Chimeric antigen-receptor (CAR) T cells lead to high response rates in myeloma, but most patients experience recurrent disease. We combined several high-dimensional approaches to study tumor/immune cells in the tumor microenvironment (TME) of myeloma patients pre– and post–B-cell maturation antigen (BCMA)-specific CAR T therapy. Lower diversity of pretherapy T-cell receptor (TCR) repertoire, presence of hyperexpanded clones with exhaustion phenotype, and BAFF⁺PD-L1⁺ myeloid cells in the marrow correlated with shorter progression-free survival (PFS) following CAR T therapy. In contrast, longer PFS was associated with an increased proportion of CLEC9A⁺ dendritic cells (DC), CD27⁺TCF1⁺ T cells with diverse T-cell receptors, and emergence of T cells expressing marrow-residence genes. Residual tumor cells at initial response express stemlike genes, and tumor recurrence was associated with the emergence of new dominant clones. These data illustrate a dynamic interplay between endogenous T, CAR T, myeloid/DC, and tumor compartments that affects the durability of response following CAR T therapy in myeloma.

There is an unmet need to identify determinants of durable responses following BCMA CAR T therapy of myeloma. High-dimensional analysis of the TME was performed to identify features of immune and tumor cells that correlate with survival and suggest several strategies to improve outcomes following CAR T therapy.

See related commentary by Graham and Maus, p. 478.

This article is highlighted in the In This Issue feature, p. 476