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Director’s Innovation Speaker Series: HIV-1 and SARS-CoV-2 Effects on Brain and Mind Health: A Tale of Two Viruses


DR. JOSHUA GORDON: Welcome, everyone. Now we can get started. My name is Joshua Gordon. I'm the director of the National Institute of Mental Health. And as I just alluded to you, we moved into our new facilities here in the neuroscience building in Rockville, Maryland, but we are still doing Director's Innovation speaker series virtually because we feel like it reaches a broader audience this way.

I'm really pleased today to have Dr. Serena Spudich with us. I'm going to be introducing her in just a moment. But before I do that, let's go over the usual housekeeping messages.

(Housekeeping comments.)

With no further ado, we're going to get into it. As we've done a couple of times over the last couple of years. We're going to have a fireside chat rather than a seminar. And I think a lot of reasons to do that with Dr. Spudich. She is a really world-renowned scientist who has pursued a path that's a little bit out of the typical realm for an academic scientist pursuing really cross-disciplinary work. And we're going to talk about that and why.

Serena is the Gilbert Glaser, professor of neurology and chief of the Division of Neurological Infections in Global Neurology, as well as co-director of the Center for Brain and Mind Health at Yale University. She's really done pioneering work on clinical and translational research that examines the effects of HIV, and more recently, SARS-CoV-2 on the nervous system and on brain health and on a range of different issues that are near and dear to us here at NIMH.

She is a graduate of Stanford and of UCSF, who made her way east to Yale, where she's been on the faculty for some time now. Lots of awards, lots of recognition, lots of great talks. I could go on and on, but I thought rather than doing that, I'd ask Serena to introduce herself, and would you mind telling us not just the CV stuff, but a little something about how you got to where you are today in doing so.

DR. SERENA SPUDICH: Absolutely. And thanks so much for the honor of being invited for this session. And I'm here, of course, representing lots and lots of physicians, physician scientists who have been interested in this intersection between viruses and the brain for many decades. And I'm just one of many.

I think that my particular path of getting interested in studying how infections affect the brain, there's many reasons, but I think one of the things is that my parents are both scientists. Neither of them are M.D.s. So, I heard a lot of science in the house and was always interested in research. My mom is from India, so as a child I spent time doing some exposure to sort of international global health types of issues.

And then as a medical student at UCSF, when I knew I was interested in neuroscience, it was the mid-1990s and we had many, many patients in the hospital who were there with complications of AIDS. And Dr. Gordon, it sounds like we intersected at UCSF at the same time. So, I'm sure you had the same experience, that as a neurology clerkship, wide-eyed, young student, I was seeing the effects of the virus or the complications of the virus ravaging the brains of young people.

I went onto to do a couple of years in medicine training, decided I really love neurology, so I did neurology training. But it was clear to me that there was a sort of gap in our understanding of generally how infections affect the brain. And I was lucky to have a number of clinical and research mentors along the way that sort of said, yeah, that's true, we really don't have answers to these questions. And so, ended up kind of in this intersection between these two kinds of traditional disciplines.

DR. GORDON: Well, I'm going to get us to that intersection pretty soon. But there was one thing in your CV. Well, there are a few things in your CV stand out. But one of them that I was intrigued about, you have a master’s in philosophy of science. Tell me about that.

DR. SPUDICH: That's pretty common for a neuroscientist. There is often a sort of overlapping fascination with science and with how the mind works. You know, many of us, I think, ended up reading Oliver Sacks and these kinds of things and got interested in personhood and the philosophy of kind of who we are. And when I was an undergraduate, yes, my main focus was neuroscience, but I ended up being interested in not only the intersection of that with philosophy of mind, but also in particular how we believe what we believe.

So, that's the history of science, right? Why is it that we have - I did a thesis on phrenology, actually, but it wasn't about, what is phrenology, but it's, why did culture accepts phrenology at that time. Why do we really think that you can tell what people's capabilities were based on the bumps on their head? And what was the cultural environment that led us to have those beliefs? And I actually think that looking critically at science for every era, and why we accept certain things as dogma or don't, is really valuable.

