Effect of Plasmodium yoelii exposure on vaccination with the 19-kilodalton carboxyl terminus of merozoite surface protein 1 and vice versa and implications for the application of a human malaria vaccine

Memory CD73+IgM+ B cells protect against Plasmodium yoelii infection and express Granzyme B

To better understand anti-malaria protective immune responses, we examined the cellular mechanisms that govern protective immunity in a murine Plasmodium yoelii 17X NL (PyNL) re-infection model. Initially, we confirmed that immune B cells generated during a primary PyNL infection were largely responsible for protection from a second PyNL infection. Using the previously identified memory B cell markers CD80, PD-L2, and CD73, we found an increase in the frequency of CD80-PD-L2-CD73+ B cells up to 55 days after a primary PyNL infection and at 4-6 days following a second PyNL infection. Moreover, injection of enriched immune CD19+CD73+ B cells into nonimmune mice were significantly more protective against a PyNL infection than CD73- B cells. Interestingly, a substantial fraction of these CD73+ B cells also expressed IgM and granzyme B, a biomolecule that has been increasingly associated with protective responses against malaria.

Isolation and Characterization of Vaccine Candidate Genes Including CSP and MSP1 in Plasmodium yoelii

Malaria is an infectious disease affecting humans, which is transmitted by the bite of Anopheles mosquitoes harboring sporozoites of parasitic protozoans belonging to the genus Plasmodium. Despite past achievements to control the protozoan disease, malaria still remains a significant health threat up to now. In this study, we cloned and characterized the full-unit Plasmodium yoelii genes encoding merozoite surface protein 1 (MSP1), circumsporozoite protein (CSP), and Duffy-binding protein (DBP), each of which can be applied for investigations to obtain potent protective vaccines in the rodent malaria model, due to their specific expression patterns during the parasite life cycle. Recombinant fragments corresponding to the middle and C-terminal regions of PyMSP1 and PyCSP, respectively, displayed strong reactivity against P. yoelii-infected mice sera. Specific native antigens invoking strong humoral immune response during the primary and secondary infections of P. yoelii were also abundantly detected in experimental ICR mice. The low or negligible parasitemia observed in the secondary infected mice was likely to result from the neutralizing action of the protective antibodies. Identification of these antigenic proteins might provide the necessary information and means to characterize additional vaccine candidate antigens, selected solely on their ability to produce the protective antibodies.

Mortality among recipients of the Merck V710 Staphylococcus aureus vaccine after postoperative S. aureus infections: an analysis of possible contributing host factors

In a blinded randomized trial, preoperative receipt of the Merck V710 Staphylococcus aureus vaccine was associated with a higher mortality rate than placebo in patients who later developed postoperative S. aureus infections. Of the tested patients, all 12 V710 recipients (but only 1 of 13 placebo recipients) with undetectable serum IL2 levels prior to vaccination and surgery died after postoperative S. aureus infection. The coincidence of 3 factors (low prevaccination IL-2 levels, receipt of V710, and postoperative S. aureus infection) appeared to substantially increase mortality in our study population after major cardiothoracic surgery. Furthermore, 9 of the 10 V710 recipients with undetectable preoperative IL17a levels and postoperative S. aureus infections died. Although the current study is hypothesis-generating and the exact pathophysiology remains speculative, these findings raise concern that immune predispositions may adversely impact the safety and efficacy of staphylococcal vaccines actively under development. The potential benefits of an effective vaccine against S. aureus justify continued but cautious pursuit of this elusive goal.

Plasmodium chabaudi AS induces pregnancy loss in association with systemic pro-inflammatory immune responses in A/J and C57BL/6 mice

The molecular mechanisms that underlie poor birth outcomes in malaria during pregnancy remain poorly defined. To assess the role of host immune responses, mice known to respond differentially to Plasmodium chabaudi AS infection were studied. Following infection at day 0 of pregnancy, A/J mice developed significantly higher parasitemia than C57BL/6 (B6) mice and succumbed to infection. Both strains had evidence of parasite accumulation in the placenta at mid-gestation and aborted, with significantly higher embryo loss in infected A/J mice on day 9. While infection-induced systemic tumour necrosis factor (TNF) and interleukin (IL)-1β in the latter were significantly higher at day 11, day 10 IL-10 levels were higher in B6 mice. No differences in the levels of splenic lymphocyte subsets, neutrophils or monocytes between infected pregnant A/J and B6 mice were observed, with most cell types expanding in response to infection regardless of pregnancy. Antibody ablation of TNF exacerbated infection in A/J mice and did not ameliorate pregnancy outcome. Thus, malaria induces poor pregnancy outcome in both the mouse strains in the context of quantitatively different systemic inflammatory responses. Further evaluation of the roles of soluble and cellular immune components, particularly at the uteroplacental level, will be required to define the most critical pregnancy-compromising mechanisms.

