Genetically Attenuated Plasmodium berghei Liver Stages Persist and Elicit Sterile Protection Primarily via CD8 T Cells

Abstract

Live-attenuated Plasmodium liver stages remain the only experimental model that confers complete sterile protection against malaria. Irradiation-attenuated Plasmodium parasites mediate protection primarily by CD8 T cells. In contrast, it is unknown how genetically attenuated liver stage parasites provide protection. Here, we show that immunization with uis3(؊) sporozoites does not cause breakthrough infection in T and B-cell-deficient rag1 ؊/؊ and IFN-␥ ؊/؊ mice.However, protection was abolished in these animals, suggesting a crucial role for adaptive immune responses and interferon-␥. Although uis3(؊) immunization induced Plasmodium-specific antibodies, Bcell-deficient mice immunized with uis3(؊) sporozoites were completely protected against wild-type sporozoite challenge infection. T-cell depletion experiments before parasite challenge showed that protection is primarily mediated by CD8 T cells. In good agreement, adoptive transfer of total spleen cells and enriched CD8 T cells from immunized animals conferred sterile protection against malaria transmission to recipient mice, whereas adoptive transfer of CD4 T cells was less protective. Importantly, primaquine treatment completely abolished the uis3(؊)-mediated protection, indicating that persistence of uis3(؊)-attenuated liver stages is crucial for their protective action. These findings establish the basic immune mechanisms underlying protection induced by genetically attenuated Plasmodium parasites and substantiate their use as vaccines against malaria.

Preerythrocytic, live-attenuated Plasmodium falciparum vaccine candidates by design

“…Immunization of mice with uis3 Ϫ , uis4 Ϫ , or p52 Ϫ parasites induced complete, long-lasting protection against infectious sporozoite challenge (7-9, 11), demonstrating that rodent malaria GAPs are highly effective vaccines. The GAP-induced protection was mediated mainly by CD8 ϩ T cells (9,13,14), but antibodies also contributed to protection (9).…”

“…Immunization of mice with uis3 Ϫ , uis4 Ϫ , or p52 Ϫ parasites induced complete, long-lasting protection against infectious sporozoite challenge (7-9, 11), demonstrating that rodent malaria GAPs are highly effective vaccines. The GAP-induced protection was mediated mainly by CD8 ϩ T cells (9,13,14), but antibodies also contributed to protection (9).To assess the potential to create a GAP vaccine for human malaria, we deleted the P52 and P36 loci in P. falciparum. The deletions did not affect the parasites throughout most of the life cycle, including sporozoite production of the attenuated lines, but resulted in significant growth defects in a hepatocytic cell line.…”

Effectiveness of Gamma Rays in Attenuating Rodent Malaria Parasites of <em>Plasmodium berghei</em> in Blood of Mice

“…It is approved that live-attenuated parasites with irradiation are protective to the host where the contents of parasites in red blood cells are low. However there was no boost conducted to the primed mice, as done by other researchers, to gain the higher degree of acquired immunity which is directly proportional to the number of immunizing doses [12]. Challenges with live parasites is also required to test whether the injection of attenuated parasites as vaccine materials could elicit an antibody in the host; it is the most relevant approach to testing the efficacy of experimental malaria vaccines.…”

Plasmodium berghei sporozoite challenge of vaccinated BALB/c mice leads to the induction of humoral immunity and improved function of CD8+ memory T cells

“…It is known that immunization with attenuated sporozoites induces humoral immune responses against Plasmodium antigens [29] and it was shown that repeated sporozoite challenges of vaccinated mice induce sporozoite-specific antibodies as well [30]. Therefore, we evaluated the contribution of sporozoite-specific antibodies to prolonged protection observed after sporozoite challenge.…”