Reduced Intensity Preparative Regimen Followed by Stem Cell Transplant (FAB)

Allogeneic stem cell transplantation with high-dose chemotherapy affords a better chance of cure of malignant and non-malignant hematological diseases compared to autologous transplantation, because of the lack of stem cell contamination and the immune mediated graft vs. leukemia effect. Unfortunately, high-dose chemotherapy and allogeneic stem cell transplantation has a substantial treatment related mortality, that is particularly high in older patients (greater than 50 yrs of age), or in those with co-morbidities such as congestive heart disease and pulmonary disease. Patients who have pre-existing infections or who have had multiple relapses with prior chemotherapy are also at high risk. In all these groups, treatment related mortality may exceed 50%, making them ineligible for high-dose chemotherapy and allogeneic stem cell transplantation.

Recently interest has increased in using less toxic chemotherapy protocols that are termed submyeloablative. The intent is to allow partial engraftment of a donor immune and hemopoietic systems with subsequent progressive replacement of the host's own hemopoiesis and immunity. As the donor immune system becomes established, patients may develop full donor chimerism, without passing through the period of prolonged aplasia associated with conventional conditioning regimens, and with less of the associated toxicity. Preliminary results in high-risk patients have shown treatment related mortality (TRM) of 15-20%, versus 50% expected, with an overall survival rate of 70-80% at 1-2 years post transplant.

As might be anticipated, the major problem with sub-ablative conditioning is that the graft failure rate is increased, with published figures of 5-30% versus 1-5% predicted in fully ablated patients. The incorporation of lymphodepleting antibodies in the preliminary conditioning regimen may allow these rejection rates to be diminished. Moreover, a highly efficient lymphodepleting MAb or MAb combination might be successfully substituted in part or in whole for cytotoxic and immunosuppressive drugs, further increasing the safety and efficacy of the subablative approach to stem cell transplantation. Our own data using the crude polyclonal mixture of antibodies in ATG as a component of pre-transplant conditioning revealed an improvement in engraftment during matched unrelated donor transplantation.The lymphodepleting monoclonal antibody Campath IH has many of the properties desired for this application, and we propose to incorporate it in our conditioning regimen. Since CAMPATH1H persists after infusion, we would expect it to have additional anti-GvHD effector function, further reducing treatment related mortality (TRM).

The following preparative regimen will be delivered to all patients:

1. Busulfan 3.2 mg/kg/day IV daily for 2 days, infused over 3 hours, on Day -5 and Day -4
2. Fludarabine 30mg/m2/day IV daily for 4 days on Day -5 to D -2
3. Campath 10 mg/day IV daily for 3 days on days -6 to D-4.

Because CAMPATH-1H infusions will provide a persisting level of antibody over the transplant period, it will contribute to anti-GvHD activity. Additional Graft vs. host disease prophylaxis will consist of FK506 administered from Day-2.

The stem cells will be infused on day 0.