Abstract 4105: Immune-modulating vaccines targeting CD73
Authors: Luo Yuting , Shi Tao , Wang Hanbing , Liu Baorui , Wei Jia 
Published: March 2024

Abstract
Background: To realize the generalizable regulation of the tumor microenvironment (TME), immune-modulating vaccines are developed to target shared antigens expressed by immunosuppressive cells and cancer cells. CD73, also known as ecto-5'-nucleotidase, is a pivotal enzyme in the adenosine metabolic pathway and is expressed on the surface of multiple cancer cells and immunosuppressive cells in the TME. In this study, we aim to develop a CD73-targeting immune modulatory peptide vaccine by predicting antigen sequences, screening immunogenic antigen peptides, and assessing their anti-tumor efficacy and capacity to improve the TME.
Methods: The expression level of CD73 on various cancer cell lines were evaluated by flow cytometry. Several online software were used to predict CD73-derived peptides that bind to the mouse MHC-I (major histocompatibility complex class I) molecules. Cells from the draining lymph nodes of healthy mice and peptide-immunized mice were harvested and stimulated by the synthetic peptides in vitro. T cell activation level, IFN-γrelease degree and their cytolytic capability towards cancer cells was measured. CD73-derived peptides were mixed with CpG to treat 4T1 tumor-bearing mice and the changes in the TME were investigated by flow cytometry. The online website (www.camoip.net) was used to analyze the correlation between CD73 expression and patient survival in the TCGA Breast invasive carcinoma (BRCA) cohort.Results: 4T1 exhibited a strikingly elevated surface expression of CD73 compared to other mouse cancer cell lines. Three CD73-derived peptides (EP1, EP2, EP3) consisting of 8-10 amino acids were synthesized. In vitro stimulation experiments indicated that EP1 and EP3 significantly elicited T-cell responses in draining lymph nodes. After stimulation, the proportions of CD25+, CD69+, CD107a+, and CD137+ cells markedly increased in CD8+ T cell populations. These cells also displayed enhanced cytotoxicity against 4T1 tumor cells. In vivo experiments demonstrated that EP3 induced a pronounced anti-tumor response in an established 4T1 tumor model without evident toxicity. Moreover, subcutaneous injection of EP3 improves the TME by promoting antigen-specific CD8+ T-cell responses, reducing M2 macrophages, and inducing neutrophil maturation. High tumor CD73 expression was also found to be associated with poor outcomes among BRCA patients, which further indicated clinical relevance.
Conclusions: In this study, we successfully identified an immunogenic vaccine targeting CD73. It expressed dual functionality by effectively triggering cytotoxic T-cell responses that directly killing CD73-highexpressing tumor cells and regulating the tumor microenvironment through eliminating immunosuppressive cells with elevated CD73 expression. These findings hold promise for a novel immune-modulating vaccine and suggest a potential therapeutic avenue for the treatment of breast cancer and other types of cancer.
Citation Format: Yuting Luo, Tao Shi, Hanbing Wang, Baorui Liu, Jia Wei. Immune-modulating vaccines targeting CD73 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4105.