Comparison of nonhuman primates identified the suitable model for COVID-19

Identification of a suitable nonhuman primate (NHP) model of COVID-19 remains challenging. Here, we characterized severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in three NHP species: Old World monkeys Macaca mulatta (M. mulatta) and Macaca fascicularis (M. fascicularis) and New World monkey Callithrix jacchus (C. jacchus). Infected M. mulatta and M. fascicularis showed abnormal chest radiographs, an increased body temperature and a decreased body weight. Viral genomes were detected in swab and blood samples from all animals. Viral load was detected in the pulmonary tissues of M. mulatta and M. fascicularis but not C. jacchus. Furthermore, among the three animal species, M. mulatta showed the strongest response to SARS-CoV-2, including increased inflammatory cytokine expression and pathological changes in the pulmonary tissues. Collectively, these data revealed the different susceptibilities of Old World and New World monkeys to SARS-CoV-2 and identified M. mulatta as the most suitable for modeling COVID-19.

Responses to acute infection with SARS-CoV-2 in the lungs of rhesus macaques, baboons and marmosets

Non-human primate models will expedite therapeutics and vaccines for coronavirus disease 2019 (COVID-19) to clinical trials. Here, we compare acute severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in young and old rhesus macaques, baboons and old marmosets. Macaques had clinical signs of viral infection, mild to moderate pneumonitis and extra-pulmonary pathologies, and both age groups recovered in two weeks. Baboons had prolonged viral RNA shedding and substantially more lung inflammation compared with macaques. Inflammation in bronchoalveolar lavage was increased in old versus young baboons. Using techniques including computed tomography imaging, immunophenotyping, and alveolar/peripheral cytokine response and immunohistochemical analyses, we delineated cellular immune responses to SARS-CoV-2 infection in macaque and baboon lungs, including innate and adaptive immune cells and a prominent type-I interferon response. Macaques developed T-cell memory phenotypes/responses and bystander cytokine production. Old macaques had lower titres of SARS-CoV-2-specific IgG antibody levels compared with young macaques. Acute respiratory distress in macaques and baboons recapitulates the progression of COVID-19 in humans, making them suitable as models to test vaccines and therapies.

Safety, immunogenicity, and efficacy of the ML29 reassortant vaccine for Lassa fever in small non-human primates

A single injection of ML29 reassortant vaccine for Lassa fever induces low, transient viremia, and low or moderate levels of ML29 replication in tissues of common marmosets depending on the dose of the vaccination. The vaccination elicits specific immune responses and completely protects marmosets against fatal disease by induction of sterilizing cell-mediated immunity. DNA array analysis of human peripheral blood mononuclear cells from healthy donors exposed to ML29 revealed that gene expression patterns in ML29-exposed PBMC and control, media-exposed PBMC, clustered together confirming safety profile of the ML29 in non-human primates. The ML29 reassortant is a promising vaccine candidate for Lassa fever.

The common marmoset: a new world primate species with limited Mhc class II variability

The common marmoset (Callithrix jacchus) is a New World primate species that is highly susceptible to fatal infections caused by various strains of bacteria. We present here a first step in the molecular characterization of the common marmoset's Mhc class II genes by nucleotide sequence analysis of the polymorphic exon 2 segments. For this study, genetic material was obtained from animals bred in captivity as well as in the wild. The results demonstrate that the common marmoset has, like other primates, apparently functional Mhc-DR and -DQ regions, but the Mhc-DP region has been inactivated. At the -DR and -DQ loci, only a limited number of lineages were detected. On the basis of the number of alleles found, the -DQA and -B loci appear to be oligomorphic, whereas only a moderate degree of polymorphism was observed for two of three Mhc-DRB loci. The contact residues in the peptide-binding site of the Caja-DRB1*03 lineage members are highly conserved, whereas the -DRB*W16 lineage members show more divergence in that respect. The latter locus encodes five oligomorphic lineages whose members are not observed in any other primate species studied, suggesting rapid evolution, as illustrated by frequent exchange of polymorphic motifs. All common marmosets tested were found to share one monomorphic type of Caja-DRB*W12 allele probably encoded by a separate locus. Common marmosets apparently lack haplotype polymorphism because the number of Caja-DRB loci present per haplotype appears to be constant. Despite this, however, an unexpectedly high number of allelic combinations are observed at the haplotypic level, suggesting that Caja-DRB alleles are exchanged frequently between chromosomes by recombination, promoting an optimal distribution of limited Mhc polymorphisms among individuals of a given population. This peculiar genetic make up, in combination with the limited variability of the major histocompatability complex class II repertoire, may contribute to the common marmoset's susceptibility to particular bacterial infections.

