Major histocompatibility complex class II polymorphisms in primates

Exploring genetic diversity and variation of Ovar-DRB1 gene in Sudan Desert Sheep using targeted next-generation sequencing

INTRODUCTION

The Ovar-DRB1 gene, a crucial element of the Major Histocompatibility Complex (MHC) Class II region, initiates adaptive immunity by presenting antigens to T-cells. Genetic diversity in sheep, particularly in MHC Class II genes like Ovar-DRB1, directly influences the specturm of presented antigens impacting immune responses and disease susceptability. Understanding the allelic diversity of Ovar-DRB1 gene in Sudan Desert Sheep (SDS) is essential for uncovering the genetic basis of immune responses and disease resistance, given the the breeds significance in Sudan's unique environment.

METHODS

Utilizing Targeted Next-Generation Sequencing (NGS) we explore allelic diversity in Ovar-DRB1 gene within SDS. Successfully ampliying and and sequencing the second exon of this gene in 288 SDS samples representing six breeds provided a comprehensive allelic profile, enabling a detalied examination of the gene's genetic makeup.

RESULTS

We identifed forty-six alleles, including four previously unreported, enrichness the genetic diversity of SDS breeds. These alleles exhibiting non-uniform distribution, varying frequencies across breeds, indicating a breed-specific genetic landscape. Certain alleles, known and novel, show higher frequencies in specific populations, suggesting potential associations with adaptive immune responses. Identifying these alleles sets the stage for investigating their functional roles and implications for disease resistance. Genetic differentiation among SDS breeds, as indicated by FST values and clustering analyses, highlights a unique genetic makeup shaped by geographic and historical factors. These differentiation patterns among SDS breeds have broader implications for breed conservation and targeted breeding to enhance disease resistance in specific populations.

CONCLUSION

This study unveils Ovar-DRB1 gene allelic diversity in SDS breeds through targeted NGS and genetic analyses, revealing new alleles that underscore the breeds' unique genetic profile. Insights into the genetic factors governing immune responses and disease resistance emerge, promising for optimization of breeding strategies for enhanced livestock health in Sudan's unique environment.

Recent selection created distinctive variability patterns on MHC class II loci in three dolphin species from the Mediterranean Sea

The major histocompatibility complex (MHC) includes highly polymorphic genes involved in antigen presentation, which is crucial for adaptive immune response. They represent fitness related genetic markers particularly informative for populations exposed to environmental challenges. Here we analyse the diversity and evolutionary traits of MHC class II DQA and DQB genes in the dolphins Stenella coeruleoalba and Grampus griseus from the Mediterranean Sea. We found substantial nucleotide and functional diversity, as well as strong evidence of balancing selection indicated by allele and supertype frequencies, Tajima's D statistics and dN/dS tests. The Risso's dolphin, considered the least abundant in the region, showed the effect of divergent allele advantage at the nucleotide and functional-peptide levels. An outstanding polymorphism was found in the striped dolphin, particularly intriguing in the DQA gene where the Ewens-Watterson test detected a selection sweep that occurred in recent history. We hypothesize that morbillivirus, which has recurrently invaded Mediterranean populations over the last decades, exerted the detected selective pressure.

The KIR repertoire of a West African chimpanzee population is characterized by limited gene, allele, and haplotype variation

Introduction

The killer cell immunoglobulin-like receptors (KIR) play a pivotal role in modulating the NK cell responses, for instance, through interaction with major histocompatibility complex (MHC) class I molecules. Both gene systems map to different chromosomes but co-evolved during evolution. The human KIR gene family is characterized by abundant allelic polymorphism and copy number variation. In contrast, our knowledge of the KIR repertoire in chimpanzees is limited to 39 reported alleles, with no available population data. Only three genomic KIR region configurations have been mapped, and seventeen additional ones were deduced by genotyping.

Methods

Previously, we documented that the chimpanzee MHC class I repertoire has been skewed due to an ancient selective sweep. To understand the depth of the sweep, we set out to determine the full-length KIR transcriptome - in our MHC characterized pedigreed West African chimpanzee cohort - using SMRT sequencing (PacBio). In addition, the genomic organization of 14 KIR haplotypes was characterized by applying a Cas9-mediated enrichment approach in concert with long-read sequencing by Oxford Nanopore Technologies.

Results

In the cohort, we discovered 35 undescribed and 15 already recorded Patr-KIR alleles, and a novel hybrid KIR gene. Some KIR transcripts are subject to evolutionary conserved alternative splicing events. A detailed insight on the KIR region dynamics (location and order of genes) was obtained, however, only five new KIR region configurations were detected. The population data allowed to investigate the distribution of the MHC-C1 and C2-epitope specificity of the inhibitory lineage III KIR repertoire, and appears to be skewed towards C2.

Discussion

Although the KIR region is known to evolve fast, as observed in other primate species, our overall conclusion is that the genomic architecture and repertoire in West African chimpanzees exhibit only limited to moderate levels of variation. Hence, the ancient selective sweep that affected the chimpanzee MHC class I region may also have impacted the KIR system.

Epstein-Barr virus-acquired immunodeficiency in myalgic encephalomyelitis-Is it present in long COVID?

Both myalgic encephalomyelitis or chronic fatigue syndrome (ME/CFS) and long COVID (LC) are characterized by similar immunological alterations, persistence of chronic viral infection, autoimmunity, chronic inflammatory state, viral reactivation, hypocortisolism, and microclot formation. They also present with similar symptoms such as asthenia, exercise intolerance, sleep disorders, cognitive dysfunction, and neurological and gastrointestinal complaints. In addition, both pathologies present Epstein-Barr virus (EBV) reactivation, indicating the possibility of this virus being the link between both pathologies. Therefore, we propose that latency and recurrent EBV reactivation could generate an acquired immunodeficiency syndrome in three steps: first, an acquired EBV immunodeficiency develops in individuals with "weak" EBV HLA-II haplotypes, which prevents the control of latency I cells. Second, ectopic lymphoid structures with EBV latency form in different tissues (including the CNS), promoting inflammatory responses and further impairment of cell-mediated immunity. Finally, immune exhaustion occurs due to chronic exposure to viral antigens, with consolidation of the disease. In the case of LC, prior to the first step, there is the possibility of previous SARS-CoV-2 infection in individuals with "weak" HLA-II haplotypes against this virus and/or EBV.

Long-read assembly of major histocompatibility complex and killer cell immunoglobulin-like receptor genome regions in cynomolgus macaque

BACKGROUND

The major histocompatibility complex (MHC) and the killer cell immunoglobulin-like receptors (KIR) are key regulators of immune responses. The cynomolgus macaque, an Old World monkey species, can be applied as an important preclinical model for studying human diseases, including coronavirus disease 2019 (COVID-19). Several MHC-KIR combinations have been associated with either a poor or good prognosis. Therefore, macaques with a well-characterized immunogenetic profile may improve drug evaluation and speed up vaccine development. At present, a complete overview of the MHC and KIR haplotype organizations in cynomolgus macaques is lacking, and characterization by conventional techniques is hampered by the extensive expansion of the macaque MHC-B region that complicates the discrimination between genes and alleles.

METHODS

We assembled complete MHC and KIR genomic regions of cynomolgus macaque using third-generation long-read sequencing approach. We identified functional Mafa-B loci at the transcriptome level using locus-specific amplification in a cohort of 33 Vietnamese cynomolgus macaques.

RESULTS

This is the first physical mapping of complete MHC and KIR gene regions in a Vietnamese cynomolgus macaque. Furthermore, we identified four functional Mafa-B loci (B2, B3, B5, and B6) and showed that alleles of the Mafa-I*01, -B*056, -B*034, and -B*001 functional lineages, respectively, are highly frequent in the Vietnamese cynomolgus macaque population.

CONCLUSION

The insights into the MHC and KIR haplotype organizations and the level of diversity may refine the selection of animals with specific genetic markers for future medical research.