Another example is that as a medical student, I worked with Dr. Stan Prusiner, whose work in prions and how they affect the brain was really rejected for a long time. And part of it, it just went so much against the dogma of our understanding. And so, I think thinking about that in a cultural context was kind of interesting and enlightening.

DR. GORDON: Yeah. Now, prions are an infectious agent, right? They're an interesting infectious agent because it's a protein, a malformed protein that can spread disease. And for those you who don't know, it can be spread by eating the brains of an organism that's been infected. But your career has been a different infectious agent. It's been focused mostly about HIV and then later about COVID.

You told us that you became interested in that because of your experiences at UCSF. But over that time, you were at UCSF, it was a time of great change in the care of individuals with HIV and in their in their prognosis. And so, many people may not be familiar - many people who think of AIDS as a disease now that's controllable with medication and became a chronic illness, may not really understand what was going on with patients in the 1990s when we really had just a few antiretrovirals at that point. And patients were still struggling to get control over the illness for most patients.

So, what were the manifestations of HIV infection when you were a student and a resident and starting out as a faculty member? And what was changing about the infection then?
DR. SPUDICH: Well, certainly as a student - my first year on the wards, was the year before the combination antiretrovirals became available. And so, it was a uniformly fatal disease. The treatments were just staving off the inevitable and people who were able to take the treatments and tolerate them, which were really very, very hard to tolerate. And we had lots and lots of patients dying of things such as cryptococcal meningitis, PML. And the thing that has been the cornerstone of my research has been just the effect of the virus, HIV itself in the brain, which was HIV dementia.

I remember going into people's rooms and having these young people in their thirties staring out the window, unable to talk and really glossed over, unable to take care of themselves, and inevitably dying. I'll say it was incredibly overwhelming. It was overwhelming as a student and as a resident after that. And I think many people felt that they didn't want to study HIV because we felt it was so difficult. On the other hand, I think it also was really inspiring because there were so many unanswered questions.

I also think that as I went on and HIV did become more manageable, we had many, many people - fewer people in hospital dying of AIDS, it became obvious that there were still really vulnerable pockets of populations in our society, of people who were falling through the cracks, developing lots of complications of AIDS. They were getting medications regularly. And of course, all the stigma associated also with HIV.

So, I think my interest in HIV evolved from partly just the kind of clinical and unanswered research questions to also developing a lot of affinity for the people at risk of HIV in the US and worldwide.

DR. GORDON: And of course, you and many others were deeply interested in studying the effects on the nervous system and we learned a lot over time. And of course, the infection shifted over time. So, you can pick whether you want to talk about HIV dementia or whether you want to talk about HAND and explain what that is, but what are some of the most significant findings from the HIV and CNS science that we've gained over the last several decades really, and how it's changed?

DR. SPUDICH: Yeah. I think very, very early on in the mid-1980s when HIV was first described, AIDS was first described, it was recognized that HIV led to dementia in people who had untreated longstanding AIDS. And early on, pathology studies, I think, revealed that there was a widespread inflammation in the brain in people who had AIDS, and that, in fact, the virus infects cells of the brain and replicates in cells of the brain.

So, really early on, it became obvious that this was a neurotrophic virus and 20 or 30 percent of people with AIDS would develop dementia. And I think that the recognition that that was actually a bystander effect so that the cells that were getting infected weren't neurons, but they were actually resident immune cells in the brain was critical to thinking about how to target treatments of that kind of thing. But I think it also raised questions of sort of, if you don't have dementia, are those immune cells getting infected earlier on and is it something that's being propagated over a long period of time?

