STUDY CALENDAR .......................................................................................................50 10. MEASUREMENT OF EFFECT........................................................................................52 10.1 Antitumor Effect – Solid Tumors ..........................................................................52 11. DATA REPORTING / REGULATORY REQUIREMENTS ..........................................53 11.1 Data Management ..................................................................................................53 11.2 Safety Meetings .....................................................................................................53 11.3 Monitoring .............................................................................................................53 12. STATISTICAL CONSIDERATIONS...............................................................................54 12.1 Overview ................................................................................................................54 12.2 Sample Size and Accrual .......................................................................................55 12.3 Statistical analysis ..................................................................................................56 REFERENCES .................................................................................................................... ..........59 APPENDIX A: Performa nce Status Criteria .................................................................................63 APPENDIX B: Guidance for Identification and Treatment of IRAEs (Version 5.0, Date: 18-Dec-2014) .................................................................................................................. ...64 APPENDIX C: Adverse Event of Clini cal Interest (ECI) Reporting Form ...................................65 APPENDIX D: Serious Adverse Event (SAE) Reporting Form ...................................................68 APPENDIX E: Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 Criteria for Evaluating Response in Solid Tumors ...............................................................................71 APPENDIX F: Immune Rela ted Response Criteria ......................................................................75 Phase 2 Study of GVAX (with CY) and pembrolizum ab in MMR-p advanced colorectal cancer J16154/Version 5 / January 17, 2018 61. OBJECTIVES 1.1 Primary Objectives 1.1.1 To determine the objective response ra te (ORR) of GVAX colon vaccine in combination with pembrolizumab in patie nts with mismatch repair-proficient (MMR-p), advanced colorectal cancer w ho have progressed af ter at least two lines of prior therapy. 1.2 Secondary Objectives 1.2.1 To assess the safety a nd tolerability of the combination GVAX/pembrolizumab in subjects with MMR-p, adva nced colorectal cancer 1.2.2 To assess the progression free survival (PFS) of subjects with MMR-p, advanced colorectal cancer who receive GVAX in combination with pembrolizumab using immune related response criteria. 1.2.3 To assess the duration of respons e among subjects who demonstrate an objective response to treatment w ith GVAX in combination with pembrolizumab. 1.2.4 To determine the overall survival (OS) of subjects with MMR-p, advanced colorectal cancer who receive GVAX in combination with pembrolizumab. 1.3 Exploratory Objectives 1.3.1 To evaluate the effects of combin ation therapy with pembrolizumab and Cy/GVAX on multiple immune pathways including suppressive pathways (including PD-L1, PD-L2, LAG3, BTLA, TIM3, IDO1, CTLA-4, and Tregs), activation pathways (including CD137, OX40, CD40, CD40L), cytokines/chemokines or their rece ptors (including CCL12, CXCR4, CCL2, CCL5, CCR2, CCR5), and tumor infiltrating lymphocytes. 1.3.2 To assess tumor burden dynamics thr ough measurements of circulating tumor biomarkers including carcinoembryonic antigen (CEA) as well as other exploratory circulating biomarkers in seri al collections of sera and plasma at baseline and throughout treatment. 1.3.3 To assess the baseline ch aracteristic of the subjects enrolled and to correlate these molecular and clinicopathologic criteria with treatment response and toxicity. 