Dynamic evolution of Mhc haplotypes in cynomolgus macaques of different geographic origins

The major histocompatibility complex (MHC) plays a key role in immune defense, and the Mhc genes of cynomolgus macaque display a high degree of polymorphism. Based on their geographic distribution, different populations of cynomolgus macaques are recognized. Here we present the characterization of the Mhc class I and II repertoire of a large pedigreed group of cynomolgus macaques originating from the mainland north of the isthmus of Kra (N = 42). Segregation analyses resulted in the definition of 81 unreported Mafa-A/B/DRB/DQ/DP haplotypes, which include 32 previously unknown DRB regions. In addition, we report 13 newly defined Mafa-A/B/DRB/DQ/DP haplotypes in a group of cynomolgus macaques originating from the mainland south of the isthmus of Kra/Maritime Southeast Asia (N = 16). A relatively high level of sharing of Mafa-A (51%) and Mafa-B (40%) lineage groups is observed between the populations native to the north and the south of isthmus of Kra. At the allelic level, however, the Mafa-A/B haplotypes seem to be characteristic of a population. An overall comparison of all currently known data revealed that each geographic population has its own specific combinations of Mhc class I and II haplotypes. This illustrates the dynamic evolution of the cynomolgus macaque Mhc region, which was most likely generated by recombination and maintained by selection due to the differential pathogenic pressures encountered in different geographic areas.

CD4+ Cytotoxic T Cells Involved in the Development of EBV-Associated Diseases

Activated cytotoxic CD4 T cells (HLA-DR+) play an important role in the control of EBV infection, especially in cells with latency I (EBNA-1). One of the evasion mechanisms of these latency cells is generated by gp42, which, via peripherally binding to the β1 domain of the β chain of MHC class II (HLA-DQ, -DR, and -DP) of the infected B lymphocyte, can block/alter the HLA class II/T-cell receptor (TCR) interaction, and confer an increased level of susceptibility towards the development of EBV-associated autoimmune diseases or cancer in genetically predisposed individuals (HLA-DRB1* and DQB1* alleles). The main developments predisposing the factors of these diseases are: EBV infection; HLA class II risk alleles; sex; and tissue that is infiltrated with EBV-latent cells, forming ectopic lymphoid structures. Therefore, there is a need to identify treatments for eliminating cells with EBV latency, because the current treatments (e.g., antivirals and rituximab) are ineffective.

Epstein-Barr Virus and the Origin of Myalgic Encephalomyelitis or Chronic Fatigue Syndrome

Myalgic encephalomyelitis or chronic fatigue syndrome (ME/CFS) affects approximately 1% of the general population. It is a chronic, disabling, multi-system disease for which there is no effective treatment. This is probably related to the limited knowledge about its origin. Here, we summarized the current knowledge about the pathogenesis of ME/CFS and revisit the immunopathobiology of Epstein-Barr virus (EBV) infection. Given the similarities between EBV-associated autoimmune diseases and cancer in terms of poor T cell surveillance of cells with EBV latency, expanded EBV-infected cells in peripheral blood and increased antibodies against EBV, we hypothesize that there could be a common etiology generated by cells with EBV latency that escape immune surveillance. Albeit inconclusive, multiple studies in patients with ME/CFS have suggested an altered cellular immunity and augmented Th2 response that could result from mechanisms of evasion to some pathogens such as EBV, which has been identified as a risk factor in a subset of ME/CFS patients. Namely, cells with latency may evade the immune system in individuals with genetic predisposition to develop ME/CFS and in consequence, there could be poor CD4 T cell immunity to mitogens and other specific antigens, as it has been described in some individuals. Ultimately, we hypothesize that within ME/CFS there is a subgroup of patients with DRB1 and DQB1 alleles that could confer greater susceptibility to EBV, where immune evasion mechanisms generated by cells with latency induce immunodeficiency. Accordingly, we propose new endeavors to investigate if anti-EBV therapies could be effective in selected ME/CFS patients.

Major histocompatibility complex class II DR and DQ evolution and variation in wild capuchin monkey species (Cebinae)

The major histocompatibility complex (MHC) is an important gene complex contributing to adaptive immunity. Studies of platyrrhine MHC have focused on identifying experimental models of immune system function in the equivalent Human Leukocyte Antigen (HLA). These genes have thus been explored primarily in captive platyrrhine individuals from research colonies. However, investigations of standing MHC variation and evolution in wild populations are essential to understanding its role in immunity, sociality and ecology. Capuchins are a promising model group exhibiting the greatest habitat diversity, widest diet breadth and arguably the most social complexity among platyrrhines, together likely resulting in varied immunological challenges. We use high-throughput sequencing to characterize polymorphism in four Class II DR and DQ exons for the first time in seven capuchin species. We find evidence for at least three copies for DQ genes and at least five for DRB, with possible additional unrecovered diversity. Our data also reveal common genotypes that are inherited across our most widely sampled population, Cebus imitator in Sector Santa Rosa, Costa Rica. Notably, phylogenetic analyses reveal that platyrrhine DQA sequences form a monophyletic group to the exclusion of all Catarrhini sequences examined. This result is inconsistent with the trans-species hypothesis for MHC evolution across infraorders in Primates and provides further evidence for the independent origin of current MHC genetic diversity in Platyrrhini. Identical allele sharing across cebid species, and more rarely genera, however, does underscore the complexity of MHC gene evolution and the need for more comprehensive assessments of allelic diversity and genome structure.

Two Human Monoclonal HLA-Reactive Antibodies Cross-React with Mamu-B*008, a Rhesus Macaque MHC Allotype Associated with Control of Simian Immunodeficiency Virus Replication

MHC class I molecules play an important role in adaptive immune responses against intracellular pathogens. These molecules are highly polymorphic, and many allotypes have been characterized. In a transplantation setting, a mismatch between MHC allotypes may initiate an alloimmune response. Rhesus macaques (Macaca mulatta, Mamu) are valuable as a preclinical model species in transplantation research as well as to evaluate the safety and efficacy of vaccine candidates. In both lines of research, the availability of nonhuman primate MHC-reactive mAbs may enable in vitro monitoring and detection of presence of particular Mamu molecules. In this study, we screened a collection of thoroughly characterized HLA class I-specific human mAbs for cross-reactivity with rhesus macaque MHC class I allotypes. Two mAbs, OK4F9 and OK4F10, recognize an epitope that is defined by isoleucine (I) at amino acid position 142 that is present on the Indian rhesus macaque Mamu-B*008:01 allotype, which is an allotype known to be associated with elite control of SIV replication. The reactive pattern of a third mAb, MUS4H4, is more complex and includes an epitope shared on Mamu-A2*05:01 and -B*001:01-encoded Ags. This is the first description, to our knowledge, of human HLA-reactive mAbs that can recognize Mamu allotypes, and these can be useful tools for in vitro monitoring the presence of the relevant allelic products. Moreover, OK4F9 and OK4F10 can be powerful mAbs for application in SIV-related research.

Similar patterns of genetic diversity and linkage disequilibrium in Western chimpanzees (Pan troglodytes verus) and humans indicate highly conserved mechanisms of MHC molecular evolution

BACKGROUND

Many species are threatened with extinction as their population sizes decrease with changing environments or face novel pathogenic threats. A reduction of genetic diversity at major histocompatibility complex (MHC) genes may have dramatic effects on populations' survival, as these genes play a key role in adaptive immunity. This might be the case for chimpanzees, the MHC genes of which reveal signatures of an ancient selective sweep likely due to a viral epidemic that reduced their population size a few million years ago. To better assess how this past event affected MHC variation in chimpanzees compared to humans, we analysed several indexes of genetic diversity and linkage disequilibrium across seven MHC genes on four cohorts of chimpanzees and we compared them to those estimated at orthologous HLA genes in a large set of human populations.

RESULTS

Interestingly, the analyses uncovered similar patterns of both molecular diversity and linkage disequilibrium across the seven MHC genes in chimpanzees and humans. Indeed, in both species the greatest allelic richness and heterozygosity were found at loci A, B, C and DRB1, the greatest nucleotide diversity at loci DRB1, DQA1 and DQB1, and both significant global linkage disequilibrium and the greatest proportions of haplotypes in linkage disequilibrium were observed at pairs DQA1 ~ DQB1, DQA1 ~ DRB1, DQB1 ~ DRB1 and B ~ C. Our results also showed that, despite some differences among loci, the levels of genetic diversity and linkage disequilibrium observed in contemporary chimpanzees were globally similar to those estimated in small isolated human populations, in contrast to significant differences compared to large populations.

