G-CSF-mobilized peripheral blood mononuclear cells added to marrow facilitates engraftment in nonmyeloablated canine recipients: CD3 cells are required

Stable mixed donor/host hematopoietic chimerism can be uniformly establishe d in dogs conditioned with 200 cGy TBI before dog leukocyte antigen (DLA)-i dentical marrow transplantation and immunosuppressed with a short course of mycophenolate mofetil (MMF) and cyclosporine (CSP) after the transplantati on. A further decrease in the TBI dose to 100 cGy or the elimination of MMF in this model results in graft rejection. Here we asked whether the additi on of G-CSF-mobilized peripheral blood mononuclear cells (G-PBMC) to marrow grafts would enhance donor engraftment in dogs conditioned with 100 cGy TB I and given postgrafting immunosuppression with CSP alone. Using this model , 7 of 9 dogs given only marrow cells rejected their grafts within 8 to 17 weeks after transplantation. In contrast, the addition of unmodified G-PBMC to marrow grafts resulted in stable mixed donor/host chimerism in 5 of 8 d ogs studied (P = .06). However, addition of the CD3-depleted fraction of G- PBMC, which contained both CD34 cells and CD14 cells, resulted in engraftme nt in only 1 of 7 recipients. Ve conclude that adding G-PBMC to marrow graf ts replaced the requirement of MMF and 100 cGy of TBI, and that CD3 cells w ere required to facilitate engraftment of marrow cells in DLA-identical rec ipients, whereas the additional CD34 cells present in G-PBMC were not suffi cient for this effect.