MHC haplotype matching for unrelated hematopoietic cell transplantation

Abstract

Background: Current criteria for the selection of unrelated donors for hematopoietic cell transplantation (HCT) include matching for the alleles of each human leukocyte antigen (HLA) locus within the major histocompatibility complex (MHC). Graft-versus-host disease (GVHD), however, remains a significant and potentially life-threatening complication even after HLA-identical unrelated HCT. The MHC harbors more than 400 genes, but the total number of transplantation antigens is unknown. Genes that influence transplantation outcome could be identified by using linkage disequilibrium (LD)-mapping approaches, if the extended MHC haplotypes of the unrelated donor and recipient could be defined.

Methods and findings: We isolated DNA strands extending across 2 million base pairs of the MHC to determine the physical linkage of HLA-A, -B, and -DRB1 alleles in 246 HCT recipients and their HLA-A, -B, -C, -DRB1, -DQB1 allele-matched unrelated donors. MHC haplotype mismatching was associated with a statistically significantly increased risk of severe acute GVHD (odds ratio 4.51; 95% confidence interval [CI], 2.34-8.70, p < 0.0001) and with lower risk of disease recurrence (hazard ratio 0.45; 95% CI, 0.22-0.92, p = 0.03).

Conclusions: The MHC harbors genes that encode unidentified transplantation antigens. The three-locus HLA-A, -B, -DRB1 haplotype serves as a proxy for GVHD risk among HLA-identical transplant recipients. The phasing method provides an approach for mapping novel MHC-linked transplantation determinants and a means to decrease GVHD-related morbidity after HCT from unrelated donors.

Figure 1. Long-Range Haplotyping of HLA-A, -B, and -DRB1 in Unrelated Individuals

(A) Schematic illustration of two HLA phenotypically identical individuals with the same or different linkages between HLA-A, -B, and -DRB1 on the MHC haplotypes. (B) DNA microarray images of four unrelated donor–recipient pairs from the study population demonstrating MHC haplotype-matched (upper left), and MHC haplotype-mismatched (HLA-A, upper right; HLA-DRB1, lower left; HLA-A and -DRB1, lower right) relationships. The two haplotypes in each sample were separated by hybridizing genomic DNA to an array that was spotted with oligonucleotide probes, each specific for one of the two HLA-B alleles in the sample. After haplotype separation, the HLA-A and HLA-DRB1 alleles carried on each haplotype were identified with the use of 57 HLA-A and 64 HLA-DRB1 oligonucleotide probes as described [32]. Actual quadruplicate hybridization patterns for 16 of the probes illustrate how the two possible alleles at each locus could be distinguished from each other. Each column of panels in the figure shows the pattern of probe hybridization with one of the two MHC haplotypes from each sample. Allele assignments are indicated above each hybridization pattern. The HLA-B probe hybridization patterns validate the linkage of HLA-B alleles with HLA-A and -DRB1 alleles. Sequences and specificity of probes can be found in [32].

Figure 2. Clinical Outcome after Haplotype-Matched (Solid Line) and Haplotype-Mismatched (Broken Line) Unrelated Donor HCT

All patients in the study were HLA-A, B, C, DRB1, DQB1 allele matched with their donors. (A) Probability of grades III–IV acute GVHD. (B) Probability of recurrent malignancy. (C) Probability of transplant-related mortality. (D) Probability of survival. One patient in the mismatched group had recurrent malignancy at 14.4 y, and one patient in the mismatched group died without recurrent malignancy at 13.2 y. Seven mismatched patients are alive without recurrent malignancy from 11.9–14.1 y, and nine mismatched patients are alive from 11.0–14.5 y. Twenty-three patients in the matched group are alive without recurrent malignancy from 10.2–18.5 y, and 28 matched patients are alive from 10.2–18.5 y. Each of these patients is indicated as censored at 10 y in (B), (C), and (D).