Episode Transcript
[Intro Music Starts Playing]
Tony: Hello and welcome back to another episode of Microbe Matters, presented by IDPITTStop, where we discuss, dissect, and demystify topics in Infectious Diseases with our experts here at UPMC and the University of Pittsburgh. I’m your host, Tony Morrison, media specialist here at Pitt ID and I’m just as curious as you may be about navigating through a world full of microscopic organisms. Please join us as we examine both the dangerous and beneficial microbial microcosms that surround us, promote public health, and showcase research and treatment of modern infectious diseases.
[Fade out Intro Music]
[Fade in Jungle Music]
Deep within a jungle, among the bramble thicket and sounds of unseen creatures, a team of researchers are in pursuit of the macaque, a species of non-human primates. Their mission is clear, but their path still uncertain. What the researchers seek is something far more elusive than just a monkey: they are looking for the cure for HIV. The macaque is a species known to share many genetic similarities with humans, and these creatures, they believe, may hold the answers they need. Answers about how HIV progresses, how it spreads, and, ultimately, how to stop it.
Among the team is Dr. Cristian Apetrei, a young researcher at the time, armed with nothing more than a sense of duty and the hope that their findings could change the course of history.
[Jungle Music Abruptly Cuts]
[Record Scratch SFX]
Okay, so maybe Dr. Apetrei didn’t wield a machete and pioneer through the dense forests alongsisde the exploration team, but the expedition was carried out to obtain research specimens for his work back in the US.
[Soft Curious Theme Fades In]
Dr. Apetrei’s journey into this field wasn’t born out of mere curiosity; it was shaped by a series of difficult, sometimes painful choices. His work, particularly in animal studies, has taken him to places few researchers are willing to go. The question was never just how to advance science—but at what cost?
As Dr. Apetrei shares, navigating the ethical terrain of animal research has never been simple. The jungle, the specimens, the experiments—they all represent a larger ethical dilemma as well. In today’s conversation, we will explore topics in viral pathogenesis, navigate through scientific ethics, and share some of the surprising discoveries linking HIV progression to digestive health.
[Soft Curious Theme Fades Out]
Tony: Welcome, Dr. Apetrei, thank you so much for coming on today’s show to discuss your seminal work in HIV research.
Dr. Apetrei: Thank you for the invitation.
Tony: So, Cris, let’s begin by considering the molecular clocks of the primate subjects in your research, and how recalibrating them allowed you to trace SIV back millions of years. How has this changed our understanding of HIV’s origins and potential future threats?
Dr. Apetrei: This is not the trivial issue. And because these monkeys are actually the origin of HIV and, on the on the other hand, they may represent a very interesting source of information for us because, they don't progress to AIDS, so they get infected at high level of prevalence, up to 90% in the wild. And we don't see disease progression.
So, understanding how they are able to cope with the infection is very important. So, all these aspects related to adaptation called for long periods of time. The monkey species were already infected when they originated. So, very old. But then the molecular clocks were telling us a completely different story. We tried to understand how to be able to recalibrate the clocks in order to get meaningful results.
Tony: Dr. Apetrei and his team found that previous estimates of SIV's age were drastically off. By studying isolated viral strains, they recalibrated these molecular clocks, revealing an ancient evolutionary history stretching back hundreds of thousands of years.
Dr. Apetrei: So, we find the island by Bioko, which is an island outside Equatorial Guinea. Very nice, very beautiful, very wild, with a lot of monkeys and everything. So, we said, okay, we’ll go on the island of Bioko, we will find a virus that has a counterpart on the mainland, and we will recalibrate the clocks.
We sampled a lot of monkeys. And every virus that we isolated was a new virus. But it didn't help us to recalibrate the clocks, because we didn't have the mainland counterpart. We established the last common ancestor 12,800 years ago, and we recalibrated it this way. All the clocks getting to hundreds of thousands of years, which was much closer to what we were seeing in pathogenesis.
Mt. Drakensberg is a very tall mountain. It's about 12,000ft. This means it's a new mountain. But then I started reading geography and actually, Mount Drakensberg was on the first mainland. Its 280 million years old. So, it was there all the time; every time when monkeys were on this Earth.
