Abstract 3289: PD-1 peptide/IL-12 combination gene therapy for the treatment of melanoma

Abstract Immune checkpoint inhibitors (ICIs) such as PD-1 targeting antibodies nivolumab and pembrolizumab are FDA approved as therapies for many cancers. These ICIs inhibit PD-1 ligand binding, removing interference with T cell function, allowing T cell proliferation, and restoring the anti-tumor activity. Potential factors predicting checkpoint blockade success include PD-L1 expression, the presence of tumor infiltrating lymphocytes, microsatellite instability, and tumor mutational burden. ICIs are most effective clinically in combination therapies. Here, we devised a simple ICI gene therapy as a possible alternative to traditional and expensive monoclonal antibodies. We designed plasmids encoding the mouse sequences homologous to the nivolumab and pembrolizumab binding regions, which overlap the PD-1 ligand binding site. We hypothesized that, when produced intratumorally, each PD-1 peptide should bind PD-L1 and block T cell binding. Since B16F10 mouse melanoma cells and tumors express PD-L1, we tested this theory in this model. We directly demonstrated peptide-PD-L1 binding histologically on B16F10 mouse melanoma tumors. Systemic expression of the encoded peptides did not induce changes in general demeanor, discomfort or weight changes in mice, implying that intratumor expression would also be non-toxic. We then tested these peptide plasmids therapeutically. Intratumor electroporation delivery of the peptide plasmids to palpable B16F10 mouse melanoma tumors significantly increased tumor doubling time and induced approximately 10% long-term tumor regression. Delivery of a plasmid encoding IL-12 induced long-term tumor regression in approximately 40% of mice as well as a reduction myeloid-derived suppressor cells and T regulatory cells and an increase infiltration of CD8+ T cells, creating an inflamed tumor microenvironment. This modulation of the tumor microenvironment suggested the potentiation of a combination therapy. This combination synergistically increased long-term regression to 80-100%, depending on the peptide plasmid delivered, over either PD-1 peptide or IL-12 gene therapy alone. These results demonstrated that the delivery of immune regulators with differing activities may be a promising and potentially inexpensive alternative to monoclonal antibody therapies. Citation Format: Loree Heller, Guilan Shi, Jody Synowiec, Richard Heller. PD-1 peptide/IL-12 combination gene therapy for the treatment of melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3289.