PARTICIPANTS ON THE HODGKIN LYMPHOMA EXPANSION COHORT: AST (SGOT) / ALT (SGPT): =< 3 x ULN AST/SGOT and ALT/SGPT ? 2.5 X ULN COHORT 2: AST (SGOT) and ALT (SGPT) =< 3 X ULN within 14 days of treatment initiation AST(SGOT)/ALT(SGPT) ? 2.5 X institutional ULN AST (SGOT) and ALT (SGPT) ? 2.5 x ULN. RANDOMIZED PHASE II CLINICAL TRIAL: Within 10 days of registration: AST (SGOT) and ALT (SGPT) =< 2.5 X ULN OR =< 5 X ULN for subjects with liver metastases AST (SGOT) >2x ULN AST/ALT (SGOT/SGPT) < 2 ULN Serum aspartate transaminase (AST/SGOT) or alanine transaminase (ALT/SGPT) ? 3.0 x upper limit of normal (ULN). In the case of documented liver involvement by lymphoma, ALT/SGPT and AST/SGOT must be ? 5.0 x ULN. EXPANDED ACCESS COHORT: AST(SGOT)/ALT(SGPT) =< 2.5 x institutional ULN -OR- AST(SGOT)/ALT(SGPT)\t=< 5 x institutional ULN if liver metastases are present AST (SGOT)/ ALT (SGPT): ? 3.0 x institutional ULN AST(SGOT)/ALT(SGPT) for patients with documented liver metastases, =< 5 x institutional ULN AST (SGOT)/ALT (SGPT) ?2 X ULN; ? 5 X ULN if there is liver involvement secondary to tumor AST (SGOT) and ALT (SGPT) ? 2.5 x ULN. AST/SGOT and ALT/SGPT ? 3.0 x ULN SGPT (ALT) ? 110 U/L and AST (SGOT) and ALT (SGPT) =< 5 x ULN in patients with documented hepatic involvement by lymphoma AST (aspartate transaminase or SGOT)/ALT (alanine aminotransferase or SGPT) ? 3.0 x ULN and total bilirubin ? 2.0 x ULN with no evidence of cholestasis • AST (SGOT) and ALT (SGPT) ? 3 times institutional ULN; if liver metastases are present, then ? 5 times ULN is allowed. Hepatic impairment, defined as AST (SGOT), or ALT (SGPT) > 2 x institutional ULN, within 21 days of initiation of protocol therapy or SGOT or SGPT > 4 x ULN For Part B participants: SGPT (ALT) concentration < 2.5 x institutional ULN SGPT (ALT) ? 110 U/L. RETREATMENT WITH MODIFIED T CELLS: ALT (SGPT): =< 5 x ULN SGPT (ALT) and SGOT (AST) less than or equal to 3 x normal for age B. Hepatic: Serum total bilirubin ?2.5 x upper limit of normal (ULN), ALT (SGPT) and AST (SGOT) ?2.5 x ULN. Aspartate aminotransferase (AST/SGOT) and alanine aminotransferase (ALT/SGPT) ? 3.0 × upper limit of normal (ULN); if liver function abnormalities are due to underlying liver metastasis, AST (SGOT) and ALT (SGPT) ? 5 × ULN. AST (SGOT), ALT (SGPT) and Alkaline phosphatase > 2.5 times ULN AST / ALT (SGPT) <2.5 x ULN AST(SGOT)/ALT(SGPT): ?3 x UNL REGISTRATION TO TREATMENT (STEP 2): AST (SGOT) and ALT (SGPT) =< 2.5 X ULN OR =< 5 X ULN for subjects with liver metastases, within 14 days prior to first dose of pembrolizumab SGOT (AST) and SGPT (ALT) > 3x institutional ULN PHASE II: AST (SGOT) and ALT (SGPT) =< 3 times institutional ULN (=< 5 times if LFT elevations due to known liver metastases) Serum AST/SGOT and ALT/SGPT ? 3.0 x ULN. Serum AST and ALT/SGPT ? 