optimization of immunosuppressive therapy for spinal grafting of human spinal stem cells in a rat model of als previous rodent studies employing monotherapy or combined immunosuppressive regimens have demonstrated a variable degree of spinal xenograft survival in several spinal neurodegenerative models including spinal ischemia trauma or amyotrophic lateral sclerosis als accordingly the characterization of optimal immunosuppressive protocols for the specific neurodegenerative model is critical to ensure reliable assessment of potential longterm therapeutic effects associated with cell replacement in the present study we characterized the survival of human spinal stem cells when grafted into the lumbar spinal cords of a rodent model of als sod1 g93a male and female rats 6067 days old four different immunosuppressive protocols were studied i fk506 q12h ii fk506 qd mycophenolate po q12h up to 7 days postop iii fk506 qd mycophenolate ip q12h up to 7 days postop and iv fk506 qd mycophenolate ip qd up to 7 days postop three weeks after cell grafting the number of surviving human cells was then systematically assessed the highest density of grafted cells was seen in animals treated with fk506 qd and mycophenolate ip qd an average 915 95 grafted cells per spinal cord section the majority of hnumapositive cells colocalized with doublecortin dcx immunoreactivity dcxpositive neurons showed extensive axodendritic sprouting toward surrounding host neurons in addition migrating grafted cells were identified up to 500 m from the graft in animals treated with fk506 q12h fk506 qd mycophenolate po q12h or fk506 qd mycophenolate ip q12h 118 34 612 78 and 994 89 expressed as percent of the fk506 qd and mycophenolate ip qd cell survival was seen respectively in contrast to animals treated with a combination of fk506 mycophenolate robust cd48 immunoreactivity was identified in the vicinity of the injection tract in animals treated with fk506 only these data suggest that a combined systemically delivered immunosuppression regimen including fk506 and mycophenolate can significantly improve survival of human spinal stem cells after intraspinal transplantation in sod1 g93a rats