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.