDR selected from the group of SEQ ID NO: 154, SEQ ID NO: 155 and SEQ ID NO: 156.

[0260] In one embodiment, the antigen binding moiety that is specific for FolR1 comprises the heavy chain CDR1 of SEQ ID NO: 151, the heavy chain CDR2 of SEQ ID NO: 152, the heavy chain CDR3 of SEQ ID NO: 153, the light chain CDR1 of SEQ ID NO: 154, the light chain CDR2 of SEQ ID NO: 155, and the light chain CDR3 of SEQ ID NO: 156.

[0261] In a further embodiment, the antigen binding moiety that is specific for FolR1 comprises a heavy chain variable region sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 157 and a light chain variable region sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 158, or variants thereof that retain functionality.

[0262] In one embodiment, the antigen binding moiety that is specific for FolR1 comprises the heavy chain variable region comprising an amino acid sequence of SEQ ID NO: 157 and the light chain variable region comprising an amino acid sequence of SEQ ID NO: 158.

[0263] In one embodiment the protease-activatable T cell activating bispecific molecule comprises a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 2, and a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 1.

[0264] In one embodiment the protease-activatable T cell activating bispecific molecule comprises the polypeptide sequence of SEQ ID NO: 2, and the polypeptide sequence of SEQ ID NO: 1.

[0265] In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for FolR1 further comprises an anti-idiotypic CD3 scFv comprising at least one of the heavy chain CDR1 of SEQ ID NO: 20, the heavy chain CDR2 of SEQ ID NO: 21, the heavy chain CDR3 of SEQ ID NO: 22, the light chain CDR1 of SEQ ID NO: 23, the light chain CDR2 of SEQ ID NO: 24, and the light chain CDR3 of SEQ ID NO: 25. In one embodiment, the anti-idiotypic scFv comprises the heavy chain CDR1 of SEQ ID NO: 20, the heavy chain CDR2 of SEQ ID NO: 21, the heavy chain CDR3 of SEQ ID NO: 22, the light chain CDR1 of SEQ ID NO: 23, the light chain CDR2 of SEQ ID NO: 24, and the light chain CDR3 of SEQ ID NO: 25.

[0266] In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for FolR1 further comprises an anti-idiotypic CD3 scFv comprising at least one of the heavy chain CDR1 of SEQ ID NO: 26, the heavy chain CDR2 of SEQ ID NO: 27, the heavy chain CDR3 of SEQ ID NO: 28, the light chain CDR1 of SEQ ID NO: 29, the light chain CDR2 of SEQ ID NO: 30, and the light chain CDR3 of SEQ ID NO: 31. In one embodiment, the anti-idiotypic scFv comprises the heavy chain CDR1 of SEQ ID NO: 26, the heavy chain CDR2 of SEQ ID NO: 27, the heavy chain CDR3 of SEQ ID NO: 28, the light chain CDR1 of SEQ ID NO: 29, the light chain CDR2 of SEQ ID NO: 30, and the light chain CDR3 of SEQ ID NO: 31.

[0267] In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for FolR1 further comprises an anti-idiotypic CD3 scFv comprising a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 41 or 42. In one embodiment, the anti-idiotypic scFv comprises the polypeptide sequence of SEQ ID NO: 41 or 42.

[0268] In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for FolR1 further comprises a linker having a protease recognition site comprising a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 36, 37, 38, 39, 40, 97, 98, 99, 100, 101, 102, 103, 104, 105 or 106. In one embodiment, the protease recognition site comprises the polypeptide sequence of SEQ ID NO: 36, 37, 38, 39, 40, 97, 98, 99, 100, 101, 102, 103, 104, 105 or 106. In one embodiment, the protease recognition site comprises the polypeptide sequence of SEQ ID NO: 36. In one embodiment, the protease recognition site comprises the polypeptide sequence of SEQ ID NO: 97. In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for ForR1 further comprises a linker comprising a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 7, 8, 9, 10, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95 or 96. In one embodiment, the linker comprises the polypeptide sequence of SEQ ID NO: 7, 8, 9, 10, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95 or 96. In one embodiment, the linker comprises the polypeptide sequence of SEQ ID NO: 7. In one embodiment, the linker comprises the polypeptide sequence of SEQ ID NO: 86.

[0269] In one embodiment the protease-activatable T cell activating bispecific molecule comprises a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 1, a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 3 and a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 72.

[0270] In one embodiment the protease-activatable T cell activating bispecific molecule comprises a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 1, a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 3 and a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 72.

[0271] In one embodiment the protease-activatable T cell activating bispecific molecule comprises a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 1, a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 3 and a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 85.

[0272] In one embodiment the protease-activatable T cell activating bispecific molecule comprises a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 1, a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 3, a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 73 and a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 74.

[0273] In one embodiment the protease-activatable T cell activating bispecific molecule comprises the polypeptide sequence of SEQ ID NO: 1, the polypeptide sequence of SEQ ID NO: 3 and the polypeptide sequence of SEQ ID NO: 72.

[0274] In one embodiment the protease-activatable T cell activating bispecific molecule comprises the polypeptide sequence of SEQ ID NO: 1, the polypeptide sequence of SEQ ID NO: 3 and the polypeptide sequence of SEQ ID NO: 85.

[0275] In one embodiment the protease-activatable T cell activating bispecific molecule comprises the polypeptide sequence of SEQ ID NO: 1, the polypeptide sequence of SEQ ID NO: 3, the polypeptide sequence of SEQ ID NO: 73 and the polypeptide sequence of SEQ ID NO: 74.

[0276] In one embodiment the protease-activatable T cell activating bispecific molecule comprises a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 137, a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 139, a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 81 and a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 138.

[0277] In one embodiment the protease-activatable T cell activating bispecific molecule comprises the polypeptide sequence of SEQ ID NO: 137, the polypeptide sequence of SEQ ID NO: 139, the polypeptide sequence of SEQ ID NO: 81 and the polypeptide sequence of SEQ ID NO: 138.

[0278] In particular embodiments the protease-activatable T cell activating bispecific molecule comprises at least one antigen binding moiety that is specific for Mesothelin. In one embodiment the Mesothelin is human Mesothelin. In one embodiment, the protease-activatable T cell activating bispecific molecule comprises at least one antigen binding moiety that is specific for human Mesothelin. In one embodiment, the antigen binding moiety that is specific for Mesothelin comprises at least one heavy chain complementarity determining region (CDR) selected from the group consisting of SEQ ID NO: 107, SEQ ID NO: 108 and SEQ ID NO: 109 and at least one light chain CDR selected from the group of SEQ ID NO: 110, SEQ ID NO: 111 and SEQ ID NO: 112.

[0279] In one embodiment, the antigen binding moiety that is specific for Mesothelin comprises the heavy chain CDR1 of SEQ ID NO: 107, the heavy chain CDR2 of SEQ ID NO: 108, the heavy chain CDR3 of SEQ ID NO: 109, the light chain CDR1 of SEQ ID NO: 110, the light chain CDR2 of SEQ ID NO: 111, and the light chain CDR3 of SEQ ID NO: 112.

[0280] In a further embodiment, the antigen binding moiety that is specific for Mesothelin comprises a heavy chain variable region sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 113 and a light chain variable region sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 114, or variants thereof that retain functionality.

[0281] In one embodiment, the antigen binding moiety that is specific for Mesothelin comprises the heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 113 and the light chain variable region comprising the amino acid sequence of SEQ ID NO: 114.

[0282] In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for Mesothelin further comprises an anti-idiotypic CD3 scFv comprising at least one of the heavy chain CDR1 of SEQ ID NO: 20, the heavy chain CDR2 of SEQ ID NO: 21, the heavy chain CDR3 of SEQ ID NO: 22, the light chain CDR1 of SEQ ID NO: 23, the light chain CDR2 of SEQ ID NO: 24, and the light chain CDR3 of SEQ ID NO: 25. In one embodiment, the anti-idiotypic scFv comprises the heavy chain CDR1 of SEQ ID NO: 20, the heavy chain CDR2 of SEQ ID NO: 21, the heavy chain CDR3 of SEQ ID NO: 22, the light chain CDR1 of SEQ ID NO: 23, the light chain CDR2 of SEQ ID NO: 24, and the light chain CDR3 of SEQ ID NO: 25.

[0283] In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for Mesothelin further comprises an anti-idiotypic CD3 scFv comprising at least one of the heavy chain CDR1 of SEQ ID NO: 26, the heavy chain CDR2 of SEQ ID NO: 27, the heavy chain CDR3 of SEQ ID NO: 28, the light chain CDR1 of SEQ ID NO: 29, the light chain CDR2 of SEQ ID NO: 30, and the light chain CDR3 of SEQ ID NO: 31. In one embodiment, the anti-idiotypic scFv comprises the heavy chain CDR1 of SEQ ID NO: 26, the heavy chain CDR2 of SEQ ID NO: 27, the heavy chain CDR3 of SEQ ID NO: 28, the light chain CDR1 of SEQ ID NO: 29, the light chain CDR2 of SEQ ID NO: 30, and the light chain CDR3 of SEQ ID NO: 31.

[0284] In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for Mesothelin further comprises an anti-idiotypic CD3 scFv comprising a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 41 or 42. In one embodiment, the anti-idiotypic scFv comprises the polypeptide sequence of SEQ ID NO: 41 or 42.

[0285] In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for Mesothelin further comprises a linker having a protease recognition site comprising a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 36, 37, 38, 39, 40, 97, 98, 99, 100, 101, 102, 103, 104, 105 or 106. In one embodiment, the protease recognition site comprises the polypeptide sequence of SEQ ID NO: 36, 37, 38, 39, 40, 97, 98, 99, 100, 101, 102, 103, 104, 105 or 106. In one embodiment, the protease recognition site comprises the polypeptide sequence of SEQ ID NO: 36. In one embodiment, the protease recognition site comprises the polypeptide sequence of SEQ ID NO: 97. In one embodiments the protease-activatable T cell activating bispecific molecule comprising at least one antigen binding moiety that is specific for Mesothelin further comprises a linker comprising a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 7, 8, 9, 10, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95 or 96. In one embodiment, the linker comprises the polypeptide sequence of SEQ ID NO: 7, 8, 9, 10, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95 or 96. In one embodiment, the linker comprises the polypeptide sequence of SEQ ID NO: 7. In one embodiment, the linker comprises the polypeptide sequence of SEQ ID NO: 86.

