Expression of Mycobacterium tuberculosis and Mycobacterium leprae proteins by vaccinia virus

Next generation: tuberculosis vaccines that elicit protective CD8+ T cells

Tuberculosis continues to cause considerable human morbidity and mortality worldwide, particularly in people coinfected with HIV. The emergence of multidrug resistance makes the medical treatment of tuberculosis even more difficult. Thus, the development of a tuberculosis vaccine is a global health priority. Here we review the data concerning the role of CD8+ T cells in immunity to tuberculosis and consider how CD8+ T cells can be elicited by vaccination. Many immunization strategies have the potential to elicit CD8+ T cells and we critically review the data supporting a role for vaccine-induced CD8+ T cells in protective immunity. The synergy between CD4+ and CD8+ T cells suggests that a vaccine that elicits both T-cell subsets has the best chance at preventing tuberculosis.

Vaccination with recombinant vaccinia viruses protects mice against Mycobacterium tuberculosis infection

A number of subunit-based vaccine candidates have recently begun to erode the exclusive position of Mycobacterium bovis bacillus Calmette-Guérin (BCG), which gives unpredictable and highly variable protection against tuberculosis. In this paper we investigated the protective capacity of the 19,000 MW and 38,000 MW glyco-lipoproteins of M. tuberculosis expressed by recombinant vaccinia viruses in a mouse Mycobacterium tuberculosis infection model. Both proteins were expressed at high levels by recombinant vaccinia-infected cells. In addition, two inoculations of C57B1/6 mice with either recombinant vaccinia virus significantly reduced the bacterial counts in the lungs of M. tuberculosis H37Rv-infected mice, when compared with the group infected with control virus. This is the first report of protection against tuberculous infection using recombinant vaccinia viruses with results that suggest that secreted glyco-lipoproteins in conjunction with the vaccinia vector represent suitable candidates for further vaccine-related studies.

Immunogenicity and protection studies with recombinant mycobacteria and vaccinia vectors coexpressing the 18-kilodalton protein of Mycobacterium leprae

The activation of antigen-specific T lymphocytes is essential for the control of leprosy infection in humans and experimental animals. T cells recognize a variety of protein antigens from Mycobacterium leprae, including the 18-kDa protein, which is limited in distribution among mycobacteria and which is absent from Mycobacterium tuberculosis and the vaccine strain, Mycobacterium bovis BCG. Adjuvant preparations of mycobacterial protein antigens have had limited protective efficacy for experimental infections in animals. Since recombinant vectors may elicit more effective T-cell responses than adjuvant preparations, recombinant vaccinia virus (VV18) and M. bovis BCG (BCG18) vectors expressing the 18-kDa protein of M. leprae were prepared. Both VV18 and BCG18 stimulated anti-18-kDa protein antibody and lymphocyte proliferative responses. Sequential immunization with VV18 followed by BCG18 induced higher levels of specific immunoglobulin G2a antibodies than immunoglobulin G1 antibodies, in contrast to immunization with VV18 or BCG18 alone. The protective efficacy of immunization with VV18 from a challenge with BCG18 was examined in two murine models of mycobacterial infection. After intravenous challenge, mice immunized with recombinant vaccinia virus exhibited lower initial levels of replication and earlier clearance of BCG18 from their spleens than mice immunized with vaccinia virus expressing an unrelated protein. After footpad infection in a dissemination model, there was earlier clearance of BCG18 from specifically immunized mice. However, immunization of mice with VV18 did not prevent a productive mycobacterial infection.

Synthetic delivery system for tuberculosis vaccines: immunological evaluation of the M. tuberculosis 38 kDa protein entrapped in biodegradable PLG microparticles

Tuberculosis remains a major public health burden which could be ameliorated by effective and well-defined subunit vaccines, particularly because the protective efficacy of current M. bovis BCG vaccines is both unpredictable and variable. The immunodominant 38 kDa antigen from Mycobacterium tuberculosis was entrapped in biodegradable poly (DL-lactide co-glycolide) (PLG) microparticles which served as a delivery system. Both cellular and humoral immune responses were assessed and compared with those obtained after immunization with the 38 kDa protein emulsified in incomplete Freund's adjuvant (IFA). Vaccination of mice with a single dose of antigen-loaded microparticles resulted in specific IgG titres peaking after five weeks comparable to those achieved after vaccination with protein emulsified in incomplete Freund's adjuvant (IFA). T-cell responses were found to be superior to those induced with antigen/IFA. The T- and B-cell epitope specificities ad judged with synthetic peptides were identical following immunization with antigen in microparticles or IFA. Differences in adjuvanticity were revealed by measuring antigen-specific IgG1, IgG2a and antigen-induced IFN-gamma secretion in vitro: substantially higher titres of IgG2a were observed following immunization with antigen/microparticles than with 38 kDa protein/IFA. This was paralleled by a tenfold higher secretion of IFN-gamma in mice injected with antigen/microparticles. Reduction in colony-forming units was not consistent in mice immunized with 38 kDa protein entrapped in microparticles which were subsequently infected with live tubercle bacilli. Taken together these results indicate that biodegradable PLG microparticles constitute a favorable candidate vaccine delivery system worthy of further assessment in the quest to develop better and defined agents protecting against tuberculosis.

