Neoadjuvant chemotherapy is linked to an amended anti-tumorigenic microenvironment in gastric cancer.

Background: Neoadjuvant chemotherapy (NAC) is a frequently intervention for patients with locally advanced gastric cancer (GC). Nevertheless, its impact on the tumor immune microenvironment remains unclear.

Methods: We used immunohistochemistry to identify T-cell subpopulations, tumor-associated neutrophils (TANs), and tumor-associated macrophages (TAMs) in the GC microenvironment (GCME) among paired samples (pre-chemotherapy and post-chemotherapy) from 48 NAC-treated patients. Multiplex immunofluorescence (mIF) was performed to assess immune biomarkers, including CK, CD4, CD8, FOXP3, PD1, PD-L1, CD163, CD86, myeloperoxidase and Arginase-1 in paired samples from 6 GC patients whose response to NAC were rigorously defined.

Results: NAC was intricately linked to enhanced CD8:CD4 ratio, reduced CD163 M2-like macrophages, augmented CD86 M1: CD163 M2-like macrophage ratio, and diminished FOXP3 regulatory T cells (T-regs) and TANs density. Based on mIF, PD1CD8T-cells, FOXP3T-regs, PD-L1 TANs, and CD163 M2-like macrophages exhibited marked reduction and greater co-localization with tumor cells following NAC. The pre-NAC FOXP3 T-regs and CD163 M2-like macrophages content was substantially elevated in the response cohort, whereas, the post-NAC CD8:CD4 and CD86 M1: CD163 M2-like macrophage ratios were intricately linked to the tumor pathologic response. We observed greater CD163 M2-like macrophages and tumor cells co-localization following NAC, which was correlated with tumor pathologic response. Lastly, multivariate analysis revealed that post-NAC CD8:CD4 and CD86 M1: CD163 M2-like macrophage ratios were stand-alone indicators of positive patient prognosis.

Conclusions: NAC converts the GCME to an anti-tumorigenic state that is conducive to enhanced patient outcome. These finding can significantly benefit the future planning of highly efficacious and personalized GC immunotherapy.