Using a novel approach for malaria vaccine development – an interview with Jonathan Kurtis

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In this interview we speak to Jonathan Kurtis (Brown University, RI, USA) about his research on malaria, which led to the discovery of a parasite protein that provides new insights into how malaria regulates infection levels within its host, along with new possibilities for a broadly effective vaccine and a new class of antimalarial drugs.

First, could you introduce yourself and tell us a bit about your background?

My name is Jonathan Kurtis, although my nickname is Jake. I am a physician scientist and Chair of the Department of Pathology Laboratory Medicine at Brown University (RI, USA).

I have been studying malaria for more than 25 years at this point, with a focus on vaccine development. I started working with a group from the Walter Reed Army Institute of Research in Kisumu (Kenya) in 1996. I was actually doing my postdoc with Patrick Duffy and his colleague, Michal Fried, both of whom were co-senior authors on the paper, so we have been working together for literally a quarter of a century on this problem.

Could you outline some of the gaps in our knowledge of malaria and why this research is an area of unmet need?

Malaria is the greatest single agent killer of children on the planet, nothing comes close. In 2018, approximately 10,000 children under the age of five died every single week. I used to refer to it as 500,000 children a year but in the era of COVID, everyone’s brain is now calibrated to 10,000 as a denominator. Every time the death toll rises above 10,000, we all get attuned to it, as we should, but when you consider COVID, which is really attacking a totally different segment of the population, and you compare it with malaria, you see that it’s hard to liken them.

I don’t mean to diminish the impact of COVID, but rather to use it as a benchmark to help us understand the true impact of malaria.

At the time of this interview, there have been over 56,000 COVID-related deaths worldwide. That’s 5 weeks’ worth of malaria deaths among children, and it was not just starting in March of 2020. The killing goes back to March of 2019 for malaria, March of 2018, March of 1818, March of 1618, it goes back time immemorial. It has been the great culling machine of the tropics, today largely in sub-Saharan Africa and Southeast Asia.

So the gap is that we have poor tools to control malaria morbidity, mortality and transmission. It is frankly the greatest unmet health need on the planet, bar none.

Could you tell us about your research and what lead you to the discovery of PfGARP?

This work, in one way or another, really did begin in 1995-1996. Some of the samples in the paper were actually collected in 1995, which is kind of crazy.

For 50 years, we have had fabulous vaccines for malaria, which is hard to believe. They were largely developed in mice, and they protect mice wonderfully from mouse malaria. No mouse has to live in fear. The problem is that they have not generalized very well to humans. So instead, we tried to build on the strengths of our group, one of which is population level epidemiology. If you go into a malaria community and look at children, you will see that some children have developed a resistance to malaria and some have not – they are still susceptible.

I can say that in one sentence but actually determining which children are resistant is a ton of work and that’s where you really need boots on the ground, epidemiologists and biostatisticians in the field to help recruit large cohorts of children and follow them over time. That was all managed by Patrick and Michal in Tanzania with their Tanzanian colleagues. Once you figure out who is resistant and who is susceptible, you can then ask the question ‘why?’ Our hypothesis is that resistant children make antibodies that recognize a unique set of malarial proteins that the susceptible children do not.

The truth is, susceptible people make antibodies to tons of malarial proteins, not just the important ones, and so you really are looking for the needle in the haystack. You are looking for the Boolean difference product – what parasite proteins are recognized by antibodies in resistant people but not recognized by antibodies in susceptible people?

We basically created molecular tools to allow us to answer that question. By using sera from resistant people and sera from susceptible people, we were able to identify the parasite genes encoding parasite proteins that are uniquely recognized by antibodies made by resistant but not by susceptible people. In that short list of antigens, GARP was at the top.

GARP is located on the exofacial surface of infected red blood cells.

How do you plan to leverage the discovery of this antigen to explore the potential development of vaccines and treatments for malaria?

There was another discovery about GARP that was actually unexpected at first. Typically when an antibody binds to a pathogen, an immune cell comes along and engulfs the pathogen, or the antibody binds to the pathogen and activates the cellular cascade of defense proteins called complement, which attacks the pathogen. However, if you take antibodies to GARP and put them in culture with parasites, the parasites die without any immune cells and without any complement. What’s more if you make recombinant antibodies and add them to parasites in culture, the parasites die as well. So you do not even need to cross-link GARP on the surface of the red cell, all you need to do is add antibody. That told us that the binding of anything to GARP, antibody to GARP in particular, causes the parasite to die, but the question is, why? We figured out that it triggers apoptosis, programmed cell death, of the parasite.

We believe this could be transferred to practice in three ways.

One option could be to make a standard vaccine where you immunize a person with the GARP protein so that they make anti-GARP antibodies.

Another approach would be to make a large amount of the monoclonal antibodies against GARP, which you could use in two ways: you could infuse it into someone before they travel, and it would protect them for about 3–6 months or you could use it to treat people in certain malarial areas before the high transmission season. The other thing you could do is use anti-GARP antibodies as a therapeutic for active malaria infection.

The third option would be to find a small drug-like molecule that mimics the binding of anti-GARP antibody to GARP to activate apoptosis. We are actively screening high throughput compound libraries to identify targets that mimic the binding of anti-GARP antibodies.

What are the next steps in optimizing a malaria vaccine?

