Long-acting il-15 agonist for treating tumor

Abstract

Described are agonistic IL-15 complexes for use in methods of treating diseases, such as solid tumors, in a human subject. The IL-15 complex contains an IL-15 and a fusion protein having an IL-15 receptor α sushi domain fused to an Fc monomer. The treatment results in an effective treatment of the diseases, without inducing treatment related serious adverse event.

Description

LONG-ACTING IL-15 AGONIST FOR TREATING TUMORCROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to PCT Application No.: PCT / CN2024 / 091740 filed on May 8, 2024, the disclosure of which is hereby incorporated by reference in its entirety.REFERENCE TO SEQUENCE LISTING SUBMITTED ELECTRONICALLY

[0002] This application contains a sequence listing with a file name “069777-7WO1 sequence_listing.xml” and a creation date of March 29, 2024, and having a size of 8.42 kb. The sequence listing is part of the specification and is herein incorporated by reference in its entirety.FIELD

[0003] The present disclosure generally relates to methods involving interleukin 15 (IL-15) agonists, such as agonistic IL-15 complexes, which agonistic IL-15 complexes can be used, for instance, in methods of treating a disease in a subject in need thereof.BACKGROUND

[0004] The cytokine interleukin-15 (IL-15) is a member of the four alpha-helix bundle family of lymphokines produced by many cells in the body. IL-15 plays a pivotal role in modulating the activity of both the innate and adaptive immune system, e.g., maintenance of the memory T-cell response to invading pathogens, inhibition of apoptosis, activation of dendritic cells, and induction of Natural Killer (NK) cell proliferation and cytotoxic activity.

[0005] The IL-15 receptor consists of three polypeptides, the type-specific IL-15 receptor alpha (“IL-15Ra”), the IL-2 / IL-15 receptor beta (or CD122) (“3”), and the common gamma chain (or CD132) (“y”) that is shared by multiple cytokine receptors. The IL-15Ra is thought to be expressed by a wide variety of cell types, but not necessarily in conjunction with 0 and y. IL-15 signaling has been shown to occur through the heterodimeric complex of IL-15Ra, 0, and y; through the heterodimeric complex of 0 and y, or through a subunit, IL-15RX, found on mast cells (Ikemizu, Shinji et al. “IL-2 and IL- 15 signaling complexes: different but the same.” Nature immunology vol. 13,12 (2012): 1141-2, PMID: 23160210; Briukhovetska, Daria et al.“Interleukins in cancer: from biology to therapy.” Nature reviews. Cancer vol. 21,8 (2021): 481 - 499, PMID: 3408378).

[0006] IL-15 is a soluble protein, but endogenous IL-15 is not readily detectable in serum or body fluids — instead, it occurs predominantly as a membrane -bound form that is expressed or acquired by several types of accessory cells (Fehniger, T A, and M A Caligiuri. “Interleukin 15: biology and relevance to human disease.” Blood vol. 97,1 (2001): 14-32, PMID: 11133738). For instance, although IL-15 mRNA is detected in cells of both hematopoietic and non- hematopoietic lineage, T cells do not produce IL-15. Instead, IL- 15 binds to the IL-15Ra, forming cell-surface complexes on T cells. IL-15 specifically binds to the IL-15Ra with high affinity via the “sushi domain” in exon 2 of the extracellular domain of the receptor (Budagian, Vadim et al. “IL-15 / IL-15 receptor biology: a guided tour through an expanding universe.” Cytokine & growth factor reviews vol. 17,4 (2006): 259-80, PMID: 16815076). After trans- endosomal recycling and migration back to the cell surface, these IL-15 complexes acquire the property to activate bystander cells expressing the IL-15R low-affinity receptor complex, inducing IL- 15 -mediated signaling via the Jak / Stat pathway. A naturally occurring soluble form of IL-15Ra (“sIL-15Ra”), which is cleaved at a cleavage site in the extracellular domain immediately distal to the transmembrane domain of the receptor has been observed (Lukic, M L et al. “Lack of the mediators of innate immunity attenuate the development of autoimmune diabetes in mice.” Journal of autoimmunity vol. 21,3 (2003): 239-46, PMID: 14599848). Tumor necrosis factor-alpha-converting enzyme (TACE / ADAM17) has been implicated as a protease involved in this process.

[0007] Based on its multifaceted role in the immune system, various therapies designed to modulate IL- 15 -mediated function have been explored. For example, the administration of exogenous IL- 15 can enhance the immune function of patients infected with human immunodeficiency virus (HIV). Despite the amount of progress made in understanding the function of IL-15, many challenges remain in IL-15 based therapies, as further discussed infra. As such, there is strong interest in the further development of new IL-15 based therapeutics.SUMMARY

[0008] The present disclosure generally relates to a method of safely administering to a human subject an agonistic interleukin 15 (IL-15) complex, comprising administering to the humansubject an effective amount of the agonistic IL-15 complex, wherein the IL-15 complex comprises: (a) a fusion protein comprising an IL-15 receptor a sushi domain fused to an Fc monomer, and (b) an IL-15, wherein the IL-15 receptor a sushi domain comprises the amino acid sequence of SEQ ID NO: 5 and the Fc monomer comprises the amino acid sequence of SEQ ID NO: 6.

[0009] Also provided is a method of treating a cancer, comprising administering to a human subject in need thereof an effective amount agonistic interleukin 15 (IL-15) complex, wherein the IL-15 complex comprises: (a) a fusion protein comprising an IL-15 receptor a sushi domain fused to an Fc monomer, and (b) an IL-15, wherein the IL-15 receptor a sushi domain comprises the amino acid sequence of SEQ ID NO: 5 and the Fc monomer comprises the amino acid sequence of SEQ ID NO: 6.

[0010] In some embodiments, the carboxyl-terminus of the IL-15 receptor a sushi domain is fused to the amino -terminus of the Fc monomer via a linker comprising the amino acid sequence of GGGGS (SEQ ID NO: 7). In some embodiments, the linker consists of the amino acid sequence of SEQ ID NO: 7 or SEQ ID NO: 8. In some embodiments, the IL-15 comprises the amino acid sequence of SEQ ID NO: 3. In some embodiments, the IL-15 consists of the amino acid sequence of SEQ ID NO: 3. In some embodiments, the IL-15 comprises the amino acid sequence of SEQ ID NO: 4. In some aspects, the IL-15 consists of the amino acid sequence of SEQ ID NO: 4.

[0011] In some embodiments, the fusion protein comprises the amino acid sequence of SEQ ID NO: 1. In some embodiments, the fusion protein comprises the amino acid sequence of SEQ ID NO: 2.

[0012] In certain embodiments, the method comprises administering to the human subject an effective amount of 3 pg / kg to 300 pg / kg of the agonistic IL-15 complex per administration.

[0013] In certain embodiments, the agonistic IL-15 complex is administered intravenously, particularly by intravenous infusion. In certain embodiments, the IL-15 complex is administered by intravenous infusion over 30-75 minutes, preferably over 45-60 minutes.

[0014] In certain embodiments, the agonistic IL-15 complex is administered subcutaneously.

[0015] In certain embodiments, the agonistic IL-15 complex is administered weekly (once every week) or once more than a week, such as once every two weeks or once every three weeks.

[0016] In certain embodiments, the human subject has a solid tumor prior to the initial administration of the effective amount of the agonistic IL-15 complex. For example, the human subject has a solid tumor such as a colorectal cancer, head and neck cancer (including nasopharyngeal and head and neck squamous cell carcinoma), pancreatic cancer, urothelial carcinoma, cholangiocarcinoma, or esophageal squamous cell cancer (ESCC).

[0017] In certain embodiments, the human subject has had at least one line of prior treatment for the solid tumor.

[0018] In certain embodiments, the human subject has received at least one prior treatment of checkpoint inhibitor (CPI) therapy. In certain embodiments, the checkpoint inhibitor is an anti- PD1 antibody, an anti-PD-Ll antibody, or an anti-CTLA4 antibody.

[0019] In certain embodiments, the method does not result in a treatment related serious adverse event. In certain embodiments, the method does not induce Dose Limiting Toxicities (DLT) in the subject. In certain embodiments, the method results in an effective treatment of the solid tumor in the human subject as measured by one or more of Objective Response Rate (ORR), Duration of Response (DoR), Progression -free Survival (PFS) and Disease Control Rate (DCR).

[0020] Other embodiments, features and advantages of the invention will be apparent from the following disclosure, including the detailed description of the invention and its preferred embodiments and the appended claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic of the study design.DETAILED DESCRIPTION

[0022] Various publications, articles and patents are cited or described in the background and throughout the specification; each of these references is herein incorporated by reference in its entirety. Discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is for the purpose of providing context for the invention. Such discussion is not an admission that any or all of these matters form part of the prior art with respect to any inventions disclosed or claimed.

[0023] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this inventionpertains. Otherwise, certain terms used herein have the meanings as set in the specification. All patents, published patent applications, and publications cited herein are incorporated by reference as if set forth fully herein.

[0024] It must be noted that as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural reference unless the context clearly dictates otherwise.

[0025] Unless otherwise stated, any numerical value, such as a % sequence identity or a % sequence identity range described herein, are to be understood as being modified in all instances by the term “about.” Thus, a numerical value typically includes ± 10% of the recited value. For example, a dosage of 10 mg includes 9 mg to 11 mg. As used herein, the use of a numerical range expressly includes all possible subranges, all individual numerical values within that range, including integers within such ranges and fractions of the values unless the context clearly indicates otherwise.

