Study of Loncastuximab Tesirine in Patients With Relapsed/Refractory Diffuse Large B-Cell Lymphoma (DLBCL) or High-Grade B-Cell Lymphoma (HGBCL) Following CAR-T Therapy Failure

The goal of this clinical trial is to evaluate whether the drug Loncastuximab Tesirine can treat patients with relapsed or refractory Diffuse Large B-Cell Lymphoma (DLBCL) or High-Grade B-Cell Lymphoma (HGBCL) who have not responded to or have had a relapse after CAR-T therapy. The main question it aims to answer is: * Can Loncastuximab Tesirine improve the overall response rate (ORR) in patients who have failed CAR-T therapy? * What are the safety and potential side effects of Loncastuximab Tesirine in this patient group? This is a single-arm clinical trial, meaning all participants will receive the same treatment and there will be no comparison group. Researchers will focus on evaluating the effectiveness of the drug in helping patients achieve a response to treatment, and they will also assess the safety of the treatment. Participants will: * Be treated with Loncastuximab Tesirine through an intravenous (IV) infusion every 3 weeks for up to 8 cycles. * Undergo regular assessments to monitor the response to treatment, including PET-CT scans and blood tests to check for markers of the disease. * Be asked to provide informed consent before beginning the study and agree to follow the study procedures, including having biopsies performed to analyze biomarkers before starting treatment. * Be followed for up to 2 years after completing the treatment to track their progress and response. This study aims to help doctors understand if Loncastuximab Tesirine can offer a new treatment option for patients who have not responded to CAR-T therapy and have limited options for further treatment. The trial will also provide more information on how to manage the safety of this treatment for these patients.