Key Clinical Summary

• High tumor mutational burden (TMB) independently predicted inferior progression-free and overall survival in relapsed/refractory large B-cell lymphoma (R/R LBCL) treated with CD19-directed CAR T-cell therapy.
• Patients in the highest TMB quartile had more than double the risk of relapse/progression, regardless of tumor burden or inflammatory status.
• Transcriptomic data suggest high TMB is associated with reduced TNF-NFκB, IL2-STAT5, and apoptosis pathway activity, indicating diminished immune signaling.

A new analysis presented at ASH 2025 identifies high tumor mutational burden as a clinically meaningful biomarker of inferior outcomes following CD19-directed CAR T-cell therapy in relapsed/refractory large B-cell lymphoma (LBCL). Using whole-exome and targeted sequencing from 119 patients, investigators demonstrated that elevated TMB—long associated with improved response to immune checkpoint blockade—functions in contrast as a negative prognostic indicator for CAR-T efficacy. The findings offer important implications for risk stratification and clinical decision-making.

Study Details and Findings

Researchers evaluated pre-treatment tumor samples from 119 patients with R/R LBCL treated with commercial CAR-T products (53% axi-cel, 17% liso-cel, 30% tisa-cel). Sequencing included whole exome sequencing (n = 91), MSK-IMPACT HEME targeted next-generation sequencing (n = 23), or both (n = 61). TMB levels were analyzed alongside clinical covariates including age, metabolic tumor volume, CAR T product, disease transformation, and InflaMix inflammatory clustering.

Median TMB by WES was 2.75 mut/Mb, aligning with previously published LBCL data. TMB showed no association with cell-of-origin, double-hit biology, MYC rearrangement, TP53 status, or patient age. However, higher TMB consistently correlated with worse outcomes. Patients in the top TMB quartile (>3.80 mut/Mb) had significantly elevated hazards for progression-free survival (HR 2.30; 95% CI 1.72–3.08; p<0.01), overall survival (HR 2.21; 95% CI 1.59–3.07; p<0.05), and relapse/progression of disease (HR 2.27; 95% CI 1.67–3.06; p<0.01).

These patterns held true in the full 119-patient cohort using targeted TMB from the MSK-IMPACT HEME panel. High TMB was not associated with higher tumor burden or elevated systemic inflammation, suggesting it captures unique biological risk. PIM1 mutation emerged as the most enriched gene alteration in high-TMB tumors (OR 13.15; adj. p<0.01).

In a subset of 42 samples with RNA sequencing, high-TMB tumors demonstrated reduced enrichment of TNF-NFκB (adj. p<0.001), IL2-STAT5 (adj. p<0.05), and apoptosis pathways (adj. p<0.05). These transcriptomic signatures imply weakened immune activation in the tumor microenvironment, potentially impairing CAR T function.

Clinical Implications

These data introduce TMB as a novel negative biomarker for CAR T responsiveness in R/R LBCL. Unlike in immune checkpoint blockade—where high TMB typically predicts favorable response due to increased neoantigen load—the CAR-T context appears biologically distinct. The attenuated inflammatory and apoptotic signaling identified in high-TMB tumors offers a mechanistic rationale: reduced immune activation may blunt CAR T expansion or cytotoxicity.

Given the concordance between whole-exome and targeted panel TMB assessment, the study supports real-world feasibility for incorporating TMB testing into pre-CAR-T evaluation. Clinicians may eventually use TMB as an adjunctive tool to identify high-risk patients who could benefit from alternative therapies, intensified monitoring, or combination immunomodulatory approaches.

Conclusion

This ASH 2025 analysis is the first to establish high TMB as an independent predictor of worse outcomes after CAR T-cell therapy in LBCL. By elucidating transcriptomic pathways linked to diminished immune signaling, the findings highlight a biologically grounded risk marker with potential clinical utility and pave the way for future therapeutic optimization.

Reference

Raj S, Gillmor A, Fei T, et al. Tumor mutational burden as a novel biomarker of resistance to CD19 CAR-T cell therapy in large B-cell lymphoma. Presented at: 2025 ASH Annual Meeting & Exposition; December 6-9, 2025; Orlando, FL, and virtual; Abstract 565.