CONCLUSIONS

We conclude, first, that highly conserved mechanisms shaped the diversity of orthologous MHC genes in chimpanzees and humans. Furthermore, our findings support the hypothesis that an ancient demographic decline affecting the chimpanzee populations - like that ascribed to a viral epidemic - exerted a substantial effect on the molecular diversity of their MHC genes, albeit not more pronounced than that experienced by HLA genes in human populations that underwent rapid genetic drift during humans' peopling history. We thus propose a model where chimpanzees' MHC genes regenerated molecular variation through recombination/gene conversion and/or balancing selection after the selective sweep.

Nucleotide diversity of functionally different groups of immune response genes in Old World camels based on newly annotated and reference-guided assemblies

Background

Immune-response (IR) genes have an important role in the defense against highly variable pathogens, and therefore, diversity in these genomic regions is essential for species’ survival and adaptation. Although current genome assemblies from Old World camelids are very useful for investigating genome-wide diversity, demography and population structure, they have inconsistencies and gaps that limit analyses at local genomic scales. Improved and more accurate genome assemblies and annotations are needed to study complex genomic regions like adaptive and innate IR genes.

Results

In this work, we improved the genome assemblies of the three Old World camel species – domestic dromedary and Bactrian camel, and the two-humped wild camel – via different computational methods. The newly annotated dromedary genome assembly CamDro3 served as reference to scaffold the NCBI RefSeq genomes of domestic Bactrian and wild camels. These upgraded assemblies were then used to assess nucleotide diversity of IR genes within and between species, and to compare the diversity found in immune genes and the rest of the genes in the genome. We detected differences in the nucleotide diversity among the three Old World camelid species and between IR gene groups, i.e., innate versus adaptive. Among the three species, domestic Bactrian camels showed the highest mean nucleotide diversity. Among the functionally different IR gene groups, the highest mean nucleotide diversity was observed in the major histocompatibility complex.

Conclusions

The new camel genome assemblies were greatly improved in terms of contiguity and increased size with fewer scaffolds, which is of general value for the scientific community. This allowed us to perform in-depth studies on genetic diversity in immunity-related regions of the genome. Our results suggest that differences of diversity across classes of genes appear compatible with a combined role of population history and differential exposures to pathogens, and consequent different selective pressures.

Comparative genetics of the major histocompatibility complex in humans and nonhuman primates

The major histocompatibility complex (MHC) is one of the most gene-dense regions of the mammalian genome. Multiple genes within the human MHC (HLA) show extensive polymorphism, and currently, more than 26,000 alleles divided over 39 different genes are known. Nonhuman primate (NHP) species are grouped into great and lesser apes and Old and New World monkeys, and their MHC is studied mostly because of their important role as animal models in preclinical research or in connection with conservation biology purposes. The evolutionary equivalents of many of the HLA genes are present in NHP species, and these genes may also show abundant levels of polymorphism. This review is intended to provide a comprehensive comparison relating to the organization and polymorphism of human and NHP MHC regions.

Construction and benchmarking of a multi-ethnic reference panel for the imputation of HLA class I and II alleles

Genotype imputation of the human leukocyte antigen (HLA) region is a cost-effective means to infer classical HLA alleles from inexpensive and dense SNP array data. In the research setting, imputation helps avoid costs for wet lab-based HLA typing and thus renders association analyses of the HLA in large cohorts feasible. Yet, most HLA imputation reference panels target Caucasian ethnicities and multi-ethnic panels are scarce. We compiled a high-quality multi-ethnic reference panel based on genotypes measured with Illumina’s Immunochip genotyping array and HLA types established using a high-resolution next generation sequencing approach. Our reference panel includes more than 1,300 samples from Germany, Malta, China, India, Iran, Japan and Korea and samples of African American ancestry for all classical HLA class I and II alleles including HLA-DRB3/4/5. Applying extensive cross-validation, we benchmarked the imputation using the HLA imputation tool HIBAG, our multi-ethnic reference and an independent, previously published data set compiled of subpopulations of the 1000 Genomes project. We achieved average imputation accuracies higher than 0.924 for the commonly studied HLA-A, -B, -C, -DQB1 and -DRB1 genes across all ethnicities. We investigated allele-specific imputation challenges in regard to geographic origin of the samples using sensitivity and specificity measurements as well as allele frequencies and identified HLA alleles that are challenging to impute for each of the populations separately. In conclusion, our new multi-ethnic reference data set allows for high resolution HLA imputation of genotypes at all classical HLA class I and II genes including the HLA-DRB3/4/5 loci based on diverse ancestry populations.

Insights into the polymorphism in HLA-DRA and its evolutionary relationship with HLA haplotypes

HLA-DRA encodes the alpha chain of the HLA-DR protein, one of the classical HLA class II molecules. Reported polymorphism within HLA-DRA is currently limited compared with other HLA genes, as only a single polymorphism encodes an amino acid difference in the translated protein. Since this SNP (rs7192, HLA00662.1:g.4276G>T p.Val217Leu) lies within exon 4, in the region encoding the cytoplasmic tail, the resulting protein is effectively monomorphic. For this reason, in-depth studies on HLA-DRA and its function have been limited. However, analysis of sequences from the 1000 Genomes Project and preliminary data from our lab reveals unrepresented polymorphism within HLA-DRA, suggesting a more complex role within the MHC than previously assumed. This study focuses on elucidating the extent of HLA-DRA polymorphism, and extending our understanding of the gene's role in HLA-DR~HLA-DQ haplotypes. Ninety-eight samples were sequenced for full-length HLA-DRA, and from this analysis, we identified 20 novel SNP positions in the intronic sequences within the 5711 bp region represented in IPD-IMGT/HLA. This polymorphism gives rise to at least 22 novel HLA-DRA alleles, and the patterns of intronic and 3' UTR polymorphism correspond to HLA-DRA~HLA-DRB345~HLA-DRB1~HLA-DQB1 haplotypes. The current understanding of the organization of the genes within the HLA-DR region assumes a single lineage for the HLA-DRA gene, as opposed to multiple gene lineages, such as in HLA-DRB. This study suggests that the intron and 3' UTR polymorphism of HLA-DRA indicates different lineages, and represents the HLA-DRA~HLA-DRB345~HLA-DRB1~HLA-DQB1 haplotypes.

Nomenclature report 2019: major histocompatibility complex genes and alleles of Great and Small Ape and Old and New World monkey species

The major histocompatibility complex (MHC) is central to the innate and adaptive immune responses of jawed vertebrates. Characteristic of the MHC are high gene density, gene copy number variation, and allelic polymorphism. Because apes and monkeys are the closest living relatives of humans, the MHCs of these non-human primates (NHP) are studied in depth in the context of evolution, biomedicine, and conservation biology. The Immuno Polymorphism Database (IPD)-MHC NHP Database (IPD-MHC NHP), which curates MHC data of great and small apes, as well as Old and New World monkeys, has been upgraded. The curators of the database are responsible for providing official designations for newly discovered alleles. This nomenclature report updates the 2012 report, and summarizes important nomenclature issues and relevant novel features of the IPD-MHC NHP Database.

Divergence between genes but limited allelic polymorphism in two MHC class II A genes in Leach's storm-petrels Oceanodroma leucorhoa

The major histocompatibility complex (MHC) is critical to host-pathogen interactions. Class II MHC is a heterodimer, with α and β subunits encoded by different genes. The peptide-binding groove is formed by the first domain of both subunits (α₁ and β₁), but studies of class II variation or natural selection focus primarily on the β subunit and II B genes. We explored MHC II A in Leach's storm-petrel, a seabird with two expressed, polymorphic II B genes. We found two II A genes, Ocle-DAA and Ocle-DBA, in contrast to the single II A gene in chicken and duck. In exon 2 which encodes the α₁ domain, the storm-petrel II A genes differed strongly from each other but showed little within-gene polymorphism in 30 individuals: just one Ocle-DAA allele, and three Ocle-DBA alleles differing from each other by single non-synonymous substitutions. In a comparable sample, the two II B genes had nine markedly diverged alleles each. Differences between the α₁ domains of Ocle-DAA and Ocle-DBA showed signatures of positive selection, but mainly at non-peptide-binding site (PBS) positions. In contrast, positive selection within and between the II B genes corresponded to putative PBS codons. Phylogenetic analysis of the conserved α₂ domain did not reveal deep or well-supported lineages of II A genes in birds, in contrast to the pronounced differentiation of DQA, DPA, and DRA isotypes in mammals. This uncertain homology complicates efforts to compare levels of functional variation and modes of evolution of II A genes across taxa.