A new primate model for multiple sclerosis in the common marmoset

Experimental autoimmune encephalomyelitis (EAE) in outbred marmoset monkeys (Callithrix jacchus) is a recently developed nonhuman primate model of multiple sclerosis. Here, Bert 't Hart and colleagues compare this model to EAE in rhesus monkeys, highlighting autoimmune mechanisms in CNS inflammation and demyelination, including the role of major histocompatibility complex restriction and preclinical evaluation of innovative immunotherapies.

Phagocytes containing a disease-promoting Toll-like receptor/Nod ligand are present in the brain during demyelinating disease in primates

Recent studies claim a central role for Toll-like receptor (TLR) ligands in stimulating autoimmune disease by activation of antigen-presenting cells in the target organ, but it is unclear if and how TLR ligands reach target organs. Most evidence comes from rodent models, and it is uncertain whether this principle holds in primates. Here we identify which cells contain peptidoglycan (PGN) in multiple sclerosis brain and in two nonhuman primate experimental autoimmune encephalomyelitis (EAE) models with different disease courses: acute (rhesus monkey) versus chronic disease (marmoset). Because persistence of TLR ligands in the central nervous system might be consequential for disease progression, we also determined the expression of two major PGN-degrading enzymes, ie, lysozyme and N-acetylmuramyl-l-alanine amidase. Distinct phagocyte subsets, including granulocytes, macrophages, and dendritic cells, contained PGN in the brain and coexpressed the inflammatory cytokine interleukin-12. The number of phagocytes carrying PGN increased in acute and chronic EAE compared with control animals, with the highest number of PGN-containing cells in acute EAE brain. Lytic enzymes were scarcely expressed in monkey and multiple sclerosis brain, favoring PGN persistence. PGN stimulated interleukin-12p70 release by leukocytes from all three primate species. The presence of PGN in the inflamed brain may have major implications because TLR2/Nod ligation potentially promotes inflammation and disease progression.

Experimental norovirus infections in non-human primates

Noroviruses, with Norwalk virus as the prototype strain, are the most common cause of viral gastroenteritis in people of all ages. Limited information on the immunology of Norovirus infections has been obtained by studies both in the natural setting and in experimentally infected volunteers. Interpretation of these studies is difficult due to the lack of information on the history of Norovirus exposure and the cross-reactivity of antibodies. An animal model for Norovirus infections would be important to study the immune response, e.g., for vaccine assessment. In the present study the susceptibility of common marmosets, cotton top tamarins, cynomolgus, and rhesus macaques to Norovirus infection was tested. Following oral inoculation, low level replication may have occurred in common marmosets and cotton top tamarins but not in cynomolgus macaques, based on short-term viral shedding; neither clinical symptoms nor antibody responses were observed in these species. In contrast, rhesus macaques were found susceptible to Norwalk virus infection as one animal shed virus for a longer period of time and developed Norwalk virus specific IgM and IgG responses. Further research on Norovirus susceptibility in rhesus macaques may yield an animal model to study the immune response and pathogenesis after Norovirus infection.

Cross-reactivity of antihuman monoclonal antibodies with cell surface receptors in the common marmoset

In this report we demonstrate that a large number of monoclonal antibodies (mAbs) against human epitopes cross-react with surface receptors on white blood cells of Callithrix jacchus, indicating species similarities. However, a variety of other mAbs do not exhibit any cross-reactivity, thus also providing evidence for distinct differences in the structure of these receptors among nonhuman primates. Such differences have to be known and taken into consideration when attempting extrapolations between species. The results presented provide the prerequisite for performing extensive studies on immunological structures and functions in marmosets under normal and pathological conditions. We conclude that the immune system of Callithrix jacchus is a convenient model for studies on immunotoxicity with relevance for man, and for this purpose it is clearly superior to that of any rodent species.