1.3.4 To assess changes in peripheral blood lymphocytes (PBL) to explore the association of lymphocyte activation markers with clinical responses. 1.4 Primary Endpoint Phase 2 Study of GVAX (with CY) and pembrolizum ab in MMR-p advanced colorectal cancer J16154/Version 5 / January 17, 2018 71.4.1 ORR, defined as the proportion of patie nts achieving a complete response (CR) or partial response (PR) based on the Response Eval uation Criteria in Solid Tumors (RECIST 1.1) at any time duri ng the study, of GVAX in combination with pembrolizumab in patients with MMR-p, advanced colorectal cancer. 1.5 Secondary Endpoints 1.5.1 Adverse events as graded by NCI CTCAE active version 1.5.2 Progression free survival 1.5.3 Duration of response 1.5.4 Overall Survival 1.6 Exploratory endpoints 1.6.1 Intratumoral changes in pre- and post-t reatment core biopsy specimens will be studied using analyses such as immunohistochemistry (IHC) and transcriptional analysis (Merck's nanostring panels) o Immune suppressive pathways including PD-L1, PD-L2, LAG3, BTLA, TIM3, IDO1, CTLA-4, and Tregs o Immune activation pathways in cluding CD137, OX40, CD40, CD40L o Cytokines/chemokines or their re ceptors including CCL12, CXCR4, CCL2, CCL5, CCR2, CCR5. o T cell receptor (TCR) repertoire (and compared to PBL) 1.6.2 Biomarker marker changes (including st andard protein biomarkers such as CEA) and correlation to evaluate fo r prognostic or predictive factors 1.6.3 Clinicopathologic characteristics (inc luding but not limited to age, sex, histology, grade, tumor mutations) and bi omarkers of response (OS, PFS, and best overall respons e) or toxicity. 1.6.4 Measure pre- and post-treatment change s in PBLs includin g effector, helper, and regulatory T cells through cell phe notyping analysis and gene expression profiling in association with clinical responses. We w ill also measure specific T cell responses as a parameter of immune response to treatment with immunotherapy. 1.7 Study Design This is an open-label, single-arm phase II study of Cy/GVAX in combination with pembrolizumab in subjects with MMR-p, ad vanced colorectal cancer who have progressed on at least two lines of prior therapies. Subjects with microsatellite repair deficiency (MMR-d; MSI) are no t eligible for this study. Therapy is administered on days 1 and 2 of a 21 day cycle. On day 1, participants will receive their first dose of cyclophosphamide (Cy) 200 mg/m 2 and pembrolizumab 200 Phase 2 Study of GVAX (with CY) and pembrolizum ab in MMR-p advanced colorectal cancer J16154/Version 5 / January 17, 2018 8mg, both administered intravenously (IV). On day 2, participants will receive GVAX, administered as 8-9 intradermal injections for a final dose of 5x108 colon cancer cells + 5x107 GM-CSF secreting cells. Participants may continue therapy every 21 days until there is disease progression. After comp leting four cycles of therapy, patients will continue pembrolizumab with every cycle of therapy and cyclophosphamide and GVAX will be administered every 4 th cycles of therapy. Due to the expectation that some patients may experience delayed clinical responses to therapy, patients with disease progressi on by radiographic imaging or laboratory parameters during a 12 week evaluation period but without rapid clinical deterioration or significant change in performance status that requires additional immediate therapy may continue to receive treatment on study. In this setting, a repeat scans will be obtained at weeks 6 and 12, and every 12 weeks thereafter from time of initial radiographic progression. This extra scan at 6 weeks after initial radiographic progression will allow earlier recognition of true progression and will ensure that the treatment is stopped adequate ly if not working. Subjects who meet the above criteria and continue to receive treatment on study despite disease progression by radiographic imaging must discontinue treatment upon documentation of disease progression on the second scan (week 6). The date of progression will be backdated to the time of first RECIST criteria progression. Tumor assessments will be made using RECIST 1.1 and immune-related response criteria (irRC). All patients will be followed by this protocol for at least 30 da ys after their last dose of study drug or until initiation of a new anti-cancer treatment, whichever occurs