Passive acquisition of hepatitis B virus antibodies after allogeneic hematopoietic cell transplantation

BACKGROUND: Newly positive hepatitis B virus (HBV) serologic results after allogeneic hematopoietic cell transplantation (HCT) may reflect passive antibody transfer from blood-derived products rather than HBV infection. We investigated the incidence and temporal patterns of hepatitis B surface antibody (anti-HBs) and antibody to hepatitis B core antibody (anti-HBc) acquisition after allogeneic HCT. STUDY DESIGN AND METHODS: We retrospectively evaluated 193 adults who underwent allogeneic HCT for hematologic diseases between May 2012 and March 2025 at a single institution in Japan. Anti-HBs, anti-HBc, and hepatitis B surface antigen (HBsAg) were assessed before and after HCT. RESULTS: Among 180 patients who were anti-HBc negative before HCT, 6 (3.3%) developed anti-HBc positivity after HCT. Among 164 patients who were anti-HBs negative before HCT, 49 (29.9%) developed anti-HBs positivity. All patients with newly detectable antibodies remained HBsAg negative, and available HBV DNA measurements showed no evidence of active HBV infection. Among patients with subsequent follow-up measurements, anti-HBc disappeared in 3 of 3 evaluable patients after a median of 240 days, whereas anti-HBs declined or disappeared in 30 of 32 evaluable patients after a median of 119 days. Among patients receiving neither fresh frozen plasma nor intravenous immunoglobulin, anti-HBs concentrations increased significantly after HCT (p< .0001), with a greater increase among those receiving ≥24 versus ≤23 platelet transfusions (p = .0437). DISCUSSION: Newly detectable HBV antibodies were common after HCT without virologic evidence of infection, suggesting passive antibody transfer from cellular blood components, particularly platelets.