Evaluation of T-cell and B-cell epitopes and design of multivalent vaccines against HTLV-1 diseases

Human T-cell lymphotropic virus Type 1 is the causative agent of Adult T-cell leukemia and HTLV-1 associated Myelopathy/Tropical Spastic Paraparesis. The viral transactivator Tax is the primary target of the cellular immune response and humoral responses are mainly directed against the envelope protein. Vaccination against HTLV-1 is a feasible option as there is little genetic and antigenic variability. The work described herein was aimed at the identification of T-cell determinants for the induction of CTL responses and B-cell determinants for the induction of antibody responses. Vaccines that incorporate multiple epitopes would have broad population coverage and may be potentially more effective in preventing CTL escape mutants. Hence, three CTL epitopes that were determined to be highly immunogenic were incorporated into a single peptide construct designed to allow for intracellular processing to liberate the individual epitopes for simultaneous priming of multispecific CTL priming. This construct was effective in inducing responses against each intended epitope. A statistically significant reduction in viral replication was observed in vaccinated mice that were challenged with recombinant Tax vaccinia virus.; Studies were also undertaken to design peptide immunogens that have a defined α-helical secondary structure that mimics the central helical region of the gp21 TM subunit of the envelope protein, for the induction of antibodies that have high affinity for the native protein with increased capacity for virus neutralization. A multicomponent single matrix strategy was applied to induce a stable helical conformation. Key mutations were also introduced to increase hydrophobic interactions for coiled coil formation. This peptide construct had a stable helical structure as determined by circular dichroism measurements. Further, the peptide was highly immunogenic in outbred mice and the antibodies were specific for the helical conformation and recognized native protein with higher affinity as compared to the wild type peptide with no mutations constructed in a similar manner.; Finally, a chimeric peptide incorporating a promiscuous T-helper epitope and a B-cell epitope derived from the C-terminal region of the TM was also successfully tested for its ability to induce virus neutralizing antibodies in rabbits. The results of these studies may have implications in HTLV-1 vaccine development.