Oral Immunization with a Live Coxsackievirus/HIV Recombinant Induces Gag p24-Specific T Cell Responses

The development of an HIV/AIDS vaccine has proven to be elusive. Because human vaccine trials have not yet demonstrated efficacy, new vaccine strategies are needed for the HIV vaccine pipeline. We have been developing a new HIV vaccine platform using a live enterovirus, coxsackievirus B4 (CVB4) vector. Enteroviruses are ideal candidates for development as a vaccine vector for oral delivery, because these viruses normally enter the body via the oral route and survive the acidic environment of the stomach.We constructed a live coxsackievirus B4 recombinant, CVB4/p24(73(3)), that expresses seventy-three amino acids of the gag p24 sequence (HXB2) and assessed T cell responses after immunization of mice. The CVB4 recombinant was physically stable, replication-competent, and genetically stable. Oral or intraperitoneal immunization with the recombinant resulted in strong systemic gag p24-specific T cell responses as determined by the IFN-gamma ELISPOT assay and by multiparameter flow cytometry. Oral immunization with CVB4/p24(73(3)) resulted in a short-lived, localized infection of the gut without systemic spread. Because coxsackieviruses are ubiquitous in the human population, we also evaluated whether the recombinant was able to induce gag p24-specific T cell responses in mice pre-immunized with the CVB4 vector. We showed that oral immunization with CVB4/p24(73(3)) induced gag p24-specific immune responses in vector-immune mice.The CVB4/p24(73(3)) recombinant retained the physical and biological characteristics of the parental CVB4 vector. Oral immunization with the CVB4 recombinant was safe and resulted in the induction of systemic HIV-specific T cell responses. Furthermore, pre-existing vector immunity did not preclude the development of gag p24-specific T cell responses. As the search continues for new vaccine strategies, the present study suggests that live CVB4/HIV recombinants are potential new vaccine candidates for HIV

Immunoregulatory role of H-2 and intra-H-2 alleles on antibody responses to recombinant preparations of B-subunits of Escherichia coli heat-labile enterotoxin (rEtxB) and cholera toxin (rCtxB)

The immunoregulatory role of H-2 and intra-H-2 alleles on antibody responses to recombinant preparations of B-subunits of Escherichia coli heat-labile enterotoxin (rEtxB) and cholera toxin (rCtxB) is reported. Oral delivery of rEtxB to congenic mice of several different H-2 haplotypes resulted in H-2 dependent serum IgG responses (H-2(d) > H-2(b) = H-2(q) > H-2(a) > H-2(k)) and a similar spectrum of intestinal IgA responses in those strains tested Responses to rEtxB and rCtxB were found to be differentially modulated by the H-2 locus, with significant differential effects in H-2(b) and H-2(d) congenic strains (H-2(d) > H-2(b) for rEtxB; H-2(b) > H-2(d) for rCtxB), Additionally, it was found that when rEtxB was fed to mice previously primed (orally) with either rEtxB or rCtxB only those mice primed with rEtxB exhibited a booster response. A second booster immunisation with rEtxB in rCtxB-primed mice produced an H-2 dependent spectrum of responses characteristic of those elicited by rEtxB, with the antibodies predominantly directed against rEtxB and not rCtxB. These results indicate that the differential response to rEtxB and rCtxB is set at the T- and B-cell level. Also, immunoregulation of antibody responses to rEtxB by intra-H-2 I-E in mice transgenic for the entire IE(a)(k) gene was investigated. No significant difference between responses in transgene-positive and -negative mice was found, suggesting that antigen presentation does not involve I-E, but occurs in the context of I-A. The implications of these results for the design of vaccines against enterotoxigenic E. coli and cholera diarrhoea are discussed

Cross-linking of cell surface ganglioside GM1 induces the selective apoptosis of mature CD8(+) T lymphocytes

Gangliosides are glycosphingolipids found ubiquitously on the surface of mammalian cells, They contain a ceramide tail that is inserted into the membrane and exposed carbohydrate and sialic acid moieties, The non-toxic B subunit oligomer (EtxB) of Escherichia coil heat-labile enterotoxin (Etx) is a potent immunogen in vivo and has profound modulatory effects on EtxB-primed lymphocytes in vitro, properties which are dependent on its ability to bind to GM1 ganglioside receptors, Here, it is shown that cross-linking GM1 by EtxB causes a differential effect on mature CD4(+) and CD8(+) T cells from lymph node cultures proliferating in response to an unrelated antigen, ovalbumin, Addition of EtxB to such cultures led to the complete depletion of CD8(+) T cells compared with enhanced activation of CD4(+) T cells [as measured by expression of CD25 (IL-2R alpha)]. By contrast, addition of a mutant EtxB, EtxB(G33D), which does not bind to GM1, failed to trigger CD8(+) T cell depletion, When EtxB was added to isolated non-immune CD8(+) lymphocytes rapid (12-18 h) alterations in nuclear morphology and the appearance of sub-G(0)/G(1) levels of DNA were induced; properties which are characteristic of cells undergoing apoptosis, EtxB(G33D) failed to trigger apoptosis, indicating that the induction of the apoptotic signal was dependent on the binding of GM1, These findings provide an insight into the potent immunogenicity and immunomodulatory properties of E. coil enterotoxins as well as heralding a novel method for the selective induction of apoptosis in mature CD8(+) T lymphocytes

Bacterial and host interactions during the biogenesis, toxicity and immunogenicity of Escherichia coli heat-labile enterotoxin

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