And by recalibrating this way, we got the virus to be 1 million years. Plus/minus, which got us to four orders of magnitude greater in ancestry of the viruses and explained where the evolution occurred. So, the good news is, yeah, we can adapt to the virus- to HIV. And the bad news is occurring hundreds of thousands of years.
Tony: So why are non-human primates such effective models for studying HIV pathogenesis? Could you highlight any specific discoveries from your animal models that directly influence human HIV treatment?
Dr. Apetrei: They're very, very important to study vaccine responses and protection because in humans we cannot do challenge experiments, of course, with HIV. So, it's very important to do meaningful experiments for testing protection to vaccine.
We can test drugs in monkeys. We can do every invasive study to see distribution of the virus reservoirs and all these very important features nowadays. And of course, we can do cure research, because if we succeed to perform a successful experiment, we can stop therapy and see if we are able to control the rebound or not, which also in humans will raise ethical questions.
Tony: Non-human primates like macaques are invaluable in HIV research. Their biology closely mirrors ours, allowing scientists to observe disease progression and test treatments in ways impossible in humans. This has led to major discoveries about immune responses and vaccine potential.
Dr. Apetrei: This being said, the monkeys also offer us the possibility of doing what we call comparative pathogenesis.
Macaques, like humans, are not the natural host of the virus. They were infected recently when we infected them with this virus and developed AIDS in a very condensed timeframe, faster than humans. But anyway, they develop AIDS in 100% of cases.
We focused on what is the reason for which a species of African monkeys did not progress to AIDS when infected with SIVs. From a scientific standpoint that was worth 20 years of failure. We said, okay, they can throw the virus because they are able to control replication. And actually, they replicate the virus at higher level.
Human responses controlled the virus better, but depleted human responses, we didn't see anything. We depleted T cell responses. We didn't see anything. We depleted in nCase- a TREX[1]! We did everything in our power to make these monkeys progress to AIDS. And they did it. But in the process, we observed that the most important correlate of the lack of disease progression in African green monkeys is their exquisite ability to maintain a healthy gut and to control chronic inflammation and immune activation.
When we first reported this, the paradigm in HIV infection was we suppress the virus, we will control infection. But then together with other data, this data in natural host significantly contributed in switching the paradigm to this inflammation and immune activation, which is actually the current paradigm of infection. Now when we suppress the virus with antiretrovirals, we still have residual inflammation, which is actually the main cause of death in HIV infected individuals. They have this persistent inflammation which increases their cardiovascular risk. So, this is one of the most important things that we brought from our studies in the field.
We tried everything in our power to manipulate the immune system, to lose control and have disease progression. And then, when we realize that they're able to maintain a healthy gut, we started thinking, how would we do something to alter the gut and see what happens?
We were in Barnes & Noble in the cooking section, and my wife was telling me, “How could we do something natural to destroy the gut?”Then I started laughing because everything in front of me was “how to maintain a healthy gut” cookbooks. We have a lot of dietary interventions to increase gut health. Let's do bad things, because these are monkeys having very good physical activity. They have a healthy diet because they eat bananas, and they are vegetarians.
They are not obese. They don't smoke, they don't get drugs and they don't drink. I mean, these are very good monkeys. And we said, okay, we put them on a diet which is equivalent of McDonald's diet for one year. One of them progressed to AIDS, one of four, which was completely unexpected.
Tony: I would have never thought that a Big Mac and a large fry could catalyze an HIV infection into full blown AIDS.
Dr. Apetrei: Probably not one Big Mac, I take home Big Macs. If you take home three per day!
Tony: Your research underscores the significant role of gut health in HIV pathogenesis, particularly since the pivotal moment you and your wife experienced at a Barnes & Noble cooking section. Could you elaborate on how microbiota translocation contributes to chronic inflammation and related comorbidities in people living with HIV? Additionally, are there any promising therapeutic approaches on the horizon that address this dysfunction?
Dr. Apetrei: We have a virus that replicates in the body, depletes CD4 cells. 80% of those cells are wiped out in three weeks. So, the question is how are we able to survive for ten years with so few memory, left? The organs are able to control this loss of cells.
