Reduced Intensity Conditioning Combined with Post-Transplant Cyclophosphamide for Graft Vs. Host Disease Prophylaxis In Older-Aged or Medically Frail Patients with Advanced Hematological Malignancies
Authors: Alousi Amin M , Andersson Borje S. , Saliba Rima M. , Botnick Wendeline , Rondon Gabriela , Shpall Elizabeth J. , Lima Marcos de , Popat Uday , Hosing Chitra , Kebriaei Partow , Khouri Issa , Qazilbash Muzaffar H. , Anderlini Paolo , Nieto Yago , Ciurea Stefan , Jones Roy , Champlin Richard 
Published: October 2019

Abstract
Abstract 2341
Graft-vs-Host Disease (GVHD) remains a common complication following matched sibling and unrelated (MUD) donor hematopoietic cell transplant (HCT). Standard GVHD prophylaxis calls for prolonged immune suppression, typically with a calcineurin-inhibitor. Recently, post-transplant cyclophosphamide (Cy) has been studied as sole prophylaxis in matched related and unrelated bone marrow (BM) transplant recipients following an ablative conditioning regimen with busulfan (Bu) and Cy. Herein, we report the results of a phase II trial exploring a reduced intensity conditioning (RIC) regimen combined with post-transplant Cy in BM and peripheral blood (PB) HCT recipients.

Methods:
Fludarabine (Flu) was administered at a dose of 40mg/m2 over 1hr followed by intravenous Bu over 3 hrs targeting a daily AUC of 4,000 microMol-min on days −6 to −3. Recipients of MUD's received ATG on days −3 to −1 (total dose 4mg/kg). Cy was given as sole GVHD prophylaxis at a dose of 50mg/kg on days +3 and +4.

Results:
31 pts with a median age of 62 yrs (range, 39–71) received a matched sibling (n=11) or unrelated donor (n=20) graft from BM (n=22) or PB (n=9) for the following diagnoses: AML/ MDS (n=25), CLL+MDS (n=2), CLL (n=1), NHL+MDS (n=1), NHL (n=1) and ALL (n=1). Disease status at the time of HCT was induction failure, relapsed and/ or chemotherapy-refractory disease in 23 pts with the remaining pts in high-risk CR1 (n=5), CR2 (n=2) or CR3 (n=1). The median co-morbidity score was 3 (range, 0–7) and 7 pts had a prior HCT (autologous n=4, allogeneic n=3). Median days to ANC > 0.5 × 109/L and platelet count >20 × 109/L were 17 (range, 13–38) and 24 (range, 11–57), respectively. Primary and secondary graft failure occurred in 1 and 2 pts, respectively. Mucositis (grade 2: n=19, grade 3: n=4) and hemorrhagic cystitis (grade 2: n=10, grade 3: n=4, grade 4: n=2) were the most common toxicities. Day 100 non-relapse mortality was 6% (95% CI, 2–25). The cumulative incidence (C.I.) of acute GVHD grades II-IV and III-IV was 56% (95% CI, 40–79) and 13% (95% CI, 5–33) which includes 4 cases of late acute GVHD. Rates of acute GVHD did not differ between PB or BM recipients (55% vs. 58%, p-value 0.9). C.I. of chronic GVHD was 11% (95% CI, 4–32). With a median follow-up of 10 months (range, 4–20), 1-yr overall and progression-free survival (PFS) was 56% (95% CI, 35–73) and 43% (95% CI, 21–63), respectively. For pts with AML/MDS, 1- yr PFS for pts in CR1, any CR and relapsed/refractory disease were: 100%, 66% (95% CI, 16–91) and 40% (95% CI, 20–60), respectively.

Conclusion:
This phase II trial of RIC with BU/Flu combined with post-transplant Cy was well tolerated and resulted in favorable survival and good disease-control in this high-risk, older-age population. Rates for acute GVHD appear comparable to historical rates with calcineurin-inhibitor based regimens, while rates for chronic GVHD appear to be lower. Rates for acute GVHD were similar for PB and BM grafts supporting the inclusion of PB grafts in future trials using post-transplant Cy as the basis for the GVHD prophylaxis regimen.

Disclosures:
No relevant conflicts of interest to declare.