• (1) Histologically confirmed relapsed/refractory HL, PMBCL, GZL, and TCL including the below subtypes:

‣ Arm 1: PTCL

• Nodal PTCL Peripheral T-cell Lymphoma- Not Otherwise Specified (PTCL-NOS)

∙ Anaplastic Large Cell Lymphoma (ALCL) T-follicular Helper Lymphomas (TFH) and its subtypes including angioimmunoblastic T-cell Lymphoma (AITL)

∙ Extranodal NK/T-cell lymphoma

∙ Subcutaneous Panniculitis T-Cell Lymphoma

⁃ Arm 2: CTCL

• Mycosis Fungoides

∙ Sezary Syndrome

⁃ Arm 3: exploratory cohort

• Classic HL

∙ PMBCL

∙ GZL

• (2) All patients must have received at least one-line systemic therapy.

‣ Patients with systemic ALCL must have received prior CD30-directed therapy.

⁃ Other PTCL subtypes that express CD30 (\>10%), must have received prior CD30-directed therapy.

⁃ Special Consideration for CTCL in Arm 2:

• Systemic therapies including bexarotene (targretin) are permissible up to 2 weeks prior to enrollment.

∙ Skin directed therapies including light therapy/phototherapy, extracorporeal photopheresis (ECP), topical steroids, or mechlorethamine (valchlor) gel are NOT considered a systemic line of therapy when given alone.

∙ Treatment with radiation, phototherapy, histone deacetylase inhibitor, retinoids, interferons, therapeutic doses of systemic corticosteroids, or denileukin diftitox (18 µg/kg/day) up to 2 weeks prior to enrollment is allowed.

∙ Treatment with alemutuzumab up to 8 weeks prior to enrollment is permissible.

• (3) Patients must not have had chemotherapy or immunotherapy within 2 weeks prior to entering the study and must have recovered from adverse events (to grade 1 or less)

• (4) Anti PD-1/PDL-1is permissible up to two weeks prior to enrollment.

• (5) Age ≥ 18

• (6) Participants must have measurable disease, as defined in the protocol

‣ Patients must have a PET-CT scan performed within ≤4 weeks.

⁃ Contrast enhanced CT scan or MRI of the neck, chest, abdomen, pelvis is permissible, however; PET is preferred.

• (7) Patients cannot have active central nervous system (CNS) disease. Patients that have been treated and asymptomatic are allowed on study.

• (8) All participants must be screened for chronic hepatitis B virus (HBV) with hepatitis B viral load and serologies (core antibody, surface antigen, and surface antibody) within 30 days prior to enrollment.

‣ Patients with positive Hep B core will need to be on HBV prophylaxis

• (9) Participants with a history of hepatitis C virus (HCV) infection must have been treated and cured. If actively on treatment, HCV viral load mut be undetectable 30 days prior to enrollment.

• (10) Participants with known human immunodeficiency virus (HIV)-infection are eligible providing they are on effective anti-retroviral therapy and have undetectable viral load at their most recent viral load test (must be within 26 weeks prior to enrollment).

• (11) Organ function as assessed by laboratory testing and Eastern Cooperate Oncology Group (ECOG) performance status 0-2 and or a Karnofsky performance score of equal or greater to 50 (see Section 20.1.1, Appendix A) for receipt of ruxolitinib and pembrolizumab.

‣ Absolute Neutrophil Count ≥ 1000/μL (not growth factor independent)

⁃ Platelets ≥ 70,000/μL (or ≥50,000/mm3 if known bone marrow involvement with dose modifications allowed. See protocol for specific instructions for dose modifications).

⁃ Baseline hemoglobin level ≥ 8 g/dL (irrespective of bone marrow involvement).

⁃ Calculated creatinine clearance ≥ 30 ml/min using the Cockcroft-Gault formula

⁃ Bilirubin ≤ 2 x upper limit of normal (ULN)

⁃ Aspartate aminotransferase (AST) ≤ 2.5 × ULN

⁃ Alanine aminotransferase (ALT) ≤ 2.5 × ULN

• (12) Ability to understand and the willingness to sign a written informed consent document.

• (13) Patients with prior history of deep vein thrombosis (DVT) that has been treated or actively requiring anticoagulation are permitted to enroll.

• (14) Due to the potential teratogenic effects, women of childbearing age must have a documented negative serum β-hCG measured within 2 weeks of starting treatment. Should a woman become pregnant or suspect she is pregnant while she is participating in this study, she should inform her treating physician and Incyte immediately (see protocol). Additionally, both women of childbearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence).

⁃ Contraception should continue for 6 months after you stop taking study drug. Similarly, women must agree to not breastfeed during the entirety of the study period.