A Role for Immune Responses against Non-CS Components in the Cross-Species Protection Induced by Immunization with Irradiated Malaria Sporozoites

Immunization with irradiated Plasmodium sporozoites induces sterile immunity in rodents, monkeys and humans. The major surface component of the sporozoite the circumsporozoite protein (CS) long considered as the antigen predominantly responsible for this immunity, thus remains the leading candidate antigen for vaccines targeting the parasite's pre-erythrocytic (PE) stages. However, this role for CS was questioned when we recently showed that immunization with irradiated sporozoites (IrrSpz) of a P. berghei line whose endogenous CS was replaced by that of P. falciparum still conferred sterile protection against challenge with wild type P. berghei sporozoites. In order to investigate the involvement of CS in the cross-species protection recently observed between the two rodent parasites P. berghei and P. yoelii, we adopted our gene replacement approach for the P. yoelii CS and exploited the ability to conduct reciprocal challenges. Overall, we found that immunization led to sterile immunity irrespective of the origin of the CS in the immunizing or challenge sporozoites. However, for some combinations, immune responses to CS contributed to the acquisition of protective immunity and were dependent on the immunizing IrrSpz dose. Nonetheless, when data from all the cross-species immunization/challenges were considered, the immune responses directed against non-CS parasite antigens shared by the two parasite species played a major role in the sterile protection induced by immunization with IrrSpz. This opens the perspective to develop a single vaccine formulation that could protect against multiple parasite species

Minimal Role for the Circumsporozoite Protein in the Induction of Sterile Immunity by Vaccination with Live Rodent Malaria Sporozoites▿ †

Immunization with live Plasmodium sporozoites under chloroquine prophylaxis (Spz plus CQ) induces sterile immunity against sporozoite challenge in rodents and, more importantly, in humans. Full protection is obtained with substantially fewer parasites than with the classic immunization with radiation-attenuated sporozoites. The sterile protection observed comprised a massive reduction in the hepatic parasite load and an additional effect at the blood stage level. Differences in the immune responses induced by the two protocols occur but are as yet little characterized. We have previously demonstrated that in mice immunized with irradiated sporozoites, immune responses against the circumsporozoite protein (CSP), the major component of the sporozoite's surface and the leading malaria vaccine candidate, were not essential for sterile protection. Here, we have employed transgenic Plasmodium berghei parasites in which the endogenous CSP was replaced by that of Plasmodium yoelii, another rodent malaria species, to assess the role of CSP in the sterile protection induced by the Spz-plus-CQ protocol. The data demonstrated that this role was minor because sterile immunity was obtained irrespective of the origin of CSP expressed by the parasites in this model of protection. The immunity was obtained through a single transient exposure of the host to the immunizing parasites (preerythrocytic and erythrocytic), a dose much smaller than that required for immunization with radiation-attenuated sporozoites

Regression of primary hepatocarcinoma in cancer-prone transgenic mice by local interferon-γ delivery is associated with macrophages recruitment and nitric oxide production

International audienceThe clinical potential of tumor therapies must be evaluated using animal models closely resembling human cancers. We investigated the impact of locally delivered interferon-gamma (IFN-gamma) on primary hepatocarcinoma spontaneously developed by T-SV40 transgenic mice. A single intratumor injection of adenovirus IFN-gamma was sufficient enough to induce in vivo production of biologically active IFN-gamma, as assessed by STAT1 activation. IFN-gamma secretion led to the regression of primary tumor, principally by apoptosis of tumor hepatocytes. The lack of T-cells infiltrates in the liver upon treatment excluded a role of a specific immune response. In contrast, indirect pathways may include tumoricidal function of macrophages. Indeed, they were massively recruited in the entire liver under IFN-gamma treatment; transmigration through hepatic blood vessels could be observed and co-localization with damaged hepatocytes was obvious. This correlated with nonparenchymal liver cell iNOS expression and high level of NO in hepatic extracts. Moreover, in vitro experiments showed that NO releasing agents induced cell death of freshly isolated tumor hepatocytes, suggesting that NO could be one of the major effector molecules. Altogether, these observations defined an important role of IFN-gamma in controlling tumor development in a model of primary hepatocarcinoma

Species-Specific Inhibition of Cerebral Malaria in Mice Coinfected with Plasmodium spp.

Recent epidemiological observations suggest that clinical evolution of Plasmodium falciparum infections might be influenced by the concurrent presence of another Plasmodium species, and such mixed-species infections are now known to occur frequently in residents of most areas of endemicity. We used mice infected with P. berghei ANKA (PbA), a model for cerebral malaria (CM), to investigate the influence of experimental mixed-species infections on the expression of this pathology. Remarkably, the development of CM was completely inhibited by the simultaneous presence of P. yoelii yoelii but not that of P. vinckei or another line of P. berghei. In the protected coinfected mice, the accumulation of CD8(+) T cells in the brain vasculature, a pivotal step in CM pathogenesis, was found to be abolished. Protection from CM was further found to be associated with species-specific suppression of PbA multiplication. These observations establish the concept of mixed Plasmodium species infections as potential modulators of pathology and open novel avenues to investigate mechanisms implicated in the pathogenesis of malaria

Comparison of the amino acid sequences of the <i>P. berghei</i> ANKA clone cy17 (34) and <i>P. falciparum</i> Welcome strain (35) CSP polypeptides.

<p>Black dots represent identical amino acid residues while bars represent amino acid residues with similar characteristics. The repeat regions (including the pre- and post-repeat sequences) are underlined.</p

Antibody reactivity induced by immunization with irradiated sporozoites.

<p>Pooled serum samples from groups of mice immunized with sporozoites from the different parasite lines were analyzed by ELISA to assay IgG and IgM responses induced against <i>P. berghei</i> CSP (A), or <i>P. falciparum</i> CSP (B), using long peptides covering the N-terminus or the C-terminus of the antigen, and short peptides that include some of the repeat units of the central repetitive region. Serums were also tested by IFAT against wet sporozoites to detect anti-CSP IgG and IgM antibodies(C). Titres are expressed as the log of the highest dilution of serum giving a positive staining.</p

Sterile protection in mice immunized with <i>P. berghei</i> irradiated sporozoites and challenged with <i>P. berghei</i> or <i>P. berghei</i> [<i>PfCS</i>] sporozoites.

<p>Mice were immunized with 1 or 3 injections of <i>P. berghei</i> (indicated on the left of the panel) before challenge with 5 000 <i>P. berghei</i> or <i>P. berghei</i> [<i>PfCS</i>] sporozoites. All naive control mice developed a patent blood-stage infection. The data are representative of those obtained in duplicate experiments.</p