Janus kinase inhibitors alter NK cell phenotypes and inhibit their antitumour capacity

Janus kinase inhibitors (JAKi) are efficacious in RA but concerns regarding the risk of cancer associated with their exposure have recently emerged. Given the role of NK cells in antitumour response, we investigated the impact of JAKi [tofacitinib (TOFA), baricitinib (BARI), upadacitinib (UPA) and filgotinib (FIL)] on NK cells.We first performed an ex vivo phenotype of NK cells in RA patients treated with TOFA, BARI or MTX. We next phenotyped sorted NK cells from healthy donors cultured with four JAKi or dimethyl sulphoxide (DMSO) at three concentrations, including the licensed dose (therapeutic concentration). Third, we assessed NK cell function using anti-NKp30 cross-linking and co-cultures with two different tumour cell lines: A549 and SU-DHL-4.Twenty-eight RA patients were included. Patients treated with TOFA had reduced expression of CD69 on NK cells compared with MTX (P < 0.05). We confirmed in vitro the negative impact of JAKi on NK cell maturation (CD57), activation (CD69) and activating receptor (NKp30), these latter two being specifically altered with TOFA and UPA. When NK cells were stimulated by NKp30, we observed reduced CD107a (P < 0.01) and IFN-γ/TNF expression (P < 0.05) with TOFA. Lastly, NK cells exposed to TOFA showed reduced CD107a (P < 0.05) and altered cytotoxicity (P < 0.05) when co-cultured with the two cell lines.JAKi have a phenotypic and functional impact on NK cell activation and impair their antitumour activity, with a variable impact depending on the JAKi. It remains an open question whether this mechanism can explain the increased tumour risk observed with TOFA.