first. NOTE: For patients who progress and remain on study, at the time of the next restaging, stable disease with clinical stability as determined by their treating physican/team can remain on study. Specifica lly, these patients do not have to have regression to <20% growth from baseline. If they do not have 20% increase from the last restaging scan, th ey may remain on study. Patients who are discontinued from the study due to an unacceptable drug-related AE will be followed until the resolution of the AE to Grade 0-1 or stabilization or until initiation of a new therapy for their cance r, whichever occurs first. Patients who discontinue from treatment will be contac ted every three months to monitor overall survival. Information about other cancer therapies after discontinuation from the study treatment will be collected. At the end of the study, subjects will be re quired to enroll in a long-term follow-up protocol, an FDA requirement for genetically modified products, in which they will be followed for at least five years (or until death) after re ceiving the last dose of any investigational agent through this protocol for disease progression, survival, and potential long term toxicity of gene thera py. The subjects will be asked to enroll in the study entitled, “Long-Term Follow-Up of Patients who Received the Allogeneic Colon Cancer Cell Vaccine Administered with a GM-CSF Producing Bystander Cell Line.” 2. BACKGROUND Phase 2 Study of GVAX (with CY) and pembrolizum ab in MMR-p advanced colorectal cancer J16154/Version 5 / January 17, 2018 92.1 Disease Type Despite the existence of excellent screeni ng and preventative stra tegies, colorectal carcinoma remains a major public health proble m in industrialized countries and a rising health problem in developing countries. About 102,480 new cases of colon cancer and 40,340 cases of rectal cancer are expected to occur in the United States in 2013, with about 50,830 deaths, accounting for approxima tely 9% of cancer deaths. Colorectal carcinoma is the third leading cause of deat h from cancer in both males and females, comprising 9% of all cancers diagnosed in men and women. It also is the third most common malignancy in both men (after prostate and lung cancers) and women (after breast and lung cancers) [1]. Surgical rese ction of the primary colorectal lesions combined with adjuvant chemotherapy a nd radiation, when indicated, remain the mainstay of therapy. Unfortunately, approximately 30% of these patients will be diagnosed with metastatic di sease at initial presentation, and an additional 25-30% of patients will subsequently develop meta static disease. Am ong these patients, approximately 20% will have disease confined to the liver, which is the dominant site of metastatic involvement [2]. Despite r ecent advances in earlier detection and improvements in chemotherapy, the median surv ival for all patients with metastatic colorectal carcinoma ranges from 11-20 months with five-year survival < 5% [3-8]. 2.2 Vaccine Therapy (GVAX) Immunotherapy is a potentially effective th erapeutic approach to the treatment of colorectal carcinoma for several reasons. First, immune-mediated tumor killing acts by mechanisms distinct from standard chemothe rapy or radiation therapy and may represent a non-cross resistant treatment modality. S econd, the immune system is capable of recognizing a diverse array of potential antigen s while orchestra ting selective and specific cytotoxic responses. This may be pa rticularly important in the killing of a heterogeneous tumor population while avoiding normal tissue toxicit y. Third, preclinical animal models using a vaccine approach for immunotherapy have been able to eliminate small burdens of established tumors, a situat ion that corresponds to a state of minimal residual disease commonly found after resection of all gro ss disease [9-14]. Fourth, completed Phase I and II trials evaluating irradiated, GM-CSF secreting allogeneic pancreatic cancer tumor vaccines have de monstrated both clinical and immunologic response [15-17]. The use of whole-cell vaccines is promising because it delivers a range of peptide antigens without the need fo r specific knowledge of the relevant target antigens. Preclinical studies show that among tumor ce lls genetically modified