Callitrichid nutrition and food sensitivity

Captive callitrichids are prone to developing intestinal problems. Their captive and natural diets differ enormously, and diet has been suggested to play a major role in wasting marmoset syndrome. Proteins in wheat, soy and milk are included in callitrichid diets of most colonies and have been linked to an immune reaction in Saguinus oedipus and Callithrix jacchus. In the present study of 23 males and females of the two species, wheat protein was tested but soy and milk products were excluded. One group had wheat and the other had rice in their diet. Blood samples and biopsies from the colon were taken. Results showed changes in the colon and an immune reaction to gliadin, a wheat protein related to coeliac disease in humans. A further immune reaction was also observed. Suggestions for further study and exclusion of cereal in the diet of these small, New World primates are discussed.

Attenuation and efficacy of live-attenuated Rift Valley fever virus vaccine candidates in non-human primates

Rift Valley fever virus (RVFV) is an important mosquito-borne veterinary and human pathogen that has caused large outbreaks of severe disease throughout Africa and the Arabian Peninsula. Currently, no licensed vaccine or therapeutics exists to treat this potentially deadly disease. The explosive nature of RVFV outbreaks and the severe consequences of its accidental or intentional introduction into RVFV-free areas provide the impetus for the development of novel vaccine candidates for use in both livestock and humans. Rationally designed vaccine candidates using reverse genetics have been used to develop deletion mutants of two known RVFV virulence factors, the NSs and NSm genes. These recombinant viruses were demonstrated to be protective and immunogenic in rats, mice, and sheep, without producing clinical illness in these animals. Here, we expand upon those findings and evaluate the single deletion mutant (ΔNSs rRVFV) and double deletion mutant (ΔNSs-ΔNSm rRVFV) vaccine candidates in the common marmoset (Callithrix jacchus), a non-human primate (NHP) model resembling severe human RVF disease. We demonstrate that both the ΔNSs and ΔNSs-ΔNSm rRVFV vaccine candidates were found to be safe and immunogenic in the current study. The vaccinated animals received a single dose of vaccine that led to the development of a robust antibody response. No vaccine-induced adverse reactions, signs of clinical illness or infectious virus were detected in the vaccinated marmosets. All vaccinated animals that were subsequently challenged with RVFV were protected against viremia and liver disease. In summary, our results provide the basis for further development of the ΔNSs and ΔNSs-ΔNSm rRVFV as safe and effective human RVFV vaccines for this significant public health threat.

Rift Valley fever (RVF) is an important neglected tropical disease that has caused severe epidemics and epizootics throughout Africa and the Arabian Peninsula. Severe outbreaks have involved tens of thousands of both human and livestock cases for which no effective, commercially available human vaccines are available. Vaccine candidates have been developed based on the complete deletion of two known RVF virus virulence factors, the NSs and NSm genes. These vaccines were previously demonstrated to be protective in rats, mice, and sheep. In this study, we expand upon those results and evaluate the vaccine candidates in a non-human primate model for RVF. The animals received a single dose of vaccine that led to the development of a robust immune response. No vaccine-induced adverse reactions, signs of clinical illness or infectious virus were detected in the vaccinated animals. All vaccinated animals that were subsequently challenged with RVF virus were protected against viremia and liver disease. These results demonstrate that the vaccines are safe and effective in non-human primates, which provides the impetus for further development of these candidates for use in humans.

Differential expression of major histocompatibility complex class I molecules in the brain of a New World monkey, the common marmoset (Callithrix jacchus)

It has been supposed that central nervous neurons do not express MHC class I molecules. However, recent studies clearly demonstrated functional MHC class I expression in the rodent brain. In the present study, we have extended these studies and investigated the presence of MHC class I transcripts and proteins in the brain of a non-human primate species, the common marmoset monkey (Callithrix jacchus). Using in-situ hybridization, we found strong expression of MHC class I transcripts in neocortex, hippocampal formation, substantia nigra and nucleus ruber. In-situ hybridization with emulsion autoradiography demonstrated MHC class I mRNA in distinct pyramidal neurons of cortex and hippocampus, in granule neurons of the dentate gyrus, in dopaminergic neurons of substantia nigra and in motor neurons of nucleus ruber. Immunocytochemistry confirmed MHC class I protein expression in these neurons. Two monoclonal antibodies, MRC-Ox18 and HB115, reacted differentially with MHC class I proteins on neuronal and non-neuronal cells, respectively. Interestingly, in marmoset monkeys that were immunosuppressed with FK506 (tacrolimus), expression of neuronal MHC class I proteins, which could be detected with MRC-Ox18, was either very low (neocortex, nucleus ruber, substantia nigra) or absent (hippocampus). In contrast, class I expression in endothelial cells, which was detected by HB115, was not affected by immunosuppression. Our data show that selected neurons in the brain of a non-human primate express MHC class I molecules and that this expression can be modulated by immunosuppression.