[0286] In one embodiment the protease-activatable T cell activating bispecific molecule comprises a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 77, a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 78, a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 81 and a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 82.

[0287] In one embodiment the protease-activatable T cell activating bispecific molecule comprises a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 76, a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 77, a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 78 and a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 79.

[0288] In one embodiment the protease-activatable T cell activating bispecific molecule comprises the polypeptide sequence of SEQ ID NO: 77, the polypeptide sequence of SEQ ID NO: 78, the polypeptide sequence of SEQ ID NO: 81 and the polypeptide sequence of SEQ ID NO: 82.

[0289] In one embodiment the protease-activatable T cell activating bispecific molecule comprises the polypeptide sequence of SEQ ID NO: 76, the polypeptide sequence of SEQ ID NO: 77, the polypeptide sequence of SEQ ID NO: 78 and the polypeptide sequence of SEQ ID NO: 79.

[0290] In one embodiment, provided is a T cell activating bispecific molecule comprises a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 76, a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 77, a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 78 and a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 81.

[0291] In one embodiment the T cell activating bispecific molecule comprises a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 77, a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 78, a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 81 and a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 84.

[0292] In one embodiment the T cell activating bispecific molecule comprises the polypeptide sequence of SEQ ID NO: 76, the polypeptide sequence of SEQ ID NO: 77, the polypeptide sequence of SEQ ID NO: 78 and the polypeptide sequence of SEQ ID NO: 81.

[0293] In one embodiment the T cell activating bispecific molecule comprises the polypeptide sequence of SEQ ID NO: 77, the polypeptide sequence of SEQ ID NO: 78, the polypeptide sequence of SEQ ID NO: 81 and the polypeptide sequence of SEQ ID NO: 84.Masking moiety

[0294] The protease-activatable T cell activating bispecific molecule of the invention comprises at least one masking moiety. Others have tried to mask binding of an antibody by capping the binding moiety with a fragment of the antigen recognized by the binding moiety (e.g., WO2013128194). This approach has several limitations. For example, using the antigen allows for less flexibility in reducing the affinity of the binding moiety. This is so because the affinity has to be high enough to be reliably masked by the antigen mask. Also, dissociated antigen could potentially bind to and interact with its cognate receptor(s) in vivo and cause undesirable signals to the cell expressing such receptor. In contrast, the approach described herein uses an anti-idiotype antibody or fragment thereof as a mask. Two countervailing considerations for designing an effective masking moiety are 1. effectiveness of the masking and 2. reversibility of the masking. If the affinity is too low, masking would be inefficient. However, if the affinity is too high, the masking process might not be readily reversible. It was not predictable whether a high affinity anti-idiotype mask or a low affinity anti-idiotype mask would work better. As described herein, higher affinity masking moieties performed overall better in masking the antigen binding side and, at the same time, could be effectively removed for activation of the molecule. In one embodiment, the anti-idiotype mask has a KD of 1-8 nM. In one embodiment, anti-idiotype mask has a KD of 2 nM at 37°C. In one specific embodiment, the masking moiety recognizes the idiotype of the first antigen binding moiety capable of specific binding to a CD3, e.g., a human CD3. In one specific embodiment, the masking moiety recognizes the idiotype of the second antigen binding moiety capable of binding to a target cell antigen.

[0295] In one embodiment, the masking moiety masks a CD3-binding moiety and comprises at least one of the heavy chain CDR1 of SEQ ID NO: 20, the heavy chain CDR2 of SEQ ID NO: 21, the heavy chain CDR3 of SEQ ID NO: 22, the light chain CDR1 of SEQ ID NO: 23, the light chain CDR2 of SEQ ID NO: 24, and the light chain CDR3 of SEQ ID NO: 25. In one embodiment, the masking moiety comprises the heavy chain CDR1 of SEQ ID NO: 20, the heavy chain CDR2 of SEQ ID NO: 21, the heavy chain CDR3 of SEQ ID NO: 22, the light chain CDR1 of SEQ ID NO: 23, the light chain CDR2 of SEQ ID NO: 24, and the light chain CDR3 of SEQ ID NO: 25. In one embodiment, the masking moiety masks a CD3-binding moiety and comprises a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 41. In one embodiment, the masking moiety masks a CD3-binding moiety and comprises the polypeptide sequence of SEQ ID NO: 41.

[0296] In one preferred embodiment, the masking moiety masks a CD3-binding moiety and comprises at least one of the heavy chain CDR1 of SEQ ID NO: 26, the heavy chain CDR2 of SEQ ID NO: 27, the heavy chain CDR3 of SEQ ID NO: 28, the light chain CDR1 of SEQ ID NO: 29, the light chain CDR2 of SEQ ID NO: 30, and the light chain CDR3 of SEQ ID NO: 31. In one embodiment, the masking moiety comprises the heavy chain CDR1 of SEQ ID NO: 26, the heavy chain CDR2 of SEQ ID NO: 27, the heavy chain CDR3 of SEQ ID NO: 28, the light chain CDR1 of SEQ ID NO: 29, the light chain CDR2 of SEQ ID NO: 30, and the light chain CDR3 of SEQ ID NO: 31. In one embodiment, the masking moiety masks a CD3-binding moiety and comprises a polypeptide sequence that is at least about 95%, 96%, 97%, 98%, 99% or 100% identical to SEQ ID NO: 42. In one preferred embodiment, the masking moiety masks a CD3-binding moiety and comprises the polypeptide sequence of SEQ ID NO: 42.

[0297] In one embodiment, the masking moiety masks a HER1-binding moiety and comprises at least one of the heavy chain CDR1 of SEQ ID NO: 48, the heavy chain CDR2 of SEQ ID NO: 49, the heavy chain CDR3 of SEQ ID NO: 50, the light chain CDR1 of SEQ ID NO: 51, the light chain CDR2 of SEQ ID NO: 52, and the light chain CDR3 of SEQ ID NO: 53. In one embodiment, the anti-idiotypic scFv comprises the heavy chain CDR1 of SEQ ID NO: 48, the heavy chain CDR2 of SEQ ID NO: 49, the heavy chain CDR3 of SEQ ID NO: 50, the light chain CDR1 of SEQ ID NO: 51, the light chain CDR2 of SEQ ID NO: 52, and the light chain CDR3 of SEQ ID NO: 53.

[0298] In one aspect for reference only, the disclosure relates to an idiotype-specific polypeptide for reversibly concealing antigen binding of an antigen-binding of a molecule. In one embodiment, the invention relates to an idiotype-specific polypeptide for reversibly concealing an anti-CD3 antigen binding site of a molecule, wherein the idiotype-specific polypeptide is an anti-idiotype scFv, wherein the idiotype-specific polypeptide is covalently attached to the molecule through a peptide linker. In one embodiment the linker is a protease-cleavable linker. In one embodiment, the linker comprises the sequence of SEQ ID NO: 7, 8, 9, or 10. In one embodiment, the linker comprises the sequence of SEQ ID NO: 7, 8, 9, 10, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95 or 96. In one embodiment, the linker comprises the polypeptide sequence of SEQ ID NO: 7. In one embodiment, the linker comprises the polypeptide sequence of SEQ ID NO: 86. In one embodiment the peptide linker comprises at least one protease recognition site. In one embodiment, the protease recognition site comprises the polypeptide sequence of SEQ ID NO: 36, 37, 38, 39, 40, 97, 98, 99, 100, 101, 102, 103, 104, 105 or 106. In one preferred embodiment, the protease recognition site comprises the protease recognition sequence RQARVVNG (SEQ ID NO: 36). In further embodiment, the linker comprises more than one protease recognition site. In one preferred embodiment, the protease recognition site comprises the protease recognition sequence VHMPLGFLGPRQARVVNG (SEQ ID NO:97). In one embodiment the protease is selected from the group consisting of metalloproteinase, e.g., matrix metalloproteinase (MMP) 1-28 and A Disintegrin And Metalloproteinase (ADAM) 2, 7-12, 15, 17-23, 28-30 and 33, serine protease, e.g., urokinase-type plasminogen activator and Matriptase, cysteine protease, aspartic protease, and cathepsin protease. In one specific embodiment the protease is MMP9 or MMP2. In a further specific embodiment, the protease is Matriptase.