The Cynomolgus Macaque MHC Polymorphism in Experimental Medicine

Among the non-human primates used in experimental medicine, cynomolgus macaques (Macaca fascicularis hereafter referred to as Mafa) are increasingly selected for the ease with which they are maintained and bred in captivity. Macaques belong to Old World monkeys and are phylogenetically much closer to humans than rodents, which are still the most frequently used animal model. Our understanding of the Mafa genome has progressed rapidly in recent years and has greatly benefited from the latest technical advances in molecular genetics. Cynomolgus macaques are widespread in Southeast Asia and numerous studies have shown a distinct genetic differentiation of continental and island populations. The major histocompatibility complex of cynomolgus macaque (Mafa MHC) is organized in the same way as that of human, but it differs from the latter by its high degree of classical class I gene duplication. Human polymorphic MHC regions play a pivotal role in allograft transplantation and have been associated with more than 100 diseases and/or phenotypes. The Mafa MHC polymorphism similarly plays a crucial role in experimental allografts of organs and stem cells. Experimental results show that the Mafa MHC class I and II regions influence the ability to mount an immune response against infectious pathogens and vaccines. MHC also affects cynomolgus macaque reproduction and impacts on numerous biological parameters. This review describes the Mafa MHC polymorphism and the methods currently used to characterize it. We discuss some of the major areas of experimental medicine where an effect induced by MHC polymorphism has been demonstrated.

Evolution of the magic bullet: Single chain antibody fragments for the targeted delivery of immunomodulatory proteins

Immunocytokines are fusion proteins that combine the specific antigen binding capacities of an antibody or derivative thereof and the potent bioactivity of a cytokine partner. These novel biopharmaceuticals have been directed to various targets of oncological as well as non-oncological origin and a handful of promising constructs are currently advancing in the clinical trial pipeline. Several factors such as the choice of a disease specific antigen, the antibody format and the modulatory nature of the payload are crucial, not only for therapeutic efficacy and safety but also for the commercial success of such a product. In this review, we provide an overview of the basic principles and obstacles in immunocytokine design with a specific focus on single chain antibody fragment-based constructs that employ interleukins as the immunoactive component. Impact statement Selective activation of the immune system in a variety of malignancies represents an attractive approach when existing strategies have failed to provide adequate treatment options. Immunocytokines as a novel class of bifunctional protein therapeutics have emerged recently and generated promising results in preclinical and clinical studies. In order to harness their full potential, multiple different aspects have to be taken into consideration. Several key points of these fusion constructs are discussed here and should provide an outline for the development of novel products based on an overview of selected formats.

No postcopulatory selection against MHC-homozygous offspring: Evidence from a pedigreed captive rhesus macaque colony

The heterozygosity status of polymorphic elements of the immune system, such as the major histocompatibility complex (MHC), is known to increase the potential to cope with a wider variety of pathogens. Pre- and postcopulatory processes may regulate MHC heterozygosity. In a population where mating occurs among individuals that share identical MHC haplotypes, postcopulatory selection may disfavour homozygous offspring or ones with two MHC haplotypes identical to its mother. We tested these ideas by determining the incidence of MHC-heterozygous and MHC-homozygous individuals in a pedigreed, partially consanguineous captive rhesus monkey colony. Bayesian statistics showed that when parents share MHC haplotypes, the distribution of MHC-heterozygous and MHC-homozygous individuals significantly fitted the expected Mendelian distribution, both for the complete MHC haplotypes, and for MHC class I or II genes separately. Altogether, we found in this captive colony no evidence for postcopulatory selection against MHC-homozygous individuals. However, the distribution of paternally and maternally inherited MHC haplotypes tended to differ significantly from expected. Individuals with two MHC haplotypes identical to their mother were underrepresented and offspring with MHC haplotypes identical to their father tended to be overrepresented. This suggests that postcopulatory processes affect MHC haplotype combination in offspring, but do not prevent low MHC heterozygosity.

Comparative genomics of the human, macaque and mouse major histocompatibility complex

The MHC is a highly polymorphic genomic region that encodes the transplantation and immune regulatory molecules. It receives special attention for genetic investigation because of its important role in the regulation of innate and adaptive immune responses and its strong association with numerous infectious and/or autoimmune diseases. The MHC locus was first discovered in the mouse and for the past 50 years it has been studied most intensively in both mice and humans. However, in recent years the macaque species have emerged as some of the more important and advanced experimental animal models for biomedical research into MHC with important human immunodeficiency virus/simian immunodeficiency virus and transplantation studies undertaken in association with precise MHC genotyping and haplotyping methods using Sanger sequencing and next-generation sequencing. Here, in this special issue on 'Macaque Immunology' we provide a short review of the genomic similarities and differences among the human, macaque and mouse MHC class I and class II regions, with an emphasis on the association of the macaque class I region with MHC polymorphism, haplotype structure and function.

The influence of positive selection and trans-species evolution on DPB diversity in the golden snub-nosed monkeys (Rhinopithecus roxellana)

Genetic variation plays a significant role in the adaptive potential of the endangered species. The variation at major histocompatibility complex (MHC) genes can offer valuable information on selective pressure related to natural selection and environmental adaptation, particularly the ability of a host to continuously resist evolving parasites. Thus, the genetic polymorphism on exon 2 of the MHC DPB1 gene in the golden snub-nosed monkeys (Rhinopithecus roxellana) was specifically analyzed. The results show that the 6 Rhro-DPB1 alleles identified from 87 individuals exhibit positive selection and trans-species polymorphism. The results also imply that although the populations of the species have experienced dramatic reduction and severe habitat fragmentation in recent Chinese history, balancing selection still maintains relatively consistent, with moderate DPB1 polymorphism. Thus, the study provides valuable information and evidence in developing effective strategies and tactics for genetic health and population size expansion of the species. It also offers strong genetic background for further studies on other primate species, particularly those in Rhinopithecus-a further endeavor that would result in fully understanding the MHC genetic information of the Asian colobines.

Next-generation genotyping of hypervariable loci in many individuals of a non-model species: technical and theoretical implications

BACKGROUND

Across species, diversity at the Major Histocompatibility Complex (MHC) is critical to disease resistance and population health; however, use of MHC diversity to quantify the genetic health of populations has been hampered by the extreme variation found in MHC genes. Next generation sequencing (NGS) technology generates sufficient data to genotype even the most diverse species, but workflows for distinguishing artifacts from alleles are still under development. We used NGS to evaluate the MHC diversity of over 300 captive and wild ring-tailed lemurs (Lemur catta: Primates: Mammalia). We modified a published workflow to address errors that arise from deep sequencing individuals and tested for evidence of selection at the most diverse MHC genes.

RESULTS

In addition to evaluating the accuracy of 454 Titanium and Ion Torrent PGM for genotyping large populations at hypervariable genes, we suggested modifications to improve current methods of allele calling. Using these modifications, we genotyped 302 out of 319 individuals, obtaining an average sequencing depth of over 1000 reads per amplicon. We identified 55 MHC-DRB alleles, 51 of which were previously undescribed, and provide the first sequences of five additional MHC genes: DOA, DOB, DPA, DQA, and DRA. The additional five MHC genes had one or two alleles each with little sequence variation; however, the 55 MHC-DRB alleles showed a high dN/dS ratio and trans-species polymorphism, indicating a history of positive selection. Because each individual possessed 1-7 MHC-DRB alleles, we suggest that ring-tailed lemurs have four, putatively functional, MHC-DRB copies.

