Rapid and Sustained Engraftment of a Single Allogeneic Ex-Vivo Expanded Cord Blood Unit (CBU) After Reduced Intensity Conditioning (RIC) in Adults. Preliminary Results of a Prospective Trial
Authors: Milpied Noel , Dazey Bernard , Ivanovic Zoran , Duchez Pascale , Vigouroux Stephane , Tabrizi Reza , Pigneux Arnaud , Dilhuydy Marie-Sarah , Bouabdallah Krimo , Leguay Thibaut , Sauvezie Mathieu , Lafarge Xavier , Marit Gerald , Boiron Jean-Michel 
Published: October 2019

Abstract
Abstract 486
CBU is a widely used source of stem cells for allogeneic transplantation (SCT). Engraftment rate and speed of a single CBU in adults remains unsatisfactory. Transplantation of 2 CBU may overcome this problem to the expense of an increased incidence of GVHD. Until now, attempts at using ex-vivo expanded CBU have been unsuccessful to promote long term engraftment of the expanded product. We report the results achieved in the first 8 Pts included in a PCT of transplantation of a single ex-vivo expanded allogeneic CBU. Eudract 2008–006665–81, Clinicaltrials.gov NCT 01034449.

Methods:
Adults patients with an indication for SCT and unable to tolerate MAC (age>45, comorbidities, previous high-dose therapy) were included after inform consent if no Id sibling, no MUD 9 (C or DQ mismatch accepted) to 10/10 HLA matches and no CBU fulfilling the HLA matching (≥ 4/6) and richness (≥ 3 to 4 × 107 TNC/kg before thawing) criteria were available. RIC consisted of Flu (40 mg/m2/d × 5d), Cyclophosphamide (50 mg/kg × 1d) ICT 2 Gy. GVHD prevention consisted of MMF (d-3 to d28) and CSA from d-3. Graft engineering: 1 CBU with > 2 TNC/kg < 3 and 4 to 6 HLA compatibilities was thawed, CD34+ cells were selected through magnetic device (Miltenyi) and submitted to ex-vivo expansion in SF medium ( HPO1-Macopharma) supplemented with SCF, Flt3l, G-CSF and TPO during 12 days, starting d-12 of the transplantation (Ivanovic, Cell Transplant 2011) CD34 neg cells were cryopreserved. On d0, expanded cells were washed and resuspended in HSA 4% and upon viability and sterility were injected to the pt. Cd34 neg cells were thawed and injected to the pt 3 h later.

Results:
From 03/2010 to 06./2011 8 pts have been included, med age 55y.o. (26–64) with AL: 3, Hodgkin's: 2, MDS: 3. Pts had received 1 to 3 lines of Tx (med:2). For 1 pt the expanded product was contaminated and this pt then received a back-up unmanipulated CBU. He engrafted correctly and is AW at 14 m with full donor chimerism. For the 7 other pts, the ex-vivo median fold expansion of CD34+ cells and TNC was 39 (29–75) and 390 (127–526) respectively, leading to a graft that contained 1.3 to 13 × 106 CD34+ cells/kg (med: 2 × 106/kg). The CD34 neg counterpart contained 3 × 106 CD3+/kg (1–5) and 0,9 × 106 CD19+ cells/kg (0,3–1,5). At d42, 6/7 pts who received the expanded graft engrafted with ≥99% donors cells. A 2d RIC was performed followed by a double CBU transplant in the patient who did not engraft. That 2d graft again failed to engraft. However the patient remains alive at 9m. For the 6 pts who engrafted with the expanded product the time to reach 500, 1000 PMN's and 20 000 plts/mm3 was 7d (6–19), 8d (6–21) and 24d (0–39) respectively. The chimerism on WBC and CD3+cells (evaluated on d 15, 42, 60, 100, 180, 365) remains full donor up to 1 year + after transplant (1y+: 2 pts; 6m+: 1pt; 180d+: 1 pt; 60d+: 1pt) or to relapse (at 1y) in the one pt who relapsed. Five pts experienced an AGVHd (grade III-IV: 1 pt). With a median FU of 10m (2 to 18m) 7 pts are alive, 6 wo disease. One pt died 1y after transplant from relapse.

Conclusion:
Ex-vivo expansion of a single CBU is feasible and reproducible. Transplantation of the expanded product together with the CD34 neg counterpart of the same CBU produces rapid, complete and sustained donor engraftment after RIC in adults.

Disclosures:
No relevant conflicts of interest to declare.