Post-Transplant Cyclophosphamide and Bortezomib Combination for Prevention of GvHD after Allogeneic Blood and Marrow Transplantation Is Feasible and Produces Favorable Outcomes

Graft versus host disease (GvHD) remains a major barrier to the progress of blood and marrow transplantation and limits its wide applicability. Standard prophylactic regimens essentially targeting T lymphocytes are partially effective and burdensome. Cyclophosphamide (Cy) administered post-transplant selectively deletes alloreactive proliferating T cells, promotes expansion of regulatory T cells, and induces long-lasting depletion of intrathymic host-reactive T cells. It is an attractive option for prevention of GvHD and has already been used alone in matched related and unrelated donor transplants. However, despite a low incidence of chronic GvHD, acute GvHD still occurs in 50% of cases and is grade III-IV in 15% of cases. Dendritic cells (DCs) play a pivotal role in the early phase of GvHD. Proteasome inhibitors such as bortezomib (Bor) have a number of immunomodulatory effects including inhibition of DCs maturation and function. We therefore initiated a phase I feasibility study combining post-transplant Cy & Bor. Twelve patients with hematological malignancies undergoing peripheral blood allogeneic transplantation from matched related (n=6) or unrelated (n=6) donors have so far been enrolled. Disease risk index (DRI) was low in 4, intermediate in 3 and high or very high in 5. The conditioning regimen combined fludarabine and busulfan (total 6.4 mg/kg). Patients receiving graft from unrelated donors also received rabbit anti-thymocyte globulin at 5-8 mg/kg. The dose of Bor was escalated in standard fashion. Three patients in each of cohorts 1 and 2 received 0.7 and 1 mg/m² respectively. The subsequent 6 patients received 1.3 mg/m². All patients received 2 IV doses, 6 hours after graft infusion and 72 hours thereafter. Cy was given at 50 mg/kg IV on days +3 and +4. Steroids were not allowed after day 0. Engraftment was prompt in all patients. Median time to neutrophil engraftment was 15.5 days (range 14-25). One patient failed to meet criteria for platelet engraftment. The patient had acyclovir-resistant herpes genitalis and CMV reactivation requiring protracted therapy with foscarnet. The remaining patients had a median time to platelet recovery of 28 days (range 15-109). All patients achieved full chimerism by day 20 except one who had residual CLL and did not reach full chimerism until day +119. No patient developed secondary graft failure. Two treatment-related deaths occurred on day +150 due to RSV pneumonitis and on day +200 due to acute sepsis. One patient with recurrent multiple myeloma after autologous transplantation died due to progressive disease. No other Common Toxicity Criteria grade 3 or 4 occurred in any patient. With a median follow-up of 21 months (range 1-27), the overall 2-year predicted disease free survival and overall survival were both 60%. Incidence of acute GvHD in 11 patients with follow-up > 100 days, was 64%: grade I 55%, grade II 9%, and grade III-IV 0%. GI and liver acute GvHD were not encountered. Only 4 patients received systemic steroids for acute GvHD; only one required > 20 mg/day of prednisone. One patient developed chronic GvHD of the liver (biopsy-proven). Another patient developed poor appetite and weight loss on day +138. Endoscopy showed gastric ulceration. No biopsy was obtained. Neither calcineurin nor m-TOR inhibitors were ever used. Two patients developed extensive HSV-genito-rectal ulcers; one had prior history of recurrent flares. When institutional guidelines were changed to start acyclovir at the beginning of conditioning as opposed to day +5, no other cases was noted. Seven patients developed CMV reactivation and required preemptive therapy only. One patient developed BK virus-induced hematuria and 1 patient developed CNS toxoplasmosis.

In summary, the calcineurin and m-TOR inhibitor-free post-transplant Cy & Bor combination for GvHD prophylaxis is feasible and safe. Although the small number of patients prevents any definite conclusion, the absence of incidence of grade III-IV acute GvHD and the sparing of the GI tract and liver are promising. Furthermore, the completion of GvHD prophylaxis by day +4 without the need for close renal and drug level monitoring are both practical and appealing. Updated results with longer follow-up will be reported at the meeting. A confirmatory phase II study is underway.