CONCLUSIONS

In the future, accurate genotyping methods for NGS data will be critical to assessing genetic variation in non-model species. We recommend that future NGS studies increase the proportion of replicated samples, both within and across platforms, particularly for hypervariable genes like the MHC. Quantifying MHC diversity within non-model species is the first step to assessing the relationship of genetic diversity at functional loci to individual fitness and population viability. Owing to MHC-DRB diversity and copy number, ring-tailed lemurs may serve as an ideal model for estimating the interaction between genetic diversity, fitness, and environment, especially regarding endangered species.

The major histocompatibility complex in Old World camelids and low polymorphism of its class II genes

BACKGROUND

The Major Histocompatibility Complex (MHC) is a genomic region containing genes with crucial roles in immune responses. MHC class I and class II genes encode antigen-presenting molecules expressed on the cell surface. To counteract the high variability of pathogens, the MHC evolved into a region of considerable heterogeneity in its organization, number and extent of polymorphism. Studies of MHCs in different model species contribute to our understanding of mechanisms of immunity, diseases and their evolution. Camels are economically important domestic animals and interesting biomodels. Three species of Old World camels have been recognized: the dromedary (Camelus dromedarius), Bactrian camel (Camelus bactrianus) and the wild camel (Camelus ferus). Despite their importance, little is known about the MHC genomic region, its organization and diversity in camels. The objectives of this study were to identify, map and characterize the MHC region of Old World camelids, with special attention to genetic variation at selected class MHC II loci.

RESULTS

Physical mapping located the MHC region to the chromosome 20 in Camelus dromedarius. Cytogenetic and comparative analyses of whole genome sequences showed that the order of the three major sub-regions is "Centromere - Class II - Class III - Class I". DRA, DRB, DQA and DQB exon 2 sequences encoding the antigen binding site of the corresponding class II antigen presenting molecules showed high degree of sequence similarity and extensive allele sharing across the three species. Unexpectedly low extent of polymorphism with low numbers of alleles and haplotypes was observed in all species, despite different geographic origins of the camels analyzed. The DRA locus was found to be polymorphic, with three alleles shared by all three species. DRA and DQA sequences retrieved from ancient DNA samples of Camelus dromedarius suggested that additional polymorphism might exist.

CONCLUSIONS

This study provided evidence that camels possess an MHC comparable to other mammalian species in terms of its genomic localization, organization and sequence similarity. We described ancient variation at the DRA locus, monomorphic in most species. The extent of molecular diversity of MHC class II genes seems to be substantially lower in Old World camels than in other mammalian species.

The fully synthetic MAG-Tn3 therapeutic vaccine containing the tetanus toxoid-derived TT830-844 universal epitope provides anti-tumor immunity

Malignant transformations are often associated with aberrant glycosylation processes that lead to the expression of new carbohydrate antigens at the surface of tumor cells. Of these carbohydrate antigens, the Tn antigen is particularly highly expressed in many carcinomas, especially in breast carcinoma. We designed MAG-Tn3, a fully synthetic vaccine based on three consecutive Tn moieties that are O-linked to a CD4⁺ T cell epitope, to induce anti-Tn antibody responses that could be helpful for therapeutic vaccination against cancer. To ensure broad coverage within the human population, the tetanus toxoid-derived peptide TT830-844 was selected as a T-helper epitope because it can bind to various HLA-DRB molecules. We showed that the MAG-Tn3 vaccine, which was formulated with the GSK proprietary immunostimulant AS15 and designed for human cancer therapy, is able to induce an anti-Tn antibody response in mice of various H-2 haplotypes, and this response correlates with the ability to induce a specific T cell response against the TT830-844 peptide. The universality of the TT830-844 peptide was extended to new H-2 and HLA-DRB molecules that were capable of binding this T cell epitope. Finally, the MAG-Tn3 vaccine was able to induce anti-Tn antibody responses in cynomolgus monkeys, which targeted Tn-expressing tumor cells and mediated tumor cell death both in vitro and in vivo. Thus, MAG-Tn3 is a highly promising anticancer vaccine that is currently under evaluation in a phase I clinical trial.

Major histocompatibility complex and mate choice in the polygynous primate: the Sichuan snub-nosed monkey (Rhinopithecus roxellana)

The highly polymorphic genes within the major histocompatibility complex (MHC) not only play a major role in immunity resistance, but also seem to provide hints for mate choice in some animal populations. In the present study we investigated MHC-related mate choice in a small natural population (group size 40-55 individuals) of a polygynous primate, the Sichuan snub-nosed monkey (Rhinopithecus roxellana). We found that there was no evidence either for MHC-disassortative mating, or for females to mate with males based on MHC heterozygosity or specific alleles. Nevertheless, of the 11 alleles identified, we found that the frequencies of 2 alleles, Rhro-DRB2 (P < 0.01) and Rhro-DRB5 (P < 0.05) were higher in offspring than in their parents. These findings suggest that MHC-DRB in this population of R. roxellana is unlikely to be associated with mating preferences. Limited female opportunities for mate choice are likely due, in part, to the harem breeding structure present in R. roxellana, and the relatively small number of resident adult males in our study band (N = 4-6). In addition, we suggest that differences in the frequency of particular alleles across generations may be linked to parasite resistance in a fluctuating environment; however, confirmation of this finding requires further study.

Immunogenicity of protein therapeutics: The key causes, consequences and challenges

The immunogenicity of protein therapeutics has so far proven to be difficult to predict in patients, with many biologics inducing undesirable immune responses directed towards the therapeutic resulting in reduced efficacy, anaphylaxis and occasionally life threatening autoimmunity. The most common effect of administrating an immunogenic protein therapeutic is the development of a high affinity anti-therapeutic antibody response. Furthermore, it is clear from clinical studies that protein therapeutics derived from endogenous human proteins are capable of stimulating undesirable immune responses in patients, and as a consequence, the prediction and reduction of immunogenicity has been the focus of intense research. This review will outline the principle causes of the immunogenicity in protein therapeutics, and describe the development of pre-clinical models that can be used to aid in the prediction of the immunogenic potential of novel protein therapeutics prior to administration in man.

A human-specific allelic group of the MHC DRB1 gene in primates

Background

Diversity among human leukocyte antigen (HLA) molecules has been maintained by host-pathogen coevolution over a long period of time. Reflecting this diversity, the HLA loci are the most polymorphic in the human genome. One characteristic of HLA diversity is long-term persistence of allelic lineages, which causes trans-species polymorphisms to be shared among closely related species. Modern humans have disseminated across the world after their exodus from Africa, while chimpanzees have remained in Africa since the speciation event between humans and chimpanzees. It is thought that modern humans have recently acquired resistance to novel pathogens outside Africa. In the present study, we investigated HLA alleles that could contribute to this local adaptation in humans and also studied the contribution of natural selection to human evolution by using molecular data.

Results

Phylogenetic analysis of HLA-DRB1 genes identified two major groups, HLA Groups A and B. Group A formed a monophyletic clade distinct from DRB1 alleles in other Catarrhini, suggesting that Group A is a human-specific allelic group. Our estimates of divergence time suggested that seven HLA-DRB1 Group A allelic lineages in humans have been maintained since before the speciation event between humans and chimpanzees, while chimpanzees possess only one DRB1 allelic lineage (Patr-DRB1*03), which is a sister group to Group A. Experimental data showed that some Group A alleles bound to peptides derived from human-specific pathogens. Of the Group A alleles, three exist at high frequencies in several local populations outside Africa.

Conclusions

HLA Group A alleles are likely to have been retained in human lineages for a long period of time and have not expanded since the divergence of humans and chimpanzees. On the other hand, most orthologs of HLA Group A alleles may have been lost in the chimpanzee due to differences in selective pressures. The presence of alleles with high frequency outside of Africa suggests these HLA molecules result from the local adaptations of humans. Our study helps elucidate the mechanism by which the human adaptive immune system has coevolved with pathogens over a long period of time.

