Frequency distribution of HLA class I and II alleles in Greek population and their significance in orchestrating the National Donor Registry Program.

Human leukocyte antigens (HLA) represent one of the most polymorphic systems in humans, responsible for the identification of foreign antigens and the presentation of immune responses. Therefore, HLA is considered to play a major role in human disorders, donor-recipient matching and transplantation outcomes. This study aimed to determine the HLA class I and II alleles and haplotypes in the Greek population. Moreover, a comparative analysis of HLA alleles and haplotype frequencies found in Greek and pooled European populations was also performed to acquire a better knowledge about the HLA alleles distribution. A total number of 1896 healthy individuals were typed for their HLA alleles in the National Tissue Typing Center of Greece. High-resolution HLA typing for the HLA-A, -B, -C and -DR, -DQ, -DP with the use of the next-generation sequencing analysis was performed, followed by data analysis for establishing the HLA allele and haplotype differences. The results of this study showed that the most frequent alleles for the HLA-A were the A*02:01:01 (27.1%), *24:02:01 (14.4%), *01:01:01 (9.3%), for the HLA-B were the B*51:01:01 (15.3%), *18:01:01 (9.7%), *35:01:01 (6.8%) and for the HLA-C were the C*04:01:01 (15.4%), *07:01:01 (13.1%), *12:03:01 (9.6%). For the HLA class II, the most frequent alleles for the HLA-DRB1 were the DRB1*11:04:01 (16.4%), *16:01:01 (11.3%), *11:01:01 (9.5%), for the HLA-DQB1 were the DQB1*03:01:01 (30.5%), *05:02:01 (15.1%), *05:01:01 (10.6%) and for the HLA-DPB1 were the DPB1*04:01:01 (34.8%), *02:01:01 (11.6%), *04:02:01 (7.3%). Additionally, the most frequent haplotypes were the A*02:01:01∼C*07:01:01-B*18:01:01∼DRB1*11:04:01 (2.3%), followed by the A*01:01:01∼C*07:01:01∼B*08:01:01∼DRB1*03:01:01 (2.2%), A*24:02:01∼C*04:01:01∼B*35:02:01∼DRB1*11:04:01 (1.4%) and A*02:01:01∼C*04:01:01∼B*35:01:01-DRB1*14:01:01 (1.2%). The results herein were comparable to those obtained from the pooled European populations. Moreover, these results can be used for the improvement of the donor-recipient matching procedure and to understand better the disease association in Greece.

T cell receptor gene repertoire profiles in subgroups of patients with chronic lymphocytic leukemia bearing distinct genomic aberrations.

Background: Microenvironmental interactions of the malignant clone with T cells are critical throughout the natural history of chronic lymphocytic leukemia (CLL). Indeed, clonal expansions of T cells and shared clonotypes exist between different CLL patients, strongly implying clonal selection by antigens. Moreover, immunogenic neoepitopes have been isolated from the clonotypic B cell receptor immunoglobulin sequences, offering a rationale for immunotherapeutic approaches. Here, we interrogated the T cell receptor (TR) gene repertoire of CLL patients with different genomic aberration profiles aiming to identify unique signatures that would point towards an additional source of immunogenic neoepitopes for T cells. Experimental design: TR gene repertoire profiling using next generation sequencing in groups of patients with CLL carrying one of the following copy-number aberrations (CNAs): del(11q), del(17p), del(13q), trisomy 12, or gene mutations in TP53 or NOTCH1. Results: Oligoclonal expansions were found in all patients with distinct recurrent genomic aberrations; these were more pronounced in cases bearing CNAs, particularly trisomy 12, rather than gene mutations. Shared clonotypes were found both within and across groups, which appeared to be CLL-biased based on extensive comparisons against TR databases from various entities. Moreover, in silico analysis identified TR clonotypes with high binding affinity to neoepitopes predicted to arise from TP53 and NOTCH1 mutations. Conclusions: Distinct TR repertoire profiles were identified in groups of patients with CLL bearing different genomic aberrations, alluding to distinct selection processes. Abnormal protein expression and gene dosage effects associated with recurrent genomic aberrations likely represent a relevant source of CLL-specific selecting antigens.

