Immune checkpoint expression and co-expression landscape in gastroesophageal adenocarcinoma

Addition of immunotherapy to standard chemotherapy marginally improved outcomes in gastroesophageal adenocarcinoma (GEAC). Recently, dual immunotherapy has shown efficacy in melanoma and non-small-cell lung cancer over single checkpoint inhibition. We sought to decipher the expression landscape of commonly targeted immune checkpoints in GEAC with a particular attention to their co-expression with programmed death-ligand 1 (PD-L1).

Targeted RNA sequencing was carried out on 65 metastatic GEAC tumors obtained from, and gene expression was measured for 394 immune transcripts. Co-expression analyses were conducted by calculating Pearson correlations for every possible pair of 15 checkpoint genes and clustering groups of similarly expressed genes. These analyses were validated using a 90-patient cohort identified from The Cancer Genome Atlas database.

The clinical cohort was primarily male (86.2%), Caucasian (93.9%), and had positive PD-L1 status (63.1%). The correlation matrix delineated two clusters of co-expression with the first including PD-L1, programmed cell death protein 1 (PD-1), cytotoxic T-lymphocyte associated protein 4 (CTLA-4), lymphocyte-activation gene 3 (LAG3), and indoleamine 2,3-dioxygenase-1 (IDO1) and the second included programmed cell death 1 ligand 2 (PD-L2), T-cell immunoglobulin and mucin domain-containing protein 3 (TIM3), and T-cell immunoreceptor with immunoglobulin and immunoreceptor tyrosine-based inhibition motif domain (TIGIT) genes. LAG3 and IDO1 genes showed strong co-expression with PD-L1 in both cohorts and PD-L1-positive and -negative subgroups. Interestingly, CD8 showed strong co-expression with CTLA-4, PD-1, LAG3, and TIGIT.

We show that immune checkpoints are often co-expressed in GEAC, suggesting possible common underlying mechanisms for checkpoint expression. Strong correlation between checkpoints like LAG3, TIM3, and IDO1 with PD-1/PD-L1 axis in GEAC argues for developing dual checkpoint inhibition therapy in this patient population. Future preclinical and clinical studies are needed to evaluate the efficacy and safety of these potential immunotherapy combinations.