Outcome After 9/10 Mismatched Unrelated Donor or Cord Blood Cells Allogeneic Stem Cell Transplantation (allo-SCT) in the Setting of Reduced-Intensity Conditioning (RIC)

Unrelated umbilical cord blood cells (UCB) have emerged as an alternative stem cell source for allo-SCT in patients who lack a matched-related or unrelated donor (MUD). Several studies found a similar outcome between HLA 4–6/6 matched UCB and HLA 8/8 matched and 7/8 mismatched unrelated donors, mainly in the setting of standard myeloablative conditioning. However, currently it is more common practice in many centres to search for 10/10 or 9/10 MUD or for double UCB. Thus far, no study focussed on the comparison of outcome of patients who received double UCB allo-SCT versus allo-SCT using 9/10 mismatched donors. With this background, this retrospective analysis assessed outcome after allo-SCT using double UCB cells or 9/10 mismatched donors in the setting of a RIC regimen.

This analysis was performed in a series of 152 consecutive adult patients treated for hematological malignancies in 2 centers adopting similar transplant procedures. 85 patients were males (56%) and the median age at time of allo-SCT was 53 years (range, 16–69). Diagnoses included 59 AML (39%), 21 MDS/MPN (14%), 42 NHL (28%), 5 Hodgkin diseases (3%), 18 ALL (12%) and 7 Myelomas (5%). 35 patients (23%) had standard risk disease and 117 patients (77%) presented with high risk disease. Conditioning regimen consisted of fludarabine, cyclophosphamide and low dose TBI for 108 patients (71%), fludarabine and busulfan for 35 patients (23%); and other regimens in the remaining 9 patients (6%). 50 patients (33%) received antithymocyte globulin. The donor was double UCB in 110 cases (“dUCB” group) and 9/10 mismatched unrelated in 42 cases (“9/10” group). During the study period, both participating centers adopted the same strategy for donor search and choice: in the absence of matched-related siblings or 10/10 MUD, 9/10 donors were searched. UCB cells were used if no 9/10 donor could be identified within a reasonable time frame (usually 2–3 months after search initiation).

With a median follow-up of 30.3 months (range, 6–72.4), the Kaplan-Meier estimate of overall survival (OS) at 2 years was comparable between both groups [52% (95%CI, 42–61%) in the dUCB group versus 48% (95%CI, 32–62%) in the 9/10 group, P=0.55]. The cumulative incidence of NRM was 26% in the dUCB group versus 24% in the 9/10 group (P=0.95). Grade 3–4 acute GVHD and extensive chronic GVHD incidences were 20% versus 21.4% (P=0.83), and 6% versus 21% (P=0.02), in the dUCB group versus the 9/10 group, respectively. The cumulative incidence of relapse was 34% in the dUCB group versus 38% in the 9/10 group (P=0.63). Finally, the estimate of progression-free survival (PFS) at 2 years was 43% (95%CI, 34–52%) in the dUCB group versus 38% (95%CI, 23–53%) in the 9/10 group (P=0.55). In multivariable analysis including the most important parameters associated with outcome (patient's age at transplantation, patient's sex, diagnosis, disease status at transplantation, use of ATG, GVHD prophylaxis), the stem cell source (dUCB versus 9/10) did not have any significant impact on OS (HR=0.92 (95% CI, 0.41–2.08); P=0.86)

These data suggest that dUCB is likely a valid alternative graft source compared to 9/10 mismatched unrelated donors in the setting of RIC allo-SCT since both donor types showed similar results in terms of OS, PFS, disease relapse, and acute GVHD incidence. However, the significantly lower incidence of extensive chronic GVHD in the dUCB group is an important and major finding, highlighting the need for a prospective randomized study in this field.

No relevant conflicts of interest to declare.