Checkpoint inhibitors in metastatic epidermal growth factor receptor-mutated non-small cell lung cancer patients: where we treating the wrong cancer?

Tumor-infiltrating CD8+ T cells in ALK-positive lung cancer are functionally impaired despite the absence of PD-L1 on tumor cells

Several lines of evidence have demonstrated that programmed cell death 1 (PD-1) inhibitors as monotherapies for anaplastic lymphoma kinase (ALK)-positive non-small cell lung cancer have little clinical activity. The underlying mechanisms remain not understood. In this study, using immunohistochemistry and in situ RT-PCR assays, we examined the expression of programmed cell death ligand 1 (PD-L1), PD-1, CD8, and interferon gamma (IFN-γ) in tumors. Both epidermal growth factor receptor (EGFR)-mutant and anaplastic lymphoma kinase (ALK)-positive tumors were associated with low or absent membrane PD-L1 expression. Interestingly, unlike EGFR-mutant tumors with few tumor-infiltrating CD8⁺ T cells, a significant number of PD-1-positive CD8⁺ T cells infiltrated the ALK-positive tumor bed; however, these cells did not express IFNG mRNA. These results demonstrate that the ALK-positive tumor microenvironment suppresses the immune function of tumor-infiltrating CD8⁺ T cells through a PD-1/PD-L1-independent mechanism, which might lead to the inability of ALK-positive tumors to respond to PD-1/PD-L1-based immunotherapy.

Immunotherapy strategy of EGFR mutant lung cancer

EGFR-mutant lung cancer is an important molecular subtype in Asia considering that almost 40%-50% of patients with lung adenocarcinoma in Asian carry the active EGFR mutaiton. People have greatly anticipated the efficacy of PD-1/PD-L1 monoclonal antibody in lung cancer treatment but anti-PD-1/PD-L1 treatment failed to positively affect these patients. The NCCN guidelines do not recommend immunotherapy to patients with NSCLC carrying EGFR mutation at present. However, the reason why EGFR-mutant lung cancer patients show poor response to anti-PD-1/PD-L1 treatment is still unknown. Immune suppression and tolerance are the main characteristics of tumor. The PD-1/PD-L1 co-inhibitory molecule is probably not the main escape route of this tumor type. The main characteristic of EGFR-mutant lung cancer is the activation of the EGFR signaling pathway. EGFR activation is likely responsible for the uninflamed tumor microenvironment of this type tumor and particiaptes in immunosuppression and immune escape. Accumulating evidence proved that activation of EGFR signaling pathway is essential to the generation of Treg and tolerogenic DCs. In this review, we summarize the efficacy of PD-1/PD-L1 monoclonal antibiodies in patients with EGFR-mutant lung cancer patients; provide evidence to analyze the potential reason why these patients cannot benefit from anti-PD-1/PD-L1 treatment, and explore the strategy that shoud be adopted in the future.