[0026] As used herein, the conjunctive term “and / or” between multiple recited elements is understood as encompassing both individual and combined options. For instance, where two elements are conjoined by “and / or,” a first option refers to the applicability of the first element without the second. A second option refers to the applicability of the second element without the first. A third option refers to the applicability of the first and second elements together. Any one of these options is understood to fall within the meaning, and therefore satisfy the requirement of the term “and / or” as used herein. Concurrent applicability of more than one of the options is also understood to fall within the meaning, and therefore satisfy the requirement of the term “and / or.”

[0027] Unless otherwise indicated, the term “at least” preceding a series of elements is to be understood to refer to every element in the series. Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the invention.

[0028] Throughout this specification and the claims which follow, unless the context requires otherwise, the word “comprise” and variations such as “comprises” and “comprising” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integer or step. When used herein the term “comprising” can be substituted with the term “containing” or “including” or sometimes when used herein with the term “having.”

[0029] When used herein “consisting of’ excludes any element, step, or ingredient not specified in the claim element. When used herein, “consisting essentially of’ does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim. Any of the aforementioned terms of “comprising,” “containing,” “including,” and “having,” whenever used herein in the context of an aspect or embodiment of the invention can be replaced with the term “consisting of’ or “consisting essentially of’ to vary scopes of the disclosure.

[0030] As used herein, the terms “antibody” and “antibodies” refer to molecules that contain an antigen binding site. Antibodies include, but are not limited to, monoclonal antibodies, multispecific antibodies, human antibodies, humanized antibodies, synthetic antibodies, chimeric antibodies, polyclonal antibodies, single domain antibodies, camelized antibodies, single -chain Fvs (scFv), single chain antibodies, Fab fragments, F(ab') fragments, disulfide -linked bispecific Fvs (sdFv), intrabodies, and anti -idiotypic (anti-Id) antibodies (including, e.g., anti-Id and anti- anti-Id antibodies to antibodies), and epitope-binding fragments of any of the above. In particular, antibodies include immunoglobulin molecules and immunologically active fragments of immunoglobulin molecules. Immunoglobulin molecules can be of any type (e.g., IgG, IgE, IgM, IgD, IgA and IgY), class (e.g., IgGl, IgG2, IgG3, IgG4, IgAl and TgA2) or subclass.

[0031] As used herein, the terms “disease” and “disorder” are used interchangeably to refer to a condition affected by IL-15 signal transduction. In particular, a "disease" and "disorder" can be a pathological condition, and more particularly a disease affected by IL-15 signal transduction.

[0032] The term “agonist” refers to a compound that binds to a receptor and elicits an agonistic intracellular response. Agonists mimic the effects of endogenous ligands, hormones, and produce physiological responses similar to those produced, for example, by endogenous ligands.

[0033] As used herein, “fragment crystallizable region” or “Fc” refers to a polypeptide containing an antibody heavy chain constant region excluding the first domain of the constant region CHI. Therefore, Fc can include the last two domains of the heavy chain constant region (CH2 and CH3) of an IgA, IgD or IgG antibody, the last three domains of the heavy chain constant region (CH2, CH3 and CH4) of an IgE and IgM antibody. The Fc can also include the flexible hinge region connected to the N-terminus of the CH2 domain. For IgA and IgM, Fc can include the J chain. For IgG, Fc contains immunoglobulin domains Cy2 and Cy3 and the hinge between Cyl and Cy2. Fc plays multiple roles in dimerization for the formation of Y-shaped structure of Ig and maintenance of the structure, and Fc-mediated effector functions andextension of serum half-life. The binding of Fc in IgG to its receptor Fc-gamma receptors (FcyRs) triggers antibody-dependent cell-mediated cytotoxicity (ADCC) and antibody -dependent cell-mediated phagocytosis to kill and clear target cells (e.g., tumor cells). The binding of Fc to the serum complement molecule (Clq) can initiate the assembly of membrane attack complex formed by complement cascade proteins to destroy target cells, which is termed complementdependent cytotoxicity (CDC). Besides mediation of effector functions, Fc can also bind to neonatal Fc receptor (FcRn) in a pH-dependent manner, which can result in the extension of the serum half-life of IgG. In addition, binding of Fc to immune -related molecules such as Fc receptors can regulate immune response in vivo. Fc can refer to this region in isolation, or in the context of an antibody, antibody fragment, or Fc fusion. The Fc can be part of an antibody, an Fc fusion, or a protein or protein domain comprising Fc. The naturally occurring Fc forms a homodimer. Particularly preferred are Fc variants, which are non-naturally occurring Fc variants obtained using synthetic biology.

[0034] As used herein, “Fc monomer” or “monomeric Fc” refers to a Fc variant that no longer forms a homodimer under physiological conditions. Examples of Fc monomer include, but are not limited to, Fc monomers described in Wang et al., 2017, Front. Immunol., vol. 8, article 1545, WO2022088484A1, and US20210206847, the content of each of which is hereby incorporated by reference in its entirety.

[0035] In some aspects, the Fc monomer of the present disclosure comprises an Fc polypeptide whose molecular weight is only half of the wild-type Fc dimer, and retains the FcRn binding performance and Protein A / G binding performance of the antibody Fc region, and can achieve high-efficiency expression in host cells, such as prokaryotic host cells, and can significantly decrease non-specific binding as compared to previously developed monomeric IgGl Fc mutants.

[0036] As used herein, the term “IL-15 functional fragment” refers to a portion of IL-15 that can serve to elicit or induce any degree of biological activity associated with IL-15. Such functional fragments include any mutated IL- 15 of any length and / or any truncated version of IL- 15 that retains a biological activity of IL-15. In some aspects, an IL- 15 functional fragment comprises or consists of the sequence of SEQ ID NO: 3. In some aspects, an IL-15 functional fragment comprises or consists of the sequence of SEQ ID NO: 4. In some aspects, an IL-15 functionalfragment comprises the sequence of any of the IL-15 sequences described throughout the present application.

[0037] “Polynucleotide” or “nucleic acid,” as used interchangeably herein, refers to polymers of nucleotides of any length and includes DNA and RNA. The nucleotides can be deoxyribonucleotides, ribonucleotides, modified nucleotides or bases, and / or their analogs, or any substrate that can be incorporated into a polymer by DNA or RNA polymerase or by a synthetic reaction. A polynucleotide may comprise modified nucleotides, such as methylated nucleotides and their analogs. “Oligonucleotide,” as used herein, refers to short, generally singlestranded, synthetic polynucleotides that are generally, but not necessarily, fewer than about 200 nucleotides in length. The terms “oligonucleotide” and “polynucleotide” are not mutually exclusive. The description above for polynucleotides is equally and fully applicable to oligonucleotides. Unless specified otherwise, the left-hand end of any single-stranded polynucleotide sequence disclosed herein is the 5’ end; the left-hand direction of double-stranded polynucleotide sequences is referred to as the 5’ direction. The direction of 5’ to 3’ addition of nascent RNA transcripts is referred to as the transcription direction; sequence regions on the DNA strand having the same sequence as the RNA transcript that are 5 ’ to the 5 ’ end of the RNA transcript are referred to as “upstream sequences”; sequence regions on the DNA strand having the same sequence as the RNA transcript that are 3 ’ to the 3 ’ end of the RNA transcript are referred to as “downstream sequences.”

[0038] The term “Cancer” as used herein refers to solid tumors or blood-bome cancers. The solid tumor of the present disclosure includes a sarcoma or cancer, such as fibrosarcoma, myxosarcoma, liposarcoma, chondrosarcoma, osteosarcoma, or another sarcoma, synovial tumor, mesothelioma, Ewing’s tumor, leiomyosarcoma, Rhabdomyosarcoma, colon cancer, lymphoid malignancies, pancreatic cancer, breast cancer, lung cancer, ovarian cancer, prostate cancer, hepatocellular carcinoma, squamous cell carcinoma, basal cell carcinoma, adenocarcinoma, sweat gland carcinoma, sebaceous gland carcinoma, papillary carcinoma, Papillary adenocarcinoma, medullary carcinoma, bronchial carcinoma, renal cell carcinoma, hepatocellular carcinoma, cholangiocarcinoma, choriocarcinoma, Wilms tumor, cervical cancer, testicular tumor, bladder cancer or central nervous system tumor (such as glioma) , Astrocytoma, medulloblastoma, craniopharyngioma, ependymoma, pineal gland, hemangioblastoma, acoustic neuroma, oligodendroglioma, hemangioma, melanoma, neuroblastoma cell tumor orretinoblastoma), or esophageal squamous cell cancer (ESCC). The blood-bome cancer of the present disclosure include leukemia, such as acute leukemia (such as acute lymphoblastic leukemia, acute myeloid leukemia, acute myeloid leukemia and myeloblasts, promyelocytic cells, myelomononuclear cells, monocytes and Erythroleukemia); chronic leukemia (such as chronic granulocytic (granulocyte) leukemia, chronic granulocytic leukemia and chronic lymphocytic leukemia), polycythemia vera, lymphoma, Hodgkin’s disease, non-Hodgkin’s lymphoma (inert And advanced forms), multiple myeloma, Waldenstrom's macroglobulinemia, heavy chain disease, myelodysplastic syndrome, hairy cell leukemia or myelodysplasia.

[0039] As used herein, “subject” means any animal, preferably a mammal, most preferably a human, to whom will be or has been treated by a method according to an embodiment of the present disclosure. The term “mammal” as used herein, encompasses any mammal. Examples of mammals include, but are not limited to, cows, horses, sheep, pigs, cats, dogs, mice, rats, rabbits, guinea pigs, non-human primates (NHPs) such as monkeys or apes, humans, etc., more preferably a human. A human subject can include a patient.

