Gender influences the birth order effect in HLA-identical Stem Cell Transplantation.

In summary, we support the existence of a birth order effect asreported before.1,6 Additionally, we show that gender might be oneof the causal factors. Interestingly, the birth order effect wassignificant in the adult female donor/female recipient SCT pairs.Our current plausible explanation is the intrauterine exposure tosibling antigens occurring during pregnancy, leading to minor Hantigen experienced T-cell responses in women.4 These responsesmight lead to immune regulation.7 Subsequent (re-)exposure tofetal antigens during pregnancy of the donor herself explains thefavorable younger female SCT donor in combination with thefemale recipient.