Decoy receptor 3 (DCR3) binding proteins and uses thereof

Abstract

The present application discloses binding proteins that selectively bind to DcR3 and uses thereof in diagnostic and purification assays as well as therapeutic methods of treatment. Also described are fusion proteins which contain a first DcR3 binding protein that binds to DcR3 and inhibits binding of its ligands and a second DcR3 binding protein that binds to DcR3 but does not inhibit binding of its ligands. The binding proteins and fusion proteins can also be used in diagnostic and purification assays as well as therapeutic methods of treatment.

Description

Docket No. WRENCH-002 / WO01 DECOY RECEPTOR 3 (DCR3) BINDING PROTEINS AND USES THEREOF CROSS REFERENCING This application claims the benefit of U.S. provisional application serial no.63 / 655,138, filed on June 3, 2024, the contents of which are hereby incorporated by reference in their entirety. SEQUENCE LISTING The present application is accompanied by a sequence listing submitted as an electronically filed XML document entitled “2025-05-31 WRENCH-001-WO01 Sequence Listing.xml”, created on May 31, 2025, and having a size of 240 KB. The content of this sequence listing is hereby incorporated by reference in its entirety. BACKGROUND Decoy receptors are a class of checkpoints that interfere with cytokine-mediated immune activation. In addition to classical immune checkpoint inhibitory immunoreceptors like PD-1, CTLA-4, and LAG3, certain soluble receptors also serve as gatekeepers of the immune response. Decoy receptors play a role as soluble immune checkpoints by sequestering immune-stimulatory cytokines, thereby preventing the activation of anti- cancer immune cells. Binding proteins targeting decoy receptors have therapeutic purposes involving the activation of immune response. Thus, there is a need for binding proteins that bind to decoy receptors for therapeutic treatments. BRIEF SUMMARY The present disclosure provides Decoy Receptor 3 (DcR3) binding proteins and anti-DcR3 fusion proteins. DcR3 is a decoy receptor for tumor necrosis factor (TNF) superfamily ligands FasL, LIGHT, and TL1A. DcR3 neutralizes these pro-apoptotic or immune-stimulating cytokines through a conserved binding interface. Because of its mechanism of action and overexpression in cancer, DcR3 has been implicated in several malignant pathways. However, the inventor has recognized and appreciated that a DcR3 binding protein or anti-DcR3 fusion protein which inhibits the interaction between DcR3 and FasL, LIGHT, and TL1A has several advantages, including a decrease in relative DcR3 levels and a corresponding increase in FasL, LIGHT, and TL1A, thereby stimulating the immune system to kill cancer cells. Such DcR3 binding proteins and anti- DcR3 fusion proteins may also bind to multiple epitopes of DcR3, including the specific binding interfaces for FasL, LIGHT, and TL1A. In one embodiment, a single domain Decoy Receptor 3 (DcR3) binding protein is provided. The single domain DcR3 binding protein inhibits the interaction between DcR3 and FasL, LIGHT, and TL1A. In some embodiments, the single domain DcR3 binding protein can bind to one or more binding interfaces of DcR3. In some embodiments, the one or more binding interfaces are selected from the group consisting of: the DcR3:FasL binding interface; the DcR3:LIGHT binding interface; and the DcR3:TL1A binding interface. In some embodiments, the single domain DcR3 binding protein binds to DcR3 at one or more amino acid positions selected from the group consisting of: H122-L127, N92, L94, R76, H77, R87, Y90, R89,Docket No. WRENCH-002 / WO01 and Y78-E86 of wild type DcR3. In some embodiments, the single domain DcR3 binding protein of claim 4, wherein the single domain DcR3 binding protein binds to DcR3 at one or more amino acid positions selected from the group consisting of: R98, N92-E99, and P75 of wild type DcR3. In some embodiments, the single domain DcR3 binding protein restores the activation of anti-cancer immune cells. In some embodiments, the single domain DcR3 binding protein inhibits DcR3 from binding with its ligands. In some embodiments, the single domain DcR3 binding protein binds to DcR3 but does not inhibit DcR3 from binding with its ligands. In some embodiments, the single domain DcR3 binding protein restores the apoptotic activity of FasL towards cancer cells. In some embodiments, the single domain DcR3 binding protein restores the activity of TL1A, and / or LIGHT, and / or FasL that were inhibited by DcR3. In some embodiments, a single domain DcR3 binding protein comprises a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence at least 90% identical to SEQ ID NOs: 1-19, the CDR-H2 has an amino acid sequence at least 90% identical to SEQ ID NOs: 20-38, and the CDR-H3 has an amino acid sequence at least 90% identical to any one of SEQ ID NO: 39-57, wherein the numbering is according to Kabat. In some embodiments, the single domain DcR3 binding protein is at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NOs: 201- 219. In some embodiments, a single domain DcR3 binding protein binds to DcR3 and inhibits DcR3 from interacting with its ligands. In such embodiments, the single domain DcR3 binding protein can comprise a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NOs: 2- 3, 7-10, 13, or 18-19; the CDR-H2 has an amino acid sequence at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NO: 21-22, 26-29, 32, or 37-38; and the CDR-H3 has an amino acid sequence at least 90%, 95%, 98%, 99%, or 100% identical to any one of SEQ ID NO: 40-41, 45-48, 51, or 56-57; wherein the numbering is according to Kabat. In some embodiments, the single domain DcR3 binding protein that binds to DcR3 and inhibits DcR3 from interacting with its ligands is at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NOs: 202-203, 207-210, 213, or 218-219. In one embodiment, a single domain DcR3 binding protein binds to DcR3 but does not inhibit DcR3 from interacting with its ligands. In such embodiments, the single domain DcR3 binding protein can comprise a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NOs: 1, 4-6, 11-12, or 14-17; the CDR-H2 has an amino acid sequence at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NO: 20, 23-25, 30-31, or 33-36; and the CDR-H3 has an amino acid sequence at least 90%, 95%, 98%, 99%, or 100% identical to any one of SEQ ID NO: 39, 42-44, 49-50, or 52-55;wherein the numbering is according to Kabat. In some embodiments, the single domain DcR3 binding protein that binds to DcR3 butDocket No. WRENCH-002 / WO01 does not inhibit DcR3 from interacting with its ligands is at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NOs: 201, 204-206, 211-212, or 214-217. In one embodiment, a VHH-Fc fusion protein comprises: (a) a first monomer comprising from N- terminus to C-terminus: a first single domain anti-DcR3 antibody or binding protein that binds to DcR3 and inhibits DcR3 from binding with its ligands, and a first Fc domain; and (b) a second monomer comprising a second Fc domain. In some embodiments, the first monomer further comprises a second single domain anti-DcR3 antibody or binding protein that binds to DcR3 and inhibits DcR3 from binding with its ligands. In some embodiments, the first single domain anti-DcR3 antibody or binding protein and the second single domain anti-DcR3 antibody or binding protein have an identical amino acid sequence. In some embodiments, the second monomer comprises, from N-terminus to C-terminus: a third single domain anti-DcR3 antibody or binding protein that binds to DcR3 and inhibits DcR3 from binding with its ligands, and a second Fc domain. In some embodiments, the third single domain anti-DcR3 antibody or binding protein has an identical amino acid sequence as the first single domain anti-DcR3 antibody or binding protein and / or the second single domain anti-DcR3 antibody or binding protein. In some embodiments, the second monomer further comprises a fourth single domain anti- DcR3 antibody or binding protein that binds to DcR3 and inhibits DcR3 from binding with its ligands. In some embodiments, the fourth single domain anti-DcR3 antibody or binding protein has an identical amino acid sequence as the first single domain anti-DcR3 antibody or binding protein, second single domain anti-DcR3 antibody or binding protein, and / or third single domain anti-DcR3 antibody or binding protein. In some embodiments, the first monomer further comprises a second single domain anti-DcR3 antibody or binding protein that binds to DcR3 but does not inhibit DcR3 from binding with its ligands. In some embodiments, the second monomer comprises, from N-terminus to C-terminus: a third single domain anti- DcR3 antibody or binding protein that binds to DcR3 and inhibits DcR3 from binding with its ligands, and a second Fc domain. In some embodiments, the third single domain anti-DcR3 antibody or binding protein has an identical amino acid sequence as the first single domain anti-DcR3 antibody or binding protein. In some embodiments, the second monomer further comprises a fourth single domain anti-DcR3 antibody or binding protein that binds to DcR3 but does not inhibit DcR3 from binding with its ligands, and a second Fc domain. In some embodiments, the fourth single domain anti-DcR3 antibody or binding protein has an identical amino acid sequence as the second single domain anti-DcR3 antibody or binding protein. In some embodiments, the first, second, third, and / or fourth single domain anti-DcR3 antibody or binding protein comprises a single domain anti-DcR3 antibody as described herein. In some embodiments, the first, second, third, and / or fourth single domain anti-DcR3 antibody binds to DcR3 and inhibits DcR3 from binding with its ligands, as described herein. In some embodiments, the first, second, third, and / or fourth singleDocket No. WRENCH-002 / WO01 domain anti-DcR3 antibody binds to DcR3 but does not inhibit DcR3 from binding with its ligands, as described herein. In some embodiments, the first and second monomers interact to form a bivalent biparatopic fusion protein. In some embodiments, a biparatopic VHH-Fc fusion protein comprises an amino acid sequence that is at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NOs: 301-306. In one embodiment, a VHH-Fc fusion protein is provided. The VHH-Fc protein comprises (a) a first monomer comprising from N-terminus to C-terminus: a first single domain anti-DcR3 antibody that binds to DcR3 and inhibits DcR3 from binding with its ligands, a second single domain anti-DcR3 antibody that binds to DcR3 but does not inhibit DcR3 from binding with its ligands, and an Fc domain, and (b) a second monomer identical to the first monomer (a), wherein the first and second monomers interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one embodiment, a VHH-Fc fusion protein is provided. The VHH-Fc protein comprises (a) a first monomer comprising from N-terminus to C-terminus: a first single domain anti-DcR3 antibody that binds to DcR3 but does not inhibit DcR3 from binding with its ligands, a second single domain anti-DcR3 antibody that binds to DcR3 and inhibits DcR3 from binding with its ligands, and an Fc domain, and (b) a second monomer identical to the first monomer (a), wherein the first and second monomers interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In some embodiments, the VHH-Fc fusion protein restores the activation of anti-cancer immune cells. In some embodiments, the VHH-Fc fusion protein inhibits DcR3 from binding with its ligands. In some embodiments, the VHH-Fc fusion protein restores the apoptotic activity of FasL towards cancer cells. In some embodiments, the VHH-Fc fusion protein potentiates the pro-apoptotic and / or cytotoxic effects of chemotherapy. In some embodiments, the VHH-Fc fusion protein restores the activation of TL1A, LIGHT, and FasL that were inhibited by DcR3. In some embodiments, the VHH-Fc fusion protein blocks one or more of the DcR3:FasL interaction, DcR3:TL1A interaction, and DcR3:LIGHT interaction. In some embodiments, the VHH-Fc fusion protein releases DcR3 within the acidic environment of endosomes, thereby resulting in an increased clearance of DcR3. In some embodiments, the first, second, third, and / or fourth single domain anti-DcR3 antibody or binding proteins are covalently attached to the N-terminus of the first or the second Fc domain. In some embodiments, the first Fc domain and second Fc domain are configured in an asymmetrical manner.In some embodiments, the first domain and the second domain comprise complementary pairs of amino acid substitutions that improve thermostability. In some embodiments, the first Fc domain comprises a set of amino acid substitutions selected from the group consisting of S354C and T366W. In some embodiments, the secondDocket No. WRENCH-002 / WO01 Fc domain comprises a set of amino acid substitutions selected from the group consisting of Y349C, T366S, L368A, and Y407V. In some embodiments, the first, second, third, and / or fourth single domain anti-DcR3 antibodies are covalently attached to the N-terminus or the C-terminus of the first or the second Fc domain via a linker. In some embodiments, the linker comprises a glycine-serine linker. In some embodiments, the glycine-serine linker comprises a sequence of (GS)n, wherein n = 1 to 10. In some embodiments, the linker comprises (GS)n, (GGS)n, (GGGS)n, (GGSG)n, (GGSGG)n, (GGGGS)n, (GGGGG)n, or (GGG)n, wherein n = 1 to 10. In some embodiments, the linker comprises (GGGGS)4 or (GGGGS)3. In one embodiment, a multispecific binding protein comprises a first domain and a second domain, wherein: (a) the first domain comprises a single domain DcR3 binding protein as described herein; and (b) the second domain binds to a target molecule that is not DcR3. In some embodiments, the second domain selectively binds to a tumor associated antigen (TAA). In some embodiments, the TAA is selected from the group consisting of B-cell maturation antigen (BCMA), carcinoembryonic antigen (CEA), epidermal growth factor receptor (EGFR), human epidermal growth factor receptor 2 (Her2), epithelial cell adhesion molecule (EpCAM), CD20, CD26, CD123, CD30, CD33, CD47, CD52, CD133, glycoprotein A33 (gpA33), mucins, tumor associated glycoprotein-72 (TAG-72), type IX collagen (CIX), glutamate carboxypeptidase II (PSMA), folate-binding protein, GD2, GD3, GM2, vascular endothelial growth factor (VEGF), vascular endothelial growth factor receptor (VEGFR), integrin, αVβ3, α5β1, ERBB2, ERBB3, mesenchymal epithelial transition (MET), insulin-like growth factor-I receptor (IGFIR), ephrin type-A receptor 3 (EPHA3), TRAIL receptor 1 (TRAILR1), TRAIL receptor 2 (TRAILR2), receptor activator of nuclear factor kappa beta (RANKL), fibroblast activation protein (FAP), claudin 18.2, mesothelin, receptor tyrosine kinase like orphan receptor 1 (ROR1), epidermal growth factor receptor variant III (EGFRVIII), six-transmembrane epithelial antigen of the prostate-2 (STEAP2), orphan G protein–coupled receptor, class C group 5 member D (GPRC5D), carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5), and tenascin. In some embodiments, the first domain and the second domain are coupled via chemical coupling, gene fusion, or a non-covalent association. In some embodiments, the multispecific binding protein further comprises a linker. In some embodiments, the linker comprises a glycine-serine linker. In some embodiments, the glycine-serine linker comprises a sequence of (GS)n, wherein n = 1 to 10. In some embodiments, the linker comprises (GS)n, (GGS)n, (GGGS)n, (GGSG)n, (GGSGG)n, (GGGGS)n, (GGGGG)n, or (GGG)n, wherein n = 1 to 10. In some embodiments, the linker comprises (GGGGS)4or (GGGGS)3. In some embodiments, the multispecific binding protein of any one of claims 52-60 wherein the multispecific protein is a bispecific protein. In some embodiments, the multispecific protein is a trispecific protein. In some embodiments, the multispecific protein binds to four different target molecules.Docket No. WRENCH-002 / WO01 In some embodiments, a single domain DcR3 antibody or binding protein or a multispecific binding protein further comprises a Fc domain. In some embodiments, the single domain DcR3 antibody or binding protein or a multispecific binding protein further comprises a half-life extension domain. In some embodiments, the half-life extension domain comprises an albumin-targeting polypeptide. In some embodiments, the single domain DcR3 antibody or binding protein, VHH-Fc fusion protein, or multispecific binding protein is non-naturally occurring. In some embodiments, a pharmaceutical composition is provided. The pharmaceutical composition can comprise (a) a single domain DcR3 antibody or binding protein, VHH-Fc fusion protein, or multispecific binding protein as described herein, and (b) a pharmaceutically acceptable carrier. In some embodiments, an isolated nucleic acid encoding a single domain DcR3 antibody or binding protein, VHH-Fc fusion protein, or multispecific binding protein is provided. In one embodiment, a vector comprising the isolated nucleic acid is provided. In some embodiments, a host cell that comprises the vector or nucleic acid is provided. In one embodiment, a method of treating a disease or condition in a subject in need thereof is provided. The method can comprise administering to the subject a therapeutically effective amount of a single domain DcR3 antibody or binding protein, VHH-Fc fusion protein, or multispecific binding protein as described herein. In some embodiments, the disease or condition comprises a proliferative disease, a tumorous disease, an inflammatory disease, an immunological disorder, an autoimmune disease, an infectious disease, a viral disease, an allergic reaction, a parasitic reaction, a graft-versus-host disease or a host-versus-graft disease. In one embodiment, a method of treating cancer in a patient is provided. The method can comprise administering a composition comprising a single domain DcR3 antibody or binding protein, VHH-Fc fusion protein, or multispecific binding protein as described herein. In some embodiments, the patient experiences an increase in tumor growth inhibition of at least about 10%, 20%, 30% 40% 50% 60% 70% 80% 90%, 100%, 125%, 150%, 175%, 200% 225% 250%, 275%, 300%, 325% 350%, 375%, 400%, 425%, 450%, 475%, 50Q%, 525%, 550%, 575%, 600%, 625%, 650%, 675%, 700%, 725%, 750%, 775%, 800%, 825%, 850%, 875%, 900%, 925%, 950%, 975%, or 1000%, as compared to a control or an untreated patient. In some embodiments, the patient experiences a decrease in tumor growth inhibition of at least about 10%, 20%, 30% 40% 50% 60% 70% 80% 90%, 100%, 125%, 150%, 175%, 200% 225% 250%, 275%, 300%, 325% 350%, 375%, 400%, 425%, 450%, 475%, 50Q%, 525%, 550%, 575%, 600%, 625%, 650%, 675%, 700%, 725%, 750%, 775%, 800%, 825%, 850%, 875%, 900%, 925%, 950%, 975%, or 1000%, as compared to a control or an untreated patient. In one embodiment, a method of reducing a tumor is provided. The method can comprise contacting the tumor with a composition comprising a single domain DcR3 antibody or binding protein, a VHH-Fc fusion protein, or a multispecific binding protein as described herein.Docket No. WRENCH-002 / WO01 In one embodiment, a method of reducing a tumor in a subject in need thereof is provided. The method can comprise administering to the subject a composition comprising a single domain DcR3 antibody or binding protein, a VHH-Fc fusion protein, or a multispecific binding protein as described herein. In one embodiment, a method of treating a subject having a cancer is provided. The method can comprise administering to the subject a composition comprising a single domain DcR3 antibody or binding protein, a VHH-Fc fusion protein, or a multispecific binding protein as described herein. In some embodiments, the cancer or tumor is selected from the group consisting of renal clear cell carcinoma (RCC), lung cancer, NSCLC, lung adenocarcinoma, lung squamous cell carcinoma, gastric adenocarcinoma, ovarian cancer, endometrial cancer, breast cancer, triple negative breast cancer (TNBC), head and neck tumor, colorectal adenocarcinoma, melanoma, and metastatic melanoma. In some embodiments, the cancer is selected from the group consisting of gallbladder carcinoma, liver carcinoma, gastric carcinoma, colon carcinoma, pancreatic carcinoma, bone sarcoma, thyroid adenocarcinoma, lung cancer, renal cell carcinoma, and breast cancer. In some embodiments, the subject is a human subject. INCORPORATION BY REFERENCE All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference. To the extent publications and patents or patent applications incorporated by reference contradict the disclosure contained in the specification, the specification is intended to supersede and / or take precedence over any such contradictory material. BRIEF DISCLOSURE OF THE DRAWINGS The novel features of the disclosure are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present disclosure will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the disclosure are utilized, and the accompanying drawings of which: FIGS. 1A-C are charts showing the expression of DcR3 and correlation with cancer outcomes. FIG. 1A shows that DcR3 transcript levels are significantly elevated in patients having pancreatic (PAAD), kidney (KIRC), rectal (READ), stomach (STAD), colon (COAD), and thymus (THYM) cancers compared to those without cancer from the TCGA database. In patients having cancer, survival is also significantly impacted by DcR3 expression (FIG. 1B). Cox regression analyses reveal that poor prognosis is associated with high DcR3 expression (FIG.1C). FIGS.2A-B are charts showing DcR3 protein expression in cancer. As shown in FIG.2A, serum levels of DcR3 are elevated in a number of solid tumor types. As shown in FIG.2B, serum levels of DcR3 correlate with metastasis in gastric cancer.Docket No. WRENCH-002 / WO01 FIG.3 depicts gel images and chromatograms showing the results of SDS-PAGE and analytical SEC- HPLC of various purified anti-DcR3 VHH-Fc fusion following expression in CHO cells and protein A purification. FIGS. 4A-B depict the results of a biolayer interferometry (BLI)-based identification of VHHs that compete with TL1A for their binding to DcR3. FIG.4A is a graphic describing the experiment design. FIG.4B is a sensorgram showing the interactions between DcR3, TL1A, and several VHH-Fc fusions. TL1A-His is immobilized on anti-His sensors followed by binding of DcR3-Fc, followed by incubation with the VHH-Fc fusions. VHHs that do not bind to DcR3 are likely blocked by TL1A binding to DcR3 and share the same binding interface. Therefore, these antibodies represent good candidates for DcR3 blocking antibodies. FIG. 5 shows charts depicting the results of SPR measurements of the binding affinity (KD) and kinetics (Kon and Koff) of DcR3 binding to certain VHHs immobilized on CM5 chips. FIG. 6 shows gel images and sensorgrams depicting the analysis of several biparatopic VHH-Fc fusions. At left are images showing the results of SDS-PAGE and analytical SEC-HPLC of four purified anti- DcR3 biparatopic VHH-Fc fusion proteins (WB52, WB53, WB54, WB55) following expression in CHO cells and protein A purification. At right are sensorgrams showing SPR measurements of the binding affinity (KD) and kinetics (Kon and Koff) of DcR3 binding to three of the biparatopic VHH-Fc fusion proteins (WB52, WB53, WB55) immobilized on CM5 chips. FIG.7 is a chart illustrating the detection of the binding of FasL to DcR3 in the absence or presence of 1 (1) or 10 (10) mg / mL of a selected biparatopic VHH-Fc fusion (WB53). FIG.8 is a chart depicting the results of Phage ELISA of several VHHs identified in the screening of a synthetic VHH library, against DcR3, or a preformed complex of DcR3 with TL1A. Those VHHs which showed binding to DcR3 inhibited by TL1A are selected to be further examined as DcR3 blockers. Those VHHs that bind to DcR3 in complex with TL1A are selected to be further examined for their use within biparatopic DcR3 binders. FIG.9 illustrates the effect of blocking DcR3 on Gemcitabine-mediated cell death. ASPC1 cells were seeded in 96-well plates at a density of 5000 cells / well. The cells were treated for 48 hours with vehicle or Gemcitabine in the presence or absence of 10 ug / mL of the DcR3 blocking antibodies WB52 and WB53. The Gemcitabine-mediated cytotoxicity was determined by measuring cell viability in response to the various treatments using the Cell Titer-Glo Luminescent assay (Promega).100% cell death was determined by addition of Triton X-100 to control wells. WB53 potentiates the cytotoxic effect of Gemcitabine. DETAILED DESCRIPTION 1. Overview Decoy receptors correspond to proteins that are often very similar to the predominant receptor, and that regulate signaling networks by binding to the target effector molecules without resulting in further propagationDocket No. WRENCH-002 / WO01 of the signal. The main targets of these decoy receptors are cytokines, thereby regulating many aspects of immune responses. Decoy receptor 3 (DcR3) is a member of the tumor necrosis factor receptor (TNFR) superfamily member 6b (TNFRSF6B) / TR6 / M68. DcR3 cDNA was initially identified from human cancer cells, and DcR3 gene amplification is also found in certain cancer cell lineages (Pitti RM, et al. Genomic amplification of a decoy receptor for Fas ligand in lung and colon cancer. Nature.1998;396(6712):699–703). Unlike most members of TNFRSF, DcR3 lacks a transmembrane domain, and is detectable in serum and cell culture medium. DcR3 binds and neutralizes the functions of three members of the tumor necrosis factor superfamily (TNFSF): FasL (CD95L / TNFSF6) (Pitti RM, et al. Genomic amplification of a decoy receptor for Fas ligand in lung and colon cancer. Nature.1998;396(6712):699–703), LIGHT (CD258 / TNFSF14) (Yu KY, et al. A newly identified member of tumor necrosis factor receptor superfamily (TR6) suppresses LIGHT- mediated apoptosis. J Biol Chem. 1999;274(20):13733–6), and TNF-like molecule 1A (TL1A / VEGI / TNFSF15) (Migone TS, et al. TL1A is a TNF-like ligand for DR3 and TR6 / DcR3 and functions as a T cell co-stimulator. Immunity. 2002;16(3):479–92). DcR3 has been shown to be a pleiotropic soluble factor to modulate cell functions via ‘decoy’ and ‘non-decoy’ actions (Lin WW, Hsieh SL. Decoy receptor 3: a pleiotropic immunomodulator and biomarker for inflammatory diseases, autoimmune diseases and cancer. Biochem Pharmacol. 2011;81(7):838–47). DcR3 is able to inhibit apoptosis and enhance angiogenesis via neutralizing members of TNF superfamily FasL, LIGHT, and TL1A. In addition, DcR3 also skews macrophages into M2 phenotype (Tai SK, et al. Decoy receptor 3 enhances tumor progression via induction of tumor-associated macrophages. J Immunol. 