Sequence-based typing of major histocompatibility complex class I chain-related gene A alleles by use of exons 2-5 information

The impact of MICB mismatches in unrelated haematopoietic stem cell transplantation

MICA polymorphisms have been associated with increased incidence of acute GvHD and adverse outcome in allogeneic haematopoietic stem cell transplantation (HSCT). MICB is another expressed member of MHC class I-related chain genes and its impact on HSCT outcome is yet to be fully defined. We typed a large cohort of patients and donors for MICB polymorphisms and investigated the impact of MICB matching on outcome after unrelated HSCT. 69.2% of the patients were 10/10 human leukocyte antigen (HLA) matched and 30.8% were 9/10 HLA matched. MICB typing was performed using a short amplicon-based NGS typing assay on the Illumina MiSeq platform. Differences in proteins were considered as mismatches. MICA polymorphisms were identified as possible confounder and were therefore included as parameter in the multivariate analyses. Due to the strong linkage disequilibrium with the classical HLA-genes, sub-stratification for HLA matching status was necessary, and no effect of MICB mismatches was seen in the 10/10 HLA matched group when compared to the MICB matched cases. However, in the 9/10 HLA matched group, MICB mismatched cases showed significantly worse disease free survival (DFS), GvHD and relapse free survival (GRFS) compared to the MICB matched cases (DFS: HR 1.24, p = 0.011; GRFS: HR 1.26, p = 0.002). MICA mismatches had no impact on any outcome parameter. According to our findings, effects previously attributed to MICA differences may have been confounded by MICB polymorphisms. We show that MICB differences contribute a small but relevant effect in 9/10 HLA-matched transplantations, which in turn highlights the possible usefulness of MICB typing in donor selection among similarly suitable 9/10 matched donors, especially when HLA-B mismatches have to be accepted.

MICA-129 Dimorphism and Soluble MICA Are Associated With the Progression of Multiple Myeloma

Natural killer (NK) cells are immune innate effectors playing a pivotal role in the immunosurveillance of multiple myeloma (MM) since they are able to directly recognize and kill MM cells. In this regard, among activating receptors expressed by NK cells, NKG2D represents an important receptor for the recognition of MM cells, being its ligands expressed by tumor cells, and being able to trigger NK cell cytotoxicity. The MHC class I-related molecule A (MICA) is one of the NKG2D ligands; it is encoded by highly polymorphic genes and exists as membrane-bound and soluble isoforms. Soluble MICA (sMICA) is overexpressed in the serum of MM patients, and its levels correlate with tumor progression. Interestingly, a methionine (Met) to valine (Val) substitution at position 129 of the α2 heavy chain domain classifies the MICA alleles into strong (MICA-129Met) and weak (MICA-129Val) binders to NKG2D receptor. We addressed whether the genetic polymorphisms in the MICA-129 alleles could affect MICA release during MM progression. The frequencies of Val/Val, Val/Met, and Met/Met MICA-129 genotypes in a cohort of 137 MM patients were 36, 43, and 22%, respectively. Interestingly, patients characterized by a Val/Val genotype exhibited the highest levels of sMICA in the sera. In addition, analysis of the frequencies of MICA-129 genotypes among different MM disease states revealed that Val/Val patients had a significant higher frequency of relapse. Interestingly, NKG2D was downmodulated in NK cells derived from MICA-129Met/Met MM patients. Results obtained by structural modeling analysis suggested that the Met to Val dimorphism could affect the capacity of MICA to form an optimal template for NKG2D recognition. In conclusion, our findings indicate that the MICA-129Val/Val variant is associated with significantly higher levels of sMICA and the progression of MM, strongly suggesting that the usage of soluble MICA as prognostic marker has to be definitely combined with the patient MICA genotype.

Matching for the MICA-129 polymorphism is beneficial in unrelated hematopoietic stem cell transplantation

Major histocompatibility complex class I polypeptide-related sequence A (MICA) is a highly polymorphic ligand of the activating NKG2D receptor on natural killer (NK) cells, γδ-T cells, and NKT cells. MICA incompatibilities have been associated with an increased graft-versus-host disease (GVHD) incidence, and the MICA-129 (met/val) dimorphism has been shown to influence NKG2D signaling in unrelated hematopoietic stem cell transplantation (uHSCT). We investigated the effect of MICA matching on survival after uHSCT. We sequenced 2172 patients and their respective donors for MICA. All patients and donors were high-resolution HLA-typed and matched for 10/10 (n = 1379), 9/10 (n = 636), or 8/10 (n = 157) HLA alleles. Within each HLA match group, cases matched and mismatched for MICA and MICA-129 were analyzed for the end points overall survival (OS), disease-free survival (DFS), nonrelapse mortality (NRM), relapse-incidence (RI), and GVHD. Mismatches at the MICA locus as well as MICA-129 increased with the number of HLA mismatches (MICA mismatched 10/10, 9.2% [n = 127]; 9/10, 22.3% [n = 142]; 8/10, 38.2% [n = 60]; MICA-129 mismatched 10/10, 3.9% [n = 54]; 9/10, 10.2% [n = 65]; 8/10, 17.2% [n = 27]). Adverse OS was observed in the 10/10 match group if MICA-129 was mismatched (10/10, hazard ratio [HR], 1.77; confidence interval [CI], 1.22-2.57; P = .003). MICA-129 mismatches correlated with a significantly worse outcome for DFS in the 10/10 HLA match group (HR, 1.77; CI, 1.26-2.50; P = .001). Higher rates of aGVHD were seen in MICA-129 mismatched cases. Our results indicate that MICA-129 matching is relevant in uHSCT. Prospective typing of patients and donors in unrelated donor search may identify mismatches for MICA-129, and compatible donor selection may improve outcome for this small but high-risk subgroup.

