LONG-TERM ENGRAFTMENT FOLLOWING IN-UTERO T-CELL-DEPLETED PARENTAL MARROW TRANSPLANTATION INTO FETAL RHESUS-MONKEYS

A major concern with allogeneic BMT for treating most inherited diseas es is the need to overcome graft rejection with conditioning chemother apy which is associated with a relatively high morbidity and mortality . This can be eliminated if the transplant is done in utero when the f etus is unable to reject donor hematopoietic stem cells (HSC). We stud ied the efficacy of T cell-depleted (TCD) parental bone marrow as a so urce of HSC for transplantation into early gestation non-defective fet al rhesus monkeys. Thirteen opposite sexed TCD transplants were done i nto 44 day fetal recipients and 12 into 61 day recipients (165 day tot al gestation). The procedure-related mortality was 8%, all in the earl ier age group. The overall survival was 60% at birth with a projected survival of 44 +/- 10% at 1.5 years with no difference between the two age groups. We used a PCR assay for the rhesus Y chromosome to detect male donor cells in female recipients (six animals transplanted at 44 days and five at 63 days). The overall engraftment rate was 73% with no difference as a function of gestational age at transplant. In six l ong-term surviving engrafted females we detected donor cells in the pe ripheral blood and bone marrow up to 3 years of age. We found a delay in the appearance of donor cells in the peripheral blood in engrafted animals, in some cases for up to 6 months post-BMT. In vitro mixed lym phocyte reaction and cell-mediated lymphocytotoxicity studies between the recipient and donor cells indicate that tolerance was induced to d onor cells. Individual and pooled erythroid and myeloid marrow colonie s grown in methyl cellulose were collected and analyzed for donor orig in by PCR. The amount of donor cells in marrows from long-term engraft ed animals was <0.1%. In a fetal recipient studied at 35 days post-BMT , donor cells were detected in bone marrow and liver in both erythroid and myeloid lineages. These results indicate that TCD parental marrow can durably engraft in utero. While the engraftment rate is similar t o that seen with fetal liver as the source of HSC, the degree of perip heral blood engraftment (percent donor cells) in this non-defective pr imate model is low. It will require increasing the percent pre- or pos tnatally for this approach to be clinically relevant in those disorder s in which there is no selective survival advantage for normal engraft ed donor cells.