2012;188(5):2464–71). DcR3 expression is hardly detectable in physiological conditions and the information regarding the physiological functions of DcR3 is relatively limited. DcR3 is upregulated in numerous cancer cells and tumor tissues. DcR3 is detectable in glioma (Huang S, et al. Overexpression of DcR3 and its significance on tumor cell differentiation and proliferation in glioma. ScientificWorldJournal.2014;2014:605236), astrocytoma (Lin CK, et al. A tissue microarray study of toll-like receptor 4, decoy receptor 3, and external signal regulated kinase 1 / 2 expressions in astrocytoma. Indian J Pathol Microbiol), vascular endothelial cells and neighboring lymph nodes of tumor, and its expression level correlates with lymphangiogenesis (Wu Q, et al. Aberrant expression of decoy receptor 3 in human breast cancer: relevance to lymphangiogenesis. J Surg Res) and lymph node metastasis (Xiong G, et al. Decoy receptor 3 expression in esophageal squamous cell carcinoma: correlation with tumour invasion and metastasis. Biomarkers. 2011;16(2):155–60). DcR3 expression level also correlates positively with clinicopathological change in bladder urothelial carcinoma (Jiang YQ, et al. Overexpression and clinicopathological contribution of DcR3 in bladder urothelial carcinoma tissues. Asian Pac J Cancer Prev.2014;15(21):9137–42), breast cancer (Wu Q, et al. Aberrant expression of decoy receptor 3 in human breast cancer: relevance to lymphangiogenesis. J Surg Res), pancreatic head carcinoma (Zhou J, et al. Decoy receptor 3 (DcR3) overexpression predicts the prognosis and pN2 in pancreatic head carcinoma. World J Surg Oncol. 2014;12:52), colorectal cancer (ZongDocket No. WRENCH-002 / WO01 L, Chen P, Wang DX. Death decoy receptor overexpression and increased malignancy risk in colorectal cancer. World J Gastroenterol. 2014;20(15):4440–5), gastrointestinal cancer (Tong J, et al. Prognostic and clinicopathological differences of DcR3 in gastrointestinal cancer: evidence from meta-analysis. Int J Clin Exp Med.2014;7(9):3096–105), and female reproductive carcinoma (Jiang M, et al. Decoy receptor 3 (DcR3) as a biomarker of tumor deterioration in female reproductive cancers: a meta-analysis. Med Sci Monit. 2016;22:1850–7). As described further herein, inhibition of DcR3 may attenuate tumor growth, suggesting that DcR3 blockers may be efficacious and enhance the efficacy of cancer therapy. Crystal structure studies have demonstrated that the interface between DcR3 and its ligands is conserved (see Liu et al., Crystal Structure of the Complex of Human FasL and its Decoy Receptor DcR3, Cell 24:11 (2016), hereby incorporated by reference in its entirety.) and therefore binding of all three DcR3 ligands could be inhibited by a single antibody if the antibody’s epitope is in the cytokine binding interface of DcR3. 2. Definitions All terms are intended to be understood as they would be understood by a person skilled in the art. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosure pertains. The following definitions supplement those in the art and are directed to the current application and are not to be imputed to any related or unrelated case, e.g., to any commonly owned patent or application. Although any methods and materials similar or equivalent to those described herein can be used in the practice for testing of the present disclosure, the preferred materials and methods are described herein. Accordingly, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. The terminology used herein is for the purpose of describing particular cases only and is not intended to be limiting. In this application, the use of the singular includes the plural unless specifically stated otherwise. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. In this application, the use of “or” means “and / or” unless stated otherwise. The terms “and / or” and “any combination thereof” and their grammatical equivalents as used herein, can be used interchangeably. These terms can convey that any combination is specifically contemplated. Solely for illustrative purposes, the following phrases “A, B, and / or C” or “A, B, C, or any combination thereof” can mean “A individually; B individually; C individually; A and B; B and C; A and C; and A, B, and C.” The term “or” can be used conjunctively or disjunctively, unless the context specifically refers to a disjunctive use. The term “about” or “approximately” can mean within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e., the limitations of the measurement system. For example, “about” can mean within 1 or moreDocket No. WRENCH-002 / WO01 than 1 standard deviation, per the practice in the art. Alternatively, “about” can mean a range of up to 20%, up to 15%, up to 10%, up to 5%, or up to 1% of a given value. Alternatively, particularly with respect to biological systems or processes, the term can mean within an order of magnitude, within 5-fold, or within 2-fold, of a value. Where particular values are described in the application and claims, unless otherwise stated the term “about” meaning within an acceptable error range for the particular value should be assumed. As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps. It is contemplated that any embodiment discussed in this specification can be implemented with respect to any method or composition of the present disclosure, and vice versa. Furthermore, compositions of the present disclosure can be used to achieve methods of the present disclosure. Reference in the specification to “some embodiments,” “an embodiment,” “one embodiment” or “other embodiments” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least some embodiments, but not necessarily all embodiments, of the present disclosures. To facilitate an understanding of the present disclosure, a number of terms and phrases are defined below. Ranges provided herein are understood to be shorthand for all of the values within the range. For example, a range of 1 to 50 is understood to include any number, combination of numbers, or sub-range from the group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50, as well as all intervening decimal values between the aforementioned integers such as, for example, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, and 1.9. With respect to sub-ranges, “nested sub-ranges” that extend from either end point of the range are specifically contemplated. For example, a nested sub-range of an exemplary range of 1 to 50 may comprise 1 to 10, 1 to 20, 1 to 30, and 1 to 40 in one direction, or 50 to 40, 50 to 30, 50 to 20, and 50 to 10 in the other direction. The term “subject” refers to an animal which is the object of treatment, observation, or experiment. By way of example only, a subject includes, but is not limited to, a mammal, including, but not limited to, a human or a non-human mammal, such as a non-human primate, bovine, equine, canine, ovine, or feline. The term “optional” or “optionally” denotes that a subsequently described event or circumstance can but need not occur, and that the description includes instances where the event or circumstance occurs and instances in which it does not. “Non-naturally occurring” (used interchangeably with “isolated”, “substantially pure” or “purified”) when applied to a polynucleotide or a polypeptide means a polynucleotide or a polypeptide that is synthesizedDocket No. WRENCH-002 / WO01 chemically or synthetically, or is purified away from associated and contaminating components. The term generally means a polynucleotide or a polypeptide that has been separated from other proteins and nucleic acids with which it naturally occurs and / or substances which are used to purify it. In some instances, polynucleotide or a polypeptide herein is about 95%, about 96%, about 97%, about 98%, about 99% or above pure. A binding protein as defined herein is said to be “specific for” or “selectively binds to” DcR3 or to a target antigen when it binds to DcR3 or to the target antigen with an affinity that is at least 5 times, at least 10 times, at least 25 times, least 50 times, least 100 times, etc., better than the affinity with which said amino acid sequence or polypeptide binds to a non-specific polypeptide. "Modification" herein is meant an amino acid substitution, insertion, and / or deletion in a polypeptide sequence or an alteration to a moiety chemically linked to a protein. For example, a modification may be an altered carbohydrate or PEG structure attached to a protein. By “amino acid modification” herein is meant an amino acid substitution, insertion, and / or deletion in a polypeptide sequence. For clarity, unless otherwise noted, the amino acid modification is always to an amino acid coded for by DNA, e g., the 20 amino acids that have codons in DNA and RNA. “Amino acid substitution” or “substitution” herein means the replacement of an amino acid at a particular position in a parent polypeptide sequence with a different amino acid. In particular, in some embodiments, the substitution is to an amino acid that is not naturally occurring at the particular position, either not naturally occurring within the organism or in any organism. For example, the substitution E272Y or 272Y refers to a variant polypeptide, in this case an Fc variant, in which the glutamic acid at position 272 is replaced with tyrosine. For clarity, a protein which has been engineered to change the nucleic acid coding sequence but not to change the starting amino acid (for example exchanging CGG (encoding arginine) to CGA (still encoding arginine) to increase host organism expression levels) is not an “amino acid substitution”; that is, despite the creation of a new gene encoding the same protein, if the protein has the same amino acid at the particular position that it started with, it is not an amino acid substitution. “Amino acid insertion" or "insertion" as used herein means the addition of an amino acid residue or sequence at a particular position in a parent polypeptide sequence. For example, -233E designates an insertion of glutamic acid after position 233 and before position 234. Additionally, -233ADE or A233ADE designates an insertion of AlaAspGlu after position 233 and before position 234. “Amino acid deletion” or “deletion” as used herein means the removal of an amino acid residue or sequence at a particular position in a parent polypeptide sequence. For example, E233-, E233#, E233(), E233_, or E233del designates a deletion of glutamic acid at position 233. Additionally, EDAZ33- or EDA233¹ designates a deletion of the sequence GluAspAla that begins at position 233. “Variant protein”, “protein variant”, “mutein”, or “variant” as used herein means a protein that differs from that of a parent protein by virtue of at least one modification. Protein variant may refer to the proteinDocket No. WRENCH-002 / WO01 itself, a composition comprising the protein, the amino acid sequence that encodes it, or the DNA sequence that encodes it Preferably, the protein variant has at least one amino acid modification compared to the parent protein, e.g. from about one to about seventy amino acid modifications, and preferably from about one to about five amino acid modifications compared to the parent, The modification can be an addition, deletion, or substitution. As described below, in some embodiments the parent protein, for example an Fc parent polypeptide, is a human wild type sequence, such as the Fc region from IgG1, IgG2, IgG3 or IgG4. The protein variant sequence herein will preferably possess at least about 80% identity with a parent protein sequence, and most preferably at least about 90% identity, more preferably at least about 95-98-99% identity. “Variant,” as used herein can also refer to particular amino acid modifications (e g, substitutions, deletions, insertions) in a variant protein (e.g., a variant Fc domain), for example, heterodimerization variants, ablation variants, etc. “Protein” means at least two covalently attached amino acids, which includes proteins, polypeptides, oligopeptides and peptides. When a biologically functional molecule comprises two or more proteins, each protein may be referred to as a “monomer” or as a “subunit”; and the biologically functional molecule may be referred to as a “complex”. Accordingly, “protein” in this context is used interchangeably with “polypeptide” and includes peptides as well. “Residue” as used herein means a position in a protein and its associated amino acid identity. For example, Asparagine 297 (also referred to as Asn297 or N297) is a residue at position 297 in the human antibody IgG1. “IgG subclass modification” or “isotype modification” as used herein means an amino acid modification that converts one amino acid of one IgG isotype to the corresponding amino acid in a different, aligned IgG isotype. For example, because IgG1 comprises a tyrosine and IgG2 a phenylalanine at EU position 296, a F296Y substitution in IgG2 is considered an IgG subclass modification. “Non-naturally occurring modification” as used herein with respect to an IgG domain means an amino acid modification that is not isotypic. For example, because none of the IgGs comprise a serine at position 434, the substitution 434S in IgGl, IgG2, IgG3, or IgG4 (or hybrids thereof is considered a non-naturally occurring modification. “Amino acid” and “amino acid identity” as used herein means one of the 20 naturally occurring amino acids that are coded for by DNA and RNA. “Decoy Receptor 3” or “DcR3” as used herein refers to a soluble protein belonging to the tumor necrosis factor receptor (TNFR) superfamily. DcR3, also known as TNFRSF6B, acts as a decoy receptor by binding to several ligands, including Fas Ligand (FasL), LIGHT (TNFSF14), and TL1A (TNFSF15), preventing them from interacting with their respective cell surface receptors. This binding inhibits the ligands’ ability to trigger apoptosis and modulate immune response. DcR3 is implicated in immune regulation,Docket No. WRENCH-002 / WO01 inflammation, and cancer, as its overexpression can allow tumor cells to evade immune surveillance and apoptosis. “DcR3 ligand” as used herein refers to a molecule, preferably a polypeptide, from any organism that binds to a conserved binding interface of Decoy Receptor 3. DcR3 ligands include members of the TNF superfamily such as FasL (Fas Ligand), LIGHT (homologous to Lymphotoxin, exhibits Inducible expression and competes with HSV Glycoprotein D for Herpesvirus entry mediator, a receptor expressed on T cells), and TL1A (TNF-like ligand 1A). These ligands interact specifically with DcR3, influencing immune modulation and apoptosis pathways, and are significant in therapeutic applications targeting immune system regulation and inflammation-related diseases. “FasL” or “Fas Ligand” refers to a transmembrane protein, also known as CD95L or TNFSF6, belonging to the tumor necrosis factor (TNF) superfamily. FasL binds to its receptor, Fas (CD95), triggering a signal transduction cascade that leads to apoptosis, or programmed cell death. This interaction is needed for maintaining immune system homeostasis, regulating immune responses, and eliminating infected, damaged, or potentially cancerous cells. FasL-mediated apoptosis plays a significant role in processes such as immune privilege, where immune responses are restricted to protect certain tissues, and in the downregulation of immune responses after an infection has been cleared. Dysregulation of FasL or its receptor can lead to autoimmune diseases, immune deficiencies, or uncontrolled cell proliferation. “LIGHT” refers to a cytokine that is a member of the tumor necrosis factor (TNF) superfamily, also known as TNFSF14. LIGHT is involved in the regulation of immune responses and interacts with several receptors, including HVEM (herpesvirus entry mediator), LTβR (lymphotoxin β receptor), and DcR3 (Decoy Receptor 3). Through these interactions, LIGHT influences T cell activation, inflammatory responses, and apoptosis. LIGHT plays a critical role in immune system regulation, including antiviral responses, tumor immunity, and the maintenance of mucosal immunity. LIGHT's activity is significant in therapeutic applications targeting autoimmune diseases, inflammation, and cancer. "TL1A" refers to a cytokine that is a member of the tumor necrosis factor (TNF) superfamily, also known as TNFSF15. TL1A binds to death receptor 3 (DR3) and Decoy Receptor 3 (DcR3), playing a key role in the regulation of immune responses. TL1A is involved in the modulation of T cell proliferation, differentiation, and apoptosis. TL1A can enhance T cell responses and promote the secretion of pro- inflammatory cytokines in the context of autoimmune diseases and inflammation. “Effector function” as used herein means a biochemical event that results from the interaction of an antibody Fc region with an Fc receptor or ligand. Effector functions include but are not limited to ADCC, ADCP, and CDC. “IgG Fc ligand” or “Fc ligand” as used herein is meant a molecule, preferably a polypeptide, from any organism that binds to the Fc region of an IgG antibody to form an Fc / Fc ligand complex. Fc ligands includeDocket No. WRENCH-002 / WO01 but are not limited to FcγRIs, FcγRIIs, FcγRIIIs, FcRn, C1q, C3, mannan binding lectin. Mannose receptor, staphylococcal protein A, streptococcal protein G, and viral FcγR. Fc ligands also include Fc receptor homologs (FcRH), which are a family of Fc receptors that are homologous to the FcγRs (Davis et al., 2002, Immunological Reviews 190:123-136, entirely incorporated by reference) Fc ligands may include undiscovered molecules that bind Fc. Particular IgG Fc ligands are FcRn and Fc gamma receptors. “FcRn” or “neonatal Fc receptor” as used herein means a protein that binds the IgG antibody Fc region and is encoded at least in part by an FcRn gene. The FcRn may be from any organism, including but not limited to humans, mice, rats, rabbits, and monkeys. As is known in the art, the functional FcRn protein comprises two polypeptides, often referred to as the heavy chain and light chain. The light chain is beta-2-microglobulin (β2- microglobulin) and the heavy chain is encoded by the FcRn gene. Unless otherwise noted herein, FcRn or an FcRn protein refers to the complex of FcRn heavy chain with β2-microglobulin. A variety of Fc variants can be used to increase binding to the FcRn, and in some cases, to increase serum half-life. In general, unless otherwise noted, the Fc monomers of the invention retain binding to the FcRn (and, as noted below, can include amino acid variants to increase binding to the FcRn). “Parent polypeptide” as used herein means a starting polypeptide that is subsequently modified to generate a variant. The parent polypeptide may be a naturally occurring polypeptide (i.e., a wildtype polypeptide), or a variant or engineered version of a naturally occurring polypeptide. Parent polypeptide may refer to the polypeptide itself, compositions that comprise the parent polypeptide, or the amino acid sequence that encodes it. “Fc” or “Fc region” or “Fc domain” as used herein means the polypeptide comprising the constant region of an antibody, in some instances, excluding all of the first constant region immunoglobulin domain (e.g., CH1) or a portion thereof, and in some cases, optionally including all or part of the hinge. For IgG, the Fc domain comprises immunoglobulin domains CH2 and CH3 (Cγ2 and Cγ3), and optionally all or a portion of the hinge region between CH1 (Cγ1) and CH2 (Cγ2). Thus, in some cases, the Fc domain includes, from N- to C- terminus, CH2-CH3 and hinge-CH2-CH3. In some embodiments, the Fc domain is that from IgGI, IgG2, IgG3 or IgG4, with IgGI hinge-CH2-CH3 and IgG4 hinge-CH2-CH3 finding particular use in many embodiments. Additionally, in certain embodiments, wherein the Fc domain is a human IgG1 Fc domain, the hinge includes a C220S amino acid substitution. Furthermore, in some embodiments where the Fc domain is a human IgG4 Fc domain, the hinge includes a S228P amino acid substitution. Although the boundaries of the Fc region may vary, the human IgG heavy chain Fc region is usually defined to include residues E216, C226, or A231 to its carboxyl-terminus, wherein the numbering is according to the EU index as in Kabat. In some embodiments, as is more fully described below, amino acid modifications are made to the Fc region, for example to alter binding to one or more FcγR or to the FcRn.Docket No. WRENCH-002 / WO01 By “hinge” or “hinge region” or “antibody hinge region” or “immunoglobulin hinge region” herein is meant the flexible polypeptide comprising the amino acids between the first and second heavy chain constant domains of an antibody. Structurally, the IgG CH1 domain ends at EU position 215, and the IgG CH2 domain begins at residue EU position 231, Thus for IgG the antibody hinge is herein defined to include positions 216 (E216 in IgG1) to 230 (P230 in IgG1), wherein the numbering is according to the EU index as in Kabat. In some embodiments, for example in the context of an Fc region, the hinge (full length or a fragment of the hinge) is included, generally referring to positions 216-230. As noted herein, pI variants can be made in the hinge region as well. As will be appreciated by those in the art, the exact numbering and placement of the heavy constant region domains can be different among different numbering systems. A useful comparison of heavy constant region numbering according to EU and Kabat is as below, see Edelman et al., 1969, Proc Natl Acad Sci USA 63:78-85 and Kabat et al., 1991, Sequences of Proteins of Immunological Interest, 5thEd., United States Public Health Service, National Institutes of Health, Bethesda, entirely incorporated by reference. “Fc variant” or “variant Fc” as used herein means a protein comprising an amino acid modification in an Fc domain. The modification can be an addition, deletion, or substitution. The Fc variants of the present invention are defined according to the amino acid modifications that compose them. Thus, for example, N434S or 434S is an Fc variant with the substitution for serine at position 434 relative to the parent Fc polypeptide, wherein the numbering is according to the EU index. Likewise, M428L / N434S defines an Fc variant with the substitutions M428L and N434S relative to the parent Fc polypeptide. The identity of the WT amino acid may be unspecified, in which case the aforementioned variant is referred to as 428L / 434S. It is noted that the order in which substitutions are provided is arbitrary, that is to say that, for example, 428L / 434S is the same Fc variant as 434S / 428L, and so on. For all positions discussed herein that relate to antibodies or derivatives and fragments thereof (e.g., Fc domains), unless otherwise noted, amino acid position numbering is according to the EU index. The “EU index” or “EU index as in Kabat” or “EU numbering” scheme refers to the numbering of the EU antibody (Edelman et al., 1969, Proc Natl Acad Sci USA 63:78-85, hereby entirely incorporated by reference). The modification can be an addition, deletion, or substitution. “Fusion protein” as used herein means the covalent joining of at least two proteins or protein domains. Fusion proteins may comprise artificial sequences, e.g. a domain linker, an Fc domain (e.g., a variant Fc domain), an anti-DcR3 binding protein, etc. as described herein. By “Fc fusion protein” or “immunoadhesin” herein is meant a protein comprising an Fc region, generally linked (optionally through a domain linker, as described herein) to one or more different protein domains. Accordingly, an “VHH-Fc fusion” includes an Fc domain linked (optionally through a domain linker) to a VHH, as described herein. In some instances, two Fc fusion proteins can form a homodimeric Fc fusion protein or a heterodimeric Fc fusion protein. In some embodiments, one monomer of a heterodimeric fusion protein includes an Fc domain alone (e.g., an “empty FcDocket No. WRENCH-002 / WO01 domain”) and the other monomer is an Fc fusion, comprising an anti-DcR3 antibody, as outlined herein. In some embodiments, one monomer of a heterodimeric fusion protein is an Fc fusion, comprising an anti-DcR3 VHH, and the other monomer is an Fc fusion, comprising another anti-DcR3 VHH, as outlined herein. In other embodiments, both the first and second monomers are Fc fusion proteins that include an Fc domain and an anti- DcR3 VHH. In other embodiments, both the first and second monomers are Fc fusion proteins that include an Fc domain and two anti-DcR3 VHHs (e.g., biparatopic antibodies). “Biparatopic” as used herein means a molecule, such as an antibody, ligand, or fusion protein, that is capable of simultaneously binding to two distinct epitopes on a single target molecule or on different target molecules. “Position” as used herein means a location in the sequence of a protein. Positions may be numbered sequentially, or according to an established format, for example the EU index for numbering of antibody domains (e.g., a CH1, CH2, CH3 or hinge domain). “Strandedness” in the context of the monomers of the heterodimeric proteins of the invention herein means that, similar to the two strands of DNA that “match”, heterodimerization variants are incorporated into each monomer so as to preserve, create, and / or enhance the ability to “match” to form heterodimers. For example, if some pI variants are engineered into monomer A (e.g. making the pI higher), then steric variants that are “charge pairs” that can be utilized as well do not interfere with the pI variants, e.g., the charge variants that make a pI higher are put on the same “strand” or “monomer” to preserve both functionalities. Similarly, for “skew” variants that come in pairs of a set as more fully outlined below, the skilled artisan will consider pI in deciding into which strand or monomer that incorporates one set of the pair will go, such that pI separation is maximized using the pI of the skews as well. “Wild type,” “wildtype”, “wild-type”, or “WT” herein means an amino acid sequence or a nucleotide sequence that is found in nature, including allelic variations. A WT protein has an amino acid sequence or a nucleotide sequence that has not been intentionally modified. The various proteins, antibodies, binding proteins, and fusion proteins provided herein are generally isolated or recombinant. “Isolated,” when used to describe the various polypeptides disclosed herein, means a polypeptide that has been identified and separated and / or recovered from a cell or cell culture from which it was expressed. Ordinarily, an isolated polypeptide will be prepared by at least one purification step. An “isolated protein” refers to a protein which is substantially free of other proteins from a cell culture such as host cell proteins. “Recombinant” means the proteins are generated using recombinant nucleic acid techniques in exogeneous host cells. “Percent (%) amino acid sequence identity” with respect to a protein sequence is defined as the percentage of amino acid residues in a candidate sequence that are identical with the amino acid residues in the specific (parental) sequence, after aligning the sequences and introducing gaps, if necessary, to achieve theDocket No. WRENCH-002 / WO01 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 measuring alignment, including any algorithms needed to achieve maximal alignment over the full length of the sequences being compared. One particular program is the ALIGN-2 program outlined at paragraphs