[0040] The terms “polypeptide” and “peptide” and “protein” are used interchangeably herein and refer to polymers of amino acids of any length. The polymer may be linear or branched, it may comprise modified amino acids, and it may be interrupted by non-amino acids. The terms also encompass an amino acid polymer that has been modified naturally or by intervention; for example, disulfide bond formation, glycosylation, lipidation, acetylation, phosphorylation, or any other manipulation or modification. Also included within the definition are, for example, polypeptides containing one or more analogs of an amino acid, including but not limited to, unnatural amino acids, as well as other modifications known in the art. It is understood that, because the polypeptides of this disclosure may be based upon antibodies or other members of the immunoglobulin superfamily, in certain embodiments, a “polypeptide” can occur as a single chain or as two or more associated chains.

[0041] As used herein, the terms “treat”, “treating” and “treatment” in the context of the administration of a therapy to a subject refer to the beneficial effects that a subject derives from a therapy, such as, but not limited to, the reduction or inhibition of the progression, spread and / or duration of a disease or disorder, the reduction or amelioration of the severity of a disease or disorder, amelioration of one or more symptoms of a disease or disorder, and / or the reduction in the duration of one or more symptom of a disease or disorder resulting from the administration ofone or more therapies. In specific embodiments, such terms in the context of cancer include, but are not limited to, one, two, or three or more results following the administration of a therapy to a subject: (1) a reduction in the growth of a tumor or neoplasm; (2) a reduction in the formation of a tumor; (3) an eradication, removal, or control of primary, regional and / or metastatic cancer; (4) a reduction in metastatic spread; (5) a reduction in mortality; (6) an increase in survival rate; (7) an increase in length of survival; (8) an increase in the number of patients in remission; (9) a decrease in hospitalization rate; (10) a decrease in hospitalization lengths; and (11) the maintenance in the size of the tumor so that it does not increase by more than 10%, or by more than 8%, or by more than 6%, or by more than 4%; preferably the size of the tumor does not increase by more than 2%.

[0042] As used herein, the terms “prevent,” “preventing” and “prevention” in the context of the administration of a therapy to a subject refer to the inhibition of the onset or recurrence of a disease or disorder in a subject.

[0043] The phrases “percent (%) sequence identity” or “% identity” or “% identical to” when used with reference to an amino acid sequence describe the number of matches (“hits”) of identical amino acids of two or more aligned amino acid sequences as compared to the number of amino acid residues making up the overall length of the amino acid sequences. In other terms, using an alignment, for two or more sequences the percentage of amino acid residues that are the same (e.g. 90%, 91%, 92%, 93%, 94%, 95%, 97%, 98%, 99%, or 100% identity over the full- length of the amino acid sequences) may be determined, when the sequences are compared and aligned for maximum correspondence as measured using a sequence comparison algorithm as known in the art, or when manually aligned and visually inspected. The same determination may be made for nucleotide sequences. The sequences which are compared to determine sequence identity may thus differ by substitution(s), addition(s) or deletion(s) of amino acids. Suitable programs for aligning protein sequences are known to the skilled person. The percentage sequence identity of protein sequences can, for example, be determined with programs such as CLUSTALW, Clustal Omega, FASTA or BLAST, e.g., using the NCBI BLAST algorithm (Altschul SF, et al (1997), Nucleic Acids Res. 25:3389-3402).

[0044] As used herein, a “non-naturally occurring” nucleic acid or polypeptide refers to a nucleic acid or polypeptide that does not occur in nature. A “non-naturally occurring” nucleic acid or polypeptide can be synthesized, treated, fabricated, and / or otherwise manipulated in a laboratoryand / or manufacturing setting. In some cases, a non-naturally occurring nucleic acid or polypeptide can comprise a naturally -occurring nucleic acid or polypeptide that is treated, processed, or manipulated to exhibit properties that were not present in the naturally -occurring nucleic acid or polypeptide, prior to treatment. As used herein, a “non-naturally occurring” nucleic acid or polypeptide can be a nucleic acid or polypeptide isolated or separated from the natural source in which it was discovered, and it lacks covalent bonds to sequences with which it was associated in the natural source. A “non-naturally occurring” nucleic acid or polypeptide can be made recombinantly or via other methods, such as chemical synthesis.

[0045] As used herein, the term “operably linked” refer to a linkage or a juxtaposition wherein the components so described are in a relationship permitting them to function in their intended manner. For example, a regulatory sequence operably linked to a nucleic acid sequence of interest is capable of directing the transcription of the nucleic acid sequence of interest, or a signal sequence operably linked to an amino acid sequence of interest is capable of secreting or translocating the amino acid sequence of interest over a membrane.

[0046] As used herein, “cytokine release syndrome” refers to a supraphysiologic response following any immune therapy that results in the activation or engagement of endogenous or infused T cells and / or other immune effector cells.

[0047] The application generally relates to a method of safely administering to a human subject an agonistic interleukin 15 (IL-15) complex comprising: (a) a fusion protein comprising an IL-15 receptor a sushi domain fused to an Fc monomer, and (b) an IL-15.

[0048] Though tumor immune checkpoint inhibitors have proven a milestone event in tumor therapy, the overall efficiency of such treatments is not high, and the objective response rate of single drug treatment is mostly in the range of 20%-30%. Based on the understanding of the tumor microenvironment, many researchers believe that immune activation against NK cells is an important way to solve the problem of low efficiency of PD-1 monoclonal antibodies.

[0049] A human IL-15, e.g., a 12-14 kD cytokine, was discovered by Grabstein et al. in 1994. It can play a role in the body's normal immune response, such as promoting the proliferation of T cells, B cells and NK cells. It has been demonstrated that IL-15 could be a useful therapeutic alternative treatment or combination treatment. For instance, IL-15 has a more biased NK cell activation activity than IL-2. In addition, IL-2 stimulates the proliferation of Treg in addition to the proliferation of killer immune cells, and these Treg suppress the immune response, leading toa diminished antitumor effect. In contrast, the specific receptor for IL-15 is IL-15Ra (CD125), which does not activate Treg cells. Therefore, from the perspective of being an immune activator, IL-15 has significant advantages over IL-2 and is expected to become a new generation of anti-tumor immune activator for 70-80% of tumor patients who do not respond to PD-1 monoclonal antibody, relying on its unique NK cell activation ability, with great market potential. As used herein, the term “IL-15” encompasses a full-length IL-15 or an IL-15 functional fragment. An “IL-15” can be a wild-type IL-15 or a variant IL-15.

[0050] In spite of its potential, the wild-type IL-15 has an extremely short half-life in vivo and very limited efficacy. In addition, IL-15 has a trans delivery mechanism, and effective IL-15 therapeutics need to consider the formation of complexes between IL-15 and IL-15Ra, which poses great difficulties. In addition to the short half-life and poor pharmacokinetics as factors limiting its clinical application, increasing the dosage of IL-15 can also induce a cytokine storm, leading to strong toxic side effects, thereby greatly limiting its clinical dosage level. Therefore, improved IL-15 therapies are of high interest and of great value.

[0051] The application also generally relates to a method of treating a cancer, comprising administering to a human subject in need thereof an agonistic interleukin 15 (IL-15) complex comprising: (a) a fusion protein comprising an IL-15 receptor a sushi domain (aSu) fused to an Fc monomer, and (b) an IL-15. As used herein, an “agonistic IL-15 complex” refers to a protein complex containing an IL- 15 and a fusion protein having an IL- 15 receptor a sushi domain fused to an Fc monomer. The IL-15 in an agonistic IL-15 complex can be a full-length IL-15 or an IL- 15 functional fragment. The IL- 15 can interact with the IL- 15 receptor a sushi domain non covalently to form the agonistic IL- 15 complex.

[0052] The present disclosure generally relates to a protein complex, i.e., an agonistic IL-15 complex, comprising an IL15 and a monomeric IL-15 receptor aSu / Fc fusion protein, and uses thereof. The agonistic IL-15 complexes described herein have a long half-life, have demonstrated good safety profiles, and have demonstrated higher anti-tumor activity as compared to other IL- 15 based treatments.

[0053] In certain embodiments, the fusion protein comprises an interleukin- 15 (IL-15) receptor a sushi domain fused to an Fc monomer, wherein the IL-15 receptor a sushi domain comprises the amino acid sequence of SEQ ID NO: 5 and the Fc monomer comprises the amino acid sequence of SEQ ID NO: 6. In some embodiments, the carboxyl-terminus of the IL-15 receptor a sushidomain is fused to the amino -terminus of the Fc monomer via a linker comprising the amino acid sequence of GGGGS (SEQ ID NO: 7), such as a linker consisting of the amino acid sequence of SEQ ID NO: 7 or SEQ ID NO: 8. In certain embodiments, the fusion protein comprises or consists of the amino acid sequence of SEQ ID NO: 1. In certain embodiments, the fusion protein comprises or consists of the amino acid sequence of SEQ ID NO: 2.

[0054] In some aspects, the IL-15 receptor a sushi domain of the present disclosure comprises the extracellular domain of IL- 15 receptor a starts from the cysteine residue (Cl) encoded by the first exon 2 and ends at the fourth exon. The cysteine residue (C4), residues Cl and C4 encoded by sub-2 are all contained in the sushi domain. The amino acid sequence of the a sushi domain of IL- 15 receptor formed by the substitution, deletion or addition of one or more amino acid residues and having corresponding activity is also included in the present disclosure.

