Targeting PD-1 and CD85j can restore intratumoral CD4⁺ GzmB⁺ T-cell functions to combat MHC-II-expressing tumors

A subset of CD4⁺ T cells with cytotoxic activity has been identified, and these cells exert their effects by expressing perforin and granzymes. Despite the progress made in characterizing cytotoxic CD4⁺ T cells in various diseases, the status of cytotoxic CD4⁺ T cells in non-small cell lung cancer (NSCLC) and the underlying mechanisms involved in promoting intratumoral cytotoxic CD4⁺ T-cell activation remain unclear.

We used flow cytometry to examine the phenotypic and functional properties of CD4⁺GzmB⁺ T cells in the peripheral blood and tumor tissues of patients with NSCLC. Loss-of-function analyses and RNA sequencing were used to identify the underlying mechanisms involved in the effects of interleukin (IL)-15 on the restoration of CD4⁺GzmB⁺ T-cell function in vitro. A patient-derived lung cancer explant model and an animal model were used to verify the effects of immune checkpoint inhibitors on CD4⁺GzmB⁺ T-cell activation.

In patients with NSCLC, impaired cytolytic function of tumor-infiltrated granzyme B (GzmB)-expressing CD4⁺ T cells was restored by IL-15 through activation of the AKT-FOXO1-T-bet axis. Moreover, IL-15 stimulation increased solute carrier family 7 member 5 (SLC7A5) expression in CD4⁺GzmB⁺ T cells in an Protein Kinase B (AKT)-dependent manner, and inhibition of SLC7A5 abrogated the effect of IL-15 on CD4⁺GzmB⁺ T cells. Additionally, we showed that the immune checkpoint molecules programmed cell death-1 (PD-1) and CD85j were mutually exclusively expressed in CD4⁺GzmB⁺ T cells and that dual targeting of PD-1 and CD85j enhanced the effector function of CD4⁺GzmB⁺ T cells by activating the AKT pathway. Notably, tumor cells expressing major histocompatibility complex (MHC)-II and IL-15 determine the effectiveness of CD4⁺GzmB⁺ T-cell-mediated antitumor immunity in response to immunotherapy.

Our study demonstrated that tumor-infiltrating CD4⁺GzmB⁺ T cells fail to eliminate tumors. Dual blockade of PD-1 and CD85j alongside IL-15 restores the effector function of CD4⁺GzmB⁺ T cells and drives CD4⁺GzmB⁺ T-cell transformation in the tumor microenvironment to combat MHC-II-expressing tumors.