Longterm Follow-up of Subjects Treated With bb2121

This is a multi-center, non-randomized, open label, longterm safety and efficacy follow-up study for subjects who have been treated with bb2121 in the Phase 1 clinical parent study, that evaluated the safety and efficacy of bb2121 in subjects with relapsed or refractory B cell maturation antigen (BCMA)-expressing multiple myeloma. bb2121 is defined as autologous T lymphocytes (T cells) transduced ex vivo with anti-BCMA02 CAR lentiviral vector encoding the chimeric antigen receptor (CAR) targeted to human BCMA suspended in cryopreservative solution. bb2121 is administered in subjects 1 time (or retreated if retreatment criteria are met) in parent clinical study. No investigational treatment will be administered in this study. After completing the parent study, eligible subjects will be followed for up to 15 years after their last bb2121 infusion in the parent study.