IN-UTERO ENGRAFTMENT OF FULLY H-2-INCOMPATIBLE VERSUS CONGENIC ADULT BONE-MARROW TRANSFERRED INTO NONANEMIC OR ANEMIC MURINE FETAL RECIPIENTS

We have established a murine in utero bone marrow transplantation mode l system and have investigated the effects of donor strain differences , cell dose, and the number of injections on murine fetal survival and engraftment rates. In a series of experiments, 1221 nonanemic C57BL/6 fetuses were injected transplacentally on day 11 of gestation with 10 (6) non-T-depleted adult bone marrow cells (BMC) from C57BL/6-CAST (co ngenic), BALB/c and DBA/1 (allogeneic) strains without recipient condi tioning. Overall fetal survival was 45%, with a 4% engraftment rate in 475 evaluable day 5 newborns. Engrafted newborns initially had up to 75-100% donor peripheral blood cell engraftment, particularly with DBA /1 BMC. Surprisingly, a significantly (P<0.05) higher incidence of eng raftment was observed using allogeneic (5.2%) as compared with congeni c donors (0.7%). However, engraftment in all groups was transient sinc e engrafted recipients studied greater-than-or-equal-to 6 weeks post-n atally had nondetectable levels of donor cells. In contrast, engraftme nt of congeneic marrow into anemic, stem cell-defective W(v)/W(v) reci pients lead to a higher incidence (40%) of engraftment that persisted for greater-than-or-equal-to 6 weeks, increasing in the level of engra ftment over time. Additional studies were performed in an attempt to f urther increase the incidence and permanence of engraftment. Neither d oubling the cell dose nor doubling the number of injections improved e ngraftment rates in recipients of allogeneic bone marrow. Similarly, p retreatment of congeneic donors with 5-fluorouracil 4 days prior to ha rvesting marrow was not effective in increasing engraftment. Despite t he inability to detect donor cells greater-than-or-equal-to 6 weeks po stallografting, 2 of 10 evaluable recipients engrafted with DBA/1 BMC had specific and permanent (> 6 months observation time) tolerance to the donor skin graft with an intact capacity to reject third-party gra fts. Thus short-term engraftment of allogeneic adult marrow stem cells can be successfully accomplished in a proportion of nonanemic fetal r ecipients. Engraftment of allogeneic donor cells can also lead to indu ction of a degree of tolerance in a proportion of recipients at maturi ty. These data form the basis of future studies directed toward unders tanding the mechanisms involved in in utero and postnatal marrow graft resistance, which will ultimately lead to designing strategies that w ill further enhance the permanence of engraftment with the use of adul t marrow cells.