Manipulating blood T cells and B cells from squirrel monkeys: some technical considerations

Owl monkey MHC-DRB exon 2 reveals high similarity with several HLA-DRB lineages

One hundred and ten novel MHC-DRB gene exon 2 nucleotide sequences were sequenced in 96 monkeys from three owl monkey species (67 from Aotus nancymaae, 30 from Aotus nigriceps and 13 from Aotus vociferans). Owl monkeys, like humans, have high MHC-DRB allele polymorphism, revealing a striking similarity with several human allele lineages in the peptide binding region and presenting major convergence with DRB lineages from several Catarrhini (humans, apes and Old World monkeys) rather than with others New World monkeys (Platyrrhini). The parallelism between human and Aotus MHC-DRB reveals additional similarities regarding variability pattern, selection pressure and physicochemical constraints in amino acid replacements. These observations concerning previous findings of similarity between the Aotus immune system molecules and their human counterparts affirm this specie's usefulness as an excellent animal model in biomedical research.

Flow cytometry identification and characterization of mononuclear cell subsets in the neotropical primate Saimiri sciureus (squirrel monkey)

BACKGROUND

The neotropical primate squirrel monkey is used in many areas of biomedical research including neuroendocrinology, immunology and infectious diseases. However, research has been hampered by the lack of immunological tools for this primate.

METHODS

A series of 67 commercially available monoclonal antibodies to human CD antigens or cytokines were tested on Saimiri mononuclear cells and the specificity was assessed by double staining using flow cytometry.

RESULTS

Monoclonal antibodies defining the main mononuclear cells subsets (monocytes, B, T, including CD4 and CD8 T cells) as well as activation markers have been identified. The conditions to specifically identify the various cell subsets using two color flow cytometry and establish their relative proportions have been set-up. We also have established normal values of the main circulating mononuclear cell subsets for adult Saimiri sciureus monkeys from the breeding unit of Institut Pasteur in French Guiana. The distribution between spleen, blood and lymph nodes has been compared.

CONCLUSIONS

These tools allow documenting the phenotype of most Saimiri mononuclear cell subsets and assessing their activation level. This opens new perspectives for vaccinology and immunopathology research in this experimental non-human primate host, in particular for malaria research.

Sequencing and analysis of genomic DNA and cDNA encoding TNF-alpha in the squirrel monkey (Saimiri sciureus)

If a number of cytokines and growth factors that have been characterized from human cells were investigated in non-human primates, results from such approaches would allow the development of assays to detect and quantitate cytokines in experimental models. Tumor necrosis factor-alpha (TNF-alpha) is an important pluripotent cytokine which plays a crucial role in host defense. As yet, no complete molecular data have been reported for the squirrel monkey TNF-alpha. Polymerase chain reaction (PCR) primers were used to trace introns, by comparing product sizes obtained using cDNA and genomic DNA as templates. The genomic DNA is composed of four exons and three introns with 1793 nucleotides. The corresponding cDNA is 702 nucleotides and phylogenetic analysis showed that the Saimiri sciureus was most closely related to that of the genus Aotus, a new-world primate, compared to old-world primates (genus Macaca and Papio). The deduced TNF-alpha protein consists of 233 amino acids with 82% identity to human, 95% to new-world monkeys and 79% to old-world monkeys. The cloned TNF-alpha cDNA will be useful to quantitate TNF-alpha at the mRNA level.

Proliferative response of peripheral blood lymphocytes to mitogens in the owl monkey Aotus nancymae

The new world primate Aotus sp. has been recommended by the World Health Organization as a model for evaluation of malaria vaccine candidates, given its susceptibility to experimental infection with the human malaria parasites Plasmodium falciparum and P. vivax. The present study examined the in vitro proliferative response of peripheral blood mononuclear cells (PBMCs) isolated from Aotus monkeys, utilizing a wide range of mitogens. Results presented herein demonstrate that the in vitro proliferative response of PBMCs from the Aotus sp. is quite variable from monkey to monkey for each of the mitogens assessed. PBMCs from the Aotus monkey exhibited a delayed kinetic proliferative response and, particularly, a different sensitivity to proliferation in response to various concentrations of Phytohemagglutinin-P and favin lectins, the phorbol ester Phorbol myristate acetate and the calcium ionophore ionomycin. Altogether, our findings are consistent with the conclusion that the in vitro proliferative response of PBMCs from the Aotus differ in their activation requirements compared with PBMCs from humans.

Differential production in vitro of antigen specific IgG1, IgG3 and IgA: a study in Schistosoma haematobium infected individuals

This study has evaluated the individual control of isotype production and the influence of external signals that can be experimentally provided in vitro, in antibody responses to two different recombinant Schistosoma antigens (Sh28GST and TPx-1). Peripheral blood mononuclear cells or enriched B cell fractions obtained from S. haematobium infected Senegalese adults were induced to terminal differentiation in vitro. The production of antibody to either antigen was donor-dependent and for each donor it was antigen-dependent. Differentiation to IgG1 and IgG3 production, and possibly IgA, specific to these conserved parasite antigens could be regulated differentially in vitro. Exogenous IL-2 and IL-10 or IL-10 and TGF-beta led to the production of specific IgG3 or IgG1 and/or IgA, respectively. This is the first report on such experimentally induced differential regulation of antigen-specific IgG1 and IgG3. This may have implications in designing protocols for protein based-vaccinations aiming at eliciting antibody responses of certain protective-type isotypes.

