HLA Is a Determinant Of The Ethnic Predisposition Of Chronic Lymphocytic Leukemia

Introduction Chronic Lymphocytic Leukemia (CLL) displays remarkable ethnic predisposition for Caucasians with a lower incidence of disease in African Americans and relative sparing of Asian Populations. In addition, CLL displays one of the highest familial predispositions of all hematologic malignancies, yet the genetic basis for these differences is not fully defined. Large scale genome wide association studies (GWAS) of CLL have identified the Human Leukocyte Antigen (HLA) locus and other loci associated with the development of CLL but the contribution of individual HLA alleles has not been extensively examined. The National Marrow Donor Program (NMDP) registry contains a large number of disease cases and donor controls across multiple populations as well as high quality classical HLA typing, making it a powerful source of data for inferring HLA associations for hematologic diseases. Using the NMDP dataset, we report the largest study of the HLA associations for chronic lymphocytic leukemia (CLL) to date. Methods Cases consisted of 2,689 US Caucasian and 298 African-American patients with CLL who underwent HLA typing performed for allogeneic donor search reported to the National Marrow Donor Program (NMDP). 50,000 controls were randomly selected for each population from US individuals who voluntarily enrolled in the NMDP unrelated donor registry. To address ambiguous haplotype phasing inherent to HLA typing, we used population haplotype frequencies to calculate probabilities for genotypes for each possible pair of HLA haplotypes. We then incorporated this typing ambiguity into a statistical model using multiple imputation, allowing us to report high-resolution allele, haplotype, and genotype associations. Patients and controls were compared using multivariate logistic regression using a generalized linear model for the covariates of age, birthdate, gender, and geographical location. To control for multiple testing, we adjusted p-values using False Discovery Rate with a cutoff of 0.05. Results We identified several HLA alleles that are associated with an increased susceptibility to the development of CLL as well as several alleles that are protective in the Caucasian as well as the African American (AA) US population. In Caucasians, A*02:01 (OR = 1.203, p = 0.00053), B*15:01 (OR = 1.264, p = 0.0105), B*38:01 (OR = 1.396, p = 0.0198), DRB1*04:02 (OR = 1.675, p = 0.0006) and DRB1*07:01 (OR = 1.223, p = 0.0006) were predisposing and A*01:01 (OR = 0.849, p = 0.01077), B*08:01 (OR = 0.853, p = 0.0437), B*27:05 (OR = 0.743, p = 0.0356) were protective. For African Americans, we find a different collection of high resolution HLA alleles: B*37:01, B*15:17 and DRB1*09:01 were predisposing to the development of CLL (OR 3.017, 3.089 and 2.144, respectively) with highly statistically significant p-values (0.0344, 0.0344, 0.00057, respectively). At the allele family level, B*44 was found to be protective in both Caucasian (OR = 0.843, p = 0.0115) and AA populations (OR = 0.485, p = 0.0309). The allele family C*07 (OR 0.848, p = 0.0046) was protective in Caucasians while C*04 was protective in AA populations (OR = 0.645, p = 0.0422). Association results also revealed additive effects of individual predisposing alleles within the same haplotype, such as the A*02:01∼C*06:02∼B*13:02∼DRB1*07:01 haplotype, which had a higher odds ratio (OR = 2.2, p = 0.000086) than either A*02:01 or DRB1*07:01. We performed a population risk analysis by applying the currently identified allelic disease associations for Caucasians to the known allele frequency seen in other populations, and determined that HLA allele frequency differences contribute to the lower risk of CLL development for both the AA and Asian populations. Conclusions We have identified several HLA associations that confer increased risk of development of CLL in both U.S. Caucasians and African Americans as well as several protective alleles. These results confirm the previously identified association with HLA*02:01 (OR 1.32, Di Bernardo, et al) with highly similar odds ratio. In addition, we identify many HLA allele associations that have not been previously observed due to low statistical power. Differences in HLA predispositions and HLA allele frequency between Caucasian, AA and Asian populations contribute to the difference in incidence of CLL in these populations and may confer inherent biologic differences due to their impact on immune surveillance. Disclosures: Hill: Celgene: Honoraria, Research Funding.

