Improving T cell activation by limiting mitochondrial-derived ATP transfer to the cytosol

CD8⁺ T cells’ metabolic programs are critical for their function and fate decisions. As the metabolic hub of the cell, the mitochondria play a crucial role in T cell-mediated immunity. However, the mechanisms by which mitochondria govern T cell responses and cellular fate are not completely understood. Recently, we demonstrated that mitochondrial oxidative phosphorylation (OXPHOS) is vital for CD8⁺ T cell activation by supporting matrix substrate-level phosphorylation, independently from ATP synthesis by complex V. Here, to unveil the underlying mechanisms adapted by CD8⁺ T cells to function independently from mitochondrial ATP we tested how depleting mitochondrial ATP from the CD8⁺ T cells’ cytoplasmic compartment affect their activation by generating a T cell-specific ADP/ATP translocase-2 knockout (Ant2^KO) model. Remarkably, we found that Ant2 deficiency improved CD8⁺ T cell activation and effector functions. We demonstrated that naïve CD8⁺ T cells overcome Ant2-deficiency by increasing their mitochondrial biomass and through the induction of selective anabolic pathways which include proline biosynthesis. Since the role of the proline biosynthesis pathway in T cell activation is unknown, we performed a study showing that similarly to naïve Ant2^KO CD8⁺ T cells, activated WT CD8⁺ T cells also engaged in proline biosynthesis, to support the increased demand for oxidation reactions within the mitochondria when OXPHOS does not meet those demands. Overall, our study provides a better understanding of the metabolic programs adapted by CD8⁺ T cells to support rapid proliferation and effector functions under conditions such as low oxygen tension and metabolic competition.