Phase 2 Study of Telomelysin (OBP-301) in Combination With Pembrolizumab in Esophagogastric Adenocarcinoma

Inclusion Criteria: * Be willing and able to provide written informed consent for the trial. * Be \>18 years of age on the day of signing the informed consent. * Have an Eastern Cooperative Oncology Group (ECOG) performance status of 0-2. * Have histologically or cytologically confirmed advanced or metastatic gastroesophageal adenocarcinoma, at least 1 cm in size and amenable to intratumoral injection. * Patient must have received at least 2 line of systemic therapy for advanced disease. * Tumor must be PD-L1 positive, as defined by a combined positive score (CPS). * Have one or more measurable lesions based on iRECIST. * Be willing to provide tissue; newly obtained biopsy specimens or formalin-fixed, paraffin-embedded (FFPE) block specimens. * Female subjects of childbearing potential have a negative urine or serum pregnancy test within 7 days prior to enrollment. If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required. If a serum pregnancy test is required it can be performed on the same day as the urine pregnancy test. The serum pregnancy test must also be completed 7 days prior to enrollment. And male / female subjects of childbearing potential must agree to use an adequate method of contraception starting with signing the informed consent through 120 days after the last dose of study medication. * Demonstrated adequate organ function as defined in following criteria. All screening labs should be performed within 14 days of enrollment. Note: Subject must not have taken transfusion, hematopoietic agent; granulocyte-colony stimulating factor (GCSF) etc., and/or oxygen supplementation within 7 days before the screening labs. * Absolute neutrophil count (ANC)\>1,000 /mm3 * Platelets\>100,000 /mm3 * Hemoglobin\>8.0 g/dL * Serum total bilirubin\<2.0 mg/dL * Aspartate aminotransferase (AST) (SGOT) and alanine aminotransferase (ALT) (SGPT)\< 3x Upper limit of normal (ULN). For subjects with liver metastases\< 5x ULN. * Serum creatinine\< 2.0 mg/dL; or if serum creatinine \> 2.0 mg/dL, measured or calculated creatinine/clearance \>45 mL/min (Cockcroft-Gault formula). * Life expectancy of ≥ 4 months from the first OBP-301 treatment. * Understand the study requirements and the treatment procedures, and is willing to comply with all specified follow-up evaluations, and provides written informed consent before any study-specific tests or procedures are performed. Exclusion Criteria: * Is currently participating and receiving study therapy or has participated in a study of an investigational agent and received study therapy within 4 weeks of study Day 1. * Has an active autoimmune disease that has required systemic treatment in past 2 years. * Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy (greater than equivalent of prednisone 20 mg/day) or any other form of immune-suppressive therapy within 7 days prior to study Day 1. * Has known active central nervous system metastases and/or carcinomatous meningitis. * Has had prior anti-cancer monoclonal antibody chemotherapy, targeted small molecule therapy, or radiation therapy within 2 weeks prior to study Day 1, who has not recovered from adverse events due to a previously administered agent. * Has a known additional malignancy within 3 years of first injection of OBP-301 that is progressing or requires active treatment, with the exception of prostate cancer controlled with androgen deprivation therapy. * Has received a live vaccine within 30 days of planned start of study therapy. * Patients known to have acute or chronic active hepatitis B virus (HBV), hepatitis C virus (HCV), or human immunodeficiency virus (HIV). * Has any evidence of active, non-infectious pneumonitis or interstitial lung disease requiring steroids. * Has an active infection requiring systemic therapy within 2 weeks of Day 1. * Has known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the trial. * Is pregnant or breastfeeding, or expecting to conceive or father children within the projected duration of the trial, starting with the screening visit through 120 days after the last dose of trial treatment. * Previous severe hypersensitivity to another monoclonal antibody * 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. * Uncontrolled intercurrent illness including, but not limited to, uncontrolled diabetes, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/psychological incompetence, whereby in the opinion of the Investigator the patient is assessed as being unable to provide information, consent, or comply with the study requirements and procedures. * Patients who are pregnant or breastfeeding, or expecting to conceive or father children within the projected timeframe of the study, starting from the time of the Screening Visit through 4 months (120 days) after the last OBP-301 administration. Females of childbearing potential must have a negative serum or urine pregnancy test at Screening. A female not of childbearing potential is one who has undergone bilateral oophorectomy or who has had no menses for 12 consecutive months.