[0299] In one embodiment the molecule which comprises the anti-CD3 antigen binding site is a T-cell activating bispecific molecule. In one particular embodiment the idiotype-specific polypeptide comprises a heavy chain variable region comprising at least one of a heavy chain complementarity determining region (CDR H) 1 amino acid sequence of DYSIH (SEQ ID NO:20); CDR H2 amino acid sequence of WINTETGEPAYADDFKG (SEQ ID NO:21); and a CDR H3 amino acid sequence of PYDYDVLDY (SEQ ID NO:22). In one particular embodiment the idiotype-specific polypeptide comprises a light chain variable region comprising at least one of: a light chain (CDR L)1 amino acid sequence of RASKSVSTSNYSYIH (SEQ ID NO:23); a CDR L2 amino acid sequence of YVSYLES (SEQ ID NO:24); and a CDR L3 amino acid sequence of QHSREFPWT (SEQ ID NO:25). In one particular embodiment the idiotype-specific polypeptide comprises: a heavy chain complementarity determining region (CDR H) 1 amino acid sequence of DYSIH (SEQ ID NO:20); a CDR H2 amino acid sequence of WINTETGEPAYADDFKG (SEQ ID NO:21); a CDR H3 amino acid sequence of PYDYDVLDY (SEQ ID NO:22); and a light chain variable region comprising: a light chain (CDR L)1 amino acid sequence of RASKSVSTSNYSYIH (SEQ ID NO:23); a CDR L2 amino acid sequence of YVSYLES (SEQ ID NO:24); and a CDR L3 amino acid sequence of QHSREFPWT (SEQ ID NO:25). In one particular embodiment the idiotype-specific polypeptide comprises a heavy chain variable region comprising at least one of: a heavy chain complementarity determining region (CDR H) 1 amino acid sequence of SYGVS (SEQ ID NO:26); a CDR H2 amino acid sequence of IIWGDGSTNYHSALIS (SEQ ID NO:27); and a CDR H3 amino acid sequence of GITTVVDDYYAMDY (SEQ ID NO:28). In one particular embodiment the idiotype-specific polypeptide comprises a light chain variable region comprising at least one of: a light chain (CDR L)1 amino acid sequence of RASENIDSYLA (SEQ ID NO:29); a CDR L2 amino acid sequence of AATFLAD (SEQ ID NO:30); and a CDR L3 amino acid sequence of QHYYSTPYT (SEQ ID NO:31). In one particular embodiment the idiotype-specific polypeptide comprises a heavy chain variable region comprising: a heavy chain complementarity determining region (CDR H) 1 amino acid sequence of SYGVS (SEQ ID NO:26); a CDR H2 amino acid sequence of IIWGDGSTNYHSALIS (SEQ ID NO:27); a CDR H3 amino acid sequence of GITTVVDDYYAMDY (SEQ ID NO:28); and a light chain variable region comprising: a light chain (CDR L)1 amino acid sequence of RASENIDSYLA (SEQ ID NO:29); a CDR L2 amino acid sequence of AATFLAD (SEQ ID NO:30); and a CDR L3 amino acid sequence of QHYYSTPYT (SEQ ID NO:31). In one embodiment, the idiotype-specific polypeptide comprises a heavy chain variable region comprising at least one of: a heavy chain complementarity determining region (CDR H) 1 amino acid sequence of SEQ ID NO:48; a CDR H2 amino acid sequence of SEQ ID NO:49; and a CDR H3 amino acid sequence of SEQ ID NO:50. In one embodiment, the idiotype-specific polypeptide comprises a light chain variable region comprising at least one of: a light chain complementarity determining region (CDR L) 1 amino acid sequence of SEQ ID NO:51; a CDR L2 amino acid sequence of SEQ ID NO:52; and a CDR L3 amino acid sequence of SEQ ID NO:53. In one embodiment, the idiotype-specific polypeptide comprises a heavy chain variable region comprising a heavy chain complementarity determining region (CDR H) 1 amino acid sequence of SEQ ID NO:48; a CDR H2 amino acid sequence of SEQ ID NO:49; and a CDR H3 amino acid sequence of SEQ ID NO:50, and a light chain variable region comprising a light chain complementarity determining region (CDR L) 1 amino acid sequence of SEQ ID NO:51; a CDR L2 amino acid sequence of SEQ ID NO:52; and a CDR L3 amino acid sequence of SEQ ID NO:53.Polynucleotides

[0300] The invention further provides isolated polynucleotides encoding a protease-activatable T cell activating bispecific molecule as described herein Polynucleotides of the invention include those that are at least about 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequences set forth in SEQ ID NOs 62-71 or SEQ ID NOs. Polynucleotides of the invention further include those that are at least about 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequences set forth in SEQ ID NOs 117-131. Polynucleotides of the invention further include those that are at least about 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequences set forth in SEQ ID NOs 162-170.

[0301] The polynucleotides encoding protease-activatable T cell activating bispecific molecules of the invention may be expressed as a single polynucleotide that encodes the entire protease-activatable T cell activating bispecific molecule or as multiple (e.g., two or more) polynucleotides that are co-expressed. Polypeptides encoded by polynucleotides that are co-expressed may associate through, e.g., disulfide bonds or other means to form a functional protease-activatable T cell activating bispecific molecule. For example, the light chain portion of an antigen binding moiety may be encoded by a separate polynucleotide from the portion of the protease-activatable T cell activating bispecific molecule comprising the heavy chain portion of the antigen binding moiety, an Fc domain subunit and optionally (part of) another antigen binding moiety. When co-expressed, the heavy chain polypeptides will associate with the light chain polypeptides to form the antigen binding moiety. In another example, the portion of the protease-activatable T cell activating bispecific molecule comprising one of the two Fc domain subunits and optionally (part of) one or more antigen binding moieties could be encoded by a separate polynucleotide from the portion of the protease-activatable T cell activating bispecific molecule comprising the the other of the two Fc domain subunits and optionally (part of) an antigen binding moiety. When co-expressed, the Fc domain subunits will associate to form the Fc domain.

[0302] In some embodiments, the isolated polynucleotide encodes the entire protease-activatable T cell activating bispecific molecule according to the invention as described herein.

[0303] In another embodiment, the present invention is directed to an isolated polynucleotide encoding a protease-activatable T cell activating bispecific molecule of the invention, wherein the polynucleotide comprises a sequence that encodes a variable region sequence. In another embodiment, the present invention is directed to an isolated polynucleotide encoding a protease-activatable T cell activating bispecific molecule, wherein the polynucleotide comprises a sequence that encodes a polypeptide sequence as shown in SEQ ID NOs 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 47, or 55. In another embodiment, the present invention is directed to an isolated polynucleotide encoding a protease-activatable T cell activating bispecific molecule, wherein the polynucleotide comprises a sequence that encodes a polypeptide sequence as shown in SEQ ID NOs 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 47, 55, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85. In another embodiment, the present invention is directed to an isolated polynucleotide encoding a protease-activatable T cell activating bispecific molecule, wherein the polynucleotide comprises a sequence that encodes a polypeptide sequence as shown in SEQ ID NOs 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 47, 55, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 132, 133, 134, 135, 136, 137, 138, 139, 140 or 141. In another embodiment, the invention is further directed to an isolated polynucleotide encoding a protease-activatable T cell activating bispecific molecule of the invention, wherein the polynucleotide comprises a sequence that is at least about 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to the nucleotide sequence shown in SEQ ID NOs 62, 63, 64, 65, 66, 67, 68, 69, 70, or 71. In another embodiment, the invention is further directed to an isolated polynucleotide encoding a protease-activatable T cell activating bispecific molecule of the invention, wherein the polynucleotide comprises a sequence that is at least about 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to the nucleotide sequence shown in SEQ ID NOs 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130 or 131. In another embodiment, the invention is further directed to an isolated polynucleotide encoding a protease-activatable T cell activating bispecific molecule of the invention, wherein the polynucleotide comprises a sequence that is at least about 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to the nucleotide sequence shown in SEQ ID NOs 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 162, 163, 164, 165, 166, 167, 168, 169 or 170. In another embodiment, the invention is directed to an isolated polynucleotide encoding a protease-activatable T cell activating bispecific molecule of the invention, wherein the polynucleotide comprises the nucleic acid sequence shown in SEQ ID NOs 62, 63, 64, 65, 66, 67, 68, 69, 70, or 71. In another embodiment, the invention is directed to an isolated polynucleotide encoding a protease-activatable T cell activating bispecific molecule of the invention, wherein the polynucleotide comprises the nucleic acid sequence shown in SEQ ID NOs 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130 or 131. In another embodiment, the invention is directed to an isolated polynucleotide encoding a protease-activatable T cell activating bispecific molecule of the invention, wherein the polynucleotide comprises the nucleic acid sequence shown in SEQ ID NOs 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 162, 163, 164, 165, 166, 167, 168, 169 or 170. In another embodiment, the invention is directed to an isolated polynucleotide encoding a protease-activatable T cell activating bispecific molecule of the invention, wherein the polynucleotide comprises a sequence that encodes a variable region sequence that is at least about 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to the amino acid sequence in SEQ ID NOs 43, 47, or 55. The invention encompasses an isolated polynucleotide encoding a protease-activatable T cell activating bispecific molecule of the invention, wherein the polynucleotide comprises a sequence that encodes the variable region sequence of SEQ ID NOs SEQ ID NOs 43, 47, or 55 with conservative amino acid substitutions.

[0304] In another embodiment, the invention is directed to an isolated polynucleotide encoding a protease-activatable T cell activating bispecific molecule of the invention, wherein the polynucleotide comprises a sequence that encodes a variable region sequence that is at least about 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to the amino acid sequence in SEQ ID NOs 43, 47, 55, 113, 114, 115 or 116. The invention encompasses an isolated polynucleotide encoding a protease-activatable T cell activating bispecific molecule of the invention, wherein the polynucleotide comprises a sequence that encodes the variable region sequence of SEQ ID NOs SEQ ID NOs 43, 47, 55, 113, 114, 115 or 116 with conservative amino acid substitutions.

[0305] In another embodiment, the invention is directed to an isolated polynucleotide encoding a protease-activatable T cell activating bispecific molecule of the invention, wherein the polynucleotide comprises a sequence that encodes a variable region sequence that is at least about 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to the amino acid sequence in SEQ ID NOs 43, 47, 55, 113, 114, 115, 116, 157, 158, 159, 160 or 161. The invention encompasses an isolated polynucleotide encoding a protease-activatable T cell activating bispecific molecule of the invention, wherein the polynucleotide comprises a sequence that encodes the variable region sequence of SEQ ID NOs SEQ ID NOs 43, 47, 55, 113, 114, 115, 116, 157, 158, 159, 160 or 161 with conservative amino acid substitutions.

[0306] In certain embodiments the polynucleotide or nucleic acid is DNA. In other embodiments, a polynucleotide of the present invention is RNA, for example, in the form of messenger RNA (mRNA). RNA of the present invention may be single stranded or double stranded.

[0307] The disclosure provides for reference only isolated polynucleotides encoding an idiotype-specific polypeptide as described herein. In some aspects, said fragment is an idiotype binding, i.e., anti-idiotype specific antibody or fragment thereof. In one aspect the idiotype-specific polypeptide is an anti-idiotypic scFv.

[0308] The disclosure provides for reference only an isolated polynucleotide encoding an idiotype-specific polypeptide wherein the polynucleotide comprises a sequence that encodes the polypeptide sequence of one or more of SEQ ID NOs 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 48, 49, 50, 51, 52, and 53. The disclosure provides for reference only an isolated polynucleotide encoding an idiotype-specific polypeptide wherein the polynucleotide comprises a sequence that encodes the polypeptide sequence of one or more of SEQ ID NOs 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 48, 49, 50, 51, 52, and 53 with conservative amino acid substitutions.

