For years, malaria vaccine developers have focused on thwarting a key moment in the malaria parasite’s life cycle: when two parasite proteins, AMA1 and RON2L, combine to form a complex that anchors the parasite to a red blood cell and eases its passage into the cell interior. Quite sensibly, researchers developed candidate vaccines that elicit antibodies capable of blocking the crucial attachment. However, because AMA1’s make-up varies widely among different parasite strains, any vaccine based on a single strain’s AMA1 cannot protect against other parasite strains and thus has limited usefulness in malaria-endemic countries. Experimental malaria vaccines have also been made by mixing AMA1 and RON2L proteins. While these do elicit more strain-transcending antibodies than AMA1-only vaccines, they are difficult to manufacture and simple mixtures of AMA1 and RON2L in vaccines do not form the kind of stable protein complex seen in nature.

Now, researchers in NIAID’s Laboratory of Malaria Immunology and Vaccinology have used structural information about the two parasite proteins along with mechanistic information about the interaction between AMA1 and RON2L to design and build an entirely novel immunogen (the component of a vaccine that elicits an immune response). When tested in rats, their “structure-based design 1” (SBD1) immunogen vaccine performed better than any AMA1 or AMA1-RON2L vaccine. It also upends the conventional wisdom that successful vaccines must elicit receptor-blocking antibodies, notes Niraj H. Tolia, Ph.D., who led the research team.

The SBD1 immunogen does not exist in nature, explains Dr. Tolia. Rather, it consists of AMA-1 that the team altered by rearranging its amino acid sequence in a way that they predicted would work well as a vaccine. Once altered, the scientists linked RON2L to a position in their immunogen to recreate the two protein AMA1-RON2L complex. The team analyzed the structure of the designed immunogen using X-ray crystallography and determined that it closely mimicked that of naturally occurring AMA1-RON2L complex. However, SBD1 has a number of advantages over a simple mixture of two component proteins, Dr. Tolia explains. For instance, it is highly stable once injected, is easy to manufacture in large quantities and consistently takes the desired, immune-stimulating shape.

In rats, SBD1 vaccine elicited significantly more potent strain-transcending antibodies than either AMA1 alone or an AMA1-RON2L complex vaccine. The ability to provide protection from multiple parasite strains is highly desirable for any malaria vaccine. Most surprisingly, Dr. Tolia says, the SBD1 vaccine provided this strain-transcending protection even though it generated no antibodies whatsoever that were aimed at blocking AMA1 from binding to RON2L and initiating attachment to the red blood cell. Instead, it appears SBD1 elicits high quality antibodies that inhibit parasite growth by targeting parts of the parasite’s proteins that lie outside of RON2L binding site and operate independently of receptor blockade, explains Dr. Tolia.

Together, the team’s observations about SBD1 make it an appealing candidate for further studies in animals and perhaps ultimately in human trials, he adds. Furthermore, other parasites, including those that cause the human diseases toxoplasmosis and babesiosis and one that causes disease in cattle and dogs, use their own forms of AMA1 protein to invade host cells. Thus, insights gained in this recent work may be applicable to the design of vaccines against those parasites as well.

Reference: PN Patel et al. Structure-based design of a strain transcending AMA1-RON2L malaria vaccine. Nature Communications. DOI: 10.1038/s41467-023-40878-7 (2023).

NIAID-Funded Study Traces Evolution of Malaria Drug Resistance in E. Africa – Emergence of Artemisinin Partial Resistance Mutations Found Across Uganda

Emerging resistance to common malaria treatments in Uganda could be connected to inconsistent use of measures to control mosquito populations, according to new findings published in the New England Journal of Medicine. The trend is worrisome, the NIAID-funded scientists state, because resistance mutations they tracked are taking root and spreading. Researchers at the University of California at San Francisco (UCSF), funded in part by NIAID’s International Centers of Excellence for Malaria Research program, led the international collaboration.

Malaria is one of the most common and serious infectious diseases. The World Health Organization (WHO) estimates that about half of the world’s population is at risk of getting malaria, which is caused primarily by Plasmodium falciparum parasites spread through the bites of female Anopheles mosquitos. In 2021, WHO estimated that about 247 million people contracted malaria in 85 countries; about 619,000 people died. About 95% of cases and deaths were in Africa.