[0055] In some embodiments, the IL-15 comprises a functional IL-15 fragment having or consisting of the amino acid sequence of SEQ ID NO: 3. In some other embodiments, the IL-15 comprises a functional IL-15 fragment having or consisting of the amino acid sequence of SEQ ID NO: 4.

[0056] In certain embodiments, the method comprises administering to the human subject an effective amount of 3 pg / kg to 300 pg / kg of the agonistic IL- 15 complex per administration. In certain embodiments, the method comprises administering to the human subject an effective amount of 3 pg / kg of the agonistic IL-15 complex per administration. In certain embodiments, the method comprises administering to the human subject an effective amount of 10 pg / kg of the agonistic IL-15 complex per administration. In certain embodiments, the method comprises administering to the human subject an effective amount of 30 pg / kg of the agonistic IL- 15 complex per administration. In certain embodiments, the method comprises administering to the human subject an effective amount of 45 pg / kg of the agonistic IL-15 complex per administration. In certain embodiments, the method comprises administering to the human subject an effective amount of 60 pg / kg of the agonistic IL-15 complex per administration. In certain embodiments, the method comprises administering to the human subject an effective amount of 90 pg / kg of the agonistic IL-15 complex per administration. In certain embodiments, the method comprises administering to the human subject an effective amount of 120 pg / kg of the agonistic IL-15 complex per administration. In certain embodiments, the method comprises administering to the human subject an effective amount of 180 pg / kg of the agonistic IL- 15complex per administration. In certain embodiments, the method comprises administering to the human subject an effective amount of 240 pg / kg of the agonistic IL-15 complex per administration. In certain embodiments, the method comprises administering to the human subject an effective amount of 240 pg / kg to 300 pg / kg of the agonistic IL-15 complex per administration.

[0057] In certain embodiments, the agonistic IL-15 complex is administered intravenously. In certain embodiments, the agonistic IL-15 complex is administered by intravenous infusion. In certain embodiments, the agonistic IL- 15 complex is administered by intravenous infusion over 30-75 minutes. In preferred embodiments, the agonistic IL-15 complex is administered by intravenous infusion over 45-60 minutes. In certain embodiments, the agonistic IL- 15 complex is administered by intravenous infusion over 30 minutes. In certain embodiments, the agonistic IL- 15 complex is administered by intravenous infusion over 45 minutes. In certain embodiments, the agonistic IL-15 complex is administered by intravenous infusion over 60 minutes.

[0058] In certain embodiments, the agonistic IL-15 complex is administered subcutaneously.

[0059] In certain embodiments, the agonistic IL-15 complex is administered weekly, bi-monthly, every three weeks, or monthly, preferably the agonistic IL-15 complex is administered weekly. As used herein, “weekly” refers to every 7 days ± 1 day.

[0060] In certain embodiments, the agonistic IL-15 complex is administered to the subject 1 to 60 times, or more than 60 times. In certain embodiments, the agonistic IL-15 complex is administered to the subject 4 times per treatment cycle. In certain embodiments, the agonistic IL- 15 complex is administered to the subject for 6 treatment cycles. In certain embodiments, the agonistic IL-15 complex is administered to the subject for 12 treatment cycles. In certain embodiments, a treatment cycle is a month. In certain embodiments, the agonistic IL-15 complex is administered to the subject weekly for at least 1 month, 2 months, 3 months, 4 months, 5 months, 6 months, 7 months, 8 months, 9 months, 10 months, 11 months, 12 months, or more than 12 months.

[0061] In certain embodiments, the human subject has a solid tumor prior to the initial administration of the effective amount of the agonistic IL-15 complex. In some aspects, the tumor is a solid tumor, such as a carcinoma, a sarcoma, or a melanoma. In some aspects, the solid tumor is selected from the group consisting of a bladder cancer, a lung cancer, a breast cancer, a colorectal cancer, a brain tumor, a prostate cancer, urothelial carcinoma,cholangiocarcinoma, a melanomas, a merkel cell carcinoma, a head and neck cancer, a small bowel cancer, a squamous cell carcinoma, metastatic solid tumor or a cervical cancer. In some aspects, the tumor is a bladder cancer. In some aspects, the tumor is a lung cancer, such as a nonsmall cell lung cancer (NSCLC). In some aspects, the tumor is a head and neck cancer. In some aspects, the tumor is a pancreatic cancer. In some aspects, the tumor is urothelial carcinoma. In some aspects, the tumor is a colorectal cancer. In certain embodiments, the tumor is incurable, unresectable, locally advanced or metastatic cancer that is refractory to standard therapies . In certain embodiments, the tumor is esophageal squamous cell cancer (ESCC).

[0062] In certain embodiments, the human subject has had at least one line of prior treatment for the solid tumor. In certain embodiments, the human subject has received at least one prior treatment of checkpoint inhibitor (CPI) therapy alone or in combination with oncolytic vaccine, antibody, or chemotherapeutic agents. In certain embodiments, the checkpoint inhibitor is an anti-PD-1 antibody, an anti-PDL-1 antibody, or an anti-CTLA-4 antibody.

[0063] As used herein, “safely administering" refers to an administration of an agonistic interleukin 15 (IL-15) complex to a human subject that does not result in an adverse event unacceptable to a regulatory agency. In certain embodiments, the method does not result in a treatment related serious adverse event. Adverse events (AEs) include cytokine release syndrome (CRS), neurotoxicity, hematological toxicity including neutropenia, thrombocytopenia, and anemia, ocular toxicity, encephalopathy, myocarditis, fatigue lasting > 7 days, nausea, vomiting, or diarrhea that persists for > 72 hours despite the use of optimal medical therapy, elevations in amylase or lipase, 4 electrolyte abnormalities that do not respond to replacement therapy and that persist for > 48 hours, endocrinopathies, including hypothyroidism and adrenal insufficiency, that cannot be adequately supplemented with hormone replacement therapy, rash with ulceration or bullae formation that does not resolve within 7 days, and hypertension that does not respond to medical therapy within 24 hours. As used herein, “serious adverse event” or “SAE” is defined as any adverse experience that meets any of the following criteria: results in death, is life threatening, requires hospitalization or prolongation of existing hospitalization (additionally, complications occurring during hospitalization are also considered AEs); results in persistent or significant disability or incapacity or substantial disruption of the ability to conduct normal life functions; important medical events that may not result in death, be life threatening, or require hospitalization may be considered serious when, based upon appropriate medical judgment, theymay jeopardize the patient and may require medical or surgical intervention to prevent one of the outcomes listed in this definition.

[0064] In certain embodiments, the method does not induce Dose Limiting Toxicities (DLT) in the subject. As used herein, “dose-limiting toxicity” or “DLT” refers to the occurrence of any adverse events that are at least possibly related to study drug.

[0065] In certain embodiments, the method results in an effective treatment of the solid tumor in the human subject as measured by one or more of Objective Response Rate (ORR), Duration of Response (DoR), Progression-free Survival (PFS) and Disease Control Rate (DCR). As used herein, “objective response rate” or “ORR” is the percentage of people in a study or treatment group who have a partial response (PR) or complete response (CR) to the treatment within a certain period of time. As used herein, “complete response” is a disappearance of all target lesions. As used herein, “partial response” is at least a 30% decrease in the sum of diameters of target lesions, taking as reference the baseline sum diameters.Numbered Embodiments

