Low doses of killed parasite in CpG elicit vigorous CD4+ T cell responses against blood-stage malaria in mice
Alberto Pinzon-Charry, Virginia McPhun, Vivian Kienzle, Chakrit Hirunpetcharat, Christian Engwerda, James McCarthy, Michael F. Good
Alberto Pinzon-Charry, Virginia McPhun, Vivian Kienzle, Chakrit Hirunpetcharat, Christian Engwerda, James McCarthy, Michael F. Good
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Research Article

Low doses of killed parasite in CpG elicit vigorous CD4+ T cell responses against blood-stage malaria in mice

Abstract

Development of a vaccine that targets blood-stage malaria parasites is imperative if we are to sustainably reduce the morbidity and mortality caused by this infection. Such a vaccine should elicit long-lasting immune responses against conserved determinants in the parasite population. Most blood-stage vaccines, however, induce protective antibodies against surface antigens, which tend to be polymorphic. Cell-mediated responses, on the other hand, offer the theoretical advantage of targeting internal antigens that are more likely to be conserved. Nonetheless, few of the current blood-stage vaccine candidates are able to harness vigorous T cell immunity. Here, we present what we believe to be a novel blood-stage whole-organism vaccine that, by combining low doses of killed parasite with CpG-oligodeoxynucleotide (CpG-ODN) adjuvant, was able to elicit strong and cross-reactive T cell responses in mice. Our data demonstrate that immunization of mice with 1,000 killed parasites in CpG-ODN engendered durable and cross-strain protection by inducing a vigorous response that was dependent on CD4+ T cells, IFN-γ, and nitric oxide. If applicable to humans, this approach should facilitate the generation of robust, cross-reactive T cell responses against malaria as well as antigen availability for vaccine manufacture.

Authors

Alberto Pinzon-Charry, Virginia McPhun, Vivian Kienzle, Chakrit Hirunpetcharat, Christian Engwerda, James McCarthy, Michael F. Good

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Figure 4

Cellular responses and cross-reactivity.

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Cellular responses and cross-reactivity. (A) To determine CD4 response, ...
(A) To determine CD4 response, A/J mice were immunized with 103 (AS) prbc in CpG-ODN (black bars) or control ODN (gray bars). Spleen cells collected 2 weeks after immunization were cultured with homologous (AS) or heterologous (P. c. chabaudi AJ [AJ]; P. yoelii YM [YM]) parasites, normal rbc (nrbc), or ConA. After 96 hours, supernatants were assayed for TNF-α, IFN-γ, IL-2 (Th1 cytokines), and IL-4 or IL-5 (Th2 cytokines) assessed. Results are mean ± SEM. (B) For proliferation, spleen cells from A/J mice immunized as above were purified at 2, 8, or 12 weeks and incubated for 96 hours with AS, AJ or YM prbc, nrbc, medium, or ConA. Numbers represent percentage of CFSEdim CD4 T cells. (C) For cytokine secretion, spleen cells from A/J mice immunized as above and purified at 2, 8, or 12 weeks were incubated for 96 hours with AS, AJ, or YM prbc, nrbc, or medium and stained for intracellular IFN-γ. Numbers represent percentage of IFN-γ+ CD4 T cells. (D) For cross-reactive antibodies, sera from A/J mice immunized with 103 (AS) prbc in CpG-ODN (black bars), control ODN (gray bars), or hyperimmune sera (HIS, white bars) were tested for IgG titers against homologous (AS) or heterologous (AJ and YM) parasites. Results represent reciprocal median total IgG titers and interquartile ranges. All data sets are representative of 5 mice per group of 3 independent experiments performed. Significant differences compared with controls are shown. *P < 0.05.