to express various cytokines, GM-CSF is the cytokine most eff ective in inducing anti-t umor immunity [18]. GM-CSF is an important growth and differen tiation factor for dendritic cells, which are potent antigen-presenting ce lls. The use of allogeneic tumor cells for vaccine development over autologous tumor cells is a ttractive for several reasons. Autologous tumor cells are not always available and the production of an autologous vaccine is technically difficult, costly, and inefficient. Supporting the use of allogeneic tumor cells is the characterization of tumor-associated an tigens in melanoma, which revealed that regardless of human leukocyte antigen (H LA) type, 50% of tumors share common antigens [19, 20]. In addition, both preclinical and human data support that the antigen- Phase 2 Study of GVAX (with CY) and pembrolizum ab in MMR-p advanced colorectal cancer J16154/Version 5 / January 17, 2018 10presenting cells important in GM-CSF based vaccination are host-deri ved suggesting that the vaccine cells and the host do not ha ve to be HLA compatible [21, 22]. Phase I Study of an Allogeneic GM-CSF-S ecreting Tumor Vaccine in Patients with Resected Pancreatic Cancer This study was the first clinical trial to test the hypothesis that GVAX can prime a systemic immune response in patients with resected pancreatic adenocarcinoma [15]. Fourteen patients with stage II or III diseas e received an initial vaccination 8 weeks following resection. This was a dose escalati on study in which 3 patients each received 1 X 107, 5 X 107, and 1 X 108 vaccine cells. An additional 5 patients received 5 X 108 vaccine cells. Study patients were jointly enrolled in an adjuvant chemoradiation protocol for 6 months. Following the completion of adjuvant chemoradiation, patients were re- assessed and those who were still in remission were treated with 3 a dditional vaccinations given one month apart at the same original dose that they received for the first vaccination. Toxicities were limited to grade I/ II local reactions at the vaccine site, and self-limited systemic rashes, including one documented case of Grover's syndrome. Systemic GM-CSF levels were evaluated as an indirect measure of the longevity of vaccine cells at the immunizing site. As was observed in pre-clinical studies, GM-CSF levels peaked at 48 hours following vaccinati on. In addition, serum GM-CSF levels could be detected for up to 96 hours following v accination. The vaccin e sites were also evaluated as a measure of the local immune r eaction to the vaccine. Eleven of 14 patients demonstrated a similar local inflammatory response to what has been observed in pre- clinical models and autologous GM-CSF vacci ne clinical trials . Post-vaccination DTH responses to autologous tumor cells have be en used in previously reported vaccine studies as a surrogate to identify and charact erize specific immune responses that are associated with vaccination. In the pancreatic cancer vaccine trial, post-vaccination DTH responses to autologous tumor cells were observed in 1 of 3 patients receiving 1X 10 8 and in 2 of 5 patients receiving 5X108 vaccine cells. Follow-up Phase II Study Integrating the Whole Cell Vaccine with Chemoradiation for Resected Pancreatic Adenocarcinoma The follow-up phase II study of 60 patients w ith resected pancreatic adenocarcinoma based on the results of thei r phase I experience was comple ted [17]. The highest dose of vaccine from the phase I study (5 X 108 vaccine cells) was used. The common toxicities associated with the vaccine in this study incl uded: local vaccine site skin reactions and systemic rashes similar in severity (grade 1- 2) to what was observed in the phase I trial. The results from this study include the following:  The administration of the whole cell vaccin e is safe and well-tolerated. Treatment related side effects included transient vacci ne injection site reactions. There has been no incidence of anaphylaxis secondary to the vaccine repo rted thus far.  