An Approach to Identify HLA Class II Immunogenic Epitopes in the Greek Population through Machine Learning Algorithms.

Current pre-transplantation routine matching involves serum anti-HLA antibodies quantification but cannot always preclude unfavorable graft outcomes. Epitope-based matching is proposed as a more precise approach, but to date no epitope-matching algorithm provides a satisfactory predictive tool for transplantation outcomes. In this study, anti-HLA-II loci responses from 1748 patients were analyzed with unsupervised machine learning algorithms, namely principal component analysis (PCA) and antigenic distances, projected as dendrograms. PCA for anti-HLA-DR anti-bodies revealed three main clusters of responses: anti-HLA-DR51 combined with anti-HLA-DRB1*01, anti-HLA-DR52 combined with anti-HLA-DRB1*08 and anti-HLA-DR53 combined with anti-HLA-DRB1*10. The dendrogram for anti-HLA-DR confirmed the pattern and showed further bisection of each cluster. Common epitopes present exclusively in all HLA molecules of each cluster were determined following the HLA epitope registry. Thus, we propose that 19 out of 123 HLA-DR epitopes are those that mainly lead anti-HLA-DR responses in the studied population. Likewise, we identified 22 out of 83 epitopes responsible for anti-HLA-DQ and 13 out of 62 responsible for anti-HLA-DP responses. Interpretation of these results may elucidate mechanisms of interlocus cross-reactivity, providing an alternative way of estimating the significance of each epitope in a population and thus suggesting a novel strategy towards optimal donor selection.

Hidden Patterns of Anti-HLA Class I Alloreactivity Revealed Through Machine Learning.

Detection of alloreactive anti-HLA antibodies is a frequent and mandatory test before and after organ transplantation to determine the antigenic targets of the antibodies. Nowadays, this test involves the measurement of fluorescent signals generated through antibody-antigen reactions on multi-beads flow cytometers. In this study, in a cohort of 1,066 patients from one country, anti-HLA class I responses were analyzed on a panel of 98 different antigens. Knowing that the immune system responds typically to "shared" antigenic targets, we studied the clustering patterns of antibody responses against HLA class I antigens without any a priori hypothesis, applying two unsupervised machine learning approaches. At first, the principal component analysis (PCA) projections of intra-locus specific responses showed that anti-HLA-A and anti-HLA-C were the most distantly projected responses in the population with the anti-HLA-B responses to be projected between them. When PCA was applied on the responses against antigens belonging to a single locus, some already known groupings were confirmed while several new cross-reactive patterns of alloreactivity were detected. Anti-HLA-A responses projected through PCA suggested that three cross-reactive groups accounted for about 70% of the variance observed in the population, while anti-HLA-B responses were mainly characterized by a distinction between previously described Bw4 and Bw6 cross-reactive groups followed by several yet undocumented or poorly described ones. Furthermore, anti-HLA-C responses could be explained by two major cross-reactive groups completely overlapping with previously described C1 and C2 allelic groups. A second feature-based analysis of all antigenic specificities, projected as a dendrogram, generated a robust measure of allelic antigenic distances depicting bead-array defined cross reactive groups. Finally, amino acid combinations explaining major population specific cross-reactive groups were described. The interpretation of the results was based on the current knowledge of the antigenic targets of the antibodies as they have been characterized either experimentally or computationally and appear at the HLA epitope registry.

Associations of ABO, D, and Lewis blood groups and HLA Class I and Class II alleles with West Nile virus Lineage 2 disease outcome in Greece, 2010 to 2013.

