Pembro + Blina Combination in Pediatric and Young Adult Patients With Relapsed/Refractory Acute Leukemia or Lymphoma

Inclusion Criteria: * Age 1-40 * Diagnosis of CD19 positive B-cell acute lymphoblastic leukemia (ALL) positive B-cell acute lymphoblastic leukemia (ALL) or CD19 positive B-cell lymphoma * Patients with CD19 positive B-ALL must have greater than or equal to 5% lymphoblast in the bone marrow AND meet one of the following criteria: * 2nd or greater relapse * Any relapse after allo-HSCT * Refractory disease * Patients with CD19 positive relapsed/refractory lymphoma must be in 2nd or greater relapse or have refractory disease with the markers of disease burden * Patients with CNS 1 or CNS 2 leukemia are eligible.Patients with CNS 3 leukemia are not eligible. However, patients with a history of CNS 3 status who have been sufficiently treated are eligible if currently CNS 1 or 2. Patients with an isolated CNS relapse are not eligible. * Karnofsky performance level greater than or equal to 50 % for patients older than 16 * Lansky performance level greater than or equal to 50 % less than or equal to 16 * Patients recovered from acute toxicities from prior anti-cancer chemotherapy including HSCT, cytotoxic therapy, prior blinatumomab, biologic, immunotherapy, monoclonal antibody, XRT and corticosteroid therapy * Patients with adequate hematological, renal, liver, cardiac, pulmonary and CNS organ functions * Female participants of child bearing age must have negative pregnancy test, abstain or use contraception for 120 days after last dose of pembrolizumab Exclusion Criteria: * Patients with the following diagnoses: CNS 3 leukemia, CNS lymphoma, active GVHD, Downs Syndrome, CNS or testicular relapse, optic nerve or retinal involvement requiring radiation therapy * Pregnant or breastfeeding * Concomitant corticosteroids, immunosuppressive therapies, investigational drugs, anti-cancer agents * Concurrent illnesses including: history of any grade autoimmune disorder, Grade 2 or higher hypothyroidism die to autoimmunity, uncontrolled infection, interstitial lung disease or pneumonitis * Patients with other concurrent malignancies * Patients who have received live vaccines within the last 30 days * Patients with history of solid organ transplant