Epidemiological study of sporotrichosis and histoplasmosis in captive Latin American wild mammals, São Paulo, Brazil

Sporotrichosis and histoplasmosis are deep mycosis with a high incidence in human beings in Brazil. In domestic animals histoplasmosis has been described only in dogs, but the occurrence of sporotrichosis among domestic animals in Brazil has been described in dogs, cats, mules and asses. There is also a case of this disease reported in a chimpanzee (Pan troglodites). The purpose of this research was to perform an epidomiological study of these mycoses using delayed hypersensitivity tests (histoplasmin and sporotrichin) in Latin American wild mammals. This research was assayed using 96 healthy animals at Parque Zoológico de São Paulo, Brazil: Primates: 33 Cebus apella--weeping-capuchin and 16 Callithrix jacchus--marmoset; Procyonidae: 37 Nasua nasua--coatimundi and 10 Felidae (Panthera onca--jaguar; Felis pardalis--ocelot Felis wiedii--margay; Felis tigrina--wild cat). For intradermic tests, the following antigens were used: Sporothrix schenkii cell suspension (sporotrichin, histoplasmin-filtrate), Histoplasma capsulatum cell suspension (histoplasmin), and Histoplasma capsulatum (polysaccharide). The positivity to histoplasmin was 44.79% (Cebidae 15.15%; Callithricidae 6.25%; Procyonidae 86.49% and Felidae 50.00%, respectively). With respect to sporotrichin, 30.21% (Cebidae 6.06%, Callithricidae 0.0%; Procyonidae 64.86% and Felidae 30.00% respectively). The pattern of infection is similar to that shown by human beings and this may suggest that these animals could be involved in the epidemiologic chain of sporotrichosis and histoplasmosis, the second most prevalent human deep mycoses in Brazil. It is important to point out the absence of similar studies in Latin American wild animals.

Effective antigen-specific immunotherapy in the marmoset model of multiple sclerosis

Mature T cells initially respond to Ag by activation and expansion, but high and repeated doses of Ag cause programmed cell death and can suppress T cell-mediated diseases in rodents. We evaluated repeated systemic Ag administration in a marmoset model of experimental allergic encephalomyelitis that closely resembles the human disease multiple sclerosis. We found that treatment with MP4, a chimeric, recombinant polypeptide containing human myelin basic protein and human proteolipid protein epitopes, prevented clinical symptoms and did not exacerbate disease. CNS lesions were also reduced as assessed in vivo by magnetic resonance imaging. Thus, specific Ag-directed therapy can be effective and nontoxic in primates.

Cross-sectional comparison of health-span phenotypes in young versus geriatric marmosets

The development of the marmoset as a translational model for healthspan and lifespan studies relies on the characterization of health parameters in young and geriatric marmosets. This cross-sectional study examined health phenotypes in marmosets for five domains of interest for human health and aging: mobility, cognition, metabolism, homeostasis, and immune function. Geriatric marmosets were found to have significant executive function impairment when compared to young animals. While geriatric animals did not show gross abnormalities in mobility and measures of locomotion, their types of movement were altered from young animals. Geriatric marmosets had alterations in cardiac function, with significantly increased mean arterial pressures; metabolism, with significantly lower VO2 ; and suppressed immune function. Further, this study sought to characterize and describe histopathology for both young and geriatric healthy marmosets. Overall this study provides a characterization of health parameters for young and geriatric marmosets which will greatly enhance future aging and interventional testing in marmosets.

