Inclusion Criteria:

          -  Advanced Solid Malignancies: Histologically documented metastatic or locally advanced,
             incurable solid malignancy (Parts A and B); histologically documented metastatic or
             locally advanced, incurable solid malignancy for which gemcitabine is clinically
             appropriate (e.g., non-small cell lung, breast, ovarian, pancreatic, and renal
             cancer); histologically documented metastatic or locally advanced, incurable solid
             malignancy for which pembrolizumab (Part D) or nivolumab (Part E) is approved. NOTE:
             Parts D and E only: Subject has either (1) received treatment with pembrolizumab or
             nivolumab for ≥4 months with a best response of stable disease and plans to continue
             treatment with either pembrolizumab or nivolumab in accordance with package insert; or
             (2) is not currently taking, but is eligible for treatment with, pembrolizumab or
             nivolumab in accordance with the approved indications for each as referenced in the
             package insert.

          -  Expected survival of at least 12 weeks after dosing.

          -  Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1

          -  Evidence of adequate organ function by standard laboratory tests.

          -  All female subjects of child bearing age must be either surgically sterile,
             postmenopausal for at least 1 year, or using an acceptable method of contraception.
             Adequate contraception for both male and female subjects must be used from the
             beginning of the screening period until at least 8 weeks after the last dose of study
             drug.

        Exclusion Criteria:

          -  Hematologic malignancies or multiple myeloma.

          -  Known, clinically important cardiac or respiratory disease

          -  Any concomitant serious physical illness other than cancer (e.g., immune deficiency
             disease, bleeding disorder, etc.) within 1 year prior to dosing. No history of
             autoimmune disease.

          -  Active, uncontrolled infections within 7 days of study entry requiring systemic
             therapy.

          -  Evidence of progression of central nervous system (CNS) metastases or symptomatic CNS
             metastases within 30 days prior to dosing.

          -  History of known or suspected autoimmune disease with the specific exceptions of
             vitiligo, atopic dermatitis, or psoriasis not requiring systemic treatment. (Parts C,
             D and E only).

          -  Clinically-significant gastrointestinal disorders, such as perforation,
             gastrointestinal bleeding, or diverticulitis (Parts D and E only).

          -  Active autoimmune disease that has required systemic treatment in past 2 years (i.e.
             with use of disease modifying agents, corticosteroids or immunosuppressive drugs).
             Replacement therapy (thyroxine, insulin, or physiologic corticosteroid replacement
             therapy for adrenal or pituitary insufficiency, etc.) is not considered a form of
             systemic treatment (Parts D and E only).

          -  History of (non-infectious) pneumonitis that required steroids or current pneumonitis
             (Parts D and E only).

          -  History of interstitial lung disease (Parts D and E only).