Identification of potential vaccine and drug target candidates by expressed sequence tag analysis and immunoscreening of Onchocerca volvulus larval cDNA libraries

The search for appropriate vaccine candidates and drug targets against onch ocerciasis has so far been confronted with several limitations due to the u navailability of biological material, appropriate molecular resources, and knowledge of the parasite biology, To identify targets for vaccine or chemo therapy development we have undertaken two approaches. First, cDNA expressi on libraries were constructed from life cycle stages that are critical for establishment of Onchocerca volvulus infection, the third-stage larvae (L3) and the molting L3. A gene discovery effort was then initiated by random e xpressed sequence tag analysis of 5,506 cDNA clones. Cluster analyses showe d that many of the transcripts were up-regulated and/or stage specific in e ither one or both of the cDNA libraries when compared to the microfilariae, L2, and both adult stages of the parasite. Homology searches against the G enBank database facilitated the identification of several genes of interest , such as proteinases, proteinase inhibitors, antioxidant or detoxification enzymes, and neurotransmitter receptors, as well as structural and houseke eping genes. Other O. volvulus genes showed homology only to predicted gene s from the free-living nematode Caenorhabditis elegans or were entirely nov el. Some of the novel proteins contain potential secretory leaders. Secondl y, by immunoscreening the molting L3 cDNA library with a pool of human sera from putatively immune individuals, we identified six novel immunogenic pr oteins that otherwise would not have been identified as potential vaccinoge ns using the gene discovery effort. This study lays a solid foundation for a better understanding of the biology of O. volvulus as well as for the ide ntification of novel targets for filaricidal agents and/or vaccines against onchocerciasis based on immunological and rational hypothesis-driven resea rch.