Characterising a microsatellite for DRB typing in Aotus vociferans and Aotus nancymaae (Platyrrhini)

Non-human primates belonging to the Aotus genus have been shown to be excellent experimental models for evaluating drugs and vaccine candidates against malaria and other human diseases. The immune system of this animal model must be characterised to assess whether the results obtained here can be extrapolated to humans. Class I and II major histocompatibility complex (MHC) proteins are amongst the most important molecules involved in response to pathogens; in spite of this, the techniques available for genotyping these molecules are usually expensive and/or time-consuming. Previous studies have reported MHC-DRB class II gene typing by microsatellite in Old World primates and humans, showing that such technique provides a fast, reliable and effective alternative to the commonly used ones. Based on this information, a microsatellite present in MHC-DRB intron 2 and its evolutionary patterns were identified in two Aotus species (A. vociferans and A. nancymaae), as well as its potential for genotyping class II MHC-DRB in these primates.

Towards the non-invasive assessment of MHC genotype in wild primates: analysis of wild Assamese macaque MHC-DRB from fecal samples

The major histocompatibility complex (MHC) plays an important role in the immune response and may thus crucially affect an individual's fitness, relevant also for studies on evolutionary ecology and wildlife conservation. Detailed knowledge on the genomic organization, polymorphism and diversity of the MHC has a narrow taxonomic focus though and among macaques is only available for rhesus and long-tailed macaques-the species most commonly kept for biomedical research. The lack of data on wild populations is largely due to the difficulty of obtaining blood or tissue samples necessary for genotyping approaches. Here, we aimed at analyzing MHC-DRB from non-invasively collected fecal samples in wild Assamese macaques (Macaca assamensis), utilizing the MHC-DRB-STR (D6S2878) microsatellite marker. Due to the fecal DNA source incomplete genotypes occurred, which may be improved in the future by method refinement. We detected 28 distinct DRB-STR lengths in 43 individuals with individual genotypes containing 1-9 MHC-DRB-STRs and defined four haplotypes segregating between families in Mendelian fashion. Our results indicate that variability and diversity of MHC-DRB in Assamese macaques is comparable to that of other macaque species and importantly, that fecal samples can be used for non-invasive analysis of MHC genes after refinement of the applied methods, opening a number of opportunities for MHC research on natural populations.

Comprehensive identification of high-frequency and co-occurring Mafa-DPA1, Mafa-DQA1, Mafa-DRA, and Mafa-DOA alleles in Vietnamese cynomolgus macaques

High-frequency alleles and/or co-occurring human leukocyte antigen alleles across loci appear to be more important than individual alleles as markers of disease risk and have clinical value as biomarkers for targeted screening or the development of new disease therapies. To better elucidate the major histocompatibility complex (MHC) background and to facilitate the experimental use of cynomolgus macaques, Mafa-DPA1, Mafa-DQA1, Mafa-DRA, and Mafa-DOA alleles were characterized, and their combinations were investigated in 30 Vietnamese macaques by gene cloning and sequencing. A total of 26 Mafa-DPA1, 18 Mafa-DQA1, 9 Mafa-DRA, and 15 Mafa-DOA alleles, including 7 high-frequency alleles, were identified in this study, respectively. In addition, 15 Mafa-DQA1, 17 Mafa-DPA1, 15 Mafa-DOA, and 2 Mafa-DRA alleles represented novel sequences that had not been documented in earlier studies. Our results also showed that the Vietnamese macaques might be valuable because no less than 30% of the test animals possessed Mafa-DRA*01:02:01 (90%), -DQA1*26:01:03 (37%), -DOA*01:02:07 (34%), and -DQA1*01:03:03 (30%). We previously reported that the combinations of MHC class II alleles, including the combination of DOA*01:02:07-DPA1*02:09 and DOA*01:02:07-DQA1*01:03:03, were detected in 17 and 14% of the animals, respectively. Interestingly, more than two Mafa-DQA1 and Mafa-DPA1 alleles were detected in one animal in this study, which suggested that they might be caused by a chromosomal duplication. If our findings can be validated by other studies, it will further enrich the number of known Mafa-DPA1 and Mafa-DQA1 polymorphisms. Our results identified the co-occurring MHC alleles across loci in a cohort of Vietnamese cynomolgus macaques, which emphasized the value of this species as a model for biomedical research.

Haplotype diversity generated by ancient recombination-like events in the MHC of Indian rhesus macaques

The Mamu-A, Mamu-B, and Mamu-DRB genes of the rhesus macaque show several levels of complexity such as allelic heterogeneity (polymorphism), copy number variation, differential segregation of genes/alleles present on a haplotype (diversity) and transcription level differences. A combination of techniques was implemented to screen a large panel of pedigreed Indian rhesus macaques (1,384 individuals representing the offspring of 137 founding animals) for haplotype diversity in an efficient and inexpensive manner. This approach allowed the definition of 140 haplotypes that display a relatively low degree of region variation as reflected by the presence of only 17 A, 18 B and 22 DRB types, respectively, exhibiting a global linkage disequilibrium comparable to that in humans. This finding contrasts with the situation observed in rhesus macaques from other geographic origins and in cynomolgus monkeys from Indonesia. In these latter populations, nearly every haplotype appears to be characterised by a unique A, B and DRB region. In the Indian population, however, a reshuffling of existing segments generated “new” haplotypes. Since the recombination frequency within the core MHC of the Indian rhesus macaques is relatively low, the various haplotypes were most probably produced by recombination events that accumulated over a long evolutionary time span. This idea is in accord with the notion that Indian rhesus macaques experienced a severe reduction in population during the Pleistocene due to a bottleneck caused by geographic changes. Thus, recombination-like processes appear to be a way to expand a diminished genetic repertoire in an isolated and relatively small founder population.

The significance of non-human primates as preclinical models of human arthritic disease

BACKGROUND

The broad immunological gap between inbred SPF-raised strains of mice and rats and the diverse rheumatoid arthritis (RA) patient population limits the predictive value of the existing disease models for clinical success of new therapies, in particular for those using highly specific biologicals.

OBJECTIVE

This review argues that because of their closer immunological and physiological proximity to patients, disease models in non-human primates (NHPs) may bridge this gap and help reduce the failure of many (± 80%) new therapies in clinical trials. In various research areas, NHPs are an accepted intermediate between disease models in rodents and the ultimate introduction for clinical use in patients. However, with the exception of transplantation, this is not the case for immune-mediated inflammatory disorders, such as RA, although useful preclinical models are being developed.

METHOD

The validity and use of the rhesus monkey model of collagen-induced arthritis as a preclinical RA model is reviewed. The discussion comprises present genetic and immunological aspects, biomarkers, and an overview of published preclinical therapy evaluations.

CONCLUSION

It is time to consider the use of NHPs with a greater evolutionary proximity to humans as models for preclinical evaluation of new human-specific drugs for arthritic disease.

[Polymorphic analysis of Mhc-DPB1 gene exon 2 in Tibetan macaques (Macaca thibetana)]

Major histocompatibility complex (MHC) molecules play an important role in the susceptibility and/or resistance to many diseases. To gain an insight into the MHC background of the Tibetan macaques (Macaca thibetana), and thereby facilitate their protection and application in biomedical research, the second exon of the Mhc-DPB1 genes from 70 Tibetan macaques in Sichuan Province were characterized by PCR, cloning, sequencing, and statistical analysis. A total of 18 Mhc-DPB1 alleles were identified from Tibetan macaques, of which one (Math-DPB1*01:06N) was a pseudogene. Math-DPB1*06:01:01 (67.14%) was the most frequent allele in all the 18 alleles detected, followed by Math-DPB1* 01:03:01 (37.14%), Math-DPB1*09:02 (25.71%), and Math-DPB1*22:01 (15.71%). The alignment of putative amino acid sequences of the 18 Math-DPB1 alleles showed that 5 variable sites were species-specific to Tibetan macaques. A phylogenetic tree constructed using DPB1 alleles in difference species demonstrated that the alleles for Math-DPB1, Mamu-DPB1, and Mafa-DPB1 tended to mix together, rather than cluster into a separate branch in a species-specific fashion, and the Trans-species polymorphism was also observed in the phylogenetic tree. Selection analysis revealed that balancing selection may play an important role in maintaining the polymorphism of Math-DPB1 genes.