Systemic GM-CSF levels were evaluated as an indirect measure of the longevity of vaccine cells at the immunizing site. As was observed in the phase I study, GM-CSF levels peaked at 48 hours following the first and second vacc ination but peaked earlier following the 3rd and 4th vaccination with diminution in amplitude. Serum GM-CSF levels following vaccine 5 peaked again at 48 hours and returned to vaccine 1 serum levels. The results would suggest the possibility that the potency of an Phase 2 Study of GVAX (with CY) and pembrolizum ab in MMR-p advanced colorectal cancer J16154/Version 5 / January 17, 2018 11allogeneic vaccine is diminished with repe ated monthly vaccinations, but returns to pre-treatment levels with an extended time interval between boosts.  Post-Immunotherapy induction of mesothelin-specific CD8+ T cells with higher avidity and increased mesothelin epitope recognition (T cell repertoire expansion) correlates with disease free survival (DFS). Phase I and II Trials of Combining GM-CSF Secreting Allogeneic Vaccines in Sequence with Immune Modulating Do ses of Cyclophosphamide (CY) Immune tolerance remains a major barrier to effective vaccine therapies. In particular, regulatory T cells (CD4 +CD25+) have been shown to play a role in inducing CD8+ T cell tolerance. Manipulating the regulatory T cells may result in more effective vaccine strategies. In mouse models, immune modula ting doses of CY in combination with GM- CSF based cell vaccines have been shown to improve tumor rejection from 0% to 10 - 30% in the HER-2/neu transgenic mouse model. The addition of CY allowed the activation of high-avidity RNEU 420-429 -specific CD8+ T cells in the mice, which rejected tumor. This effect was abrogated by CD4+CD25+ T cells derived from neu-N transgenic mice suggesting that CY before vaccination may block T regulatory cells allowing for recruitment of latent high -avidity neu-specific CD8+ T cells [23]. A feasibility study of the GM-CSF-secreting, all ogeneic vaccine administered alone or in sequence with CY in patients with stage 4 pa ncreatic cancer, has been completed. This study consisted of two cohorts: Cohort A- 30 patients administered a maximum of six doses of vaccine using our two pancreatic cance r cell lines (2.5x108 of each cell line) intradermally at 21 day intervals; Cohor t B- 20 patients administered CY 250 mg/m2 IV one day prior to each vaccina tion (administered as in Cohor t A). Results from this study represent the first demonstration that integr ating immunomodulatory doses of CY with a GM-CSF-secreting vaccine in patients with advanced pancreatic cancer is safe and feasible to administer. These data suggest that the vaccin e given in sequence with CY results in anti-tumor activity, where median survivals in Cohort A and Cohort B were 2.3 months and 4.3 months respectively in a pati ent population that had received > 2 prior chemotherapies. In additi on, mesothelin-specific CD8 + T cell responses can be detected in stage 4 patients treated with the vaccine and may correlate with time to progression and overall survival [24]. A phase I dose ranging study was completed that evaluated the safety and immunogenicity of administer ing an allogeneic HER2-pos itive granulocyte-macrophage colony-stimulating factor (GM- CSF) secreting tumor vaccine in combination with low- dose CY and doxorubicin in pati ents with metasta tic breast cancer. Patients received three monthly immunizations with a booster vaccine 6-8 months from study entry. This study found that low dose CY can augment th e magnitude of vaccine-induced humoral immunity, but the therapeutic window for enhancing immune responses was narrow. Specifically, 200 mg/m2 of CY augmented th e magnitude of HER2-specific humoral immunity, whereas doses above 200 mg/m2 we re more likely to suppress both delayed type hypersensitivity and an tibody responses. The addition of CY did not potentiate vaccine-related toxicity [25]. Thus, these findings provide the scientific rationale to continue to test combinations of vaccine with other more potent immune modifying agents. Phase 2 Study of GVAX (with CY) and pembrolizum ab in MMR-p advanced colorectal cancer J16154/Version 5 / January 17, 2018 12 Safety and Feasibility Study of an Allogeneic Colon Cancer Cell Vaccine Administered with a GM-CSF Secreting Byst ander Cell line in Combination with Cyclophosphamide in Patients with Metastatic Colon Cancer Nine patients were treated in this dose-esc alating safety and feasibility study. Prior to treatment, six patients underwent curative me tastasectomy for hepatic