Vaccine candidates in STD

Non-pathogenic Borrelia burgdorferi expressing Treponema pallidum TprK and Tp0435 antigens as a novel approach to evaluate syphilis vaccine candidates

BACKGROUND

Syphilis is resurgent in many developed countries and still prevalent in developing nations. Current and future control campaigns would benefit from the development of a vaccine, but although promising vaccine candidates were identified among the putative surface-exposed integral outer membrane proteins of the syphilis spirochete, immunization experiments in the rabbit model using recombinant antigens have failed to fully protect animals upon infectious challenge. We speculated that such recombinant immunogens, purified under denaturing conditions from Escherichia coli prior to immunization might not necessarily harbor their original structure, and hypothesized that enhanced protection would result from performing similar immunization/challenge experiments with native antigens.

METHODS

To test our hypothesis, we engineered non-infectious Borrelia burgdorferi strains to express the tp0897 (tprK) and tp0435 genes of Treponema pallidum subsp. pallidum and immunized two groups of rabbits by injecting recombinant strains intramuscularly with no adjuvant. TprK is a putative integral outer membrane protein of the syphilis agent, while tp0435 encodes the highly immunogenic T. pallidum 17-kDa lipoprotein, a periplasmic antigen that was also shown on the pathogen surface. Following development of a specific host immune response to these antigens as the result of immunization, animals were challenged by intradermal inoculation of T. pallidum. Cutaneous lesion development was monitored and treponemal burden within lesions were assessed by dark-field microscopy and RT-qPCR, in comparison to control rabbits.

RESULTS

Partial protection was observed in rabbits immunized with B. burgdorferi expressing TprK while immunity to Tp0435 was not protective. Analysis of the humoral response to TprK antigen suggested reactivity to conformational epitopes.

CONCLUSIONS

Immunization with native antigens might not be sufficient to obtain complete protection to infection. Nonetheless we showed that non-infectious B. burgdorferi can be an effective carrier to deliver and elicit a specific host response to T. pallidum antigens to assess the efficacy of syphilis vaccine candidates.

Inactivation of HSV-2 by ascorbate–Cu(II) and its protecting evaluation in CF-1 mice against encephalitis

Ascorbate is an important antioxidant. However, in the presence of transition metals such as Cu(II) or Fe(III), it also has pro-oxidant capabilities. The effect of ascorbate-Cu(II) in the in vitro infection of herpes simplex virus type 2 (HSV-2) and its protecting effect in a murine model was investigated. HSV-2 was treated with different concentrations of ascorbate in the presence of Cu(II). A group of CF-1 mice were treated with the inactivated virus and other treated with maintenance medium containing only ascorbate-Cu(II). Weeks later, mice were challenged intranasally with infectious viruses. HSV-2 was completely inactivated by 2mM ascorbate plus 1mM Cu(II). Ascorbate or Cu(II) alone did not inactivate the virus. Compared with the control group, 60% of the immunized animals did not show any sign of encephalitis and survived the herpes virus infection, while a 7% survival rate was observed in the control group (P = 0.056). We concluded that the in vitro treatment of HSV-2 with ascorbate-Cu(II) is not only able to inactivate the virus, but also suggested that the viral particles induced a protective response against herpes encephalitis. This inactivation may provide an alternative method to develop new agents therapeutics.