This study tests a new treatment called IMPT-314 for people with aggressive B-cell NHL (non-Hodgkin lymphoma). NHL is a type of cancer that starts in white blood cells. IMPT-314 uses special cells called CAR T-cells to fight cancer. CAR T-cells are your own cells changed in a lab to attack cancer. In this study, the treatment is given by a single infusion, or drip, into a vein after chemotherapy. The study has two parts. In Phase 1, about 90 people will help find the best dose. In Phase 2, 60 more people will join to see how well the treatment works. The active treatment lasts for about 2 years, with long-term follow-up for 15 years. Participants must be 18 or older and have tried other treatments without success. It's important to know that participants can't join if they have other serious health issues or have had certain treatments recently.

• Study lasts for about 2 years, with long-term follow-up for 15 years.
• Participants must have tried other treatments that didn't work.
• Some health conditions or recent treatments may prevent joining the study.