Outbreaks of viral infections, such as measles, are regularly observed and pose a serious threat to allogeneic HCT-recipients. The question how long cellular and humoral protective host immunity persists, and whether donor immunity can be transferred has not been clarified. Here, we present a retrospective analysis of humoral immunity, i.e. serial antibody titers against measles, mumps, and rubella in 331 patients who underwent allogeneic HCT at our single center between 2002-2015. Associations

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... between the loss of protective antibody levels and clinical patient characteristics and transplant parameters were examined. In general, antibody protection against measles persisted longer with 72% of patients maintaining sufficient titers at 5 years post HCT even without re-vaccination while at that time only 65% and 50% of patients had protective immunity against rubella and mumps, respectively. The great majority of donors were seropositive for all three viruses, however, it appeared that donor humoral immunity could not be transferred and had no impact on the post-HCT serostatus. Rather, the most relevant factor for persistence of protective antibody titers against measles and rubella was whether patients were born before introduction of the respective vaccine, and thus were immunized by the wild-type disease inducing virus instead of the vaccine. Moreover, the presence of moderate and severe chronic graft-versus host disease (GVHD) was associated with more rapid loss of immune protection. In contrast, underlying disease, intensity of the conditioning regimen, use of anti-thymocyte globulin, age, and graft source did not have an influence on antibody titers. Overall, our findings suggest that the majority of antibodies against measles, mumps, and rubella originate from residual host cells, whereas the donor immune status appears to have no influence on antibody protection post-HCT.