Cord-blood engraftment with ex vivo mesenchymal-cell coculture

Abstract

Background: Poor engraftment due to low cell doses restricts the usefulness of umbilical-cord-blood transplantation. We hypothesized that engraftment would be improved by transplanting cord blood that was expanded ex vivo with mesenchymal stromal cells.

Methods: We studied engraftment results in 31 adults with hematologic cancers who received transplants of 2 cord-blood units, 1 of which contained cord blood that was expanded ex vivo in cocultures with allogeneic mesenchymal stromal cells. The results in these patients were compared with those in 80 historical controls who received 2 units of unmanipulated cord blood.

Results: Coculture with mesenchymal stromal cells led to an expansion of total nucleated cells by a median factor of 12.2 and of CD34+ cells by a median factor of 30.1. With transplantation of 1 unit each of expanded and unmanipulated cord blood, patients received a median of 8.34×10(7) total nucleated cells per kilogram of body weight and 1.81×10(6) CD34+ cells per kilogram--doses higher than in our previous transplantations of 2 units of unmanipulated cord blood. In patients in whom engraftment occurred, the median time to neutrophil engraftment was 15 days in the recipients of expanded cord blood, as compared with 24 days in controls who received unmanipulated cord blood only (P<0.001); the median time to platelet engraftment was 42 days and 49 days, respectively (P=0.03). On day 26, the cumulative incidence of neutrophil engraftment was 88% with expansion versus 53% without expansion (P<0.001); on day 60, the cumulative incidence of platelet engraftment was 71% and 31%, respectively (P<0.001).

Conclusions: Transplantation of cord-blood cells expanded with mesenchymal stromal cells appeared to be safe and effective. Expanded cord blood in combination with unmanipulated cord blood significantly improved engraftment, as compared with unmanipulated cord blood only. (Funded by the National Cancer Institute and others; ClinicalTrials.gov number, NCT00498316.).

Figure 1. Expansion of Cord Blood with Mesenchymal Stromal Cells

Panels A and B show the median numbers of total nucleated cells and CD34+ cells, respectively, in the cord-blood grafts before and after ex vivo expansion, as compared with the numbers in units of unmanipulated cord blood. I bars represent the interquartile range. The numbers of nucleated cells and CD34+ cells were higher in the unit of expanded cord blood than in the unit of unmanipulated cord blood (P<0.001 and P = 0.01, respectively). The median numbers of colony-forming units in culture (CFU-C) before and after ex vivo expansion are shown in Panel C. There were significant increases in nucleated cells, CD34+ cells, and CFU-C in the unit of expanded cord blood as compared with the values before expansion (P<0.001 for all comparisons). Nucleated cells were expanded by a median factor of 12.2 (range, 1.0 to 29.8), the CD34+ cells by a median factor of 30.1 (range, 0 to 137.8), and CFU-C by a median factor of 17.5 (range, 0 to 435.0). The percentages of various types of cells in the cord-blood unit before and after ex vivo expansion in mesenchymal-cell cocultures are shown in Panel D. The units of mesenchymal-cell–expanded cord blood had increased proportions of monocytes (P<0.001) and granulocytes (P = 0.003), decreased proportions of T lymphocytes (P<0.001) and B lymphocytes (P<0.001), and similar proportions of CD34+ cells (P = 0.99) and natural killer (NK) cells (P = 0.85). Percent of CD45+ cells refers to the percent of the various cells in this gate on flow cytometry. The doses of nucleated cells and CD34+ cells in each unit and the total doses of nucleated cells, CD34+ cells, and CFU-C infused in the transplant recipients are shown in Panel E.

Figure 2. Cumulative Incidences of Neutrophil Engraftment and Platelet Engraftment

A total of 24 patients who received 2 units of cord blood, 1 of which contained cord blood that was expanded ex vivo in cocultures with STRO-3+ mesenchymal cells, were compared with 80 control patients who received 2 units of unmanipulated cord blood and whose data were reported to the Center for International Blood and Marrow Transplant Research (CIBMTR). Controls were matched according to age, diagnosis, intensity of the preparative regimen, and prophylaxis against graft-versus-host disease. Panel A shows the cumulative incidence of neutrophil recovery. At 26 days, the cumulative incidence was 88% among recipients of expanded cord blood and 53% among CIBMTR controls (P<0.001). Panel B shows the cumulative incidence of platelet recovery. At 60 days, the cumulative incidence was 71% among recipients of expanded cord blood and 31% among CIBMTR controls (P<0.001). Data on platelet engraftment were not available for one CIBMTR control. Ex vivo expansion led to more rapid neutrophil and platelet engraftment and to a higher proportion of patients with engraftment of both cell types.

Figure 3. Correlation of Total Nucleated Cells and CD34+ Cells with Neutrophil Engraftment

In the units of expanded cord blood, the number of total nucleated cells per kilogram of body weight (Panel A) correlated with the speed of neutrophil engraftment (Spearman correlation coefficient, −0.51; P = 0.004), and the number of −CD34+ cells per kilogram (Panel B) also correlated with the speed of neutrophil engraftment (Spearman correlation coefficient, −0.48; P = 0.006).