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 7

Induction of CD4 T cell memory.

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Induction of CD4 T cell memory. (A) To assess the role of CD4 T cells in...
(A) To assess the role of CD4 T cells in protracted protection, A/J mice immunized with 103 (AS) prbc in control ODN or CpG-ODN were depleted of CD4 T cells 12 weeks after immunization. Mice were challenged i.v. with 105 homologous (AS) prbc immediately after depletion (left panels, effector) or 21 days after depletion to allow for naive/helper CD4 T cells to replenish (right panels, helper). Parasitemias were monitored. Results are representative of 3 separate experiments and data for individual mice are shown. †Animals that succumbed to infection. (B) To assess for cytokine secretion in memory CD4 T cells, spleen cells from A/J mice immunized with 103 (AS) prbc in CpG-ODN were purified 12 weeks after immunization, incubated for 96 hours in the presence of homologous (AS) prbc, and cells stained for intracellular IFN-γ and IL-2. Numbers represent percentages of cytokine+ CD4 T cells. (C) To identify the specificity of CD4 T cell memory subsets, IFN-γ secretion and expression of lymph node homing receptor (CD62L) were assessed by harvesting spleen cells from A/J mice immunized with 103 (AS) prbc in CpG-ODN at 12 weeks after immunization. Cells were incubated for 96 hours in the presence of homologous (AS) prbc and stained. Numbers represent percentages of IFN-γ+ CD62LloCD4 T cells. (D) To determine the existence of memory populations, spleen cells from A/J mice immunized with 103 (AS) prbc in CpG-ODN were FACS-sorted into CM (CD44hiCD62Lhi) and EM (CD44hiCD62Llo) populations directly ex vivo. CM and EM cells were then incubated for 96 hours in the presence of homologous (AS) prbc and stained for intracellular cytokine (IFN-γ) and proliferation (BrDU). Numbers represent percentages of CD4 T cells in corresponding quadrants. Results are representative of 3 independent experiments performed.