The prevalence ofCryptosporidiumspecies and subtypes in human faecal samples in Ireland

SUMMARYCryptosporidiumis an important cause of diarrhoeal disease worldwide and, as several recent waterborne outbreaks have shown, poses a significant threat to public health in Ireland. We identified theCryptosporidiumspp. in 199 positive human stool samples by PCR–RFLP of the 18S rRNA and COWP gene loci. Subspecies were identified in 104 samples by sequence analysis of the 60 kDa glycoprotein (gp60) gene fragment. OverallC. parvumwas identified in 80%, andC. hominisin 20% of cases. No otherCryptosporidiumspp. were detected.C. parvumwas by far the most common species in the rural, more sparsely populated west of Ireland and exhibited a pronounced spring peak coincident with a peak in the national cryptosporidiosis incidence rate. Our data indicated a trend towards higher proportions ofC. hominisin older age groups. Ninety-nine per cent of all subtypedC. parvumisolates belonged to allele family IIa, of which allele IIaA18G3R1 was by far the most common (63%). According to a recent study by Thompson and colleagues [Parasitology Research(2007),100, 619–624] this allele is also the most common in Irish cattle. Subtyping of theC. hominisisolates indicated that they belonged to a geographically widely distributed allele (IbA10G2) known to have caused several water- and foodborne outbreaks around the world. The predominance ofC. parvum, its geographic and seasonal distribution and the IIaA18G3R1 subtype underlines the importance of zoonoticCryptosporidiumtransmission in Ireland.

Missense mutation of the interleukin-12 receptor β1 chain–encoding gene is associated with impaired immunity againstMycobacterium avium complex infection

Interleukin-12 (IL-12) plays an important role in the production of interferon gamma (IFN-γ) and is essential for protection against intracellular pathogens such as Mycobacterium andSalmonella. A 31-year-old man had disseminatedMycobacterium avium complex (MAC) infection. The production of IFN-γ by peripheral blood mononuclear cells stimulated with phytohemagglutinin (PHA-PBMCs) was found severely impaired (40.7 pg/mL compared with 833 ± 289 pg/mL for the patient's and healthy subjects' (n = 3) PHA- PBMCs, respectively), and the patient's PHA-PBMCs completely lacked surface IL-12 receptor β1 (IL-12Rβ1) chain. The IL-12Rβ1 gene transcript in his PHA-PBMCs had an R213W substitution in each allele. Family history showed that both parents were heterozygotes in the R213W substitution. Transfection of a human embryonal kidney cell line 293 (HEKC293) with wild-type IL-12Rβ1wt gene led to cell surface IL-12Rβ1 expression; however, no expression was seen in HEKC293 transfected with the mutated IL-12Rβ1R213W gene. TheIL-12Rβ1 gene transcript, but no IL-12Rβ1 protein, was detected in PHA-PBMCs and T cells, suggesting a post-translational event(s), most likely a shortened turnover of the protein. The R213W substitution was not detected in the cells of 32 healthy persons or of 25 patients with tuberculosis or MAC infection. Six amino acid substitutions (Q214R, M365T, G378R, H438Y, A525T, and G594E) were identified, but the incidences of such substitutions were not significantly different between the groups. The Q214R substitution is reportedly linked to IL-12Rβ1 deficiency; however, the study showed that 19 and 10 of 57 Japanese and 6 and 4 of 33 healthy white persons were heterozygous and homozygous for Arg-214, respectively, suggesting that the Q214R substitution represents a polymorphism and is not related to IL-12Rβ1 deficiency but that the R213W substitution is responsible for IL-12Rβ1 deficiency.