Azacitidine and Abatacept in Relapsed or Refractory T-Cell Lymphoma

Background: T-cell lymphoma is a blood cancer that affects immune system cells. People tend to survive less than 1 year if this disease does not respond to treatment (is refractory) or comes back after treatment (relapses). Azacitidine and abatacept are 2 drugs that are used to treat other diseases. Researchers want to know if these drugs, used together, can help people with T-cell lymphoma. Objective: To learn if azacitidine combined with abatacept can shrink tumors in people with T-cell lymphoma. Eligibility: People aged 18 years and older with T-cell lymphoma that either came back or did not respond to treatment. Design: Participants will be screened. They will have a physical exam with blood tests. They will have a test of their heart function. They will have imaging scans of their tumors. A sample of tumor tissue may be taken. Azacitidine is injected under the skin of the thigh, abdomen, or upper arm. Abatacept is infused through a needle inserted into a vein in the arm. Participants will receive the study drugs in 28-day cycles for up to 13 cycles. They will come to the clinic for each treatment. They will come to the clinic on day 1 and day 15 of the first cycle. After that, they will come to the clinic on the first 5 or 7 days of each cycle. Each clinic visit will take no more than 8 hours. Imaging scans and other tests will be repeated during the study. Participants will have follow-up visits for up to 5 years after they stop taking the study drugs....