Immune checkpoint blockade (ICB) has improved cancer care, but ICB is only effective in some patients. The molecular mechanisms that influence ICB therapy response are not completely understood. The non-classical MHC class I molecule HLA-E and its mouse ortholog, Qa-1b, present a limited set of peptides in a TAP1-dependent manner to the NKG2A/CD94 heterodimer to transduce an inhibitory signal to natural killer (NK) and CD8þ T cells. However, deficiency of TAP1 allows Qa-1b to present an alternative peptidome to Qa-1b–restricted T-cell receptors of cytotoxic T cells. In this study, we used CRISPR–Cas9 to study the relationship between TAP1, Qa-1b, and response to anti-PD1 therapy. We hypothesized that immunotherapy response in TAP1-deficient tumors would be influenced by Qa-1b. Strikingly, using a syngeneic orthotopic mouse model, we found that although TAP1-deficient tumors were resistant to anti-PD1 treatment, antiPD1 response was significantly enhanced in tumors lacking both TAP1 and Qa-1b. This increased sensitivity is partially dependent on NK cells. TAP1-deficient tumors were associated with an increase of intratumoral regulatory T cells (Treg) and neutrophils, whereas tumors lacking both TAP1 and Qa-1b exhibited an increased CD8þ T-cell to Treg ratio. These data suggest that direct inhibition of Qa-1b may alter the immune microenvironment to reverse resistance to anti-PD1 therapy, particularly in the context of antigen-processing defects. Implications: This study reveals important functional crosstalk between classical TAP-dependent MHC complexes and Qa-1b/ HLA-E, particularly in tumors with impaired antigen-processing machinery. This can dramatically influence immunotherapy efficacy.
CITATION STYLE
Zhang, X., Sabio, E., Krishna, C., Ma, X., Wang, J., Jiang, H., … Chan, T. A. (2021). Qa-1b modulates resistance to anti–PD-1 immune checkpoint blockade in tumors with defects in antigen processing. Molecular Cancer Research, 19(6), 1076–1084. https://doi.org/10.1158/1541-7786.MCR-20-0652
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