Abstract
Minor histocompatibility antigens (mHAg) are T-cell peptide antigens derived from polymorphic endogenous gene products encoded throughout the genome. Despite extensive human genetic diversity, recent experimental evidence suggests that a mHAg set may be limited in size because alloimmune responses directed against them can be dominated by only a few specific peptides. To extend upon these observations, we performed a genome-wide scan to identify susceptibility loci for graft-versus-host disease (GVHD) in a murine model. We previously identified B10.BR (H2k) mice to be resistant, and BALB.K (H2k) mice susceptible, to lethal GVHD when transplanted with hematopoietic cells from MHC-matched AKR/J (H2k) donors (Cao et al. PNAS2003:11571). In the present study B10.BR, BALB.K, or (B10.BR x BALB.K)F1 mice were lethally irradiated and injected with AKR/J bone marrow at radioprotective doses plus 2.0 or 3.0 x 106 purified splenic T-cells. Confirming our prior observations, B10.BR mice survived to day 60 whereas all BALB.K mice died prior to day 10 from GVHD. All (B10.BR x BALB.K)F1 mice also died after a median of 10 days, indicating that GVHD susceptibility in BALB.K mice is a dominant trait. (B10.BR x BALB.K)F1 mice were then backcrossed to the GVHD-resistant B10.BR parent. Resulting [B10.BR x (B10.BR x BALB.K)]BC mice (n = 180) were genotyped and similarly irradiated and injected with AKR/J bone marrow plus 3.0 x 106 splenic T-cells. Forty (22%) BC mice died with signs of GVHD prior to day 100. Surprisingly, a 90-marker genome-wide scan for this phenotype, lethal GVHD prior to day 100, revealed highly significant linkage (P <.001) only to chromosome 16. Linkage analysis was performed with MapManager QTX 0.29 using Kosambi’s map function. As shown in Figure 1, interval mapping for chromosome 16 with additional markers revealed a broad and complex linkage pattern encompassing 2 markers, D16Mit4 (27.3 cM) and D16Mit189 (55.2 cM), that had peak LOD scores of 8.8 and 8.0 respectively. Another genetic locus on chromosome 13 flanked by markers D13Mit248 and D13Mit149 with a peak LOD score of 2.3 by interval mapping was suggestively linked. While an evaluation of candidate genes within the support intervals is in progress, these results thus far suggest that the critical gene dose required for inducing lethal GVHD may be remarkably small. If validated as encoding for immunodominant mHAg, these results furthermore suggest that a functionally relevant mHAg set may be definable for clinical genotyping.
Genome-wide association analyses identify two susceptibility loci for pachychoroid disease central serous chorioretinopathy