ABSTRACT
A non-human primate model for the induction of protective immunity against the pre-erythrocytic stages of Plasmodium vivax malaria using radiation-attenuated P. vivax sporozoites may help to characterize protective immune mechanisms and identify novel malaria vaccine candidates. Immune responses and protective efficacy induced by vaccination with irradiated P. vivax sporozoites were evaluated in malaria-naive Aotus monkeys. Three groups of six monkeys received two, five, or ten intravenous inoculations, respectively, of 100,000 irradiated P. vivax sporozoites; control groups received either 10 doses of uninfected salivary gland extract or no inoculations. Immunization resulted in the production low levels of antibodies that specifically recognized P. vivax sporozoites and the circumsporozoite protein. Additionally, immunization induced low levels of antigen-specific IFN-γ responses. Intravenous challenge with viable sporozoites resulted in partial protection in a dose-dependent manner. These findings suggest that the Aotus monkey model may be able to play a role in preclinical development of P. vivax pre-erythrocytic stage vaccines.
Subject(s)
Malaria Vaccines/immunology , Malaria, Vivax/prevention & control , Plasmodium vivax/immunology , Sporozoites/immunology , Sporozoites/radiation effects , Animals , Antibodies, Protozoan/blood , Antibody Specificity , Aotidae , Female , Fluorescent Antibody Technique , Interferon-gamma/biosynthesis , Leukocytes, Mononuclear/immunology , Male , Plasmodium vivax/radiation effects , Protozoan Proteins/immunologyABSTRACT
This study describes a successful Plasmodium vivax sporozoite infection in Aotus lemurinus griseimembra. Twenty-eight naive or previously infected monkeys, either splenectomized or spleen intact, were inoculated intravenously or subcutaneously with Plasmodium vivax sporozoites of the Salvador I strain or with two wild isolates (VCC-4 and VCC-5; Vivax-Cali-Colombia). The monkeys were successfully infected regardless of the parasite strain, spleen presence, or inoculation route and showed prepatent periods that ranged from 16 to 89 days. Only one monkey inoculated intravenously failed to develop parasitemia. Since immune protection against malaria pre-erythrocytic forms is mediated by both helper and cytolytic T cells that may home in the spleen and P. vivax cultures are not yet available; the use of spleen-intact A. lemurinus griseimembra, susceptible to both adapted and non-adapted strains of P. vivax sporozoites, is a valuable model for evaluation of pre-erythrocytic vaccine candidates.
