CD36 Promotes Iron Accumulation and Dysfunction in CD8+ T Cells via the p38-CEBPB-TfR1 Axis in Early-stage Hepatocellular Carcinoma.

Abstract

Background: The identification of factors that lead to CD8⁺ T cell dysfunction within the tumor microenvironment (TME) holds great promise for the development of innovative immunotherapies. However, the precise mechanisms underlying the exhausted phenotype of CD8⁺ T cells infiltrating early-stage hepatocellular carcinoma (HCC) tumors remains unclear.

Methods: Single-cell RNA sequencing was performed using a murine HCC model. Flow cytometry and additional experimental approaches were employed to investigate the underlying mechanisms of CD8⁺ T cell exhaustion.

Results: CD8+ T cells infiltrating early-stage HCC tumors exhibited a functionally exhausted phenotype, which escalated with HCC progression. At early stages of murine and human HCC tumors, the TME was characterized by significant iron accumulation. Moreover, tumor-infiltrating CD8+ T cells in early-stage murine HCC tumors exhibited higher levels of intracellular ferrous iron compared to splenic CD8+ T cells. This excessive iron led to increased lipid peroxide levels and impaired the effector function of CD8+ T cells. Mechanistically, CD36 upregulated the major iron uptake protein transferrin receptor 1 (TfR1) by mediating the activation of oxidized low-density lipoprotein (oxLDL)-p38-CEBPB axis. Depletion of CD36 in CD8+ T cells inhibited the upregulation of TfR1 expression and the increase of intracellular ferrous iron levels triggered by iron-enriched conditions. Furthermore, constitutively activated nuclear factor erythroid 2-related factor 2 (NRF2) effectively suppressed iron accumulation and lipid peroxidation, thereby preserving the effector functions of intratumoral CD8+ T cells and ultimately inhibiting tumor growth.

Conclusions: Our findings reveal a previously unidentified mechanism mediated by CD36 that regulating the progressive dysfunction of CD8+ T cells in early HCC TME and provide a potential novel therapeutic approach to restore T cells function.