Pemetrexed combined with dual immune checkpoint blockade enhances cytotoxic T lymphocytes against lung cancer

Chemotherapy, in combination with immune checkpoint blockade (ICB) targeting to programmed death‐1 (PD‐1) or its ligand PD‐L1, is one of the first‐line treatments for patients with advanced non–small‐cell lung cancer (NSCLC). However, a large proportion of patients, especially those with PD‐L1 negative tumors, do not benefit from this treatment. This may be due to the existence of multiple immunosuppressive mechanisms other than the PD‐1/PD‐L1 axis. Human leukocyte antigen‐G (HLA‐G) has been identified as an immune checkpoint protein (ICP) and a neoexpressed tumor‐associated antigen (TAA) in a large proportion of solid tumors. In this study, we evaluated the induction of HLA‐G as well as PD‐L1 using sublethal doses of chemotherapeutics including pemetrexed in different NSCLC cell lines. Except for gefitinib, most of the chemotherapeutic agents enhanced HLA‐G and PD‐L1 expression in a dose‐dependent manner, whereas pemetrexed and carboplatin treatments showed the most consistent upregulation of PD‐L1 and HLA‐G in each cell line. In addition to protein levels, a novel finding of this study is that pemetrexed enhanced the glycosylation of HLA‐G and PD‐L1. Pemetrexed potentiated the cytotoxicity of cytotoxic T lymphocytes (CTLs) to treat NSCLC. Both in vitro and in vivo experiments revealed that CTL‐mediated cytotoxicity was most pronounced when both anti‐PD‐L1 and anti‐HLA‐G ICBs were combined with pemetrexed treatment. In conclusion, anti‐HLA‐G could be an intervention strategy in addition to the anti‐PD‐1/PD‐L1 pathway for NSCLC. Moreover, dual targeting of PD‐L1 and HLA‐G combined with pemetrexed might have a better extent of CTL‐based immunotherapy.