- SUMMARY Bone marrow transplantation (BMT) recipients are immunosuppressed and are at risk for contracting severe infections. Recently, adoptive transfer of immunity against hepatitis B virus (HBV) was documented in BMT recipients receiving bone marrow from ‘naturally’ HBV-infected individuals who recovered spontaneously, or those transplanted with bone marrow cells obtained from actively immunized donors. Furthermore, reconstitution of the immune system in a BMT recipient who was a hepatitis surface antigen (HBsAg)+/HBV DNA+ carrier with HBV immune bone marrow ceils led to clearance of the replicating virus, presumably through adoptive cell-mediated immunotherapy. We report three cases of induction of immunity to HBV by selective adoptive transfer by i.v. injection of peripheral blood lymphocytes (PBL) obtained from BMT donors who were actively immunized against HBV after harvesting of bone marrow. Ail three BMT recipients developed anti-HBs antibodies. In one BMT case in whom antibodies to HBsAg developed following adoptive transfer of immune PBL, a mild booster effect was documented in the BMT recipient upon immunization with a recombinant hepatitis B vaccine. The two remaining patients lost their antibodies to HBsAg in association with relapse of leukaemia. This immune manipulation may open the door to evaluation of adoptive transfer of immunity to HBV through selective transplantation of HBV immune lymphocytes in selected patients such as those with persistent HBV infection, as well as liver transplant recipients who require protection of the graft against HBV re-infection.