Phenotypically and functionally unique CD86 expression CD8 T cell subset shapes immune regulation in the tumor...

The tumor microenvironment (TME) promotes immune evasion by fostering regulatory immune programs. Although CD8⁺ regulatory T cells have been described, their identity, upstream drivers and impact in tumors remain incompletely defined.

To define the phenotype, regulation determinants, and functional of CD86^high CD8⁺ T cells in tumor immunity.

Murine tumor models were used to isolate tumor-infiltrating lymphocytes (TILs) for flow cytometry (FCM), functional co-cultures, and RNA-seq. Upstream cues were probed through cytokine stimulation and transcription factor analyses. Dendritic cells (DCs) conditioning was tested with bone marrow derived DCs and OT-I/OT-II antigen-specific systems. The in vivo function of CD86 on CD8⁺ T cells was evaluated using conditional Cd86 knockout in CD8⁺ T cells mouse model.

CD86 was markedly upregulated on tumor-infiltrating CD8⁺ T cells, defining a CD86^high subset that accumulated in tumors. Transcriptomic profiling revealed enrichment of immunoregulatory and terminal-exhaustion programs while preserving effector modules. CD86^high cells upregulated Il12rb1 and IRF5; exogenous IL-12 increased the frequency and intensity of CD86 expression showing dose and time dependent effects, whereas IRF5 inhibition curtailed this induction, establishing an IL-12-IRF5 axis controlling CD86. Functionally, CD86^high CD8⁺ T cells selectively suppressed antigen-specific OT-I/OT-II responses, reducing IFN-γ, IL-2, and Ki-67, and reprogrammed DCs toward a regulatory phenotype characterized by increased IDO, IL-10, CTLA-4, and CD39. Genetic ablation of Cd86 in CD8⁺ T cells reduced tumor growth, diminished CD39 and PD-1 on TILs, enhanced IFN-γ and granzyme B, and remodeled the myeloid compartment toward immunostimulatory DCs with elevated CD40/CD80/CD86 and reduced IDO/IL-10/CTLA-4/CD39.

CD86^high CD8⁺ T cells constitute a distinct immunoregulatory subset in cancer. Their differentiation is driven by an IL-12-IRF5 program, and their crosstalk with DCs via CD86/CTLA-4 engagement promotes tolerogenic remodeling of the TME. Targeting CD86 on CD8⁺ T cells may disrupt this suppressive circuit and potentiate antitumor immunity.