Pembro Plus CAR T-cell Therapy in R/R in PMBCL

Inclusion Criteria: * Histologically confirmed diagnosis of PMBCL, EBV+ DLBCL or THRLBCL at one of the participating institutions. * Availability of archival or freshly collected tumor tissue before study enrollment. If archival tissue is unavailable or is determined to be inadequate, tumor tissue must be obtained from a biopsy performed at screening, unless an exception is given after consultation with the sponsor-investigator. * Eligible for standard of care CAR T-cell therapy with progression after at least two prior lines of therapy OR refractory to initial chemoimmunotherapy OR relapse within 12 months of front-line chemoimmunotherapy OR one prior line of therapy and not fit for HSCT. * ECOG Performance Status of 0 or 1. * Left ventricular ejection fraction (LVEF) ≥ 50% on cardiac multiple-gated acquisition (MUGA) scan or cardiac echocardiogram (ECHO). * Adequate hematologic function (unless due to underlying disease, as established for example, by extensive bone marrow involvement or due to hypersplenism secondary to the involvement of the spleen by lymphoma per the investigator), defined as follows: * ANC ≥ 1,000/μL * Hemoglobin ≥ 8 g/dL * Platelet count ≥ 50,000/μL * Participants must have adequate organ as defined below: * Total bilirubin ≤1.5 ×ULN OR direct bilirubin ≤ULN for participants with total bilirubin levels \>1.5 × ULN * AST(SGOT)/ALT(SGPT) ≤2.5 × ULN (≤5 × ULN for participants with liver involvement) * Adequate renal function defined by seru…