Effects of extending the duration of postgrafting immunosuppression and substituting granulocyte-colony-stimulating factor-mobilized peripheral bloodmononuclear cells for marrow in allogeneic engraftment in a nonmyeloablative canine transplantation model

Stable mixed donor/host hematopoietic chimerism was uniformly achieved in d ogs given 200 cGy total body irradiation (TBI) before and immunosuppression with mycophenolate mofetil (MMF) for 28 days and cyclosporine (CSP) for 35 days after transplantation of marrow from dog leukocyte antigen-identical littermates. When the TBI dose was lowered to 100 cGy, donor marrow engraft ment in 6 dogs was only transient, lasting 3 to 12 weeks. In this study, we asked whether stable engraftment in this model could be achieved: (1) by s ubstituting recombinant canine granulocyte-colony-stimulating factor-mobili zed peripheral blood mononuclear cells (G-PBMCs) for marrow and (2) by exte nding CSP administration from 35 to 100 days. Eighteen dogs were given G-PB MC grafts and MMF for 28 days. Eight of the 18 dogs received CSP for 35 day s and 10 for 100 days. We found that substituting G-PBMCs for marrow did no t increase the incidence of stable allogeneic engraftment (P = .11). Howeve r, increasing the duration of posttransplantation immunosuppression with CS P from 35 to 100 days favorably influenced stable donor engraftment (P = .0 6).