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Abstract. We conducted a phase II, randomized, double-blind, placebo-controlled, safety and immunogenicity study of a serially passaged, plaque-purified live chikungunya (CHIK) vaccine in 73 healthy adult volunteers. Fiftynine volunteers were immunized one time subcutaneously with the CHIK vaccine and 14 were immunized with placebo (tissue culture fluid). Vaccinees were clinically evaluated intensively for one month, and had repeated blood draws for serological assays (50% plaque-reduction neutralization test) for one year. Except for transient arthralgia in five CHIK vaccinees, the number and severity of local and systemic reactions and abnormal laboratory tests after immunization were similar in CHIK vaccinees and placebo recipients. Fifty-seven (98%) of 58 evaluable CHIK vaccinees developed CHIK neutralizing antibody by day 28, and 85% of vaccinees remained seropositive at one year after immunization. No placebo recipients seroconverted. This promising live vaccine was safe, produced well-tolerated side effects, and was highly immunogenic.

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We examined the sera of volunteers vaccinated with recombinant gp160 of human immunodeficiency virus type 1 (HIV-1) and control volunteers for the presence of anti-(anti-gp160 idiotype) antibodies which antigenically mimic gp160 and, therefore, bind to CD4 on human cells. Anti-CD4 antibodies were detected in the sera of 3 of 5 rgp160 recipients and 1 of 5 controls by indirect immunofluorescence using CD4-transfected HeLa cells or enzyme-linked immunosorbent assay (ELISA) using recombinant soluble CD4 as the solid phase. The control volunteer who was positive subsequently developed antibodies to HIV-1 by Western blot analysis. The anti-CD4 antibodies detected in the sera of the rgp160 vaccinees and the control volunteer appeared to be anti-idiotypic in nature, reacting with a paratope expressed on goat anti-gp160 antibodies but not on antibodies from normal goat serum. Binding to either transfected CD4+ HeLa cells or blotted anti-gp160 serum could be inhibited by preincubating the anti-CD4 serum with soluble CD4, or preincubating the cells or blotted anti-gp160 serum with recombinant gp160. Anti-CD4 antibodies were initially detectable only after the antibody response to gp160 began to decrease in the vaccinees, and the HIV-1-infected volunteer mounted a detectable anti-HIV-1 antibody response only after a decline in the anti-CD4 antibodies in his serum. These data strongly suggest that anti-CD4 antibodies which are anti-idiotypic to a paratope expressed on anti-gp160 antibodies are generated in response to both vaccination with rgp160 and infection with HIV-1.(ABSTRACT TRUNCATED AT 250 WORDS)