Implications of PD-L1 expression on the immune microenvironment in HER2-positive gastric cancer

In the KEYNOTE-811 study, anti-HER2 and immunotherapy treatments resulted in longer survival in HER2-positive gastric cancer patients with CPS ≥ 1, whereas CPS < 1 patients lacked notable benefits. We studied this in a real-world cohort of 106 HER2-positive, CPS < 1 patients and found no survival differences between those treated with anti-HER2 therapy alone or with added immunotherapy. Thus, we investigate the tumor microenvironment variations in 160 HER2-positive patients, CPS ≥ 1 cases exhibited elevated spatial effective scores of immune cells, including CD4, CD8 subtypes, and NK cells, compared to CPS < 1. Furthermore, through single-cell sequencing in eight HER2-positive individuals, gene expressions revealed regulation of T-cell co-stimulation in CPS ≥ 1 and IL-1 binding in CPS < 1 cases. Notably, we discovered a CPS < 1 subtype marked by CXCR4⁺M2 macrophages, associated with poor prognosis, whose proportion and expression were reduced when benefiting from anti-HER2 therapy. These findings suggest CPS ≥ 1 patients, due to their immune microenvironment composition, may respond better to anti-PD-1/PD-L1 therapy.