This research study looks at how well the medicine duvelisib helps T cells, a type of white blood cell, in people with a disease called diffuse large B-cell lymphoma (DLBCL). DLBCL is a cancer of the lymph nodes that has either come back or not responded to treatment. Duvelisib is a special drug that can change T cells to make them work better. The study checks if taking duvelisib before making a treatment called CAR-T cell therapy can improve the T cells.

Key Points:

• Participants will take duvelisib by mouth twice a day for 2 weeks.
• After duvelisib, patients receive a CAR-T cell infusion and are followed up 100 days after.
• Participants must not have certain health conditions and must be willing to use contraception and attend regular check-ups.

Researchers want to see if duvelisib helps grow healthy T cells and how long it takes to make CAR-T cells. They also check the safety of duvelisib and how well patients follow the treatment plan. This study is for patients willing to follow the study rules and who have the specific type of cancer mentioned.