The immune response to mycobacterial infection: development of new vaccines

Pulmonary tuberculosis continues to flourish worldwide despite our most vigorous attempts to control it. After nearly a century of study we still know very little about the virulence factors of M. tuberculosis of M. bovis or how they trigger the protective immune response within the infected host. This anti-tuberculous response is mediated by a population of specifically sensitised T lymphocytes which activate the monocytes entering the developing lesion from the bloodstream. The immunologically activated macrophage induces a persistent bacteriostasis which is usually sufficient to protect the host although it will not eliminate the infection altogether so that reactivation can occur whenever the cellular defences are depleted as a result of aging or immunosuppressive chemotherapy. Protective immunogens released by actively growing tubercle bacilli give rise to a protective cell-mediated, rather than a humoral (non-protective) immunity. The genes responsible for the production of these "protective" antigens are being cloned and transferred to suitable mycobacterial vectors by means of the newly developed "shuttle phasmid". Development of such recombinants constitute the first step in preparing more effective anti-tuberculous vaccines for future use against these important human and animal pathogens.

Lipid synthesis in mycobacteria: characterization of the biotin carboxyl carrier protein genes from Mycobacterium leprae and M. tuberculosis

The causative agents of leprosy and tuberculosis, Mycobacterium leprae and Mycobacterium tuberculosis, have a lipid-rich cell envelope which contributes to virulence and antibiotic resistance. Acyl coenzyme A carboxylase, which catalyzes the first committed step of lipid biosynthesis, consists in mycobacteria of two subunits, one of which is biotinylated. Genes from M. leprae and M. tuberculosis encoding a biotinylated protein have been cloned and sequenced. Analysis of the derived protein sequences demonstrated the presence of biotin-binding sites and putative ATP-bicarbonate interactions sites, consistent with the proteins having a biotin carboxylase function as well as their being biotin carrier proteins.

Antigen-dependent in vitro culture of protective T cells from BCG-primed mice

Induction of protective immunity against pathogenic mycobacteria depends on vaccination with live organisms such as Bacille Calmette-Guérin (BCG). However, it is not known how many and which antigens are involved in the protective host response. In this study, we developed a system of antigen-dependent in vitro culture which is suitable for the analysis of protective subunits, presented in a soluble form. Spleen cells from Mycobacterium bovis BCG-immune mice, enriched for T cells and depleted of adherent cells on a column of G-10 Sephadex, were cultured for periods varying between 3 and 14 days before transfer and challenge with M. tuberculosis in irradiated hosts. Following 10 days in culture, immune T cells sustained their capacity to transfer protection to tuberculous infection when incubated in the presence of either live BCG or a soluble extract from M. tuberculosis, but lost this ability when cultured in the absence of antigen, or in the presence of the polyclonal mitogen concanavalin A. One immunodominant antigen, represented by the recombinant 38-kD antigen, failed to sustain the adoptive protection, despite pronounced stimulation of lymphoproliferation in culture. Antigenic in vitro stimulation of protective T cells was accompanied by enhanced responsiveness to exogenous IL-2. The experimental system described may be generally suitable to test in vitro the protective potentials of soluble molecular subunits of mycobacteria.

Mycobacterial protein antigens: a compilation

In response to recommendations from the Steering Committees responsible for co-ordination of World Health Organization programmes for research on the immunology of leprosy (IMMLEP) and tuberculosis (IMMTUB), a list was prepared summarizing the properties of mycobacterial proteins currently under investigation with respect to their immunological activities. After consultation with more than 40 laboratories world-wide this list was extended to form the compilation shown below and is intended to provide a comprehensive and convenient reference for future studies in this field.

Identification of p53 as a sequence-specific DNA-binding protein

The tumor-suppressor gene p53 is altered by missense mutation in numerous human malignancies. However, the biochemical properties of p53 and the effect of mutation on these properties are unclear. A human DNA sequence was identified that binds specifically to wild-type human p53 protein in vitro. As few as 33 base pairs were sufficient to confer specific binding. Certain guanines within this 33-base pair region were critical, as methylation of these guanines or their substitution with thymine-abrogated binding. Human p53 proteins containing either of two missense mutations commonly found in human tumors were unable to bind significantly to this sequence. These data suggest that a function of p53 may be mediated by its ability to bind to specific DNA sequences in the human genome, and that this activity is altered by mutations that occur in human tumors.

Modulation of experimental autoimmunity: treatment of adjuvant arthritis by immunization with a recombinant vaccinia virus

Live recombinant vaccinia viruses, expressing antigens from pathogenic microorganisms, are studied for their use as vaccines designed for the protection against infectious diseases. Infections with these vaccinia virus recombinants, expressing proteins or epitopes from viruses, parasites, or bacteria, have resulted in the development of specific neutralizing antibodies or cytotoxic T lymphocytes. Here, we describe the generation of a recombinant vaccinia virus expressing the mycobacterial 65-kDa heat shock protein (HSP65). A vaccinia recombinant virus was constructed by placing the gene for the Mycobacterium bovis BCG HSP65 under control of a vaccinia virus promoter and inserting this mycobacterial gene in the thymidine kinase locus of the vaccinia virus genome. Mycobacterial HSP65 is a critical antigen in the autoimmune model of adjuvant arthritis induced in Lewis rats by the immunization with Mycobacterium tuberculosis. We report the induction of immunity directed to this mycobacterial HSP65 by testing for the presence of specific antibodies and T-cell proliferation. Furthermore, induction of such immunity resulted in a reduction of arthritis severity when given to rats before or, even more interestingly, during development of arthritis. Disease reduction was not found after administration of HSP65 in the absence of vaccinia virus as a vector when given during arthritis development. Therefore, recombinant vaccinia virus may offer new prospectives for specific intervention in autoimmunity.