Therapeutic blockade of PD-L1 and LAG-3 rapidly clears established blood-stage Plasmodium infection

Plasmodium infection of erythrocytes induces clinical malaria. Parasite-specific CD4⁺ T cells correlate with reduced parasite burdens and severity of human malaria, and are required to control blood-stage infection in mice. However, the characteristics of CD4⁺ T cells that determine protection or parasite persistence remain unknown. Here we show that P. falciparum infection of humans increased expression of an inhibitory receptor (PD-1) associated with T cell dysfunction. In vivo blockade of PD-L1 and LAG-3 restored CD4⁺ T cell function, amplified T follicular helper cell and germinal center B cell and plasmablast numbers, enhanced protective antibodies and rapidly cleared blood-stage malaria in mice. Thus, chronic malaria drives specific T cell dysfunction, which can be rescued to enhance parasite control using inhibitory therapies.

Immunogenicity of novel nanoparticle-coated MSP-1 C-terminus malaria DNA vaccine using different routes of administration

An important aspect in optimizing DNA vaccination is antigen delivery to the site of action. In this way, any alternative delivery system having higher transfection efficiency and eventual superior antibody production needs to be further explored. The novel nanoparticle, pDNA/PEI/γ-PGA complex, is one of a promising delivery system, which is taken up by cells and is shown to have high transfection efficiency. The immunostimulatory effect of this novel nanoparticle (NP) coated plasmid encoding Plasmodium yoelii MSP1-C-terminus was examined. Groups of C57BL/6 mice were immunized either with NP-coated MSP-1 plasmid, naked plasmid or NP-coated blank plasmid, by three different routes of administration; intravenous (i.v.), intraperitoneal (i.p.) and subcutaneous (s.c). Mice were primed and boosted twice at 3-week intervals, then challenged 2 weeks after; and 100%, 100% and 50% mean of survival was observed in immunized mice with coated DNA vaccine by i.p., i.v. and s.c., respectively. Coated DNA vaccine showed significant immunogenicity and elicited protective levels of antigen specific IgG and its subclass antibody, an increased proportion of CD4(+) and CD8(+) T cells and INF-γ and IL-12 levels in the serum and cultured splenocyte supernatant, as well as INF-γ producing cells in the spleen. We demonstrate that, NP-coated MSP-1 DNA-based vaccine confers protection against lethal P. yoelii challenge in murine model across the various route of administration and may therefore, be considered a promising delivery system for vaccination.

Effect of nanoparticle coating on the immunogenicity of plasmid DNA vaccine encoding P. yoelii MSP-1 C-terminal

In order to assess a new strategy for DNA vaccine formulation and delivery, plasmid encoding Plasmodium yoelii MSP-1 C-terminal was formulated with newly designed nanoparticle-an anionic ternary complex of polyethylenimine and γ-polyglutamic acid (pVAX-MSP-1/PEI/γ-PGA), and intravenously administered to C57BL/6 mice in four different doses, three times at 3-week interval. Antibody response as determined by ELISA, IFA and Western blot, was dose-dependent and subsequent challenge with 10(5)P. yoelii-infected red blood cells revealed 33-60% survival in repeated experiments at a dose of 80 μg pDNA/mouse. IgG subtypes and cytokine levels in the serum and culture supernatants of stimulated spleen cells were also measured. Antigen-specific IgG response provoked by the DNA vaccination was dominated by IgG1 and IgG2b. Although the elevation of IL-12p40 and IFN-γ was marginal (P≥0.354) in the coated group, interleukin-4 levels were significantly higher (P≥0.013) in the coated group than in the naked or control group, suggesting a predominant Th2-type CD4(+) T cell response. These results therefore, overall indicate the possibility of selection and optimization of DNA vaccine formulation for intravenous delivery and may be useful in designing a nanoparticle-coated DNA vaccine that could optimally elicit a desired antibody response for various disease conditions.

Protective immune responses elicited by immunization with a chimeric blood-stage malaria vaccine persist but are not boosted by Plasmodium yoelii challenge infection

An efficacious malaria vaccine remains elusive despite concerted efforts. Using the Plasmodium yoelii murine model, we previously reported that immunization with the C-terminal 19 kDa domain of merozoite surface protein 1 (MSP1(19)) fused to full-length MSP8 protected against lethal P. yoelii 17XL, well beyond that achieved by single or combined immunizations with the component antigens. Here, we continue the evaluation of the chimeric PyMSP1/8 vaccine. We show that immunization with rPyMSP1/8 vaccine elicited an MSP8-restricted T cell response that was sufficient to provide help for both PyMSP1(19) and PyMSP8-specific B cells to produce high and sustained levels of protective antibodies. The enhanced efficacy of immunization with rPyMSP1/8, in comparison to a combined formulation of rPyMSP1(42) and rPyMSP8, was not due to improved conformation of protective B cell epitopes in the chimeric molecule. Unexpectedly, rPyMSP1/8 vaccine-induced antibody responses were not boosted by exposure to P. yoelii 17XL infected RBCs. However, rPyMSP1/8 immunized and infected mice mounted robust responses to a diverse set of blood-stage antigens. The data support the further development of an MSP1/8 chimeric vaccine but also suggest that vaccines that prime for responses to a diverse set of parasite proteins will be required to maximize vaccine efficacy.