metastases of colorectal adenocarcinoma and the other thre e had nonresectable metastatic colorectal adenocarcinoma. The investigational colon can cer vaccine consists of three components: a) SW837 cell line derived from a primary colorectal adenocarcinoma, b) SW620 cell line derived from a lymph node metastasis of colorectal adenocarcinoma, and c) K562/GM-CSF cell line, which is a K562 cell lin e derived from a CML patient in a blast crisis and subsequently tran sfected with a plasmid vector encoding human GM-CSF. A classical ‘3+3’ dose escalation design was adopt ed in this trial. Three patients were treated at dose level 1 (5x107 colon cancer cells + 4 x 107 K562). No dose limited toxicities (DLT) were observed in the first 3 patients, therefore six patients were treated at dose level 2 (5x10 8 colon cancer cells + 2 x 108 K562). No DLTs were observed at dose level 2. Patients received up to four monthly vaccin ations. Patients received an immunomodulatory dose of cyclophosphamide 200mg/m2 intravenously one day prior to each vaccine administration. Local reactions at vaccination sites includi ng erythema, induration, pruritis, and tenderness were observed with every vaccination in all patients, similar to those reported in patients who received GM-CSF producing tumor vaccine of other disease types. Minimal systemic toxicities were observed. The most common side-effects are transient, low grade fever, chill, nausea and headache. Fever and chill are likely attributive to the vaccine treatment; and nausea is likely attr ibutive to the cyclophosphamide treatment. Headache may be attributive to ondansetron, which was given as an optional anti-emetic prophylactic treatment prior to the administ ration of cyclophosphamide. There has been no incidence of anaphylaxis secondary to the vaccine reported thus far. Grade 3 lymphopenia was transiently observed in one patient, presumably attributive to the cyclophosphamide treatment. Thus, the hi gher dose level comprised of 2.5 x 10 8 cells per colon tumor cell lines and 2 x 108 GM-CSF-producing K562 cells is considered to have an acceptable degree of safety. In addition, cyclophosphamide at 200 mg/m2 intravenously was well tolerated. 2.3 Anti-PD-1 /PD-L1 therapy (Pembrolizumab (MK-3475 or Keytruda)) The importance of intact immune surveillanc e in controlling outgrowth of neoplastic transformation has been known for decades [26]. Accumulating evidence shows a correlation between tumo r-infiltrating lymphocytes (TILs) in cancer tissue and favorable prognosis in various malignancies. In particular, the presence of CD8+ T-cells and the ratio of CD8+ effector T-cells / FoxP3+ regulatory T-cells seems to correlate with improved prognosis and long-term survival in solid malignancies such as ovarian, colorectal and pancreatic cancer, hepato cellular carcinoma, malignant MEL and RCC. TILs can be expanded ex vivo and re-infused, inducing dura ble objective tumor responses in cancers such as melanoma [27, 28]. Phase 2 Study of GVAX (with CY) and pem brolizu mab in MMR-p advanced colorectal cancer J16154/Version 5 / January 17, 2018 13The PD-1 receptor-ligand interaction is a major pathway hijacked by tumors to suppress immune control. The normal f unction of PD-1, expressed on the cell surface of activated T-cells under healthy conditions, is to dow n-modulate unwanted or excessive immune responses, including autoimmune reactions. Th e ligands for PD-1 (PD-L1 and PD-L2) are constitutively expressed or can be i nduced in various tumo rs [29-32]. Binding of either PD-1 ligand to PD-1 in hibits T-cell activation trigge red through the T-cell receptor. PD-L1 is expressed at low levels on various non-hematopoietic tissu es, most notably on vascular endothelium, whereas PD-L2 protei n is only detectably expressed on antigen- presenting cells found in lymphoid tissue or chronic inflammatory environments. PD-L2 is thought to cont rol immune T-cell activation in lymphoid organs, whereas PD-L1 serves to dampen unwarranted T-cel l function in peripheral tissues [29]. Although healthy organs express little (if any) PD-L1, a variety of cancers were demonstrated to express abundant levels of this T-cell inhibitor. High expression of PD-L1 on tumor cells (and to a lesser extent of PD-L2) has been found to correlate with