Abstract 19: Cord Blood HLA Diversity and Impact on Matching

Abstract Introduction HLA matching is a key factor for Cord Blood Unit (CBU) selection. HLA haplotype frequencies vary widely among donors, and can be difficult to accurately determine without family typing. Maternal HLA typing is performed as part of preparation for CBU shipment. It is a unique opportunity to identify HLA haplotypes in the CBU without relying on statistical tools. Objectives To identify parental haplotypes and assess their frequency and the impact on matching at transplant. Methods The past 100 units shipped from our bank were evaluated. HLA typing was performed for CBU and mother, at A, B, C, DRB1 and DQB1 (G level). Maternal typing was used to assign haplotypes (Figure 1-A), then frequencies were determined using published work on donor populations (Maiers M et al, Hum Immunology 2007). In order to assess the rarity of the combinations, we calculated the probability of finding an identical CBU in global inventory (n=803,869). Combinations with at least one possible CBU were assigned “Common” (C), less than one “Rare” (R). CBU with undocumented haplotypes were classified as “Unique” (U) (Figure 1-B). Results Parental haplotypes were successfully assigned for 97 CBU, identifying 194 haplotypes (Figure 1-A); 55 (28%) were not previously described. 50 CBU were classified as U (52%), 23 as R and 24 as C (Figure 1-B). U CBU were more frequently from minority donors (70%), as compared to the R and C groups (35% and 50%, respectively, p=0.01), and they were more likely to be NCBI funded (63%, vs 15% for R and 22% for C, p=0.02). R CBU had lower allele match than C, but the difference was not statistically different with U CBU, which achieved a match 6/8 or higher in 40% of cases (Figure 1C). Discussion More than 50% of the CBU had at least one undocumented haplotype. Both common and rare haplotypes in CBU achieved high allele match, predictive of good clinical outcome. This probably reflects the two categories of patients receiving CBU transplants: the ones with a common HLA and many donors but needing urgent transplant, and the ones with rare HLA making donor search futile and CBU the only option. Figure 1