SUMMARYWe report on a new approach toward protection against tuberculosis, based on passive inoculation with immunoglobulin A (IgA) antibodies. In a mouse model of tuberculous lung infection, intranasal inoculations of mice with an IgA monoclonal antibody (mAb) against the a-crystallin antigen of Mycobacterium tuberculosis reduced up to 10-fold the lung bacterial counts at nine days after either aerosol-or intranasal challenge. This effect involved synergism between mAb inoculations shortly before and 3 days after infection. Monomeric IgA reduced the colony-forming unit counts to the same extent as the polymeric IgA, suggesting antibody targeting to Fca, rather than poly-immunoglobulin receptors on infected lung macrophages. The protective effect was of short duration, presumably due to the rapid degradation of the intranasally applied IgA. Our results provide evidence of an alternative approach which could be further developed toward immunoprophylaxis against tuberculosis in immunocompromised subjects.

The lungs are considered to have an impaired capacity to contain infection by pathogenic mycobacteria, even in the presence of effective systemic immunity. In an attempt to understand the underlying cellular mechanisms, we characterized the γδ T cell population following intranasal infection with Mycobacterium bovis bacillus Calmette-Guérin (BCG). The peak of γδ T cell expansion at 7 days postinfection preceded the 30 day peak of αβ T cell expansion and bacterial count. The expanded population of γδ T cells in the lungs of BCG-infected mice represents an expansion of the resident Vγ2 T cell subset as well as an influx of Vγ1 and of four different Vδ gene-bearing T cell subsets. The γδ T cells in the lungs of BCG-infected mice secreted IFN-γ following in vitro stimulation with ionomycin and PMA and were cytotoxic against BCG-infected peritoneal macrophages as well as against the uninfected J774 macrophage cell line. The cytotoxicity was selectively blocked by anti-γδ TCR mAb and strontium ions, suggesting a granule-exocytosis killing pathway. Depletion of γδ T cells by injection of specific mAb had no effect on the subsequent developing CD4 T cell response in the lungs of BCG-infected mice, but significantly reduced cytotoxic activity and IFN-γ production by lung CD8 T cells. Thus, γδ T cells in the lungs might help to control mycobacterial infection in the period between innate and classical adaptive immunity and may also play an important regulatory role in the subsequent onset of αβ T lymphocytes.

The eradication of smallpox (variola) and the subsequent cessation of routine vaccination have left modern society vulnerable to bioterrorism employing this devastating contagious disease. The existing, licensed vaccines based on live vaccinia virus (VACV) are contraindicated for a substantial number of people, and prophylactic vaccination of large populations is not reasonable when there is little risk of exposure. Consequently, there is an emerging need to develop efficient and safe therapeutics to be used shortly before or after exposure, either alone or in combination with vaccination. We have characterized the human antibody response to smallpox vaccine (VACV Lister) in immunized volunteers and isolated a large number of VACV-specific antibodies that recognize a variety of different VACV antigens. Using this broad antibody panel, we have generated a fully human, recombinant analogue to plasma-derived vaccinia immunoglobulin (VIG), which mirrors the diversity and specificity of the human antibody immune response and offers the advantage of unlimited supply and reproducible specificity and activity. The recombinant VIG was found to display a high specific binding activity toward VACV antigens, potent in vitro VACV neutralizing activity, and a highly protective efficacy against VACV challenge in the mouse tail lesion model when given either prophylactically or therapeutically. Altogether, the results suggest that this compound has the potential to be used as an effective postexposure prophylaxis or treatment of disease caused by orthopoxviruses.