HLA match likelihoods for Indian patients seeking unrelated donor transplantation grafts: a population-based study.

BACKGROUND For patients who do not have a suitable human leukocyte antigen (HLA)-matched family donor, unrelated donor registries of adult volunteers and banked umbilical cord blood (UCB) units provide the potential for successful haemopoietic stem-cell transplantation. The size and genetic composition of such registries determines the proportion of patients who will be able to find a suitable match. We aimed to assess the proportion of positive matches for Indian patients. METHODS Using HLA data from ten existing donor and UCB registries and clinical transplant centres in India, we built population-based genetic models for 14 Indian regions to model Indian registry growth to predict the likelihood of identifying a suitable donor-either an adult donor or UCB-for Indian patients. We computed ranking tables of the top ten haplotypes in each regional group and compared these with four US samples from the National Marrow Donor Program (NMDP) registry. FINDINGS The mean proportion of individuals who would have a 10/10 adult donor match within India ranged from 14·4% with a registry size of 25 000 to 60·6% with a registry size of 1 000 000. Only when donor registries increased to 250 000 did the match rate within India exceed that found by searching the US-NMDP registry combined with an Indian registry of 25 000 donors. The proportion of matches increased logarithmically with increased registry size (R(2)=0·993). For a UCB registry size of 25 000, 96·4% of individuals would find a 4/6 match; however, only 18·3% would have a 6/6 match. INTERPRETATION Serial match modelling and follow-up comparisons can identify the relative and progressively greater value of an India-based donor registry and UCB banking network to serve the Indian population. Understanding regional HLA haplotype diversity could guide registry growth and maximise benefit to patients. Similar modelling could guide planning for the needs of other ethnically distinct populations. FUNDING University of Minnesota and the Indian Council for Medical Research.