poor prognosis and survival in various cancer types, includi ng renal cell carcinom a (RCC) [33], pancreatic carcinoma [34], hepatocellular carcinoma [35], ovarian carcinoma [36]. Furthermore, PD-1 has been suggested to regulate tumor-specific T-ce ll expansion in patients with malignant melanoma [37]. The observed correlation of clinical prognosis with PD-L1 expression in multiple cancers suggests that the PD-1/PD-L1 pathway plays a critical role in tumor immune evasion and should be considered as an attractive target for therapeutic intervention. Pembrolizumab is a potent and highly se lective humanized monoclonal antibody (mAb) of the IgG4/kappa isotype designed to directly block the interaction between PD-1 and its ligands, PD-L1 and PD-L2. KeytrudaTM (pem brolizumab) has recently been approved in the United Stated for the treatment of patients with unresectable or metastatic non- small-cell lung cancer (NSCLC) and melanoma. Phase 2 Study of GVAX (with CY) and pembrolizum ab in MMR-p advanced colorectal cancer J16154/Version 5 / January 17, 2018 14 2.4 Preclinical and Clinical Trial Data Refer to the Investigator’s Brochure [IB] for Preclinical and Clinical Data 2.5 Rationale PD-1 checkpoint inhibitors have shown durable re sponses in a wide variety of tumors. However, in colorectal cancer, single agent pd-1 blockade with pembrolizumab has little or no activity in the majority of patients . A small subset of advanced colorectal carcinoma (<5%) is MMR-deficient (MMR-d) colorectal carcinoma. MMR-d, also referred to as microsatellite instability (MSI), is biologically marked by genomic instability with the potential of high num bers of neo-antigens and well described Phase 2 Study of GVAX (with CY) and pembrolizum ab in MMR-p advanced colorectal cancer J16154/Version 5 / January 17, 2018 15increases in tumor-inf iltrating lymphocytes (TILs) co mpared to other subtypes. In exploratory clinical trials, single agent pembrolizumab has been shown durable objective responses in many patients with MMR-d cance rs. However, MMR-p co lorectal cancer is the largest subtype of colorectal cancer, es timated to be between 90-95% of advanced disease. How to overcome the ineffectiveness of pembrolizumab in MMR-p colorectal cancer is therefore an important objective. The preclinical/clinical researchers at Johns Hopkins with GVAX in pancreatic cancer and colon cancer have sugge sted that GVAX may prime an immune checkpoint inhibitor insensitive cancer into a sensitive one. We recently reported the results of a novel study of GVAX given as both neo-adju vant and adjuvant therapy, e ither alone or with immune modulating doses of cyclophosphamide (Cyt oxan, Cy) to deplete regulatory T cells (Tregs) [38]. Pathological ex amination of PDA tumor tissu e resected just two weeks following a single neoadjuvant dose of GVAX identified the formation of novel vaccine- induced, immunologically active, tertiary ly mphoid aggregates, organized lymph node- like structures that are not observed in tumo r tissue resected from unvaccinated patients. Our study showed for the first time that a vaccine-based immunotherapy can reprogram an immunologically quiescent tumor microenvi ronment (TME) into an immunologically active TME. However, activated T cells secrete interferon- , which in turn upregulates the PD-1/PD-L1 pathway. These data support an emerging concept that vaccines are required to induce a T cell response that is capable of infiltrating the TME. However, vaccination is just the first step toward establishing an effective antitumor immune response, converting the TME into an environm ent similar to what is observed in MMR-d colon cancer exhibiting infiltrating but immunosuppressed T cells prior to immunotherapy treatment. Thus, we hypothesi ze that treatment with GVAX primes the TME for anti-PD-1/PD-L1-targeted therapy [39]. To support this hypothesis, we showed in a preclinical model of PDA that combining anti-PD-1 and anti-PD-L1 antibodies with GVAX+Cy enhances the infiltration of effector T cells into PDA tumors as well as the cure rate in PDA tumor-bearing mice [40]. Others have showed the synergistic effect of anti-PD-1 antibody and colon GVAX in colon tumor-bearing mice [41]. We found that GVAX treatment can also induce the membranous expression of PD-L1 in colon tu mors in the mouse model. Therefore, we propose a clinical trial concept to examine th e objective response rate of the combination of pembrolizumab and GVAX in MMR- p, advanced colorectal cancer. 