Post-Transplantation Cyclophosphamide (PT-CY) After Myeloablative Conditioning Regimen (MAC) In Unmanipulated Haploidentical Bone Marrow Transplantation (hBMT) Is Highly Effective As Gvhd Prophylaxis and Disease Free Survival In Pediatric and Adult Patients With High Risk Leukemia
Authors: Domenica Simone Maria , Proia Anna , Severino Alessandro , Shardlow Alison , Natale Novella , Spirito Francesca , Garzia Mariagrazia , Montante Barbara , Locasciulli Anna , Majolino Ignazio 
Published: October 2019

Introduction
BMT from HLA haploidentical family members (hBMT), using either T-cell depleted or T-cell replete grafts, is increasingly employed in patients who urgently need (but lack) a donor. After the promising results in hBMT obtained by the Baltimore group (Luznik et al., Biol Blood Marrow Transplant 2008, Blood 2010) introducing post-transplant high-dose cyclophosphamide (PT-CY) following a non-myeloablative conditioning regimen, the Genoa group (Raiola et al., Biol Blood Marrow Transplant 2013) has shown, in the haploidentical setting that a myeloablative conditioning (MAC) with PT-CY (on day +3 and +5), cyclosporine from day zero and mycophenolate mofetil (MMF) from day +1, is associated with a high rate of engraftment, acceptable TRM and GVHD, and induces durable remission with low incidence of relapse in a high proportion of patients with high-risk hematologic malignancies. We now report a series of 13 heavly pretreated high-risk leukemia patients who underwent a MAC protocol consisted of TBF regimen: Thiotepa (10 mg/kg), Busulfan (9,6 mg/kg) and Fludarabine (150 mg/mq). As graft versus host disease (GVHD) prophylaxis, 2 patients received a 5 drugs combination (ATG-Fresenius, CSA, MTX, MMF and Basiliximab) and stem cells source was G-CSF-primed haploidentical bone marrow (hBM) cells (Di Bartolomeo et al., Blood 2013). In 11 patients stem cells source was non-primed unmanipulated hBM cells, and GVHD prophylaxis consisted of PT-CY (50mg/kg) iv on day +3 and +4, CSA 2.5 mg/kg/day and MMF 45 mg/kg/day from day +4.

Results
From 2008 to 2013, 11 adult patients (M/F=8/3; median age 40 years, range 23 to 62) and 2 pediatric patients (M/F=1/1, age 4 and 7 years) with high risk ALL (1 pediatric; 2 adult), AML (1 pediatric; 8 adults) and one Richter evolution of CLL, underwent T replete hBMT. At time of transplant 10 patients were in CR (CR1=9, CR2=1), 1 in a good PR and 2 had refractory disease. Grafts contained a median of 5.68 x 108/kg nucleated BM cells (range 0.7-62.1), 2.14x106/kg CD34+ cells (range 0.55-7.09) and 34.7x106/kg CD3+ cells (range 16-93.4). 12 patients are evaluable for engraftment. This occurred in 100% for neutrophils and 93% for platelets, with a median time to neutrophil recovery (> 0.5 x 109/L) of 22.5 days (range, 13-40) and to platelet recovery (> 20.0 x 109/L) of 27.5 days (range, 17-49). All patients had full donor chimerism by day +30. Non relapse mortality (NRM) was 23%: 2 pt died for sepsis (one before engraftment), 1 for aGVHD. 4 patients had grade I and 3 grade II aGvHD, respectively. Only one patient had a grade III, and another had grade IV fatal GVHD. 3 patients had only limited chronic GvHD. Up to now, only 3 patients have relapsed and of these 2 have died. 8 patients (61.5%) are currently surviving, 7 of them are disease-free with median follow-up time of 165 days (range 32-896 days) from transplant.

Conclusion
Our preliminary results confirm that haplo-BMT following a MAC regimen, is a feasible treatment in pediatric and adult patients, and that PT-CY is highly effective as GVHD prophylaxis, producing a high rate of stable engraftment with encouraging non relapse mortality and relapse-free survival.

Disclosures:
No relevant conflicts of interest to declare.