[0066] Subject matter described in this application includes, but is not limited to, the following numbered embodiments:1. A method of safely administering to a human subject an agonistic interleukin 15 (IL- 15) complex, comprising administering to the human subject the agonistic IL-15 complex at an effective amount of 3 pg / kg to 300 pg / kg per administration, wherein the IL-15 complex comprises: (a) a fusion protein comprising an IL- 15 receptor a sushi domain fused to an Fc monomer, and (b) an IL-15, wherein the IL-15 receptor a sushi domain comprises the amino acid sequence of SEQ ID NO: 5 and the Fc monomer comprises the amino acid sequence of SEQ ID NO: 6.2. A method of treating a cancer, comprising administering to a human subject in need thereof an agonistic interleukin 15 (IL-15) complex at an effective amount of 3 pg / kg to 300 pg / kg per administration, wherein the IL-15 complex comprises: (a) a fusion protein comprising an IL-15 receptor a sushi domain fused to an Fc monomer, and (b) an IL-15, wherein the IL-15 receptor a sushi domain comprises the amino acid sequence of SEQ ID NO: 5 and the Fc monomer comprises the amino acid sequence of SEQ ID NO: 6.3. The method of embodiment 1 or 2, wherein the carboxyl-terminus of the IL-15 receptor a sushi domain is fused to the amino -terminus of the Fc monomer via a linker comprisingthe amino acid sequence of SEQ ID NO: 7. . The method of any one of embodiments 1 to 3, wherein the linker consists of the amino acid sequence of SEQ ID NO: 8. . The method of any one of embodiments 1-4, wherein the IL- 15 comprises the amino acid sequence of SEQ ID NO: 3. . The method of any one of embodiments 1-4, wherein the IL-15 comprises the amino acid sequence of SEQ ID NO: 4. a. The method of any one of embodiments 1-6, wherein the fusion protein comprises the amino acid sequence of SEQ IED NO: 1. b. The method of any one of embodiments 1-6, wherein the fusion protein comprises the amino acid sequence of SEQ IED NO: 2. . The method of any one of embodiments l-7b, wherein the agonistic IL-15 complex is administered intravenously, particularly by intravenous infusion. . The method of embodiment 8, wherein the IL-15 complex is administered by intravenous infusion over 30-75 minutes, preferably over 45-60 minutes. 0. The method of any one of embodiments 1-7, wherein the agonistic IL- 15 complex is administered subcutaneously. 1. The method of any one of embodiments 1-10, wherein the agonistic IL- 15 complex is administered to the human subject at the effective amount of 10 pg / kg, 15 pg / kg, 30 pg / kgm, 45 pg / kg, 60 pg / kg, 75 pg / kg or 90 pg / kg per administration. 2. The method of any one of embodiments 1-10, wherein the agonistic IL-15 complex is administered to the human subject at the effective amount of 100 pg / kg, 125 pg / kg, 150 pg / kg or 175 pg / kg per administration. 3. The method of any one of embodiments 1-10, wherein the agonistic IL- 15 complex is administered to the human subject at the effective amount of 200 pg / kg, 225 pg / kg, 250 pg / kg, 275 pg / kg or 300 pg / kg per administration. 4. The method of any one of embodiments 1-13, wherein the agonistic IL-15 complex is administered once every week. 5. The method of any one of embodiments 1-13, wherein the agonistic IL- 15 complex is administered once every two weeks. 6. The method of any one of embodiments 1-13, wherein the agonistic IL- 15 complex isadministered once every three weeks. b. The method of any one of embodiments 1-13, wherein the agonistic IL-15 complex is administered once every month. . The method of any of the foregoing embodiments, wherein the human subject has a solid tumor prior to the initial administration of the effective amount of the agonistic IL-15 complex. . The method of embodiment 17, wherein the human subject has had at least one line of prior treatment for the solid tumor. . The method of embodiment 18, wherein the human subject has had at least one prior treatment of checkpoint inhibitor (CPI) therapy. . The method of embodiment 19, wherein the human subject has had at least one prior treatment of an anti-PDl antibody, an anti-PD-Ll antibody, or an anti-CTLA4 antibody.. The method of any one of embodimentsl7-20, wherein the solid tumor is colorectal cancer, head and neck cancer (including nasopharyngeal and head and neck squamous cell carcinoma), pancreatic cancer, urothelial carcinoma, cholangiocarcinoma, or esophageal squamous cell cancer (ESCC). . The method of any one of the foregoing embodiments, wherein the method does not result in a treatment related serious adverse event. . The method of any of the foregoing embodiments, wherein the method does not induce Dose Limiting Toxicities (DLT) in the subject. . The method of any one of embodiments 13-17, wherein the method results in an effective treatment of the solid tumor in the human subject, e.g., as measured by one or more of Objective Response Rate (ORR), Duration of Response (DoR), Progression -free Survival (PFS) and Disease Control Rate (DCR). . The method of any of the foregoing claims, wherein the human subject has one or more of the following:1. > 18 years and <80 years old.2. Histologically or cytologically confirmed incurable, unresectable, locally advanced or metastatic cancer that is refractory to standard therapies3. Prior therapy:• Progressed on or are intolerant to all standard therapies including checkpoint inhibitors (such as PD-1, PDL-1, CTLA-4) as a single agent or in combination with oncolytic vaccine, antibody, or chemotherapeutic agents4. Patient has at least 1 measurable target lesion or evaluable disease according to RECIST version 1.15. Eastern Cooperative Oncology Group (ECOG) performance status 0 or 16. Patient’s life expectancy > 6 months7. Adequate hepatic function as evidenced by meeting all of the following requirements:• Total bilirubin < 1.5 x institutional upper limit of normal (ULN); or < 5 * institutional ULN for patients who have serum bilirubin increases due to underlying Gilbert’s Syndrome (familial benign unconjugated hyperbilirubinemia).• Aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP) < 2.5 x ULN; AST or ALT < 5 x ULN if liver metastases are present8. Adequate renal function as serum creatinine < 1.5 x ULN and calculated creatinine clearance (CrCL) > 60 mL / min (Cockcroft-Gault Equation).9. Hematological function defined as:• Absolute neutrophil count > 1,500 / pL without growth factor support in the 2 weeks prior to study entry• Hemoglobin > 9 g / dL without transfusion in the 2 weeks prior to study entry• Platelet count > 100,000 / pL without transfusion in the 2 weeks prior to study entry10. Prothrombin (PT), international normalized ratio (INR), or activated partial thromboplastin time (aPTT) < 1.5 x ULN; use of full dose anticoagulants is permitted. The method of any of the foregoing claims, wherein the human subject does not have one or more of the following:1) Use of systemic corticosteroids in a dose equivalent to > 10 mg / day of prednisone or other immunosuppressive agent within 2 weeks prior to study entry;2) Previous treatment with an IL-2 or IL-15 agonist, including but not limited to rhIL-15(NCI), ALT-803 (ALTOR), NKTR-214 (Nektar).27. The agonistic interleukin 15 (IL-15) complex for use in a method of any of the foregoing claims.SEQUENCE LISTINGEXAMPLESExample 1: Clinical study of an agonistic interleukin 15 complex

[0067] This is a First-in-Human, Phase I, open-label, multicenter, dose-escalation and cohort expansion clinical study to evaluate the safety, tolerability, pharmacokinetics (PK), pharmacodynamics (PD), and preliminary antitumor activity of FL115 when administered intravenously (IV) to adult patients with locally advanced or metastatic solid tumors who have progressed on, cannot tolerate, or do not have a standard-of-care therapy. The study consists of two parts: a dose-escalation phase (Part A) and a cohort expansion phase (Part B).

[0068] FL115 (also named FL115-V2), an agonistic interleukin 15 complex according to an embodiment of the application, contains a monomeric IL-15 receptor aSu / Fc fusion protein having the amino acid sequence of SEQ ID NO: 2 and a mutant IL15 having the amino acid sequence of SEQ ID NO: 3. FL115 will be administered intravenously once a week or weekly (QW), 4 times per treatment cycle. Each subject can receive up to 12 treatment cycles (i.e., 48 administrations). Except for Cycle 2 Day 1, all the visits after Cycle 1, all study drug administration treatment should occur within ± 2 days of the planned visit date. For each patient, the first infusion of study drug will be administered over approximately 60 minutes (± 5 minutes) with monitoring of infusion-related AEs. If no infusion-related AEs are noted, subsequent doses can be given over approximately 45 minutes (± 5 minutes). The infusion rate may be decreased to manage an infusion-related adverse event (AE): for example, if a patient experiences an AE, the duration of infusion may be increased to more than 60 minutes. The actual start / stop time of infusion will be documented and entered in the eCRF. Any dose interruption during the infusion must be documented in the source document. The baseline body weight will be utilized for dose calculation. If there is a change in body weight >10% relative to the weight at the time of the last dose calculation, the dose will be recalculated.

[0069] Patients must remain in the clinic for a minimum of 8 hours after infusion on Cycle 1 Day 1 and Cycle 1 Day 22 to allow for the evaluation of vital signs, PK sample blood draws, and monitoring of infusion reactions. In addition, all patients will remain in the clinic for 24 hours to be monitored for any drug-related side effects including cytokine release syndrome (CRS) postfirst infusion only. Additional inpatient clinical monitoring for any future infusion will be at the discretion of the treating physician.Table 1. Objectives and Endpoints

[0070] Inclusion CriteriaPatients must meet all of the following criteria to be eligible for participation in this study:1. Male or female > 18 years and <80 years old.2. Willing and able to provide signed and dated informed consent prior to any study - related procedures and willing and able to comply with all study procedures3. Histologically or cytologically confirmed incurable, unresectable, locally advanced or metastatic cancer that is refractory to standard therapies4. Prior therapy:• Progressed on or are intolerant to all standard therapies including checkpoint inhibitors (such as PD-1, PDL-1, CTLA-4) as a single agent or in combination with oncolytic vaccine, antibody, or chemotherapeutic agents5. Patient has at least 1 measurable target lesion or evaluable disease according to RECIST version 1.16. Eastern Cooperative Oncology Group (ECOG) performance status 0 or 17. Patient’s life expectancy > 6 months8. Adequate hepatic function as evidenced by meeting all of the following requirements:• Total bilirubin < 1.5 x institutional upper limit of normal (ULN); or < 5 * institutional ULN for patients who have serum bilirubin increases due to underlying Gilbert’s Syndrome (familial benign unconjugated hyperbilirubinemia).• Aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP) < 2.5 x ULN; AST or ALT < 5 x ULN if liver metastases are present9. Adequate renal function as serum creatinine < 1.5 x ULN and calculated creatinine clearance (CrCL) > 60 mL / min (Cockcroft-Gault Equation).10. Hematological function defined as:• Absolute neutrophil count > 1,500 / pL without growth factor support in the 2 weeks prior to study entry• Hemoglobin > 9 g / dL without transfusion in the 2 weeks prior to study entry• Platelet count > 100,000 / pL without transfusion in the 2 weeks prior to study entry11. Prothrombin (PT), international normalized ratio (INR), or activated partial thromboplastin time (aPTT) < 1.5 x ULN; use of full dose anticoagulants is permitted. These laboratory test values should be maintained within the therapeutic range and closely monitored by the Investigator.12. Female patients of childbearing potential and male patients with partners of childbearing potential agree to use a highly effective form(s) of contraception during study treatment that results in a low failure rate of < 1% per year when used consistently and correctly. Male patients must always use a condom. Female patients of reproductive potential must not be pregnant, breastfeeding, or planning to conceive children within the duration of the study, beginning at the Screening visit (Initial Visit) through 120 days or for an additional 5 half-lives after the last dose of study treatment, whichever is longer. For female patients of reproductive potential, confirmation that the patient is not pregnant must be obtained by a negative serum pregnancy test result obtained during Screening.Note: Women will not be considered in the category of 'female patients of reproductive potential' if they have undergone surgical sterilization (including hysterectomy, bilateral oophorectomy or total hysterectomy), or who are postmenopausal (defined as no menses for more than 12 consecutive months without medical interference). Highly effective methods of contraception include combined (estrogen and progestogen containing) hormonal contraception, progestogen-only hormonal contraception associated with inhibition of ovulation together with another additional barrier method always containing a spermicide, intrauterine device (IUD), intrauterine hormone-releasing system (IUS), bilateral tubal occlusion or vasectomized partner (on the understanding that this is the only 1 partner during the whole study duration), and sexual abstinence. Oral contraception should always be combined with an additional contraceptive method because of a potential interaction with the study drug.13. Able to stay in a 24-hour inpatient unit after 1st infusion visit and subsequent dosing visits as needed.