It really does hinge on funding frankly. The US National Institute of Health is very interested in the basic science aspects of malaria, but it is not really set up to carry discoveries through what we call in the field the ‘valley of death.’ This is where you get a great piece of science but before you can actually turn it into a therapy, you have to develop it, and the big drug companies are not that interested in taking on the risks on the cool science because it has not yet been developed sufficiently. This creates a gap between what the governmental or federal funding agencies will do, and what the big pharma companies want to see coming into their pipelines. This is precisely where we are located with GARP right now.

So in order to get more traditional pharma companies interested in GARP, we would need to get into a Phase I trial, which requires optimization in nonhuman primates. We have already shown that two different formulations of GARP can protect non-human primates from P. falciparum. We would like to optimize these formulations in non-human primates first and then move on into a Phase I trial.

When do you think a vaccine may be ready by?

It’s difficult to say. Ocean Biomedical (RI, USA) has expressed interest in GARP. They have licensed the IP at this point and are committed to infusing sufficient funds into this development program to get us through the optimization in monkeys and on to Phase I studies, and we are expecting that to be done in 18–24 months. We are actively looking at combining GARP with our other vaccine candidate, PfSEA-1, which was published in Science about 5 years ago.

Going into more detail about how GARP kills, if you look at the blood stage of malaria, you have merozoites that bind to and infect the red cells, and they turn into a form called a ring stage, which develops into a trophozoite stage, which segments into dozens of merozoites that infect all new red blood cells. This stage is called the schizont stage. Our GARP protein is expressed by that trophozoite, and so anti-GARP kills trophozoite-infected red cells. SEA (schizont egress antigen) is our other vaccine candidate. Antibodies to SEA block parasites from exiting the red blood cell, so they are trapped inside.

So we have a target that kills the trophozoite and a target that traps any surviving schizonts. Putting both targets together should give us some synergy of activity. Even if a few parasites escape the GARP targeting, they will get mopped up by the SEA targeting.

Could you tell us more about the development platform that led to this discovery and how it could be used in other disease areas such as SARS-CoV-2?

Yes absolutely, and this is something that Ocean Biomedical is quite interested in because they are in fact committed to applying it to other pathogens.

It’s really fairly straightforward and yet has not really been utilized for vaccine discovery by many groups. The idea is that some individuals, after being exposed to any given pathogen, develop resistance after exposure and some people do not. In our case it was malaria, but we have also used it to discover vaccine candidates for schistosomiasis. The platform is predicated on high quality epidemiologic, typically longitudinal, studies to discern who has developed resistance and who has not.

In the case of malaria, you’ve got to be careful. If you are sickle trait positive, you are actually resistant to malaria. So if I just look cross-sectionally at a group of kids, and some of them have very few parasites while some kids have lots of parasites, I could think that the kids with no parasites are actually resistant because of antibodies when, in fact, they could just be the sickle trait positive. So you really need to be careful of all the non-immunologic factors that influence parasitemia, and this is true across whatever disease category you are thinking about. Bringing it back to COVID, if there’s someone who has lived in a glass bubble for the last few months, they will be COVID negative. This does not mean they are resistant to COVID, it is just that they have had no exposure. So you really have to consider the non-immunologic factors that can influence the expression of the disease or susceptibility to it.

We use that epidemiologic approach in order to be very certain about who has developed resistance and who has not. Then we do whole proteome differential screening, where we take the genome of the pathogen we are interested in and interrogate each gene and ask whether that gene makes a protein that is differentially recognized by the plasma and the serum from the resistant person or the serum from the susceptible person. We multiplex this massively, it’s not one by one, we do tens of thousands at a time, and ultimately what you find is a list of genes that encode proteins from the pathogen that are uniquely recognized by resistant individuals but not susceptible individuals. If we were to do this on COVID, it only has handful of genes. We would not be looking so much at the whole gene level, we would actually be looking at the specific short peptide level to identify which peptides in the virus are targeted by antibodies in the sera of individuals who have recovered versus individuals who have succumbed, that would be one approach.

Finally, is there anything else you would like to add about your research or thoughts on the field?

I think the key for our kind of work is to really embrace and emphasize that it’s a huge team. It’s a team effort of scientists that understand epidemiology and biostatistics, molecular biology, protein chemistry, cell biology, cell death and non-human primate studies. It really takes a huge team located both in the endemic countries, where 60–70 people are employed to run a study like this, as well as people literally all over the world. So we have had folks at major institutions throughout the United States that contributed to this and I think anyone planning on doing this kind of work really has to realize that it’s going to be a team effort.

Yes, in order to make these sorts of discoveries, you really need to be able to collaborate globally.

It’s so true. The era of the lone wolf is really over. If you look back at big journals like Science and Nature 20–30 years ago, it was common to see manuscripts with only one or two authors on them. If you look now, we have I think 33 authors and everybody on this list has really contributed, it requires a very broad set of experiences. So with us, we would make a discovery that suggested a new area we needed to look into and if we were not experts in that area, we would just call up our friends, and so the number of authors accrued over time, it’s actually kind of fun. I was once giving a talk at Yale University (CT, USA) and someone asked me a question, and it was such a good question, and I had no idea what the answer was. I came up to him afterwards and he suggested an experiment. We did it the next week and it turned out exactly as he had predicted and so now he is an author on our paper.

We are a global community, and a central question of our time is: are we going to tolerate half a million children under the age of five dying of malaria every year or are we a global community that’s actually going to prioritize doing something about that?

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Disclaimer
The opinions expressed in this interview are those of the interviewee and do not necessarily reflect the views of Infectious Diseases Hub or Future Science Group.

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