Participants of a phase III clinical trial who were enrolled at Royal Brisbane and Women’s Hospital and at risk for HCMV reactivation were included for analysis (n = 85). (A and B) Cumulative incidence of HCMV viremia in all at-risk patients (n = 85) and a subset of patients who received unrelated donor graft (n = 54). Broken lines represent the placebo arm, and solid lines represent the tocilizumab arm. (B) Cumulative incidence of HCMV viremia among patients who had grade 0–1 acute GVHD (n = 55) and a subset of patient who received an unrelated donor graft (n = 31). (C–E) Plasma HCMV-specific IgG levels were determined at day 30 after BMT in at-risk patients (n = 82; 1 patient was excluded because of HCMV viremia prior to day 0, and 2 patients did not have a plasma sample stored). (C) Correlation between day 30 HCMV IgG levels and donor (D) and recipient (R) serostatus. (D) Correlation between day 30 HCMV IgG levels and HCMV viremia among HCMV-seropositive recipients. Patients were categorized according to early viremia (within the first 5 weeks after BMT), late viremia (from weeks 5–14 after BMT), and no viremia (no detectable viremia within the first 14 weeks, after which HCMV monitoring was no longer routinely performed. (E) Correlation between day 30 HCMV IgG levels and the treatment arm among HCMV-seropositive recipients and the subset receiving an unrelated donor graft (right). (F) CD19⁺ B cell counts in the peripheral blood 30 and 60 days after BMT in HCMV-seropositive recipients. Dashed line indicates the lower limit of normal for B cell counts at 80 × 10⁶/mL. (G) Proportions of IgD⁺CD27^– naive B cells, IgD^–CD27⁺ mature B cells, and CD38^hi plasmablasts within the CD19⁺ B cell compartment in the peripheral blood at day 60. (H) Concentration of albumin in the plasma at day 14 in all the participants from the RBWH cohort. Data are presented as the median ± IQR and were analyzed with the Mann-Whitney U test (*P < 0.05, **P < 0.01, and ****P < 0.0001).