Chimeric virus-like particles and capsomeres induce similar CD8+ T cell responses but differ in capacity to induce CD4+ T cell responses and antibody responses

Despite extensive research, the development of an effective malaria vaccine remains elusive. The induction of robust and sustained T cell and antibody response by vaccination is an urgent unmet need. Chimeric virus-like particles (VLPs) are a promising vaccine platform. VLPs are composed of multiple subunit capsomeres which can be rapidly produced in a cost-effective manner, but the ability of capsomeres to induce antigen-specific cellular immune responses has not been thoroughly investigated. Accordingly, we have compared chimeric VLPs and their sub-unit capsomeres for capacity to induce CD8+ and CD4+ T cell and antibody responses. We produced chimeric murine polyomavirus VLPs and capsomeres each incorporating defined CD8+ T cell, CD4+ T cell or B cell repeat epitopes derived from Plasmodium yoelii CSP. VLPs and capsomeres were evaluated using both homologous or heterologous DNA prime/boost immunization regimens for T cell and antibody immunogenicity. Chimeric VLP and capsomere vaccine platforms induced robust CD8+ T cell responses at similar levels which was enhanced by a heterologous DNA prime. The capsomere platform was, however, more efficient at inducing CD4+ T cell responses and less efficient at inducing antigen-specific antibody responses. Our data suggest that capsomeres, which have significant manufacturing advantages over VLPs, should be considered for diseases where a T cell response is the desired outcome.David J. Pattinson, Simon H. Apte, Nani Wibowo, Tania Rivera-Hernandez, Penny L. Groves, Anton P. J. Middelberg, and Denise L. Doola

Immunomics-guided discovery of serum and urine antibodies for diagnosing urogenital schistosomiasis: a biomarker identification study

Background Sensitive diagnostics are needed for effective management and surveillance of schistosomiasis so that current transmission interruption goals set by WHO can be achieved. We aimed to screen the Schistosoma haematobium secretome to find antibody biomarkers of schistosome infection, validate their diagnostic performance in samples from endemic populations, and evaluate their utility as point of care immunochromatographic tests (POC-ICTs) to diagnose urogenital schistosomiasis in the field.Methods We did a biomarker identification study, in which we constructed a proteome array containing 992 validated and predicted proteins from S haematobium and screened it with serum and urine antibodies from endemic populations in Gabon, Tanzania, and Zimbabwe. Arrayed antigens that were IgG-reactive and a select group of antigens from the worm extracellular vesicle proteome, predicted to be diagnostically informative, were then evaluated by ELISA using the same samples used to probe arrays, and samples from individuals residing in a low-endemicity setting (ie, Pemba and Unguja islands, Zanzibar, Tanzania). The two most sensitive and specific antigens were incorporated into POC-ICTs to assess their ability to diagnose S haematobium infection from serum in a field-deployable format.Findings From array probing, in individuals who were infected, 208 antigens were the targets of significantly elevated IgG responses in serum and 45 antigens were the targets of significantly elevated IgG responses in urine. Of the five proteins that were validated by ELISA, Sh-TSP-2 (area under the curve [AUC](serum)=0.98 [95% CI 0.95-1.00]; AUC(urine)=0.96 [0.93-0.99]), and MS3_01370 (AUCserum=0.93 [0.89-0.97]; AUC(urine)=0.81 [0.72-0.89]) displayed the highest overall diagnostic performance in each biofluid and exceeded that of S haematobium-soluble egg antigen in urine (AUC=0.79 [0.69-0.90]). When incorporated into separate POC-ICTs, Sh-TSP-2 showed absolute specificity and a sensitivity of 75% and MS3_01370 showed absolute specificity and a sensitivity of 89%.Interpretation We identified numerous biomarkers of urogenital schistosomiasis that could form the basis of novel antibody diagnostics for this disease. Two of these antigens, Sh-TSP-2 and MS3_01370, could be used as sensitive, specific, and field-deployable diagnostics to support schistosomiasis control and elimination initiatives, with particular focus on post-elimination surveillance. Copyright (C) 2021 The Author(s). Published by Elsevier Ltd.Host-parasite interactio