Not completely, not ideally, but they slow the complete destruction. And we have the examples of the natural host, which when infected with this virus is also depleting 90%. But then they control the viral load and control inflammation, limiting the continuous destruction of cells, which results in a partial restoration of those cells. The essence of pathogenesis is the introduction of a microbe in a place where normally it does not have access.
We don't say what kind of microbe; it may be a good microbe, but it shouldn't be there, and it kills you. And there are examples. You go to the dentist, you have a tooth extracted, and then you get staphylococcus directly into the circulation, and you die of endocarditis.
That microbial flora from that gut is able to get through the mucosal barrier into the internal milieu and first in the liver, then in the lymph nodes and then in the blood. That is a bad thing. And every microbe which is present in the blood is very bad news for us- it’s sepsis.
But this is below sepsis level. The lesions are not extensive. The translocation of the micro business is not spectacular but is exactly enough to maintain a status of chronic inflammation that will actually make us to age quicker, to have any kind of subsequent diseases.
Tony: One of the biggest breakthroughs in HIV research is the realization that gut health plays a crucial role. Dr. Apetrei's studies show that chronic inflammation, triggered by a weakened gut barrier, significantly impacts disease progression. This shifts the focus from just suppressing the virus to also maintaining gut integrity.
Dr. Apetrei: Chronic inflammation is actually the major killer in the world. More than half of the people which are dying in the world every year are dead by a disease, which is directly or indirectly related to chronic inflammation. There is a significant higher risk of microbial and infection for people which are having this kind of chronic inflammation due to the bridges in the intestinal barrier.
Tony: You've developed new strains of SHIV for research. Could you describe how studying SHIV models aids in bridging the gap between animal research and human treatment trials?
Dr. Apetrei: The Type Trial hit and up to that moment, everybody was focusing on cellular immune responses as the main mechanism for virus action.
The type trial told us, yeah, it's very important to help CTLs, but actually we know this from basic immunology, CTLs, CD8 cells, is what heals an infection, yeah? The CTLs are eliminating the cells infected with viruses. But what prevents an infection is human-immune responses.
The type trial was the first telling us yeah actually you need antibodies and they can do that if you have a mature immune system. And that was the moment when we had to revise a lot of things, amongst which the way we are doing the animal works.
So, the antibodies which would protect against HIV II would not protect against HIV I, which means that in macaques you cannot study the most important correlate of humoral protection, which is the antibodies.
And what we did in the past, we engrafted HIV I sequences in the envelope region which codes for the surface of the virus towards which the antibodies are there. So, we engraphed this HIV I sequences in the HIV II structure, or SIV structure, and we infect macaques with these chimeras.
Tony: To develop better HIV vaccines, researchers engineered SHIV— a hybrid virus that mimics HIV more closely in animal models. This advancement allows scientists to test immune responses and potential treatments in ways that standard SIV models could not.
Dr. Apetrei: The problem was that in the beginning, the SHIVs, as we call them, were very nice and they were very effective in being protected for viruses and everything. And this was actually the reason for which the first major trial failed miserably- the step trial. Because these viruses, instead of using CD4 and CCR5 as main receptor and coreceptor, they were using CXCR4, and that is a completely different story.
I mean they don't go to the to infect central memory cells. It's a different distribution of the receptor. You have a different pathogenesis. And actually, what we saw later. The infection was self-controlled in some of these cases. So, we absolutely needed SHIVs that use CCR5.
And I don't take any merit in this it was the creativity of the Philadelphia group. They did everything to generate this what we call transmitted founder viruses, which not only modeled a virus which has an envelope of HIV I but modeled the viruses which are actually transmitted in HIV I infection, because those are different from the viruses later on the infection. And this is actually what you need in order to develop good antibodies.
Tony: With the with the shift in HIV care towards managing comorbidities like cardiovascular disease, how does your research help predict or even prevent these issues for patients on antiretroviral therapies?
Dr. Apetrei: Yeah. So, this was another thing that we needed to adapt. I remember, it was CROI 2008. As we were flying home, my wife was telling me,
“You go to CROI and it's so interesting. You see clinical things. You see things that have direct application, and I'd like to do this.”