So, my particular interest - and I'll say my NIMH K23 award, my very first NIH grant, was focused on looking at people with really early HIV and looking to see whether the nervous system was affected really early. And that work spawned a lot of projects, both here and abroad, that have essentially shown us that we don't have dementia early on in the course of HIV. But the virus enters the brain, replicates in the brain, causes inflammation and smoldering changes you actually probably associate with the milder forms of impairment that people get - this HAND term.

DR. GORDON: So, let's delve into that a little bit. So, your work and others showed that it gets in the brain, it's doing stuff early and there are impacts on brain function. So, before I ask you explain what HAND is, let me just follow up on that. Is that true even if someone gets treated early in the infection? Is it still again in the brain? And do any retroviral therapies that we that we have today, do they squelch that, or are they only partially affected?

DR. SPUDICH: So, that's sort of a two-part question. So, first of all, are there effects in the brain if people get treated? Certainly, the effects on the brain are very, very attenuated once people go on treatment. So, it seems that for the most part, the replication of the virus - which is controlled by the current therapies - the virus isn't eradicated by the current therapies, but you just stop the stages of the lifecycle that allow it to make more of itself. That seems to be mainly affected in the brain. So, we don't detect a lot of viral replications by looking, for example, at spinal fluid samples in people who are living with HIV on suppressive therapy.

The problem is, is that some of the other ongoing processes are probably still present in people during therapy. So, one thing is that there seems to be ongoing levels of immune activation. So, markers of microglial activation, for example, are still abnormal despite therapy. There's also probably some level of injury prior to people starting the treatment that they've accrued in whatever period of time they stayed off therapy.

So, most people, when they start HIV treatment, are not starting in very, very early infection. They're starting at some point when they present to the medical system with symptoms, with disease, or potentially in a screening process. The question of whether the really early treatment can ameliorate some of those changes in the brain is exactly what we're trying to study, for example, in the cohort in Thailand that you've now visited, where people are identified within the very, very first weeks of acquiring HIV and started on treatment, and there have been some benefits in that context.

DR. GORDON: So, we'll come back to that. But so, the bottom line is that you can see these immune system effects that persist even after you've got control over the virus, and you do get control over the virus replication in the brain. I'll just point out to our audience here, that's something we're familiar with in mental health. We know that there are neuro-immune interactions. We know that we see signs of immune dysregulation in mental illnesses sometimes, not necessarily all the time. And so, some of the same issues that you're dealing with in HIV effects may also be related to the other issues that we're dealing with in depression or in some of the other mental illnesses where neuro-immune mechanisms are thought to play a role.

Can you tell us now, what is HAND and is that the mainstay of your concern in terms of what's going on with the immune function in these folks on treatment with HIV?

DR. SPUDICH: Yeah. HAND is semantic. It's a term. It's a term that's that stands for HIV associated neurocognitive disorder. And essentially, it was developed by sort of an expert group of individuals who got together and said people who are living with well-treated HIV - which is the majority of people, for example, in the U.S. today and even worldwide, most people have access to antiretroviral therapy now - seem to not be having - not everyone who is well treated has cognitive function that's the same as people living without HIV. And that's based essentially on formal neuropsychological testing and categorizing people compared to healthy controls.

There is some controversy about HAND because saying what's the appropriate control for someone who's living with HIV, a lot of people living with HIV in the US, for example, may have other risk factors for cognitive or mood disorders, and that may include substance use, that may include early life trauma, that may include low levels of educational attainment. There are a number of different things that people may be at risk for. So, comparing people who are sort of published healthy controls in their performance to people living with HIV is problematic.

I think that there is some really convincing evidence that even optimizing all of those other risk factors, there's still some residual challenges that some portion of people living with HIV seem to have compared to people without HIV. And the good news is we have long lifespans now for people living with HIV. But the idea of that is to optimize the health of those people for their whole lives, both in terms of their cognitive as well as their mental health status.

DR. GORDON: And you mentioned those immune markers, dysregulation, immune markers, et cetera. Is there any correlation between the presence of some of those neurophysiological findings and the presence of symptoms in the neurocognitive domain?

