Safety of SNK01 in Subjects With Pathologically Confirmed Metastatic and/or Unresectable Cancer Refractory to Conventional Therapy

Inclusion Criteria: * Voluntary written informed consent signed by patient, obtained prior to study enrollment. * Males and females ages 18 to 75 years, inclusive. * Pathologically confirmed diagnosis of refractory cancer that has failed three or more prior lines of conventional standard of care therapy. * Diagnosed with any histologically confirmed malignancy whose disease is confirmed to be metastatic and/or unresectable for which standard curative or beneficial treatments are no longer effective. * Eastern Cooperative Oncology Group (ECOG) performance status \<2. * At least 4 weeks since any prior systemic therapy (excluding corticosteroid therapy) to treat the underlying malignancy (standard or investigational). * At least 2 weeks since prior palliative radiotherapy. * Adequate bone marrow function: * Neutrophils: 2.0-8.0 K/uL * Platelet Count: 140-440 K/uL * Hemoglobin: 10.0-18.0 g/dL * No ongoing transfusion requirements * Adequate hepatic function: * Serum total bilirubin \< 1.5 x upper limit of normal (ULN) * Serum albumin ≥ 3.0 g/dL * Alanine transaminase (ALT) and aspartate transaminase (AST) ≤ 2.5 x ULN * International normalized ratio (INR) ≤ 1.5 x ULN * Adequate renal function with creatinine ≤ 2.0 mg/dL. * Negative pregnancy test for women of childbearing potential and use of effective contraception (hormonal or barrier method of birth control) during study. Exclusion Criteria: * Pregnant and/or lactating females. * Life expectancy of less than three months. * Currently being treated by "biological therapy" as defined by the National Cancer Institute (example: checkpoint inhibitors, adoptive cell transfer, monoclonal antibodies, treatment vaccines, cytokines, Bacillus Calmette-Guerin (BCG), chimeric antigen receptor T cell therapy (CAR-T), and natural killer cell therapy). * Patients tested positive for hepatitis B and/or C surface antigen. * High fever or any active or unresolved infection, including human immunodeficiency virus (HIV) positive. * Autoimmune disease requiring therapy; immunodeficiency, or any disease process requiring immunosuppressive therapy. * Prior clinical trial requiring patient to receive an investigational drug within two weeks of enrollment. * Congestive heart failure, unstable angina or other underlying cardiac disease; history of thrombosis currently requiring anticoagulation. * Mental or psychological illness preventing cooperation with treatment, efficacy evaluations, or unable to understand the informed consent process. * Subjects who have undergone prior organ transplantation, including allogeneic stem-cell transplantation. * Adult subjects who lack capacity to consent for themselves and for whom consent must be provided by a legally authorized representative. * For SNK01+avelumab arm only: Subjects with prior hypersensitivity to avelumab or its excipients, including known severe hypersensitivity reactions to monoclonal antibodies (NCI CTCAE v4.03 Grade ≥ 3). * For SNK01+avelumab arm only: Subjects with a significant immune-mediated adverse event due to a prior checkpoint inhibitor immunotherapy that led to permanent discontinuation of the therapy.