This this would be a very good idea. “What do you think we should do?” And we started looking. And then one day she came and said I want to study hypercoagulability and HIV infection.
And I said, “yeah, it will be very difficult without having markers.” So, there is actually a paper that was published recently. It was the famous Kuller paper. Kuller was working at the School of Public Health here in which they were establishing the main predictor of death in subjects living with HIV with or without ART.
There are actually three: D-dimer, IL6, C-reactive protein, all these markers of inflammation and we wanted to see if we can use D-dimer. We included both macaques and African monkeys, and it was a tremendous correlation because D-dimer was only increasing in progressive infection and not in the non-progressive ones.
At the time when that paper was published, a lot of people were discussing whether the hyper coagulability is the result of administering antiretrovirals or not. And again, we have antiretrovirals in our monkeys demonstrating in these models that there is a clear correlation between the increases in hyper coagulability and the progression to AIDS.
And actually, it turns out D-dimer was, for us, the best predicting marker for infection in every monkey species. At that point we started focusing on comorbidities. We can also look at strategies to heal the gut.
I like the term comorbidity. This is what actually AIDS looks like nowadays. I can give you a long list of comorbidities, or I can say a single word: chronic inflammation, which triggers everything else.
Tony: Given your extensive work with non-human primates and the discoveries that have resulted, research involving these animals often presents significant ethical challenges. How do you ensure the humane treatment of the primates while balancing the need for scientific advancements that could lead to critical breakthroughs?
Dr. Apetrei: In humans, when the subject is very immune suppressed or very advanced in the disease, we do everything in our power to keep that basic patient alive. In animal work, we have to abide the ICoC rules and the ethics committee, we don't need to put the animals to suffer.
Dr. Apetrei: I think that is probably the major waste of animals; animals should expand the data from humans. Animals should go there where we cannot go in humans. But I think one of the problems with the clinical research is that you have a very large group of patients and you have to establish and try to balance the groups and everything. In animal studies, you can control every single aspect of the research.
You can even select what kind of monkeys with the same genetic pedigree. You can infect them at the same time in the same way. You can do exactly the same sampling. You can get to sample invasively and get into tissues, lymph nodes. So, this is an incredibly powerful tool, an incredibly expensive tool.
It's always a balance of what we include in what we are doing.
Tony: Absolutely—any time animals are involved in research, the ethical and logistical complexities become unavoidable. It’s a balancing act that always requires careful consideration.
Dr. Apetrei: It's always a very delicate balance that we have to follow. Sometimes it's complicated to do it. But when we are doing what we are doing, when you are doing pathogenesis, so you introduce something- an infectious agent, and you have to see the host response. No single tissue culture will show you this because you need to develop the novel immune responses. Those are new molecules, new substances, new structures which are built within the entire body. And there are also special tissue relations. I don't think there is an alternative to this.
[Fade in Theme Music]
Tony: Dr. Apetrei, your point about the invaluable role of non-human primates in understanding pathogenesis and immune responses really drives home just how complex and nuanced this research is. While there are always ethical challenges, the insights we gain are irreplaceable when it comes to tackling diseases like HIV.
On behalf of our listeners, I want to sincerely thank you for sharing your expertise today. It's been an enlightening conversation.
Dr. Apetrei: And thank you for the invitation. It was a pleasure to talk about this.
Tony: Science is a journey of difficult questions and even tougher answers. But as we’ve heard today, it’s also a journey of compassion, responsibility, and a relentless hope for a healthier future.
And that wraps up today’s episode of Microbe Matters. I’m Tony Morrison, reminding you that every breakthrough begins with an idea—sometimes even one sparked in the aisles of your local Barnes & Noble.
[Fade out Theme Music]
Tony: Thanks for listening! If you enjoyed today’s topic, please rate, write a review, and be sure to subscribe to the show wherever you listen to podcasts, so you never miss an episode!
Want to keep up with the latest ID PittStop news? Follow us on social media at @IDPittStop, where you can view behind the scenes content, discover more of our research, and be the first to know about upcoming projects.
