An immunoablative regimen of fludarabine and cyclophosphamide prevents fully MHC-mismatched murine marrow graft rejection independent of GVHD

Abstract

The prevention of graft rejection in the setting of nonmyeloablative transplant approaches might be mediated by chemotherapy-induced host immunoablation and by the graft-promoting effects of graft-versus-host disease (GVHD). To evaluate whether host immunoablation alone might allow for alloengraftment, we developed an F1-into-parent murine marrow rejection model using host preparative regimens of lethal total body irradiation (TBI; 950 cGy), sublethal irradiation (600 cGy), or combinations of fludarabine (Flu) and cyclophosphamide (Cy). A preparative regimen selectivity index (SI) was calculated to determine whether host lymphocytes were preferentially depleted relative to myeloid cells (SI = number of host myeloid/number host T lymphoid cells remaining after preparative regimen administration). Saline-treated recipients were assigned an SI value of 1.0. Recipients of lethal TBI had reduced myeloid cells relative to T cells (SI = 0.6). In contrast, all Flu/Cy regimens preferentially depleted host T cells: recipients of Flu (100 mg/kg per day)/Cy (50 mg/kg per day) for 10 days (SI = 28.1); recipients of Flu (100 mg/kg per day)/Cy (100 mg/kg per day) for 10 days (SI = 64.1); and recipients of Flu (100 mg/kg per day)/Cy (50 mg/kg per day) for 19 or 27 days (SI = 74.6). The 10-day regimen of Flu/Cy (50 mg/kg per day) did not severely reduce host T cell numbers, nor did it prevent F1 marrow rejection (<1% chimerism, n = 14). In contrast, the 10-day regimen of Flu/Cy (100 mg/kg per day) reduced T-cell numbers below that of lethal TBI recipients and prevented F1 marrow rejection (11.4% chimerism, n = 15); donor chimerism was predominant in lymphoid cells and was stable through day 240 post-BMT. Additionally, the 19- or 27-day regimen of Flu/Cy, which most selectively depleted host T cells, also prevented F1 marrow rejection (6.3% chimerism, n = 15). These results therefore demonstrate that optimized Flu-containing, immunoablative preparative regimens can prevent fully MHC-disparate marrow rejection independent of GVHD.

Durable engraftment of major histocompatibility complex–incompatible cells after nonmyeloablative conditioning with fludarabine, low-dose total body irradiation, and posttransplantation cyclophosphamide

“…Fludarabine, given to mice for 5 consecutive days at a dose of 100 mg/kg per day (25% of the LD 10 ), decreases the absolute number of splenic CD4 ϩ and CD8 ϩ T cells by 25% and 15%, respectively (data not shown). A similar level of T-cell depletion, using the same dose of fludarabine in the mouse, has been reported recently by Petrus et al 47 In addition, these investigators have shown that Cy is very potent in reducing lymphocytes in the mouse and that the combination of fludarabine and Cy has a synergistic effect in depleting host T cells. However, because the metabolism and toxicity of these drugs differ significantly in humans and mice, caution must be exercised when translating the results of studies in mice to the clinic.…”

Rapid and complete donor chimerism in adult recipients of unrelated donor umbilical cord blood transplantation after reduced-intensity conditioning

“…The engraftment results with the Cy/Flu/TBI regimen are consistent with findings of murine studies suggesting that the immunoablation associated with the combination of cyclophosphamide and fludarabine is conducive to donor engraftment in the setting of HLA mismatch. 26,27 These data demonstrate that despite the low total nucleated CD34 ϩ and T-cell dose and reduced alloreactivity associated with UCB, UCBT using reduced-intensity conditioning is associated with sustained donor engraftment in most adult patients. Interestingly, graft failure was restricted to patients without recent pretransplantation combination chemotherapy or prior autologous transplantation.…”

Fludarabine in combination with cyclophosphamide decreases incidence of GVHD and maintains effective graft-versus-leukemia effect after allogeneic stem cell transplantation in murine lymphocytic leukemia

“…Most recently, Petrus et al 14 have shown that a fludarabine-containing regimen prevents mismatched murine marrow graft rejection, while Luznik et al 23 have also shown convincingly that a fludarabine-containing regimen can result in durable engraftment in incompatible murine donor transplants.…”

“…In this respect, there is some recent experimental evidence showing that it may be effective in transplantation across histocompatibility barriers in mice. 14 Furthermore, it is also able to induce bilateral tolerance or stable chimerism after marrow or skin transplantation, 15 thereby altering the incidence of graft rejection and the extent of GVHD encountered. In earlier pilot murine studies, we were also able to show an anti-GVHD prophylactic effect after marrow transplantation in mice.…”