Engraftment of bone marrow and fetal liver cells after in utero transplantation in MDX mice

Background/Purpose: In utero hematopoietic stem cell transplantation (IUHSCTx) has been experimentally or clinically effective only in circumstances in which there is a survival advantage for donor cells. A survival advantage exists for normal muscle cells in muscular dystrophy. Because hematopoietic and mesenchymal stem cells may have the capacity to differentiate into muscle cells, the authors hypothesized that in utero bone marrow (BM) or fetal liver (FL) stem cell transplantation may be used to treat muscular dystrophy. Methods: Time-dated 14-day-gestation fetal muscular dystrophy mice (mdx) were injected intraperitoneally with 1 to 5 × 10⁶ BM or FL cells per fetus from Rosa26 donor mice (transgenic for lacZ). Four weeks after birth, peripheral blood from the pups was analyzed for hematopoietic chimerism by using fluorescence-activated cell sorting (FACS) for the Ly-9.1 marker. Chimeric mice (6 BM and 2 FL recipients) were sacrificed at 12 to 14 months of age, muscles were stained with X-gal, and analyzed by 1- to 2/-μm plastic sections. Polymerase chain reaction (PCR) for lacZ was performed in other organs to determine systemic engraftment. Results: At the time of death, all animals that were chimeric at 4 weeks continued to show hematopoietic chimerism of 0.2% to 9% by FACS. Engrafted donor cells were found in multiple sections from hindlimb skeletal muscles, diaphragms, and hearts from both BM and FL recipients. These cells had incorporated into the host muscles, and their morphology was consistent with myogenic differentiation. PCR of BM, liver, spleen, thymus, kidney, and lung for lacZ was positive in multiple animals. Conclusions: IUHSCTx leads to widespread engraftment of donor cells in multiple muscle compartments of hematopoietic chimeras. The advantage for normal myocytes offered in the mdx model allows engraftment and myogenic differentiation of transplanted BM or FL cells by morphology at a relatively higher frequency in muscle relative to other tissues, without the need for host conditioning. Because muscular dystrophy now can be detected early in gestation, such a strategy may offer a future alternative in the clinical treatment of this disease.