Induction and expression of intestinal humoral immunity in HIV-infected individuals: prospects for vaccination against secondary enteric infections

Hookworm infection: Toward development of safe and effective peptide vaccines

Hookworms are hematophagous nematode parasites that have infected a billion people worldwide. Anthelmintic drugs have limited efficacy and do not prevent reinfection. Therefore, prophylactic vaccines are in high demand. Whole parasite vaccines are allergic and unsafe; thus, research into subunit vaccines has been warranted. A comprehensive overview of protein or peptide subunit vaccines' safety, protective efficacy, and associated immune responses is provided herein. The differences between the immune responses against hookworm infection by patients from epidemic versus nonepidemic areas are discussed in detail. Moreover, the different immunologic mechanisms of protection are discussed, including those that rely on allergic and nonallergic humoral and antibody-dependent cellular responses. The allergic and autoimmune potential of hookworm antigens is also explored, as are the immunoregulatory responses induced by the hookworm secretome. The potential of oral mucosal immunizations has been overlooked. Oral immunity against hookworms is a long-lived and safer immune response that is associated with elimination of infection and protective against reinfections. However, the harsh conditions of the gastrointestinal environment necessitates special oral delivery systems to unlock vaccines' protective potential. The potential for development of safer and more effective peptide- and protein-based anthelmintic vaccines is explored herein.

Humoral immune responses to HIV in the mucosal secretions and sera of HIV-infected women

Although sera and all external secretions contain antibodies to human immunodeficiency virus (HIV), their levels, specificity, isotypes, and relevant effector functions display a great degree of variability. Antibodies that bind HIV antigens and neutralize the virus are predominantly associated with the IgG isotype in sera and in all external secretions, even where total levels of IgG are much lower than those of IgA. Rectal fluid that contains high IgA, but low IgG levels, displayed low neutralizing activity independent of antibodies. Therefore, external secretions should be evaluated before and after selective depletion of Ig. At the systemic level, HIV-specific IgA may interfere with the effector functions of IgG, as suggested by recent studies of individuals systemically immunized with an experimental HIV vaccine. Although HIV-specific IgG and IgA antibodies may exhibit their protective activities at mucosal surfaces through interference with viral entry and local neutralization at the systemic level, such antibodies may display discordant effector functions.

Implication of nanoparticles/microparticles in mucosal vaccine delivery

Although polymeric nanoparticles/microparticles are well established for the mucosal administration of conventional drugs, they have not yet been developed commercially for vaccine delivery. The limitation of the mucosal (particularly oral) route of delivery, including low pH, gastric enzymes, rapid transit and poor absorption of large molecules, has made mucosal vaccine delivery challenging. Nevertheless, several polymeric delivery systems for mucosal vaccine delivery are currently being evaluated. The polymer-based approaches are designed to protect the antigen in the gut, to target the antigen to the gut-associated lymphoid tissue or to increase the residence time of the antigen in the gut through bioadhesion. M-cell targeting is a potential approach for mucosal vaccine delivery, which can be achieved using M-cell-specific lectins, microbial adhesins or immunoglobulins. While many hurdles must be overcome before targeted mucosal vaccine delivery becomes a practical reality, this is a potential area of research that has important implications for future vaccine development. This review comprises various aspects that could be decisive in the development of polymer based mucosal vaccine delivery systems.

Humoral immune responses to the human immunodeficiency virus type-1 (HIV-1) in the genital tract compared to other mucosal sites

Infection with the human immunodeficiency virus-1 (HIV-1) must be considered as a primarily mucosal disease. On a worldwide basis, the absolute majority of HIV infections occur through mucosal surfaces of the genital and intestinal tracts, and the earliest and most dramatic immunologic alterations are induced by the virus in mucosal tissues. However, individual compartments of mucosal components of the immune system display remarkable differences with respect to dominant antibody isotypes, virus phenotypes, densities and origins of cells involved in innate and specific immunity, presence or absence of inductive sites, and routes of immunizations that induce humoral and cellular responses. In this regard, the mucosal immune system of the female and male genital tracts exhibit several features which are distinct from other mucosal tissues, including dominance of the IgG isotype, local as well as pronounced systemic origin of antibodies, the absence of organized lymphoepithelial inductive sites and limited humoral responses stimulated by local antigen administration. Furthermore, it is evident that, irrespective of the route of infection, HIV-1 induces easily detectable IgG but not IgA specific antibody responses. These differences must be considered in the design of protective vaccines against infection with HIV and other agents of sexually transmitted diseases.