DR. SPUDICH: Yeah. There is some evidence of that. That's been the hypothesis a long time. Really getting at the neuroimmune environment. It's hard to directly measure. You can look at brain autopsy tissue and find elevated proliferation of microglia, this kind of thing. But there's obviously lots of reasons that you're looking at a piece of autopsy tissue. That's not necessarily the fact that person was living with HIV.

And then there's some very nice data, I would say, that's utilized spinal fluid and looked for immune activation markers and also some that's used neuroimaging. And those are the tools that we use, as you know, in mental health and neurology. Some of those have also been being correlated to cognitive testing, cognitive performance, self-reported mood issues, that kind of thing. And so, I think the ongoing neuroimmune perturbation is sort of the best hypothesis that we have.

DR. GORDON: Yeah. This is also related to similar issues that we're dealing with in understanding the pathophysiology of other mental illnesses, is that the idea of somehow doing causal tests in human beings to prove that these hypotheses work is a challenging one, but it's one that we really need to pursue.

You mentioned the program that I visited in Thailand. Just so everyone knows, I was out in Thailand in August for the World Psychiatric Association meeting, and it just happened to coincide with the meeting of you and your collaborators that was taking place in a clinic there that you work with. Tell us two things. One, what you do in Thailand. What's the project that you're running? And second is why do it there? What's the - both from a personal and scientific reason - why do the work in this global setting of need?

DR. SPUDICH: Yeah. It's such an honor to describe that study and there are many, many people who are involved in directing those studies. I'm very fortunate to be a collaborator and to be able to help direct the CNS-focused aspects of the study. Thailand is a country that has a very, very well-organized health system. It also has a higher prevalence of HIV than we have in the US. And there are small pockets of very concentrated high-risk groups in Thailand.

It turns out that a number of years ago, a wonderful collaborator, (Name) who is a Thai investigator who also now here in the US, set up a study that was basically screening a large anonymous testing center. So, people who had concern for either having a sexually transmitted disease or having HIV, those people came to the center, and they were asked, would you be willing to be screened for acute HIV? What that means is that most of the testing that we do for HIV is an antibody test. Everyone's familiar now with antibody antigen tests. But in the very first weeks of HIV, the antibody test is negative. However, you can test that sample also for the presence of the virus by a PCR test.

So, basically a fantastic infrastructure was set up to screen every single sample for that very, very acute period where the viral PCR was positive, but the antibody is negative. So, what we do, what our neuro studies are in Thailand is that we partner with a group that's overseeing an amazing cohort where people are identified during very, very acute infection, offered immediate antiretroviral therapy, and then are followed and they've been followed now for ten years and more.

So, this cohort can answer lots and lots of questions, first of all, about the acute pathogenesis of HIV in an unprecedented way that's never been looked at before but can also answer questions about whether or not really early treatment can ameliorate every single aspect of living with HIV. And there's also been a big focus in that cohort on HIV cure, because the concept was that maybe if you treat people within two or three weeks of acquiring HIV, you can prevent the virus from setting up shop around the body.

Fortunately, that has already been answered and it's not happening. So, basically, even though people are starting treatment two or three weeks after acquiring the virus, the virus has already set up reservoirs throughout the body. And unfortunately, we've shown that even within five days of acquiring HIV, the virus can be detected in the nervous system.

So, we're not preventing the entry of the virus by that early treatment, but it does look as if it's possible that we're able to prevent some of the severe ongoing inflammation by dampening it down extremely early. And some of the studies that we're doing there are looking not only at the acute pathogenesis, but at that effect of really early treatment.

DR. GORDON: And can you then measure these neurocognitive effects in this in this cohort?

DR. SPUDICH: It's actually amazing. I didn't mention, from the beginning of the study they have allowed us to embed a variety of different kinds of neurological and psych measures.

DR. GORDON: Would you follow that in the cohort longitudinally on these individuals?

