Characterisation of the Immunomodulatory Effects of Meningococcal Opa Proteins on Human Peripheral Blood Mononuclear Cells and CD4+ T Cells

Abstract

Opa proteins are major surface-expressed proteins located in the Neisseria meningitidis outer membrane, and are potential meningococcal vaccine candidates. Although Opa proteins elicit high levels of bactericidal antibodies following immunisation in mice, progress towards human clinical trials has been delayed due to previous findings that Opa inhibits T cell proliferation in some in vitro assays. However, results from previous studies are conflicting, with different Opa preparations and culture conditions being used. We investigated the effects of various Opa+ and Opa- antigens from N. meningitidis strain H44/76 in a range of in vitro conditions using peripheral blood mononuclear cells (PBMCs) and purified CD4+ T cells, measuring T cell proliferation by CFSE dilution using flow cytometry. Wild type recombinant and liposomal Opa proteins inhibited CD4+ T cell proliferation after stimulation with IL-2, anti-CD3 and anti-CD28, and these effects were reduced by mutation of the CEACAM1-binding region of Opa. These effects were not observed in culture with ex vivo PBMCs. Opa+ and Opa- OMVs did not consistently exert a stimulatory or inhibitory effect across different culture conditions. These data do not support a hypothesis that Opa proteins would be inhibitory to T cells if given as a vaccine component, and T cell immune responses to OMV vaccines are unlikely to be significantly affected by the presence of Opa proteins.

Unaltered Fungal Burden and Lethality in Human CEACAM1-Transgenic Mice During Candida albicans Dissemination and Systemic Infection

“…However, also after systemic infection via the tail vein, which has a lower variance due to the controlled number of Candida cells reaching the blood stream, no differences in the systemic response or in the fungal burden of kidneys, liver, spleen, and brain of both genotypes were identified at the time of death. We and many other different groups demonstrated in various in vitro and in vivo models that CEACAM1 attenuates the host response to pathogens or pathogen-associated patterns (PAMPs) as a (co-) inhibitory receptor: it mitigates responses of neutrophils, T cells, NK cells, and B cells (Pantelic et al, 2005; Nagaishi et al, 2006; Lee et al, 2007; Slevogt et al, 2008; Pan and Shively, 2010; Chen et al, 2012; Lu et al, 2012; Singer et al, 2014; Huang et al, 2015; Jones et al, 2016; Horst et al, 2018b; Gur et al, 2019a,b). So far, no systemic infection model for bacterial pathogens was tested in CEACAM1-humanized mice, but human CEACAM1 was able to replace its mouse orthologue and to regulate immune responses in a viral model for systemic infection (Khairnar et al, 2018).…”

Bacterial membrane vesicles: Biogenesis, immune regulation and pathogenesis

“…For example, N. meningitidis OMVs can either inhibit the activation and proliferation of human CD4 + T cells, creating immunosuppression around the infection site (Lee et al, ) or induce the proliferation of CD4 + T cells (Jones et al, ). These contradictory findings may be explained by differences in bacterial strains and experimental conditions (Jones et al, ), highlighting that in order to enable greater comparisons between published findings regarding the immunomodulatory functions of OMVs, consistent methods of vesicle production and quantification are required. H. pylori OMVs modulate the host immune response by stimulating the release of both pro‐inflammatory (IL‐6) and anti‐inflammatory (IL‐10) cytokines from human mononuclear cells, thereby inhibiting CD4 + T cell proliferation and inducing T‐cell apoptosis (Winter, Letley, Rhead, Atherton, & Robinson, ).…”

“…However, the differences in the ability of OMVs to activate or suppress immune responses may be dependent on their cargo and their bacterial origin. For example, N. meningitidis OMVs can either inhibit the activation and proliferation of human CD4 + T cells, creating immunosuppression around the infection site (Lee et al, ) or induce the proliferation of CD4 + T cells (Jones et al, ). These contradictory findings may be explained by differences in bacterial strains and experimental conditions (Jones et al, ), highlighting that in order to enable greater comparisons between published findings regarding the immunomodulatory functions of OMVs, consistent methods of vesicle production and quantification are required.…”