[0309] The polynucleotides encoding idiotype-specific polypeptides useful in the invention may be expressed as a single polynucleotide that encodes the entire idiotype-specific polypeptide or as multiple (e.g., two or more) polynucleotides that are co-expressed. Polypeptides encoded by polynucleotides that are co-expressed may associate through, e.g., disulfide bonds or other means to form a functional idiotype-specific polypeptide, e.g., a masking moiety. For example, in one embodiment the idiotype-specific polypeptide is an anti-idiotypic scFv (single chain variable fragment) wherein the light chain variable portion of the anti-idiotypic scFv may be encoded by a separate polynucleotide from the portion of the anti-idiotypic scFv comprising the heavy chain variable portion of the anti-idiotypic scFv. When co-expressed, the heavy chain polypeptides will associate with the light chain polypeptides to form the anti-idiotypic scFv. In some embodiments, the isolated polynucleotide encodes the idiotype-specific polypeptide that is useful in the invention as described herein.

[0310] In certain embodiments the polynucleotide or nucleic acid is DNA. In other embodiments, a polynucleotide of the present invention is RNA, for example, in the form of messenger RNA (mRNA). RNA of the present invention may be single stranded or double stranded.Recombinant Methods

[0311] Protease-activatable T cell activating bispecific molecules of the invention may be obtained, for example, by solid-state peptide synthesis (e.g., Merrifield solid phase synthesis) or recombinant production. For recombinant production one or more polynucleotide encoding the protease-activatable T cell activating bispecific molecule (fragment), e.g., as described above, is isolated and inserted into one or more vectors for further cloning and / or expression in a host cell. Such polynucleotide may be readily isolated and sequenced using conventional procedures. In one embodiment a vector, preferably an expression vector, comprising one or more of the polynucleotides of the invention is provided. Methods which are well known to those skilled in the art can be used to construct expression vectors containing the coding sequence of a protease-activatable T cell activating bispecific molecule (fragment) along with appropriate transcriptional / translational control signals. These methods include in vitro recombinant DNA techniques, synthetic techniques and in vivo recombination / genetic recombination. See, for example, the techniques described in Maniatis et al., MOLECULAR CLONING: A LABORATORY MANUAL, Cold Spring Harbor Laboratory, N.Y. (1989); and Ausubel et al., CURRENT PROTOCOLS IN MOLECULAR BIOLOGY, Greene Publishing Associates and Wiley Interscience, N.Y (1989). The expression vector can be part of a plasmid, virus, or may be a nucleic acid fragment. The expression vector includes an expression cassette into which the polynucleotide encoding the protease-activatable T cell activating bispecific molecule (fragment) (i.e. the coding region) is cloned in operable association with a promoter and / or other transcription or translation control elements. As used herein, a "coding region" is a portion of nucleic acid which consists of codons translated into amino acids. Although a "stop codon" (TAG, TGA, or TAA) is not translated into an amino acid, it may be considered to be part of a coding region, if present, but any flanking sequences, for example promoters, ribosome binding sites, transcriptional terminators, introns, 5' and 3' untranslated regions, and the like, are not part of a coding region. Two or more coding regions can be present in a single polynucleotide construct, e.g., on a single vector, or in separate polynucleotide constructs, e.g., on separate (different) vectors. Furthermore, any vector may contain a single coding region, or may comprise two or more coding regions, e.g., a vector of the present invention may encode one or more polypeptides, which are post- or co-translationally separated into the final proteins via proteolytic cleavage. In addition, a vector, polynucleotide, or nucleic acid of the invention may encode heterologous coding regions, either fused or unfused to a polynucleotide encoding the protease-activatable T cell activating bispecific molecule (fragment) of the invention, or variant or derivative thereof. Heterologous coding regions include without limitation specialized elements or motifs, such as a secretory signal peptide or a heterologous functional domain. An operable association is when a coding region for a gene product, e.g., a polypeptide, is associated with one or more regulatory sequences in such a way as to place expression of the gene product under the influence or control of the regulatory sequence(s). Two DNA fragments (such as a polypeptide coding region and a promoter associated therewith) are "operably associated" if induction of promoter function results in the transcription of mRNA encoding the desired gene product and if the nature of the linkage between the two DNA fragments does not interfere with the ability of the expression regulatory sequences to direct the expression of the gene product or interfere with the ability of the DNA template to be transcribed. Thus, a promoter region would be operably associated with a nucleic acid encoding a polypeptide if the promoter was capable of effecting transcription of that nucleic acid. The promoter may be a cell-specific promoter that directs substantial transcription of the DNA only in predetermined cells. Other transcription control elements, besides a promoter, for example enhancers, operators, repressors, and transcription termination signals, can be operably associated with the polynucleotide to direct cell-specific transcription. Suitable promoters and other transcription control regions are disclosed herein. A variety of transcription control regions are known to those skilled in the art. These include, without limitation, transcription control regions, which function in vertebrate cells, such as, but not limited to, promoter and enhancer segments from cytomegaloviruses (e.g., the immediate early promoter, in conjunction with intron-A), simian virus 40 (e.g., the early promoter), and retroviruses (such as, e.g., Rous sarcoma virus). Other transcription control regions include those derived from vertebrate genes such as actin, heat shock protein, bovine growth hormone and rabbit â-globin, as well as other sequences capable of controlling gene expression in eukaryotic cells. Additional suitable transcription control regions include tissue-specific promoters and enhancers as well as inducible promoters (e.g., promoters inducible tetracyclins). Similarly, a variety of translation control elements are known to those of ordinary skill in the art. These include, but are not limited to ribosome binding sites, translation initiation and termination codons, and elements derived from viral systems (particularly an internal ribosome entry site, or IRES, also referred to as a CITE sequence). The expression cassette may also include other features such as an origin of replication, and / or chromosome integration elements such as retroviral long terminal repeats (LTRs), or adeno-associated viral (AAV) inverted terminal repeats (ITRs).

[0312] Polynucleotide and nucleic acid coding regions of the present invention may be associated with additional coding regions which encode secretory or signal peptides, which direct the secretion of a polypeptide encoded by a polynucleotide of the present invention. For example, if secretion of the protease-activatable T cell activating bispecific molecule is desired, DNA encoding a signal sequence may be placed upstream of the nucleic acid encoding a protease-activatable T cell activating bispecific molecule of the invention or a fragment thereof. According to the signal hypothesis, proteins secreted by mammalian cells have a signal peptide or secretory leader sequence which is cleaved from the mature protein once export of the growing protein chain across the rough endoplasmic reticulum has been initiated. Those of ordinary skill in the art are aware that polypeptides secreted by vertebrate cells generally have a signal peptide fused to the N-terminus of the polypeptide, which is cleaved from the translated polypeptide to produce a secreted or "mature" form of the polypeptide. In certain embodiments, the native signal peptide, e.g., an immunoglobulin heavy chain or light chain signal peptide is used, or a functional derivative of that sequence that retains the ability to direct the secretion of the polypeptide that is operably associated with it. Alternatively, a heterologous mammalian signal peptide, or a functional derivative thereof, may be used. For example, the wild-type leader sequence may be substituted with the leader sequence of human tissue plasminogen activator (TPA) or mouse β-glucuronidase.

[0313] DNA encoding a short protein sequence that could be used to facilitate later purification (e.g., a histidine tag) or assist in labeling the protease-activatable T cell activating bispecific molecule may be included within or at the ends of the protease-activatable T cell activating bispecific molecule (fragment) encoding polynucleotide.

[0314] In a further embodiment, a host cell comprising one or more polynucleotides of the invention is provided. In certain embodiments a host cell comprising one or more vectors of the invention is provided. The polynucleotides and vectors may incorporate any of the features, singly or in combination, described herein in relation to polynucleotides and vectors, respectively. In one such embodiment a host cell comprises (e.g., has been transformed or transfected with) a vector comprising a polynucleotide that encodes a protease-activatable T cell activating bispecific molecule of the invention. As used herein, the term "host cell" refers to any kind of cellular system which can be engineered to generate the protease-activatable T cell activating bispecific molecules of the invention or fragments thereof. Host cells suitable for replicating and for supporting expression of protease-activatable T cell activating bispecific molecules are well known in the art. Such cells may be transfected or transduced as appropriate with the particular expression vector and large quantities of vector containing cells can be grown for seeding large scale fermenters to obtain sufficient quantities of the protease-activatable T cell activating bispecific molecule for clinical applications. Suitable host cells include prokaryotic microorganisms, such as E. coli, or various eukaryotic cells, such as Chinese hamster ovary cells (CHO), insect cells, or the like. For example, polypeptides may be produced in bacteria in particular when glycosylation is not needed. After expression, the polypeptide may be isolated from the bacterial cell paste in a soluble fraction and can be further purified. In addition to prokaryotes, eukaryotic microbes such as filamentous fungi or yeast are suitable cloning or expression hosts for polypeptide-encoding vectors, including fungi and yeast strains whose glycosylation pathways have been "humanized", resulting in the production of a polypeptide with a partially or fully human glycosylation pattern. See Gerngross, Nat Biotech 22, 1409-1414 (2004), and Li et al., Nat Biotech 24, 210-215 (2006). Suitable host cells for the expression of (glycosylated) polypeptides are also derived from multicellular organisms (invertebrates and vertebrates). Examples of invertebrate cells include plant and insect cells. Numerous baculoviral strains have been identified which may be used in conjunction with insect cells, particularly for transfection of Spodoptera frugiperda cells. Plant cell cultures can also be utilized as hosts. See e.g., US Patent Nos. 5,959,177, 6,040,498, 6,420,548, 7,125,978, and 6,417,429 (describing PLANTIBODIES ™< technology for producing antibodies in transgenic plants). Vertebrate cells may also be used as hosts. For example, mammalian cell lines that are adapted to grow in suspension may be useful. Other examples of useful mammalian host cell lines are monkey kidney CV1 line transformed by SV40 (COS-7); human embryonic kidney line (293 or 293T cells as described, e.g., in Graham et al., J Gen Virol 36, 59 (1977)), baby hamster kidney cells (BHK), mouse sertoli cells (TM4 cells as described, e.g., in Mather, Biol Reprod 23, 243-251 (1980)), monkey kidney cells (CV1), African green monkey kidney cells (VERO-76), human cervical carcinoma cells (HELA), canine kidney cells (MDCK), buffalo rat liver cells (BRL 3A), human lung cells (W138), human liver cells (Hep G2), mouse mammary tumor cells (MMT 060562), TRI cells (as described, e.g., in Mather et al., Annals N.Y. Acad Sci 383, 44-68 (1982)), MRC 5 cells, and FS4 cells. Other useful mammalian host cell lines include Chinese hamster ovary (CHO) cells, including dhfr -< CHO cells (Urlaub et al., Proc Natl Acad Sci USA 77, 4216 (1980)); and myeloma cell lines such as YO, NS0, P3X63 and Sp2 / 0. For a review of certain mammalian host cell lines suitable for protein production, see, e.g., Yazaki and Wu, Methods in Molecular Biology, Vol. 248 (B.K.C. Lo, ed., Humana Press, Totowa, NJ), pp. 255-268 (2003). Host cells include cultured cells, e.g., mammalian cultured cells, yeast cells, insect cells, bacterial cells and plant cells, to name only a few, but also cells comprised within a transgenic animal, transgenic plant or cultured plant or animal tissue. In one embodiment, the host cell is a eukaryotic cell, preferably a mammalian cell, such as a Chinese Hamster Ovary (CHO) cell, a human embryonic kidney (HEK) cell or a lymphoid cell (e.g., Y0, NS0, Sp20 cell). Standard technologies are known in the art to express foreign genes in these systems. Cells expressing a polypeptide comprising either the heavy or the light chain of an antigen binding domain such as an antibody, may be engineered so as to also express the other of the antibody chains such that the expressed product is an antibody that has both a heavy and a light chain.