[0279] to

[0280] of US Patent Publication No.20160244525, hereby incorporated by reference. The degree of identity between an amino acid sequence provided herein (“invention sequence”) and the parental amino acid sequence is calculated as the number of exact matches in an alignment of the two sequences, divided by the length of the “invention sequence,” or the length of the parental sequence, whichever is the shortest. The result is expressed in percent identity. The percent identity between two amino acid sequences can be determined using the algorithm of E. Meyers and W. Miller (Comput. Appl. Biosci., 4:11-17 (1988)) which has been incorporated into the ALIGN program (version 2.0), using a PAM120 weight residue table, a gap length penalty of 12 and a gap penalty of 4. In addition, the percent identity between two amino acid sequences can be determined using the Needleman and Wunsch (J. Mol. Biol., 48:444-453 (1970)) algorithm which has been incorporated into the GAP program in the GGG software package (available commercially), using either a BLOSUM 62 matrix or a PAM250 matrix, and a gap weight of 16, 14, 12, 10, 8, 6, or 4 and a length weight of 1, 2, 3,4, 5, or 6. In some embodiments, two or more amino acid sequences are at least 50%, 60%, 70%, 80%, or 90% identical. In some embodiments, two or more amino acid sequences are at least 95%, 97%, 98%, 99%, or even 100% identical. In general, the percentage identity for comparison between amino acid sequences is at least 75%, at least 80%, at least 90%, with at least about 95, 96, 97, 98 or 99% percent identity being preferred. The percentage identity may be along the whole amino acid sequence, for example the entire protein sequence, such as a heavy chain or along a portion of a heavy chain. For example, included within the definition of the anti- DcR3 antibodies disclosed herein are those that share identity along the entire variable region (for example, where the identity is 95 or 98% identical along the variable region, and in some embodiments at least 95% or at least 98%). “Fused” or “covalently linked” means that the components (e g., an an anti-DcR3 antibody and an Fc domain) are linked by peptide bonds, either directly or indirectly via domain linkers, as outlined herein. The strength, or affinity, of specific binding can be expressed in terms of the dissociation constant (KD) of the interaction, wherein a smaller KD represents greater affinity, and a larger KD represents lower affinity. Binding properties can be determined by methods well known in the art such as bio-layer interferometry (BLI) and surface plasmon resonance-based methods (SPR). One such method entails measuring the rates of antigen-binding site / antigen or receptor / ligand complex association and dissociation, wherein ratesDocket No. WRENCH-002 / WO01 depend on the concentration of the complex partners, the affinity of the interaction, and geometric parameters that equally influence the rate in both directions. Thus, both the association rate (ka) and the dissociation rate (kd) can be determined, and the ratio of kd / ka is equal to the dissociation constant KD (See Nature 361.186- 187 (1993) and Davies et al. (1990) Annual Rev Biochem 59:439-473). Specific binding for a particular molecule or an epitope can be exhibited, for example, by a molecule (e.g., a DcR3 binding protein) having a KD for its binding partner (e.g., DcR3) of at least about 10-4M, at least about 10-5M, at least about 10-6M, at least about 10-7M, at least about 10-8M, at least about 10-9M, alternatively at least about 10-10M, at least about 10-11M, at least about 10-12M, or greater. Typically, an antigen binding molecule that specifically binds an antigen will have a KD that is 20, 50, 100, 500, 1000, 5,000, 10,000 or more times greater for a control molecule relative to the antigen or epitope. 3. Single Domain DcR3 Binding Proteins Described herein are single domain DcR3 binding proteins specifically binding to DcR3. A single domain DcR3 binding protein can be, for example, a VHH (a camelid). In one aspect, the single domain DcR3 binding protein comprises a domain which specifically or selectively binds to human DcR3. (i) Decoy Receptor 3 (DcR3) In addition to classical immune checkpoint inhibitory immunoreceptors like PD-1, CTLA-4, and LAG3, certain soluble receptors also serve as gatekeepers of the immune response. Decoy receptors play a role as soluble immune checkpoints by sequestering immune-stimulatory cytokines, thereby preventing the activation of anti-cancer immune cells. Decoy Receptor 3 (DcR3) is a decoy receptor for tumor necrosis factor (TNF) superfamily ligands FasL, LIGHT, and TL1A. DcR3 neutralizes these immune-stimulating cytokines through a conserved binding interface. DcR3 transcripts are often elevated in human cancers (FIG. 1A) and DcR3 overexpression correlates with poor outcomes. For example, DcR3 has been shown to be upregulated at the protein level in many solid tumors (FIG. 2A) and high levels of circulating DcR3 correlate with tumor metastasis in gastric cancer (FIG.2B). Because of its mechanism of action and overexpression in cancers, DcR3 has been implicated in a number of malignant pathways, such as the protection of cancer from apoptosis; cancer cell survival, proliferation, migration, and invasion; enhancement of angiogenesis; T-cell suppression and apoptosis; and M2 polarization. DcR3 engages TNG ligands FasL, LIGHT, and TL1A in a structurally similar fashion. Each of the FasL:DcR3, TL1A:DcR3, and LIGHT:DcR3 complexes display a hexameric organization and have a similar mode of DcR3 recognition. See Liu et al., Crystal Structure of the Complex of Human FasL and its Decoy Receptor DcR3, Cell 24:11 (2016), hereby incorporated by reference in its entirety. Crystal structures have shown that the recognition of invariant residues and backbone atoms in DE loops of the ligands (see Liu, Figure 2A) contribute to DcR3’s promiscuous binding. For example, three residues (Q80, Y84, R89) of DcR3 are involved in the recognition of invariant side chain (FasL, Y218) and backbone (FasL K217, D221)Docket No. WRENCH-002 / WO01 determinants. Additionally, Y90 of DcR3 participates in hydrophobic interactions with Y166 and G167 of FasL, which correspond to residues L123 and G124 in TL1A and L118 and G119 in LIGHT. As shown in Figures 2B-D of Liu, DcR3 residues H122-L127, N92, L94, R76, H77, R87, Y90, R89, and Y78-E86 bind to this conserved conformational epitope used by each of the DcR3 ligands. Specifically, FasL binds to DcR3 at residues R98, H122-L127, N92, L94, P75-H77, R87, Y90, R89, and Y78-86 (DcR3 : FasL binding interface); TL1A binds to DcR3 at residues H122-L127, N92-E99, R76, H77, R87, Y90, R89, and Y78-86 (DcR3 : TL1A binding interface); and LIGHT binds to DcR3 at H122-L127, N92-E99, R76, H77, R87, Y90, R89, and Y78- E86 (DcR3 : LIGHT binding interface). Accordingly, each of FasL, TL1A, and LIGHT bind to DcR3 at a conserved binding interface of H122-L127, N92, L94, R76, H77, R87, Y90, R89, and Y78-E86, though some additional residues are implicated for each ligand. (ii) Anti-DcR3 Antibodies The present disclosure provides antibodies, antigen binding domains, and binding proteins that specifically bind to Decoy Receptor 3 (DcR3), and which may contain a number of specific, enumerated sites of CDRs. Such antibodies, antigen binding domains, and binding proteins result in increased levels of circulating DcR3 ligands including FasL, LIGHT, and TL1A. The inventor has recognized and appreciated that because DcR3 serum levels are upregulated in many human cancers, an antibody that specifically blocks the binding of and disassociates DcR3 from its ligands will increase levels of the immune-stimulating cytokines FasL, LIGHT, and TL1A, thereby restoring immune function and improving survival for cancer patients. In certain diseases, immune function can be compromised due to a deficiency in FasL, LIGHT, and TL1A. For instance, some cancers exhibit an overexpression of DcR3, resulting in a significant reduction in DcR3 ligands and enabling the cancer to evade immune response. According to at least some embodiments of the disclosure, the anti-DcR3 antibodies (including antigen-binding fragments) bind to DcR3, release endogenous DcR3 ligands from DcR3, and block the interaction between DcR3 and its ligands, thereby releasing increased levels of FasL, LIGHT, and TL1A. The heightened levels of these ligands restore and enhance immune function, promoting the activation, proliferation, and secretion of cytokines and chemokines by various immune cells such as T cells, Myeloid cells, and Dendritic cells, . This therapeutic approach holds promise for treating diseases such as cancer and pathogen infections, utilizing anti-DcR3 antibodies to restore immune function. Accordingly, anti-DcR3 antibodies according to the disclosure find use in treating diseases such as cancer. The disclosure provides anti-DcR3 antibodies. As described herein, DcR3, also called Decoy Receptor 3 and TNFRSF6B, relates to amino acid and nucleic acid sequences shown in RefSeq accession identifiers NP_003814, NM_032945, and NM_003823; UniProt O95407, and Ensembl ENSG00000243509. The DcR3 gene is located on chromosome 20 (20q13.33), has three exons, and has both expressed (SEQ ID NO: 401) and mature (SEQ ID NO: 402) forms. In some embodiments, antibodies of the disclosure are specific for DcR3.Docket No. WRENCH-002 / WO01 The present disclosure provides single domain anti-DcR3 antibodies. (For convenience, “anti-DcR3 antibodies” and “DcR3 antibodies” are used interchangeably). The anti-DcR3 antibodies of the invention specifically bind to human DcR3, including, e.g., anti-DcR3 antibodies including those with CDRs identical to those shown in Table 10. Single-domain anti-DcR3 antibodies may also commonly be referred to as VHHs and nanobodies. VHHs are a distinct class of antibody fragments derived from heavy-chain-only antibodies prevalent in camelids such as camels, llamas, and alpacas. Specifically, VHHs are defined by their single- variable domain structure, which sets them apart from conventional antibodies characterized by two heavy chains and two light chains. This single-domain architecture imparts unique advantages to VHHs, including their diminutive size, exceptional stability, solubility, and remarkable specificity and affinity for target antigens. Further, this single-domain architecture allows for multiple VHHs to be fused to other proteins, such as an Fc region, resulting in multiparatopic and multispecific proteins and bivalent and tetravalent fusion proteins, as further described herein. The inventors have recognized and appreciated that VHHs are particularly useful as an anti-DcR3 antibody. Such single-domain antibodies are easier to produce, in part due to a reduction in complexity and lack of unintended VH / VL pairing. Further, up to four VHHs may be fused directly to an Fc, but only two for IgG. Increasing the possible valency from bivalent to tetravalent is particularly beneficial as a single molecule can bind to multiple DcR3 molecules or multiple sites on DcR3, and thus inhibit larger quantities of DcR3 from sequestering its ligands. Some embodiments of anti-DcR3 antibodies of the disclosure (including antigen-binding fragments) can compete with DcR3 ligands to prevent their binding. For example, the single-domain antibodies may bind to DcR3 at the same epitope as for FasL, LIGHT, and TL1A, and thus may displace these ligands from DcR3, resulting in an increased level of FasL, LIGHT, and TL1A in circulation. As DcR3 associates and disassociates with its ligands, DcR3 will more readily bind to single-domain antibodies of the disclosure. Accordingly, such antibodies bind to DcR3 and inhibit DcR3 from binding with its ligands. Such antibodies can be used in treating diseases such as cancer and pathogen infection. Antibodies of the disclosure can bind to one or more binding interfaces of DcR3. In some embodiments, the one or more binding interfaces are selected from the group consisting of: the DcR3:FasL binding interface; the DcR3:LIGHT binding interface; and the DcR3:TL1A binding interface. In some embodiments, the single domain DcR3 binding protein binds to DcR3 at a conserved binding interface for each of its ligands. In such embodiments, the single domain DcR3 binding protein binds to DcR3 at one or more amino acid positions selected from the group consisting of: H122-L127, N92, L94, R76, H77, R87, Y90, R89, and Y78-E86 of wild type DcR3. In some embodiments, the single domain DcR3 binding protein binds to DcR3 at additional residues that represent the binding interface for individual ligands. In such embodiments, the single domain DcR3 binding protein binds to DcR3 at one or more amino acid positions selected from the group consisting of: R98,Docket No. WRENCH-002 / WO01 N92-E99, and P75 of wild type DcR3. In this way, antibodies of the disclosure can bind to DcR3 and inhibit DcR3 from interacting with its ligands. Antibodies of the disclosure thus have the potential to restore the activity of TL1A, LIGHT, and / or FasL that were inhibited by DcR3. For example, antibodies of the disclosure can restore the apoptotic activity of FasL towards cancer cells and activate anti-cancer immune cells, In other embodiments, anti-DcR3 antibodies of the disclosure (including antigen-binding fragments) bind to DcR3 but not at the same binding interface as for FasL, LIGHT, and TL1A. Such antibodies may not displace FasL, LIGHT, and TL1A or inhibit their binding with DcR3. As will be described in further detail below and as supported by the Examples, such antibodies can be combined with antibodies that do bind to the same binding interface as for FasL, LIGHT, and TL1A, yielding biparatopic antibodies with additional benefits. In some embodiments, the anti-DcR3 antibodies have pH-sensitive binding affinities to DcR3. For soluble protein antigens such as DcR3, the concentration of that protein antigen in an extracellular fluid depends on the equilibrium between its production and its removal via endocytosis and lysosomal degradation. Administration of a specific antibody can profoundly increase the half-life of an antigen by trapping it in an antigen–antibody complex that is recycled by FcRn in endosomes. The inventor has recognized that this issue can be addressed by the use of antibodies that are pH-sensitive and release bound antigen in acidified endosomes during antibody recycling. A conventional high-affinity antibody usually binds an antigen and remains in complex with the antigen for a long time. This effect results from a desired mechanism for a low dissociation rate. However, once the antibody and antigen are bound, the antibody is unable to target and bind to additional antigens. In contrast to conventional antibodies, pH-sensitive antibodies can release their antigens upon internalization into endosomes. For example, an antibody that has a high binding affinity for its antigen at (e.g.) pH 6.5 or pH 7.4 will bind well to antigens in the tumor microenvironment and blood, respectively. However, once the antibody- antigen complex is internalized through endocytosis into endosomes (having an acidic environment with a pH of 5.8), the pH-sensitive binding between the antibody and antigen may be disrupted, leading to dissociation and subsequent degradation of the antigen. Following dissociation, the antibodies may be released into the lumen of the endosomes and are subsequently recycled and reused to bind their target again. For example, antibodies may be transported back to the cell surface, or released into the extracellular environment, where they can bind to new antigens and participate in subsequent immune responses, while the antigens remain in the endosome and are subject to degradation. In this way, antibodies of the disclosure can work in cycles of antigen binding — endocytosis — antigen releasing — recycling into the extracellular fluid — antigen binding, and which may be commonly referred to as “recycling antibodies” or “antigen clearance-enhancing antibodies”. Such recycling antibodies have particular utility in the context of single-domain antibodies, DcR3, and anti- DcR3 antibody-Fc fusion proteins, as further described herein.Docket No. WRENCH-002 / WO01 Accordingly, in some embodiments, the binding affinity of the DcR3 antibody for DcR3 is pH- sensitive. In such embodiments, the binding affinity of a DcR3 antibody for DcR3 may be 10-fold, 20-fold, 30- fold, 40-fold, 50-fold, 60-fold, 70-fold, 80-fold, 90-fold, or 100-fold less at a pH of 5.8 or lower, as compared to the binding affinity at a pH of 6.5 or above. In some embodiments, the binding affinity of the anti-DcR3 antibody for DcR3 is 10-fold, 20-fold, 30-fold, 40-fold, 50-fold, 60-fold, 70-fold, 80-fold, 90-fold, or 100-fold less at a pH of 5.8 or lower, as compared to the binding affinity at a pH of 7.4 or above. In some embodiments, the binding affinity of the anti-DcR3 antibody for DcR3 is 100-fold, 200-fold, 300-fold, 400-fold, 500-fold, 600-fold, 700-fold, 800-fold, 900-fold, or 1000-fold less at a pH of 5.8 or lower, as compared to the binding affinity at a pH of 6.5 or 7.4 or above. Specific binding for DcR3 or a DcR3 epitope can be exhibited, for example, by an antibody having a KD of at least about 10-5 M, at least about 10-6 M, at least about 10-7 M, at least about 10-8 M, at least about 10-9 M, alternatively at least about 10-10 M, at least about 10-11 M, at least about 10-12 M, at least about 10- 13 M, at least about 10-14 M, or greater, where KD refers to a dissociation rate of a particular antibody-antigen interaction. Typically, an antibody that specifically binds an antigen will have a KD that is 20-, 50-, 100-, 500- , 1000-, 5,000-, 10,000-, 100,000- or more times greater for a control molecule relative to the DcR3 antigen or epitope. However, as supported by the Examples, for optimal binding to DcR3, the antibodies of the disclosure preferably have a KD (also referred to as the binding affinity) of less than 50nM, less than 40nM, less than 30nM, less than 20nM, less than 10 nM, less than 5nM, less than 1nM, or less than 100pM, at a pH of 6.5 – 7.4. In some embodiments, the antibodies of the disclosure preferably bind to human DcR3 with a KD of less than 50nM, less than 40nM, less than 30nM, less than 20nM, less than 10 nM, less than 5nM, less than 1nM, or less than 100 pM, at a pH of 6.5 – 7.4, wherein KD is determined by known methods, e.g. surface plasmon resonance (SPR, e.g. Biacore instrument), Bio-Layer interferometry (BLI, e.g. Octet instrument), ELISA, KinExA, and most typically BLI or SPR at 25 or 37C. Also, specific binding for a particular antigen or an epitope can be exhibited, for example, by an antibody having a KA or Ka for an DcR3 antigen or epitope of at least 20-, 50-, 100-, 500-, 1000-, 5,000-, 10,000-, 100,000- or more times greater for the epitope relative to a control, where KA or Ka refers to an association rate of a particular antibody-antigen interaction. The disclosure provides antigen binding domains, including single domain antibodies, which contain a number of specific, enumerated sets of CDRs, as provided in Table 10. As discussed herein, the disclosure further provides variants of the above components, including variants in the CDRs, as outlined above. In one aspect, a single domain anti-DcR3 binding protein comprises an amino acid sequence of any of the clones of Table 7. In one aspect, a single domain anti-DcR3 binding protein comprises a CDR-H1 having a sequence selected from any CDR-H1 in Table 10. In one aspect, a single domain anti-DcR3 binding proteinDocket No. WRENCH-002 / WO01 comprises a CDR-H2 having a sequence selected from any CDR-H2 in Table 10. In one aspect, a single domain anti-DcR3 binding protein comprises a CDR-H3 having a sequence selected from any CDR-H3 in Table 10. In one aspect, a single domain anti-DcR3 binding protein comprises a CDR-H1, a CDR-H2, and a CDR-H3 selected from any CDR-H1, any CDR-H2, and any CDR-H3 in Table 10, wherein the selected CDR-H1, CDR- H2, and CDR-H3 are paired according to Table 11. In one aspect, a single domain DcR3 binding protein described herein comprises an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to SEQ ID Nos: 201-219. In some embodiments, the amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions relative to a reference sequence, but retains the ability to bind to DcR3 as of the unmodified sequence. In some embodiments, a total of from 1 to 10 amino acids are substituted, inserted and / or deleted. In some embodiments, substitutions, insertions, or deletions occur in regions outside the complementarity-determining region (CDR). (1) WB29 (Anti-DcR3-3.1 VHH) In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 1, the CDR-H2 has an amino acid sequence of SEQ ID NO: 20, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 39, wherein the numbering is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 58, the CDR-H2 has an amino acid sequence of SEQ ID NO: 77, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 96, wherein the numbering is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 115, the CDR-H2 has an amino acid sequence of SEQ ID NO: 134, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 153, wherein the numbering is according to IMGT. In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 1; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 20; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 39, wherein the number is according to Kabat.Docket No. WRENCH-002 / WO01 In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 58; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 77; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 96, wherein the number is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 115; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 134; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 153, wherein the number is according to IMGT. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 201. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising the amino acid sequence of SEQ ID NO: 201. In some aspects, the single domain anti-DcR3 binding protein or antibody binds to DcR3, but does not inhibit DcR3 from interacting with its ligands. (2) WB30 (Anti-DcR3-3.4 VHH) In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 2, the CDR-H2 has an amino acid sequence of SEQ ID NO: 21, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 40, wherein the numbering is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 59, the CDR-H2 has an amino acid sequence of SEQ ID NO: 78, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 96, wherein the numbering is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 116, the CDR-H2 has an amino acid sequence of SEQ ID NO: 135, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 154, wherein the numbering is according to IMGT.Docket No. WRENCH-002 / WO01 In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 2; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 21; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 40, wherein the number is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 59; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 78; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 96, wherein the number is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 116; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 135; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 154, wherein the number is according to IMGT. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 202. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising the amino acid sequence of SEQ ID NO: 202. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with its ligands. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with TL1A. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with FasL. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with LIGHT. (3) WB31 (Anti-DcR3-3.5 VHH) In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 3, the CDR-H2 has an amino acid sequence of SEQ ID NO: 22, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 41, wherein the numbering is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 60, the CDR-H2 has an amino acidDocket No. WRENCH-002 / WO01 sequence of SEQ ID NO: 79, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 98, wherein the numbering is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 117, the CDR-H2 has an amino acid sequence of SEQ ID NO: 136, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 155, wherein the numbering is according to IMGT. In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 3; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 22; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 41, wherein the number is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 60; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 79; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 98, wherein the number is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 117; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 136; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 155, wherein the number is according to IMGT. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 203. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising the amino acid sequence of SEQ ID NO: 203. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with its ligands. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with TL1A. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with FasL. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with LIGHT. (4) WB32 (Anti-DcR3-3.10 VHH)Docket No. WRENCH-002 / WO01 In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 4, the CDR-H2 has an amino acid sequence of SEQ ID NO: 23, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 42, wherein the numbering is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 61, the CDR-H2 has an amino acid sequence of SEQ ID NO: 80, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 99, wherein the numbering is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 118, the CDR-H2 has an amino acid sequence of SEQ ID NO: 137, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 156, wherein the numbering is according to IMGT. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 4; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 23; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 42, wherein the number is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 61; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 80; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 99, wherein the number is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 118; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 137; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 156, wherein the number is according to IMGT. In one aspect, the present disclosure provides a single domain anti-DcR3-binding protein or antibody comprising an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 204. In one aspect, the present disclosureDocket No. WRENCH-002 / WO01 provides a single domain anti-DcR3-binding protein or antibody comprising the amino acid sequence of SEQ ID NO: 204. In some aspects, the single domain anti-DcR3 binding protein or antibody binds to DcR3, but does not inhibit DcR3 from interacting with its ligands. (5) WB33 (Anti-DcR3-3.15 VHH) In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 5, the CDR-H2 has an amino acid sequence of SEQ ID NO: 24, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 43, wherein the numbering is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 62, the CDR-H2 has an amino acid sequence of SEQ ID NO: 81, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 100, wherein the numbering is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 119, the CDR-H2 has an amino acid sequence of SEQ ID NO: 138, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 157, wherein the numbering is according to IMGT. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 5; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 24; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 43, wherein the number is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 62; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 81; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 100, wherein the number is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 119; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%,Docket No. WRENCH-002 / WO01 99%, or 100% identical to SEQ ID NO: 138; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 157, wherein the number is according to IMGT. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 205. