Impact of HLA Haplotype Matching On Engraftment in Reduced Intensity Cord Blood Transplantation.

HLA-mismatched unrelated cord blood transplantation (UCBT) is feasible and, in retrospective comparative analyses, allows survival rates similar to conventional unrelated HLA-matched adult-derived grafts. Although it is clear that the degree of UCB HLA mismatch in patients has a negative effect on outcomes, the biologic implications of HLA haplotype itself have not been explored for UCBT. In unrelated bone marrow transplantation, an effect of HLA haplotype matching on GVHD has been clarified. (S.Morishima. et al. Blood 2010). This study was conducted to determine the impact of HLA haplotype matching in reduced intensity UCBT.

To determine the impact of HLA haplotype matching with outcomes after UCBT, We retrospectively reviewed patients with hematologic malignancies who underwent reduced intensity CBT at Toranomon Hospital from August 2006 and December 2010 consecutively. Patients who had prior history of transplantation, were in poor performance status (ECOG PS >3), had active bacterial or fungal infections at the time of conditioning were excluded. Then, the remaining 164 consecutive patients were reviewed. The most frequently used conditioning regimens were fludarabine, alkylating agent (melphalan or busulfan) with total body irradination (TBI), tacrolimus plus mycophenolate mofetil for GVHD prophylaxis. DNAs of 164 pairs were analysed for HLA-A, -B, and -DRB1 based on High Resolution typing, and we have determined the HLA haplotype based on Japanese common HLA haplotypes referred from the previous reports.

For A, B, DR based on high resolution typing the following mismatch occurred: no mismatch 3(2%), one mismatch 12(7%), two mismatch 58(35%), three mismatch 60(37%), four mismatch 28(17%), five mismatch 3(2%) in the GvH direction, and: no mismatch 2(1%), one mismatch 16(10%), two mismatch 55(34%), three mismatch 56(34%), four mismatch 32(20), five mismatch 3(2%) in the HvG direction. Then 37 among 164 pairs were defined as the HLA haplotype matched group. The number of total nucleated cells and CD34⁺ cells were not significantly different between HLA haplotype matched group and non-matched group. The cumulative incidence of neutrophil recovery was higher in HLA haplotype matched group than in non-matched group.( 94.6% vs. 80.3% up to day 60, p=0.0027). Lower incidence of pre-engraftment immune reaction(PIR) and acute GVHD were observed in haplotype matched group (37.8 % vs. 47.9 % up to day 60 post-transplant, P = 0.32), III to IV acute GVHD( 18.9% vs. 27.7% up to day 100 post-transplant, p=0.29). The cumulative incidences of relapse tended to be lower in haplotype matched group than in non-matched group (21.5% vs. 31.5%, P=0.28).Overall survival (OS) was estimated as 36.0 % at 3 years post-transplant. There were no significant differences between mathed and non-matched group in the cumulative incidence of OS (36.8 % vs. 34.3% at 3 years post-transplant, P = 0.84).

HLA haplotype matching in UCBT was found to have a significant impact on engraftment in this analysis.

No relevant conflicts of interest to declare.