Tumor CD19 Expression Determines Distinct Clinical Outcomes after CD19 CAR T-cell Therapy in Large B-cell Lymphoma

It remains uncertain whether lower CD19 expression is clinically relevant for outcomes of CD19-directed chimeric antigen receptor T-cell (CAR-T) therapy for large B-cell lymphoma (LBCL). We conducted an integrative analysis of tumor CD19 levels with centralized quantitative assessment by flow cytometry (FC), immunohistochemistry (IHC), and RNA sequencing (RNA-seq) in an LBCL cohort (n = 301). Pretreatment CD19 by FC correlated with 1-year progression-free survival following axicabtagene ciloleucel or lisocabtagene maraleucel (16%, 53%, and 64% for CD19low, CD19intermediate, and CD19high, respectively; P = 0.005). After CAR-T relapse, the proportion of CD19low tumors increased (from 17% to 35%). Concordant associations were observed by IHC and RNA-seq. Transcriptomic profiling linked lower CD19 to inflammatory pathways, validated in an external LBCL cohort (n = 1,017). Genetic loss of the CD19 locus was observed in 8% of pre-CAR-T tumors and 11% of post-CAR-T tumors (P = 0.82), whereas no CD19 coding mutations were identified. Overall, CD19 expression is a clinically meaningful determinant of CAR-T outcomes, supporting quantitative assessment to improve risk stratification. SIGNIFICANCE: CD19 expression reflects clinical outcomes of CD19-directed CAR-T therapy in LBCL. Standardized, quantitative assessment-particularly by FC-identifies patients at higher risk of treatment failure, informs post-CAR-T relapse biology, and provides actionable insights to guide risk stratification and therapeutic decision-making in routine clinical practice. See related commentary by Perkey and Kline, p. 852.