Lymphatic filariasis due to Brugia malayi and Wucheraria bancrofti is a debilitating disease that affects more than 200 million people worldwide. Mass chemotherapy is effective in reducing infection intensity in some endemic areas, suggesting that control against this infection is feasible. In endemic areas a group of individuals broadly defined as endemic normal (EN), remain refractive to infection despite frequent exposure to the infection. These individuals carry circulating protective antibodies that could kill infective larvae (L3) of B. malayi and W. bancrofti in vitro. Mechanism of this immune killing is not known. Nevertheless, these findings show that active immunization against lymphatic filariasis is possible, provided the antigens that generated the protective immune responses could be identified. Using an interative screening of a phage display expression library of B. malayi L3 with EN sera, we identified three antigens (BmALT-2, BmVAH and BmCol-4) that are specifically responsible for generating the protective immune responses. Homologues of all three antigens were subsequently cloned from W. bancrofti and show significant cross-reactivity. Preliminary immunization studies showed that significant protection (40-72%) could be achieved in mice and jird models following a prime (DNA) boost (recombinant protein) approach using all three antigens. Experiences from vaccine development against malaria suggest that a multivalent vaccine confer significantly higher protection than a single antigen alone. Therefore, in this application we are proposing to develop a multivalent vaccine comprising the three protective antigens (ALT-2, VAH and BmCol-4). There are four specific aims to this proposal. Since antigenic poly morphism has been reported in filariasis, Aim 1 will first determine whether there is any antigenic polymorphism in the three candidate vaccine antigens isolated from wild collected parasites. Preliminary studies show that both cells and antibodies are important in the protective responses in EN individuals. Therefore, Aim 2 will identify the characteristics of the protective immune responses to the vaccine constructs in human. Based on the information gathered from aims 1 and 2, Aim 3 will construct a multivalent vaccine consisting of hybrid gene of the three candid antigens in pVAX vector and fusion protein for boosting.
Aim 4 will then evaluate and optimize the multivalent vaccine in animal models and determine the optimum protocol for human vaccination. The proposed studies are based on solid preliminary data and are hypotheses driven. Results from these studies, we believe will advance our knowledge towards developing a defined vaccine against lymphatic filariasis in the human.
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