We have successfully produced host range mutations in all 4 serotypes of dengue virus which are the result of deletions in the membrane spanning domain of the virus envelope protein. We have shown that these viruses grow efficiently in insect cells but poorly in mammalian cells. In collaboration with the company "Arbovax" we have shown that these mutations elicit protective immunity in mice and in the case of serotype 2 dengue virus in monkeys. A tetravalent formulation designed to produce protective immunity against all 4 serotypes has just completed testing in monkeys. Significant effort will be dedicated to the analysis of the outcome of this trial.