Immunosuppressive Myeloid Cells Induce Nitric Oxide-Dependent DNA Damage and p53 Pathway Activation in CD8⁺ T Cells

Area of Science:

• Immunology
• Cancer Biology
• Cellular Signaling

Background:

• Tumor-infiltrating myeloid-derived suppressor cells (MDSCs) are linked to poor cancer survival.
• MDSCs suppress T cell-mediated anti-tumor immunity.
• The precise stage of T cell activation inhibited by MDSCs remains unclear.

Purpose of the Study:

• To investigate whether MDSCs inhibit early or later stages of T cell activation.
• To elucidate the molecular mechanisms by which MDSCs impair T cell function.

Main Methods:

• Co-culture of CD8+ T cells with dendritic cells (DCs) and MDSCs.
• Analysis of T cell proliferation, apoptosis, and activation markers.
• Single-cell RNA-sequencing of T cells.
• Confocal microscopy for DNA damage and p53 localization.
• Inhibition of inducible nitric oxide synthase (iNOS) in MDSCs.
• Studies in KPC pancreatic tumor models (wild-type and Nos2-deficient mice).

Main Results:

• MDSCs inhibited CD8+ T cell proliferation and induced apoptosis, even with high-affinity antigen presentation by DCs.
• T cells showed early activation markers despite MDSC presence, indicating later-stage inhibition.
• Single-cell RNA-seq revealed a p53 transcriptional signature in T cells co-cultured with MDSCs.
• MDSCs induced DNA damage and nuclear p53 accumulation in T cells via an iNOS-dependent pathway.
• Inhibition of iNOS or Nos2 gene deletion in MDSCs reduced T cell DNA damage.
• DNA damage in T cells was observed in KPC tumors and was lower in Nos2-deficient mice.

Conclusions:

• MDSCs do not block early T cell activation but rather induce DNA damage in CD8+ T cells.
• This DNA damage is mediated by MDSC-derived nitric oxide through iNOS.
• MDSCs activate the p53 pathway in CD8+ T cells, contributing to immune suppression in cancer.