Mannosylated liposomes formulated with whole parasite P. falciparum blood-stage antigens are highly immunogenic in mice

Nanotherapeutics against malaria: A decade of advancements in experimental models

Malaria, caused by different species of protists of the genus Plasmodium, remains among the most common causes of death due to parasitic diseases worldwide, mainly for children aged under 5. One of the main obstacles to malaria eradication is the speed with which the pathogen evolves resistance to the drug schemes developed against it. For this reason, it remains urgent to find innovative therapeutic strategies offering sufficient specificity against the parasite to minimize resistance evolution and drug side effects. In this context, nanotechnology-based approaches are now being explored for their use as antimalarial drug delivery platforms due to the wide range of advantages and tuneable properties that they offer. However, major challenges remain to be addressed to provide a cost-efficient and targeted therapeutic strategy contributing to malaria eradication. The present work contains a systematic review of nanotechnology-based antimalarial drug delivery systems generated during the last 10 years. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

Advances in Babesia Vaccine Development: An Overview

Babesiosis is a tick-borne zoonotic disease, which is caused by various species of intracellular Babesia parasite. It is a problem not only for the livestock industry but also for global health. Significant global economic losses, in particular in cattle production, have been observed. Since the current preventive measures against babesiosis are insufficient, there is increasing pressure to develop a vaccine. In this review, we survey the achievements and recent advances in the creation of antibabesiosis vaccine. The scope of this review includes the development of a vaccine against B. microti, B. bovis, B. bigemina, B. orientalis and B. divergens. Here, we present different strategies in their progress and evaluation. Scientists worldwide are still trying to find new targets for a vaccine that would not only reduce symptoms among animals but also prevent the further spread of the disease. Molecular candidates for the production of a vaccine against various Babesia spp. are presented. Our study also describes the current prospects of vaccine evolution for successful Babesia parasites elimination.

Mannose in vaccine delivery

Adjuvants and vaccine delivery systems are used widely to improve the efficacy of vaccines. Their primary roles are to protect antigen from degradation and allow its delivery and uptake by antigen presenting cells (APCs). Carbohydrates, including various structures/forms of mannose, have been broadly utilized to target carbohydrate binding receptors on APCs. This review summarizes basic functions of the immune system, focusing on the role of mannose receptors in antigen recognition by APCs. The most popular strategies to produce mannosylated vaccines via conjugation and formulation are presented. The efficacy of mannosylated vaccines is discussed in detail, taking into consideration factors, such as valency and number of mannose in mannose ligands, mannose density, length of spacers, special arrangement of mannose ligands, and routes of administration of mannosylated vaccines. The advantages and disadvantages of mannosylation strategy and future directions in the development of mannosylated vaccines are also debated.

A vaccine for human babesiosis: prospects and feasibility

Babesiosis is a tick-borne disease caused by intraerythrocytic Babesia parasites. It is a well-known illness in companion animals and livestock, resulting in substantial economic losses in the cattle industry. Babesiosis is also recognized as an emerging zoonosis of humans in many countries worldwide. There is no vaccine against human babesiosis. Currently, preventive measures are focused on vector avoidance. Although not always effective, treatment includes antimicrobial therapy and exchange transfusion. In this review, we discuss the host's immune response to the parasite, vaccines being used to prevent babesiosis in animals, and lessons from malaria vaccine development efforts to inform the development of a human babesiosis vaccine. An effective human vaccine would be a significant advance towards curtailing this rapidly emerging disease.

Investigation of liposomal self-adjuvanting peptide epitopes derived from conserved blood-stage Plasmodium antigens

Malaria is a vector born parasitic disease causing millions of deaths every year. Despite the high mortality rate, an effective vaccine against this mosquito-borne infectious disease is yet to be developed. Up to date, RTS,S/AS01 is the only vaccine available for malaria prevention; however, its efficacy is low. Among a variety of malaria antigens, merozoite surface protein-1(MSP-1) and ring-infected erythrocyte surface antigen (RESA) have been proposed as promising candidates for malaria vaccine development. We developed peptide-based Plasmodium falciparum vaccine candidates that incorporated three previously reported conserved epitopes from MSP-1 and RESA into highly effective liposomal polyleucine delivery system. Indeed, MSP-1 and RESA-derived epitopes conjugated to polyleucine and formulated into liposomes induced higher epitope specific antibody titres. However, immunized mice failed to demonstrate protection in a rodent malaria challenge study with Plasmodium yoelii. In addition, we found that the three reported P. falciparum epitopes did not to share conformational properties and high sequence similarity with P. yoelii MSP-1 and RESA proteins, despite the epitopes were reported to protect mice against P. yoelii challenge.

