Donor and recipient age predicts antiviral antibody repertoires. Overall, persons in middle age (40-55 years) had higher epitopes scores, total viruses recognized, and higher diversity compared with both younger and older donors and recipients, and donor age more highly predicted d100 scores (n = 11, <40 years; n = 15, 40-55 years; n = 11, >55 years), whereas recipient age was more strongly predictive at d365 (n = 10, <40 years; n = 18, 40-55; n = 19, >55 years). Dots shown are estimates from generalized linear models, and whiskers depict 95% CIs for each estimate. (A) Simpson’s diversity within donor sample vs donor age: a lower score equates to higher levels of diversity of antiviral antibodies. (B) Donor age predicts total recognized epitopes at d100. (C) Donor age predicts all non-CMV epitopes (CMV epitopes removed to adjust for D/R CMV status) also at d100. (D) Recipient age predicts non-CMV epitopes pre-HCT. (E) Recipient age predicts total epitopes at d365. (F) Trend toward recipient age predicting non-CMV epitopes at d365 with significant differences between age 40-55 and >55.