[0071] Exclusion Criteria1. Prior major surgery, chemotherapy, immunotherapy, or radiation therapy within 14 days prior to initiation of study treatment. No adverse event (AE) is evident from prior anticancer therapy except Grade 2 alopecia, sensory neuropathy, lymphopenia, and endocrinopathies controlled with hormone replacement. Palliative radiotherapy to a single area of metastasis is allowed (consult with assigned Medical Monitor)2. Prior allogeneic stem cell, bone marrow, or solid organ transplant.3. Live virus vaccine within 30 days prior to study entry4. Known active autoimmune disease or history of autoimmune disease requiring systemic therapy within 2 years prior to entry; except hypothyroidism, vitiligo, Grave’s disease, Hashimoto’s disease, or Type 1 diabetes mellitus5. Use of systemic corticosteroids in a dose equivalent to > 10 mg / day of prednisone or other immunosuppressive agent within 2 weeks prior to study entry. Use of inhaled, topical, or ophthalmological steroids are allowed6. Symptomatic CNS metastases. Patients with asymptomatic CNS metastases who are radiologically and neurologically stable > 4 weeks following CNS-directed therapy and are on a stable or decreasing dose of corticosteroids (e.g., prednisone less than 10 mg / day or equivalent) are eligible for study entry7. Uncontrolled hypertension (systolic blood pressure > 160 mmHg and diastolic blood pressure > 99 mmHg), with symptoms or a known history of hypertension crisis, or hypertensive encephalopathy8. Severe cardiovascular disease, including cerebrovascular accident (CVA), transient ischemic attack (TIA), myocardial infarction, or unstable angina within 6 months of study entry; NewYork Heart Association (NYHA) class III or IV heart failure within 6 months of study entry; uncontrolled arrhythmia within 6 months of study entry9. Resting QTcF interval > 470 msec on ECG at baseline; no concomitant medications that would prolong the QT interval; known family history of long QT syndrome. Left ventricular ejection fraction <40% at baseline.10. Concurrent malignancy within 2 years except cervical carcinoma in situ, localized squamous cell cancer of the skin, basal cell carcinoma, prostate cancer under active surveillance, ductal carcinoma in situ of the breast, or < T1 urothelial carcinoma11. Known active infection including HIV, hepatitis B or C, or tuberculosis, requiring active therapy; exceptions are as follows:• Patients infected with the HIV virus will be eligible if their CD4 count is > 350 cells / mm3 and the patient is on anti-retroviral therapy with an HIV viral load that is below the level of detection.• Active Hepatitis B or C. HBV carriers without active disease (HBV DNA titer < 1000 cps / mL or 200 lU / mL), or inactive Hepatitis C (negative HCV RNA test) may be enrolled.12. Previous treatment with IL-2 or IL-15 agonists, including but not limited to rhIL-15 (NCI), ALT-803 (ALTOR), NKTR-214 (Nektar). Known or suspected hypersensitivity to FL115 or its excipients; known history of a Grade 3 or 4 allergic reaction to IL treatment or another fusion protein.13. Women of childbearing potential who do not consent to use 2 highly effective methods of birth control (including 1 barrier method) during treatment and for an additional 5 half-lives or 120 days after the last administration of study drug, whichever is longer.14. Men with a partner of childbearing potential who do not consent to use 2 highly effective methods of birth control (including 1 barrier method) during treatment and for an additional 5 half-lives or 120 days after the last administration of study drug, whichever is longer.15. Any condition that the Investigator or primary physician believes may not be appropriate for the patient’s participation in the study.

[0072] Dose Escalation

[0073] Based on the results of nonclinical studies as well as the published study results of similar products, this study plans to assess 7 cohorts with a step-by-step dose-escalation design, as follows:• Cohort 1 : 3 pg / kg weekly FL115• Cohort 2: 10 pg / kg weekly FL115• Cohort 3: 30 pg / kg weekly FL115• Cohort 4: 60 pg / kg weekly FL115• Cohort 5: 120 pg / kg weekly FLU 5• Cohort 6: 180 pg / kg weekly FL115• Cohort 7: 240 pg / kg weekly FL115

[0074] In the event of a > Grade 2 cytokine release syndrome (CRS) in any patients in the dose cohort during the DLT period, the maximum dose increment is 50% for the next dose cohort. Dose escalation will continue until the maximum tolerated dose (MTD) is met or the highest testing dose (HTD) 240 pg / kg is tested.

[0075] Accelerated dose escalation: Cohort 1 (3 pg / kg):• One patient will be enrolled.• If the patient does not experience a > Grade 2 drug-related AE within the DLT evaluation period, dose escalation to Cohort 2 will proceed.• If the patient experiences a > Grade 2 drug-related AE, 2 additional patients will be enrolled for further assessment and the study will revert to a 3+3 design at that point. If no DLT occurs, next dose cohort will start. If 2 or more patients experience DLT (6 patients), dose escalation and the study will stop.

[0076] Accelerated dose escalation: Cohort 2 (10 pg / kg):• One patient will be enrolled.• If the patient does not experience a > Grade 2 drug-related AE within the DLT evaluation period, dose escalation to Cohort 3 will proceed.• If the patient experiences a > Grade 2 drug-related AE, 2 additional patients will be enrolled for further assessment. If no DLT occurs, the next dose cohort will start. If 2 or more patients experience DLT (6 patients), dose escalation and the study will stop.

[0077] Fibonacci 3 + 3 dose-escalation: Cohorts 3 to 7 (30 to 240 pg / kg):• Three patients will be enrolled for each dose cohort,• If none of the initial 3 patients experiences a DLT at 30 pg / kg, dose escalation will move to the next cohort.• If 1 of the initial 3 patients experiences a DLT, 3 additional patients will be enrolled for the cohort. If < 1 of 6 patients experiences a DLT, escalation to the next cohort will proceed.• If > 2 patients experience a DLT, dose escalation will stop, and the previous dose level will be considered the MTD.• If all the dose levels tested are well tolerated with no MTD being reached, dose escalation will stop at the 240 pg / kg dose level, which will be defined as the HTD.Table 2 Dose-escalation ScheduleAbbreviations: D = day; DLT = dose-limiting toxicity; N = number of patients.* Doses are in pg / kg. For the 3 and 10 pg / kg dose levels, only 1 patient per cohort will be planned using an accelerated titration design. If there is any occurrence of a treatment-related > Grade 2 toxicity occurring in the first cycle of the safety evaluation window following the first dose of treatment, the first 2 dose levels will be converted to a 3 + 3 design.

[0078] Dose-limiting Toxicity

[0079] Dose-limiting toxicity will be evaluated during Cycle 1 (28 days) of treatment. Adverse events that occur after Cycle 1 will be considered when determining whether the dose should be escalated.

[0080] Adverse events, other than those associated with CRS and related neurotoxicity events, will be graded according to the NCI CTCAE version 5.0. For AEs associated with CRS and neurotoxicity events, the American Society for Transplantation and Cellular Therapy (ASTCT) Consensus Grading will be used. (Lee et. al., 2019) Dose-limiting toxicity is defined as the occurrence of any of the following adverse events that are, as determined by the Investigator, at least possibly related to study drug.

[0081] Hematological Toxicity

[0082] Hematologic toxicity is defined as:• Grade 4 neutropenia lasting > 5 days despite adequate medical intervention• Febrile neutropenia, defined as: neutrophil count <1.0x l09 / L (1000 / mm3), and a single body temperature >38.3°C or continuous body temperature >38°C for more than 1 hour• Grade 3 or 4 neutropenia with documented infection• Grade 3 thrombocytopenia with clinically significant bleeding (i.e., requiring hospitalization, transfusion of blood products, or other emergency medical intervention)• Grade 4 thrombocytopenia that persists for >3 days despite adequate medical intervention• Grade 4 anemia

[0083] Non-hematological Toxicity

[0084] Any of the following Grade 2 AEs• Ocular toxicity requiring systemic therapy.• Encephalopathy for > Grade 2 toxicity requiring medical intervention.• Myocarditis for > Grade 2 toxicity requiring medical intervention.

