Characterizing Interactions Between PD-1 and PD-L1 in Cell-Based Models of Ovarian Cancer and Investigating the Effect of Chemotherapy on Cancer-Derived Exosomes

Abstract

Cancer cells gain immunosuppressive abilities when exploiting immune checkpoint pathways by upregulating proteins such as PD-L1 to avoid T-cell detection. PD-L1 binds to PD-1 on the surface of T-cells, resulting in deactivated T-cells that do not attack the cancer cell. However, current drugs targeting this vulnerability are expensive, have poor tissue penetration, and can have reduced efficacy in the presence of soluble PD-L1. Our research goal is to design a peptide inhibitor to bind to either PD-1 or PD-L, blocking the interaction and preventing T-cell deactivation so the immune system will attack cancer cells. Furthermore, we will examine the soluble protein content of cancer-derived exosomes to better understand their role in modulating responses to checkpoint therapy. To test the peptides, we have been developing a co-culture model system consisting of a PD-1 positive cell line (Jurkat T-cells) and a PD-L1 positive line (1A9.and OVCAR8). Stimulation with phytohemagglutinin-L (PHA-L) shows strong induction of PD-1 on the Jurkat T line. We also show the presence of PD-L1 on the surface of the OVCAR8 cell line. Furthermore, examination of OVCAR8 extracellular vesicles (EV) shows not only PD-L1 but also LC3B and CD63 proteins. Interestingly, levels of these proteins fluctuate following cisplatin treatment. Future work will involve testing the peptides in the co-culture model with and without EV pre-treatment to evaluate EV effect on peptide potency.