178P - Comprehensive immunophenotype analysis in anti-PD-1 antibody sensitive and resistant syngeneic mouse model unravels perforin-expressing CD4+T cells dominant cytolytic activity

Background

The emergence of immune checkpoint inhibitors targeting the PD-1/PD-L1 pathway has revolutionized cancer treatment, resulting in significantly improved clinical outcomes. However, resistance mechanisms remain a critical challenge.

Methods

This study aimed to elucidate immunophenotypic changes in syngeneic mouse models sensitive (MC-38) or resistant (LLC1) to anti-PD-1 monoclonal antibody (mAb) treatment. Flow cytometry analysis was performed to unravel significant alterations in immune cell populations within tumor microenvironments (TME) and tumor-draining lymph nodes (TdLNs).

Results

In the MC-38 model, anti-PD-1 mAb treatment led to increased dendritic cells (DCs) and macrophages, while decreasing myeloid-derived suppressor cells (MDSCs) in tumors. Upregulation of antigen presentation molecules (MHC class I and II) and immune checkpoint or functional molecules (CD80, CD86, CCR7, PD-L1) was observed on tumor-associated DCs and macrophages. Additionally, significant increases in tumor-infiltrating CD4+ T cells, CD8+ T cells, especially T_CM and T_EM cells, regulatory T cells, NK cells, and NKT cells were noted. Importantly, the treatment enhanced cytotoxic potential of various lymphocytes, with perforin emerging as the most reliable marker associated with treatment efficacy. Correlation analysis revealed strong negative associations between tumor volume and perforin-expressing CD4+ T cells and NKT cells. Conversely, the LLC1 model showed minimal immunophenotypic changes upon anti-PD-1 mAb treatment.

Conclusions

These findings provide comprehensive insights into the immune landscape modifications induced by anti-PD-1 mAb therapy and identify key immunological markers such as perforin, particularly in CD4+ T cells and NKT cells, and DC/MDSCs ratios that may predict therapeutic outcomes. This study offers insights into the predictive biomarkers and potential combination strategies for enhancing the efficacy of PD-1-targeted immunotherapy in resistant tumors.

Legal entity responsible for the study

Shin Nippon Biomedical Laboratories.

Funding

Shin Nippon Biomedical Laboratories.

Disclosure

All authors have declared no conflicts of interest.