Suppressing phosphatidylserine externalization overcomes cancer immune evasion and enhances immunotherapy

To uncover novel drivers of ICB resistance, we performed an in vivo CRISPR-Cas9 screen in mice with increasing levels of immune pressure. This screen identified phosphatidylserine (PS) externalization as a potent mediator of immune escape.

Tumors with elevated surface PS exposure prevented reinvigoration of CD8+ T cells upon PD-1 blockade, which was associated with increased recruitment of immunosuppressive myeloid cells. Targeting of PS Synthase 1 (PTDSS1) or either of the scramblases, XKR8 or ANO6, sensitized tumors to ICB in vivo. These findings demonstrate that elevated PS exposure constitutes a mechanism of resistance to ICB, and that targeting regulators of PS externalization represents a promising strategy to enhance the efficacy of immunotherapy in refractory tumors.