HTLV type 1 infection in squirrel monkeys (Saimiri sciureus): a promising animal model for HTLV type 1 human infection

We show that the squirrel monkey Saimiri sciureus is susceptible to experimental infection with either syngeneic or allogeneic HTLV-1-immortalized cells. As in humans, such experimental inoculation leads to chronic infection, and HTLV-1 provirus was detected in PBMCs by PCR. Chronically infected monkeys developed high titers of antibodies against the structural proteins of the virus, as do HTLV-1-infected humans. Furthermore, in serially sacrificed squirrel monkeys infected with HTLV-1, proviral DNA was detected at primary phases of infection in PBMCs, spleens, and lymph nodes. Tax/rex mRNA was also detected by RT-PCR in the PBMCs of two monkeys at 12 days after inoculation and in the spleen and lymph nodes of the monkey sacrificed on Day 12. In this animal, scattered HTLV-1-tax/rex mRNA-positive lymphocytes were detected by in situ hybridization in frozen sections of the spleen. These results indicate that PBMCs, spleen, and lymph nodes serve as major reservoirs for HTLV-1 during the early phase of infection. To evaluate the relationship between viral expression and the immune response during infection, humoral and cytotoxic T cell responses (CTL) were studied at various times after inoculation. Antibodies to HTLV-1 were detected 3 weeks after infection and anti-p40Tax and anti-Env CTL activity was detected 2 months after infection and remained detectable thereafter. Our results indicate that the squirrel monkey provides a useful animal model for studying the pathogenesis of HTLV-1 and for evaluating new candidate vaccines.

HTLV-I infection in squirrel monkeys (Saïmiri sciureus) using autologous, homologous, or heterologous HTLV-I-transformed cell lines

Peripheral blood mononuclear cells (PBMC) from three adult male squirrel monkeys (Saïmiri sciureus) were transformed by human T-cell leukemia/lymphoma virus type I (HTLV-I) by cocultivation with lethally irradiated human MT-2 cells. Three permanent monkey T-cell lines producing HTLV-I were obtained and characterized. Six weeks after inoculation seroconversion was observed in three of three monkeys inoculated with autologous transformed T cells and in two of three monkeys receiving homologous cells. Proviral DNA was detected in their PBMC at various times after inoculation, with the highest proviral load and antibody titers being found in monkeys infected with homologous cells. Monkeys inoculated with heterologous MT-2 cells did not seroconvert, and HTLV-I provirus was detected only transiently in their PBMC. To determine whether in vitro and in vivo HTLV-I infection of squirrel monkey cells led to a selection of monkey-adapted viral mutants, comparative sequencing of the proviral gp21 env between ex vivo monkey HTLV-I-infected PBMC, the inoculum, and MT-2 cells was done and no significant differences were detected. The squirrel monkey, which is naturally free of simian T-cell leukemia/ lymphoma virus, thus appears to be a suitable model for evaluating HTLV-I candidate vaccines and for studying the pathogenesis of HTLV-I.

Antigens linked to synthetic microspheres induce immune responses in primates in the absence of adjuvant

Although most strategies of vaccination require immunopotentiation to induce efficient immune responses, the development of new adjuvants for human vaccines is highly limited by safety problems. In order to overcome this problem, we developed a new vaccine formulation based on the covalent linkage of protein or peptide to synthetic microspheres. In previous experiments performed in mice, we demonstrated that these particulate antigens induce strong antigen-specific CD4+ T cell proliferative responses in the absence of adjuvant. In the present study, we analyzed the immunogenicity in primate Saimiri sciureus monkeys of two different proteins linked to synthetic microspheres. Immune responses induced by these particulate proteins administered without adjuvant were compared to those stimulated by the soluble antigens injected with alum. We currently demonstrated that, in monkeys, particulate antigens administered without adjuvant, induced good PBMC proliferative response and antibody production. Furthermore, the analysis of antibody responses using mAbs specific for different Saimiri sciureus immunoglobulins showed that the antibody response profiles were different in monkeys immunized with soluble versus particulate form of antigens. Results of this study demonstrate that particulate form of antigen may stimulate qualitatively different immune responses as compared to alum and therefore suggest that this new antigen formulation could be an attractive candidate for the development of vaccines.

Towards a vaccine against asexual blood stage infection by Plasmodium falciparum

In this paper, we will summarize the progress obtained in the malaria vaccine project developed by the Institut Pasteur groups interacting through the International Network of Pasteur Institutes over the last fifteen years. While trying to follow the progress in scientific and technological concepts and methodologies, the basic approach was still essentially the same as that followed by Pasteur and his acolytes to try to artificially reproduce the natural processes that lead to the development of immunity to infection and disease. A longitudinal study of two villages from the Sine Saloum area of Senegal, Dielmo and N'Diop, conducted in recent years by teams of the Institut Pasteur of Dakar, Senegal, in collaboration with the local ORSTOM malaria unit has led to the detailed analysis of the natural acquisition of premunition against Plasmodium falciparum malaria in endemic areas. The Saimiri model developed at the Pasteur Institute in Cayenne, was an important step forward in terms of studies on the mechanisms of action of protective antibodies and on vaccinations assays. If we accept the conclusions of the Pasteur groups' research on the experimental primate model and on the development of natural immunity (premunition) in highly endemic areas, the main inhibitor of progress in vaccine development is our poor understanding of the regulation of the immune response. Therefore, the general approaches that were followed for vaccine development must now be further explored using the continually developing tools of immunology and molecular biology, to elucidate regulations of the immune responses to the parasite, and identify the molecular mechanisms used by the parasite to generate and change antigen specificities.