BACKGROUND: West Nile virus (WNV) infection, commonly asymptomatic, may cause mild West Nile fever (WNF) or potentially fatal neuroinvasive disease (WNND). An outbreak of 262 cases of the new Lineage 2 strain in Greece in 2010 continued with high mortality (17%) in WNND. The objective was to investigate ABO, D, and Lewis blood groups, as well as HLA Class I and Class II alleles, in relation to WNV Lineage 2 disease morbidity. STUDY DESIGN AND METHODS: A cohort of 132 Greek WNV cases in 2010 to 2013 (65% male; mean age 64 years; 41% WNF, 59% WNND) was compared to 51,339 healthy WNV-negative blood donors and 246 healthy subjects. RESULTS: Blood group A was more common in WNV cases (51%) than blood donors (39%) and group O less common (32% vs. 42%). D negativity within group A was higher in WNV than in blood donors (18% vs. 10%, p = 0.044). The frequency of secretors (Lewis(a-b+)) was 60% in WNV and 68% in donors (p = 0.16). HLA alleles C*08, DRB1*O4:O5, and DQB1*O2 occurred significantly less frequently in WNV than controls (p < 0.05 unadjusted for multiple testing) and DRB1*10:O1 more frequently (p = 0.039). CONCLUSION: This first study of symptomatic WNV Lineage 2 suggests A/D negativity as a new risk factor associated with WNV infection and level of morbidity. Further studies are required of the possibility that HLA C*08, DRB1*O4:O5, and DQB1*O2 are protective alleles and DRB1*10:O1 a "susceptible" allele to WNV infection and the role of secretor status in relation to WNV infection.

Antigen Selection Shapes the T-cell Repertoire in Chronic Lymphocytic Leukemia.

PURPOSE: The role of antigen(s) in shaping the T-cell repertoire in chronic lymphocytic leukemia, although relevant for understanding malignant cell interactions with cognate T cells, is largely unexplored. EXPERIMENTAL DESIGN: Here we profiled the T-cell receptor ß chain gene repertoire in 58 chronic lymphocytic leukemia patients, focusing on cases assigned to well-characterized subsets with stereotyped clonotypic B-cell receptor immunoglobulins, therefore those cases most evidently selected by antigen (subsets #1, #2, and #4). RESULTS: Remarkable repertoire skewing and oligoclonality were observed, and differences between subsets were noted regarding both T-cell receptor ß chain gene usage and the extent of clonality, with subset #2 being the least oligoclonal. Longitudinal analysis of subset #4 cases revealed that although the repertoire may fluctuate over time, certain clonotypes persist, thus alluding to persistent antigenic stimulation. Shared ("stereotyped") clonotypes were found between different patients, reflecting selection by common antigenic elements. Cross-comparison of our dataset with public databases showed that some T-cell clonotypes may have expanded secondary to common viral infections; however, the majority of clonotypes proved to be disease-specific. CONCLUSIONS: Overall, the T-cell receptor ß chain repertoire in chronic lymphocytic leukemia is likely shaped by antigen selection and the implicated antigenic elements may concern epitopes that also select the malignant B-cell progenitors or, more intriguingly, chronic lymphocytic leukemia-derived epitopes.

Familial CD3+ T large granular lymphocyte leukemia: evidence that genetic predisposition and antigen selection promote clonal cytotoxic T-cell responses.

CD3+ T-large granular lymphocyte (T-LGL) proliferations often present with cytopenias and splenomegaly and are linked to autoimmunity, especially rheumatoid arthritis and Felty's syndrome. We report here the intra-family occurrence of T-LGL leukemia in a father and son, both presenting with cytopenias and splenomegaly. Both patients carried the HLA-DRB1*04 allele, strongly associated with rheumatoid arthritis and Felty's syndrome, exhibited distinctive histopathological features suggestive of immune-mediated suppression of hematopoiesis and expressed a remarkably skewed T-cell receptor beta chain gene repertoire with overtime evolution (clonal drift). Immunoinformatics analysis and comparisons with clonotype sequences from various entities revealed (quasi)identities between (i) father and son, and (ii) father or son and patients with autoimmune disorders, T-LGL leukemia or chronic idiopathic neutropenia. Altogether, our results further corroborate antigen selection in the ontogeny of T-LGL leukemia and point to the interplay between genetics and the (micro)environment in shaping the outcome of cytotoxic T cell responses.