Identification of minimal CD8+ and CD4+ T cell epitopes in the Plasmodium yoelii hepatocyte erythrocyte protein 17 kDa

Immunization of mice with subunit vaccines based on the Plasmodium yoelii 17 kDa hepatocyte erythrocyte protein (PyHEP17), orthologue of Plasmodium falciparum exported protein 1 (PfExp1), induces antigen-specific immune responses and protects against sporozoite challenge. To aid in the characterization of candidate subunit vaccines based on this antigen, we have mapped the immunodominant and subdominant CD8+ and CD4+ T cell epitopes on PyHEP17. Using a panel of 29 15-mer synthetic peptides representing the complete sequence of PyHEP17 (amino acids 1–153), and overlapping each other by 10 residues, we identified an immunogenic region between amino acids 61–85. To define the minimal CD4+ and CD8+ T cell epitopes within this region, we synthesized 25 9-mer peptides overlapping each other by one residue. We screened the capacity of the 15-mer and 9-mer peptides to be recognized by splenocytes and lymph node cells from mice immunized with PyHEP17 plasmid DNA or peptides in Freund's adjuvant, as assessed by cytokine secretion, lymphoproliferation, and cytotoxicity. The profile of response to the T cell epitopes varied depending upon the immunization regimen. Antigen-specific T cell responses were detected to three 15-mer peptides (residues 61–75, 66–80 and 71–85) representing two 10-mer epitopes mapping to residues 66–75 (LTKNKKSLRK) and 71–80 (KSLRKINVAL). IFN-γ responses after DNA immunization predominantly mapped to two overlapping 9-mer peptides (residues 73–81 and 74–82) sharing an eight amino acid overlap (residues 74–81, RKINVALA), whereas CTL responses predominantly mapped to four 9-mer peptides (residues 61–69, 70–78, 76–84, and 84–92). In addition, a subdominant 10-mer CD8+ T cell epitope recognized by peptide immunization but not DNA immunization mapped to residues 31–40 (GKYGSQNVIK). The identification of these epitopes will allow the evaluation of delivery systems for malaria vaccine candidates as well as the delineation of protective immune mechanisms

Multi-gene vaccination against malaria: a multistage, multi-immune response approach

An ideal malaria vaccine will induce immune responses against each stage of the Plasmodium spp life cycle. During its complicated life cycle, the parasite exists extracellularly in the host's bloodstream, within cells that express major histocompatibility complex (MHC) molecules (hepatocytes), within cells that do not express MHC molecules (erythrocytes) and within the mosquito vector. Different arms of the immune system are required to attack the parasite at the different stages. Therefore, a multistage vaccine must be a multi-immune response vaccine. In addition, given the unique antigenicities of the different stages of the life cycle, implicit in this definition is that the vaccine be multivalent. Here, Denise Doolan and Stephen Hoffman present the rationale for developing a multistage, multivalent, multi-immune response malaria vaccine and explain why, among currently available technologies, DNA vaccines may offer the best prospect for success

