A new study identifies the protein SLFN5 as a key barrier to effective treatment in Pancreatic Ductal Adenocarcinoma (PDAC). SLFN5 acts as an “intracellular immune checkpoint,” helping tumors remain “cold” by evading immune attack and resisting standard therapies. High levels of SLFN5 are linked to poor patient survival. While Interferons normally activate anti-tumor defenses, SLFN5 suppresses these signals by binding to DNA and blocking the genes that trigger immune responses, essentially muting the body’s natural anti-cancer alarms.
Using CRISPR/Cas9 to delete SLFN5 in human and mouse PDAC cells, researchers found that tumors became highly responsive to Interferon. The loss of SLFN5 reduced cancer cell proliferation and spheroid formation while boosting the production of anti-tumor proteins. SLFN5 normally binds to Interferon-Stimulated Response Element (ISRE) promoters to block gene activation; removing it “unlocks” these genes, reviving the immune response against the tumor.
In mouse models, targeting SLFN5 reshaped the tumor microenvironment. Tumors without SLFN5 showed more pro-inflammatory M1 macrophages and fewer immunosuppressive M2 macrophages. CD8+ T cells and Natural Killer (NK) cells infiltrated the tumor in greater numbers and were more active, secreting Granzyme B and IFN-γ to kill cancer cells. Combining SLFN5 loss with Interferon-α treatment yielded the longest survival and slowest tumor growth. Researchers suggest that targeting SLFN5 could both inhibit tumor growth and make pancreatic cancers more susceptible to immunotherapies like Pembrolizumab, offering a promising new strategy against this hard-to-treat disease.