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising the amino acid sequence of SEQ ID NO: 205. In some aspects, the single domain anti-DcR3 binding protein or antibody binds to DcR3, but does not inhibit DcR3 from interacting with its ligands. (6) WB34 (Anti-DcR3-3.16 VHH) In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 6, the CDR-H2 has an amino acid sequence of SEQ ID NO: 25, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 44, wherein the numbering is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 63, the CDR-H2 has an amino acid sequence of SEQ ID NO: 82, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 101, wherein the numbering is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 120, the CDR-H2 has an amino acid sequence of SEQ ID NO: 139, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 158, wherein the numbering is according to IMGT. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 6; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 25; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 44, wherein the number is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 63; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%,Docket No. WRENCH-002 / WO01 or 100% identical to SEQ ID NO: 82; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 101, wherein the number is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 120; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 139; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 158, wherein the number is according to IMGT. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 206. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising the amino acid sequence of SEQ ID NO: 206. In some aspects, the single domain anti-DcR3 binding protein or antibody binds to DcR3, but does not inhibit DcR3 from interacting with its ligands. (7) WB74 (Anti-DcR3-3.8X VHH) In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 7, the CDR-H2 has an amino acid sequence of SEQ ID NO: 26, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 45, wherein the numbering is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 64, the CDR-H2 has an amino acid sequence of SEQ ID NO: 83, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 102, wherein the numbering is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 121, the CDR-H2 has an amino acid sequence of SEQ ID NO: 140, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 159, wherein the numbering is according to IMGT. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 7; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%,Docket No. WRENCH-002 / WO01 or 100% identical to SEQ ID NO: 26; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 45, wherein the number is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 64; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 83; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 102, wherein the number is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 121; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 140; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 159, wherein the number is according to IMGT. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 207. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising the amino acid sequence of SEQ ID NO: 207. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with its ligands. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with TL1A. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with FasL. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with LIGHT. (8) WB75 (Anti-DcR3-3.4X VHH) In one aspect, the present disclosure provides a single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 8, the CDR-H2 has an amino acid sequence of SEQ ID NO: 27, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 46, wherein the numbering is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 65, the CDR-H2 has an amino acid sequence of SEQ ID NO: 84, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 103, wherein the numbering is according to Chothia.Docket No. WRENCH-002 / WO01 In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 122, the CDR-H2 has an amino acid sequence of SEQ ID NO: 141, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 160, wherein the numbering is according to IMGT. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 8; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 27; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 46, wherein the number is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 65; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 84; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 103, wherein the number is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 122; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 141; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 160, wherein the number is according to IMGT. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 208. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising the amino acid sequence of SEQ ID NO: 208. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with its ligands. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with TL1A. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with FasL. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with LIGHT. (9) WB76 (Anti-DcR3-3.16X VHH) In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 9, the CDR-H2 has an amino acidDocket No. WRENCH-002 / WO01 sequence of SEQ ID NO: 28, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 47, wherein the numbering is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 66, the CDR-H2 has an amino acid sequence of SEQ ID NO: 85, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 104, wherein the numbering is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 123, the CDR-H2 has an amino acid sequence of SEQ ID NO: 142, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 161, wherein the numbering is according to IMGT. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 9; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 28; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 47, wherein the number is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 66; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 85; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 104, wherein the number is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 123; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 142; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 161, wherein the number is according to IMGT. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 209. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising the amino acid sequence of SEQ ID NO: 209. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with its ligands. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3Docket No. WRENCH-002 / WO01 and inhibits DcR3 from interacting with TL1A. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with FasL. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with LIGHT. (10) WB77 (Anti-DcR3-3.15X VHH) In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 10, the CDR-H2 has an amino acid sequence of SEQ ID NO: 29, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 48, wherein the numbering is according to Kabat. In one aspect, the present disclosure provides a single domain IDcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 67, the CDR-H2 has an amino acid sequence of SEQ ID NO: 86, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 105, wherein the numbering is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 124, the CDR-H2 has an amino acid sequence of SEQ ID NO: 143, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 162, wherein the numbering is according to IMGT. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 10; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 29; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 48, wherein the number is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 67; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 86; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 105, wherein the number is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 124; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 143; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 162, wherein the number is according to IMGT.Docket No. WRENCH-002 / WO01 In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 210. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising the amino acid sequence of SEQ ID NO: 210. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with its ligands. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with TL1A. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with FasL. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with LIGHT. (11) WB78 (Anti-DcR3-3.3X VHH) In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 11, the CDR-H2 has an amino acid sequence of SEQ ID NO: 30, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 49, wherein the numbering is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 68, the CDR-H2 has an amino acid sequence of SEQ ID NO: 87, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 106, wherein the numbering is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 125, the CDR-H2 has an amino acid sequence of SEQ ID NO: 144, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 163, wherein the numbering is according to IMGT. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 11; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 30; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 49, wherein the number is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 68; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%,Docket No. WRENCH-002 / WO01 or 100% identical to SEQ ID NO: 87; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 106, wherein the number is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 125; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 144; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 163, wherein the number is according to IMGT. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 211. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising the amino acid sequence of SEQ ID NO: 211. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 but does not inhibit DcR3 from interacting with its ligands. (12) WB79 (Anti-DcR3-3.5X VHH) In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 12, the CDR-H2 has an amino acid sequence of SEQ ID NO: 31, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 50, wherein the numbering is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 69, the CDR-H2 has an amino acid sequence of SEQ ID NO: 88, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 107, wherein the numbering is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 126, the CDR-H2 has an amino acid sequence of SEQ ID NO: 145, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 164, wherein the numbering is according to IMGT. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 12; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%,Docket No. WRENCH-002 / WO01 or 100% identical to SEQ ID NO: 31; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 50, wherein the number is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 69; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 88; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 107, wherein the number is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 126; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 145; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 164, wherein the number is according to IMGT. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 212. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising the amino acid sequence of SEQ ID NO: 212. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 but does not inhibit DcR3 from interacting with its ligands. (13) WB80 (Anti-DcR3-3.14X VHH) In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 13, the CDR-H2 has an amino acid sequence of SEQ ID NO: 32, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 51, wherein the numbering is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 70, the CDR-H2 has an amino acid sequence of SEQ ID NO: 89, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 108, wherein the numbering is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 127, the CDR-H2 has an amino acidDocket No. WRENCH-002 / WO01 sequence of SEQ ID NO: 146, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 165, wherein the numbering is according to IMGT. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 13; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 32; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 51, wherein the number is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 70; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 89; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 108, wherein the number is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 127; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 146; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 165, wherein the number is according to IMGT. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 213. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising the amino acid sequence of SEQ ID NO: 213. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with its ligands. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with TL1A. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with FasL. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with LIGHT. (14) WB83 (Anti-DcR3-3.24X VHH) In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 14, the CDR-H2 has an amino acid sequence of SEQ ID NO: 33, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 52, wherein the numbering is according to Kabat.Docket No. WRENCH-002 / WO01 In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 71, the CDR-H2 has an amino acid sequence of SEQ ID NO: 90, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 109, wherein the numbering is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 128, the CDR-H2 has an amino acid sequence of SEQ ID NO: 147, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 166, wherein the numbering is according to IMGT. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 14; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 33; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 52, wherein the number is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 71; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 90; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 109, wherein the number is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 128; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 147; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 166, wherein the number is according to IMGT. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 214. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising the amino acid sequence of SEQ ID NO: 214. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 but does not inhibit DcR3 from interacting with its ligands. (15) WB84 (Anti-DcR3-3.28X VHH)Docket No. WRENCH-002 / WO01 In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 15, the CDR-H2 has an amino acid sequence of SEQ ID NO: 34, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 53, wherein the numbering is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 72, the CDR-H2 has an amino acid sequence of SEQ ID NO: 91, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 110, wherein the numbering is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 129, the CDR-H2 has an amino acid sequence of SEQ ID NO: 148, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 167, wherein the numbering is according to IMGT. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 15; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 34; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 53, wherein the number is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 72; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 91; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 110, wherein the number is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 129; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 148; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 167, wherein the number is according to IMGT. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 215. In one aspect, the present disclosureDocket No. WRENCH-002 / WO01 provides a single domain anti-DcR3 binding protein or antibody comprising the amino acid sequence of SEQ ID NO: 215. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 but does not inhibit DcR3 from interacting with its ligands. (16) WB85 (Anti-DcR3-3.29X VHH) In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 16, the CDR-H2 has an amino acid sequence of SEQ ID NO: 35, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 54, wherein the numbering is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 73, the CDR-H2 has an amino acid sequence of SEQ ID NO: 92, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 111, wherein the numbering is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 130, the CDR-H2 has an amino acid sequence of SEQ ID NO: 149, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 168, wherein the numbering is according to IMGT. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 16; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 35; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 54, wherein the number is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 73; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 92; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 111, wherein the number is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 130; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%,Docket No. WRENCH-002 / WO01 99%, or 100% identical to SEQ ID NO: 149; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 168, wherein the number is according to IMGT. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 216. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising the amino acid sequence of SEQ ID NO: 216. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 but does not inhibit DcR3 from interacting with its ligands. (17) WB86 (Anti-DcR3-3.31X VHH) In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 17, the CDR-H2 has an amino acid sequence of SEQ ID NO: 36, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 55, wherein the numbering is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 74, the CDR-H2 has an amino acid sequence of SEQ ID NO: 93, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 112, wherein the numbering is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 131, the CDR-H2 has an amino acid sequence of SEQ ID NO: 150, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 169, wherein the numbering is according to IMGT. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 17; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 36; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 55, wherein the number is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 74; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%,Docket No. WRENCH-002 / WO01 or 100% identical to SEQ ID NO: 93; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 112, wherein the number is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 131; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 150; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 169, wherein the number is according to IMGT. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 217. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising the amino acid sequence of SEQ ID NO: 217. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 but does not inhibit DcR3 from interacting with its ligands. (18) WB87 (Anti-DcR3-3.18X VHH) In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 18, the CDR-H2 has an amino acid sequence of SEQ ID NO: 37, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 56, wherein the numbering is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 75, the CDR-H2 has an amino acid sequence of SEQ ID NO: 94, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 113, wherein the numbering is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 132, the CDR-H2 has an amino acid sequence of SEQ ID NO: 151, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 170, wherein the numbering is according to IMGT. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 18; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%,Docket No. WRENCH-002 / WO01 or 100% identical to SEQ ID NO: 37; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 56, wherein the number is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 75; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 94; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 113, wherein the number is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 132; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 151; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 170, wherein the number is according to IMGT. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 218. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising the amino acid sequence of SEQ ID NO: 218. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with its ligands. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with TL1A. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with FasL. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with LIGHT. (19) WB88 (Anti-DcR3-3.26X VHH) In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 19, the CDR-H2 has an amino acid sequence of SEQ ID NO: 38, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 57, wherein the numbering is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 76, the CDR-H2 has an amino acid sequence of SEQ ID NO: 95, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 114, wherein the numbering is according to Chothia.Docket No. WRENCH-002 / WO01 In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR- H3, wherein the CDR-H1 has an amino acid sequence of SEQ ID NO: 133, the CDR-H2 has an amino acid sequence of SEQ ID NO: 152, and the CDR-H3 has an amino acid sequence of SEQ ID NO: 171, wherein the numbering is according to IMGT. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 19; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 38; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 57, wherein the number is according to Kabat. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 76; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 95; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 114, wherein the number is according to Chothia. In one aspect, the present disclosure provides a single domain DcR3-binding protein or antibody comprising: (a) a CDR-H1 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 133; (b) a CDR-H2 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 152; and (c) a CDR-H3 is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 171, wherein the number is according to IMGT. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 219. In one aspect, the present disclosure provides a single domain anti-DcR3 binding protein or antibody comprising the amino acid sequence of SEQ ID NO: 219. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with its ligands. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with TL1A. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with FasL. In some aspects, the single domain DcR3 binding protein or antibody binds to DcR3 and inhibits DcR3 from interacting with LIGHT. 4. Multispecific Binding Proteins In one aspect, provided herein is a multispecific binding protein comprising a first domain and a second domain according to the present disclosure. The multispecific binding protein can, in some instances, bind to two, three, four, or more different proteins. In some embodiments, the first domain comprises a single domainDocket No. WRENCH-002 / WO01 DcR3 binding protein as described herein. In some embodiments, the second domain, an optional third domain, and / or an optional fourth domain binds to a target molecule that is not DcR3. In some embodiments, the multispecific protein is a bispecific protein. In some embodiments, the multispecific protein is a trispecific protein. In some embodiments, the single domain DcR3 binding protein described herein and the second domain described herein are coupled via chemical coupling, gene fusion, or a non-covalent association. In some embodiments, the single domain DcR3 binding protein described herein and the second domain described herein are coupled via chemical coupling. In some embodiments, the single domain DcR3 binding protein described herein and the second domain described herein are coupled via gene fusion. In some embodiments, the single domain DcR3 binding protein described herein and the second domain described herein are coupled via non-covalent association. The domain or the domains which do(es) not bind to DcR3 binds to a target antigen. The target antigen can be, for example, a cell surface molecule. Cell surface molecules include, but are not limited to, proteins, lipids, and / or polysaccharides. In some embodiments, a target antigen can be present on a tumor cell, a virally infected cell, a bacterially infected cell, a damaged red blood cell, an arterial plaque cell, a fibrotic tissue cell, etc. A target antigen can be involved in and / or associated with a disease, disorder, or condition. In particular, a target antigen can be associated with a proliferative disease, a tumorous disease, an inflammatory disease, an immunological disorder, an autoimmune disease, an infectious disease, a viral disease, an allergic reaction, a parasitic reaction, a graft-versus-host disease or a host-versus-graft disease. A tumorous disease can be, for example, a cancer. Cancers can be primary cancers or metastatic cancers. In some embodiments, a target antigen is a tumor associated antigen (TAA) expressed on a tumor cell. Alternatively in some embodiments, a target antigen is associated with a pathogen or a parasite (such as a virus, a bacterium, a fungus, etc.), a self-antigen, etc. In some embodiments, a target antigen is a tumor associated antigen (TAA) and the TAA can be, for example, a B-cell maturation antigen (BCMA), carcinoembryonic antigen (CEA), epidermal growth factor receptor (EGFR), human epidermal growth factor receptor 2 (Her2), epithelial cell adhesion molecule (EpCAM), CD20, CD26, CD123, CD30, CD33, CD47, CD52, CD133, glycoprotein A33 (gpA33), mucins, tumor associated glycoprotein-72 (TAG-72), type IX collagen (CIX), glutamate carboxypeptidase II (PSMA), folate-binding protein, GD2, GD3, GM2, vascular endothelial growth factor (VEGF), vascular endothelial growth factor receptor (VEGFR), integrin, αVβ3, α5β1, ERBB2, ERBB3, mesenchymal epithelial transition (MET), insulin-like growth factor-I receptor (IGFIR), ephrin type-A receptor 3 (EPHA3), TRAIL receptor 1 (TRAILR1), TRAIL receptor 2 (TRAILR2), receptor activator of nuclear factor kappa beta (RANKL), fibroblast activation protein (FAP), claudin 18.2, mesothelin, receptor tyrosine kinase like orphan receptor 1 (ROR1), epidermal growth factor receptor variant III (EGFRVIII), six-transmembrane epithelial antigen of theDocket No. WRENCH-002 / WO01 prostate-2 (STEAP2), orphan G protein–coupled receptor, class C group 5 member D (GPRC5D), carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5), tenascin, etc. In some embodiments, the multispecific binding protein can be produced by linking a single domain DcR3 binding domain described herein and one or more other domain(s) described herein together using a linker. The linker can comprise, for example, Gly-Ser linker. The length of the linker is such that it can associate intermolecularly two or more domains. Examples of linkers for use in the multispecific binding proteins described herein include, but are not limited to, (GS)n (SEQ ID NO: 503), (GGS)n (SEQ ID NO: 504), (GGGS)n (SEQ ID NO: 505), (GGSG)n (SEQ ID NO: 506), (GGSGG)n (SEQ ID NO: 507), (GGGGS)n (SEQ ID NO: 508), (GGGGG)n (SEQ ID NO: 509), or (GGG)n (SEQ ID NO: 510), wherein, for each, n is 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. In one instance, the linker can be (GGGGS)4 (SEQ ID NO: 511) or (GGGGS)3 (SEQ ID NO: 512). A multispecific binding protein, in some instances, can optionally contain an Fc domain. Examples of Fc domains include, but are not limited to, an IgG1, IgG4, etc. A multispecific binding protein, in some embodiments, comprises a half-life extension domain. Examples of half-life extension domains include, but are not limited to, an Fc domain or an albumin-targeting polypeptide. 