Immune profiling of gastric adenocarcinomas in EU and LATAM countries identifies global differences in immune subgroups and microbiome influence.

Background: Gastric cancer (GC) patients from European (EU) and especially Latin American (LATAM) countries are underrepresented in previous large-scale multi-omic studies that have identified clinically relevant subgroups. The LEGACY study aimed to profile the molecular and immunological features of GCs from EU and LATAM countries.

Methods: Tumor biopsies from 95 EU and 56 LATAM GCs were profiled with immunohistochemistry (CD3, CD8, FOXP3, PD-L1, MSI and HER2), Nanostring mRNA expression analyses, and microbiome sequencing.

Results: Immune profiling identified four distinct immune clusters: a T cell dominant cluster with enriched activation pathways, a macrophage dominant cluster and an immune excluded microenvironment which were equally distributed among the countries. A fourth cluster of mostly Mexican patients consisted of excessive T cell numbers accompanied by enhanced cytokine signaling in absence of enhanced antigen presentation and cytotoxicity signatures and a strong association with H. pylori infection.

Discussion: Both EU and LATAM countries have GCs with a T cell inflamed microenvironment that might benefit from checkpoint inhibition. We identified a highly inflamed GC subgroup that lacked antigen presentation and cytotoxicity associated with H. pylori CagA-positive strains, suggesting their contribution to tumor immune tolerance. Future studies are needed to unravel whether these cancers benefit from immunotherapy as well.