Virus-like particles expressing microneme-associated antigen of Plasmodium berghei confer better protection than those expressing apical membrane antigen 1

Abstract

Malaria is a global disease affecting a large portion of the world's population. Although vaccines have recently become available, their efficacies are suboptimal. We generated virus-like particles (VLPs) that expressed either apical membrane antigen 1 (AMA1) or microneme-associated antigen (MIC) of Plasmodium berghei and compared their efficacy in BALB/c mice. We found that immune sera acquired from AMA1 VLP- or MIC VLP-immunized mice specifically interacted with the antigen of choice and the whole P. berghei lysate antigen, indicating that the antibodies were highly parasite-specific. Both VLP vaccines significantly enhanced germinal center B cell frequencies in the inguinal lymph nodes of mice compared with the control, but only the mice that received MIC VLPs showed significantly enhanced CD4+ T cell responses in the blood following P. berghei challenge infection. AMA1 and MIC VLPs significantly suppressed TNF-α and interleukin-10 production but had a negligible effect on interferon-γ. Both VLPs prevented excessive parasitemia buildup in immunized mice, although parasite burden reduction induced by MIC VLPs was slightly more effective than that induced by AMA1. Both VLPs were equally effective at preventing body weight loss. Our findings demonstrated that the MIC VLP was an effective inducer of protection against murine experimental malaria and should be the focus of further development.

Keywords: Plasmodium berghei; malaria; vaccine; virus-like particle.

Fig. 1

Immunization scheduling and vaccine-induced antibody response detection. Schematic depicting the animal experimental schedule (A). Antigen specificity of AMA1 and MIC antibodies evaluated by ELISA in sera of VLP-immunized mice collected at regular intervals (B, C). Parasite specificity of the 2 immune sera tested against the whole lysate antigen of P. berghei (D). Data are presented as mean±SD.

Fig. 2

Flow cytometry analysis of GC B and CD4⁺ T cells. Single-cell suspensions were acquired from ILN and blood for GC B cell and CD4⁺ T cell quantification, respectively. Frequencies of GC B cells (A, B) and CD4⁺ T cells (C) assessed using flow cytometry. Data are presented as mean±SD. *P<0.05 and ***P<0.001.

Fig. 3

Splenic cytokine production assessment. Spleens of challenge-infected mice were collected to evaluate cytokine production. Homogenized spleen supernatants underwent ELISA to determine the concentrations of TNF-α (A), IFN-γ (B), and IL-10 (C). Data are presented as mean±SD. *P<0.05 and **P<0.001.

Fig. 4

Parasite burden and malaria-induced weight loss. Changes in parasitemia and body weight of mice were recorded at regular intervals. Parasitemia in the blood of P. berghei-infected mice was monitored over 45 days (A), and changes were compared at 45 dpi (B). Weight changes of P. berghei-infected mice were monitored for 45 days (C), and differences between the immunized groups and the infection control were compared at 38 dpi (D). Data are presented as mean±SD. **P<0.01, ***P<0.001 and ****P<0.0001.