🧬 What if mitochondrial ATP does more than power T cells—what if it directly helps determine their identity by controlling chromatin accessibility? A fascinating new Cell study provides a mechanistic bridge between immunometabolism and epigenetics, showing that mitochondrial ATP production can support the chromatin remodeling required for CD8⁺ T-cell effector differentiation. The key molecule is D-α-hydroxybutyrate (DAHB). Rather than functioning primarily as a fuel, DAHB acts as a metabolic signal that reprograms activated CD8⁺ T cells: DAHB → OXPHOS ↑ → fatty-acid oxidation ↑ → phosphocreatine ↑ → local ATP buffering → BAF-dependent chromatin remodeling → effector genes ↑ → stronger antitumor immunity. That is a remarkable metabolism-to-chromatin circuit. 🔥 DAHB pushes CD8⁺ T cells toward a cytotoxic phenotype DAHB strongly increased: Perforin IFN-γ TNF-family members GZMB CCL3/CCL4 and DAHB-pretreated OT-I cells showed approximately 3-fold greater tumor-cell cytotoxicity. But the metabolic mechanism was unexpected. DAHB increased ATP-coupled mitochondrial respiration while suppressing glycolysis. Estimated ATP production shifted substantially: OXPHOS-derived ATP ↑ ~82% glycolytic ATP ↓ ~23%. Stable-isotope tracing showed that DAHB itself was not meaningfully oxidized through the TCA cycle. Instead, it doubled fatty-acid oxidation and redirected glucose away from lactate production toward biosynthetic pathways, including the pentose-phosphate and serine/glycine pathways. So: DAHB is not primarily the fuel. It changes which fuels the T cell uses. ⚡ Then comes the central discovery: phosphocreatine Untargeted metabolomics identified phosphocreatine (PCr) as the most strongly induced metabolite after DAHB treatment. This is intriguing because the creatine–phosphocreatine system is usually associated with tissues such as skeletal muscle, heart and brain, where it rapidly transports and buffers high-energy phosphate. Here, activated T cells appear to exploit the same system. DAHB increased: OXPHOS → mitochondrial ATP → PCr ↑ → CKB ↑ and blocking phosphocreatine production with cyclocreatine or creatine-kinase inhibition: ⬇️ perforin ⬇️ IFN-γ ⬇️ tumor killing. Even more interestingly, CKB accumulated near the nuclear envelope, with DAHB producing >6-fold enrichment of CKB–Lamin B1 proximity signals. This suggests that PCr may function as an intracellular energy shuttle: mitochondria → PCr → nucleus → ATP delivering energetic capacity precisely where ATP-consuming nuclear processes occur. 🧬 And one of those processes is chromatin remodeling ATAC-seq showed that DAHB increased chromatin accessibility at key effector loci: Prf1 Ifng Tnf while inhibition of PCr synthesis largely reversed these changes. The investigators then targeted the ATP-dependent BAF/mSWI-SNF chromatin remodeling complex. Both BAF degradation and inhibition of its BRG1/BRM ATPase activity reduced DAHB-induced perforin and IFN-γ and eliminated the increased accessibility of effector loci. This creates an elegant mechanistic sequence: FAO ↓ mitochondrial OXPHOS ↓ ATP ↓ phosphocreatine ↓ nuclear ATP buffering ↓ BAF chromatin-remodeling activity ↓ open Prf1 / Ifng / Tnf loci ↓ CYTOTOXIC T-CELL DIFFERENTIATION The graphical abstract on page 1 captures this beautifully: mitochondrial ATP is converted into a PCr-based energetic shuttle that connects mitochondrial metabolism to nuclear BAF activity and ultimately cytotoxicity. 🎯 The antitumor consequences were substantial Ex vivo DAHB conditioning of antigen-specific OT-I cells improved control of EL4-OVA tumors after adoptive transfer. DAHB also enhanced anti-CTLA-4 therapy in immunocompetent MC38 colorectal cancer and B16 melanoma models, whereas this benefit disappeared in lymphocyte-deficient RAG2-KO mice—supporting an adaptive immune mechanism. Figure 6 on page 11 is especially compelling: DAHB improves tumor control across adoptive-transfer and checkpoint-blockade experiments. And the TIL phenotype is interesting. DAHB-treated tumors contained CD8⁺ T cells with: ⬆️ CD44 ⬆️ TCF1 ⬆️ antigen-specific gp100⁺ cells ⬇️ PD-1⁺CD39⁺ cells ⬆️ polyfunctional IFN-γ⁺TNF-α⁺ responses ⬆️ T-bet. Importantly, residual PD-1⁺CD39⁺ cells expressed more TCF1, suggesting enrichment toward a precursor-exhausted rather than terminally exhausted state. 👨‍⚕️ And the biology translated to human T cells Under chronic stimulation, DAHB-treated human CD8⁺ T cells maintained: IFN-γ ↑ TNF-α ↑ PCr ↑ ATP/ADP better preserved and cyclocreatine partially reversed these effects. Human CD8⁺ T cells engineered with the NY-ESO-1-specific 1G4 TCR also showed greater cytokine production and stronger killing of A375 melanoma cells after DAHB treatment. Most importantly, in an A375 xenograft model: DAHB alone → little effect on tumor growth but 1G4 T-cell ACT + DAHB → significantly improved tumor control. That distinction argues that DAHB is functioning primarily as a metabolic adjuvant for T cells, rather than simply acting directly on cancer cells. 💡 The conceptual implication is broader than DAHB We often describe mitochondrial metabolism as providing enough ATP for cells to “function.” This study suggests something more specific: Energy availability can regulate cell fate because chromatin remodeling itself has an energetic cost. ATP is therefore not merely downstream fuel for an already differentiated effector T cell. Mitochondrial energy production may participate directly in establishing the epigenetic accessibility required to become and remain an effector cell. That has potentially important implications for: CAR-T manufacturing TCR-engineered T cells tumor-infiltrating lymphocytes checkpoint blockade metabolic preconditioning of adoptive cell therapies. Instead of engineering only receptors and signaling domains, perhaps we should also engineer the bioenergetic infrastructure that maintains their chromatin state. There are important caveats. The molecular sensor through which DAHB activates mitochondrial ETC activity remains unknown. The concentrations used experimentally were high, whether microbiota-derived DAHB ever reaches comparable concentrations in vivo is unclear, and the safety/tolerability of therapeutic systemic DAHB in humans remains untested. Still, the mechanistic concept is striking: MITOCHONDRIA → ATP → PHOSPHOCREATINE → BAF → CHROMATIN ACCESSIBILITY → T-CELL FATE → ANTITUMOR IMMUNITY Metabolism and epigenetics are not separate layers of T-cell biology. They may be connected by something as fundamental as where ATP is produced—and where that energy is delivered. 📄 Ng C, Fung TS, Li D, et al. Mitochondrial ATP promotes T cell differentiation through chromatin accessibility. Cell. 2026;189. DOI: 10.1016/j.cell.2026.08.023 #CancerImmunology #Immunometabolism #TCells #Mitochondria #OXPHOS #Phosphocreatine #Chromatin #Epigenetics #BAF #TCellExhaustion #Immunotherapy #CART #CellTherapy #CancerMetabolism