Development and Evaluation of a Cryopreserved Whole-Parasite Vaccine in a Rodent Model of Blood-Stage Malaria

Infection with malaria parasites continues to be a major global public health issue. While current control measures have enabled a significant decrease in morbidity and mortality over the last 20 years, additional tools will be required if we are to progress toward malaria parasite eradication. Malaria vaccine research has focused on the development of subunit vaccines; however, more recently, interest in whole-parasite vaccines has reignited. Whole-parasite vaccines enable the presentation of a broad repertoire of antigens to the immune system, which limits the impact of antigenic polymorphism and genetic restriction of the immune response. We previously reported that whole-parasite vaccines can be prepared using chemically attenuated parasites within intact red blood cells or using killed parasites in liposomes, although liposomes were less immunogenic than attenuated parasites. If they could be frozen or freeze-dried and be made more immunogenic, liposomal vaccines would be ideal for vaccine deployment in areas where malaria is endemic. Here, we develop and evaluate a Plasmodium yoelii liposomal vaccine with enhanced immunogenicity and efficacy due to incorporation of TLR4 agonist, 3D(6-acyl) PHAD, and mannose to target the liposome to antigen-presenting cells. Following vaccination, mice were protected, and strong cellular immune responses were induced, characterized by parasite-specific splenocyte proliferation and a mixed Th1/Th2/Th17 cytokine response. Parasite-specific antibodies were induced, predominantly of the IgG1 subclass. CD4⁺ T cells and gamma interferon were critical components of the protective immune response. This study represents an important development toward evaluation of this whole-parasite blood-stage vaccine in a phase I clinical trial. IMPORTANCE Malaria is a mosquito-borne infectious disease that is caused by parasites of the genus, Plasmodium. There are seven different Plasmodium spp. that can cause malaria in humans, with P. falciparum causing the majority of the morbidity and mortality. Malaria parasites are endemic in 87 countries and continue to result in >200 million cases of malaria and >400,000 deaths/year, mostly children <5 years of age. Malaria infection initially presents as a flu-like illness but can rapidly progress to severe disease in nonimmune individuals if treatment is not initiated promptly. Existing control strategies for the mosquito vector (insecticides) and parasite (antimalarial drugs) are becoming increasingly less effective due to the development of resistance. While artemisinin combination therapies are frontline treatment for P. falciparum malaria, resistance has been documented in numerous countries. A highly effective malaria vaccine is urgently required to reduce malaria-attributable clinical disease and death and enable progression toward the ultimate goal of eradication.

Lipid-Based Nanoparticles for Delivery of Vaccine Adjuvants and Antigens: Toward Multicomponent Vaccines

Despite the many advances that have occurred in the field of vaccine adjuvants, there are still unmet needs that may enable the development of vaccines suitable for more challenging pathogens (e.g., HIV and tuberculosis) and for cancer vaccines. Liposomes have already been shown to be highly effective as adjuvant/delivery systems due to their versatility and likely will find further uses in this space. The broad potential of lipid-based delivery systems is highlighted by the recent approval of COVID-19 vaccines comprising lipid nanoparticles with encapsulated mRNA. This review provides an overview of the different approaches that can be evaluated for the design of lipid-based vaccine adjuvant/delivery systems for protein, carbohydrate, and nucleic acid-based antigens and how these strategies might be combined to develop multicomponent vaccines.

Pre-clinical evaluation of a whole-parasite vaccine to control human babesiosis

Babesia spp. are tick-transmitted intra-erythrocytic protozoan parasites that infect humans and animals, causing a flu-like illness and hemolytic anemia. There is currently no human vaccine available. People most at risk of severe disease are the elderly, immunosuppressed, and asplenic individuals. B. microti and B. divergens are the predominant species affecting humans. Here, we present a whole-parasite Babesia vaccine. To establish proof-of-principle, we employed chemically attenuated B. microti parasitized red blood cells from infected mice. To aid clinical translation, we produced liposomes containing killed parasite material. Vaccination significantly reduces peak parasitemia following challenge. B cells and anti-parasite antibodies do not significantly contribute to vaccine efficacy. Protection is abrogated by the removal of CD4⁺ T cells or macrophages prior to challenge. Importantly, splenectomized mice are protected by vaccination. To further facilitate translation, we prepared a culture-based liposomal vaccine and demonstrate that this performs as a universal vaccine inducing immunity against different human Babesia species.