[0315] In one embodiment, a method of producing a protease-activatable T cell activating bispecific molecule according to the invention is provided, wherein the method comprises culturing a host cell comprising a polynucleotide encoding the protease-activatable T cell activating bispecific molecule, as provided herein, under conditions suitable for expression of the protease-activatable T cell activating bispecific molecule, and recovering the protease-activatable T cell activating bispecific molecule from the host cell (or host cell culture medium).

[0316] The components of the protease-activatable T cell activating bispecific molecule are genetically fused to each other. Protease-activatable T cell activating bispecific molecules can be designed such that its components are fused directly to each other or indirectly through a linker sequence. The composition and length of the linker may be determined in accordance with methods well known in the art and may be tested for efficacy. Examples of linker sequences between different components of protease-activatable T cell activating bispecific molecules are found in the sequences provided herein. Additional sequences may also be included to incorporate a cleavage site to separate the individual components of the fusion if desired, for example an endopeptidase recognition sequence.

[0317] In certain embodiments the one or more antigen binding moieties of the protease-activatable T cell activating bispecific molecules comprise at least an antibody variable region capable of binding an antigenic determinant. Variable regions can form part of and be derived from naturally or non-naturally occurring antibodies and fragments thereof. Methods to produce polyclonal antibodies and monoclonal antibodies are well known in the art (see e.g., Harlow and Lane, "Antibodies, a laboratory manual", Cold Spring Harbor Laboratory, 1988). Non-naturally occurring antibodies can be constructed using solid phase-peptide synthesis, can be produced recombinantly (e.g., as described in U.S. patent No. 4,186,567) or can be obtained, for example, by screening combinatorial libraries comprising variable heavy chains and variable light chains (see e.g., U.S. Patent. No. 5,969,108 to McCafferty).

[0318] Any animal species of antibody, antibody fragment, antigen binding domain or variable region can be used in the protease-activatable T cell activating bispecific molecules of the invention. Non-limiting antibodies, antibody fragments, antigen binding domains or variable regions useful in the present invention can be of murine, primate, or human origin. If the protease-activatable T cell activating bispecific molecule is intended for human use, a chimeric form of antibody may be used wherein the constant regions of the antibody are from a human. A humanized or fully human form of the antibody can also be prepared in accordance with methods well known in the art (see e. g. U.S. Patent No. 5,565,332 to Winter). Humanization may be achieved by various methods including, but not limited to (a) grafting the non-human (e.g., donor antibody) CDRs onto human (e.g., recipient antibody) framework and constant regions with or without retention of critical framework residues (e.g., those that are important for retaining good antigen binding affinity or antibody functions), (b) grafting only the non-human specificity-determining regions (SDRs or a-CDRs; the residues critical for the antibody-antigen interaction) onto human framework and constant regions, or (c) transplanting the entire non-human variable domains, but "cloaking" them with a human-like section by replacement of surface residues. Humanized antibodies and methods of making them are reviewed, e.g., in Almagro and Fransson, Front Biosci 13, 1619-1633 (2008), and are further described, e.g., in Riechmann et al., Nature 332, 323-329 (1988); Queen et al., Proc Natl Acad Sci USA 86, 10029-10033 (1989); US Patent Nos. 5,821,337, 7,527,791, 6,982,321, and 7,087,409; Jones et al., Nature 321, 522-525 (1986); Morrison et al., Proc Natl Acad Sci 81, 6851-6855 (1984); Morrison and Oi, Adv Immunol 44, 65-92 (1988); Verhoeyen et al., Science 239, 1534-1536 (1988); Padlan, Molec Immun 31(3), 169-217 (1994); Kashmiri et al., Methods 36, 25-34 (2005) (describing SDR (a-CDR) grafting); Padlan, Mol Immunol 28, 489-498 (1991) (describing "resurfacing"); Dall'Acqua et al., Methods 36, 43-60 (2005) (describing "FR shuffling"); and Osbourn et al., Methods 36, 61-68 (2005) and Klimka et al., Br J Cancer 83, 252-260 (2000) (describing the "guided selection" approach to FR shuffling). Human antibodies and human variable regions can be produced using various techniques known in the art. Human antibodies are described generally in van Dijk and van de

[0319] Winkel, Curr Opin Pharmacol 5, 368-74 (2001) and Lonberg, Curr Opin Immunol 20, 450-459 (2008). Human variable regions can form part of and be derived from human monoclonal antibodies made by the hybridoma method (see e.g., Monoclonal Antibody Production Techniques and Applications, pp. 51-63 (Marcel Dekker, Inc., New York, 1987)). Human antibodies and human variable regions may also be prepared by administering an immunogen to a transgenic animal that has been modified to produce intact human antibodies or intact antibodies with human variable regions in response to antigenic challenge (see e.g., Lonberg, Nat Biotech 23, 1117-1125 (2005). Human antibodies and human variable regions may also be generated by isolating Fv clone variable region sequences selected from human-derived phage display libraries (see e.g., Hoogenboom et al. in Methods in Molecular Biology 178, 1-37 (O'Brien et al., ed., Human Press, Totowa, NJ, 2001); and McCafferty et al., Nature 348, 552-554; Clackson et al., Nature 352, 624-628 (1991)). Phage typically display antibody fragments, either as single-chain Fv (scFv) fragments or as Fab fragments.

[0320] In certain embodiments, the antigen binding moieties useful in the present invention are engineered to have enhanced binding affinity according to, for example, the methods disclosed in U.S. Pat. Appl. Publ. No. 2004 / 0132066. The ability of the protease-activatable T cell activating bispecific molecule of the invention to bind to a specific antigenic determinant can be measured either through an enzyme-linked immunosorbent assay (ELISA) or other techniques familiar to one of skill in the art, e.g., surface plasmon resonance technique (analyzed on a BIACORE T100 system) (Liljeblad, et al., Glyco J 17, 323-329 (2000)), and traditional binding assays (Heeley, Endocr Res 28, 217-229 (2002)). Competition assays may be used to identify an antibody, antibody fragment, antigen binding domain or variable domain that competes with a reference antibody for binding to a particular antigen, e.g., an antibody that competes with the V9 antibody for binding to CD3. In certain embodiments, such a competing antibody binds to the same epitope (e.g., a linear or a conformational epitope) that is bound by the reference antibody. Detailed exemplary methods for mapping an epitope to which an antibody binds are provided in Morris (1996) "Epitope Mapping Protocols," in Methods in Molecular Biology vol. 66 (Humana Press, Totowa, NJ). In an exemplary competition assay, immobilized antigen (e.g., CD3) is incubated in a solution comprising a first labeled antibody that binds to the antigen (e.g., V9 antibody, described in US 6,054,297) and a second unlabeled antibody that is being tested for its ability to compete with the first antibody for binding to the antigen. The second antibody may be present in a hybridoma supernatant. As a control, immobilized antigen is incubated in a solution comprising the first labeled antibody but not the second unlabeled antibody. After incubation under conditions permissive for binding of the first antibody to the antigen, excess unbound antibody is removed, and the amount of label associated with immobilized antigen is measured. If the amount of label associated with immobilized antigen is substantially reduced in the test sample relative to the control sample, then that indicates that the second antibody is competing with the first antibody for binding to the antigen. See Harlow and Lane (1988) Antibodies: A Laboratory Manual ch.14 (Cold Spring Harbor Laboratory, Cold Spring Harbor, NY).