Large-scale MHC class II genotyping of a wild lemur population by next generation sequencing

The critical role of major histocompatibility complex (MHC) genes in disease resistance, along with their putative function in sexual selection, reproduction and chemical ecology, make them an important genetic system in evolutionary ecology. Studying selective pressures acting on MHC genes in the wild nevertheless requires population-wide genotyping, which has long been challenging because of their extensive polymorphism. Here, we report on large-scale genotyping of the MHC class II loci of the grey mouse lemur (Microcebus murinus) from a wild population in western Madagascar. The second exons from MHC-DRB and -DQB of 772 and 672 individuals were sequenced, respectively, using a 454 sequencing platform, generating more than 800,000 reads. Sequence analysis, through a stepwise variant validation procedure, allowed reliable typing of more than 600 individuals. The quality of our genotyping was evaluated through three independent methods, namely genotyping the same individuals by both cloning and 454 sequencing, running duplicates, and comparing parent-offspring dyads; each displaying very high accuracy. A total of 61 (including 20 new) and 60 (including 53 new) alleles were detected at DRB and DQB genes, respectively. Both loci were non-duplicated, in tight linkage disequilibrium and in Hardy-Weinberg equilibrium, despite the fact that sequence analysis revealed clear evidence of historical selection. Our results highlight the potential of 454 sequencing technology in attempts to investigate patterns of selection shaping MHC variation in contemporary populations. The power of this approach will nevertheless be conditional upon strict quality control of the genotyping data.

Evolution of HLA-DRB genes

The HLA region shows diversity concerning the number and content of DRB genes present per haplotype. Similar observations are made for the equivalent regions in other primate species. To elucidate the evolutionary history of the various HLA-DRB genes, a large panel of intron sequences obtained from humans, chimpanzees, rhesus macaques, and common marmosets has been subjected to phylogenetic analyses. Special attention was paid to the presence and absence of particular transposable elements and/or to their segments. The sharing of different parts of the same long interspersed nuclear element-2 (LINE2, L2) and various Alu insertions by the species studied demonstrates that one precursor gene must have been duplicated several times before the Old World monkey (OWM) and hominid (HOM) divergence. At least four ancestral DRB gene families appear to have been present before the radiation of OWM and HOM, and one of these even predates the speciation of Old and New World primates. Two of these families represent the pseudogenes DRB6/DRB2 and DRB7, which have been locked in the genomes of various primate species over long evolutionary time spans. Furthermore, all phylogenies of different intron segments show consistently that, apart from the pseudogenes, only DRB5 genes are shared by OWM and HOM, and they demonstrate the common history of certain DRB genes/lineages of humans and chimpanzees. In contrast, the evolutionary history of some other DRB loci is difficult to decipher, thus illustrating the complex history of the evolution of DRB genes due to a combination of mutations and recombination-like events. The selected approach allowed us to shed light on the ancestral DRB gene pool in primates and on the evolutionary relationship of the various HLA-DRB genes.

Multilocus definition of MHC haplotypes in pedigreed cynomolgus macaques (Macaca fascicularis)

Cynomolgus macaques (Macaca fascicularis) are used widely in biomedical research, and the genetics of their MHC (Mhc-Mafa) has become the focus of considerable attention in recent years. The cohort of Indonesian pedigreed macaques that we present here was typed for Mafa-A, -B, and -DR, by sequencing, as described in earlier studies. Additionally, the DRB region of these animals was characterised by microsatellite analyses. In this study, full-length sequencing of Mafa-DPA/B and -DQA/B in these animals was performed. A total of 75 different alleles were observed; 22 of which have not previously been reported, plus 18 extended exon 2 alleles that were already known. Furthermore, two microsatellites, D6S2854 and D6S2859, were used to characterise the complex Mafa-A region. Sequencing and segregation analyses revealed that the length patterns of these microsatellites are unique for each Mafa-A haplotype. In this work, we present a pedigreed colony of approximately 120 cynomolgus macaques; all of which are typed for the most significant polymorphic MHC class I and class II markers. Offspring of these pedigreed animals are easily characterised for their MHC by microsatellite analyses on the Mafa-A and -DRB regions, which makes the cumbersome sequencing analyses redundant.

Engineering reduced-immunogenicity enzymes for amino acid depletion therapy in cancer

Cancer has become the leading cause of death in the developed world and has remained one of the most difficult diseases to treat. One of the difficulties in treating cancer is that conventional chemotherapies often have unacceptable toxicities toward normal cells at the doses required to kill tumor cells. Thus, the demand for new and improved tumor specific therapeutics for the treatment of cancer remains high. Alterations to cellular metabolism constitute a nearly universal feature of many types of cancer cells. In particular, many tumors exhibit deficiencies in one or more amino acid synthesis or salvage pathways forcing a reliance on the extracellular pool of these amino acids to satisfy protein biosynthesis demands. Therefore, one treatment modality that satisfies the objective of developing cancer cell-selective therapeutics is the systemic depletion of that tumor-essential amino acid, which can result in tumor apoptosis with minimal side effects to normal cells. While this strategy was initially suggested over 50 years ago, it has been recently experiencing a renaissance owing to advances in protein engineering technology, and more sophisticated approaches to studying the metabolic differences between tumorigenic and normal cells. Dietary restriction is typically not sufficient to achieve a therapeutically relevant level of amino acid depletion for cancer treatment. Therefore, intravenous administration of enzymes is used to mediate the degradation of such amino acids for therapeutic purposes. Unfortunately, the human genome does not encode enzymes with the requisite catalytic or pharmacological properties necessary for therapeutic purposes. The use of heterologous enzymes has been explored extensively both in animal studies and in clinical trials. However, heterologous enzymes are immunogenic and elicit adverse responses ranging from anaphylactic shock to antibody-mediated enzyme inactivation, and therefore have had limited utility. The one notable exception is Escherichia colil-asparaginase II (EcAII), which has been FDA-approved for the treatment of childhood acute lymphoblastic leukemia. The use of engineered human enzymes, to which natural tolerance is likely to prevent recognition by the adaptive immune system, offers a novel approach for capitalizing on the promising strategy of systemic depletion of tumor-essential amino acids. In this work, we review several strategies that we have developed to: (i) reduce the immunogenicity of a nonhuman enzyme, (ii) engineer human enzymes for novel catalytic specificities, and (iii) improve the pharmacological characteristics of a human enzyme that exhibits the requisite substrate specificity for amino acid degradation but exhibits low activity and stability under physiological conditions.

Frequency of the major histocompatibility complex Mamu-A*01 allele in experimental rhesus macaques in China

BACKGROUND

In Indian rhesus macaques, the major histocompatibility complex Mamu gene, especially the Mamu-A*01 allele, plays an important role in simian immunodeficiency virus susceptibility and disease progression. The Mamu-A*01 allele is one of the protective genes mostly being studied in simian acquired immunodeficiency syndrome.

METHODS

PCR was used to amplify the Mamu-A*01 allele in 130 Chinese-origin rhesus macaques. Identification of the allele was then confirmed by sequencing and IFN-γ ELISPOT assay.

RESULTS

The Mamu-A*01 allele was detected in 3.85% (5 of 130) of the experimental Chinese-origin rhesus macaques. The sequence homology reached 99.1% in comparison with Indian rhesus macaques. A significantly large number of spots were observed in Mamu-A*01-positive monkeys when analyzed by ELISPOT with Gag181-189 epitope stimulation.

CONCLUSIONS

Our study suggests that Mamu-A*01-positive Chinese-origin rhesus monkeys are suitable for use in AIDS studies.