5. Fusion Proteins Embodiments of anti-DcR3 antibodies according to the disclosure may be fused to an Fc domain, resulting in various novel Fc fusion proteins. The inventor has recognized and appreciated that such fusion proteins have numerous advantages, including but not limited to biparatopic binding of DcR3, e.g., by the use of two different anti-DcR3 antibodies each binding to DcR3, and together preventing the interaction of DcR3 with its ligands. For example, a first VHH that binds to DcR3 and displaces DcR3 ligands (i.e., inhibits DcR3 from binding with its ligands) and a second VHH that binds to DcR3 but does not displace DcR3 ligands (i.e., does not inhibit DcR3 from binding with its ligands) can be combined to create a single molecule that will both bind to DcR3 with high precision and simultaneously increase circulating levels of FasL, LIGHT, and TL1A. (i) Fc Fusion Proteins In one aspect, a fusion protein is a heterodimeric Fc fusion protein. Such a heterodimeric fusion protein includes a first monomer and a second monomer comprising a first Fc domain and a second Fc domain, respectively. As will be described in further detail below, the first and second monomers may further comprise anti-DcR3 antibodies, thus providing Fc-fusion proteins. As will be appreciated, discussion herein of components of the fusion proteins encompassed by the present disclosure is applicable to both homodimeric and heterodimeric Fc fusion proteins as appropriate, unless otherwise specified. The Fc domains can be derived from IgG Fc domains, e.g., IgG1, IgG2, IgG3 or IgG4 Fc domains, with IgG1 Fc domains finding particular use in the invention. As described herein, IgG1 Fc domains may beDocket No. WRENCH-002 / WO01 used, often, but not always in conjunction with ablation variants to ablate effector function. Similarly, when low effector function is desired, IgG4 Fc domains may be used. In some embodiments, the first Fc domain and second Fc domain comprise complementary pairs of amino acid substitutions that improve thermostability. Such substitutions employ a “knob in hole” strategy in which one domain is modified with a “knob” mutation while the other is modified with a corresponding “hole” mutation. The knob can refer to a bulky amino acid substitution that creates a protrusion in the Fc region. The “hole” mutation involves a complementary amino acid substitution in the opposing domain of the Fc region, creating a depression or cavity in the Fc region. When the two domains are paired together, the knob from one domain fits into the hole of the other, resulting in a stable heterodimeric fusion protein. Accordingly, in such embodiments, the first Fc domain can comprise a set of amino acid substitutions (the knob) selected from the group consisting of S354C and T366W. In such embodiments, the second Fc domain can comprise a set of amino acid substitutions (the hole) selected from the group consisting of Y349C, T366S, L368A, and Y407V. In some embodiments, the Fc Knob is selected from Table 9 (SEQ ID NO: 501). In some embodiments, the Fc Hole is selected from Table 9 (SEQ ID NO: 502). In some embodiments, the Fc Knob is at least 90%, 95%, 98%, 99%, or 100% identical to its sequence from Table 9 (SEQ ID NO: 501). In some embodiments, the Fc Hole is at least 90%, 95%, 98%, 99%, or 100% identical to its sequence from Table 9 (SEQ ID NO: 502). For any of the dimeric fusion proteins described herein, the carboxy-terminal portion of each chain defines a constant region primarily responsible for effector function. Kabat et al. collected numerous primary sequences of the variable regions of heavy chains and light chains. Based on the degree of conservation of the sequences, they classified individual primary sequences into the CDRs and the framework and made a list thereof (see SEQUENCES OF IMMUNOLOGICAL INTEREST, 5thedition, NIH publication, No.91-3242, E A. Kabat et al, entirely incorporated by reference). Throughout the present specification, the Kabat numbering system is generally used when referring to a residue in the variable domain (approximately, residues 1-107 of the light chain variable region and residues 1-113 of the heavy chain variable region) and the EU numbering system for Fc regions (e.g., Kabat et al, supra (1991)). In the IgG subclass of immunoglobulins, there are several immunoglobulin domains in the heavy chain. By “immunoglobulin (Ig) domain” herein is meant a region of an immunoglobulin having a distinct tertiary structure. Of interest in the present Fc fusion proteins are the heavy chain domains, including the constant heavy (CH) domains and the hinge domains. In the context of IgG antibodies, the IgG isotypes each have three CH regions. Accordingly, “CH” domains in the context of IgG are as follows: “CH1” refers to positions 118-215 according to the EU index as in Kabat. “Hinge” refers to positions 216-230 according to the EU index as in Kabat. “CH2” refers to positions 231-340 according to the EU index as in Kabat, and “CH3” refers to positions 341-447 according to the EU index as in Kabat. As shown in Table 1, the exact numbering and placement ofDocket No. WRENCH-002 / WO01 the heavy chain domains can be different among different numbering systems. As shown herein and described below, the pI variants can be in one or more of the CH regions, as well as the hinge region, discussed below. Table 1 EU Numbering Kabat Numbering CH1 118-215 114-223 fusioninclude modifications within the Fc region, typically to alter one or more functional properties of the antibody, such as serum half-life, complement fixation, Fc receptor binding, and / or antigen-dependent cellular cytotoxicity. In some embodiments, each of the first and second monomers include an Fc domain that has the formula hinge- CH2-CH3. In some embodiments, each of the first and second monomers include an Fc domain that has the formula CH2-CH3. In some embodiments, amino acid substitutions can be made in the Fc region, in general for altering binding to FcγR receptors. By “Fc gamma receptor”, “Fcγ”, or “Fcgamma” as used herein is meant any member of the family of proteins that bind the IgG antibody Fc region and is encoded by an FcγR gene. In humans this family includes but is not limited to FcγRI (CD64), including isoforms FcγRIa, FcγRlb, and FcγRIc, FcγRII (CD32), including isoforms FcyRlla (including allotypes H I 3 l and R131), FcγRIIb (including FcγRIIb-i and FcγRIIb-2), and FcγRIIc; and FcTRIII (CD l6), including isoforms FcyRIIIa (including allotypes V158 and F158) and FcγRIIIb (including allotypes FcγRIIIb-NA I and FcγRIIIb-NAZ) (Jefferis et al, 2002, Immunol Lett 82:57-65, entirely incorporated by reference), as well as any undiscovered human FcγRs or FcγR isoforms or allotypes. An FcγR may be from any organism, including but not limited to humans, mice, rats, rabbits, and monkeys. Mouse FcγRs include but are not limited to FcγRI (CD64), FcγRII (CD32), FcγRIII-I (CD16), and FcγRIII-2 (CD16-2), as well as any undiscovered mouse FcγRs or FcγR isoforms or allotypes. There are a number of useful Fc substitutions that can be made to alter binding to one or more of the FcγR receptors. Substitutions that result in increased binding as well as decreased binding can be useful. For example, it is known that increased binding to FcγRIIIa generally results in increased ADCC (antibody dependent cell-mediated cytotoxicity; the cell mediated reaction wherein nonspecific cytotoxic cells that express FcγRs recognize bound antibody on a target cell and subsequently cause lysis of the target cell. Similarly, decreased binding to FcγRIIb (an inhibitory receptor) can be beneficial as well in some circumstances. Amino acid substitutions that find use in the present invention include those listed in U. S. Ser. No.11 / 124,620 (particularly FIG.41) and U.S. Patent No.6,737,056, both of which are expressly incorporatedDocket No. WRENCH-002 / WO01 herein by reference in their entirety and specifically for the variants disclosed therein. Particular variants that find use include, but are not limited to, 236A, 239D, 239E, 332E, 332D, 239D / 332E, 267D, 267E, 328F, 267E / 328F, 236A / 332E, 239D / 332E / 330Y, 239D, 332E / 330L, 299T and 297N. In addition, the fusion proteins of the invention may be modified to increase their biological half-life. Various approaches are possible. For example, one or more of the following mutations can be introduced: T252L, T254S, T256F, as described in U.S. Pat. No. 6,277,375 to Ward. Alternatively, to increase the biological half-life, the Fc region can be altered within the CH1 or CL region to contain a salvage receptor binding epitope taken from two loops of a CH2 domain of an Fc region of an IgG, as described in U.S. Pat. Nos.5,869,046 and 6,121,022 by Presta et al. Additional mutations to increase serum half-life are disclosed in U.S. Patent Nos.8,883,973, 6,737,056 and 7,371,826, and include 428L, 434A, 434S, and 428L / 434S. In yet other embodiments, the Fc region is altered by replacing at least one amino acid residue with a different amino acid residue to alter the effector functions of the antibody. For example, one or more amino acids selected from amino acid residues 234, 235, 236, 237, 297, 318, 320 and 322 can be replaced with a different amino acid residue such that the antibody has an altered affinity for an effector ligand but retains the antigen-binding ability of the parent antibody. The effector ligand to which affinity is altered can be, for example, an Fc receptor or the C1 component of complement. This approach is described in further detail in U S. Pat Nos.5,624,821 and 5,648,260, both by Winter et al. In another example, one or more amino acids selected from amino acid residues 329, 331, and 322 can be replaced with a different amino acid residue such that the fusion protein has altered Clq binding and / or reduced or abolished complement dependent cytotoxicity (CDC). This approach is described in further detail in U.S. Pat Nos.6,194,551 by Idusogie et al. In another example, one or more amino acid residues within amino acid positions 231 and 239 are altered to thereby alter the ability of the fusion protein to fix complement. This approach is described further in PCT Publication WO 94 / 29351 by Bodmer et al. In yet another example, the Fc region is modified to increase the ability of the antibody to mediate antibody dependent cellular cytotoxicity (ADCC) and / or to increase the affinity of the antibody for an FcY receptor by modifying one or more amino acids at the following positions: 238, 239, 248, 249, 252, 254, 255, 256, 258, 265, 267, 268, 269, 270, 272, 276, 278, 280, 283, 285, 286, 289, 290, 292, 293, 294, 295, 296, 298, 301, 303, 305, 307, 309, 312, 315, 320, 322, 324, 326, 327, 329, 330, 331, 333, 334, 335, 337, 338, 340, 360, 373, 376, 378, 382, 388, 389, 398, 414, 416, 419, 430, 434, 435, 437, 438, or 439. This approach is described further in PCT Publication WO 00 / 42072 by Presta. Moreover, the binding sites on human IgG1 for FcγRI, FcγRII, FcγRIII, and FcRn have been mapped and variants with improved binding have been described (see Shields, R. L. et al. (2001) J. Biol. Chem.276:6591-6604). Specific mutations at positions 256, 290, 298, 333, 334 and 339 are shown to improve binding to FcγRIII. Additionally, the following combination mutants are shown to improve FcγRIII binding: T256A / S298A, S298A / E333A, S298A / K224A, and S298A / E333A / K334ADocket No. WRENCH-002 / WO01 Furthermore, mutations such as M252Y / SZ54T / TZ56E or M428L / N434S improve binding to FcRn and increase antibody circulation half-life (see Chan CA and Carter PJ (2010) Nature Rev. Immunol.10:301-316). In some embodiments, specific residues of an Fc region fused to one or more proteins or antibodies of the disclosure are mutated to exhibit higher affinity to FcRn at a pH of 6 or below, e.g., pH 5.8. After being taken up into cells via pinocytosis or receptor-mediated endocytosis, antibodies are sorted into endosomes. Within the slightly acidic environment of the endosome, the Fc may bind to FcRn, protecting the antibody from degradation. The antibody-FcRn complex may then be recycled back to the cell surface, where it is released into the bloodstream. Such Fc mutations will thus result in increased half-life of the fusion protein. Accordingly, an increased affinity for FcRn at a pH of 6 or below will increase the percentage of antibodies that are recycled and reused, increasing potency. In some embodiments, the Fc will comprise modifications at one or more amino acids position selected from the group consisting of M252, S254, T256, T307, L309, M428 and N434, as compared to wild-type Fc. In one embodiment, the variant Fc has a modification at M252, S254, T256. In one embodiment, the variant Fc has a modification at M428 and L434. In one embodiment, the variant Fc has a modification at M252 and M428. In one embodiment, the variant Fc has a modification at M252, S254, and N434. In one embodiment, the variant Fc has a modification at T307 and M428. In one embodiment, the variant Fc has a modification at T307 and N434. In one embodiment, the variant Fc has a modification at L309 and M428. In one embodiment, the variant Fc has a modification at L309 and N434. In such embodiments, the modifications increase the affinity of the fusion protein to FcRn at a pH of 6 or below, e.g., a pH of 5-6. In some embodiments, the variant Fc-VHH fusion protein will exhibit increased thermostability by 1, 2, 5, and up to 10C compared to the wildtype Fc. In some embodiments, the variant Fc-VHH fusion protein will exhibit decreased thermostability by 1, 2, 5 and up to 10C compared to the wildtype Fc. In some embodiments, the variant Fc-VHH fusion will exhibit increased half-life, including human FcRn transgenic mice, as compared to a corresponding wild-type Fc-VHH fusion. In some embodiments, the combination of the pH-sensitive binding to DcR3 and Fc variants will augment the clearance of DcR3. In some embodiments, the combination of the pH-sensitive binding to DcR3 and Fc variants will augment the clearance of DcR3 from human FcRn transgenic mice. In still another embodiment, the glycosylation of a fusion protein is modified. For example, an aglycosylated Fc region can be made (i.e., the antibody lacks glycosylation). Glycosylation can be altered to, for example, increase the affinity of a single domain antibody of the disclosure for antigen or reduce effector function such as ADCC. Such carbohydrate modifications can be accomplished by, for example, altering one or more sites of glycosylation within the antibody sequence, for example N297. For example, one or more amino acid substitutions can be made that result in elimination of one or more variable region framework glycosylation sites to thereby eliminate glycosylation at that site.Docket No. WRENCH-002 / WO01 Additionally or alternatively, a fusion protein can be made that has an altered type of glycosylation, such as a hypofucosylated Fc region having reduced amounts of fucosyl residues or an antibody having increased bisecting GlcNac structures. Such altered glycosylation patterns have been demonstrated to increase the ADCC ability of antibodies. Such carbohydrate modifications can be accomplished by, for example, expressing the fusion protein in a host cell with altered glycosylation machinery. Cells with altered glycosylation machinery have been described in the art and can be used as host cells in which to express recombinant antibodies according to at least some embodiments of the invention to thereby produce an antibody with altered glycosylation. For example, the cell lines Ms704, Ms705, and Ms709 lack the fucosyltransferase gene, FUT8 (u (1,6) fucosyltransferase), such that antibodies expressed in the Ms704, Ms705, and Ms709 cell lines lack fucose on their carbohydrates. The Ms704, Ms705, and Ms709 FUT8 cell lines are created by the targeted disruption of the FUT8 gene in CHO / DG44 cells using two replacement vectors (see U.S. Patent Publication No. 20040110704 by Yamane et al. and Yamane-Ohnuki et al. (2004) Biotechnol Bioeng 87:614- 22). As another example, EP 1,176,195 by Hanai et al. describes a cell line with a functionally disrupted FUT8 gene, which encodes a fucosyl transferase, such that antibodies expressed in such a cell line exhibit hypofucosylation by reducing or eliminating the α 1,6 bond-related enzyme. Hanai et al also describe cell lines which have a low enzyme activity for adding fucose to the N-acetylglucosamine that binds to the Fc region of the antibody or does not have the enzyme activity, for example the rat myeloma cell line YB2 / 0 (ATCC CRL 1662). PCT Publication WO 03 / 035835 by Presta describes a variant CHO cell line, Lec13 cells, with reduced ability to attach fucose to Asn(297)-linked carbohydrates, also resulting in hypofucosylation of antibodies expressed in that host cell (see also Shields, R. L. et al. (2002) J. Biol. Chem. 277.26733-26740). PCT Publication WO 99 / 54342 by Umana et al. describes cell lines engineered to express glycoprotein-modifying glycosyl transferases (e.g., β(1,4)-N-acetylglucosaminyltransferase III (GnTIII)) such that antibodies expressed in the engineered cell lines exhibit increased bisecting GlcNac structures which results in increased ADCC activity of the antibodies (see also Umana et al. (1999) Nat. Biotech. 17:176-180). Alternatively, the fucose residues of the antibody may be cleaved off using a fucosidase enzyme. For example, the fucosidase u-L- fucosidase removes fucosyl residues from antibodies (Tarentino, A L. et al (1975) Biochem.14:5516-23). Another modification of fusion proteins herein that is contemplated by the invention is pegylation or the addition of other water-soluble moieties, typically polymers, e.g., in order to enhance half-life. An Fc region can be pegylated to, for example, increase the biological (e.g., serum) half-life of the fusion protein. To pegylate a fusion protein, the fusion protein, or fragment thereof, typically is reacted with polyethylene glycol (PEG), such as a reactive ester or aldehyde derivative of PEG, under conditions in which one or more PEG groups become attached to the fusion protein or fragment. Preferably, the pegylation is carried out via an acylation reaction or an alkylation reaction with a reactive PEG molecule (or an analogous reactive water-soluble polymer) As used herein, the term “polyethylene glycol” is intended to encompass any of the forms of PEGDocket No. WRENCH-002 / WO01 that have been used to derivatize other proteins, such as mono (C1-C10) alkoxy- or aryloxy-polyethylene glycol or polyethylene glycol-maleimide. In certain embodiments, the fusion protein to be pegylated is an aglycosylated fusion protein. Methods for pegylating proteins are known in the art and can be applied to the fusion proteins according to at least some embodiments of the invention. See for example, EP 0154316 by Nishimura et al. and EP 0401384 by Ishikawa et al. (ii) Anti-DcR3-Fc Fusion Proteins The present disclosure also provides single-domain anti-DcR3 antibodies (e.g., VHHs) which are fused with Fc regions to create new bifunctional antibody formats. This fusion strategy combines the antigen-binding specificity of single domain antibodies with the diverse effector functions typically mediated by the Fc region of conventional antibodies. The fusion process can be achieved through various molecular biology techniques, including genetic engineering and recombinant DNA technology. One approach involves genetically linking the coding sequences of VHHs and Fc regions in-frame, enabling their expression as a single polypeptide chain. Alternatively, fusion proteins can be constructed through chemical conjugation or bioconjugation methods, where VHHs and Fc regions are chemically linked post-translationally. These fusion constructs can be designed to optimize the spatial orientation and functional integrity of both domains, ensuring the retention of their individual properties while facilitating synergistic interactions. As described herein, VHHs are defined by their single-variable domain structure, which sets them apart from conventional antibodies characterized by two heavy chains and two light chains. This single-domain architecture imparts unique advantages to VHHs, including their diminutive size, exceptional stability, solubility, and remarkable specificity and affinity for target antigens. The inventor has recognized and appreciated that VHHs are particularly useful as an anti-DcR3 antibody when fused to an Fc region. Such single-domain antibodies are easier to produce, in part due to a reduction in complexity and lack of unintended VH / VL pairing. Further, up to four VHHs may be fused directly to an Fc, but only two Fabs for IgG. Increasing the possible valency from bivalent to tetravalent is particularly beneficial as a single molecule can bind to multiple DcR3 molecules (thus removing it from circulation) or bind to single DcR3 molecules at multiple sites, increasing the displacement of FasL, TL1A, and LIGHT and making these ligands more readily accessible. Another advantage of fusion proteins of the disclosure is the property of biparatopic binding to DcR3. As will be described in more detail below and supported by the Examples, a first VHH that binds to DcR3 and displaces DcR3 ligands and a second VHH that binds to DcR3 but does not displace DcR3 ligands can be combined to create a single molecule that will both bind to DcR3 with high precision and simultaneously increase circulating levels of FasL, LIGHT, and TL1A. In one aspect, provided herein is a VHH-Fc fusion protein which may also be referred to as a “single domain anti-DcR3-Fc fusion protein” or a “VHH-Fc fusion protein”. Such a VHH-Fc fusion protein includesDocket No. WRENCH-002 / WO01 a first monomer comprising a single domain anti-DcR3 antibody and a first Fc domain, and a second monomer comprising a second Fc domain. In some embodiments, a VHH-Fc fusion protein comprises (a) a first monomer comprising from N- terminus to C-terminus: a single domain anti-DcR3 antibody as described herein, and a first Fc domain; and (b) a second monomer comprising a second Fc domain. In some embodiments, the VHH-Fc fusion protein comprises one or more single domain anti-DcR3 antibodies, such as 1, 2, 3, or 4 single domain anti-DcR3 antibodies. In some embodiments, the VHH-Fc fusion protein may comprise one or more single domain anti- DcR3 antibodies, and one or more single domain antibodies that do not bind to DcR3. Increasing the number of antibodies per fusion protein results in an increase in the inhibitory ratio between target and fusion protein by increasing the number of relevant binding domains. In some embodiments, the one or more single domain antibodies that do not bind to DcR3 bind to a tumor-associated antigen (TAA). In some embodiments, the TAA can be any TAA as described herein, e.g., those TAAs with regards to embodiments of multispecific binding proteins as discussed herein. In some embodiments, the VHH selectively binds to an immune checkpoint such as Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), Programmed cell death protein 1 (PD-1), Programmed death-ligand 1 (PD-L1), Lymphocyte-activation gene 3 (LAG-3), T cell immunoglobulin and mucin-domain containing-3 (TIM-3), T cell immunoglobulin and ITIM domain (TIGIT), V-domain Ig suppressor of T cell activation (VISTA), IL- 18BP, etc.). In some embodiments, a VHH-Fc fusion protein can bind to two or more distinct epitopes of DcR3 and yield synergistic effects. In some embodiments, a VHH-Fc fusion protein can bind to a first epitope of DcR3 that inhibits DcR3 from interacting with its ligands, and can bind to a second epitope of DcR3 that does not inhibit DcR3 from interacting with its ligands. In some embodiments, a VHH-Fc fusion protein comprises (a) a first monomer comprising from N-terminus to C-terminus: a first single domain anti-DcR3 antibody that binds to DcR3 and inhibits DcR3 from binding with its ligands, and a first Fc domain; and (b) a second monomer comprising from N-terminus to C-terminus: a second single domain anti-DcR3 antibody that binds to DcR3 but does not inhibit DcR3 from binding with its ligands, and a second Fc domain. As supported by the Examples, this property of biparatopic binding at two distinct epitopes (a ligand-competing epitope, and a non- ligand binding competing epitope) can exhibit higher affinity to DcR3 while simultaneously increasing the availability of the DcR3 ligands FasL, LIGHT, and TL1A. In one embodiment, a VHH-Fc fusion protein comprises a first VHH and a second VHH, wherein the first and second VHH are paired according to Table 4. In such embodiments, the first VHH and second VHH can each comprise a CDR-H1, CDR-H2, and CDR-H3, wherein the CDR-H1, CDR-H2, and CDR-H3 for the first VHH and second VHH are selected from Table 10 and paired according to Table 4. In such embodiments, the first VHH and second VHH can each comprise a CDR-H1, CDR-H2, and CDR-H3, wherein the CDR-H1,Docket No. WRENCH-002 / WO01 CDR-H2, and CDR-H3 have at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the CDR-H1, CDR-H2, and CDR-H3 selected from Table 10 and paired according to Table 4. In one embodiment, a VHH-Fc fusion protein described herein comprises an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to SEQ ID Nos: 301-306. In some embodiments, the amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions relative to a reference sequence, but retains the ability to bind to DcR3 as of the unmodified sequence. In some embodiments, a total of from 1 to 10 amino acids are substituted, inserted and / or deleted. In some embodiments, substitutions, insertions, or deletions occur in regions outside the complementarity-determining region (CDR). In some embodiments, the VHH-Fc fusion protein restores the activation of anti-cancer immune cells. In some embodiments, the VHH-Fc fusion protein inhibit DcR3 from binding with its ligands. In some embodiments, the VHH-Fc fusion protein restores the apoptotic activity of FasL towards cancer cells. In some embodiments, the VHH-Fc fusion protein potentiates the pro-apoptotic and / or cytotoxic effects of chemotherapy. In some embodiments, the VHH-Fc fusion protein restores the activation of TL1A, LIGHT, and FasL that were inhibited by DcR3. In some embodiments, the VHH-Fc fusion protein blocks one or more of the DcR3:FasL interaction, DcR3:TL1A interaction, and DcR3:LIGHT interaction. (1) WB52 (WB30 + WB32 fusion protein) In one aspect, the present disclosure provides a biparatopic VHH-Fc fusion protein that comprises (a) a first monomer comprising from N-terminus to C-terminus: a first single domain anti-DcR3 antibody having an amino acid sequence of SEQ ID NO: 202, a second single domain anti-DcR3 antibody having an amino acid sequence of SEQ ID NO: 204 and a first Fc domain; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein that comprises (a) a first monomer comprising from N-terminus to C-terminus: a first single domain anti-DcR3 antibody having an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 202, a second single domain anti-DcR3 antibody having an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 204, and an Fc domain; and (b) a second monomer identical to monomer (a), where monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein that comprises an amino acid sequence of SEQ ID NO: 302. In one aspect, the present disclosure provides a VHH-Fc fusion protein thatDocket No. WRENCH-002 / WO01 comprises an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 302. In one aspect, the present disclosure provides a VHH-Fc fusion protein comprising a first single domain DcR3 binding protein or antibody comprising: (a) a first monomer comprising from N-terminus to C-terminus: a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 2, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 21, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 40, a second single domain DcR3 binding protein or antibody comprising a CDR-H1, a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 4, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 23, and the CDR- H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 42, and an Fc domain; wherein the numbering is according to Kabat; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein comprising: (a) a first monomer comprising from N-terminus to C-terminus: a first single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 59, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 78, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 96, a second single domain DcR3 binding protein or antibody comprising a CDR-H1, a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 61, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 80, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 99, and an Fc domain; wherein the numbering is according to Chothia; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein comprising: (a) a first monomer comprising from N-terminus