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Summary:Traditional qualitative gel electrophoresis approaches lack accurate and quantitative assessment of mixed chimerism in BMT patients. The likelihood of informative markers is greatly increased using simultaneous amplification of 10 highly polymorphic loci with fluorescent-labeled primers in an automated DNA sequencer. This allows for more precise interpretation of mixed chimerism with a detection level approximating 1%. To evaluate this approach to quantitative assessment of chimeric populations we mixed varying proportions of samples from two unrelated donors, by either mixing aliquots of DNA isolated from whole blood, or by first counting the white blood cells and mixing varying proportions of cells together prior to DNA isolation. The allelic-peak area ratios were identical to allelic-peak height ratios and corresponded to the proportion of mixed DNA, regardless of the method used to create the mixture. Formulas to provide routine, consistent and quantitative interpretation of mixed chimerism are presented. We analyzed 14 allograft recipients and one autologous BMT patient with transfusion-induced GVHD. In all cases, at least four out of nine markers were informative. Inter-laboratory concordance of results was also obtained with an eight marker panel using an automated Alf-Express. In conclusion, the automated DNA fluorescent-labeled primer approach using an eight to 10 marker panel is quantitative and informative in assessing chimerism.

The human leukocyte antigen (HLA) class II genotype DQA1*0301-DQB1*0302/DQA1*0501-DQB1*0201 has been identified as a marker strongly predisposing to insulin-dependent diabetes mellitus (IDDM) in Caucasian populations. Its frequency in control populations (1-3%) is still, however, 1 order of magnitude higher than the prevalence of IDDM, suggesting that its penetrance can be modified by protective factors. In this study we searched for such a factor in the DRB1 locus by studying DRB1*04 polymorphism in 174 European Caucasian IDDM patients and 73 nondiabetic control subjects, all sharing the HLA-DR3/DR4 phenotype. Significant protection was encoded by the DRB1*0403 allele, which was observed in 5 of 49 control subjects (10%) and none of 171 IDDM patients (0%) with the DQA1*0301-DQB1*0302/DQA1*0501-DQB1*0201 genotype (RR = 0.02 [0.01-0.18], P < 0.0005). These data support the concept that protective HLA class II genes can overrule the risk caused by HLA-DQ susceptibility dimers. They also contribute to a possible strategy to screen for nondiabetic individuals with increased genetic risk of developing IDDM.

The polymorphic variable number of tandem repeats in the 5' upstream region of the human insulin gene is a well-known non-human leukocyte antigen locus contributing to genetic susceptibility to IDDM. Controversy exists about the question as to whether INS susceptibility haplotypes are or are not preferentially inherited together with HLA-DR4 haplotypes. We investigated whether genetic interaction between INS and the HLA complex can be better defined using DQ genotypic and phenotypic markers in addition to DR serology. The 5' INS 1/1 genotype was positively associated with IDDM both in non-DR4 subjects (relative risk = 4.3; 95% confidence interval, 1.6-11.5) and DR4 subjects (relative risk = 4.2; 95% confidence interval, 1.9-9.0). Further subdivision of IDDM patients and matched control subjects according to HLA-DQA1 and HLA-DQB1 genotype or phenotype also failed to show any association between 5' INS and HLA class II genes in diabetic patients. The 5' INS and HLA class II polymorphisms therefore provide independent risk markers, which may both contribute to the genetic screening of a high-risk population among nondiabetic individuals.

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