Immunotherapies, such as immune checkpoint inhibitors (ICI), anti-cancer vaccines and adoptive T cell transfer, are promising treatments for cancer patients. However, ICI have not shown therapeutic benefit for most mismatch repair-proficient colorectal and pancreatic ductal adenocarcinoma tumors (PDAC), which are aggressive and deadly (Li et al. in Biomedicines 12:2175, 2024). Tumor metabolism can enhance immunological tolerance, but hinder immune cell function. In a recent publication in Nature Cancer, Scolaro et al. (Scolaro et al. in Nature Cancer 5:1206–1226, 2024) showed that cytidine deaminase (CDA) upregulation may play a crucial role in shaping the immunosuppressive landscape of human PDAC and other tumors. CDA targeting in pancreatic cancer cell lines led to reduced tumor growth, weight and total regression after treatment aimed at the programmed cell death protein 1 receptor (PD-1) immune checkpoint protein. CDA inhibition, both genetically and pharmacologically, overcame immunotherapy resistance in PDAC models. CDA targeting in PDAC cells altered the tumor microenvironment (TME), enabling T cells to respond to anti-PD-1. In mice with sgNT and sgCda tumors receiving anti-PD-1 treatment, they reduced the number of CD8+ T cells. CDA reduction in cancer cells makes tumors more sensitive to immunotherapy, presumably by overcoming immunosuppressive tumor-associated macrophages (TAMs) and forcing them to adopt an immunostimulatory phenotype. The study also found that cancer cells produce a TME rich in UDP (and UTP) by taking advantage of the CDA-mediated pyrimidine salvage pathway. This setting inhibits the recruitment and activation of CD8+ T cells by promoting the infiltration and immunosuppressive characteristics of P2Y6 receptor–expressing TAMs.