Characterization of the major histocompatibility complex class II DOB, DPB1, and DQB1 alleles in cynomolgus macaques of Vietnamese origin

Major histocompatibility complex (MHC) molecules play an important role in the susceptibility and/or resistance to many diseases. To gain an insight into the MHC background and to facilitate the experimental use of cynomolgus macaques, the second exon of the MhcMafa-DOB, -DPB1, and -DQB1 genes from 143 cynomolgus macaques were characterized by cloning to sequencing. A total of 16 Mafa-DOB, 16 Mafa-DPB1, and 34 Mafa-DQB1 alleles were identified, which revealed limited, moderate, and marked allelic polymorphism at DOB, DPB1, and DQB1, respectively, in a cohort of cynomolgus macaques of Vietnamese origin. In addition, 16 Mafa-DOB, 5 Mafa-DPB1, and 8 Mafa-DQB1 alleles represented novel sequences that had not been reported in earlier studies. Almost of the sequences detected at the DOB and DQB1 locus in the present study belonged to DOB*01 (100%) and DQB1*06 (62%) lineages, respectively. Interestingly, four, three, and one high-frequency alleles were detected at Mafa-DOB, -DPB1, and -DQB1, respectively, in this monkeys. The alleles with the highest frequency among these monkeys were Mafa-DOB*010102, Mafa-DPB1*13, and Mafa-DQB1*0616, and these were found in 33 (25.6%) of 129 monkeys, 32 (31.37%) of 102 monkeys, and 30 (31%) of 143 monkeys, respectively. The high-frequency alleles may represent high priority targets for additional characterization of immune function. We also carried out evolutionary and population analyses using these sequences to reveal population-specific alleles. This information will not only promote the understanding of MHC diversity and polymorphism in the cynomolgus macaque but will also increase the value of this species as a model for biomedical research.

HLA-DP, HLA-DQ, and HLA-DR have different requirements for invariant chain and HLA-DM

The MHC is central to the adaptive immune response. The human MHC class II is encoded by three different isotypes, HLA-DR, -DQ, and -DP, each being highly polymorphic. In contrast to HLA-DR, the intracellular assembly and trafficking of HLA-DP molecules have not been studied extensively. However, different HLA-DP variants can be either protective or risk factors for infectious diseases (e.g. hepatitis B), immune dysfunction (e.g. berylliosis), and autoimmunity (e.g. myasthenia gravis). Here, we establish a system to analyze the chaperone requirements for HLA-DP and to compare the assembly and trafficking of HLA-DP, -DQ, and -DR directly. Unlike HLA-DR1, HLA-DQ5 and HLA-DP4 can form SDS-stable dimers supported by invariant chain (Ii) in the absence of HLA-DM. Uniquely, HLA-DP also forms dimers in the presence of HLA-DM alone. In model antigen-presenting cells, SDS-stable HLA-DP complexes are resistant to treatments that prevent formation of SDS-stable HLA-DR complexes. The unexpected properties of HLA-DP molecules may help explain why they bind to a more restricted range of peptides than other human MHC class II proteins and frequently present viral peptides.

Sequence analysis of the grey mouse lemur (Microcebus murinus) MHC class II DQ and DR region

We here report the genomic organisation of the grey mouse lemur (Microcebus murinus) MHC class II DQ and DR region based on BAC clone analysis. The sequenced Mimu-MHC haplotype spans 343 kb and encompasses the genes TAP2, DOB, DQB, DQA, DRB, DRA, BTNL2 and a further BTNL gene. The DQ and DR genes of this haplotype are not duplicated. Mimu-DOB is not transcribed and represents a pseudogene due to deletions and premature stop codons. Analysis of BAC clone DNA, a cDNA sample and eight genomic DNA samples suggests that Mimu-DRB, Mimu-DQA and Mimu-DQB are highly polymorphic with the majority of peptide-binding residues being affected by polymorphisms. In contrast, Mimu-DRA is moderately polymorphic, and the variable amino acid positions are not part of the peptide-binding region. Phylogenetic analysis of Mimu-DQA and Mimu-DQB and other primate DQA and DQB genes indicates that duplication of DQA and DQB loci occurred in Anthropoidea after the split from Strepsirrhini.

Characterisation and comparative analysis of MHC-DPA1 exon 2 in the owl monkey (Aotus nancymaae)

The Aotus nancymaae (owl monkey) is an important animal model in biomedical research, particularly for the preclinical evaluation of vaccine candidates against Plasmodium falciparum and Plasmodium vivax, which require a precisely typed major histocompatibility complex. The exon 2 from A. nancymaae MHC-DPA1 gene was characterised in order to infer its allelic diversity and evolutionary history. Aona-DPA1 shows no polymorphism and is related to other primate DPA alleles (including Catarrhini and Platyrrhini), constituting an ancient trans-specific and strongly supported lineage with different variability and selective patterns when compared to other primate-MHC-DPA1 lineages. A. nancymaae monkeys have thus a smaller MHC-DP polymorphism than MHC-DQ or MHC-DR.

MHC evolution in three salmonid species: a comparison between class II alpha and beta genes

The genes of the major histocompatibility complex (MHC) are amongst the most variable in vertebrates and represent some of the best candidates to study processes of adaptive evolution. However, despite the number of studies available, most of the information on the structure and function of these genes come from studies in mammals and birds in which the MHC class I and II genes are tightly linked and class II alpha exhibits low variability in many cases. Teleost fishes are among the most primitive vertebrates with MHC and represent good organisms for the study of MHC evolution because their class I and class II loci are not physically linked, allowing for independent evolution of both classes of genes. We have compared the diversity and molecular mechanisms of evolution of classical MH class II alpha and class II beta loci in farm populations of three salmonid species: Oncorhynchus kisutch, Oncorhynchus mykiss and Salmo salar. We found single classical class II loci and high polymorphism at both class II alpha and beta genes in the three species. Mechanisms of evolution were common for both class II genes, with recombination and point mutation involved in generating diversity and positive selection acting on the peptide-binding residues. These results suggest that the maintenance of variability at the class IIalpha gene could be a mechanism to increase diversity in the MHC class II in salmonids in order to compensate for the expression of one single classical locus and to respond to a wider array of parasites.

MHC, mate choice and heterozygote advantage in a wild social primate

Preferences for mates carrying dissimilar genes at the major histocompatibility complex (MHC) may help animals increase offspring pathogen resistance or avoid inbreeding. Such preferences have been reported across a range of vertebrates, but have rarely been investigated in social species other than humans. We investigated mate choice and MHC dynamics in wild baboons (Papio ursinus). MHC Class II DRB genes and 16 microsatellite loci were genotyped across six groups (199 individuals). Based on the survey of a key segment of the gene-rich MHC, we found no evidence of mate choice for MHC dissimilarity, diversity or rare MHC genotypes. First, MHC dissimilarity did not differ from random expectation either between parents of the same offspring or between immigrant males and females from the same troop. Second, female reproductive success was not influenced by MHC diversity or genotype frequency. Third, population genetic structure analysis revealed equally high genotypic differentiation among troops, and comparable excess heterozygosity within troops for juveniles, at both Mhc-DRB and neutral loci. Nevertheless, the age structure of Mhc-DRB heterozygosity suggested higher longevity for heterozygotes, which should favour preferences for MHC dissimilarity. We propose that high levels of within-group outbreeding, resulting from group-living and sex-biased dispersal, might weaken selection for MHC-disassortative mate choice.

Extensive DRB region diversity in cynomolgus macaques: recombination as a driving force

The DR region of primate species is generally complex and displays diversity concerning the number and combination of distinct types of DRB genes present per region configuration. A highly variable short tandem repeat (STR) present in intron 2 of nearly all primate DRB genes can be utilized as a quick and accurate high through-put typing procedure. This approach resulted previously in the description of unique and haplotype-specific DRB-STR length patterns in humans, chimpanzees, and rhesus macaques. For the present study, a cohort of 230 cynomolgus monkeys, including self-sustaining breeding groups, has been examined. MtDNA analysis showed that most animals originated from the Indonesian islands, but some are derived from the mainland, south and north of the Isthmus of Kra. Haplotyping and subsequent sequencing resulted in the detection of 118 alleles, including 28 unreported ones. A total of 49 Mafa-DRB region configurations were detected, of which 28 have not yet been described. Humans and chimpanzees possess a low number of different DRB region configurations in concert with a high degree of allelic variation. In contrast, however, allelic heterogeneity within a given Mafa-DRB configuration is even less frequently observed than in rhesus macaques. Several of these region configurations appear to have been generated by recombination-like events, most probably propagated by a retroviral element mapping within DRB6 pseudogenes, which are present on the majority of haplotypes. This undocumented high level of DRB region configuration-associated diversity most likely represents a species-specific strategy to cope with various pathogens.