Characterizing immune heterogeneity in gastric cancer by high-throughput T-cell receptor sequencing: predictive...

Gastric cancer (GC) exhibits significant immunological heterogeneity, posing a major challenge for achieving durable responses to immunotherapy. Robust immune biomarkers for predicting treatment efficacy need to be identified. T-cell receptor (TCR) repertoire profiling has emerged as a promising approach for characterizing anti-tumor immune dynamics and therapeutic responsiveness. The aim of this study was to characterize immune heterogeneity in gastric cancer by high-throughput TCR sequencing and identify predictive clonotypes and functional signatures.

High-throughput single-cell T-cell receptor beta (TCRβ) sequencing was performed on 89 longitudinal peripheral blood samples collected from 23 GC patients undergoing immunotherapy. TCR repertoire features, including diversity indices, clonal architecture, V-J gene usage, and complementarity-determining region 3 (CDR3) sequence characteristics, were systematically analyzed. The patients were stratified based on dynamic changes in TCR diversity during treatment.

Based on TCR diversity dynamics, the patients were classified into three TCR diversity dynamic patterns: sustained high-diversity, diversity-declining pattern, and fluctuating-diversity pattern. An early decline in clonal richness, as measured by the Chao1 index, was associated with subsequent treatment resistance. The responders showed pronounced oligoclonal T-cell expansion, while the non-responders showed polyclonal dispersion. A conserved V-J gene pairing (TRBV20-1/TRBJ2-7) was observed across patients at the repertoire level. Additionally, a shared public CDR3 sequence (CASSIGLAGFNTGELFF), associated with the TRBV19/TRBJ2-2 combination in the clone-level longitudinal analysis, was detected in more than half of the cohort and was correlated with favorable immune features, including glycine enrichment in CDR3 regions and enhanced clonal expansion. This clone-level specificity should be distinguished from the most prevalent repertoire-wide V-J pairing, TRBV20-1/TRBJ2-7.

Distinct TCR repertoire characteristics are closely associated with immunotherapy outcomes in GC. Early changes in TCR diversity and the presence of public clonotype-like features may represent candidate biomarkers of therapeutic efficacy that warrant validation in larger cohorts. These findings provide an exploratory basis for future development of TCR-based response monitoring strategies and for further investigation of personalized immunotherapeutic approaches.