Patients with head and neck squamous carcinoma (HNSCC) have a poor prognosis (Johnson, Burtness, et al. 2020). Although therapies that modulate immune checkpoint molecules on T cells, such as programmed death protein-1 and programmed death ligand-1, show promising clinical responses for some cancer types (Herbst, Soria, et al. 2014, Powles, Eder, et al. 2014), the response rate to T-cell-based immunotherapy is generally low (Chen, Li, et al. 2018, Gotwals, Cameron, et al. 2017). Therefore, research focusing on other types of immune cells or immune checkpoint molecules is needed to develop new treatment strategies.
Natural killer (NK) cells not only directly eliminate tumor cells but also modulate adaptive immunity by releasing large amounts of cytokines such as interferon (IFN)-γ (Lee, Park, et al. 2017, Liu, Galat, et al. 2021). NK cells highly infiltrate into the tumor microenvironment (TME) of HNSCC (Charap, Enokida, et al. 2020, Mandal, Şenbabaoğlu, et al. 2016). However, tumor cells often show resistance to NK cells (Elmusrati, Wang, et al. 2021, Sordo-Bahamonde, Vitale, et al. 2020). Thus, cytokines such as interleukin (IL)-2 and IL-15 are used to enhance NK cell activity (Croxatto, Martini, et al. 2017, Koehl, Brehm, et al. 2013, Lehmann, Zeis, et al. 2001, Miller, Soignier, et al. 2005, Rautela and Huntington 2017) by modulating multiple inhibitory receptors on tumor cells (Paul and Lal 2017, Sentman, Barber, et al. 2006).
NKG2A, which dimerizes with CD94, is an inhibitory receptor expressed on NK cells and T cells that binds to HLA-E, a non-classical HLA class I molecule containing leader peptides of other HLA class I molecules (Iwaszko and Bogunia-Kubik 2011, Leibson 1998). Although HLA-E expression is often weak or absent on the cell surface of tumor cells, it is increased by IFN-γ from immune cells and protects against NK cell-induced lysis (Lo Monaco, Tremante, et al. 2011, Nguyen, Beziat, et al. 2009). Levels of HLA-E can increase within the TME due to antitumor responses, and the overexpression of HLA-E in several types of solid tumors is associated with poor prognosis (Benevolo, Mottolese, et al. 2011, de Kruijf, Sajet, et al. 2010, Gooden, Lampen, et al. 2011, Morinaga, Iwatsuki, et al. 2022). HLA-E plays a more predominant role in inhibiting NK cells than other HLA class I molecules (Sheffer, Lowry, et al. 2021) and also inhibits antibody-dependent cellular cytotoxicity (ADCC) (Ehlers, Beelen, et al. 2021, Levy, Sycz, et al. 2009, Ward, Bonaparte, et al. 2004). Several studies show that NKG2A blockade promotes the antitumor immunity of T cells and NK cells (André, Denis, et al. 2018, Ducoin, Oger, et al. 2022, Kamiya, Seow, et al. 2019, Ruggeri, Urbani, et al. 2016, Zaghi, Calvi, et al. 2019). Monalizumab, a novel IgG4 monoclonal antibody (mAb) targeting NKG2A, was recently developed (van Hall, André, et al. 2019). A preclinical study shows that monalizumab inhibits tumor progression by increasing NK cell and T cell activity, and clinical trials of monalizumab in combination with cetuximab are ongoing (André, Denis, et al. 2018, Cohen, Bauman, et al. 2020, Galot, Le Tourneau, et al. 2021, Herbst, Majem, et al. 2022, Salomé, Sfakianos, et al. 2022). However, factors predicting tumor response to monalizumab are not yet understood. In particular, it is unclear whether the level of HLA-E expression on tumor cells predicts response to monalizumab therapy.
The objective of this study was to evaluate the association between HLA-E surface expression on HNSCC cell lines and the efficacy of monalizumab on NK cells. We also investigated the correlation between NK cell activity and monalizumab efficacy after stimulation of NK cells by cytokines ex vivo.