to C-terminus: a first single domain DcR3 binding protein or antibody comprisingDocket No. WRENCH-002 / WO01 a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 116, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 135, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 154, a second single domain DcR3 binding protein or antibody comprising a CDR-H1, a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 118, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 137, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 156, and an Fc domain; wherein the numbering is according to IMGT; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In some aspects, the fusion protein is biparatopic. In some aspects, the first single domain anti-DcR3 antibody binds to DcR3 but does not inhibit DcR3 from interacting with its ligands. In some aspects, the second single domain anti-DcR3 antibody binds to DcR3 and inhibits DcR3 from interacting with its ligands. In some aspects, the first and second antibodies bind to DcR3 at a different epitope. In some aspects, the first single domain anti-DcR3 antibody is clone WB32 with a CDR-H1, CDR-H2, and CDR-H3 sequence selected from Table 10. In some aspects, the second single domain anti-DcR3 antibody is clone WB30 with a CDR-H1, CDR- H2, and CDR-H3 sequence selected from Table 10. (2) WB53 (WB31 + WB32 fusion protein) In one aspect, the present disclosure provides a biparatopic VHH-Fc fusion protein that comprises (a) a first monomer comprising from N-terminus to C-terminus: a first single domain anti-DcR3 antibody having an amino acid sequence of SEQ ID NO: 203, a second single domain anti-DcR3 antibody having an amino acid sequence of SEQ ID NO: 204 and a first Fc domain; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein that comprises (a) a first monomer comprising from N-terminus to C-terminus: a first single domain anti-DcR3 antibody having an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 203, a second single domain anti-DcR3 antibody having an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 204, and an Fc domain; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein.Docket No. WRENCH-002 / WO01 In one aspect, the present disclosure provides a VHH-Fc fusion protein comprises an amino acid sequence of SEQ ID NO: 302. In one aspect, the present disclosure provides a VHH-Fc fusion protein that comprises an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 302. In one aspect, the present disclosure provides a VHH-Fc fusion protein comprising (a) a first monomer comprising from N-terminus to C-terminus: a first single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 3, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 22, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 41, a second single domain DcR3 binding protein or antibody comprising a CDR-H1, a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 4, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 23, and the CDR- H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 42, and an Fc domain; wherein the numbering is according to Kabat; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein comprising (a) a first monomer comprising from N-terminus to C-terminus: a first single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 60, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 79, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 98, a second single domain DcR3 binding protein or antibody comprising a CDR-H1, a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 61, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 80, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 99, and an Fc domain; wherein the numbering is according to Chothia; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein.Docket No. WRENCH-002 / WO01 In one aspect, the present disclosure provides a VHH-Fc fusion protein comprising (a) a first monomer comprising from N-terminus to C-terminus: a first single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 117, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 136, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 155, a second single domain DcR3 binding protein or antibody comprising a CDR-H1, a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 118, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 137, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 156, and an Fc domain; wherein the numbering is according to IMGT; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In some aspects, the fusion protein is biparatopic. In some aspects, the first single domain anti-DcR3 antibody binds to DcR3 and inhibits DcR3 from interacting with its ligands. In some aspects, the second single domain anti-DcR3 antibody binds to DcR3 but does not inhibit DcR3 from interacting with its ligands. In some aspects, the first and second antibodies bind to DcR3 at a different epitope. In some aspects, the first single domain anti-DcR3 antibody is clone WB31 with a CDR-H1, CDR-H2, and CDR-H3 sequence selected from Table 10. In some aspects, the second single domain anti-DcR3 antibody is clone WB32 with a CDR-H1, CDR- H2, and CDR-H3 sequence selected from Table 10. (3) WB54 (WB32 + WB30 fusion protein) In one aspect, the present disclosure provides a biparatopic VHH-Fc fusion protein that comprises (a) a first monomer comprising from N-terminus to C-terminus: a first single domain anti-DcR3 antibody having an amino acid sequence of SEQ ID NO: 204, a second single domain anti-DcR3 antibody having an amino acid sequence of SEQ ID NO: 202 and an Fc domain; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein that comprises (a) a first monomer comprising from N-terminus to C-terminus: a first single domain anti-DcR3 antibody having an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 204,a second single domain anti-DcR3 antibody having an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 202, and an FcDocket No. WRENCH-002 / WO01 domain; and (b) a second monomer identical to monomer (a), where monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein that comprises an amino acid sequence of SEQ ID NO: 303. In one aspect, the present disclosure provides a VHH-Fc fusion protein that comprises an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 303. In one aspect, the present disclosure provides a VHH-Fc fusion protein comprising (a) a first monomer comprising from N-terminus to C-terminus: a first single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 4, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 23, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 42, a second single domain DcR3 binding protein or antibody comprising a CDR-H1, a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 2, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 21, and the CDR- H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 40, and an Fc domain; wherein the numbering is according to Kabat; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein comprising (a) a first monomer comprising from N-terminus to C-terminus: a first single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 61, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 80, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 99, a second single domain DcR3 binding protein or antibody comprising a CDR-H1, a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 59, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 78, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 96, and an Fc domain; wherein the numbering is according to Chothia; and (b)Docket No. WRENCH-002 / WO01 a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein comprising (a) a first monomer comprising from N-terminus to C-terminus: a first single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 118, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 137, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 156, a second single domain DcR3 binding protein or antibody comprising a CDR-H1, a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 116, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 135, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 154, and an Fc domain; wherein the numbering is according to IMGT; and (b) a second monomer identical to monomer (a); where monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In some aspects, the fusion protein is biparatopic. In some aspects, the first single domain anti-DcR3 antibody binds to DcR3 but does not inhibit DcR3 from interacting with its ligands. In some aspects, the second single domain anti-DcR3 antibody binds to DcR3 and inhibits DcR3 from interacting with its ligands. In some aspects, the first and second antibodies bind to DcR3 at a different epitope. In some aspects, the first single domain anti-DcR3 antibody is clone WB32 with a CDR-H1, CDR-H2, and CDR-H3 sequence selected from Table 10. In some aspects, the second single domain anti-DcR3 antibody is clone WB30 with a CDR-H1, CDR- H2, and CDR-H3 sequence selected from Table 10. (4) WB55 (WB32 + WB31 fusion protein) In one aspect, the present disclosure provides a biparatopic VHH-Fc fusion protein that comprises (a) a first monomer comprising from N-terminus to C-terminus: a first single domain anti-DcR3 antibody having an amino acid sequence of SEQ ID NO: 204, a second single domain anti-DcR3 antibody having an amino acid sequence of SEQ ID NO: 203 and a first Fc domain; and (b) a second monomer identical to monomer (a), where monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein that comprises (a) a first monomer comprising from N-terminus to C-terminus: a first single domain anti-DcR3 antibody having an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identicalDocket No. WRENCH-002 / WO01 to SEQ ID NO: 204, and a first Fc domain; a second single domain anti-DcR3 antibody having an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 203, and an Fc domain; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein comprises an amino acid sequence of SEQ ID NO: 304. In one aspect, the present disclosure provides a VHH-Fc fusion protein that comprises an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 304. In one aspect, the present disclosure provides a VHH-Fc fusion protein comprising (a) a first monomer comprising from N-terminus to C-terminus: a first single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 4, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 23, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 42, a second single domain DcR3 binding protein or antibody comprising a CDR-H1, a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 3, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 22, and the CDR- H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 41, and an Fc domain; wherein the numbering is according to Kabat; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein comprising (a) a first monomer comprising from N-terminus to C-terminus: a first single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 61, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 80, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 99, a second single domain DcR3 binding protein or antibody comprising a CDR-H1, a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 60, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 79, and theDocket No. WRENCH-002 / WO01 CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 98, and an Fc domain; wherein the numbering is according to Chothia; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein comprising (a) a first monomer comprising from N-terminus to C-terminus: a first single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 118, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 137, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 156, a second monomer comprising from N-terminus to C-terminus: a second single domain DcR3 binding protein or antibody comprising a CDR-H1, a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 117, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 136, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 155, and an Fc domain; wherein the numbering is according to IMGT; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In some aspects, the fusion protein is biparatopic. In some aspects, the first single domain anti-DcR3 antibody binds to DcR3 but does not inhibit DcR3 from interacting with its ligands. In some aspects, the second single domain anti-DcR3 antibody binds to DcR3 and inhibits DcR3 from interacting with its ligands. In some aspects, the first and second antibodies bind to DcR3 at a different epitope. In some aspects, the first single domain anti-DcR3 antibody is clone WB32 with a CDR-H1, CDR-H2, and CDR-H3 sequence selected from Table 10. In some aspects, the second single domain anti-DcR3 antibody is clone WB31 with a CDR-H1, CDR- H2, and CDR-H3 sequence selected from Table 10. (5) WB72 (WB30 + WB31 fusion protein) In one aspect, the present disclosure provides a biparatopic VHH-Fc fusion protein that comprises (a) a first monomer comprising from N-terminus to C-terminus: a first single domain anti-DcR3 antibody having an amino acid sequence of SEQ ID NO: 202, a second single domain anti-DcR3 antibody having an amino acid sequence of SEQ ID NO: 203 and an Fc domain; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein.Docket No. WRENCH-002 / WO01 In one aspect, the present disclosure provides a VHH-Fc fusion protein that comprises (a) a first monomer comprising from N-terminus to C-terminus: a first single domain anti-DcR3 antibody having an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 202, a second single domain anti-DcR3 antibody having an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 203, and an Fc domain; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein that comprises an amino acid sequence of SEQ ID NO: 305. In one aspect, the present disclosure provides a VHH-Fc fusion protein that comprises an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 305. In one aspect, the present disclosure provides a VHH-Fc fusion protein comprising (a) a first monomer comprising from N-terminus to C-terminus: a first single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 2, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 21, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 40, a second single domain DcR3 binding protein or antibody comprising a CDR-H1, a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 3, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 22, and the CDR- H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 41, and an Fc domain; wherein the numbering is according to Kabat; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein comprising (a) a first monomer comprising from N-terminus to C-terminus: a first single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 59, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 78, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 96, a second single domain DcR3 binding protein or antibody comprising a CDR-H1, a CDR-H2, andDocket No. WRENCH-002 / WO01 a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 60, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 79, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 98, and an Fc domain; wherein the numbering is according to Chothia; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein comprising (a) a first monomer comprising from N-terminus to C-terminus: a first single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 116, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 135, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 154,a second single domain DcR3 binding protein or antibody comprising a CDR-H1, a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 117, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 136, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 155, and an Fc domain; wherein the numbering is according to IMGT; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In some aspects, the fusion protein is biparatopic. In some aspects, the first single domain anti-DcR3 antibody binds to DcR3 and inhibits DcR3 from interacting with its ligands. In some aspects, the second single domain anti-DcR3 antibody binds to DcR3 and inhibits DcR3 from interacting with its ligands. In some aspects, the first and second antibodies bind to DcR3 at a different epitope. In some aspects, the first single domain anti- DcR3 antibody is clone WB30 with a CDR-H1, CDR-H2, and CDR-H3 sequence selected from Table 10. In some aspects, the second single domain anti-DcR3 antibody is clone WB31 with a CDR-H1, CDR-H2, and CDR-H3 sequence selected from Table 10. (6) WB73 (WB31 + WB30 fusion protein) In one aspect, the present disclosure provides a biparatopic VHH-Fc fusion protein that comprises (a) a first monomer comprising from N-terminus to C-terminus: a first single domain anti-DcR3 antibody having an amino acid sequence of SEQ ID NO: 203, a second single domain anti-DcR3 antibody having an amino acidDocket No. WRENCH-002 / WO01 sequence of SEQ ID NO: 202 and an Fc domain; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein that comprises (a) a first monomer comprising from N-terminus to C-terminus: a first single domain anti-DcR3 antibody having an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 203, a second single domain anti-DcR3 antibody having an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 202, and an Fc domain; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein comprises an amino acid sequence of SEQ ID NO: 306. In one aspect, the present disclosure provides a VHH-Fc fusion protein that comprises an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 306. In one aspect, the present disclosure provides a VHH-Fc fusion protein comprising (a) a first monomer comprising from N-terminus to C-terminus: a first single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 3, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 22, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 41, a second single domain DcR3 binding protein or antibody comprising a CDR-H1, a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 2, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 21, and the CDR- H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 40, and an Fc domain; wherein the numbering is according to Kabat; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein comprising (a) a first monomer comprising from N-terminus to C-terminus: a first single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 60, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 79, and the CDR-H3 has an aminoDocket No. WRENCH-002 / WO01 acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 98, a second single domain DcR3 binding protein or antibody comprising a CDR-H1, a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 59, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 78, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 96, and an Fc domain; wherein the numbering is according to Chothia; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In one aspect, the present disclosure provides a VHH-Fc fusion protein comprising (a) a first monomer comprising from N-terminus to C-terminus: a first single domain DcR3 binding protein or antibody comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 117, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 136, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 155, a second single domain DcR3 binding protein or antibody comprising a CDR-H1, a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 116, the CDR-H2 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 135, and the CDR-H3 has an amino acid sequence is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 154, and an Fc domain; wherein the numbering is according to IMGT; and (b) a second monomer identical to monomer (a); wherein monomers (a) and (b) interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein. In some aspects, the fusion protein is biparatopic. In some aspects, the first single domain anti-DcR3 antibody binds to DcR3 and inhibits DcR3 from interacting with its ligands. In some aspects, the second single domain anti-DcR3 antibody binds to DcR3 and inhibits DcR3 from interacting with its ligands. In some aspects, the first and second antibodies bind to DcR3 at a different epitope. In some aspects, the first single domain anti- DcR3 antibody is clone WB31 with a CDR-H1, CDR-H2, and CDR-H3 sequence selected from Table 10. In some aspects, the second single domain anti-DcR3 antibody is clone WB30 with a CDR-H1, CDR-H2, and CDR-H3 sequence selected from Table 10. (iii) Domain Linkers In some embodiments of fusion proteins according to the disclosure, a single domain anti-DcR3 antibody is covalently attached to an Fc domain by a linker (e.g., (VHH)1-L-Fc). In some embodiments, twoDocket No. WRENCH-002 / WO01 single domain anti-DcR3 antibodies are covalently attached to an Fc domain by a linker (e.g., (VHH)1-L-Fc-L- (VHH)1; or (VHH)1-L-(VHH)1-L-Fc; or (VHH)1-L-Fc-L-(VHH)1. In some embodiments, the linker is a “domain linker”. While any suitable linker can be used, many embodiments utilize a glycine-serine polymer, including for example (GS)n, (GGS)n, (GSGGS)n, (GGGGS)n, and (GGGS)n, where n is an integer of at least 0 (and generally from 0 to 1 to 2 to 3 to 4 to 5), as well as any peptide sequence that allows for recombinant attachment of the two domains with sufficient length and flexibility to allow each domain to retain its biological function. In certain cases, useful linkers include (GGGGS)1 or (GGGGS)1. In some cases, charged domain linkers can be used. 6. Nucleic Acid Compositions Provided herein are nucleic acid molecules encoding a single domain DcR3 binding protein, a multispecific binding protein, or a fusion protein according to the disclosure. In some embodiments, the nucleic acid molecules are provided as a DNA sequence. In other embodiments, nucleic acid molecules are provided as a messenger RNA transcript. Nucleic acid molecules can be prepared using known methods. In certain embodiments, , a single domain DcR3 binding protein, multispecific binding protein, or a fusion protein can be encoded by a nucleic acid sequence. Such a nucleic acid sequence can be included within an appropriate vector for expression and secretion using recombinant and / or synthetic techniques. With regard to a multispecific binding protein described herein, it will be understood that each of the first and the second (and, optionally, a third and / or fourth) domain can be encoded by nucleic acid sequences on the same vector or different vectors. If a linker is to be present in a multispecific protein, it can be encoded by a nucleic acid sequence and be operably linked to the first domain or the second domain (and optionally, a third and / or fourth domain). The nucleic acid sequences can be operably linked to one or more of the following: a signal peptide, a promoter, a transcription terminator, a polyA sequence, etc. for appropriate expression in a host cell. Other domains (e.g., half-life extension domains), can also be incorporated into one or more nucleic acid sequence(s) for expression. Depending on the vector system and host cell utilized, any number of suitable transcription and translation elements, including constitutive and inducible promoters, may be used. The promoter can be selected such that it drives the expression of the polynucleotide in the respective host cell. A nucleic acid molecule encoding a binding protein of the present disclosure can be recombined with vector DNA in accordance with conventional techniques, including blunt-ended or staggered-ended termini for ligation, restriction enzyme digestion to provide appropriate termini, filling in of cohesive ends as appropriate, alkaline phosphatase treatment to avoid undesirable joining, and ligation with appropriate ligases. Techniques for such manipulations are disclosed, e.g., by Maniatis et al., Molecular Cloning, Lab. Manual (Cold Spring Harbor Lab. Press, NY, 1982 and 1989), and Ausubel, 1987, 1993, and can be used to construct nucleic acid sequences which encode a binding protein. Accordingly, the disclosure provides for a vector comprising theDocket No. WRENCH-002 / WO01 isolated nucleic acids set forth herein. Vectors of particular interest include plasmids, phagemids, phage derivatives, viruses (e.g., retroviruses, adenoviruses, adeno-associated viruses, herpes viruses, lentiviruses, and the like), and cosmids. Once isolated, a polynucleotide sequence may be placed into an expression vector, which is then transfected into a host cell such as, for example, an E. coli cell, a simian COS cell, a human embryonic kidney 293 cell (e.g., 293E cell), a Chinese hamster ovary (CHO) cell, or a myeloma cell that does not otherwise produce a binding protein, to obtain the synthesis of binding proteins in the recombinant host cells. Recombinant production of binding proteins is well known in the art. Expression control sequences (e.g., regulatory sequences) refer to DNA sequences necessary for the expression of an operably linked coding sequence in a particular host organism. The control sequences that are suitable for prokaryotes, for example, include a promoter, optionally an operator sequence, and a ribosome binding site. Eukaryotic cells are known to optionally utilize promoters, polyadenylation signals, and / or enhancers, if needed. A variety of expression vector / host systems may be utilized to contain and express the polynucleotide encoding the single domain DcR3 binding protein, multispecific binding protein, or fusion protein. Examples of expression vectors for expression in E.coli are pSKK (Le Gall et al., J Immunol Methods. (2004) 285(1):111- 27) or pcDNA5 (Invitrogen) for expression in mammalian cells, PICHIAPINK™ Yeast Expression Systems (Invitrogen), BACUVANCE™ Baculovirus Expression System (GenScript), etc. Thus, the single domain DcR3 binding proteins, multispecific binding proteins, or fusion proteins as described herein, in some embodiments, are produced by introducing a vector encoding the protein as described above into a host cell and culturing said host cell under conditions whereby the protein domains are expressed, and which may be isolated and, optionally, further purified. Any of the DcR3 binding proteins, multispecific binding proteins, fusion proteins, or nucleic acid molecules encoding such proteins described herein can be non-naturally occurring (e.g., synthetic, recombinant, isolated, substantially purified, etc.). In one instance, the binding protein or nucleic acid molecule is synthetic. In another instance, the binding protein or nucleic acid molecule is recombinant. In another instance, the binding protein or nucleic acid molecule is isolated. In another instance, the binding protein or nucleic acid molecule is substantially purified. 7. Treatments Once made, the subject single-domain anti-DcR3 antibodies, multispecific binding proteins, and fusion proteins find use in a number of oncology applications, such as by promoting DcR3-related immune cell activation and cancer cell apoptosis (e.g., FasL, TL1A, and LIGHT are no longer suppressed) and proliferation. Accordingly, the subject single domain anti-DcR3 antibodies, multispecific binding proteins, and Fc fusion proteins find use in the treatment of these cancers. Such proteins, antibodies, binding proteins, and fusion proteins may be administered together as a single treatment, or separately.Docket No. WRENCH-002 / WO01 (i) Formulations for In Vivo Administration Provided herein is a pharmaceutical composition comprising (a) a single domain DcR3 binding protein, a multispecific binding protein, or an Fc-fusion protein, a nucleic acid molecule encoding the protein, a vector, or a host cell described herein, and (b) a pharmaceutically acceptable carrier. The term “pharmaceutically acceptable” refers to approved or approvable by a regulatory agency of the Federal or a state government or listed in the U.S. Pharmacopeia (U.S.P.) or other generally recognized pharmacopeia for use in animals, including humans. A “pharmaceutically acceptable carrier” refers to a carrier that can be administered to a subject, together with an active agent, and which does not destroy the pharmacological activity thereof and is nontoxic when administered in doses sufficient to deliver a therapeutic amount of the agent. Formulations of the anti-DcR3 binding proteins, multi-specific binding proteins, and Fc fusion proteins used in accordance with the present invention may be prepared for storage by mixing a protein having the desired degree of purity with optional pharmaceutically acceptable carriers, excipients or stabilizers (as generally outlined in Remington’s Pharmaceutical Sciences 16thedition, Osol, A. Ed.

