Total Marrow Irradiation for Second Allogeneic Haematopoietic Stem Cell Transplantation in Patients with Advanced Acute Leukemia
Authors: Dominietto Alida , Vagge Stefano , Hui Susanta , Di Grazia Carmen , Lamparelli Teresa , Bregante Stefania , Raiola Anna Maria , Varaldo Riccardo , Gualandi Francesca , Corvò Renzo , Angelucci Emanuele 
Published: February 2021

Background. Relapse after allogeneic haematopoietic stem cell transplantation (HSCT) is associated with very poor outcomes. A myeloablative conditioning regimen for patients with advanced acute leukemia before second allogeneic HSCT is crucial to better control the disease, but the risk of transplant mortality due to toxic complications is very high. Total Marrow Irradiation (TMI) is a novel high precision radiation treatment, alternative to standard Total Body Irradiation (TBI) conditioning regimen, allows to deliver therapeutic radiation doses over extensive selected targets while substantially reducing radiation to vital organs to preserve their functions.
Aim of the pilot study. To evaluate the efficacy of high dose per fraction TMI in combination with thiotepa, fludarabine and alkeran as conditioning regimen in 9 patients with acute leukemia relapsed after a first allogeneic HSCT.
Patients and Methods. Nine patients relapsed after first allogeneic HSCT received a second allogeneic HSCT, 7 from haploidentical, 1 from unrelated (UD) 10/10 and 1 from HLA-identical sibling (SIB) donor. The conditioning regimen consisted of: TMI 8 Gy in 5 patients on day -8 -7 or TMI 12 Gy in 4 patients on day -9 -8 -7, plus Thiotepa 5 mg/Kg on day -6, Fludarabine 50 mg/mq on day -5 -4 -3, alkeran 140 mg/mq on day -2. TMI was delivered in daily single fraction dose of 4 Gy, instead of the conventional 2 Gy in order to potentially enhance the biological effective dose approximately 20% to 60% (for a total dose of 12 Gy), considering alpha/beta ratio between 10-1.49, while total dose of 8 Gy in 2 fractions schedule is potentially equivalent to six fractions of conventional TBI for low alpha/beta ratio. Graft versus host disease (GvHD) prophylaxis for SIB and UD consisted of cyclosporine methotrexate and ATG, whereas for HAPLO it was high dose post-transplant cyclophosphamide (PT-CY), cyclosporine and mycophenolate. The median age was 45 years (range, 19-70 years); 3 patients were in remission, 6 had active disease at the time of the second allogeneic HSCT. The median number of nucleated cells infused was 4.3 x 10e8/Kg (range 2.6-7.7). Four patients received peripheral blood and 5 patients received unmanipulated bone marrow cells.
Results. The median time to neutrophil counts of &gt; 0.5 x 10e9/L was 16 days (range 13-22) and to platelet counts of &gt; 20 x 10e9/L was 19 days (range 11-27) respectively. All the patients showed a full donor chimerism on day 30 after transplant; none of the patients had rejection. Three patients developed acute graft versus-host disease (aGvHD) grade I-II and 1 patient had moderate chronic GvHD. During the neutropenic phase of the transplant one patient developed a sepsis from Pseudomonas Aeruginosa; one patient had pericardial effusion and one patient had mucositis grade II. The median follow up was 528 days (range 227-858). Day +30 and day +100 transplant related mortality were 0. Two patients died of transplant related complications; both died of interstitial pneumonia and received TMI 12 Gy. Two patients died of leukemia and they were not in remission at the time of the transplant. The actuarial 17 months disease free-survival (DFS) is 53%.
Conclusions. This is the first report demonstrating the safety and the efficacy of the TMI conditioning regimen in patients with advanced acute leukemia receiving second allogeneic transplantation with encouraging outcome in terms of engraftment, early toxocity, GvHD and relapse.

Disclosures
No relevant conflicts of interest to declare.