Competence of Retransplanted Homologous Marrow Cells in Relation to Time after Original Transplantation into Irradiated Mice

Summary

C57BL and 101 parental bone-marrow cells, grown for different periods of time in irradiated (C57BL × 101) F₁ recipients, were retransplanted into secondary F₁ recipients in an attempt to evaluate the competence of the regrafted marrow. When either type of parental bone-marrow was allowed to grow in primary recipients for less than 30 days and subsequently transplanted into secondary recipients, the survival of secondary recipients was inferior to that of primary recipients. However, when parental bone-marrow remained in primary recipients more than 30 days, the survival of secondary recipients was superior to that of primary recipients. These effects may be ascribed to alterations of the immunological competence of the donor-marrow rather than to its failure to take or to its rejection, since the functional haematopoietic cells in all secondary recipients were principally of donor-type as judged by red-cell markers; i.e. sensitization of the marrow may have been exhibited when it was retransplanted early, but immunological paralysis, exhaustion, or partial tolerance was manifested when it was retrans-planted after periods of 30 days or longer.