Study of Brexucabtagene Autoleucel in Adults With Rare B-cell Malignancies

This study will use a basket study design with separate, indication-specific substudies, to investigate r/r RT and r/r BL. After completing the treatment period, all participants will be followed in the post-treatment follow-up period. Thereafter, participants will transition to a separate long-term follow-up study (KT-US-982-5968) to continue follow-up out to 15 years. All substudies have been early terminated by the sponsor. Below is summary of enrollment in each Substudy: * Substudy-A This substudy was withdrawn. Therefore no participants were enrolled. * Substudy-B enrollment closed, actual enrollment is 6. * Substudy-C enrollment closed, actual enrollment is 12. * Substudy-D enrollment closed, actual enrollment is 1.