DR. SPUDICH: We do neurocognitive testing, we have a number of psychiatric and mood assessments, and those are standard and many, many times over time in the cohort. And then we've also been able to embed optional procedures that include lumbar puncture or an MRI. That's obviously not everyone, but a lot of people are doing them.

DR. GORDON: And what are you finding?

DR. SPUDICH: Yeah. So, basically what we're finding is, as I mentioned, the virus gets in very, very early. Inflammation, those very, very first weeks of infection you see T-cell infiltration into the CNS. You see markers of inflammation on brain imaging. We see a lot of elevations of cytokines and chemokines in the CSF.

But amazingly, if we start treatment that early and we're following people two and three or five years out, we're seeing no residual inflammation in the CNS. We're seeing cognitive performance that in a small battery, a pretty limited battery, seems to be returning to normal range compared to Thai controls that are matched. And the only thing that we're not certain about is some of the MRI imaging, some of our preliminary imaging suggesting that there is still some brain atrophy in people despite the early treatment. But we're following that up with a really rigorous, well-controlled study.

DR. GORDON: So, in essence, you're able with this group, with this precious resource that exists in Thailand, to ask that, to do a causal test. I mean, it's not precisely causative of inflammation because you're not purposefully using anti-inflammatories or something like that. But at least a causal test of the role of that early period of viral replication in establishing that immune pathway.

DR. SPUDICH: Absolutely.

DR. GORDON: Yeah, that is really wonderful. That gives me a good reason about scientifically why you're there in Thailand. But having visited that clinic in Bangkok and learned about the program, I know it's more than just science that drives that interest of yours. So, what does it mean for you personally to be able to do science in a country like Thailand, where, as you said, the prevalence of HIV is higher and it's a real significant problem for that community to deal with?

DR. SPUDICH: It's so hard for me to describe. Actually, the work that I've done in Thailand has been some of the most meaningful of my life. I'll say I have three kids and a husband, and I never, ever planned to spend a lot of my research internationally just because of the challenges that poses being a mom. But ever since I very first had the opportunity to get involved in this project from a research standpoint, I thought, I cannot turn it down; this is exactly what I want to do.

And then as I very first went there, which was now about ten years ago, I experienced, I think, what you were exposed to in a brief way. It's just an incredible group of collaborators. There's an unbelievable infrastructure for doing research in Thailand, and it's getting involved in studying a disease that is really a global health condition with communities outside of our standard research communities, particularly in our academic centers here in the US, gives an entirely different perspective. So, the perspective is wonderful. The sense of collegiality and a shared mission across cultures, languages, sites is just very heartening. I think it makes you really feel inspired and excited.
And the other thing is, I hope you saw, the expertise and the experience that's there is completely different and complementary to ours. They have much more experience with certain kinds of things about the populations, about the problems, and about access that it does bring to light issues that are really, really relevant for us to learn about.

DR. GORDON: That particular clinic that we were at has a focus, a specialty, and a real skill at reaching segments of the population in Thailand that are heavily affected by HIV. But it required that skill to be able to reach into particularly the transgender community, which is really, it was wonderful to witness and to see exactly that; how complementary skills can enrich our research base and inform not only approaches that work in Thailand, but then science, as you were just discussing, that will work around the globe. So, thank you for the work that you do there and for bringing that to us today.

Now, of course two years ago, almost three years ago now, we were hit with the COVID pandemic. And I know that you pivoted a portion of your research to address that. And I'll just point out, which probably already obvious to folks listening, is that some of the concerns around neuroinflammation effects on cognition, these are concerns with COVID, although the physiology might be different.

Can you talk to us about engaging directly scientifically with the COVID pandemic while you are already doing this other work? And in particular, maybe you can mention some of the tools or discoveries from your HIV work that have informed our understanding or allowed us to make some inroads in understanding what's going on with COVID?