Nucleic acid malaria vaccines

During the twentieth century, the primary approach to malaria prevention has been to interfere with transmission of the parasite between the infected mosquito and the human host using physical barriers, insecticides and prophylactic drugs. Despite these measures, it is estimated that there are 300-500 new Plasmodium infections and 1-2 million deaths annually due to malaria. Thus, there have been major efforts to develop malaria vaccines. This is thought to be a feasible approach because immunization with radiation-attenuated Plasmodium spp. sporozoites induces sterile protective immunity against malaria in rodents, primates and humans(reviewed in Ref. 2). The complex life cycle of the Plasmodium spp. parasites and the extensive variability among strains of the same Plasmodium species dictate, however, that an effective malaria vaccine will probably need to induce protective antibodies as well as effector CD4+ and CD8+ T lymphocytes specific for variants of multiple antigens expressed at different stages of the life cycle. It is our view that nucleic acid vaccines offer an excellent approach to developing a multivalent vaccine that effectively activates all arms of the immune system. Furthermore, such vaccines may overcome the additional problem inherent in subunit vaccine development: major histocompatibility complex (MHC) restriction of the protective immune responses to identified target epitopes. Supporting data and rationale for our view are presented here. The major emphasis of the work thus far has been to use plasmid DNA to induce protective CD8+ cytotoxic T lymphocytes (CTL), but the induction of protective antibody and CD4+ T cell responses is being investigated

Evidence for limited activation of distinct CD4⁺ T cell subsets in response to the Plasmodium falciparum circumsporozoite protein in Papua New Guinea

Both CD4⁺ and CD8⁺ T cells, as well as antibody, are known to be important in sporozoite immunity. Data from animal studies suggest that cytokines, in particular γ-interferon and interleukin-6, are involved. The interplay of these various factors and their importance in vaccine development has, however, not yet been elucidated. In this study, we have studied cellular and humoral responses of individuals naturally exposed to malaria in a highly endemic region of Papua New Guinea to the circumsporozoite protein of Plasmodium falciparum, a prime vaccine candidate antigen. A paucity of any CD4⁺ lymphoproliferative response to this protein by Papua New Guineans was notable which parallels our recent observation of a paucity of CD8⁺ T cell response and contrasts markedly with the responses of other endemic populations. There was nevertheless a significant antibody response to the central conserved B cell epitope, (NANP)ₙ, as well as to other critical epitopes. An inverse relationship between γ-interferon production and interleukin-6 production and a positive correlation between γ-interferon production and CS peptide-specific lymphoproliferation was observed. High levels of peptide-specific IL-6 production were associated with high levels of peptide-specific serum antibodies. Our data provide evidence for the limited activation of distinct CD4⁺ T cell subsets and for the existence of functionally distinct subpopulations of human CD4⁺ T cells with respect to cytokines known to be important in sporozoite immunity

Progress toward a malaria vaccine: Efficient induction of protective anti-malaria immunity

Malaria can be a very severe disease, particularly in young children, pregnant women (mostly in primipara), and malaria naive adults, and currently ranks among the most prevalent infections in tropical and subtropical areas throughout the world. the widespread occurrence and the increased incidence of malaria in many countries, caused by drug-resistant parasites (Plasmodium falciparum and P. vivax) and insecticide-resistant vectors (Anopheles mosquitoes), indicate the need to develop new methods of controlling this disease.Experimental vaccination with irradiated sporozoites can protect animals and humans against the disease, demonstrating the feasibility of developing an effective malaria vaccine. However, developing a universally effective, long lasting vaccine against this parasitic disease has been a difficult task, due to several problems. One difficulty stems from the complexity of the parasite's life cycle. During their life cycle, malaria parasites change their residence within the host, thus avoiding being re-exposed to the same immunological environment. These parasites also possess some distinct antigens, present at different life stages of the parasite, the so-called stage-specific antigens, While some of the stage-specific antigens can induce protective immune responses in the host, these responses are usually genetically restricted, this being another reason for delaying the development of a universally effective vaccine. the stage-specific antigens must be used as immunogens and introduced into the host by using a delivery system that should efficiently induce protective responses against the respective stages. Here we review several research approaches aimed at inducing protective anti-malaria immunity, overcoming the difficulties described above.NYU, Sch Med, Dept Med & Mol Parasitol, New York, NY 10010 USAUniversidade Federal de São Paulo, Dept Microbiol Imunol & Parasitol, BR-04023062 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Microbiol Imunol & Parasitol, BR-04023062 São Paulo, BrazilWeb of Scienc