This is a prospective study for the Long-Term Follow-Up (LTFU) of safety and efficacy of all participants exposed to gene modified (GM) T cell therapy in accordance with Health Authorities' guidance for participants treated with gene therapy products. Participants who received at least one infusion of gene modified T cells in a 2seventy bio (prior to April 2024) or Regeneron Pharmaceuticals sponsored study will be asked to participate in this LTFU protocol, upon either premature discontinuation from, or completion of the parent treatment protocol. Participants enrolled in this LTFU protocol will have safety assessments, laboratory evaluations, and complete patient-reported outcome (PRO) questionnaires at scheduled intervals as applicable.