RNA-seq of activated murine CD8+ T-cells cultured in high (0.625 mg/mL holotransferrin) or low iron (0.001 mg/mL holotransferrin) conditions with or without 40 mM aspartate

Iron is an irreplaceable co-factor for metabolism and iron deficiency affects >1 billion people, causing anaemia and impairing immunity. How iron deprivation influences normal cellular function remains poorly characterised. In activated CD8+ T-cells we found that iron scarcity profoundly stalled proliferation and disrupted mitochondrial redox control without influencing cell viability. The TCA cycle was partially redirected to a reductive trajectory, and the repressive H3K27me3 histone mark, usually decreased post-activation, was maintained. Surprisingly, aspartate, which is crucial for proliferation, was increased in stalled iron deficient cells but was not utilised cytosolically, indicating trapping within depolarised mitochondria. Exogenous aspartate increased ATP, suppressed H3K27me3 and markedly rescued clonal expansion. We propose that iron scarcity creates a metabolic bottleneck impairing activation and proliferation of T-cells, and which is bypassed by resupplying biochemical processes with aspartate. These findings reveal mechanistic consequences of iron deficiency and shed light on the response of T-cells to nutritional variation.