High resolution radiographic and fine immunologic definition of TB disease progression in the rhesus macaque.

Mycobacterium tuberculosis infection in non-human primates parallels human tuberculosis, and provides a valuable vaccine evaluation model. However, this model is limited by the availability of real-time, non-invasive information regarding disease progression. Consequently, we have combined computed tomography scanning with enumeration of antigen-specific T cell responses. Four rhesus monkeys were infected with M. tuberculosis strain H37Rv (1000 cfu) in the right lower lobe via a bronchoscope. All uniformly developed progressive tuberculosis, and required euthanasia at 12 weeks. Computed tomography scanning provided detailed real-time imaging of disease progression. At necropsy, computed tomography and pathohistologic findings were tightly correlated, and characteristic of human disease. Immunologic monitoring demonstrated progressive evolution of high frequency M. tuberculosis-specific CD4(+) and CD8(+) T cell responses. Peripheral blood effector cell frequencies were similar to those observed in tissues. In summary, computed tomography scanning in conjunction with immunologic monitoring provides a non-invasive, accurate, and rapid assessment of tuberculosis in the non-human primate.

HLA-E-dependent presentation of Mtb-derived antigen to human CD8+ T cells.

Previous studies in mice and humans have suggested an important role for CD8+ T cells in host defense to Mtb. Recently, we have described human, Mtb-specific CD8+ cells that are neither HLA-A, B, or C nor group 1 CD1 restricted, and have found that these cells comprise the dominant CD8+ T cell response in latently infected individuals. In this report, three independent methods are used to demonstrate the ability of these cells to recognize Mtb-derived antigen in the context of the monomorphic HLA-E molecule. This is the first demonstration of the ability of HLA-E to present pathogen-derived antigen. Further definition of the HLA-E specific response may aid development of an effective vaccine against tuberculosis.

Human dendritic cells presenting adenovirally expressed antigen elicit Mycobacterium tuberculosis--specific CD8+ T cells.

Previous studies in murine and human models have suggested an important role for CD8+ T cells in host defense to Mycobacterium tuberculosis (Mtb). Consequently, a successful tuberculosis vaccine may require the elicitation of sustained CD4+ and CD8+ T cell responses. We tested the hypothesis that the potent CD4+ T cell antigen Mtb39 is also a CD8+ T cell antigen. A recombinant adenovirus-expressing Mtb39 (adenoMtb39) was used to infect monocyte-derived dendritic cells. Using interferon-gamma enzyme-linked immunospot, Mtb39-specific CD8+ T lymphocytes were detected in three healthy individuals with latent tuberculosis infection who also had strong anti-Mtb39-specific CD4+ T cell responses. An Mtb39-specific CD8+ T cell line was generated using Mtb39-expressing dendritic cells. Mtb39-specific T cell clones were obtained by limiting dilution cloning. All seven T cell clones obtained were HLA-B44 restricted. Using a panel of synthetic overlapping peptides representative of Mtb39, the peptide epitope was identified for two clones. Furthermore, all T cell clones recognized Mtb-infected dendritic cells and were cytolytic. We conclude that infection of dendritic cells with adenoviral vectors expressing Mtb proteins allows for measurement of antigen-specific CD8+ T cell responses from peripheral blood mononuclear cells. The technique will be useful in defining CD8+ T cell antigens and in measuring immunogenicity of tuberculosis vaccines.

HIV-1 Vpr does not inhibit CTL-mediated apoptosis of HIV-1 infected cells.

HIV-1 infected persons develop a robust CTL response to HIV antigens, yet HIV-1 is able to evade this host response and successfully replicate. The mechanism(s) of evasion is not completely defined but has been suggested to include resistance of infected cells to CTL-mediated apoptosis. The HIV-1 Vpr protein induces G2 arrest by indirectly inhibiting activation of cyclin B/p34cdc2 kinase. Granzyme B, the principle mediator of CTL-induced apoptosis, prematurely activates this same kinase complex. Therefore, we assessed the susceptibility of HIV-1 infected cells to CTL-mediated apoptosis to determine whether the expression of Vpr protected the infected cells from CTL-induced apoptosis. Antigen-specific CD8(+) CTL were able to induce apoptosis in HIV-1 infected cells and cells labeled with peptide corresponding to the CTL epitope with equivalent efficiency. This demonstrates that neither HIV-1 Vpr nor any other HIV protein directly inhibits CTL effector functions. Furthermore, we confirm that HIV-1 Nef is able to provide partial protection from CTL recognition of infected cells. Thus, the inability of CTL to control HIV-1 infection is likely not due to direct inhibition of CTL-mediated apoptosis.