Post-Transplant High Dose Cyclophosphamide and Bortezomib As Graft-Versus-Host Disease Prophylaxis Following Allogeneic Hematopoietic Stem Cell Transplantation

Introduction. Prevention of graft-versus-host disease (GvHD) following allogeneic hematopoietic cell transplantation (AHCT) remains a major challenge. The combination of methotrexate (MTX) and a calcineurin inhibitor has been the standard regimen for prophylaxis in patients receiving matched sibling donor (MSD) or matched unrelated donor (MUD) transplants for the past few decades. However, over 50% of patients undergoing AHCT still develop acute or chronic GvHD or even both, causing high rates of morbidity and mortality. Moreover, calcineurin inhibitors also have untoward toxic side effects. High dose post-transplant cyclophosphamide (PTCy), initially introduced for GvHD prevention in the setting of haploidentical transplantation, has now been studied in MSD and MUD transplants. We adopted a novel approach to prevent GvHD using a short course of PTCy and bortezomib. We hypothesized that such combination is safe and effective and omits the need for calcineurin or m-TOR inhibitors.

Study Design. We report the outcomes of a prospective cohort of patients who received PTCy and bortezomib for GvHD prevention following MSD or MUD transplants. Twenty-eight patients were treated in a phase I-II trial and their clinical outcomes were previously reported (al-Homsi AS et al, BBMT 2019). Most of the remaining patients were treated on an extension trial. GvHD prevention consisted of PTCy 50 mg/kg IV on day +3 and +4, and bortezomib 1.3mg/m ² IV 6 hours after transplant and again 72 hours after. Patients receiving MUD transplants also received rabbit ATG (thymoglobulin®) 5mg/kg total IV fractionated on day -4 to -2. All patients received peripheral blood grafts and standard supportive care as per Institutional policy. G-CSF was administered routinely until neutrophil engraftment.

Results. Fifty-eight patients are included in this analysis. Median age was 60 (range 22-78) years. Fifty-three percent of patients were male. Underlying malignancies consisted of myeloid and lymphoid malignancies in 79.3% and 20.6%, respectively. Acute myeloid leukemia (50%) and myelodysplastic syndromes (24.1%) were the most common diseases. At transplant, disease risk index was low, intermediate, high and very high in 19.0%, 48.3%, 31.0% and 1.7% of patients, respectively. Median Pretransplant Assessment of Mortality Score (PAM) was 16.7 (5.4-29.4). Grafts were from MSD in 24.1% or MUD in 75.9% of patients. Recipient (R)/Donor (D) CMV status at transplant was as follows: R+/D+: 43%; R+/D-: 21%; R-/D+: 14% and R-/D-: 22%. Conditioning regimens consisted of reduced intensity fludarabine and busulfan in all but 2 patients who were conditioned with myeloablative fludarabine and busulfan. Overall, the regimen was remarkably well tolerated. Median times to neutrophil and platelet engraftment were 16 (13-28) and 26 (15-57) days respectively. No patient experienced primary graft failure. CMV and EBV reactivation rates were 46.6% and 24%. Cumulative incidences of grade II-IV and grade III-IV acute GVHD were 35% (95% CI: 22%-47%) and 15% (95% CI: 7%-25%) at day +120, respectively. Cumulative incidence of chronic GvHD was 14% at 1 year . Overall, 34% of patients required immunosuppression with systemic steroids after day +4 either for grade III-IV acute or chronic GvHD. Disease relapse rate was 26%. One-year cumulative incidence of transplant-related mortality was 14% (95% CI: 6%-25%). Median overall survival was 30.7 (95% CI: 15.7-not yet reached) months. One-year overall survival was 72% (95% CI: 57%-82%). One-year composite GvHD (acute and chronic) free and relapse free survival (GRFS) was 41.6% (95% CI: 28.9%-54%).

Conclusion. PTCy and bortezomib combination for GvHD prophylaxis following MSD and MUD transplants is well tolerated and effective. It offers an alternative regimen to calcineurin and m-TOR inhibitor-containing regimens and may be preferred in certain settings including patients with limited resources, poor medication compliance, and with impaired renal function. A comparison of this cohort to a matched control group of patients receiving methotrexate and cyclosporine for GvHD prevention is ongoing.