Karl et al¹ analyzed serum and peripheral blood mononuclear cells collected at serial time points (between d+30 and d+120) from a cohort of 66 allo-HCT recipients. Signs of oxidative stress, T-cell gene signatures, and phenotypes were evaluated in relation to the clinical outcome. Elevated concentrations of 8-OHdG as a marker for oxidative DNA damage were detected in the serum and circulating immune cells of allo-HCT recipients. T cells with high concentrations of 8-OHdG were characterized by enhanced activation and premature exhaustion, whereas their cytokine production and killing capacity were reduced compared with 8-OHdG^lo cells. Thereby, high concentrations of 8-OHdG were associated with an increased risk of malignancy relapse and a shorter overall survival. Professional illustration by Patrick Lane, ScEYEnce Studios.