Inclusion Criteria:

          1. Have histologically confirmed microsatellite stable metastatic colorectal cancer and
             have received at least one line of treatment for metastatic colorectal cancer
             including fluoropyrimidines, oxaliplatin and/or irinotecan

          2. Be willing and able to provide written informed consent/assent for the trial

          3. Be 18 years of age on day of signing informed consent

          4. Have measurable disease

          5. Have biopsiable disease. If biopsy is attempted and unsuccessful (the patient
             undergoes an invasive procedure), the patient may still be treated

          6. Have a performance status of 0 or 1 on the ECOG Performance Scale at study entry

          7. Demonstrate adequate organ function

          8. Female subject of childbearing potential must have a negative urine or serum
             pregnancy test within 72 hours prior to receiving the first dose of study medication

          9. Female subjects of childbearing potential must be willing to use 2 methods of birth
             control or be surgically sterile, or abstain from heterosexual activity for the
             course of the study through 120 days after the last dose of study medication

         10. Male subjects must agree to use an adequate method of contraception starting with the
             first dose of study therapy through 120 days after the last dose of study therapy

         11. In patients with liver metastases, there should be <50% involvement of the liver with
             no tumors greater than 5 cm in size

         12. Patients must have had < 3 prior therapies in the metastatic setting.

        Exclusion Criteria:

          1. Patients whose tumors have progressed at the first restaging during first line
             therapy

          2. Is currently participating in or has participated in a study of an investigational
             agent or using an investigational device within 4 weeks of the first dose of
             treatment

          3. Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any
             other form of immunosuppressive therapy within 7 days prior to the first dose of
             trial treatment

          4. Has had a prior monoclonal antibody within 4 weeks prior to study Day 1 or who has
             not recovered from adverse events due to agents administered more than 4 weeks
             earlier

          5. Has had prior chemotherapy, targeted small molecule therapy, or radiation therapy
             within 4 weeks (6 weeks for nitrosureas or mitomycin C) prior to study Day 1 or who
             has not recovered from adverse events due to a previously administered agent

          6. Has a known additional malignancy that is progressing or requires active treatment

          7. Has known central nervous system (CNS) metastases and/or carcinomatous meningitis

          8. Has an active autoimmune disease requiring systemic treatment within the past 3
             months or a documented history of clinically severe autoimmune disease, or a syndrome
             that requires systemic steroids or immunosuppressive agents.

          9. Has evidence of interstitial lung disease or active, non-infectious pneumonitis.

         10. Has an active infection requiring systemic therapy.

         11. Any clinical or radiological ascites or pleural effusions

         12. Has a history or current evidence of any condition, therapy, or laboratory
             abnormality that might confound the results of the trial, interfere with the
             subject's participation for the full duration of the trial, or is not in the best
             interest of the subject to participate, in the opinion of the treating investigator

         13. Has known psychiatric or substance abuse disorders that would interfere with
             cooperation with the requirements of the trial

         14. Is pregnant or breastfeeding, or expecting to conceive or father children within the
             projected duration of the trial

         15. Has received prior therapy with an anti-PD-1, anti-PD-L1, anti-PD-L2, anti-CD137,
             anti-OX-40, anti-CD40, or anti-Cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4)
             antibody (including ipilimumab or any other antibody or drug specifically targeting
             T-cell co-stimulation or checkpoint pathways). Prior therapies with other
             immunomodulatory agents must be reviewed by the PI and may be cause for ineligibility

         16. Has a known history of Human Immunodeficiency Virus (HIV) (HIV 1/2 antibodies)

         17. Has known active Hepatitis B or Hepatitis C

         18. Has received a live vaccine within 30 days prior to the first dose of trial treatment

         19. Any known cardiac abnormalities