396PD IL-2 synergizes with PD-1/PD-L1 blockade via CD28/CHK1 pathway to enhance CD81 T cell responses in lung squamous cell carcinoma

Abstract

Background Immune checkpoint inhibitors targeting PD-1/PD-L1 have shown striking response in lung squamous cell carcinoma (SQCLC). However, the response rate was only about 20%. To figure out an effective strategy to increase the response rate is in urgent warrant. Combinatorial approach would be an option. Cytokine IL-2, which is secreted by activated T cells, is a potential anti-tumor agent. To address this issue, we set up a humanized cell and animal model to evaluate the combination effect of IL-2 and anti-PD-1or anti-PD-L1. Further evaluation was conducted to explore possible signal pathway involved in this process. Methods To examine the effect of IL-2 and PD-L1 blockade, tumor infiltrated lymphocytes (TILs) were isolated and cultured in IL-7, IL-15, CD3 coated system in vitro.Moreover, the anti-tumor activity of IL-2 and aPD-1 was evaluated in a squamous carcinoma burdened murine model. To understand the mechanism, microarray assay were performed, and flow cytometry, western blotting and IHC was conducted to identify the effect of IL-2 to regulate CD28/CHK1 pathway in TILs. Results we found that the frequency of CD8þ PD-1þTILs varied. In the co-cultured model of TILs and squamous cancer cell line system, we validated that the release of IFN-c and TNF-a increased in IL-2 combined with aPD-1 and/or a-PD-L1 group than in IL-2 only group. Moreover, the proliferation ability of T cells was evidently increased in IL-2 combined with aPD-1 and/or aPD-L1 group. In vivo, we found that the volume of tumor burden shrunk evidently in the combination group.In microarray assay we found that treated with IL-2 could increase the expression of CD28 and CHK1/2 pathway in T cells, and flow cytometry assay validated the increased expression of CD28 and CHK1 in TILs. Conclusions Combining IL-2 with inhibitors targeting PD-1/PD-L1 pathway shows significant effects on enhancing the proliferation activity and cytotoxicity of CD8þT cells in response to squamous cancer cells. Moreover, the CD28/CHK1 pathway was activated when TILs were treated with the combination therapy. These results suggest that combining IL-2 with PD-1/PD-L1 blockade would be a regimen for battles against lung squamous cell carcinoma. Legal entity responsible for the study Guangdong Lung Cancer Institute Guangdong General Hospital and Guangdong Academy of Medical Sciences Funding Guangdong Lung Cancer Institute Guangdong General Hospital and Guangdong Academy of Medical Sciences Disclosure All authors have declared no conflicts of interest.