Phase 1/2 Study to Evaluate the Safety and Efficacy of ATA188 in Subjects With Progressive Multiple Sclerosis

The purpose of this study is to evaluate the safety and tolerability of ATA188 as a monotherapy in Parts 1 and 2, to determine the recommended Part 2 dose (RP2D) of ATA188 as monotherapy in Part 1, and to evaluate the effect of ATA188 treatment on clinical disability, as assessed by confirmed Expanded Disability Status Scale (EDSS) improvement at 12 months in Part 2 in participants with progressive forms of multiple sclerosis (MS) (primary progressive multiple sclerosis \[PPMS\] and secondary progressive multiple sclerosis \[SPMS\]).