[0321] Protease-activatable T cell activating bispecific molecules prepared as described herein may be purified by art-known techniques such as high performance liquid chromatography, ion exchange chromatography, gel electrophoresis, affinity chromatography, size exclusion chromatography, and the like. The actual conditions used to purify a particular protein will depend, in part, on factors such as net charge, hydrophobicity, hydrophilicity etc., and will be apparent to those having skill in the art. For affinity chromatography purification an antibody, ligand, receptor or antigen can be used to which the protease-activatable T cell activating bispecific molecule binds. For example, for affinity chromatography purification of protease-activatable T cell activating bispecific molecules of the invention, a matrix with protein A or protein G may be used. Sequential Protein A or G affinity chromatography and size exclusion chromatography can be used to isolate a protease-activatable T cell activating bispecific molecule essentially as described in the Examples. The purity of the protease-activatable T cell activating bispecific molecule can be determined by any of a variety of well-known analytical methods including gel electrophoresis, high pressure liquid chromatography, and the like. For example, the heavy chain fusion proteins expressed as described in the Examples were shown to be intact and properly assembled as demonstrated by reducing SDS-PAGE (see, e.g., FIGs. 8-12). Three bands were resolved at approximately Mr 25,000, Mr 50,000 and Mr 75,000, corresponding to the predicted molecular weights of the protease-activatable T cell activating bispecific molecule light chain, heavy chain and heavy chain / light chain fusion protein.

[0322] Assays protease-activatable T cell activating bispecific molecules provided herein may be identified, screened for, or characterized for their physical / chemical properties and / or biological activities by various assays known in the art.

[0323] Affinity assays

[0324] The affinity of the protease-activatable T cell activating bispecific molecule for an Fc receptor or a target antigen can be determined in accordance with the methods set forth in the Examples by surface plasmon resonance (SPR), using standard instrumentation such as a BIAcore instrument (GE Healthcare), and receptors or target proteins such as may be obtained by recombinant expression. Alternatively, binding of protease-activatable T cell activating bispecific molecules for different receptors or target antigens may be evaluated using cell lines expressing the particular receptor or target antigen, for example by flow cytometry (FACS). A specific illustrative and exemplary embodiment for measuring binding affinity is described in the following and in the Examples below.

[0325] According to one embodiment, K D is measured by surface plasmon resonance using a BIACORE ®< T100 machine (GE Healthcare) at 25 °C.

[0326] To analyze the interaction between the Fc-portion and Fc receptors, His-tagged recombinant Fc-receptor is captured by an anti-Penta His antibody (Qiagen) immobilized on CM5 chips and the bispecific constructs are used as analytes. Briefly, carboxymethylated dextran biosensor chips (CM5, GE Healthcare) are activated with N-ethyl-N'-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) according to the supplier's instructions. Anti Penta-His antibody is diluted with 10 mM sodium acetate, pH 5.0, to 40 µg / ml before injection at a flow rate of 5 µl / min to achieve approximately 6500 response units (RU) of coupled protein. Following the injection of the ligand, 1 M ethanolamine is injected to block unreacted groups. Subsequently the Fc-receptor is captured for 60 s at 4 or 10 nM. For kinetic measurements, four-fold serial dilutions of the bispecific construct (range between 500 nM and 4000 nM) are injected in HBS-EP (GE Healthcare, 10 mM HEPES, 150 mM NaCl, 3 mM EDTA, 0.05 % Surfactant P20, pH 7.4) at 25 °C at a flow rate of 30 µl / min for 120 s.

[0327] To determine the affinity to the target antigen, bispecific constructs are captured by an antihuman Fab specific antibody (GE Healthcare) that is immobilized on an activated CM5-sensor chip surface as described for the anti Penta-His antibody. The final amount of coupled protein is is approximately 12000 RU. The bispecific constructs are captured for 90 s at 300 nM. The target antigens are passed through the flow cells for 180 s at a concentration range from 250 to 1000 nM with a flowrate of 30 µl / min. The dissociation is monitored for 180 s.

[0328] Bulk refractive index differences are corrected for by subtracting the response obtained on reference flow cell. The steady state response was used to derive the dissociation constant K D by non-linear curve fitting of the Langmuir binding isotherm. Association rates (k on ) and dissociation rates (k off ) are calculated using a simple one-to-one Langmuir binding model (BIACORE ®< T100 Evaluation Software version 1.1.1) by simultaneously fitting the association and dissociation sensorgrams. The equilibrium dissociation constant (K D ) is calculated as the ratio k off / k on . See, e.g., Chen et al., J Mol Biol 293, 865-881 (1999).Activity assays

[0329] Biological activity of the protease-activatable T cell activating bispecific molecules of the invention can be measured by various assays as described in the Examples. Biological activities may for example include the induction of proliferation of T cells, the induction of signaling in T cells, the induction of expression of activation markers in T cells, the induction of cytokine secretion by T cells, the induction of lysis of target cells such as tumor cells, and the induction of tumor regression and / or the improvement of survival.Compositions, Formulations, and Routes of Administration

[0330] In a further aspect, the invention provides pharmaceutical compositions comprising any of the protease-activatable T cell activating bispecific molecules provided herein, e.g., for use in any of the below therapeutic methods. In one embodiment, a pharmaceutical composition comprises any of the protease-activatable T cell activating bispecific molecules provided herein and a pharmaceutically acceptable carrier. In another embodiment, a pharmaceutical composition comprises any of the protease-activatable T cell activating bispecific molecules provided herein and at least one additional therapeutic agent, e.g., as described below.

[0331] Further provided is a method of producing a protease-activatable T cell activating bispecific molecule of the invention in a form suitable for administration in vivo, the method comprising (a) obtaining a protease-activatable T cell activating bispecific molecule according to the invention, and (b) formulating the protease-activatable T cell activating bispecific molecule with at least one pharmaceutically acceptable carrier, whereby a preparation of protease-activatable T cell activating bispecific molecule is formulated for administration in vivo.

[0332] Pharmaceutical compositions of the present invention comprise a therapeutically effective amount of one or more protease-activatable T cell activating bispecific molecule dissolved or dispersed in a pharmaceutically acceptable carrier. The phrases "pharmaceutical or pharmacologically acceptable" refers to molecular entities and compositions that are generally non-toxic to recipients at the dosages and concentrations employed, i.e. do not produce an adverse, allergic or other untoward reaction when administered to an animal, such as, for example, a human, as appropriate. The preparation of a pharmaceutical composition that contains at least one protease-activatable T cell activating bispecific molecule and optionally an additional active ingredient will be known to those of skill in the art in light of the present disclosure, as exemplified by Remington's Pharmaceutical Sciences, 18th Ed. Mack Printing Company, 1990. Moreover, for animal (e.g., human) administration, it will be understood that preparations should meet sterility, pyrogenicity, general safety and purity standards as required by FDA Office of Biological Standards or corresponding authorities in other countries. Preferred compositions are lyophilized formulations or aqueous solutions. As used herein, "pharmaceutically acceptable carrier" includes any and all solvents, buffers, dispersion media, coatings, surfactants, antioxidants, preservatives (e.g., antibacterial agents, antifungal agents), isotonic agents, absorption delaying agents, salts, preservatives, antioxidants, proteins, drugs, drug stabilizers, polymers, gels, binders, excipients, disintegration agents, lubricants, sweetening agents, flavoring agents, dyes, such like materials and combinations thereof, as would be known to one of ordinary skill in the art (see, for example, Remington's Pharmaceutical Sciences, 18th Ed. Mack Printing Company, 1990, pp. 1289-1329). Except insofar as any conventional carrier is incompatible with the active ingredient, its use in the therapeutic or pharmaceutical compositions is contemplated.

[0333] The composition may comprise different types of carriers depending on whether it is to be administered in solid, liquid or aerosol form, and whether it need to be sterile for such routes of administration as injection. Protease-activatable T cell activating bispecific molecules of the present invention (and any additional therapeutic agent) can be administered intravenously, intradermally, intraarterially, intraperitoneally, intralesionally, intracranially, intraarticularly, intraprostatically, intrasplenically, intrarenally, intrapleurally, intratracheally, intranasally, intravitreally, intravaginally, intrarectally, intratumorally, intramuscularly, intraperitoneally, subcutaneously, subconjunctivally, intravesicularlly, mucosally, intrapericardially, intraumbilically, intraocularally, orally, topically, locally, by inhalation (e.g., aerosol inhalation), injection, infusion, continuous infusion, localized perfusion bathing target cells directly, via a catheter, via a lavage, in cremes, in lipid compositions (e.g., liposomes), or by other method or any combination of the forgoing as would be known to one of ordinary skill in the art (see, for example, Remington's Pharmaceutical Sciences, 18th Ed. Mack Printing Company, 1990). Parenteral administration, in particular intravenous injection, is most commonly used for administering polypeptide molecules such as the protease-activatable T cell activating bispecific molecules of the invention.

[0334] Parenteral compositions include those designed for administration by injection, e.g., subcutaneous, intradermal, intralesional, intravenous, intraarterial intramuscular, intrathecal or intraperitoneal injection. For injection, the protease-activatable T cell activating bispecific molecules of the invention may be formulated in aqueous solutions, preferably in physiologically compatible buffers such as Hanks' solution, Ringer's solution, or physiological saline buffer. The solution may contain formulatory agents such as suspending, stabilizing and / or dispersing agents. Alternatively, the protease-activatable T cell activating bispecific molecules may be in powder form for constitution with a suitable vehicle, e.g., sterile pyrogen-free water, before use. Sterile injectable solutions are prepared by incorporating the protease-activatable T cell activating bispecific molecules of the invention in the required amount in the appropriate solvent with various of the other ingredients enumerated below, as required. Sterility may be readily accomplished, e.g., by filtration through sterile filtration membranes. Generally, dispersions are prepared by incorporating the various sterilized active ingredients into a sterile vehicle which contains the basic dispersion medium and / or the other ingredients. In the case of sterile powders for the preparation of sterile injectable solutions, suspensions or emulsion, the preferred methods of preparation are vacuum-drying or freeze-drying techniques which yield a powder of the active ingredient plus any additional desired ingredient from a previously sterile-filtered liquid medium thereof. The liquid medium should be suitably buffered if necessary and the liquid diluent first rendered isotonic prior to injection with sufficient saline or glucose. The composition must be stable under the conditions of manufacture and storage, and preserved against the contaminating action of microorganisms, such as bacteria and fungi. It will be appreciated that endotoxin contamination should be kept minimally at a safe level, for example, less that 0.5 ng / mg protein. Suitable pharmaceutically acceptable carriers include, but are not limited to: buffers such as phosphate, citrate, and other organic acids; antioxidants including ascorbic acid and methionine; preservatives (such as octadecyldimethylbenzyl ammonium chloride; hexamethonium chloride; benzalkonium chloride; benzethonium chloride; phenol, butyl or benzyl alcohol; alkyl parabens such as methyl or propyl paraben; catechol; resorcinol; cyclohexanol; 3-pentanol; and m-cresol); low molecular weight (less than about 10 residues) polypeptides; proteins, such as serum albumin, gelatin, or immunoglobulins; hydrophilic polymers such as polyvinylpyrrolidone; amino acids such as glycine, glutamine, asparagine, histidine, arginine, or lysine; monosaccharides, disaccharides, and other carbohydrates including glucose, mannose, or dextrins; chelating agents such as EDTA; sugars such as sucrose, mannitol, trehalose or sorbitol; salt-forming counter-ions such as sodium; metal complexes (e.g., Zn-protein complexes); and / or non-ionic surfactants such as polyethylene glycol (PEG). Aqueous injection suspensions may contain compounds which increase the viscosity of the suspension, such as sodium carboxymethyl cellulose, sorbitol, dextran, or the like. Optionally, the suspension may also contain suitable stabilizers or agents which increase the solubility of the compounds to allow for the preparation of highly concentrated solutions. Additionally, suspensions of the active compounds may be prepared as appropriate oily injection suspensions. Suitable lipophilic solvents or vehicles include fatty oils such as sesame oil, or synthetic fatty acid esters, such as ethyl cleats or triglycerides, or liposomes.