Marmoset fine B cell and T cell epitope specificities mapped onto a homology model of the extracellular domain of human myelin oligodendrocyte glycoprotein

Aberrant association of autoantibodies with myelin oligodendrocyte glycoprotein (MOG), an integral membrane protein of the central nervous system (CNS) myelin, has been implicated in the pathogenesis of multiple sclerosis (MS). Sensitization of nonhuman primates (Callithrix jacchus marmosets) against the nonglycosylated, recombinant N-terminal domain of rat MOG (residues 1-125) reproduces an MS-like disease in which MOG-specific autoantibodies directly mediate demyelination. To assess the interrelationship between MOG structure and the induction of autoimmune CNS diseases and to enable structure-based rational design of therapeutics, a homology model of human MOG(2-120) was constructed based on consensus residues found in immunoglobulin superfamily variable-type proteins having known structures. Possible sites for posttranslational modifications and dimerization have also been identified and analyzed. The B cell and T cell epitopes have been identified in rat MOG-immunized marmosets, and these sequences are observed to map primarily onto accessible regions in the model, which may explain their ability to generate potent antibody responses.

Genomics and diversity of the common marmoset monkey NK complex

The common marmoset monkey (Callithrix jacchus) is a New World primate that is increasingly used in biomedical research as a model organism. Due to the occurrence of natural bone marrow chimerism, it represents a particularly useful primate model in immunological research. In this study, we describe the genomic organization of the CD94, NKG2, and LY49L genes in the NK complex (NKC) of the common marmoset based on complete sequencing of a bacterial artificial chromosome clonal contig. This region of the marmoset NKC is 1.5 times smaller than its human counterpart, but the genes are colinear and orthologous. One exception is the activating NKG2CE gene, which is probably an ancestral form of the NKG2C- and NKG2E-activating receptor genes of humans and great apes. The two completely sequenced marmoset bacterial artificial chromosome clones are derived from distinct haplotypes, which differ by 200 sites in the overlapping sequence. Analyses of NKC genes in nine additional marmoset individuals revealed a moderate degree of polymorphism of the CD94, NKG2A, NKG2CE, and NKG2D genes. Furthermore, expression analyses identified several alternatively spliced transcripts, particularly of the CD94 gene. Several products of alternative splicing of NKC genes are highly conserved among primates. Alternative transcriptional start sites were found, but these probably do not lead to a change of the translational start site or result in longer or shorter cytoplasmic regions of these type II membrane receptors.

Analysis of a human sperm CD52 glycoform in primates: identification of an animal model for immunocontraceptive vaccine development

Sperm agglutination antigen-1 (SAGA-1) is a human male reproductive tract glycoform of CD52. Unique modification of CD52 N-linked oligosaccharide chains in the epididymis and vas deferens results in the appearance of a carbohydrate epitope that is localized over the entire surface of human spermatozoa. SAGA-1 was characterized by the sperm-inhibitory murine monoclonal antibody (mAb) S19, and it is the target antigen of a human mAb (H6-3C4) associated with antibody-mediated infertility. Collectively, sperm surface localization, antibody inhibition of sperm function, and potential reproductive-tissue specificity identify SAGA-1 as an attractive candidate contraceptive immunogen. To establish an animal model for the study of SAGA-1 in immunologic infertility and immunocontraceptive development, we investigated the appearance of the S19 carbohydrate epitope in nonhuman primates. The S19 mAb demonstrated little to no immunoreactivity by Western blot analysis with protein extracts of spermatozoa from the baboon, marmoset, bonnet, cynomolgus, and pigtailed macaques. Immunohistochemical analysis identified CD52 in the bonnet monkey epididymis; however, the N-linked carbohydrate moiety recognized by the S19 mAb, and unique to SAGA-1, was absent. In contrast, the S19 carbohydrate epitope was identified in chimpanzee sperm extracts by Western blot analysis and in chimpanzee epididymal tissue sections by immunohistochemical analysis, indicating that it is conserved in this close relative of the human. Chimpanzee testis, seminal vesicle, and prostate do not express the S19 epitope. Although anti-CD52 immunoreactivity was identified in the spleen, the carbohydrate moiety recognized by the S19 mAb was absent, corroborating data in the human that demonstrated tissue-specific glycosylation of sperm CD52. Immunofluorescent analysis indicated that the chimpanzee homologue of sperm CD52 was present over the entire spermatozoon. In addition, the S19 mAb agglutinated chimpanzee spermatozoa in a manner similar to the effect observed on human spermatozoa. These data indicate that the distinctive carbohydrate moiety of human sperm CD52 is present in the chimpanzee, and they identify the chimpanzee as the most appropriate primate model to study the potential of this unique CD52 glycoform as a contraceptive immunogen.