For decades a combination of measures has resulted in effective malaria control in Africa: preventing malaria transmission with bed nets treated with insecticides; spraying insecticides indoors; treating malaria with artemisinin-based combination medicines; and preventing malaria with other drugs.

Artemisinins – originally extracted from the sweet wormwood plant, but also now available synthetically – rapidly eliminate malaria parasites from the bloodstream. They are used in combination with other longer-lasting drugs to effectively treat malaria. Beginning in 2008, however, studies in Southeast Asia identified poor results from artemisinins and eventually from artemisinin-based combination malaria treatments. Scientists soon found the primary reason – a protein (PfK13) in P. falciparum had developed mutations that made it partially resistant to artemisinins.

Since then, scientists in Africa have watched for the same mutations to emerge. The NEJM study identified five of these mutations, each of which may lead to partial resistance, that have emerged in different parts of Uganda. Their work used data from malaria cases and annual patient surveillance throughout Uganda between 2014 and 2022.

They found that two of the five key mutations appeared in far northern Uganda in 2016-17. The mutations then spread across much of northern Uganda and nearby regions, appearing in up to 54% of cases in one district. The other three key mutations emerged in western Uganda in about 2021-22, with prevalence up to 20% to 40% in different districts.

The study notes that in parts of Uganda where indoor spraying stopped between 2014 and 2018, cases of malaria quickly surged. Likewise, the emergence of any of the five key resistance mutations also surged, suggesting that the emergence was aided by malaria epidemics in populations where malaria had previously been well-controlled.

The researchers have different theories about how and why the mutations emerged. Their leading hypothesis, which they have targeted for more study, is that in populations with a low level of immunity to malaria, an epidemic increases the likelihood that resistance will emerge. “In northern Uganda,” the study states, “this scenario occurred after the withdrawal of effective malaria control, leading to high incidence of malaria in a population with relatively low antimalarial immunity.” They also suggest that fluctuating malaria transmission contributed to the emergence of drug resistance in southwestern Uganda. They emphasize the importance of maintaining malaria control interventions, with attention to malaria outbreaks, to decrease the likelihood of emergence or spread of drug resistance.

Others working on the project with UCSF include scientists from the Infectious Diseases Research Collaboration and Makerere University in Uganda; the University of Tubingen in Germany; Brown University in Rhode Island; and Dominican University of California.

Reference: 

M Conrad et al. Evolution of Partial Resistance to Artemisinins in Malaria Parasites in Uganda. New England Journal of Medicine DOI: 10.1056/NEJMoa2211803 (2023).

NIAID’s VRC, S. Africa’s Afrigen Kick Off Vaccine-Sharing Efforts
Training Aimed at Making mRNA Technology Available Globally 

A team of vaccine production experts from South Africa recently finished training in Maryland as part of a global mRNA vaccine collaboration. The experts are working with scientists at NIAID’s Vaccine Research Center (VRC) to produce vaccines against a list of troubling infectious diseases.

The mRNA vaccine platform, which became commonly used during the COVID-19 pandemic, works by delivering a piece of genetic material to cells that instructs the body to make a protein fragment resembling one from a target pathogen (such as a virus). The immune system then recognizes and remembers the fragment, enabling it to mount a strong response if the body is exposed to that pathogen. The mRNA vaccine production process involves inserting the selected virus protein gene into a plasmid (a circular piece of DNA), the production of which was the topic of the visit from the South African scientists.

The seven-member team from Afrigen Biologics and Vaccines, a biotechnology company based in Cape Town, South Africa, arrived on July 21 for two weeks of collaboration and learning with VRC scientists. They focused on vaccine manufacturing at the VRC’s Vaccine Clinical Materials Program in Frederick, Maryland. Specific aspects included topics such as: inoculum growth, nutrient feeding, quality control, and other steps needed to make an mRNA vaccine. The Afrigen team also met with VRC leadership, including the recently appointed VRC Director, Dr. Ted Pierson. 

