with use of diseas e modifying agents, corticosteroids or immunosuppressive drugs). Replacement therapy (eg., thyroxine, insulin, or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency, etc.) is not considered a form of systemic treatment. 3.2.5 Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within 7 da ys prior to the first dose of trial treatment. 3.2.6 Has an active infection requiring systemic therapy. 3.2.7 Has a known history of active TB (Bacillus Tuberculosis) 3.2.8 Has a known history of Human Imm unodeficiency Virus (HIV) (HIV 1/2 antibodies). 3.2.9 Has known history of Hepatitis B or Hepatitis C 3.2.10 Has history of (non-infectious) pneumon itis that required steroids, evidence of interstitial lung disease or activ e, non-infectious pneumonitis. 3.2.11 Must not require supplemental oxygen or have a pulse oximetry < 92% on room air. 3.2.12 Has a history or current evidence of any condition, therapy, or laboratory abnormality that might confound the result s of the trial, interfere with the Phase 2 Study of GVAX (with CY) and pembrolizum ab in MMR-p advanced colorectal cancer J16154/Version 5 / January 17, 2018 18subject’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. 3.2.13 Has known psychiatric or substance abus e disorders that would interfere with cooperation with the requir ements of the trial. 3.2.14 Is pregnant or breastfeeding, or expecting to conceive or father children within the projected duration of the trial, star ting with the pre-screening or screening visit through 120 days after the last dose of trial treatment. Women of childbearing potential must have a negative urine HCG (refer to Section 3.1.7 ) 3.2.15 Is currently participating and receivi ng study therapy or has participated in a study of an investigational agent and received study therapy or used an investigational device within 4 week s of the first dose of treatment. 3.2.16 Has had prior chemotherapy, targeted small molecule therapy, or radiation therapy within 2 weeks pr ior to study Day 1 or who has not recovered (i.e., ≤ Grade 1 or at baseline) from adverse events due to a previously administered agent. Note: Subjects with ≤ Grade 2 neuropathy are an exception to this criterion and may qualify for the study. 3.2.17 Patients who have had surgery within 4 weeks of dosing of investigational agent, excluding minor procedures (d ental work, skin biopsy, etc), celiac plexus block, and biliary stent placement. 3.2.18 Has had a prior anti-cancer monoclona l antibody (mAb) with in 4 weeks prior to study Day 1 or who has not recovered (i.e., ≤ Grade 1 or at baseline) from adverse events due to agents administered more than 4 weeks earlier. 3.2.19 Has received a live vaccine within 30 days of planned start of study therapy. Note: Seasonal influenza vaccines for in jection are generally inactivated flu vaccines and are allowed; however intr anasal influenza vaccines (e.g., Flu- Mist®) are live attenuated v accines, and are not allowed. 3.2.20 Has received prior therapy with any other systemic immunotherapy treatment, including but not limited to: IL-2, in terferon, anti-PD-1 antibodies, anti-PD- L2 antibodies, anti-CD137 antibodies, anti-OX-40 antibodies, anti-CD40 antibodies, anti-CTLA-4 antibodies, ther apeutic anticancer vaccines, cellular immunotherapies including chimeric antig en receptor–modified T cells, or bi- specific CD3 antibodies. 3.2.21 Patients receiving growth factors in cluding, but not limited to, granulocyte- colony stimulating factor (G-CSF), GM-C SF, erythropoietin, within 14 days of study drug administration. Use of su ch agents while on study is also prohibited. Phase 2 Study of GVAX (with CY) and pembrolizum ab in MMR-p advanced colorectal cancer J16154/Version 5 / January 17, 2018 19 3.2.22 Hypersensitivity to pembrolizumab or any of its excipients. 3.2.23 Patient has a known or suspected hype rsensitivity to GM-CSF, hetastarch, corn, dimethyl sulfoxide, fetal bovine seru m, trypsin (porcine origin), yeast or any other component of GVAX vaccine. 3.2.24 Patient is unwilling or unable to follow the study schedule for any reason. 3.2.25 Presence of any tissue or organ a llograft, regardless of need for immunosuppression, including co rneal allograft. Patient s with a history of allogeneic hematopoietic stem cell transplant will also be excluded. 3.3 Inclusion of Women and Minorities Both men and women of all races and ethnic groups are eligible for this trial. 4. TREATMENT PLAN 4.1 Agent Administration Treatment will be administered on an outpatient basis. Reported adverse events and potential risks are described in Section 6 . Appropriate dose modifications are described in Section 5 . No investigational or commercial agents or therapies other than those described below may be administer ed with the intent to treat the patient's malignancy. Table 1: Study Regimen Agent Premedications, Precautions Dose Route Cyclophosphamide Subjects may be pre-medicated with anti-emetics 200 mg/m2 in 100 mL NS IV infusion over 30 minutes GVAX Lidocaine-based topical anesthetic (approximately 2.5 grams per site, at least 1 hour prior to vaccination) 5x108 (colon cancer cells) + 5x107 (GM-CSF secreting cells) 8-9 Intradermal injections Pembrolizumab No prophylactic pre-medications unless indicated by previous experience in an individual subject 200 mg IV over 30 minutes Pembrolizumab should be administered after cyclophosphamide, with a minimum of 30 min wait time between infusions. Infusion times are approximate (+/- 10 min) and may need to be adjusted ba sed on subject tolerability. Phase 2 Study of GVAX (with CY) and pembrolizum ab in MMR-p advanced colorectal cancer J16154/Version 5 / January 17, 2018 20 Please see Section 5.2 for guidance regarding dosing delays. 4.1.1 GVAX GVAX is administered through a tota l of 8-9 intradermal injections. Because the spatial distribution of v accine cells among three or more lymph node regions primes a more potent an ti-tumor immune response distributed equally among the right and left thighs, and the non-dominant arm. In the event that the specified limb is contraindicated, the dominant arm may be used. No pre-medications will be administer ed except a lidocaine-based topical anesthetic (may include but is not limited to EMLA or ELA-MAX) cream, which will be applied to the injection site at least 1 hour prior to vaccination to diminish the discomfort associated with intradermal injections. The patient must be observed in the clinic for at least 60 minutes after the first vaccine and 30 minutes for subsequent vaccinati ons. Acute reactions will be managed using standard therapy for acute drug reac tions as per institu tional standard of care and reported to the sponsor. 4.1.2 Cyclophosphamide (CY, Cytoxan R) Cy is a FDA-approved and widely used chemotherapy agent. Subjects may be pr e-medicated prior to administration with anti-emetics per institutional guide lines.