Characterization of the expressed immunoglobulin IGHV repertoire in the New World marmoset Callithrix jacchus

The common marmoset (Callithrix jacchus jacchus) is a member of the Callithrichinae, a family of outbred New World primates with limited MHC polymorphisms and a propensity to develop spontaneous or experimentally induced autoimmunity. C. jacchus marmosets are susceptible to experimental allergic encephalomyelitis (EAE), and spontaneously develop autoimmune colitis and thyroiditis. Such disease models approximate the complexity of human autoimmune disorders, and allow an investigation of the respective roles of T-cell and antibody responses to self-antigens in outbred species. A key issue for further definition of the pathogenic antibody responses in human autoimmunity is to understand the diversity of the immunoglobulin repertoire in primate models. Here, we characterized the expressed immunoglobulin IGHV repertoire of the C. jacchus marmoset. Six IGHV subgroups were identified which show a high degree of sequence similarity to their human IGHV counterparts (IGHV1, IGHV3, IGHV4, IGHV5, IGHV6, and IGHV7). As in the expressed human IGHV repertoire, the framework regions are more conserved when compared to the complementarity-determining regions (CDRs), with the greatest degree of variability located in CDR3. Predicted structural features are highly conserved between C. jacchus and human IGHV. This information now provides a framework for studies of the antigen-specific repertoire of pathogenic antibodies in EAE and other immune-mediated diseases.

Dynamics of cellular immune responses in the acute phase of dengue virus infection

In this study, we examined the dynamics of cellular immune responses in the acute phase of dengue virus (DENV) infection in a marmoset model. Here, we found that DENV infection in marmosets greatly induced responses of CD4/CD8 central memory T and NKT cells. Interestingly, the strength of the immune response was greater in animals infected with a dengue fever strain than in those infected with a dengue hemorrhagic fever strain of DENV. In contrast, when animals were re-challenged with the same DENV strain used for primary infection, the neutralizing antibody induced appeared to play a critical role in sterilizing inhibition against viral replication, resulting in strong but delayed responses of CD4/CD8 central memory T and NKT cells. The results in this study may help to better understand the dynamics of cellular and humoral immune responses in the control of DENV infection.

MHC (major histocompatibility complex)-DRB genes and polymorphisms in common marmoset

A New World monkey, the common marmoset (Callithrix jacchus), will be used as a preclinical animal model to study the feasibility of cell and gene therapy targeting immunological and hematological disorders. For elucidating the immunogenetic background of common marmoset to further studies, in the present study, polymorphisms of MHC-DRB genes in this species were examined. Twenty-one Caja-DRB exon 2 alleles, including seven new ones, were detected by means of subcloning and the polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) methods followed by nucleotide sequencing. Based on the alignment of these allele sequences, we designed two pairs of specific primers and established a PCR-SSCP method for DNA-based histocompatibility typing of the common marmoset. According to the family segregation data and phylogenetic analyses, we presumed that Caja-DRB alleles could be classified into five different loci. Southern blotting analysis also supported the existence of multiple DRB loci. The patterns of nucleotide substitutions suggests that positive selection operates in the antigen-recognition sites of Caja-DRB genes.

Natural antibodies to EBV-VCA antigens in common marmosets (Callithrix jacchus) and response after EBV inoculation

Healthy common marmosets from two separate colonies, one in England and one in France, were found to have antibodies cross-reacting with Epstein-Barr virus structural antigens (EBV-VCA). All seropositive animals were at least 2 years old. Experimental EBV infection of marmosets of different ages led to seroconversion of inoculated weanlings. Adult animals either developed antibody for the first time or showed an increase in their existing titers. Both control and infected animals developed a progressive interstitial nephritis. The lymphocytic infiltration was more extensive, diffuse and immature in appearance in inoculated animals, but no definite evidence of lymphoproliferative disease or lymphoma was found.

