Fetal Tolerance, Chimerism and Sickle Cell Disease ( Translational Study )

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In utero hematopoietic stem cell transplantation (IUHSCTx) is a promising approach for the treatment of a varlet)' of hematologic disorders including the hemoglobinopathies. However, in the absence of a selective advantage for normal cells, clinical and experimental efforts at IUHSCTx have generally resulted in limited or no detectable engraftment, suggesting the existence of major barriers to engraftment in the hematopoietically competitive recipient. The long-term objective of this project is to overcome these barriers and develop clinically applicable strategies to increase engraftment to therapeutic levels to allow clinical expansion of IUHSCTx to the treatment of Sickle Cell Disease(SCD). We have developed three approaches in the mouse model based on IUHSCTx induced donor specific tolerance to create high level mixed hematopoietic chimerism, across full MHC barriers, without the use of myeloablation or immunosuppression. In this application we plan to exploit donor specific tolerance to create high level chimerism, using established and new strategies, in mufine models of ! hemoglobinopathy and to determine what levels of chimerism is required to cure SCD. The specific aims of this proposal are: 1) To establish high level mixed chimerism after IUHSCTx by the prenatal cotransplantation of donor derived HSC and immanomodnlatory cell populations. Specific donor cell populations will be cotransplanted with HSC prenatally to create a competitive advantage for donor cells. 2) To establish high level mixed ehimerism after IUHSCTx in the hemoglobinopathy recipient by strategies based on prenatal tolerance induction to facilitate postnatal enhancement of chimerism using nonmyeloablative approaches. Limited mixed chimerismachieved by IUHSCTx in routine SCD will be converted to high level or co,_lplete donor chimerism after birth by non-toxic regimens. 3) To establish in a nonmyeloablated murine model of SCD, what level of mixed chimerism is sufficient to prevent sickling crises and organ d_mage associated with SCD. The ability to create various levels of mixed chimerism in the murine SCD model combined with phenotypic and functional assays of SCD should allow the question of what level of chimerism is necessary to completely treat SCD to be addressed. The studies in this proposal are designed to test strategies to improve engraftment after IUHSCTx for SCD and will direct subsequent studies in a large animal model.