The development and characterization of transgenic Leishmania major expressing murine CD40L

Abstract

Leishmanization is the inoculation of live Leishmania into the host to vaccinate against subsequent infections. This approach has been largely discontinued due to safety concerns. We have previously shown that combining CD40L with Leishmania antigen preferentially induces a type 1 immune response and provides some protection to vaccinated mice. In the present study, we developed transgenic L. major which express and secrete the extracellular portion of CD40L (L. major CD40LE). We hypothesized that these organisms would be less virulent but more immunogenic than wild-type organisms, and therefore be more effective at leishmanization. Transgenic parasites expressing CD40L mRNA and protein were developed. These parasites had similar growth characteristics to wild-type organisms. Susceptible BALB/c mice infected with these parasites developed significantly smaller lesions containing fewer parasites than animals infected with wild-type organisms. Infection of C57BL/6 CD40L-/- mice with transgenic L. major resulted in significantly smaller lesions than infection with wild-type L. major, indicating in vivo biological activity of the transgenic protein. Infection of resistant C57BL/6 mice with low doses of transgenic parasites induced a significant amount of protection against subsequent high dose infection with wild-type organisms. These results demonstrate that transgenic organisms expressing CD40L are less virulent than wild-type organisms while retaining full immunogenicity. The implications of this study are that parasites expressing immune-modulatory molecules may be improved alternatives to traditional leishmanization.