[0335] Active ingredients may be entrapped in microcapsules prepared, for example, by coacervation techniques or by interfacial polymerization, for example, hydroxymethylcellulose or gelatin-microcapsules and poly-(methylmethacylate) microcapsules, respectively, in colloidal drug delivery systems (for example, liposomes, albumin microspheres, microemulsions, nanoparticles and nanocapsules) or in macroemulsions. Such techniques are disclosed in Remington's Pharmaceutical Sciences (18th Ed. Mack Printing Company, 1990). Sustained-release preparations may be prepared. Suitable examples of sustained-release preparations include semipermeable matrices of solid hydrophobic polymers containing the polypeptide, which matrices are in the form of shaped articles, e.g., films, or microcapsules. In particular embodiments, prolonged absorption of an injectable composition can be brought about by the use in the compositions of agents delaying absorption, such as, for example, aluminum monostearate, gelatin or combinations thereof.

[0336] In addition to the compositions described previously, the protease-activatable T cell activating bispecific molecules may also be formulated as a depot preparation. Such long acting formulations may be administered by implantation (for example subcutaneously or intramuscularly) or by intramuscular injection. Thus, for example, the protease-activatable T cell activating bispecific molecules may be formulated with suitable polymeric or hydrophobic materials (for example as an emulsion in an acceptable oil) or ion exchange resins, or as sparingly soluble derivatives, for example, as a sparingly soluble salt.

[0337] Pharmaceutical compositions comprising the protease-activatable T cell activating bispecific molecules of the invention may be manufactured by means of conventional mixing, dissolving, emulsifying, encapsulating, entrapping or lyophilizing processes. Pharmaceutical compositions may be formulated in conventional manner using one or more physiologically acceptable carriers, diluents, excipients or auxiliaries which facilitate processing of the proteins into preparations that can be used pharmaceutically. Proper formulation is dependent upon the route of administration chosen.

[0338] The protease-activatable T cell activating bispecific molecules may be formulated into a composition in a free acid or base, neutral or salt form. Pharmaceutically acceptable salts are salts that substantially retain the biological activity of the free acid or base. These include the acid addition salts, e.g., those formed with the free amino groups of a proteinaceous composition, or which are formed with inorganic acids such as for example, hydrochloric or phosphoric acids, or such organic acids as acetic, oxalic, tartaric or mandelic acid. Salts formed with the free carboxyl groups can also be derived from inorganic bases such as for example, sodium, potassium, ammonium, calcium or ferric hydroxides; or such organic bases as isopropylamine, trimethylamine, histidine or procaine. Pharmaceutical salts tend to be more soluble in aqueous and other protic solvents than are the corresponding free base forms.Therapeutic Methods and Compositions

[0339] Any of the protease-activatable T cell activating bispecific molecules provided herein may be used in therapeutic methods. Protease-activatable T cell activating bispecific molecules of the invention can be used as immunotherapeutic agents, for example in the treatment of cancers.

[0340] For use in therapeutic methods, protease-activatable T cell activating bispecific molecules of the invention would be formulated, dosed, and administered in a fashion consistent with good medical practice. Factors for consideration in this context include the particular disorder being treated, the particular mammal being treated, the clinical condition of the individual patient, the cause of the disorder, the site of delivery of the agent, the method of administration, the scheduling of administration, and other factors known to medical practitioners.

[0341] In one aspect, protease-activatable T cell activating bispecific molecules of the invention for use as a medicament are provided. In further aspects, protease-activatable T cell activating bispecific molecules of the invention for use in treating a disease are provided. In certain embodiments, protease-activatable T cell activating bispecific molecules of the invention for use in a method of treatment are provided. In one embodiment, the invention provides a protease-activatable T cell activating bispecific molecule as described herein for use in the treatment of a disease in an individual in need thereof. In certain embodiments, the invention provides a protease-activatable T cell activating bispecific molecule for use in a method of treating an individual having a disease comprising administering to the individual a therapeutically effective amount of the protease-activatable T cell activating bispecific molecule. In certain embodiments the disease to be treated is a proliferative disorder. In a particular embodiment the disease is cancer. In certain embodiments the method further comprises administering to the individual a therapeutically effective amount of at least one additional therapeutic agent, e.g., an anti-cancer agent if the disease to be treated is cancer. In further embodiments, the invention provides a protease-activatable T cell activating bispecific molecule as described herein for use in inducing lysis of a target cell, particularly a tumor cell. In certain embodiments, the invention provides a protease-activatable T cell activating bispecific molecule for use in a method of inducing lysis of a target cell, particularly a tumor cell, in an individual comprising administering to the individual an effective amount of the protease-activatable T cell activating bispecific molecule to induce lysis of a target cell. An "individual" according to any of the above embodiments is a mammal, preferably a human.

[0342] In a further aspect, the invention provides for the use of a protease-activatable T cell activating bispecific molecule of the invention in the manufacture or preparation of a medicament. In one embodiment the medicament is for the treatment of a disease in an individual in need thereof. In a further embodiment, the medicament is for use in a method of treating a disease comprising administering to an individual having the disease a therapeutically effective amount of the medicament. In certain embodiments the disease to be treated is a proliferative disorder. In a particular embodiment the disease is cancer. In one embodiment, the method further comprises administering to the individual a therapeutically effective amount of at least one additional therapeutic agent, e.g., an anti-cancer agent if the disease to be treated is cancer. In a further embodiment, the medicament is for inducing lysis of a target cell, particularly a tumor cell. An "individual" according to any of the above embodiments may be a mammal, preferably a human. In a further aspect, the invention provides a method for treating a disease. In one embodiment, the method comprises administering to an individual having such disease a therapeutically effective amount of a protease-activatable T cell activating bispecific molecule of the invention. In one embodiment a composition is administered to said invididual, comprising the protease-activatable T cell activating bispecific molecule of the invention in a pharmaceutically acceptable form. In certain embodiments the disease to be treated is a proliferative disorder. In a particular embodiment the disease is cancer. In certain embodiments the method further comprises administering to the individual a therapeutically effective amount of at least one additional therapeutic agent, e.g., an anti-cancer agent if the disease to be treated is cancer. An "individual" according to any of the above embodiments may be a mammal, preferably a human. In one embodiment, an "individual" is a human.

[0343] In certain embodiments the disease to be treated is a proliferative disorder, particularly cancer. Non-limiting examples of cancers include bladder cancer, brain cancer, head and neck cancer, pancreatic cancer, lung cancer, breast cancer, ovarian cancer, uterine cancer, cervical cancer, endometrial cancer, esophageal cancer, colon cancer, colorectal cancer, rectal cancer, gastric cancer, prostate cancer, blood cancer, skin cancer, squamous cell carcinoma, bone cancer, and kidney cancer. Other cell proliferation disorders that can be treated using a protease-activatable T cell activating bispecific molecule of the present invention include, but are not limited to neoplasms located in the: abdomen, bone, breast, digestive system, liver, pancreas, peritoneum, endocrine glands (adrenal, parathyroid, pituitary, testicles, ovary, thymus, thyroid), eye, head and neck, nervous system (central and peripheral), lymphatic system, pelvic, skin, soft tissue, spleen, thoracic region, and urogenital system. Also included are pre-cancerous conditions or lesions and cancer metastases. In certain embodiments the cancer is chosen from the group consisting of renal cell cancer, skin cancer, lung cancer, colorectal cancer, breast cancer, brain cancer, head and neck cancer. A skilled artisan readily recognizes that in many cases the protease-activatable T cell activating bispecific molecule may not provide a cure but may only provide partial benefit. In some embodiments, a physiological change having some benefit is also considered therapeutically beneficial. Thus, in some embodiments, an amount of protease-activatable T cell activating bispecific molecule that provides a physiological change is considered an "effective amount" or a "therapeutically effective amount". The subject, patient, or individual in need of treatment is typically a mammal, more specifically a human.

[0344] In some embodiments, an effective amount of a protease-activatable T cell activating bispecific molecule of the invention is administered to a cell. In other embodiments, a therapeutically effective amount of a protease-activatable T cell activating bispecific molecule of the invention is administered to an individual for the treatment of disease.

[0345] For the prevention or treatment of disease, the appropriate dosage of a protease-activatable T cell activating bispecific molecule of the invention (when used alone or in combination with one or more other additional therapeutic agents) will depend on the type of disease to be treated, the route of administration, the body weight of the patient, the type of T cell activating bispecific antigen binding molecule, the severity and course of the disease, whether the T cell activating bispecific antigen binding molecule is administered for preventive or therapeutic purposes, previous or concurrent therapeutic interventions, the patient's clinical history and response to the protease-activatable T cell activating bispecific molecule, and the discretion of the attending physician. The practitioner responsible for administration will, in any event, determine the concentration of active ingredient(s) in a composition and appropriate dose(s) for the individual subject. Various dosing schedules including but not limited to single or multiple administrations over various time-points, bolus administration, and pulse infusion are contemplated herein.