[1980] ), in the form of lyophilized formulations or aqueous solutions. Acceptable carriers, buffers, excipients, or stabilizers are nontoxic to recipients at the dosages and concentrations employed, and include 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 TWEEN™, PLURONICS™ or polyethylene glycol (PEG). (ii) Therapeutic Uses The anti-DcR3 antibodies, multispecific binding proteins, and fusion proteins described herein find use in treating patients, such as human subjects, generally with a condition associated with DcR3 or free DcR3 ligand levels. The term “treatment” as used herein, refers to both therapeutic treatment and prophylactic or preventative measures, which in this example relates to treatment of cancer. Those in need of treatment include those already with cancer as well as those in which the cancer is to be prevented. Hence, the mammal to be treated herein may have been diagnosed as having cancer or may be predisposed or susceptible to the cancer. As used herein the term “treating” refers to preventing, delaying the onset of, curing, reversing, attenuating, alleviating, minimizing, suppressing, halting the deleterious effects or stabilizing of discernible symptoms ofDocket No. WRENCH-002 / WO01 the above-described cancerous diseases, disorders or conditions. It also includes managing cancer as described above. By “manage” it is meant reducing the severity of the disease, reducing the frequency of episodes of the disease, reducing the duration of such episodes, reducing the severity of such episodes, slowing / reducing cancer cell growth or proliferation, slowing progression of at least one symptom, amelioration of at least one measurable physical parameter and the like. For example, immunostimulatory anti-DcR3 immune molecules should promote T cells, Myeloid cells, Dendritic cells, or cytokine immunity against target cells, e.g., cancer, infected or pathogen cells and thereby treat cancer or infectious diseases by depleting the cells involved in the disease condition. The anti-DcR3 antibodies, multispecific binding proteins, and fusion proteins as disclosed herein are provided in therapeutically effective dosages. A “therapeutically effective dosage” of an anti-DcR3 immune molecule according to at least some embodiments of the present invention preferably results in a decrease in severity of disease symptoms, an increase in frequency and duration of disease symptom-free periods, an increase in lifespan, disease remission, or a prevention or reduction of impairment or disability due to the disease affliction. For example, for the treatment of DcR3 positive tumors, a “therapeutically effective dosage” preferably inhibits cell growth or tumor growth by at least about 20%, more preferably by at least about 40%, even more preferably by at least about 60%, and still more preferably by at least about 80% relative to untreated subjects. The ability of a compound to inhibit tumor growth can be evaluated in an animal model system predictive of efficacy in human tumors. Alternatively, this property of a composition can be evaluated by examining the ability of the compound to inhibit, such as inhibition in vitro by assays known to the skilled practitioner. A therapeutically effective amount of a therapeutic compound can decrease tumor size, or otherwise ameliorate symptoms in a subject. One of ordinary skill in the art would be able to determine a therapeutically effective amount based on such factors as the subject’s size, the severity of the subject’s symptoms, and the particular composition or route of administration selected. (iii) Cancer Treatment The anti-DcR3 antibodies, multispecific binding proteins, and fusion proteins as disclosed herein, alone or in combination with other therapeutic agents, find particular use in the treatment of cancer. In general, embodiments of the disclosure are immunomodulatory, in that rather than directly attack cancerous cells, the anti-DcR3 antibodies, multispecific proteins, and fusion proteins of the disclosure stimulate the immune system, generally by inhibiting the action of DcR3 and promoting increased levels of DcR3 ligands (TL1A, LIGHT, FasL). Thus, unlike tumor-targeted therapies, which are aimed at inhibiting molecular pathways that are crucial for tumor growth and development, and / or depleting tumor cells, cancer immunotherapy is aimed to stimulate the patient’s own immune system to eliminate cancer cells, providing long-lived tumor destruction. Various approaches can be used in cancer immunotherapy, among them are therapeutic cancer vaccines toDocket No. WRENCH-002 / WO01 induce tumor-specific T cell responses, and immunostimulatory antibodies (i.e., antagonists of inhibitory receptors = immune checkpoints) to remove immunosuppressive pathways. Clinical responses with targeted therapy or conventional anti-cancer therapies tend to be transient as cancer cells develop resistance, and tumor recurrence takes place. However, the clinical use of cancer immunotherapy in the past few years has shown that this type of therapy can have durable clinical responses, showing dramatic impact on long term survival. However, although responses are long term, only a small number of patients respond (as opposed to conventional or targeted therapy, where a large number of patients respond, but responses are transient). By the time a tumor is detected clinically, it has already evaded the immune-defense system by acquiring immunoresistant and immunosuppressive properties and creating an immunosuppressive tumor microenvironment through various mechanisms and a variety of immune cells. Accordingly, the anti-DcR3 antibodies, multispecific binding proteins, and fusion proteins as disclosed herein are useful in treating cancer. Due to the nature of an immune-oncology mechanism of action, DcR3 does not necessarily need to be overexpressed on or correlated with a particular cancer type; that is, the goal is to have the anti-DcR3 antibodies, multispecific binding proteins, and fusion proteins de-suppress T cells, Myeloid cells and Dendritic cells activation, such that the immune system will go after the cancer. “Cancer,” as used herein, refers broadly to any neoplastic disease (whether invasive or metastatic) characterized by abnormal and uncontrolled cell division causing malignant growth or tumor (e.g., unregulated cell growth). The term “cancer” or “cancerous” as used herein should be understood to encompass any neoplastic disease (whether invasive, noninvasive or metastatic) which is characterized by abnormal and uncontrolled cell division causing malignant growth or tumor, non-limiting examples of which are described herein. This includes any physiological condition in mammals that is typically characterized by unregulated cell growth. “Cancer therapy” herein refers to any method that prevents or treats cancer or ameliorates one or more of the symptoms of cancer. Typically, such therapies will comprise administration of immunostimulatory anti- DcR3 antibodies (including antigen-binding fragments), multispecific binding proteins, or fusion proteins either alone or in combination with chemotherapy or radiotherapy or other biologics and for enhancing the activity thereof, i.e., in individuals wherein expression of DcR3 suppresses antitumor responses and the efficacy of chemotherapy or radiotherapy or biologic efficacy. The anti-DcR3 antibodies, multi-specific proteins, and fusion proteins of the disclosure, as a monotherapy or as part of a combination therapy as described herein, can be used in the treatment of solid tumors (including, for example, cancers of the lung, liver, breast, brain, GI tract) and blood cancers (including for example, leukemia and preleukemic disorders, lymphoma, plasma cell disorders) carcinoma, lymphoma, blastoma, sarcoma, and leukemia or lymphoid malignancies. In some embodiments, the cancer is early. In someDocket No. WRENCH-002 / WO01 embodiments, the cancer is advanced (including metastatic) In some embodiments, the cancers amenable for treatment of the invention include cancers that express DcR3 and further include non-metastatic or non- invasive, as well as invasive or metastatic cancers, including cancers where DcR3 expression by immune, stromal, or diseased cells suppresses antitumor responses and anti-invasive immune responses. In some embodiments, the anti-DcR3 antibodies can be used for the treatment of vascularized tumors. In some embodiments, the cancer for treatment using the anti-DcR3 antibodies of the present invention includes carcinoma, lymphoma, sarcoma, and / or leukemia. In some embodiments, the cancer for treatment using the anti-DcR3 antibodies of the present invention includes vascularized tumors, melanoma, nonmelanoma skin cancer (squamous and basal cell carcinoma), mesothelioma, squamous cell cancer, lung cancer, small-cell lung cancer, non-small cell lung cancer, neuroendocrine lung cancer (including pleural mesothelioma, neuroendocrine lung carcinoma), NSCL (large cell), NSCLC large cell adenocarcinoma, non-small cell lung carcinoma (NSCLC), NSCLC squamous cell, soft-tissue sarcoma, Kaposi’s sarcoma, adenocarcinoma of the lung, squamous carcinoma of the lung, NSCLC with PDLI >=50% TPS, neuroendocrine lung carcinoma, atypical carcinoid lung cancer, cancer of the peritoneum, esophageal cancer, hepatocellular cancer, liver cancer (including HCC), gastric cancer, stomach cancer (including gastrointestinal cancer), pancreatic cancer, glioblastoma, cervical cancer, ovarian cancer, urothelial cancer, bladder cancer, hepatoma, glioma, brain cancer (as well as edema, such as that associated with brain tumors), breast cancer (including, for example, triple negative breast cancer), testis cancer, testicular germ cell tumors, colon cancer, colorectal cancer (CRC), colorectal cancer MSS (MSS-CRC); refractory MSS colorectal; MSS (microsatellite stable status), primary peritoneal cancer, primary peritoneal ovarian carcinoma, microsatellite stable primary peritoneal cancer, platinum resistant microsatellite stable primary peritoneal cancer, CRC (MSS unknown), rectal cancer, endometrial cancer (including endometrial carcinoma), uterine carcinoma, salivary gland carcinoma, kidney cancer, renal cell cancer (RCC), renal cell carcinoma (RCC), gastro-esophageal junction cancer, prostate cancer, vulval cancer, thyroid cancer, hepatic carcinoma, carcinoid carcinoma, head and neck cancer, B-cell lymphoma (including non-Hodgkin’s lymphoma, as well as low grade / follicular non-Hodgkin’s lymphoma (NHL), small lymphocytic (SL) NHL, intermediate grade / follicular NHL, intermediate grade diffuse NHL, Diffuse Large B cell lymphoma, high grade immunoblastic NHL, high grade lymphoblastic NHL, high grade small non-cleaved cell NHL, bulky disease NHL, mantle cell lymphoma, AIDS-related lymphoma, and Waldenstrom’s Macroglobulinemia, Hodgkin’s lymphoma (HD), chronic lymphocytic leukemia (CLL), acute lymphoblastic leukemia (ALL), T cell Acute Lymphoblastic Leukemia (T-ALL), Acute myeloid leukemia (AML), Hairy cell leukemia, chronic myeloblastic leukemia, multiple myeloma, post-transplant lymphoproliferative disorder (PTLD), abnormal vascular proliferation associated with phakomatoses, Meigs’ syndrome, Merkel Cell cancer, MSI-high cancer, KRAS mutant tumors, adult T-cell leukemia / lymphoma, adenoid cystic cancer (including adenoid cystic carcinoma), melanoma, malignant melanoma, metastaticDocket No. WRENCH-002 / WO01 melanoma, pancreatic cancer, pancreatic adenocarcinoma, ovarian cancer (including ovarian carcinoma), pleural mesothelioma, cervical squamous cell carcinoma (cervical SCC), anal squamous cell carcinoma (anal SCC), carcinoma of unknown primary, gallbladder cancer, pleural mesothelioma, chordoma, endometrial sarcoma, chondrosarcoma, uterine sarcoma, uveal melanoma, amyloidosis, AL-amyloidosis, astrocytoma, and / or Myelodysplastic syndromes (MDS). The anti-DcR3 antibodies, multi-specific proteins, and fusion proteins of the disclosure, as a monotherapy or as part of a combination therapy as described herein, have particular utility in digestive cancers such as gallbladder carcinoma, liver carcinoma, gastric carcinoma, colon carcinoma, pancreatic carcinoma, bone sarcoma, thyroid adenocarcinoma, lung cancer, renal cell carcinoma, and some subtypes of breast cancer, especially as defined in Bou-Dargham MJ, Liu Y, Sang Q-XA, Zhang J (2018), Subgrouping breast cancer patients based on immune evasion mechanisms unravels a high involvement of transforming growth factor- beta and decoy receptor 3. PLoS ONE 13(12): e0207799. https: / / doi.org / 10.1371 / journal.pone.0207799, hereby incorporated by reference in its entirety., hereby incorporated by reference in its entirety. In some embodiments, the cancer is a gastric carcinoma, renal cell carcinoma, etc. The inventor has recognized and appreciated that these cancers are associated with overexpression of DcR3 and antibodies and fusion proteins of the disclosure have applicability to that. In some embodiments, the cancer for treatment using the anti-DcR3 antibodies, multispecific binding proteins, and fusion proteins as disclosed herein includes cancer selected from the group consisting of renal clear cell carcinoma (RCC), lung cancer, NSCLC, lung adenocarcinoma, lung squamous cell carcinoma, gastric adenocarcinoma, ovarian cancer, endometrial cancer, breast cancer, triple negative breast cancer (TNBC), head and neck tumor, colorectal adenocarcinoma, melanoma, and metastatic melanoma. (iv) Anti-DcR3 Antibody Monotherapies The anti-DcR3 antibodies, multispecific binding proteins, and fusion proteins as disclosed herein find particular use in the treatment of cancer as a monotherapy. Due to the nature of an immuno-oncology mechanism of action, DcR3 does not necessarily need to be overexpressed on or correlated with a particular cancer type, that is, the goal is to have the anti-DcR3 antibodies de-suppress T cell cell activation, such that the immune system will go after the cancers. Any of the anti-DcR3 antibodies, multispecific binding proteins, and fusion proteins as disclosed herein finds use as a monotherapy. (v) Anti-DcR3 Antibody Combination Therapies As is known in the art, combination therapies comprising a therapeutic agent targeting an immunotherapy target and an additional therapeutic agent, specific for the disease condition, are showing great promise. For example, in the area of immunotherapy, there are a number of promising combination therapies using a chemotherapeutic agent (either a small molecule drug or an anti-tumor antibody) or with an immuno- oncology antibody.Docket No. WRENCH-002 / WO01 The terms “in combination with” and “co-administration” are not limited to the administration of said prophylactic or therapeutic agents at exactly the same time. Instead, it is meant that the protein or antibody and the other agent or agents are administered in a sequence and within a time interval such that they may act together to provide a benefit that is increased versus treatment with only either the antibody of the present invention or the other agent or agents. It is preferred that the antibody and the other agent or agents act additively, and especially preferred that they act synergistically. Accordingly, the anti-DcR3 antibodies, multispecific binding proteins, and fusion proteins as disclosed herein may be administered concomitantly with one or more other therapeutic regimens or agents. In some embodiments, the antibodies of the present invention are administered in the same formulation with one or more other therapeutic regimens or agents. In some embodiments, the antibodies of the present invention are administered in a separate and / or different formulation from the one or more other therapeutic regimens or agents. The additional therapeutic regimes or agents may be used to improve the efficacy or safety of the antibody. Also, the additional therapeutic regimes or agents may be used to treat the same disease or a comorbidity rather than to alter the action of the antibody. For example, an antibody or protein as disclosed herein may be administered to the patient along with chemotherapy, radiation therapy, or both chemotherapy and radiation therapy. In some embodiments, the anti-DcR3 antibodies, multispecific binding proteins, and fusion proteins as disclosed herein can be combined with one of a number of checkpoint receptor antibodies. In some embodiments, a patient’s tumor may be evaluated for expression of receptors and the results then used to inform a clinician as to which antibodies to administer. Any of the anti-DcR3 antibodies, multispecific binding proteins, and fusion proteins as disclosed herein finds use as part of a combination therapy. In some embodiments, the combination or composition further comprises an additional active agent, e.g., a second antigen binding protein. Optionally, the second antigen binding protein binds to a negative regulator of the immune system, an immune suppressor, or an immune checkpoint protein, including but not limited to PD-I, PD-L I, CTLA-4, PDL2, B7-H3, B7-H4, CEACAM-I, TIGIT, PVR, LAG3, CD112, PVRIG, CD96, TIM3, and / or BTLA, or co-stimulatory receptor: ICOS, OX40, 41BB, CD27,and / or GITR. In some embodiments, the anti-DcR3 antibodies, multispecific binding proteins, and fusion proteins as disclosed herein are used in combination with an antibody to an immune checkpoint inhibitor protein. In some embodiments, the immune checkpoint inhibitor protein is selected from the group consisting of an anti-PVRIG antibody, an anti-PD-1 antibody, an anti-PD-L1 antibody, an anti-TIGIT antibody, an anti-CTLA-4 antibody, an anti-PD-L2 antibody, an anti-B7-H3 antibody, an anti B7-H4 antibody, an anti-CEACAM-1 antibody, an anti-PVR antibody, an anti-LAG3 antibody, an anti-CD112 antibody, an anti-CD96 antibody, an anti-TIM3 antibody, an anti-BTLA antibody, an anti- ICOS antibody, an anti-OX40 antibody, or an anti-41BB antibody, an anti-CD27 antibody, or an anti-GITR antibody.Docket No. WRENCH-002 / WO01 The anti-DcR3 antibodies, multispecific binding proteins, and fusion proteins as disclosed herein may be administered in combination with one or more other prophylactic or therapeutic agents, including but not limited to cytotoxic agents, chemotherapeutic agents, cytokines, growth inhibitory agents, anti-hormonal agents, kinase inhibitors, anti-angiogenic agents, cardioprotectants, immunostimulatory agents, immunosuppressive agents, agents that promote proliferation of hematological cells, angiogenesis inhibitors, protein tyrosine kinase (PTK) inhibitors, or other therapeutic agents. In some embodiments, the chemotherapeutic agent is selected from the group consisting of Platinum, Oxaliplatin, Cisplatin, Paclitaxel (taxol), Sorafenib, Doxorubicin, Sorafenib, 5-FU, and Gemcitabine, Irinotecan (CPT-11). In some embodiments, the other therapeutic is an agent used in radiation therapy for the treatment of cancer. Accordingly, in some embodiments, the active agents described herein are administered in combination with one or more of platinum coordination compounds, topoisomerase inhibitors, antibiotics, antimitotic alkaloids and difluoronucleosides. In some embodiments, the anti-DcR3 antibodies, multispecific binding proteins, and fusion proteins as disclosed herein are used in combination with one or more inflammasome activators. In some embodiments, the inflammasome activator is an CD39 inhibitor. In some embodiments, the CD39 inhibitor is an anti-CD39 antibody. According to at least some embodiments, the = anti-DcR3 antibodies, multispecific binding proteins, and fusion proteins as disclosed herein could be used in combination with any of the known in the art standard of care cancer treatment (as can be found, for example, on the World Wide Web at cancer.gov / cancertopics). Administration of the pharmaceutical composition comprising the anti-DcR3 antibodies, multispecific binding proteins, and fusion proteins as disclosed herein (e.g., anti-DcR3 antibodies including those with CDRs identical to those shown in Table 10), preferably in the form of a sterile aqueous solution, may be done in a variety of ways. As is known in the art, protein therapeutics are often delivered by IV infusion. The antibodies of the present invention may also be delivered using such methods. For example, administration may be veinous or by intravenous infusion with 0.9% sodium chloride as an infusion vehicle. Such techniques are disclosed in Remington’s Pharmaceutical Sciences 16thedition, Osol, A. Ed., 1980. The dosing amounts and frequencies of administration are, in some embodiments, selected to be therapeutically or prophylactically effective. As is known in the art, adjustments for protein degradation, systemic versus localized delivery, and rate of new protease synthesis, as well as the age, body weight, general health, sex, diet, time of administration, drug interaction and the severity of the condition may be necessary, and will be ascertainable with routine experimentation by those skilled in the art. In order to treat a patient, a therapeutically effective dose of the nti-DcR3 antibodies, multispecific binding proteins, and fusion proteins asDocket No. WRENCH-002 / WO01 disclosed herein may be administered. By “therapeutically effective dose” herein is meant a dose that produces the effects for which it is administered. EXAMPLES The application may be better understood by reference to the following non-limiting examples, which are provided as exemplary embodiments of the application. The following examples are presented in order to more fully illustrate embodiments and should in no way be construed, however, as limiting the broad scope of the application. Example 1: DcR3 levels correlate with poor outcomes in cancer Expression of DcR3 transcripts is elevated in human cancers and correlates with poor survival. For example, as shown in FIG.1A, DcR3 has been shown to be significantly elevated in patients having pancreatic (PAAD), kidney (KIRC), rectal (READ), stomach (STAD), colon (COAD), and thymus (THYM) cancers compared to those without cancer. In patients having cancer, survival is also significantly impacted by DcR3 expression (FIG. 1B). Cox regression analyses reveal that poor prognosis is associated with high DcR3 expression (FIG.1C). DcR3 serum levels are also elevated in a number of solid tumor types and correlate with metastasis. DcR3 is upregulated at the protein level in many solid tumors (FIG. 2A). High levels of circulating DcR3 correlate with tumor metastasis in gastric cancer (FIG.2B). Example 2: Expression and characterization of the anti-DcR3 VHH-Fc fusion proteins Anti-DcR3 VHHs were identified through the screening of a semi-synthetic VHH library against DcR3 proteins. ELISA-positive candidates were sequenced and expressed as VHH Fc fusion proteins ((VHH)1-Fc). The VHH-Fc fusion proteins were expressed individually in CHO cells and purified using Protein A affinity columns. The purity of these recombinant proteins was assessed by SDS-PAGE using reducing (R) and non- reducing (NR) conditions (FIG. 3, gel images), as well as by size exclusion-high-performance liquid chromatography (FIG. 3, chromatograms). The VHH-Fc fusion proteins that exhibited high levels of purity in both analytical methods were selected for further analysis and characterization (WB29, WB30, WB31, WB32, WB33, WB34). Example 3: Characterization of the ability of the Single domain Binding Protein against DcR3 to compete with TL1A binding to DcR3. Binding competition between the anti-DcR3 binders expressed as VHH-Fc fusion proteins and TL1A was evaluated by a label-free biolayer interferometry (BLI) assay on an Octet Red 96 (Pall ForteBio, USA). As shown in FIG.4A, the experiment was designed to identify 1) antibodies that compete with TL1A for binding to DcR3; 2) antibodies that bind to DcR3 but do not compete with TL1A for binding with DcR3; and antibodies that do not bind to DcR3. All experiments were performed at 25°C in PBS buffer with 0.01% Tween-20 (PBST). As shown in FIG.4B, TL1A-His was loaded onto anti-His probe sensors at a concentration of 5 µg / mlDocket No. WRENCH-002 / WO01 for 120 s in Stage 1 (“Loading”), and then DcR3-Fc fusion protein at a concentration of 100 nM was loaded onto the biosensor for 200 s to obtain saturation in Stage 2 (“Assoc.1”) and generate TL1A-DcR3 complexes. VHH-Fc fusion proteins were loaded on the biosensor at concentrations of 100 nM for another 200 s in Stage 3 (“Assoc.2”). As shown in FIG.4B, several of the VHHs, including WB29, WB32, WB33, and WB34 bound to the TL1A-DcR3 complex (see Assoc. 2, the top four curves), indicating that their epitope on DcR3 is not masked by TL1A. In contrast, VHHs WB30 and WB31 did not show any binding to the TL1A-DcR3 complex (see Assoc.2, the lower two curves), indicating that binding of TL1A to DcR3 prevented their binding, suggesting that their epitopes were masked by TL1A. Thus, these two VHHs represent good candidates as inhibitors of DcR3 binding to its ligands. Furthermore, VHHs from the group that did not compete with TL1A (such as WB32, that exhibited the strongest binding to DcR3) have strong potential to be included as a biparatopic binder in combination with single domain antibodies that do compete with TL1A (e.g., WB30 and WB31). These biparatopics, via binding to DcR3 at two distinct epitopes (A ligand binding-competing epitope, and a non-ligand binding competing epitope) could exhibit higher affinity to DcR3, and therefore represent good blocking binders that also displace TL1A from DcR3. Table 2 VHH Binds to DcR3 Competes with TL1A for binding to DcR3The binding affinity (Kd) and kinetics (Kon and Koff) were measured for DcR3 binding to several anti- DcR3 VHHs (WB30, WB31, WB32) using a Biacore S-200 instrument. Each experiment cycle began with the immobilization of a VHH-Fc fusion protein to a CM5 chip. Upon capture of the VHH-Fc fusion protein to the sensor surface, 6 two-fold serial dilutions of mouse DcR3-Fc protein starting from 400 nmol / L were injected over all channels at 30 mL / min for 180 seconds. The dissociation of the DcR3 was monitored for 1,200 seconds. Several blank buffer samples were injected (1,000 seconds at 30 mL / minute) over the flow cell and used for reference surface subtraction. Chip surface was regenerated with 10 mL / min injection of glycine-HCl pH 1.5 for 60 seconds after each cycle. The resulting sensorgrams were processed and double- referenced using Biacore S-200 evaluation software. Where appropriate, the sensorgrams were fit with a simple 1:1 kineticDocket No. WRENCH-002 / WO01 binding model. As shown in FIG.5 and Table 3 below, the VHHs tested exhibited an affinity between 10 and 100 nM to DcR3. Table 3 VHH Kon (1 / Ms) Koff (1 / s) KD (nM) WB30 3.72E+04 2.50E-03 67.2of VHHs that bind to the ligand-binding interface of DcR3, as well as of VHHs that bind to DcR3 at another epitope. These features were taken advantage of to create biparatopic anti-DcR3 VHHs, by combining in one protein, one VHH that binds to the ligand-binding interface of DcR3 with another VHH that binds to a different epitope (such as WB30+WB32; or WB31+WB32). These biparatopic anti-DcR3 VHH-Fc fusion proteins were expressed individually in CHO cells and purified using Protein A affinity columns. The purity of these recombinant proteins was assessed by SDS-PAGE using reducing (R) and non-reducing (NR) conditions, as well as by size exclusion-high-performance liquid chromatography (FIG.6, left). The biparatopic proteins that exhibited high levels of purity in both analytical methods (WB52, WB53, WB55) were selected for further characterization by SPR measurements (FIG.6, right). The selected biparatopic anti-DcR3 VHH-Fc fusion proteins were subjected to SPR experiments to measure their binding affinity and kinetics to DcR3, as described above. The biparatopic proteins exhibited a higher affinity (< 5 nM) for DcR3 compared to their monoparatopic counterparts. These biparatopic binders represent good candidates for further analysis and characterization. Table 4 Fusion Protein 1stVHH 2ndVHH Kon (1 / Ms) Koff (1 / s) KD (nM)Competition of the anti-DcR3 binders (mono- and bi-paratopic) with FasL was assessed by ELISA. Binding of FasL to DcR3 was measured in the absence or presence of either 1 ug / mL or 10 ug / mL of the anti-Docket No. WRENCH-002 / WO01 DcR3 binders. EC50 in the absence of anti-DcR3 binders was compared to EC50 in the presence of the DcR3 binders. One biparatopic anti-DcR3 VHH-Fc fusion protein (WB53) appeared to be the best binder to compete with FasL binding to DcR3 with a 20-fold increase of EC50 in the presence of 10 ug / mL of the binder. Example 7: Anti-DcR3 VHH identification from a synthetic VHH phage display library. Additional VHHs were identified by 3 rounds of panning: Round 1: Binding to DcR3-Fc In the presence of hFc; Round 2: Binding to DcR3-Fc in the presence of a control human IgG1; and Round 3: Binding to DcR3-Fc in the presence of a control human IgG1. Phage ELISA against DcR3, alone or in complex with TL1A were carried out (FIG.8). VHHs that exhibited binding to DcR3 and a loss of binding in the presence of TL1A (WB74, WB75, WB76, WB77, WB80, WB87, and WB88) were selected as they represent potential blocking antibodies. Other VHHs that bind to DcR3 in complex with TL1A (such as WB78, WB83, WB84, WB85, and WB86) can be used to produce biparatopic binders that will combine one VHH that binds to the ligand-binding interface of DcR3 with another VHH that binds to a different epitope. Table 5 VHH Binds to DcR3 Competes with TL1A for binding to DcR3 WB74 Y YBXPC3 cells are to be seeded with 7500 per well of a 96-well plate. After 24 hours 50 uL of media can be removed and replaced with 50 uL of fresh media (5% serum) that contains the different treatment conditions: In order to establish an EC50 (dose-response) of FasL-mediated apoptosis, and to determine the effect of DcR3 blocking antibodies, cells can be incubated with increasing concentrations of FasL in the absence or presence of the anti-DcR3 antibodies at 1ug / mL or 10 ug / mL. Cells can be incubated with the treatment conditions forDocket No. WRENCH-002 / WO01 48 hours, then processed for Cell Titer Glow assay-based cell death determination. Those dilutions which show at 2-fold, 5-fold, 10-fold, or more increase in the EC50 of FasL-mediated cell death would be considered to be reflective as a potentiation of FasL-mediated cell death by these fusion proteins. Example 9: Potentiation of chemotherapy-induced cell death by DcR3 blockers ASPC1 cells (a human pancreatic cancer-derived cell line) were seeded in 96-well plates at a density of ~5000 cells / well and treated for 48 h with gemcitabine at concentrations of 1 nM and 1 mM, in the absence or presence of 10 ug / mL of the DcR3 blocking antibodies WB52 and WB53. To determine gemcitabine-induced cytotoxicity, cell viability in response to the different treatment conditions was determined using CellTiterGlow assay (FIG. 9). Interestingly, WB53 potentiates the cytotoxic effect of Gemcitabine. Notably, 1 nM of Gemcitabine in the presence of WB53 leads to the same cytotoxic effect as 1 mM Gemcitabine alone (106fold enhancement of Gemcitabine’s cytotoxicity). SEQUENCES Table 6 below lists exemplary amino acid sequences of Decoy Receptor 3 (DcR3) and its ligands. Name SEQ ID NO D R 4 1Table 7 below lists exemplary full-length amino acid sequences of single domain anti-DcR3 binding proteins. Name SEQ ID NODocket No. WRENCH-002 / WO01 Name SEQ ID NO WB33 205 Table 8 below lists exemplary amino ac d sequences o b para op c fusion proteins, which include certain combinations of single domain anti-DcR3 antibodies from Table 4. For example, as shown in the first column below, the fusion protein WB52 is a combination of a first VHH (WB30) and a second VHH (WB32). The amino acid sequence for each VHH can be found in Table 7, and the CDR regions for each VHH can be found in Table 10. Name SEQ ID NOTable 9 below lists exemplary amino acid sequences of Fc regions. Name SEQ ID NODocket No. WRENCH-002 / WO01 Fc Knob 501 Fc Hole 502 Table 10 below lists exemplary aminoentarity-determining regions (CDRs) from single domain DcR3 binding proteins. Name Region Nomenclature SEQ ID NO WB29 (Anti-DcR3-3.1 VHH) CDR-H1 Kabat 1Docket No. WRENCH-002 / WO01 Name Region Nomenclature SEQ ID NO IMGT 155Docket No. WRENCH-002 / WO01 Name Region Nomenclature SEQ ID NO Chothia 83Docket No. WRENCH-002 / WO01 Name Region Nomenclature SEQ ID NO WB78 CDR-H1 Kabat 11Docket No. WRENCH-002 / WO01 Name Region Nomenclature SEQ ID NO IMGT 147Docket No. WRENCH-002 / WO01 Name Region Nomenclature SEQ ID NO Chothia 75Table 11 below lists exemplary CDR pairings of the single domain binding proteins. Name SEQ ID NosDocket No. WRENCH-002 / WO01 Name SEQ ID Nos Nomenclature CDR1 CDR2 CDR3Docket No. WRENCH-002 / WO01 Name SEQ ID Nos Nomenclature CDR1 CDR2 CDR3While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.