DR. SPUDICH: Yeah, sure. I think that when COVID hit, I think there was already an understanding that there are potential effects of coronaviruses in the brain. And I actually have a fantastic colleague here at Yale who's an infectious disease doctor who does a lot of neurology work. And she came to me and said, I think we should set up some studies to study how this virus is going to affect the brain. And I was like, what we need to do is just stay out of it and not get this virus.

But she actually was very, very energetic (Name) and got some acute COVID studies up and running. And what we started to find, very surprisingly, is that the virus is just completely different than HIV is in the brain. And I talked about the fact that very, very early on you can detect HIV virions in the central nervous system either by looking at spinal fluid or looking at the brain tissue. It's been really interesting to say, okay, using the same kinds of approaches and tools, looking at spinal fluid, looking at neuroimaging, looking at brain autopsies during cognitive testing, you can deploy all of those tools that have been honed to study all sorts of other neurologic and psychiatric diseases. And you just find something completely different than you expected.

There was a lot of hypotheses that SARS-CoV-2 would enter the brain. We even wrote a review paper that showed all the different pathways that the virus would be able to enter the brain early on. And then really, people have barely detected the virus in the brain. And yet there seems to be an instigation of inflammation in the brain very, very early in people who are symptomatic, I would say, with neurologic or psychiatric conditions during acute COVID.
And so, some of the patterns seem to be overlapping, but some of them are also quite different. And I think that that's been surprising. And I actually think the initial firehose of information that came out very early, some of it had to be backtracked because people had such assumptions of what was going to be happening in the brain. But I think thoroughly rigorous studies are starting to reveal more really about the pathogenesis of SARS-CoV-2 in the brain.

DR. GORDON: You've already said some of it has to do with the immune system. Do we know anything more specifically about that pathophysiology that you want to share with us?

DR. SPUDICH: I think it's kind of interesting.  Basically, it looks as if the - again, combining data that you can directly get from the nervous system really looks at either cerebrospinal fluid data or looking at brain autopsy data. The caveat with those sets of data that we have available to us right now is that essentially it is 100 percent focused on hospitalized patients or patients with severe disease or people who died of COVID. So, my major caveat is we really don't know that much about all the rest of us who get COVID and recover what actually happened in the nervous system when we got the virus.

There is good evidence that although there's not a lot of virus detected in the brain, there is increases in monocytes in the cerebrospinal fluid and macrophage entry into the brain. There is instigation of microglial activation in the brain and there is some evidence of just general kind of cytokine inflammation. Not as much T-cell infiltration and not the development of microglial nodules around virus, again, because not much virus has been detected, but a generalized immune activation.

The other thing that's been really a salient finding is evidence of anti-Sars-Cov-2 antibody responses. Some of those responses then being auto reactive to brain tissue.

DR. GORDON: I want to unpack those different things, and then and then I want to go to some audience questions. It seems like you've got a panoply of players that could be causing problems in COVID patients. Let me just say at the outset, because we're all on the same page, we know that there are increased rates of new-onset mental illness of various kinds, including psychosis, in individuals with COVID-19. So, we know that exists. And we can look at these players as potentially causing those syndromes.

You mentioned it's not the case that you've got T-cells going into the brain trying to find virus and get rid of it. Because that makes sense because there's no virus there, or very little virus there. But you have these different immune system cells that are getting in there, macrophages, monocytes. You've got activation of the endogenous immune cells of the brain, the microglia. And you've got cytokines.

And cytokines are of course the hormones of the immune system. And there's a long literature of cytokines even when they're produced peripherally, correct me if I'm wrong, getting into the brain and at least in animal models causing behavioral and cognitive and emotional changes in people and in animals. So, you've got a whole milieu of potential mediators. It'll be interesting to see how that plays out over time, to see what we might need to do to help people who are suffering afterwards.

