Data from Immunosuppressive Myeloid Cells Induce Nitric Oxide–Dependent DNA Damage and p53 Pathway Activation in CD8<sup>+</sup> T Cells

Abstract

<div>Abstract<p>Tumor-infiltrating myeloid-derived suppressor cells (MDSC) are associated with poor survival outcomes in many human cancers. MDSCs inhibit T cell–mediated tumor immunity in part because they strongly inhibit T-cell function. However, whether MDSCs inhibit early or later steps of T-cell activation is not well established. Here we show that MDSCs inhibited proliferation and induced apoptosis of CD8<sup>+</sup> T cells even in the presence of dendritic cells (DC) presenting a high-affinity cognate peptide. This inhibitory effect was also observed with delayed addition of MDSCs to cocultures, consistent with functional data showing that T cells expressed multiple early activation markers even in the presence of MDSCs. Single-cell RNA-sequencing analysis of CD8<sup>+</sup> T cells demonstrated a p53 transcriptional signature in CD8<sup>+</sup> T cells cocultured with MDSCs and DCs. Confocal microscopy showed induction of DNA damage and nuclear accumulation of activated p53 protein in a substantial fraction of these T cells. DNA damage in T cells was dependent on the iNOS enzyme and subsequent nitric oxide release by MDSCs. Small molecule–mediated inhibition of iNOS or inactivation of the <i>Nos2</i> gene in MDSCs markedly diminished DNA damage in CD8<sup>+</sup> T cells. DNA damage in CD8<sup>+</sup> T cells was also observed in KPC pancreatic tumors but was reduced in tumors implanted into <i>Nos2</i>-deficient mice compared with wild-type mice. These data demonstrate that MDSCs do not block early steps of T-cell activation but rather induce DNA damage and p53 pathway activation in CD8<sup>+</sup> T cells through an iNOS-dependent pathway.</p></div>