Genotoxic Stress Induces Senescence-Associated ADAM10-Dependent Release of NKG2D MIC Ligands in Multiple Myeloma Cells

Genotoxic stress can promote antitumor NK cell responses by upregulating the surface expression of activating ligands on cancer cells. Moreover, a number of studies suggested a role for soluble NK group 2D ligands in the impairment of NK cell tumor recognition and killing. We investigated whether genotoxic stress could promote the release of NK group 2D ligands (MHC class I-related chain [MIC]A and MICB), as well as the molecular mechanisms underlying this event in human multiple myeloma (MM) cells. Our results show that genotoxic agents used in the therapy of MM (i.e., doxorubicin and melphalan) selectively affect the shedding of MIC molecules that are sensitive to proteolytic cleavage, whereas the release of the short MICA*008 allele, which is frequent in the white population, is not perturbed. In addition, we found that a disintegrin and metalloproteinase 10 expression is upregulated upon chemotherapeutic treatment both in patient-derived CD138(+)/CD38(+) plasma cells and in several MM cell lines, and we demonstrate a crucial role for this sheddase in the proteolytic cleavage of MIC by means of silencing and pharmacological inhibition. Interestingly, the drug-induced upregulation of a disintegrin and metalloproteinase 10 on MM cells is associated with a senescent phenotype and requires generation of reactive oxygen species. Moreover, the combined use of chemotherapeutic drugs and metalloproteinase inhibitors enhances NK cell-mediated recognition of MM cells, preserving MIC molecules on the cell surface and suggesting that targeting of metalloproteinases in conjunction with chemotherapy could be exploited for NK cell-based immunotherapeutic approaches, thus contributing to avoid the escape of malignant cells from stress-elicited immune responses.

Microarrays for high-throughput genotyping of MICA alleles using allele-specific primer extension

The role of major histocompatibility complex (MHC) class I chain-related gene A (MICA), a ligand of NKG2D, has been defined in human diseases by its allele associations with various autoimmune diseases, hematopoietic stem cell transplantation (HSCT) and cancer. This study describes a practical system to develop MICA genotyping by allele-specific primer extension (ASPE) on microarrays. From the results of 20 control primers, strict and reliable cut-off values of more than 30,000 mean fluorescence intensity (MFI) as positive and less than 3000 MFI as negative, were applied to select high-quality specific extension primers. Among 55 allele-specific primers, 44 primers could be initially selected as optimal primer. Through adjusting the length, six primers were improved. The other failed five primers were corrected by refractory modification. MICA genotypes by ASPE on microarrays showed the same results as those by nucleotide sequencing. On the basis of these results, ASPE on microarrays may provide high-throughput genotyping for MICA alleles for population studies, disease-gene associations and HSCT.

The distribution of MICA alleles in an Austrian population: evidence for increasing polymorphism

The Major Histocompatibility Complex Class I Chain-Related Gene A (MICA) is located 46.4 Kb centromeric to HLA-B locus on chromosome 6; 84 alleles have been described so far. To assess the distribution of MICA alleles in an Austrian population, 322 unrelated Austrian blood donors have been typed for MICA by direct sequencing of amplified exons 2-5; sequencing of exon 6 and separating alleles by haplotype specific primers or by cloning was performed to resolve ambiguities. HLA-B was typed at low level resolution and linkage disequilibrium was determined. We observed 20 already known and four novel MICA alleles. MICA*008:01/04 was the most frequent allele (42%), followed by MICA*002:01 (11%) and MICA*009:01 (9%), three alleles (MICA*029, *067 and *068) were observed only once. No deviation from the Hardy Weinberg equilibrium was observed. Linkage disequilibrium between MICA and HLA-B alleles was observed, most extensively between MICA*008:01/04 and HLA-B*07. Our population data are in agreement with other European populations. The fact that four novel alleles have been observed indicates that the polymorphism of MICA is larger than currently estimated.