Phase 2 Multi-center Study of Anti-PD-1 During Lymphopenic State After HDT/ASCT for Multiple Myeloma

Inclusion Criteria: * Subjects with MM (Multiple Myeloma) of any stage * Has no Progressive Disease (PD) AND has suboptimal response with primary therapy * Has measurable disease * Has no prior hematopoietic stem cell transplant of any type * Has performance status of 0 or 1 (Eastern Cooperative Oncology, ECOG, Performance Scale) * Has had a successful peripheral blood stem cell collection with G-CSF (Filgrastim) +/- Plerixafor (Mozobil) only * Be willing and able to provide written informed consent * Female subjects of child bearing age should have negative urine or serum pregnancy test * Female subjects of child bearing age must be willing to use 2 methods of birth control or be surgically sterile or abstain from heterosexual activity * Male subjects must agree to use an adequate method of contraception * Subject must be able to swallow capsules * Must demonstrate adequate organ function Exclusion Criteria: * Has history of repeat infections, amyloidosis, hyperviscosity, plasma cell leukemia, POEMS syndrome, Waldenstrom's macroglobulinemia, non-secretory multiple myeloma, or IgM myeloma * Has known CNS (Central Nervous System) involvement or history of resolved CNS involvement * Has an active autoimmune disease or history of autoimmune disease that requires systemic treatment with steroids of immunosuppressive agents. * Has active, non-infectious pneumonitis * Has diagnosis of immunosuppressive disorder or on immunosuppressive therapy within 7 days of transplant admission * Is currently participating in or has previously participated in the study of an investigational drug/device within 4 weeks of transplant admission * Prior therapy with an anti-PD-1, anti-PD-L1, anti-PD-L2, anti-CD137, or CTLA-4 * Has had prior monoclonal antibody, chemotherapy, small molecule therapy, or radiation within 2 weeks of transplant admission * Has not recovered from adverse events due to previously administered agent * Must be free of additional malignancy for at least 5 years * Has an active infection requiring systemic therapy * Has known psychiatric or substance abuse disorders that would interfere with requirements of the study * Is pregnant or breastfeeding or expecting to conceive * Has known HIV, Hepatitis B, or Hepatitis C infection * Has clinically significant coagulopathy * Has known symptomatic heart failure, unstable angina pectoris, or cardiac arrhythmia * Has received any type of hematopoietic cell transplant * Has received a live vaccine within 30 days of transplant admission * Is or has an immediate family member whos is investigational site or sponsor staff directly involved with this study