Cross-reactivity of anti-human chemokine receptor and anti-TNF family antibodies with common marmoset (Callithrix jacchus) leukocytes

The common marmoset (Callithrix jacchus) is a New World primate species frequently employed for immunological models of human disease. We used flow cytometry to screen a panel of new anti-human antibodies from the HLDA8 workshop to establish cross-reactivity with marmoset peripheral blood mononuclear cells. Seventy-seven antibodies were screened of which nine antibodies showed binding. Cross-reactivity of anti-human monoclonal antibodies with CC and CXC chemokine receptors CCR3, CCR6, CCR7, and CCR8 was demonstrated on untreated marmoset mononuclear cells. Stimulation of marmoset mononuclear cells with ConA and/or PMA-ionomycin resulted in an up-regulated expression of CXCR1, CXCR3, and CXCR4. The expression of TNF-family related molecules TACI and APRIL on marmoset mononuclear cells was also identified. These studies extend the range of cross-reactive antibodies to now include anti-chemokine and anti-TNF family antibodies for this important pre-clinical model species and should provide useful tools for investigation of immunological processes in marmoset monkey models.

Characterization of an Epstein-Barr virus-related gammaherpesvirus from common marmoset (Callithrix jacchus)

A gammaherpesvirus related to Epstein-Barr virus (EBV; Human herpesvirus 4) infects otherwise healthy common marmosets (Callithrix jacchus). Long-term culture of common marmoset peripheral blood lymphocytes resulted in outgrowth of spontaneously immortalized lymphoblastoid cell lines, primarily of B cell lineage. Electron microscopy of cells and supernatants showed herpesvirus particles. There were high rates of serological cross-reactivity to other herpesviruses (68-86%), but with very low geometric mean antibody titres [1:12 to human herpesvirus 6 and 1:14 to Herpesvirus papio (Cercopithecine herpesvirus 12)]. Sequence analysis of the conserved herpesvirus DNA polymerase gene showed that the virus is a member of the lymphocryptovirus subgroup and is most closely related to a lymphocryptovirus from rhesus macaques and is closely related to EBV and Herpesvirus papio. High seroprevalence (79%, with geometric mean antibody titre of 1:110) among 28 common marmosets from two geographically distinct colonies indicated that the virus is likely present in many common marmosets in captivity. A New World primate harbouring a lymphocryptovirus suggests that this subgroup arose much earlier than previously thought.

Double expression of CD34 and CD117 on bone marrow progenitors is a hallmark of the development of functional mast cell of Callithrix jacchus (common marmoset)

Mast cells (MCs) are developed from hematopoietic progenitor cells and play an important role in inflammation. Study of the kinetics of development and accumulation of primate MC in vivo is crucial for the control of human inflammatory diseases, as evolution of the immune system is quite rapid and inflammation including MC response is considered to be different between mouse and human. In the present study, we examined the development of MC from hematopoietic progenitors of Callithrix jacchus (common marmoset), an experimental animal of nonhuman primates. Bone marrow cells were fractionated for the expression of CD34 and CD117 by cell sorting. MCs were developed in vitro or by transplanting the cells to NOD/SCID/IL-2γc knockout (NOG) mice. In vitro culture of CD34(+)CD117(+) (double positive, DP) cells with stem cell factor could generate high-affinity Fc epsilon receptor (FcεR)-expressing CD117(+) cells with typical granules. The developed MC released β-hexosaminidase and produced leukotriene C(4) after the stimulation of FcεRI. Transplantation of DP cells gave rise to a marked expansion of CD34(-)CD45(+)CD117(+)FcεR(+) cells in NOG mice. They expressed transcripts encoding chymase 1 and tryptase β. Differentiation of CD34(-)CD117(+) cells to MCs was relatively limited compared with the DP cells, similarly to human MCs. These results suggest that this marmoset system provides a good model for human MC development.

Further evaluation of a live hepatitis A vaccine in marmosets

Live, attenuated F' hepatitis A vaccine virus was studied in vivo in Saguinus labiatus marmosets for possible reversion to virulence, for possible establishment of persistent infection and for its capacity as a parenterally administered vaccine to induce immunity to oral infection. Serial transmission of the virus in S. labiatus, using infectious stool extracts for the second and third passages, produced no evidence of reversion of the F' vaccine virus to virulence. Monitoring for live HAV in stools over a 135-day period post-inoculation of marmosets with the F' vaccine revealed no evidence of persistent infection. Vaccinated animals were also shown to be resistant to infection on challenge by the oral route as well as by the previously demonstrated parenteral route.