3.0 x ULN. AST(SGOT) and ALT(SGPT) <2.5 x ULN REGISTRATION #2 - PRIOR TO CONSOLIDATION CHEMOTHERAPY: SGOT (AST) or SGPT (ALT) =< 2.5 x IULN SGOT (AST) ? 3 x ULN AST (SGOT) and ALT (SGPT): ?2.5xULN OR ?5xULN for subjects with liver metastases AST (SGOT) and ALT (SGPT) <2 X institutional ULN (for subjects with hepatic metastases <5 X institutional ULN) AST (SGOT) and ALT (SGPT) ? 3.0 x ULN AST/SGOT and ALT/SGPT ? 3 x upper limit of normal (ULN) or ? 5.0 x ULN if liver tumor is present. AST/SGOT and ALT/SGPT ?2.5×ULN ALT (SGPT) ? 2.5 X ULN for age AST/SGOT and ALT/SGPT > 3.0 x ULN AST (SGOT) and ALT (SGPT) ? 2.5 X ULN OR ? 5 X ULN for patients with liver metastases Hepatic: Serum total bilirubin ?2.5 x upper limit of normal (ULN), ALT (SGPT) and AST (SGOT) ?2.5 x ULN. AST (SGOT) and ALT (SGPT) ? 3.0 x ULN); if liver metastases are present, then ? 5 x ULN is allowed SGOT and SGPT >= 5 x ULN; liver biopsy preferred for such patients Obtained within 2 weeks from study entry: SGOT, SGPT =< 5 X ULN if liver metastasis present The patient has serum total bilirubin < 2 g/dL (unless the patient has a diagnosis of Gilbert's disease), SGOT (ALT) <3.5×ULN, and SGPT (AST) <3.5×ULN AST (SGOT) and ALT (SGPT) < = 3 x ULN. Exception for patients with liver metastasis: ALT (SGPT) =< 8 x ULN AST (SGOT), ALT (SGPT) ? 5 × ULN is allowed: AST (SGOT) ? 3 × the ULN; ALT (SGPT) ? 3 × the ULN; AST(SGOT)/ALT(SGPT) =< 2.5 X institutional ULN AST/ALT (SGOT/SGPT) < 2.5 x ULN for the reference laboratory or < 5 x --ULN in the presence of liver metastases SELUMETINIB ARM: AST/SGOT or ALT/SGPT > 2.5 x ULN (>= 5 ULN in presence of liver metastases) AST/SGOT and/or ALT/SGPT > 2.5 x ULN, (> 5 x ULN if liver metastases present) Serum total bilirubin ? 1.5 x ULN and AST/SGOT and ALT/SGPT ? 2.5 x ULN or ? 5 x ULN if liver metastases are present. CROSSOVER (STEP 2) REGISTRATION: SGOT (AST) or SGPT (ALT) =< 2.5 x IULN Total bilirubin ? ULN, SGOT (AST) and SGPT (ALT)< 1.5 x ULN. AST and/or ALT may be up to 5X ULN if with known liver metastases provided bilirubin is normal. AST(SGOT)/ALT(SGPT) <2.5 X institutional ULN unless due to disease SGPT (ALT) ? 135 U/L and SGOT (AST) ? 3X ULN. (for the purpose of this study, the upper limit of normal [ULN] for SGPT [ALT] is 45 U/L). Hepatic function: Serum total bilirubin ? 1.5 x ULN (upper limit of normal); AST (SGOT) and ALT (SGPT) ? 3 x ULN, except in patients with tumor involvement of the liver who must have AST and ALT ? 5 x ULN AST (SGOT) and ALT (SGPT) ? 2.5 x ULN. For subjects with documented liver metastases, ALT and AST ? 5 × ULN AST/SGOT, ALT/SGPT ?2.5 x ULN, unless liver metastases are clearly present, then ?5.0 x ULN AST(SGOT)/ALT(SGPT) ?3 X ULN (including patients with liver metastases) SGOT(AST) and SGPT(ALT) ? 3 x ULN i.e. equivalent to ? Grade 1 NCI-CTCAE v.4.03