USE OF THE RHESUS-MONKEY AS AN EXPERIMENTAL-MODEL TO TEST THE DEGREE OF EFFICACY OF AN ANTISPOROZOITE PEPTIDE MALARIA VACCINE CANDIDATE COMBINED WITH COPOLYMER-BASED ADJUVANTS

Humoral response against sporozoites is not effective in protecting in dividuals from getting malaria. Reduction in the infectivity of sporoz oites has not been quantified for most anti-sporozoite vaccines tested . Quantification requires animal models providing predictable prepaten t periods, e.g., time elapsed between sporozoite inoculation and detec tion of parasitemia, to be used as an indicator of activity against sp orozoites. A delay in prepatent period from vaccinated animals would t herefore reflect a protective effect in reducing the number of parasit es. We report the vaccination of rhesus monkeys with a synthetic pepti de reproducing part of the repeated region of the circumsporozoite pro tein of Plasmodium cynomolgi. This peptide was conjugated to the carri er protein diphtheria toroid and injected with four adjuvant formulati ons that differed only by the type of emulsion or immunomodulator. Bec ause all five control animals had a synchronous prepatent period after challenge with live sporozoites, it was possible to quantify the prot ective efficacy for each vaccine formulation, even though all monkeys developed parasitemia. Sporozoite elimination correlated with the immu nomodulator and the type of emulsion. Such elimination was related nei ther to antibody titer against the immunizing peptide or the whole spo rozoite, nor to antibody isotype induced by the vaccine formulation.