DR. SPUDICH: Well, and I think that it's also important, critical to not necessarily lump all of these conditions together. So, you mentioned, for example, psychosis, and I'll say that a fantastic physician investigator who has just joined you in the Intramural Program at NIMH, Chris Bartley, has done beautiful work. Again, in one case with a sample from a patient that we have seen, identifying autoantibodies that seem to be reactive to brain tissue in people with this very, very distinct, really disturbing and problematic post-COVID or COVID-associated psychosis.

But that may be a distinct entity that may be different from people who are generally having encephalopathy during COVID. Maybe the general encephalopathy is related more to this sort of cytokines, and some of those may be simply spillover from the blood versus something, a very local reaction. And so, I think one of the challenges that we have studying the nervous system, cognitive and mental health disorders in COVID, is conflating them all and assuming they all have the same cause.

DR. GORDON: I didn't even mention, of course, the autoantibodies. I'm glad you did. We know that autoantibodies can cause psychosis. And here we have, I guess, a case that Chris showed where it seems like they really did in the post COVID. So, you've got these different players, maybe they're acting in different individuals, giving different outcomes.

And then of course, the question that many of us have is, which of these might resolve spontaneously over time versus which of those might be persistent. We know that there's long-COVID, but long-COVID is months. Is it going to be years? And that's up in the air.

Let's take a few questions from the audience. We've been talking about how the HIV virus gets into the brain and COVID doesn’t. I'm going to put a couple of questions here together and ask you if we know why the HIV virus gets in and why the COVID virus does not, in particular how it crosses or doesn't cross the blood brain barrier.

DR. SPUDICH: There has been a long history of research looking at how the HIV virus gets into the brain. And I think some of the very best evidence is actually supplied by some macaque models, where Simian immunodeficiency virus, which is the HIV that infects macaques, how giving macaques natalizumab and then trying to infect their brains with HIV, there's no evidence of infection in the brain.

So this suggests that the virus that's circulating in the blood has to travel to the brain via immune cells that are then blocked by giving them natalizumab. And that's been the hypothesis for years and years, and there's been a variety of different types of in vitro data to suggest that. But that's really the first more translational study that I've seen.

So we believe that HIV essentially primarily affects immune cells, primarily CD-4 T-cells circulating in the body. And as we know, immune cells patrol and traverse the blood brain barrier and go into the brain. And even a constituent like a healthy person, in the setting of HIV, the infected immune cells are activated, and they probably even have cell surface markers that have them honed to tissues. So, it's sort of this Trojan horse mechanism that's thought to bring the virus into the brain.

HIV has very high levels of viremia. There is a lot of blood virus. SARS-CoV-2 and COVID, most of the virus is in the nasopharynx and in the lungs. There's not actually a lot of virus in the blood. And in fact, sometimes you can't detect virus in the blood using standard assays and you have to use very, very sensitive assays to even find a virus in the blood.
So from the first place, you have to then be thinking about a route for a different system from the nose or from the lungs to get into the brain. The other thing is that the cells that SARS-CoV-2 can enter are based on the presence of receptors on their surface, the ACE-2 receptors which are totally different than the cells that are infected by HIV. It totally uses completely different cell types and cell receptors. And so, you don't necessarily have tropism for brain cells with SARS-CoV-2, because there's not a lot of data suggesting that the variety of brain cells that could potentially harbor infection actually have those receptors on their surface.

So even if the virus does somehow traverse perhaps the cribriform plate, which was one of the early hypotheses, there may not be productive infection of brain cells just based on the cell surface markers on the surface of those cells.

DR. GORDON: Okay. Here's an interesting question that speaks to the generalizability of the work that you're doing in Thailand. What is the standard of care or most commonly prescribed ART regimen in the Thai cohort? And what do you think are some findings in this cohort that can or can't be extrapolated to US populations? I guess maybe this question is thinking because of potential differences in what is prescribed.

DR. SPUDICH: Yeah. Well, we're very, very fortunate that the Thai cohort has had sort of two eras of very standardized regimens. So, most of the research studies, for example, that I do here in the US, we recruit people who are already on a variety of different regimens. And so, you have a hodgepodge of different treatment histories and this kind of thing.