3. PATIENT SELECTION 3.1 Eligibility Criteria 3.1.1 Pathologically confirmed, mismatch re pair-proficient adenocarcinoma of colorectum, who have received at leas t two prior lines of therapy in the metastatic setting. 3.1.1.1 Mismatch repair proficiency can be assessed for eligibility by immunohistochemistry (intact expr ession of MLH1, MSH2, PMS2, and MSH6) or by molecular testing in a CLIA-certified laboratory for microsatellite instability (0 or 1 microsatellites unstable) Phase 2 Study of GVAX (with CY) and pembrolizum ab in MMR-p advanced colorectal cancer J16154/Version 5 / January 17, 2018 163.1.2 Measurable disease by RECIST v1.1. 3.1.3 Age >18 years 3.1.4 ECOG performance status 0-1 ( Appendix A ) 3.1.5 Estimated life expectancy of greater than 3 months 3.1.6 Adequate hematologic, renal, a nd liver function as defined below: Absolute neutrophil count > 1,500 cells/mm 3 Hemoglobin > 9g/dL (transfusion allowed but must demonstrate stability after transfusion) Platelets > 75K/mm3 Serum creatinine ≤ 2.0mg/dL AST and ALT ≤ 3 x ULN Total bilirubin ≤ 1.5 x ULN* *Subjects with Gilbert’s Syndrome should ha ve direct bilirubi n within normal institutional limits 3.1.7 Women of childbearing potential (WOCBP) must ha ve a negative urine or serum pregnancy test for the patient to be eligible for trial enrolment. In a case of a positive HCG test, a vaginal ultrasound must be used to confirm a lack of pregnancy. 3.1.8 WOCBP must be willing to use e ither two adequate barrier methods or a barrier method plus a hormonal method of contraception to prevent pregnancy, or to abstain from hetero sexual activity (complete abstinence) throughout the study, starting with visit 1 through 120 days after the last dose of study therapy. Approve d contraceptive methods include for example; intrauterine device, diaphr agm with spermicide, cervi cal cap with spermicide, male condoms, female condoms with sp ermicide, or oral contraceptives. Spermicides alone are not an acceptable method of contraception. Non-pregnant, non-breast-feeding women may be enrolled if they are considered highly unlikely to conceive . Highly unlikely to conc eive is defined as 1) surgically sterilized, or 2) postmenopausal (a woman who is ≥45 years of age and has not had menses for greater than 2 years will be considered postmenopausal), or 3) amenorrheaic fo r <2 years without a hysterectomy and oophorectomy and with a documented FSH value in the postmenopausal range, or 4) not heterosexually active for the duration of the study, or 5) heterosexually active and will ing to use 2 methods of birth control (which is also required for the female partners of male patients). Male patients must agree to use an adequate method of contraception, or to abstain from heterosexual activity (compl ete abstinence), starting with the first dose of study drug through 120 days afte r the last dose of study therapy. 3.1.9 Ability to understand and the willingne ss to sign a written informed consent Phase 2 Study of GVAX (with CY) and pembrolizum ab in MMR-p advanced colorectal cancer J16154/Version 5 / January 17, 2018 17document. 3.2.10 Willing to undergo tumor biopsy at baseline and during treatment (during week 6 or 7). Please note that tumor biopsy is not needed in subjects where the tumor is not accessible or if tumor biopsy is considered not in patient’s best interest. 3.2 Exclusion Criteria 3.2.1 Has a known additional malignancy that is progressing or requires active treatment. Exceptions include basal ce ll carcinoma of the skin or squamous cell carcinoma of the skin that has under gone potentially cura tive therapy or in situ cervical cancer. 3.2.2 Has known central nervous system (C NS) metastases and/or carcinomatous meningitis. 3.2.3 Patients with malignant small bowel obs truction within the last 6 months, on parenteral nutrition, clin ically significant ascites (p alpable on physical exam and/or causing symptoms) or ascites re quiring fluid removal more than twice in the last 6 weeks. 3.2.4 Has active autoimmune disease that ha s required systemic treatment in the past 2 years (i.e.