NKG2A blockade as a potential strategy to improve NK cell-mediated ADCC in HER2+ breast cancer

Several studies support the contribution of antibody-dependent NK cell cytotoxicity (ADCC) to the clinical efficacy of anti-HER2 therapeutic antibodies in HER2-positive breast cancer. Novel anti-HER2 antibody drug conjugates (ADCs) might also act, in part, via NK cells, but this has not been properly addressed. However, not all patients respond to treatment or eventually relapse and there is a need to develop novel strategies to enhance the activity of anti-HER2 therapies. Currently, several biologics targeting NK cell inhibitory receptors (e.g., NKG2A, KIR, TIGIT) are in clinical development and could be used in combinatorial strategies. We hypothesized that the blockade of CD94/NKG2A, an inhibitory receptor specific for HLA-E, could enhance the clinical activity of anti-HER2 antibodies. Our results showed that CD94/NKG2A was one of the major functional checkpoints expressed by breast tumor-associated NK cells as well as by most NK cell products obtained upon in vitro expansion. Gene expression profiling of HER2-positive breast tumors disclosed the correlation between NK cells, KLRC1 (encoding for NKG2A) and HLA-E with differential overall survival to trastuzumab, pointing to the possibility of enhancing the efficacy of HER2 therapeutic antibodies by blocking the NKG2A-HLA-E axis. Mechanistic studies in in vitro and in vivo preclinical models showed that soluble factors secreted along anti-HER2 antibody-dependent NK-mediated ADCC promoted and adaptive response in bystander breast cancer cells including the up-regulation of HLA-I, HLA-E and PD-L1, which could reduce subsequent NK cell activity. Certainly, the blockade of NKG2A enhanced anti-HER2 antibody-dependent NK cell cytotoxicity against breast tumor spheroids and boosted the anti-tumor efficacy of anti-HER2 antibodies and NK cell infusions in a humanized in vivo model of HER2+ breast cancer. Of note, the increase in cytotoxicity associated to NKG2A blockade was significantly higher when using NK cells from HLA-B-21M/M as compared to HLA-B-21T/T individuals, pointing to the putative interest of HLA-B-21M/T genotype as a predictive biomarker for the clinical activity of NKG2A blocking agents. Finally, the blockade of CD94/NKG2A-HLA-E axis also enhanced the anti-tumor activity of the recently approved anti-HER2 antibody-drug conjugates, trastuzumab-emtansine (T-DM1) and trastuzumab-deruxtecan (T-DXd), despite their limited capacity to trigger NK cell-mediated ADCC. Our study provides the conceptual and