Ebola virus: the search for vaccines and treatments

Ebola viruses belong to the family Filoviridae, which are among the most virulent infectious agents known. These viruses cause acute, and frequently fatal, hemorrhagic fever in humans and nonhuman primates. Currently, no vaccines or treatments are available for human use. This review describes Ebola viruses, with a particular focus on the status of research efforts to develop vaccines and therapeutics and to identify the immune mechanisms of protection.

Susceptibility to secondary Francisella tularensis live vaccine strain infection in B-cell-deficient mice is associated with neutrophilia but not with defects in specific T-cell-mediated immunity

Previous studies have demonstrated a role for B cells, not associated with antibody production, in protection against lethal secondary infection of mice with Francisella tularensis live vaccine strain (LVS). However, the mechanism by which B cells contribute to this protection is not known. To study the specific role of B cells during secondary LVS infection, we developed an in vitro culture system that mimics many of the same characteristics of in vivo infection. Using this culture system, we showed that B cells do not directly control LVS infection but that control of LVS growth is mediated primarily by LVS-primed T cells. Importantly, B cells were not required for the generation of effective memory T cells since LVS-primed, B-cell-deficient (BKO) mice generated CD4(+) and CD8(+) T cells that controlled LVS infection similarly to LVS-primed CD4(+) and CD8(+) T cells from wild-type mice. The control of LVS growth appeared to depend primarily on gamma interferon and nitric oxide and was similar in wild-type and BKO mice. Rather, the inability of BKO mice to survive secondary LVS infection was associated with marked neutrophil influx into the spleen very early after challenge. The neutrophilia was directly associated with B cells, since BKO mice reconstituted with naive B cells prior to a secondary challenge with LVS had decreased bacterial loads and neutrophils in the spleen and survived.

Infection of B cell-deficient mice with CDC 1551, a clinical isolate of Mycobacterium tuberculosis: delay in dissemination and development of lung pathology

Long-term survival of mice infected with Mycobacterium tuberculosis is dependent upon IFN-gamma and T cells, but events in early phases of the immune response are not well understood. In this study, we describe a role for B cells during early immune responses to infection with a clinical isolate of M. tuberculosis (CDC 1551). Following a low-dose infection with M. tuberculosis CDC 1551, similar numbers of bacteria were detected in the lungs of both B cell knockout (IgH 6-, BKO) and C57BL/6J (wild-type) mice. However, despite comparable bacterial loads in the lungs, less severe pulmonary granuloma formation and delayed dissemination of bacteria from lungs to peripheral organs were observed in BKO mice. BKO mice reconstituted with naive B cells, but not those given M. tuberculosis-specific Abs, before infection developed pulmonary granulomas and dissemination patterns similar to wild-type animals. Further analysis of lung cell populations revealed greater numbers of lymphocytes, especially CD8+ T cells, macrophages, and neutrophils in wild-type and reconstituted mice than in BKO mice. Thus, less severe lesion formation and delayed dissemination of bacteria found in BKO mice were dependent on B cells, not Abs, and were associated with altered cellular infiltrate to the lungs. These observations demonstrate an important, previously unappreciated, role for B cells during early immune responses to M. tuberculosis infections.

Importance of B cells, but not specific antibodies, in primary and secondary protective immunity to the intracellular bacterium Francisella tularensis live vaccine strain

Although there appears to be little if any role for specific antibodies in protection against intracellular bacteria, such as the model pathogen F. tularensis live vaccine strain (LVS), the role of B cells themselves in primary and secondary infection with such bacteria has not been examined directly. We show here that mice deficient in mature B cells and antibodies (B-cell knockout mice) are marginally compromised in controlling primary sublethal infection but are 100-fold less well protected against secondary lethal challenge than are their normal counterparts. This defect in optimal specific protective immunity was readily reconstituted by the transfer of primed, and to a lesser degree, unprimed B cells, but not by the transfer of specific antibodies. The results indicate a previously unappreciated role for B cells in secondary immunity to intracellular pathogens through a function other than antibody production.

Effective, nonsensitizing vaccination with culture filtrate proteins against virulent Mycobacterium bovis infections in mice

Vaccination of mice with Mycobacterium bovis culture filtrate proteins (CFP), prepared in a variety of adjuvants (aluminum hydroxide, Quil-A, and dimethyldioctyldecyl ammonium bromide [DDA]), provided significant protection against an aerosol challenge of virulent M. bovis. Additionally, vaccination with CFP in DDA or Quil-A did not sensitize mice to M. bovis purified protein derivative.