[0346] The protease-activatable T cell activating bispecific molecule is suitably administered to the patient at one time or over a series of treatments. Depending on the type and severity of the disease, about 1 µg / kg to 15 mg / kg (e.g., 0.1 mg / kg - 10 mg / kg) of protease-activatable T cell activating bispecific molecule can be an initial candidate dosage for administration to the patient, whether, for example, by one or more separate administrations, or by continuous infusion. One typical daily dosage might range from about 1 µg / kg to 100 mg / kg or more, depending on the factors mentioned above. For repeated administrations over several days or longer, depending on the condition, the treatment would generally be sustained until a desired suppression of disease symptoms occurs. One exemplary dosage of the T cell activating bispecific antigen binding molecule would be in the range from about 0.005 mg / kg to about 10 mg / kg. In other non-limiting examples, a dose may also comprise from about 1 microgram / kg body weight, about 5 microgram / kg body weight, about 10 microgram / kg body weight, about 50 microgram / kg body weight, about 100 microgram / kg body weight, about 200 microgram / kg body weight, about 350 microgram / kg body weight, about 500 microgram / kg body weight, about 1 milligram / kg body weight, about 5 milligram / kg body weight, about 10 milligram / kg body weight, about 50 milligram / kg body weight, about 100 milligram / kg body weight, about 200 milligram / kg body weight, about 350 milligram / kg body weight, about 500 milligram / kg body weight, to about 1000 mg / kg body weight or more per administration, and any range derivable therein. In non-limiting examples of a derivable range from the numbers listed herein, a range of about 5 mg / kg body weight to about 100 mg / kg body weight, about 5 microgram / kg body weight to about 500 milligram / kg body weight, etc., can be administered, based on the numbers described above. Thus, one or more doses of about 0.5 mg / kg, 2.0 mg / kg, 5.0 mg / kg or 10 mg / kg (or a...

Claims

1. A protease-activatable T cell activating bispecific molecule comprising (a) a first antigen binding moiety capable of specific binding to CD3, wherein the first antigen binding moiety is an antibody or fragment thereof; (b) a second antigen binding moiety capable of specific binding to a target cell antigen wherein the second antigen binding moiety is an antibody or fragment thereof; and (c) a masking moiety covalently attached to the protease-activatable T cell activating bispecific molecule through a protease-cleavable linker, wherein the masking moiety is capable of specific binding to the idiotype of the first or the second antigen binding moiety thereby reversibly concealing the first or the second antigen binding moiety, wherein the masking moiety is an anti-idiotypic scFv.

2. The protease-activatable T cell activating bispecific molecule of claim 1, wherein the masking moiety is covalently attached to the first antigen binding moiety and reversibly conceals the first antigen binding moiety.

3. The protease-activatable T cell activating bispecific molecule of claim 1 or 2, wherein the masking moiety is covalently attached to the heavy chain variable region of the first antigen binding moiety.

4. The protease-activatable T cell activating bispecific molecule of any one of claims 1 to 3, wherein the second antigen binding moiety is capable of specific binding to a target cell antigen selected from the group consisting of FolRl, HER1, HER2 and Mesothelin.

5. The protease-activatable T cell activating bispecific molecule of any one of claims 1 to 4, wherein the first and the second antigen binding moiety are fused to each other, optionally via a peptide linker.

6. The protease-activatable T cell activating bispecific molecule of any one of claims 1 to 5, additionally comprising an Fc domain composed of a first and a second subunit capable of stable association.

7. The protease-activatable T cell activating bispecific molecule of claim 6, wherein the Fc domain is an IgG, specifically an IgG1 or IgG4, Fc domain.

8. The protease-activatable T cell activating bispecific molecule of any one of claims 6 or 7, wherein the Fc domain exhibits reduced binding affinity to an Fc receptor and / or reduced effector function, as compared to a native IgG1 Fc domain.

9. The protease-activatable T cell activating bispecific molecule of any one of claims 1 to 8, wherein the masking moiety comprises a heavy chain variable region comprising: (a) a heavy chain complementarity determining region CDR H1 amino acid sequence of SYGVS (SEQ ID NO:26); (b) a CDR H2 amino acid sequence of IIWGDGSTNYHSALIS (SEQ ID NO:27); (c) a CDR H3 amino acid sequence of GITTVVDDYYAMDY (SEQ ID NO:28); and a light chain variable region comprising: (d) a light chain (CDR L)1 amino acid sequence of RASENIDSYLA (SEQ ID NO:29); (e) a CDR L2 amino acid sequence of AATFLAD (SEQ ID NO:30); and (f) a CDR L3 amino acid sequence of QHYYSTPYT (SEQ ID NO:31).

10. The protease-activatable T cell activating bispecific molecule of any one of claims 1 to 9, wherein the protease cleavable linker comprises at least one protease recognition sequence.

11. The protease-activatable T cell activating bispecific molecule of claim 10, wherein the protease cleavable linker comprises the protease recognition sequence RQARVVNG (SEQ ID NO:36).

12. The protease-activatable T cell activating bispecific molecule of any one of claims 1 to 11, wherein the first antigen binding moiety is capable of specific binding to CD3 and comprises a heavy chain variable region comprising: a) a heavy chain complementarity determining region CDR H1 amino acid sequence of TYAMN (SEQ ID NO:44); b) a CDR H2 amino acid sequence of RIRSKYNNYATYYADSVKG (SEQ ID NO:45); and c) a CDR H3 amino acid sequence of HGNFGNSYVSWFAY (SEQ ID NO:46); and a light chain variable region comprising: d) a light chain (CDR L)1 amino acid sequence of GSSTGAVTTSNYAN (SEQ ID NO:17); e) a CDR L2 amino acid sequence of GTNKRAP (SEQ ID NO:18); and f) a CDR L3 amino acid sequence of ALWYSNLWV (SEQ ID NO:19).

13. The protease-activatable T cell activating bispecific molecule of any one of claims 1 to 12, wherein the first antigen binding moiety is capable of specific binding to CD3 and comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 43 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 55.

14. The protease-activatable T cell activating bispecific molecule of any one of claims 1 to 13, wherein the second antigen binding moiety is capable of specific binding to FolR1 and comprises a heavy chain variable region comprising: a) a heavy chain complementarity determining region CDR H1 amino acid sequence of NAWMS (SEQ ID NO: 14); b) a CDR H2 amino acid sequence of RIKSKTDGGTTDYAAPVKG (SEQ ID NO: 15); and c) a CDR H3 amino acid sequence of PWEWSWYDY (SEQ ID NO: 16); and a light chain variable region comprising: d) a light chain (CDR L)1 amino acid sequence of GSSTGAVTTSNYAN (SEQ ID NO: 17); e) a CDR L2 amino acid sequence of GTNKRAP (SEQ ID NO: 18); and f) a CDR L3 amino acid sequence of ALWYSNLWV (SEQ ID NO: 19).

15. An idiotype-specific polypeptide for reversibly concealing an anti-CD3 antigen binding site of a molecule, wherein the idiotype-specific polypeptide is an anti-idiotype scFv, wherein the idiotype-specific polypeptide is covalently attached to the molecule through a peptide linker.

16. The idiotype-specific polypeptide of claim 15, wherein the linker is a protease-cleavable linker.

17. The idiotype-specific polypeptide of claim 15 or of claim 16, wherein the peptide linker comprises at least one protease recognition site.

18. The idiotype-specific polypeptide of claim 17, wherein the protease cleavable linker comprises the protease recognition sequence RQARVVNG (SEQ ID NO:36).

19. The idiotype-specific polypeptide of any one of claims 17 or 18, wherein the molecule is a T-cell activating bispecific molecule.

20. The idiotype-specific polypeptide of any one of claims 15 to 19, comprising a heavy chain variable region comprising: (a) a heavy chain complementarity determining region CDR H1 amino acid sequence of SYGVS (SEQ ID NO:26); (b) a CDR H2 amino acid sequence of IIWGDGSTNYHSALIS (SEQ ID NO:27); (c) a CDR H3 amino acid sequence of GITTVVDDYYAMDY (SEQ ID NO:28); and a light chain variable region comprising: (d) a light chain (CDR L)1 amino acid sequence of RASENIDSYLA (SEQ ID NO:29); (e) a CDR L2 amino acid sequence of AATFLAD (SEQ ID NO:30); and (f) a CDR L3 amino acid sequence of QHYYSTPYT (SEQ ID NO:31).

21. A pharmaceutical composition comprising the protease-activatable T cell activating bispecific molecule of any one of claims 1 to 14 or the the idiotype-specific polypeptide of any one of claims 15 to 20 and a pharmaceutically acceptable carrier.

22. A protease-activatable T cell activating bispecific molecule of any one of claims 1 to 14, the idiotype-specific polypeptide of any one of claims 15 to 20 or the pharmaceutical composition of claim 21 for use as a medicament.

23. The protease-activatable T cell activating bispecific molecule for use according to claim 22, wherein the medicament is for treating or delaying progression of cancer, treating or delaying progression of an immune related disease, or enhancing or stimulating an immune response or function in an individual.

24. An isolated polynucleotide encoding the protease-activatable T cell activating bispecific antigen binding molecule of any one of claims 1 to 14 or the idiotype-specific polypeptide of any one of claims 15 to 20.

25. A vector, particularly an expression vector, comprising the polynucleotide of claim 24.

26. A host cell comprising the polynucleotide of claim 24 or the vector of claim 25.

27. A method of producing a protease-activatable T cell activating bispecific molecule or an idiotype-specific polypeptide, comprising the steps of a) culturing the host cell of claim 26 under conditions suitable for the expression of the protease-activatable T cell activating bispecific molecule or the idiotype-specific polypeptide and b) recovering the protease-activatable T cell activating bispecific molecule or the idiotype-specific polypeptide.