We investigated the impact of Cyclophosphamide (PTCy) administration on xenogeneic GVHD (xGVHD) and allogeneic graft-versus-leukemia (GvL) effects in a humanized mice model (NSG). 

To investigate the impact of PTCy on xGVHD, NSG mice were transplanted with 2x10^7 human PBMC and receive a single i.p. injection of PTCy (100 mg/kg) 3 days after infusion. The survival of mice was observed and flow cytometry analyses for immmune cells recovery was made from mouse blood and organs on day 6 (60 hours after PTCy in PTCy-treated mice) and day 21 after PBMC infusion .
The impact of PTCy on GvL effects was assessed in NSG-HLA-A2/HHD mice  injected with human (HLA-A0201) AML cell line THP-1 transfected with the luciferase gene on day 0 with or without human PBMC. Two groups receive a single i.p. injection of PTCy (100 mg/kg) 3 days after infusion, the survival and the bioluminescence of tumors was observed.

PTCy significantly delayed xGVHD but xGVHD was not abrogated and the majority of treated mice eventually succumbed from xGVHD. On day 21, (human) blood T-cell counts were significantly lower while Treg frequency was significantly higher in PTCy than in control mice. On day 6, PTCy mice had dramatically lower proportions of proliferative and activated CD4 and CD8 T cells and a much higher proportion of apoptotic T cells.
Regarding GvL experiments, THP-1+ PBMC mice had no detectable tumor but died from GVHD while THP-1 + PTCy + PBMC mice had the best survival with detectable tumors but to a lesser extent than THP-1+PTCy mice. 
In vitro experiment showed that Tregs were more resistant than conventional T cells  to apoptosis induced by Mafosfamide (a PTCy analog).
These results suggest that PTCy prevents xGVHD by depleting proliferative T cells and favoring recovery of Tregs. Further, GvL effects were not abrogated, although decreased, by PTCy.

Cyclophosphamide prevents xenogeneic graft-versus-host disease , without abrogating graft-versus-leukemia effects