[0085] Any of the following Grade 3 to 4 AEs with the following restrictions:• Grade 3 fatigue lasting > 7 days• Grade 3 nausea, vomiting, or diarrhea that persists for > 72 hours despite the use of optimal medical therapy.• Symptomatic Grade 3 or higher elevations in amylase or lipase.• Symptomatic Grade 4 electrolyte abnormalities that do not respond to replacement therapy and that persist for > 48 hours.• Grade 3 endocrinopathies, including hypothyroidism and adrenal insufficiency, that cannot be adequately supplemented with hormone replacement therapy. (Note: Type 1 diabetes mellitus that requires insulin therapy and all other endocrinopathies will be counted as DLTs. Any new-onset endocrinopathy that requires hospitalization will also be counted as a DLT.)• Grade 3 rash with ulceration or bullae formation that does not resolve to < Grade 2 within 7 days.• Grade 3 or 4 hypertension that does not respond to medical therapy within 24 hours.• AST / ALT >5 x ULN or > 3 * ULN with concomitant bilirubin > 2 * ULN in the absence of other cause (e.g., cholestasis).• Exceptions: Treatable, reversible laboratory abnormalities, and asymptomatic and treated within 72 hours• Grade 3 Persistent Cytokines Releasing Syndromes (CRS) symptoms which require hospitalization or patient inability to perform the routine functions after 72 -hours post infusion.

[0086] Other• Any Grade 5 adverse events• Any treatment-related toxicity that causes the subject to permanently discontinue treatment during Cycle 1 (except for Grade 3 or 4 infusion -related reactions)• Any deaths, except disease progression, with known underlying cause, and unrelated to study drug.

[0087] In addition to the safety data collected during the dose-finding phase of the study, the occurrence of late toxicity (i.e., safety data from all patients for up to 30 days from the last dose of FL115) will be considered in the determination of the RP2D and schedule to be taken forward into the cohort expansion phase of the study.

[0088] MTD / MAD / RED / RP2D

[0089] The maximum tolerated dose (MTD) is defined as the highest dose level at which < 1 out of 6 patients experience DLT during the DLT observation period. During the DLT observation period, if the number of patients with DLT in a dose group is > 2 out of 6 patients, then this dose level exceeds the MTD and is considered the maximum tolerated dose (MAD), and the dose escalation will be terminated. If the terminated dose is the lowest dose group, additional dose levels may be added below this (e.g., < 3 pg / kg). If the terminated dose level is not the lowest dose group, the previous dose level will be expanded to 6 patients and will define the MTD if < I of 6 patients experiences a DLT. If the MTD is not reached at the tested maximum dose of 240 pg / kg, then the MAD would be 240 pg / kg or a higher dose that can continue to be escalated after comprehensive evaluation by SMC. The recommended expansion dose (RED) will be determined based on the SMC’s evaluation of the study data, including safety and tolerance / PK / PD / preliminary anti-tumor activity, etc.

[0090] During the cohort expansion phase, if > 33% of patients experience a DLT, this will be considered to have exceeded the MTD and the next lower dose level will be expanded.

[0091] If the predefined highest dose still does not reach the MTD, the Sponsor and the Investigator will jointly discuss further dose escalation or define the recommended Phase 2 dose (RP2D) based on assessments of all accumulated safety, PK, pharmacodynamic, ADA and efficacy data. Given that immunotherapy agents can cause late toxicity, the RP2D determination will consider the safety findings up to 30 days from the last administration of FL115.

[0092] Cohort Expansion

[0093] This part of the study includes patients with unresectable locally advanced or metastatic solid tumors, who have failed all standard treatments, currently have no standard treatment, or are not available at this stage, and meet the following criteria:• Cohort Bl (n=15): subjects with advanced stage non-small cell lung cancer (NSCLC) that progresses or relapses after treatment with at least one anti - PD-1 / PD-L1 and platinum- containing chemotherapy, and without having known mutation(s) of epidermal growth factor receptor (EGFR) / anaplastic lymphoma kinase / oncogene or c-ros oncogene 1 (ALK / ROS1) fusion(s).• Cohort B2 (n=15): Other advanced solid tumors with disease progression or recurrence after standard therapy, such as colorectal cancer, head and neck cancer (including nasopharyngeal and head and neck squamous cell carcinoma), pancreatic cancer, urothelial carcinoma, cholangiocarcinoma, or tumors for which efficacy has been observed in Part A.

[0094] Serious Adverse Events (SAE)

[0095] A serious adverse event is defined as any adverse experience that meets any of the following criteria:• Results in death;• Is life threatening;• Requires hospitalization or prolongation of existing hospitalization. Additionally, complications occurring during hospitalization are also considered AEs;• Results in persistent or significant disability or incapacity or substantial disruption of the ability to conduct normal life functions;• Important medical events that may not result in death, be life threatening, or require hospitalization may be considered serious when, based upon appropriate medical judgment, they may jeopardize the patient and may require medical or surgical intervention to prevent one of the outcomes listed in this definition.

[0096] Progressive disease that is not complicated by other adverse events should not be reported as an SAE.

[0097] Assessments and Analysis

[0098] Pharmacokinetics

[0099] Blood samples will be collected at specific time points from all patients to determine the serum concentration FL115 using a validated immunoassay for PK analyses. The actual time ofeach blood collection will be recorded. After preparation, samples will be stored at -70°C before shipment to the laboratories.

[0100] In Cycle 1, for the first infusion, blood samples for PK analyses will be collected predose (within 60 minutes pre-dose) and post-dose (after end of infusion) at 1, 2, 4, 8, and 24 hours, and at 72 hours (Day 4). For the second and third infusions, PK samples will be drawn during the visit on Days 8 and 15 (at 1 hour pre-dose and 1 hour post-dose). For the fourth infusion on Day 22, PK samples will be drawn pre-dose and post-dose (after end of infusion) at 1, 2, 4, 8, and 24 hours, then at 72 hours (Day 4), and at 168 hours (Day 8) before Cycle 2 Day 1 dosing.

[0101] The main PK parameters will be calculated using a noncompartmental model using WinNonlin (version 6.4 or above) software to comprehensively reflect the characteristics of drug absorption, distribution, metabolism, and excretion in humans. The main PK parameters will be: AUC, Cmax, Tmax, tA, Vss, CL, etc. Descriptive statistical analysis will be performed for PK parameters in different dose groups or cohorts, and arithmetic mean, standard deviation, coefficient of variation, median, maximum, minimum values and geometric mean of PK parameters will be calculated for each dose group or cohort.

[0102] Immunogenicity

[0103] Blood samples for analysis of the incidence and titer of anti-drug antibodies (AD As) to FL115 will be collected at the scheduled time points. Samples with an increased titer to FL115 will be assessed for the presence of neutralizing antibodies (Nabs). ADA samples will be collected at the time of any infusion-related events and 30 days after the event.

[0104] The changes of ADA and NAb produced by patients after treatment will be assessed. The potential immunogenicity of FL115 will be assessed by summarizing the number according to dose cohorts and percentage of patients with detectable AD As. The impact of AD As on PK will be assessed if data permit. Samples will be collected for later evaluation of neutralizing capacity for AD As. Only patients who received at least 1 dose of FL115 and provided a baseline sample and at least 1 sample after treatment will be evaluated.

[0105] Pharmacodynamics and biomarker

[0106] For pharmacodynamic analyses of NK cells, T cells (CD8, CD4, Treg), macrophages, monocytes, etc., and cytokines (interferon gamma, GM-CSF, IL-1, IL-2, IL 6, IL-12, IL-18 and TNF-a), PD-L1 and serum PD-1, blood samples will be collected during Cycle 1 pre-dose(within 60 minutes pre-dose) and post-dose (after end of infusion) at 1, 2, 4, 8, 24, and 72 hours (Day 4), then on Days 8 and 15 (1 hour pre-dose and 1 hour post-dose). On Day 22 (fourth dosing) pharmacodynamic samples will be collected pre-dose (60 minutes pre-dose) and postdose (after end of infusion) at 1, 2, 4, 8, and 24 hours, then at 72 hours (Day 4), and at 168 hours (Day 8) before Cycle 2 Day 1 dosing. Pharmacodynamic samples will also be collected 1 hour pre-dose and 1 hour post-dose at the first infusion of each cycle (Cycle 2 Day 1, Cycle 3 Day 1, Cycle 4 Day 1 etc.). A sample will also be drawn at the EOT visit, which should be at least 4 weeks from the last collection or otherwise can be omitted.

[0107] Anti-tumor response

[0108] Tumor assessments may include the following evaluations: physical examination (with photograph and measurement of skin lesions, as applicable); cross-sectional imaging using computed tomography (CT) or magnetic resonance imaging (MRI) scan of the chest, abdomen, and pelvis (pelvis scan is optional unless known pelvic disease is present at baseline); nuclear bone scan for patients with known / suspected bone lesions; and CT or MRI scan of the brain (in the Screening period and as clinically warranted based on symptoms / findings during the treatment period). The preferred method of disease assessment is CT with contrast. If CT with contrast is contraindicated, CT of the chest without contrast and MRI scan of the abdomen / pelvis with contrast is preferred. The same imaging modality should be used for tumor assessments throughout the study for each patient.

[0109] At baseline, tumor lesions will be selected and categorized as target or non -target lesions. Target lesions include those lesions that can be accurately measured in at least 1 dimension as > 20 mm with conventional techniques or > 10 mm with CT scan. Malignant lymph nodes with a short axis diameter > 15 mm can be considered target lesions. Up to a maximum of 2 target lesions per organ and 5 target lesions in total will be identified at baseline. These lesions should be representative of all involved organs and selected based on their size (those with the longest diameter) and their suitability for accurate repeated measurements. A sum of the longest lesion diameter (LLD) for all target lesions will be calculated and reported as the baseline sum LLD. Lor malignant lymph nodes identified as target lesions, the short axis diameter will be used in the sum of LLD calculation. Lytic bone lesions with a soft tissue component that is measurable can be considered target lesions. All other lesions (or sites of disease) should be identified as non-target lesions (including blastic bone lesions).

