Systemic immunosuppression plus local production of CTLA4-Ig to control rejection of transgenic pig neuroblasts in non-human primates

Background: Parkinson's disease (PD) results from the selective degeneration of dopaminergic neurons in the substantia nigra. Transplantation of neural precursors has been attempted as a therapeutic approach in PD patients with variable outcomes. In this context, we studied porcine cell survival, maturation and functional recovery using a challenging model of xenogeneic intrastriatal implantation of mesencephalic dopaminergic-enriched grafts in PD primates. Methods: PD was induced in 23 macaques by repeated exposure to MPTP. Once stable lesions were obtained, PD monkeys were unilaterally injected in the left putamen with neural cells from 9 to 10 CTLA4-Ig+ (n = 18) or wild type pig embryos (n = 6). All primates were immunosuppressed using a clinically applicable immunosuppressive regimen based on cyclosporin A, mycophenolate sodium and steroids. The immunosuppressive therapy lasted for at least one month. Xenograft survival and function was determined by clinical neurological assessment, analysis of locomotor activity (Ethovision software), brain imaging (PET scan with 18F- DOPA), and histological studies at the end of each experiment. Results: Behavioural studies performed for up to 957 days showed an optimal recovery of spontaneous locomotion in primates receiving CTLA4-Ig+ transgenic neurons plus systemic immunosuppression for at least 6 months. In these animals, recovery was associated with a partial restoration of dopaminergic activity detected by PET scans in all primates transplanted with CTLA4-Ig+ neural precursors and submitted to long term immunosuppression. Histological analysis of the brains revealed the presence of large porcine xenografts composed of dopaminergic, serotoninergic and GABAergic differentiated neurons and various glial components that were not observed in animals receiving wild type neurons. Longterm presence of the xenograft was usually associated with local infiltration by T cells and CD80/86 positive microglial cells, expressing indoleamine dioxygenase (IDO) that was observed only in recipients of CTLA4-Ig+ pig embryos. Conclusions: These studies demonstrate that transplantation of porcine embryonic grafts in the striatum of immunosuppressed PD primates may enable long term xenograft survival and differentiation, associated with considerable improvement of locomotor activity. Our data also suggest a synergistic immunomodulatory effect due to local blockade of T cell costimulation.