Comparison Of Unrelated Cord Blood (CB) and Peripheral Blood Stem Cell (PB) Transplantation In Adults With Myelodysplastic Syndrome (MDS) After Reduced Intensity Conditioning Regimen (RIC): A Collaborative Study From Eurocord and Chronic Malignancies Working Party (CMWP-EBMT)

Outcome of patients with intermediate or high risk IPSS myelodysplastic syndrome (MDS) is poor in the absence of hematopoietic stem cell transplantation (HSCT). Choice of the best stem cell source is debated in this poor risk population. Unrelated cord blood transplantation (UCBT) has been used for patients lacking an HLA identical donor. This is the first study comparing well matched unrelated adult peripheral blood (PB) stem cell transplant to mismatched UCBT for patients with MDS.

Patients with MDS transplanted from 2005 to 2011 with either unrelated CB or PB receiving a reduced intensity conditioning (RIC) were included. All PB donors were Human Leucocyte Antigens (HLA)-allele matched (10/10) or one allele mismatched (9/10) (-A, -B, -C, DRB1, -DQB1). Overall survival (OS) and disease-free survival (DFS) were estimated by Kaplan-Meier. Relapse incidence (RI), non-relapse mortality (NRM), engraftment, acute and chronic graft-versus-host disease (GVHD) were calculated using cumulative incidence (CInc) methods. Risk factors for outcomes were analyzed by Cox and Fine & Gray models.

502 patients transplanted with PB or 129 with CB (80 with double units) were compared. Among the PB recipients, 363 (72%) were 10/10 matched and 123 (25%) 9/10 matched. Most CB (98%) recipients had at least one HLA mismatch on 6 antigens tested (-A, -B antigen level and DRB1 allelic level), 32% had one mismatch and 66% had 2 mismatches. Median follow-up was 12 months for PB and 24 months for CB. MDS was transformed into AML in 416 patients. MDS WHO classification was: RA in 37, RCMD in 31, RAEB1 in 50 and RAEB2 in 87 and unclassified in 10 patients. Considering only patients with MDS, cytogenetic according to IPSS was: good in 96, intermediate in 57 and poor in 65 patients. PB and CB groups were different for age, gender, incidence of secondary AML (CB: 71% vs PB: 64%) and conditioning regimen. CInc of engraftment was lower in CB patients, 78 vs 96% (p<0.0001). Grade II to IV acute GVHD was 29% and 31% for PB and CB. Chronic GVHD was more frequent after PB (42% vs 23%, p=0.001). The unadjusted 2-year OS and DFS were better in patients transplanted with PB (46% vs 30% and 43% vs 28%, p=0.0001). There was no statistical difference for OS and DFS between single and double UCBT. RI was not significantly different (25 vs 30%, p=0.09) whereas NRM was higher in patients transplanted with CB (42 vs 33%, p=0.02). In multivariate analysis, OS (Hazard ratio (HR): 0.59, 95% confidence interval (CI): 0.44-0.80) and DFS (HR: 0.57, 1.89, 0.79) were higher in patients transplanted with PB compared to CB. Furthermore, after adjustment, CB was also a risk factor for higher NRM ((PB, HR: 0.55, 95%CI: 0.37-0.80) and RI ((PB, HR: 0.62, 95%CI: 0.39-0.97).

The analyses were performed using 3 groups of patients according to donor HLA type: PB 10/10, PB 9/10 and CB. The unadjusted 2-year OS and DFS were better with PB 10/10 than with PB 9/10 or CB: 49%, 37% and 30% (p=0.0001) and 45%, 36%, 28% (p<0.0001), respectively. NRM was not significantly different between CB and PB 9/10: 42% vs 36%. RI was similar after CB and PB 9/10: 28% vs 30%. Chronic GVHD was significantly lower after CB (PB 9/10: 37% vs CB 23%, p=0.004). The multivariate analysis showed an advantage of OS for PB 10/10 compared to PB 9/10 (HR: 1.45, 95%CI: 1.06-1.97, p=0.02) whereas there was no significant difference between PB 9/10 and CB (HR: 1.24, 95%CI: 0.84-1.83, p=0.29). Likewise, DFS was better after PB 10/10 (HR: 0.57, 95%CI: 0.43-0.77, p=0.05) and it was similar after PB 9/10 or CB (HR: 1.34, 95%CI: 0.92-1.97, p=0.13). In the 9/10 PB no differences in the results were observed according to the specific mismatched locus (A, B, DRB1, vs C, DQB1)

Despite the limitation of a retrospective registry based study and the short term follow up, our study shows that transplants with PB from matched unrelated donor gives the best outcomes. In the absence of a 10/10 unrelated matched PB donor, a 9/10 PB donor or mismatched CB give similar results. Therefore, for MDS patients without a HLA 10/10 unrelated donor a 9/10 regardless of the specificity of the locus where the mismatch occurs mismatched HLA locus or a HLA mismatched CB are both alternative options for transplantation.

Gluckman:Cord use: Honoraria; gamida: Honoraria.