Background HLA-E is overexpressed by approximately 80% of solid tumors, including malignant glioblastoma and is emerging as a major check point turning of NKG2A+ CD8 T cells and NK cells in the tumor microenvironment and circulation.1 2 This axis operates side-by-side with PD-L1 to block both T and NK cells.3 Blockade of this suppressive pathway unleashes cytotoxic lymphocytes and prevents metastasis.1 This notion is supported by CRISPR screens in mice, identifying Qa-1 (the mouse orthologue to HLA-E) as a limiting factor for immunotherapy.4
Methods We engineered a novel chimeric A/C Switch receptor, combining the strong HLA-E binding affinity NKG2A receptor’s ectodomain with the activating signaling of NKG2C receptor’s endodomain (figure 1A). We transduced NK-92 cells as well as primary NK and T cells with the A/C Switch and tested the efficacy against a battery of cancer cell lines with varying HLA-E densities (figure 1B, 1C). Cell viability, transduction efficiency, functional responses (CD107a, IFN-g, TNF-a) as well as target cell killing in vitro and in vivo were examined.
Results Our results showed that A/C Switch-transduced NK and T cells displayed superior and specific cytotoxic function and killing potential when challenged with tumor cells exhibiting medium to high HLA-E expression (figure 1D). In co-culture experiments with normal cells that are known to express low levels of HLA-E, A/C Switch T cells did not cause target cell death. We also observed that an equilibrium between A/C Switch transduction level and HLA-E expression governs the activity of the modified T cells, creating a therapeutic window to safeguard against on-target off-tumor toxicities. Furthermore, A/C Switch-expressing human T cells demonstrated enhanced anti-tumor function in a xenograft model of glioblastoma (figure 1E, 1F).
Conclusions NKG2A/C-switched cytotoxic cells display powerful and focused activity against tumor cells expressing medium to high levels of HLA-E, while sparing healthy cells. We propose that this novel A/C Switch receptor may operate alone to control tumor cells expressing high levels of HLA-E or in combination with other engineered specificities to overcome the suppressive NKG2A/HLA-E checkpoint.
Liu X, Song J, Zhang H, et al. Immune checkpoint HLA-E:CD94-NKG2A mediates evasion of circulating tumor cells from NK cell surveillance. Cancer Cell. 2023;41(2):272–287.e9.
André P, Denis C, Soulas C, et al. Anti-NKG2A mAb Is a Checkpoint Inhibitor that Promotes Anti-tumor Immunity by Unleashing Both T and NK Cells. Cell. 2018;175(7):1731–1743.e13.
Salomé B, Sfakianos JP, Ranti D, et al. NKG2A and HLA-E define an alternative immune checkpoint axis in bladder cancer. Cancer Cell. 2022;40(9):1027–1043.e9.
Dubrot J, Du PP, Lane-Reticker SK, et al. In vivo CRISPR screens reveal the landscape of immune evasion pathways across cancer. Nat Immunol. 2022;23(10):1495–1506.
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