The visit represented a significant milestone for an ongoing research collaboration established in March 2022 between NIAID and Afrigen. Their objective is to share knowledge, expertise, and data to expedite mRNA vaccine production globally. As part of the collaboration, NIAID – specifically scientists at the VRC – are making plasmid DNA that will be used for Afrigen’s in vitro transcription process. Additionally, the VRC is providing technology transfer and training on plasmid DNA manufacturing, which the Afrigen group observed during the visit. In turn, Afrigen is sharing knowledge and expertise with NIAID scientists about the in vitro transcription and lipid nanoparticle formulation processes. The mutually beneficial scientific collaboration will advance each institution’s work toward establishing mRNA vaccine production capabilities to support their respective missions.

The World Health Organization, the COVAX Vaccine Manufacturing Taskforce, and the Medicines Patent Pool established a formal agreement in July 2021 to build capacity in low- and middle-income countries to make mRNA vaccines, now known as the mRNA technology transfer programme. Afrigen was chosen as a center of excellence and training, or “technology transfer hub,” as part of the mRNA technology transfer programme. The hub is designed to improve the health and security of member nations by creating sustainable, locally owned mRNA vaccine manufacturing in those nations. Because mRNA vaccines can be cheaper to produce, quickly developed in response to outbreaks, and easily modified when new variants of pathogens emerge, the ability to produce these vaccines in low- and middle-income nations will contribute significantly to global health security.

Afrigen is working to establish mRNA vaccine production technology—initially for a COVID-19 vaccine candidate—and will work with local partners to conduct research to evaluate the vaccines, along with manufacturing the vaccines at scale. The eventual goal is to be able to share this established process with manufacturers across multiple countries. 

Though the effort began with COVID-19 in mind, the scientists are mutually hoping to use the mRNA vaccine platform to develop and test vaccines against an array of infectious diseases found globally, such as HIV, tuberculosis, malaria, influenza, cancer-associated viruses and more.

Afrigen scientists spent time getting to know colleagues at the Vaccine Research Center’s Vaccine Production Program (VPP) and Vaccine Clinical Materials Program (VCMP), including during a meet-and-greet with VRC leadership and staff at the VCMP pilot plant in Frederick, Maryland.

Credit: NIAID

NIAID scientists and colleagues are one step closer to developing a safe and effective therapy against alphaviruses with the identification of SKT05, a monoclonal antibody (mAb) derived from macaques vaccinated with virus-like particles (VLPs) representing three encephalitic alphaviruses.

Spread by mosquitos, alphaviruses primarily affect people in one of two ways: causing severe neurological impairment such as encephalitis (brain swelling) or crippling muscle pain similar to arthritis. Western, eastern and Venezuelan equine encephalitis viruses (EEV) are examples of the former, while chikungunya and Ross River viruses are examples of the latter.

Building on studies from the past decade, scientists in NIAID’s Vaccine Research Center and colleagues knew that macaques produce dozens of different protective antibodies when experimentally vaccinated against the EEVs. In a new study published in Cell, the research team identified 109 mAbs in macaques immunized with the experimental western, eastern, and Venezuelan EEV VLP vaccine. All antibodies were individually tested for binding and neutralization against the three EEVs, with the best ones also assessed against arthritogenic alphaviruses not included in the vaccine. Collaborators included scientists from NIAID’s Laboratory of Viral Diseases, USAMRIID’s Virology Division, and Columbia University.

Their work identified SKT05 as the most broadly reactive antibody – remarkably, it also provided protection against both types of alphaviruses, those that cause encephalitis and those that cause arthritic-like disease. High-resolution structural studies further revealed that the way SKT05 binds to alphaviruses could make it resistant to surface changes that can occur in viruses – which means the mAb is likely to have lasting effectiveness.

Further studies are planned to investigate potential clinical development of SKT05. They aim to better define how SKT05 interacts with viruses and whether it can confer protective benefits against additional alphaviruses.

References:
M Sutton et al. Vaccine elicitation and structural basis for antibody protection against alphaviruses. Cell DOI: https://doi.org/10.1016/j.cell.2023.05.019 (2023).

EE Coates, et al. Safety and immunogenicity of a trivalent virus-like particle vaccine against western, eastern, and Venezuelan equine encephalitis viruses: a phase 1, open-label, dose-escalation, randomised clinical trial. Lancet Infectious Diseases (2022).

SY Ko, et al. A virus-like particle vaccine prevents equine encephalitis virus infection in nonhuman primates. Science Translational Medicine (2019).