[0110] Target Response

[0111] Percentage change in target lesion size will be evaluated by the following formulae:1. When determining complete response or partial response: [(Post value - Baseline value) / Baseline value] x 1002. When determining progressive disease:[(Post value - Smallest value since treatment started) / (Smallest value since treatment started)] x 100Target response will be classified according to the modified Response Evaluation Criteria inSolid Tumors (iRECIST) Target Lesion Response Criteria in Table 3 once confirmed.Table 3. iRECIST Target Response CriteriaNon-target response will be classified according to the iRECIST Non-Target Lesion ResponseCriteria in Table 4.Table 4. iRECIST Non-target Response CriteriaOverall response will be classified according to the iRECIST Overall Response Criteria Table 5.Table 5. iRECIST Overall Response Criteria♦Previously identified in assessment immediately before this timepoint.“i” indicates immune responses assigned using iRECIST. iCR = complete response; iPR = partial response; iSD = stable disease; iUPD = unconfirmed progression; non- iCR / non-iUPD = criteria for neither CR nor PD have been met; iCPD = confirmed progression; RECIST = Response Evaluation Criteria in Solid TumoursAll post-baseline response assessments should follow the same lesions identified at baseline. The same mode of assessment (e.g., CT) used to identify / evaluate lesions at baseline should be used throughout the course of the study unless patient safety necessitates a change (e.g., allergic reaction to contrast media).

[0112] Alternatively, during the study period, the subject’s tumor status will be assessed according to the RECIST vl.l standards. Target lesion records include the number and location of lesions, and a description of the maximum diameter measurement of each lesion (except lymph nodes) and the minimum diameter measurement of the lymph node, the sum of diameters including all target lesions. If tumor evaluation is performed, the baseline tumor evaluation during the screening period can be exempted. Radiographic imaging will be performed every 8 weeks (±7 days) during treatment.

[0113] Evaluation of tumor efficacy until disease progression, death, loss to follow-up, withdrawal of informed consent, completion of 12 treatment cycles, start antineoplastic treatment, completion of the study, or study termination by the sponsor, whichever occurs first before the next scheduled evaluation begins. In cases where PD is suspected, investigators may conduct an unplanned tumor evaluation. When overall response is assessed as partial response (PR) or complete remission (CR), the same imaging method is used 4-6 weeks (+7 days) after the first recording.

[0114] For subjects who permanently discontinue treatment for reasons other than PD, tumor imaging evaluation still needs to be performed according to the scheduled tumor evaluation time. Assessment until 12 treatment cycles have been completed, subject starts new anti -tumor treatment, PD, death, or withdrawal of informed consent, lost to follow-up or the sponsor terminated the study, whichever occurred first.

[0115] Statistical Analysis

[0116] After the trial protocol is finalized, the statistical analysis plan (SAP) will be developed by the statistician. Statistical analysis will be descriptive in nature and will be performed using SAS statistical software. Measurement data will be described using mean, standard deviation, median, maximum, and minimum values. Categorical data will be described using frequency, or constituent ratio (%).

[0117] Efficacy Analyses

[0118] Tumor response (objective response rate [ORR] and disease control rate [DCR]) will be evaluated according to iRECIST or RECIST 1.1; duration of response (DOR) and progression- free survival (PFS) will also be evaluated.

[0119] Objective Tumor Response and Disease Control Rate

[0120] The percentage of patients who achieve an objective confirmed complete or partial overall tumor response using iRECIST-informed RECIST 1.1 or RECIST 1.1 will be evaluated by dose cohort and overall response. The 95% confidence interval of the response rate will be evaluated. Disease control (confirmed response or SD lasting for at least 6 months) will be analyzed in a similar manner.

[0121] Duration of Response

[0122] The duration of overall response will be evaluated by dose cohort and overall response. The duration of overall response is measured from the time measurement criteria are met for complete response (CR) or partial response (PR) (whichever is first recorded) until the first date that recurrent or iCPD is objectively documented.

[0123] Progression-free Survival

[0124] PFS will be evaluated by dose cohort and overall response using Kaplan -Meier methods. PFS will be defined as the time from the date of first treatment to the date of iCPD or death (any cause) whichever occurs first. Patients who do not have disease progression or have not died at the end of follow up will be censored at the last known date the patient was progression free. Overall survival (OS) is defined as the time from the start of treatment to death. The analysis method of OS is the same as the PFS analysis method mentioned above.

[0125] It will be evident to one skilled in the art that the present disclosure is not limited to the foregoing illustrative examples, and that it can be embodied in other specific forms without departing from the essential attributes thereof. It is therefore desired that the examples be considered in all respects as illustrative and not restrictive, reference being made to the appended claims, rather than to the foregoing examples, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

[0126] It will be readily apparent to one skilled in the art that varying substitutions and modifications may be made to the invention disclosed herein without departing from the scope and spirit of the invention.

[0127] All patents and publications mentioned in the specification are indicative of the levels of those skilled in the art to which the invention pertains.

[0128] The invention illustratively described herein suitably may be practiced in the absence of any element or elements, limitation or limitations which is not specifically disclosed herein. Thus, for example, in each instance herein any of the terms “comprising,” “consisting essentially of,” and “consisting of’ may be replaced with either of the other two terms. The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention that in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. In addition, where features or aspects of the invention are described in terms of Markush groups, those skilled in the art will recognize that the invention is also thereby described in terms of any individual member or subgroup of members of the Markush group. For example, if X is described as selected from the group consisting of bromine, chlorine, and iodine, claims for X being bromine and claims for X being bromine and chlorine are fully described. Other embodiments are within the following claims.

Claims

CLAIMSWe claim:

1. A method of safely administering to a human subject an agonistic interleukin 15 (IL- 15) complex, comprising administering to the human subject the agonistic IL- 15 complex at an effective amount of 3 pg / kg to 300 pg / kg per administration, wherein the IL- 15 complex comprises: (a) a fusion protein comprising an IL-15 receptor a sushi domain fused to an Fc monomer, and (b) an IL-15, wherein the IL-15 receptor a sushi domain comprises the amino acid sequence of SEQ ID NO: 5 and the Fc monomer comprises the amino acid sequence of SEQ ID NO: 6.

2. A method of treating a cancer, comprising administering to a human subject in need thereof an agonistic interleukin 15 (IL- 15) complex at an effective amount of 3 pg / kg to 300 pg / kg per administration, wherein the IL-15 complex comprises: (a) a fusion protein comprising an IL-15 receptor a sushi domain fused to an Fc monomer, and (b) an IL- 15, wherein the IL- 15 receptor a sushi domain comprises the amino acid sequence of SEQ ID NO: 5 and the Fc monomer comprises the amino acid sequence of SEQ ID NO: 6.

3. The method of claim 1 or 2, wherein the carboxyl-terminus of the IL-15 receptor a sushi domain is fused to the amino -terminus of the Fc monomer via a linker comprising the amino acid sequence of SEQ ID NO: 7.

4. The method of any one of claims 1-3, wherein the linker consists of the amino acid sequence of SEQ ID NO: 8.

5. The method of any one of claims 1-4, wherein the IL- 15 comprises the amino acid sequence of SEQ ID NO: 3.

6. The method of any one of claims 1-4, wherein the IL-15 comprises the amino acid sequence of SEQ ID NO: 4.

7. The method of any one of claims 1-6, wherein the fusion protein comprises the amino acid sequence of SEQ IED NO: 1 or SEQ ID NO:2.

8. The method of any one of claims 1-7, wherein the agonistic IL- 15 complex is administered intravenously, particularly by intravenous infusion.

9. The method of claim 8, wherein the IL-15 complex is administered by intravenous infusion over 30-75 minutes, preferably over 45-60 minutes.

10. The method of any one of claims 1-7, wherein the agonistic IL-15 complex is administeredsubcutaneously.

11. The method of any one of claims 1-10, wherein the agonistic IL- 15 complex is administered to the human subject at the effective amount of 10 pg / kg, 15 pg / kg, 30 pg / kgm, 45 pg / kg, 60 pg / kg, 75 pg / kg, 90 pg / kg, 100 pg / kg, 125 pg / kg, 150 pg / kg, 175 pg / kg, 200 pg / kg, 225 pg / kg, 250 pg / kg, 275 pg / kg or 300 pg / kg per administration.

12. The method of any one of claims 1-11, wherein the agonistic IL- 15 complex is administered once every week, once every two weeks, or once every three weeks.

13. The method of any of the foregoing claims, wherein the human subject has a solid tumor prior to the initial administration of the effective amount of the agonistic IL-15 complex.

14. The method of claim 13, wherein the human subject has had at least one line of prior treatment for the solid tumor, such as at least one prior treatment of checkpoint inhibitor (CPI) therapy, e.g., an anti-PDl antibody, an anti-PD-Ll antibody, or an anti-CTLA4 antibody.

15. The method of any one of claims 13 and 14, wherein the solid tumor is colorectal cancer, head and neck cancer (including nasopharyngeal and head and neck squamous cell carcinoma), pancreatic cancer, urothelial carcinoma, cholangiocarcinoma, or esophageal squamous cell cancer (ESCC).

16. The method of any one of the foregoing claims, wherein the method does not result in a treatment related serious adverse event.

17. The method of any of the foregoing claims, wherein the method does not induce Dose Limiting Toxicities (DLT) in the subject.

18. The method of any one of claims 13-17, wherein the method results in an effective treatment of the solid tumor in the human subject, e.g., as measured by one or more of Objective Response Rate (ORR), Duration of Response (DoR), Progression-free Survival (PFS) and Disease Control Rate (DCR).

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