PD‐L1+ macrophage and tumor cell abundance and proximity to T cells in the pretreatment large B‐cell lymphoma microenvironment impact CD19 CAR‐T cell immunotherapy efficacy

Abstract CD19‐targeted chimeric antigen receptor T‐cell (CAR‐T) immunotherapy has transformed the management of relapsed/refractory large B‐cell lymphoma (LBCL), yet durable remissions are observed in less than half of treated patients. The tumor microenvironment (TME) is a key and understudied factor impacting CD19 CAR‐T therapy outcomes. Using NanoString nCounter transcriptome profiling ( n = 24) and multiplex immunohistochemistry (mIHC, n = 15), we studied the TME in pretreatment biopsies from patients with LBCL undergoing CD19 CAR‐T therapy. Patients who achieved complete response (CR) after CAR‐T therapy demonstrated higher expression of genes associated with T‐cell trafficking and function, whereas those who did not achieve CR had higher expression of genes associated with macrophages and T‐cell dysfunction. Distinct patterns of immune infiltration and fibrosis in the TME were associated with CAR‐T therapy outcomes, and these findings were corroborated using artificial intelligence‐assisted image analyses. Patients who achieved CR had a lower proportion of the biopsy occupied by an interspersed immune infiltrate and a higher proportion of hypocellular/fibrotic regions. Furthermore, mIHC revealed lower density of CD4 + T cells and higher densities of both macrophages and tumor cells expressing PD‐L1 in non‐CR patients. Spatial analysis revealed that PD‐1 + T cells were in close proximity to PD‐L1 + macrophages or PD‐L1 + tumor cells in patients who did not compared to those who did achieve CR after CAR‐T therapy. These findings suggest that morphologic patterns in the TME and engagement of the PD‐1/PD‐L1 axis in pretreatment biopsies may impact CD19 CAR‐T immunotherapy response in patients with LBCL.