Claims

Docket No. WRENCH-002 / WO01 CLAIMS 1. A VHH-Fc fusion protein, comprising: (a) a first monomer comprising from N-terminus to C-terminus: a first single domain anti-DcR3 antibody that binds to DcR3 and inhibits DcR3 from binding with its ligands, wherein the first single domain anti-DcR3 antibody is at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NOs: 202-203, 207-210, 213, or 218-219, and a first Fc domain; and (b) a second monomer comprising a second Fc domain.

2. The VHH-Fc fusion protein of claim 1, wherein the first single domain anti-DcR3 antibody binds to DcR3 at one or more amino acid positions selected from the group consisting of: H122-L127, N92, L94, R76, H77, R87, Y90, R89, and Y78-E86 of wild type DcR3.

3. The VHH-Fc fusion protein of claim 2, wherein the first single domain anti-DcR3 antibody binds to DcR3 at one or more amino acid positions selected from the group consisting of: R98, N92-E99, and P75 of wild type DcR3.

4. The VHH-Fc fusion protein of claim 1, wherein the first monomer of (a) further comprises a second single domain anti-DcR3 antibody that binds to DcR3 and does not inhibit DcR3 from binding with its ligands, wherein the second single domain DcR3 antibody is at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NOs: 201, 204-206, 211-212, or 214-217.

5. The VHH-Fc fusion protein of claim 4, wherein the second single domain anti-DcR3 antibody is located C-terminal to the first Fc domain.

6. The VHH-Fc fusion protein of claim 4, wherein the first and second single domain anti-DcR3 antibodies bind to DcR3 at a different epitope.

7. The VHH-Fc fusion protein of claim 4, wherein the second monomer of (b) has an identical amino acid sequence as the first monomer of (a), wherein the first and second monomers interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein.

8. The VHH-Fc fusion protein of claim 7, wherein the VHH-Fc fusion protein restores the activation of anti-cancer immune cells.Docket No. WRENCH-002 / WO01 9. The VHH-Fc fusion protein of claim 7, wherein the VHH-Fc fusion protein inhibits DcR3 from binding with its ligands.

10. The VHH-Fc fusion protein of claim 7, wherein the VHH-Fc fusion protein restores the apoptotic activity of FasL towards cancer cells.

11. The VHH-Fc fusion protein of claim 7, wherein the VHH-Fc fusion protein potentiates the pro- apoptotic and / or cytotoxic effects of chemotherapy.

12. The VHH-Fc fusion protein of claim 7, wherein the VHH-Fc fusion protein restores the activation of TL1A, LIGHT, and FasL that were inhibited by DcR3.

13. The VHH-Fc fusion protein of claim 7, wherein the VHH-Fc fusion protein blocks one or more of the DcR3:FasL interaction, DcR3:TL1A interaction, and DcR3:LIGHT interaction.

14. The VHH-Fc fusion protein of claim 7, wherein the fusion protein releases DcR3 within the acidic environment of endosomes, thereby resulting in an increased clearance of DcR3.

15. The VHH-Fc fusion protein of claim 7, wherein the single domain anti-DcR3 antibody or single domain anti-DcR3 antibodies are covalently attached to the N-terminus of the first or the second Fc domain.

16. The VHH-Fc fusion protein of claim 7, wherein the first Fc domain and second Fc domain are configured in an asymmetrical manner.

17. The VHH-Fc fusion protein of claim 7, wherein the first domain and the second domain comprise complementary pairs of amino acid substitutions that improve thermostability.

18. The VHH-Fc fusion protein of claim 7, wherein the second Fc domain comprises a set of amino acid substitutions selected from the group consisting of Y349C, T366S, L368A, and Y407V.

19. The VHH-Fc fusion protein of claim 7, wherein the single domain anti-DcR3 antibodies are covalently attached to the N-terminus or the C-terminus of the first or the second Fc domain via a linker.Docket No. WRENCH-002 / WO01 20. The VHH-Fc fusion protein of claim 18, wherein the linker comprises (GS)n, (GGS)n, (GGGS)n, (GGSG)n, (GGSGG)n, (GGGGS)n, (GGGGG)n, or (GGG)n, wherein n = 1 to 10.

21. A single domain Decoy Receptor 3 (DcR3) binding protein, wherein the single domain DcR3 binding protein inhibits the interaction between DcR3 and FasL, LIGHT, and TL1A.

22. The single domain DcR3 binding protein of claim 21, wherein the single domain DcR3 binding protein can bind to one or more binding interfaces of DcR3.

23. The single domain DcR3 binding protein of claim 22, wherein the one or more binding interfaces are selected from the group consisting of: the DcR3:FasL binding interface; the DcR3:LIGHT binding interface; and the DcR3:TL1A binding interface.

24. The single domain DcR3 binding protein of any one of claims 21-23, wherein the single domain DcR3 binding protein binds to DcR3 at one or more amino acid positions selected from the group consisting of: H122- L127, N92, L94, R76, H77, R87, Y90, R89, and Y78-E86 of wild type DcR3.

25. The single domain DcR3 binding protein of claim 24, wherein the single domain DcR3 binding protein binds to DcR3 at one or more amino acid positions selected from the group consisting of: R98, N92-E99, and P75 of wild type DcR3.

26. The single domain DcR3 binding protein of any one of claims 21-25, wherein the single domain DcR3 binding protein restores the activation of anti-cancer immune cells.

27. The single domain DcR3 binding protein of any one of claims 21-26, wherein the single domain DcR3 binding protein inhibits DcR3 from binding with its ligands.

28. The single domain DcR3 binding protein of any one of claims 21-26, wherein the single domain DcR3 binding protein binds to DcR3 but does not inhibit DcR3 from binding with its ligands.

29. The single domain DcR3 binding protein of any one of claims 21-28, wherein the single domain DcR3 binding protein restores the apoptotic activity of FasL towards cancer cells.Docket No. WRENCH-002 / WO01 30. The single domain DcR3 binding protein of any one of claims 21-29, wherein the single domain DcR3 binding protein restores the activity of TL1A, and / or LIGHT, and / or FasL that were inhibited by DcR3.

31. The single domain DcR3 binding protein of any one of claims 21-30, wherein the single domain DcR3 binding protein comprises a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR- H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence at least 90% identical to SEQ ID NOs: 1-19, the CDR-H2 has an amino acid sequence at least 90% identical to SEQ ID NOs: 20-38, and the CDR-H3 has an amino acid sequence at least 90% identical to any one of SEQ ID NO: 39-57, wherein the numbering is according to Kabat.

32. A single domain DcR3 binding protein comprising a variable heavy chain complementarity- determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence at least 90% identical to SEQ ID NOs: 1-19, the CDR-H2 has an amino acid sequence at least 90% identical to SEQ ID NO: 20-38, and the CDR-H3 has an amino acid sequence at least 90% identical to any one of SEQ ID NO: 39-57, wherein the numbering is according to Kabat.

33. The single domain DcR3 binding protein of claim 31 or claim 32, wherein the CDR-H1 is at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NOs: 1-19, the CDR-H2 is at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NOs: 20-38, and the CDR-H3 is at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NOs: 39-57, wherein the numbering is according to Kabat.

34. A single domain DcR3 binding protein that binds to DcR3 and inhibits DcR3 from interacting with its ligands, comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR-H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NOs: 2-3, 7-10, 13, or 18-19; the CDR-H2 has an amino acid sequence at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NO: 21-22, 26-29, 32, or 37-38; and the CDR-H3 has an amino acid sequence at least 90%, 95%, 98%, 99%, or 100% identical to any one of SEQ ID NO: 40-41, 45-48, 51, or 56- 57; wherein the numbering is according to Kabat.

35. A single domain DcR3 binding protein that binds to DcR3 but does not inhibit DcR3 from interacting with its ligands, comprising a variable heavy chain complementarity-determining region 1 (CDR-H1), a CDR- H2, and a CDR-H3, wherein the CDR-H1 has an amino acid sequence at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NOs: 1, 4-6, 11-12, or 14-17; the CDR-H2 has an amino acid sequence at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NO: 20, 23-25, 30-31, or 33-36; and the CDR-H3 has an amino acidDocket No. WRENCH-002 / WO01 sequence at least 90%, 95%, 98%, 99%, or 100% identical to any one of SEQ ID NO: 39, 42-44, 49-50, or 52- 55; wherein the numbering is according to Kabat.

36. A single domain DcR3 binding protein of any one of claims 21-31, wherein the single domain DcR3 binding protein is at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NOs: 201-219.

37. A single domain DcR3 binding protein that binds to DcR3 and inhibits DcR3 from interacting with its ligands, wherein the single domain DcR3 binding protein is at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NOs: 202-203, 207-210, 213, or 218-219.

38. A single domain DcR3 binding protein that binds to DcR3 but does not inhibit DcR3 from interacting with its ligands, wherein the single domain DcR3 binding protein is at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NOs: 201, 204-206 , 211-212, or 214-217.

39. A VHH-Fc fusion protein, comprising: a first monomer comprising from N-terminus to C-terminus: a first single domain anti-DcR3 antibody that binds to DcR3 and inhibits DcR3 from binding with its ligands, and a first Fc domain; and a second monomer comprising a second Fc domain.

40. The VHH-Fc fusion protein of claim 39, where the first monomer further comprises a second single domain anti-DcR3 antibody that binds to DcR3 and inhibits DcR3 from binding with its ligands.

41. The VHH-Fc fusion protein of claim 40, wherein the first single domain anti-DcR3 antibody and the second single domain anti-DcR3 antibody have an identical amino acid sequence.

42. The VHH-Fc fusion protein of any one of claims 39-41, wherein the second monomer comprises, from N-terminus to C-terminus: a third single domain anti-DcR3 antibody that binds to DcR3 and inhibits DcR3 from binding with its ligands, and a second Fc domain.

43. The VHH-Fc fusion protein of claim 42, wherein the third single domain anti-DcR3 antibody has an identical amino acid sequence as the first single domain anti-DcR3 antibody and / or the second single domain anti-DcR3 antibody.

44. The VHH-Fc fusion protein of any one of claims 39-43, wherein the second monomer further comprises a fourth single domain anti-DcR3 antibody that binds to DcR3 and inhibits DcR3 from binding with its ligands.Docket No. WRENCH-002 / WO01 45. The VHH-Fc fusion protein of claim 44, wherein the fourth single domain anti-DcR3 antibody has an identical amino acid sequence as the first single domain anti-DcR3 antibody, second single domain anti-DcR3 antibody, and / or third single domain anti-DcR3 antibody.

46. The VHH-Fc fusion protein of claim 39, where the first monomer further comprises a second single domain anti-DcR3 antibody that binds to DcR3 but does not inhibit DcR3 from binding with its ligands.

47. The VHH-Fc fusion protein of claim 46, wherein the second monomer comprises, from N-terminus to C-terminus: a third single domain anti-DcR3 antibody that binds to DcR3 and inhibits DcR3 from binding with its ligands, and a second Fc domain.

48. The VHH-Fc fusion protein of claim 47, wherein the third single domain anti-DcR3 antibody has an identical amino acid sequence as the first single domain anti-DcR3 antibody.

49. The VHH-Fc fusion protein of claim 47, wherein the second monomer further comprises a fourth single domain anti-DcR3 antibody that binds to DcR3 but does not inhibit DcR3 from binding with its ligands, and a second Fc domain.

50. The VHH-Fc fusion protein of claim 49, wherein the fourth single domain anti-DcR3 antibody has an identical amino acid sequence as the second single domain anti-DcR3 antibody.

51. The VHH-Fc fusion protein of any one of claims 39-50, wherein the first and second monomers interact to form a bivalent biparatopic fusion protein.

52. A VHH-Fc fusion protein, comprising: (a) a first monomer comprising from N-terminus to C-terminus: a first single domain anti-DcR3 antibody that binds to DcR3 and inhibits DcR3 from binding with its ligands, a second single domain anti-DcR3 antibody that binds to DcR3 but does not inhibit DcR3 from binding with its ligands, and an Fc domain; and (b) a second monomer identical to the first monomer (a); wherein the first and second monomers interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein.

53. A VHH-Fc fusion protein, comprising: (a) a first monomer comprising from N-terminus to C-terminus: a first single domain anti-DcR3 antibody that binds to DcR3 but does not inhibit DcR3 from binding with its ligands, a second single domain anti-DcR3 antibody that binds to DcR3 and inhibits DcR3 from binding withDocket No. WRENCH-002 / WO01 its ligands, and an Fc domain; and (b) a second monomer identical to the first monomer (a); wherein the first and second monomers interact to form a homodimer comprising a bivalent biparatopic Fc fusion protein.

54. The VHH-Fc fusion protein of any one of claims 39-53, wherein the first, second, third, and / or fourth single domain anti-DcR3 antibody comprises the single domain anti-DcR3 antibody of any one of claims 21- 38.

55. The VHH-Fc fusion protein of any one of claims 39-54, wherein the single domain anti-DcR3 antibody that binds to DcR3 and inhibits DcR3 from binding with its ligands comprises the single domain anti-DcR3 antibody of claim 34 or claim 37.

56. The VHH-Fc fusion protein of any one of claims 39-55, wherein the single domain anti-DcR3 antibody that binds to DcR3 but does not inhibit DcR3 from binding with its ligands comprises the single domain anti- DcR3 antibody of claim 35 or claim 38.

57. A biparatopic VHH-Fc fusion protein comprising an amino acid sequence that is at least 90%, 95%, 98%, 99%, or 100% identical to SEQ ID NOs: 301-306.

58. The VHH-Fc fusion protein of any one of claims 39-57, wherein the VHH-Fc fusion protein restores the activation of anti-cancer immune cells.

59. The VHH-Fc fusion protein of any one of claims 39-58, wherein the VHH-Fc fusion protein inhibits DcR3 from binding with its ligands.

60. The VHH-Fc fusion protein of any one of claims 39-59, wherein the VHH-Fc fusion protein restores the apoptotic activity of FasL towards cancer cells.

61. The VHH-Fc fusion protein of any one of claims 39-60, wherein the VHH-Fc fusion protein potentiates the pro-apoptotic and / or cytotoxic effects of chemotherapy.

62. The VHH-Fc fusion protein of any one of claims 39-61, wherein the VHH-Fc fusion protein restores the activation of TL1A, LIGHT, and FasL that were inhibited by DcR3.Docket No. WRENCH-002 / WO01 63. The VHH-Fc fusion protein of any one of claims 39-62, wherein the VHH-Fc fusion protein blocks one or more of the DcR3:FasL interaction, DcR3:TL1A interaction, and DcR3:LIGHT interaction.

64. The VHH-Fc fusion protein of any one of claims 39-63, wherein the fusion protein releases DcR3 within the acidic environment of endosomes, thereby resulting in an increased clearance of DcR3.

65. The VHH-Fc fusion protein of any one of claims 39-64, wherein the single domain anti-DcR3 antibody or single domain anti-DcR3 antibodies are covalently attached to the N-terminus of the first or the second Fc domain.

66. The VHH-Fc fusion protein of any one of claims 39-65, wherein the first Fc domain and second Fc domain are configured in an asymmetrical manner.

67. The fusion protein of any one of claims 39-66, wherein the first domain and the second domain comprise complementary pairs of amino acid substitutions that improve thermostability.

68. The fusion protein of any one of claims 39-67, wherein the first Fc domain comprises a set of amino acid substitutions selected from the group consisting of S354C and T366W.

69. The fusion protein of any one of claims 39-68, wherein the second Fc domain comprises a set of amino acid substitutions selected from the group consisting of Y349C, T366S, L368A, and Y407V.

70. The fusion protein of any one of claims 39-69, wherein the single domain anti-DcR3 antibodies are covalently attached to the N-terminus or the C-terminus of the first or the second Fc domain via a linker.

71. The fusion protein of claim 70, wherein the linker comprises a glycine-serine linker.

72. The fusion protein of claim 71, wherein the glycine-serine linker comprises a sequence of (GS)n, wherein n = 1 to 10.

73. The fusion protein of claim 70, wherein the linker comprises (GS)n, (GGS)n, (GGGS)n, (GGSG)n, (GGSGG)n, (GGGGS)n, (GGGGG)n, or (GGG)n, wherein n = 1 to 10.

74. The fusion protein of claim 70 or claim 73, wherein the linker comprises (GGGGS)4 or (GGGGS)3.Docket No. WRENCH-002 / WO01 75. A multispecific binding protein, comprising a first domain and a second domain, wherein: the first domain comprises a single domain DcR3 binding protein of any one of claims 21-38 or claims 1-20 (new claims); and the second domain that binds to a target molecule that is not DcR3.

76. The multispecific binding protein of claim 75, wherein the second domain selectively binds to a tumor associated antigen (TAA).

77. The multispecific binding protein of claim 76, wherein the TAA is selected from the group consisting of B-cell maturation antigen (BCMA), carcinoembryonic antigen (CEA), epidermal growth factor receptor (EGFR), human epidermal growth factor receptor 2 (Her2), epithelial cell adhesion molecule (EpCAM), CD20, CD26, CD123, CD30, CD33, CD47, CD52, CD133, glycoprotein A33 (gpA33), mucins, tumor associated glycoprotein-72 (TAG-72), type IX collagen (CIX), glutamate carboxypeptidase II (PSMA), folate-binding protein, GD2, GD3, GM2, vascular endothelial growth factor (VEGF), vascular endothelial growth factor receptor (VEGFR), integrin, $\alpha$V$\beta$3, $\alpha$5$\beta$1, ERBB2, ERBB3, mesenchymal epithelial transition (MET), insulin-like growth factor-I receptor (IGFIR), ephrin type-A receptor 3 (EPHA3), TRAIL receptor 1 (TRAILR1), TRAIL receptor 2 (TRAILR2), receptor activator of nuclear factor kappa beta (RANKL), fibroblast activation protein (FAP), claudin 18.2, mesothelin, receptor tyrosine kinase like orphan receptor 1 (ROR1), epidermal growth factor receptor variant III (EGFRVIII), six-transmembrane epithelial antigen of the prostate-2 (STEAP2), orphan G protein–coupled receptor, class C group 5 member D (GPRC5D), carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5), and tenascin.

78. The multispecific binding protein of any one of claims 75-77, wherein the first domain and the second domain are coupled via chemical coupling, gene fusion, or a non-covalent association.

79. The multispecific binding protein of any one of claims 75-78, further comprising a linker.

80. The multispecific binding protein of claim 79, wherein the linker comprises a glycine-serine linker.

81. The multispecific binding protein of claim 80, wherein the glycine-serine linker comprises a sequence of (GS)n, wherein n = 1 to 10.

82. The multispecific binding protein of claim 79, wherein the linker comprises (GS)n, (GGS)n, (GGGS)n, (GGSG)n, (GGSGG)n, (GGGGS)n, (GGGGG)n, or (GGG)n, wherein n = 1 to 10.Docket No. WRENCH-002 / WO01 83. The multispecific binding protein of claim 79 or claim 82, wherein the linker comprises (GGGGS)4 or (GGGGS)3.

84. The multispecific binding protein of any one of claims 75-83 wherein the multispecific protein is a bispecific protein.

85. The multispecific binding protein of any one of claims 75-84, wherein the multispecific protein is a trispecific protein.

86. The multispecific binding protein of any one of claims 75-85, wherein the multispecific protein binds to four different target molecules.

87. The single domain DcR3 binding protein of any one of claims 21-38, or the multispecific binding protein of any one of claims 75-86, further comprising a Fc domain.

88. The single domain DcR3 binding protein of any one of claims 21-38, or the multispecific binding protein of any one of claims 75-87, further comprising a half-life extension domain.

89. The half-life extension domain of claim 88 which comprises an albumin-targeting polypeptide.

90. The single domain DcR3 antibody or binding protein of any one of claims 21-38, VHH-Fc fusion protein of any one of claims 1-20 or claims 39-74, or the multispecific binding protein of any one of claims 75- 89 that is non-naturally occurring.

91. A pharmaceutical composition comprising (a) the single domain DcR3 binding protein of any one of claims 21-38, the VHH-Fc fusion protein of any one of claims 1-20 or claims 39-74, or the multispecific binding protein of any one of claims 75-89; and (b) a pharmaceutically acceptable carrier.

92. An isolated nucleic acid encoding the single domain DcR3 binding protein of any one of claims 21-38, the VHH-Fc fusion protein of any one of claims 1-20 or claims 39-74, or the multispecific binding protein of any one of claims 75-89.

93. A vector comprising the isolated nucleic acid of claim 92.Docket No. WRENCH-002 / WO01 94. A host cell that comprises the vector of claim 93 or the nucleic acid of claim 92.

95. A method of treating a disease or condition in a subject in need thereof comprising administering to the subject a therapeutically effective amount of the single domain DcR3 binding protein of any one of claims 21-38, the VHH-Fc fusion protein of any one of claims 1-20 or claims 39-74, or the multispecific binding protein of any one of claims 75-89.

96. The method of claim 95, wherein the disease or condition comprises a proliferative disease, a tumorous disease, an inflammatory disease, an immunological disorder, an autoimmune disease, an infectious disease, a viral disease, an allergic reaction, a parasitic reaction, a graft-versus-host disease or a host-versus-graft disease.

97. A method of treating cancer in a patient, comprising administering a composition comprising the single domain DcR3 binding protein of any one of claims 21-38, the VHH-Fc fusion protein of any one of claims 1- 20 or claims 39-74, or the multispecific binding protein of any one of claims 75-89.

98. The method of claim 97, wherein said cancer is selected from the group consisting of renal clear cell carcinoma (RCC), lung cancer, NSCLC, lung adenocarcinoma, lung squamous cell carcinoma, gastric adenocarcinoma, ovarian cancer, endometrial cancer, breast cancer, triple negative breast cancer (TNBC), head and neck tumor, colorectal adenocarcinoma, melanoma, and metastatic melanoma.

99. The method of claim 98, wherein said cancer is selected from the group consisting of gallbladder carcinoma, liver carcinoma, gastric carcinoma, colon carcinoma, pancreatic carcinoma, bone sarcoma, thyroid adenocarcinoma, lung cancer, renal cell carcinoma, and breast cancer.

100. The method of treatment according to claim 98 or claim 99, wherein the patient experiences an increase in tumor growth inhibition of at least about 10%, 20%, 30% 40% 50% 60% 70% 80% 90%, 100%, 125%, 150%, 175%, 200% 225% 250%, 275%, 300%, 325% 350%, 375%, 400%, 425%, 450%, 475%, 500%, 525%, 550%, 575%, 600%, 625%, 650%, 675%, 700%, 725%, 750%, 775%, 800%, 825%, 850%, 875%, 900%, 925%, 950%, 975%, or 1000%, as compared to a control or an untreated patient.

101. The method of treatment according to any one of claims 97-100, wherein the patient experiences a decrease in tumor growth inhibition of at least about 10%, 20%, 30% 40% 50% 60% 70% 80% 90%, 100%, 125%, 150%, 175%, 200% 225% 250%, 275%, 300%, 325% 350%, 375%, 400%, 425%, 450%, 475%, 500%,Docket No. WRENCH-002 / WO01 525%, 550%, 575%, 600%, 625%, 650%, 675%, 700%, 725%, 750%, 775%, 800%, 825%, 850%, 875%, 900%, 925%, 950%, 975%, or 1000%, as compared to a control or an untreated patient.

102. A method of reducing a tumor comprising contacting the tumor with a composition comprising a single domain DcR3 binding protein of any one of claims 21-38, a VHH-Fc fusion protein of any one of claims 1-20 or claims 39-74, or a multispecific binding protein of any one of claims 75-89.

103. A method of reducing a tumor in a subject in need thereof comprising administering to the subject a composition comprising a single domain DcR3 binding protein of any one of claims 21-38, a VHH-Fc fusion protein of any one of claims 1-20 or claims 39-74, or a multispecific binding protein of any one of claims 75- 89.

104. A method of treating a subject having a cancer, comprising administering to the subject a composition comprising a single domain DcR3 binding protein of any one of claims 21-38, a VHH-Fc fusion protein of any one of claims 1-20 or claims 39-74, or a multispecific binding protein of any one of claims 75-89.

105. The method of any one of claims 95-104, wherein the subject is a human subject.

106. A single domain anti-DcR3 antibody or binding protein of any one of claims 21-38, multispecific binding protein of any one of claims 75-89, or VHH-Fc fusion protein of any one of claims 1-20 or claims 39- 74, wherein the antibody or binding protein, multispecific binding protein, or VHH-Fc fusion protein promotes T cells, Myeloid cells, Dendritic cells, or cytokine immunity against target cells, e.g., cancer.

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