Humoral immune responses to the human immunodeficiency virus type-1 (HIV-1) in the genital tract compared to other mucosal sites

Infection with the human immunodeficiency virus-1 (HIV-1) must be considered as a primarily mucosal disease. On a worldwide basis, the absolute majority of HIV infections occur through mucosal surfaces of the genital and intestinal tracts, and the earliest and most dramatic immunologic alterations are induced by the virus in mucosal tissues. However, individual compartments of mucosal components of the immune system display remarkable differences with respect to dominant antibody isotypes, virus phenotypes, densities and origins of cells involved in innate and specific immunity, presence or absence of inductive sites, and routes of immunizations that induce humoral and cellular responses. In this regard, the mucosal immune system of the female and male genital tracts exhibit several features which are distinct from other mucosal tissues, including dominance of the IgG isotype, local as well as pronounced systemic origin of antibodies, the absence of organized lymphoepithelial inductive sites and limited humoral responses stimulated by local antigen administration. Furthermore, it is evident that, irrespective of the route of infection, HIV-1 induces easily detectable IgG but not IgA specific antibody responses. These differences must be considered in the design of protective vaccines against infection with HIV and other agents of sexually transmitted diseases.

Induction of HIV Immunity in the Genital Tract After Intranasal Delivery of a MVA Vector: Enhanced Immunogenicity After DNA Prime-Modified Vaccinia Virus Ankara Boost Immunization Schedule

Vaccines intended to prevent mucosal transmission of HIV should be able to induce multiple immune effectors in the host including Abs and cell-mediated immune responses at mucosal sites. The aim of this study was to characterize and to enhance the immunogenicity of a recombinant modified vaccinia virus Ankara (MVA) expressing HIV-1 Env IIIB Ag (MVAenv) inoculated in BALB/c mice by mucosal routes. Intravaginal inoculation of MVAenv was not immunogenic, whereas intranasally it induced a significant immune response to the HIV Ag. Intranasal codelivery of MVAenv plus cholera toxin (CT) significantly enhanced the cellular and humoral immune response against Env in the spleen and genitorectal draining lymph nodes, respectively. Heterologous DNAenv prime-MVAenv boost by intranasal immunization, together with CT, produced a cellular immune response in the spleen 10-fold superior to that in the absence of CT. A key finding of these studies was that both MVAenv/MVAenv and DNAenv/MVAenv schemes, plus CT, induced a specific mucosal CD8(+) T cell response in genital tissue and draining lymph nodes. In addition, both immunizations also generated systemic Abs, and more importantly, mucosal IgA and IgG Abs in vaginal washings. Specific secretion of beta-chemokines was also generated by both immunizations, with a stronger response in mice immunized by the DNA-CT/MVA-CT regimen. Our findings are of relevance in the area of vaccine development and support the optimization of protocols of immunization based on MVA as vaccine vectors to induce mucosal immune responses against HIV.

Mucosal immunisation and adjuvants: a brief overview of recent advances and challenges

Mucosal immunisation may be used both to prevent mucosal infections through the activation of anti-microbial immunity and to treat selected autoimmune, allergic or infectious-immunopathological disorders through the induction of antigen-specific tolerance. The development of mucosal vaccines, whether for prevention of infectious diseases or for immunotherapy, requires antigen delivery and adjuvant systems that can efficiently help to present vaccine or immunotherapy antigens to the mucosal immune system. Promising advances have recently been made in the design of more efficient mucosal adjuvants based on detoxified bacterial toxin derivatives or CpG motif-containing DNA, and perhaps even more striking progress has been done in the use of virus-like particles as mucosal delivery systems for vaccines and of cholera toxin B subunit as antigen vector for immunotherapeutic tolerance induction. However, it is a memento that two recently developed mucosal vaccines for human use against rotavirus diarrhoea and influenza were withdrawn after a short period in the market because of adverse reactions among the vaccinees, thus emphasising the difficult and challenging task also for mucosal immunisation of combining vaccine and adjuvant efficacy with safety and acceptability.