MYOBLAST TRANSPLANTATION IN NONDYSTROPHIC DOG

Dog myoblasts obtained from muscle biopsies were infected in vitro wit h a defective retroviral vector containing a cytoplasmic beta-galactos idase (beta-Gal) gene. These myoblasts were initially transplanted in the irradiated muscles of SCID mice and beta-Gal positive muscle fiber s were observed. beta-Gal myoblasts were also transplanted back either in the donor dogs (autotransplantation model) or in unrelated recipie nt dogs (allotransplantation model). Following these myoblast injectio ns, a rapid inflammatory reaction developed within the muscle as indic ated by an expression of P-selectin and of pro-inflammatory cytokine m RNAs (interleukin 6 (IL-6) and transforming growth factor beta (TGF-be ta)), and by a neutrophil infiltration. Following either auto-or allot ransplantation in inadequately or non-immunosuppressed dogs, a specifi c immune reaction also developed within 2 weeks as indicated by the in filtration of CD4+ and of CD8+ lymphocytes, the increased expression o f IL-10 and granzyme B mRNAs and the presence of antibodies reacting w ith the injected cells. Some dogs were immunosuppressed with several c ombinations of FK506, cyclosporine (CsA) and RS-61443. In dogs immunos uppressed with CsA combined with RS-61443, only a few myoblasts and my otubes expressing beta-Gal were observed 1-2 weeks after the transplan tation, but no muscle fibers expressing beta-Gal were observed after 4 weeks, and antibodies against the injected cells were formed. In dogs immunosuppressed with FK506 alone, although no antibodies against the injected cells were produced, there were no small cells and no muscle fibers expressing beta-Gal 1 month after the transplantation. However , FK506 triggered diarrhea and vomiting in dogs. When the dogs were im munosuppressed with FK506 combined with CsA and RS-61443, muscle fiber s expressing beta-Gal were present 4 weeks after the transplantation a nd no antibodies reacting with donor myoblasts were detected. These re sults indicate that the combination of three immunosuppressive agents (i.e., FK506, CsA and RS-61443) is effective in controlling the specif ic immune reactions following myoblast transplantation in dogs and the y underline that the outcome of myoblast transplantation is dependent in part on an adequate immunosuppression. These results obtained here in normal dogs may justify myoblast transplantation in dystrophic dogs despite the side effects of FK506. (C) 1998 Elsevier Science B.V.