A key mechanism of tumor resistance to immune cells is mediated by expression of peptide-loaded HLA class I molecule (HLA-E) in tumor cells, which suppresses NK cell activity via ligation of the NK inhibitory receptor CD94/NK group 2 member A (NKG2A). Gene expression data from approximately 10,000 tumor samples showed widespread HLAE expression, with levels correlating with those of KLRC1 (NKG2A) and KLRD1 (CD94). To bypass HLA-E inhibition, we developed a way to generate highly functional NK cells lacking NKG2A. Constructs containing a single-chain variable fragment derived from an anti-NKG2A antibody were linked to endoplasmic reticulum–retention domains. After retroviral transduction in human peripheral blood NK cells, these NKG2A protein expression blockers (PEBLs) abrogated NKG2A expression. The resulting NKG2Anull NK cells had higher cytotoxicity against HLA-E–expressing tumor cells. Transduction of anti-NKG2A PEBL produced more potent cytotoxicity than interference with an anti-NKG2A antibody and prevented de novo NKG2A expression without affecting NK cell proliferation. In immunodeficient mice, NKG2Anull NK cells were substantially more powerful than NKG2A+ NK cells against HLA-E–expressing tumors. Thus, NKG2A downregulation evades the HLA-E cancer immune checkpoint and increases the antitumor activity of NK cell infusions. Because this strategy is easily adaptable to current protocols for clinical-grade immune cell processing, its clinical testing is feasible and warranted.
Takahiro Kamiya, See Voon Seow, Desmond Wong, Murray Robinson, Dario Campana
Phenotypic and functional effects of NKG2A downregulation by PEBL.