Improved Immune Reconstitution Following Pre-Emptive CD8-Depleted Donor Lymphocyte Infusions (DLIs) after Haploidentical Stem Cell Transplantation (SCT) Using a Reduced-Intensity Conditioning (RIC) Regimen.
Authors: Corradini Paolo , Raganato Anna , Carrabba Matteo , Gandola Lorenza , Lombardo Claudia , Carniti Cristiana , Farina Lucia , Milani Raffaella , Dodero Anna 
Published: April 2020

Abstract
Allogeneic stem cell transplantation (SCT) from an haploidentical family donor has been reported as a viable option in acute leukemias when matched donors are unavailable. However, the extensive T-cell depletion (TCD), required to prevent graft-versus-host disease (GVHD), is associated to delayed immune recovery and high transplant-related mortality. In an ongoing phase I–II trial for patients (pts) with advanced hematological malignancies, we combined a RIC regimen, including thiotepa (10 mg/kg), fludarabine (120 mg/ms), cyclophosphamide (60 mg/kg) and TBI (2 Gy), with pre-emptive administration of CD8-depleted DLIs (starting from 1x104 up to 1x105 cells/kg). Ex-vivo and in-vivo TCD were carried out by CD34+ cell selection using the CliniMACS device and alemtuzumab (30 mg day −2), respectively. The aim of the study was to investigate in a dose finding study the safety and the impact on immune-reconstitution of CD8-depleted DLIs. Six-teen pts with hematological malignancies (n=14 NHL/HD, n=1 ALL, n=1 AML) were included, median age was 35 years (range, 15–65), 10 (63%) were chemorefractory, and 68% and 75% had failed a previous auto or at least 3 CT lines, respectively. Pts received a median of 10.6 x106/Kg CD34+ and 1x104/kg CD3+. All pts engrafted with full donor chimerism from day +30. At a median follow-up of 9 months, 12 pts were alive and 4 died (n=1 infection, n=3 disease). The estimated OS at 2 years was 58%; 7 of 16 (44%) relapsed at median time of 100 days after SCT. CD8-depletion of 14 donor lymphocyte aphereses was performed with a new depletion protocol (Clinimacs CD8-Microbeads) that reduces the content of CD8+ cells by at least 3 logs. The median CD3+, CD4+, CD56+/CD3+, CD20+ cell recovery were 62% (range, 35–91%), 88% (63–128%), 51% (8–78%), 76% (33–128%), respectively. Before DLIs, only 1 of 16 pts (6%) developed de novo acute GVHD (grade II). A total of 22 CD8-depleted DLIs were administered to 9 of 16 pts without any engraftment problem. The first cohort of pts (n=5) received a total dose of 3–6x104/kg CD8depleted DLIs starting at day +45 divided in 3 monthly infusions: none of them developed aGVHD. Given no toxicity, we escalated doses and the second cohort (n=4) received a total dose of 10–25x104/kg CD8-depleted DLIs divided in 3 monthly infusions: 3 pts had acute GVHD (grade II). Overall, the incidence of acute GVHD was higher (75% vs 0%, P&lt;0.04) in pts receving larger numbers of donor cells. Interestingly, the median values of CD4+/ul and CD8+/ul were 98 (range, 8–612) and 150 (range, 15–988) at 4 months; 247 (range, 55–333) and 235 (range, 3–1000) at 5 months after SCT. The median value of CD19+/ul cells were 134 (range, 0–292) and 160 (range, 0–256) at 4 and 5 months, respectively. NK cells remained between the value of 394/ul and 569/ul in the first 6 months after SCT. Our results suggest that: (1) haploidentical SCT with RIC regimen is feasible with a high rate of engraftment and a low acute GVHD incidence; (2) pre-emptive CD8-depleted DLIs are feasible without GVHD until the total dose of 6 x104/kg; 3) higher doses can induce acute GVHD, but no grade III–IV was observed; 4) despite the limited number of pts, we observed a faster immune recovery and a relatively low mortality rate for infections.