Ex Vivo Mesenchymal Precursor Cell-Expanded Cord Blood Transplantation Following Reduced Intensity Conditioning Regimens

Introduction: Double-unit cord blood (CB) transplantation (DCBT) after myeloablative conditioning, where one CB unit is expanded ex-vivo with mesenchymal precursor cells (MPC)-co-culture led to significantly improved neutrophil and platelet engraftment compared to historical controls.¹ Our aim was to determine the efficacy of this technique after reduced-intensity conditioning (RIC) regimens.

Methods: We evaluated consecutive adult patients with hematological malignancies who received RIC regimens followed by DCBT where one unit was infused unmanipulated and second unit was expanded ex-vivo with MPC prior to infusion ("MPC group" n=27), as described previously,¹ andcompared themwith historical cohort who received two unmanipulated CB units ("controls" n= 51) from 2003-2015. Two RIC regimens were used - Flu/Cy/TBI (flu 40 mg/m2, cy 50 mg/kg and TBI 200cGy) (n=40) and Flu/Mel (flu 40 mg/m2 and mel 140 mg/m2) (n=38) with rabbit ATG 3mg/kg. Tacrolimus and MMF were used for GVHD prophylaxis. Primary endpoint was median time to engraftment of neutrophils (≥ 0.5 X 10⁹/L X 3 consecutive days) and platelets (≥ 20 X 10⁹/L X 7 consecutive days without transfusion).

Results: Diagnoses were AML/MDS (N=38; 49%), ALL (N=13; 17%),NHL (N=18; 23%), HD (N=3; 4%), CML (N=1; 1%), and CLL (N=4; 5%). Baseline patient characteristics were similar among the groups [Table 1]. Majority of CB units (66%) were 5-6/8 matched at HLA-A, B, C and DRB1 by high resolution testing. Infused median total nucleatedcells (TNC) (x10⁷/Kg) were 4 and 8, and median CD34 cells (x10⁵/Kg)were 4.3 and 19.7, respectively for control and MPC groups. Co-culture with MPCs led to expansion of TNC by a median of 11.1 and of CD34+ cells by a median of 49.3.

Among engrafted patients, median time to neutrophil engraftment was 12 (range 1-28) days in MPC group as compared with 16 (range 5-48) days in controls (p=0.02); the median time to platelet engraftment was 31 days and 37 days, respectively (P=0.3). On day 26, the cumulative incidence of neutrophil engraftment was 78% in MPC group versus 67% in controls (P=0.1). On day 60, the cumulative incidence of platelet engraftment was 74% and 74%, respectively (P=0.7). [Figure 1]

Conditioning regimen also affected the time to neutrophil recovery. Among patients with Flu/Mel, the median time to neutrophil engraftment was 14 days in MPC-group (n=13) compared with 22 days in controls (n=19) (p=0.001). Patients with Flu/Cy/TBI regimen had faster time to engraftment; median time to neutrophil engraftment was 6 days in MPC group (n=10) and 11 days in controls (n=27) (p=0.04). However, the median time to platelet engraftment was similar in MPC- and control groups in patients who received either Flu/Mel (37 vs 44 days, p=0.1) or Flu/Cy/TBI regimen (29 vs 31 days, p=0.5).

There was no difference in the cumulative incidence of day 100 non-relapse mortality (4% vs. 11%, p=0.6), 6^th month mortality (25% vs 24%, p=0.6), grade II-IV acute GVHD (28% vs 27%, p=0.9), 2-year chronic GVHD (29% vs 20%; p=0.9) and estimates of 2-year OS (32% vs. 34%) between patients with ex-vivo expanded and unmanipulated CB units.

Conclusions: Transplantation of CB units expanded with MPC appeared to be safe and effective. Using MPC-expanded CB units significantly improved time to engraftment following Flu/Mel or Flu/Cy/TBI RIC regimens as compared with unmanipulated units.

References

1. de Lima M, McNiece I, Robinson SN, et al. Cord-blood engraftment with ex vivo mesenchymal-cell coculture. NEJM. 2012;367(24):2305-2315

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