In the Thai cohort, based on collaborations with pharmaceutical organizations that donated medications, there was an era where participants were on Efavirenz based therapies, a certain backbone. And then in 2017, there was an era of transition where the individuals were then switched and then new individuals were put on a dolutegravir-based background, which is an integrase inhibitor, a totally different mode of action.

So, on one hand, that's the standard of care globally is a dolutegravir-based background. That's actually the standard of care of first line in the US as well. And we're very fortunate that our study participants in Thailand have access to that regimen, partly because of joining the study. But it's allowed us to then compare the cognitive, the mood effects of those medications.

And one of the things that's been really important is that there was early data suggesting that dolutegravir, this integrase-based inhibitor, actually had negative neuropsychiatric effects, and people were concerned that it may actually lead to more disorders. But what we've essentially found is that's not true. And compared to the prior regimen, which used to be the standard of care, there's actually an improvement in some of those neuropsychiatric effects on the regimen. So, that's helpful because people have that concern.

DR. GORDON: That's really helpful. And of course, there was concern that HAND in general, the HIV associated neurocognitive disorder might be a function of the antiretrovirals as opposed to a function of the virus itself. And your data, I guess, would then suggest that maybe not, because people are taking these antiretrovirals and if anything, they're preventing or lessening the likelihood of getting HAND.

DR. SPUDICH: I think that there may still be some potential neurotoxicity of some of these regimens, but I think it's completely outweighed by the neurotoxicity of HIV. So, they could control the virus - but it's an important question. It wasn't until 2012 that the W.H.O. said that who everybody gets HIV should go on treatment right away. And the reason was that people were worried about the toxicity of the medications.

DR. GORDON: While we're talking about HAND, there's another question; do the deficits associated with HAND present in activities of daily living or are they apparent only on cognitive tests?

DR. SPUDICH: Yeah, that's a wonderful question. And that's been part of the controversy about this sort of HAND designation, because in fact, that designation HAND encompasses people who have abnormalities - or, again, I don't want to pathologize the term - but they're performing to standard deviations lower than comparison, non-HIV people on testing, but they're asymptomatic. That's actually a large category. It's called asymptomatic neurocognitive impairment. So, those people are not necessarily complaining of symptoms or having functional deficits.

And then there's a proportion that have what's called mild neurocognitive disorder. And those are actually people who are reporting cognitive symptoms or having problems with activities of daily living.

The controversy is, what is the meaning of people who don't have any symptoms. One of the pushbacks would be that, well, unless you really do functional evaluations, you can't tell whether people are having impairment because they may not be reporting symptoms or be aware of them. But that is also one of the controversies with HAND. We see very little dementia. Mostly what we're seeing is people with mild conditions.

DR. GORDON: And that's something we in psychiatry are very familiar with the notion that just because somebody doesn't volunteer that they're experiencing something doesn't mean that they aren't and then you always have to ask.

Let's move to COVID. And we actually have a good, I think, transition question, which is interesting and portrays the creativity that we have here at NIMH. Do we have information on COVID outcomes in individuals using HIV Prep? And let me go ahead and make that a little bit more complex and say, really anyone in the HIV spectrum: infected, on antiretrovirals, or taking antiretrovirals or Prep. Do we have information on COVID in this population of people?

DR. SPUDICH: That's a really great question, and I think it's a really important question. And the question of whether or not we have outcome data for people who are on Prep who have acquired COVID, I have never seen those data. It's a great question. It must be available. There are large communities of people who are taking Prep every day to prevent HIV. And many of those people, the majority of people in the US got COVID. So, I think those studies could be done and it would be very interesting to look to see whether the antiviral effects or something else about the effects of Prep may be protective in some way.

DR. GORDON: I just got back now from Cape Town, South Africa, where we have a number of studies and NIMH supports looking at Prep in various populations. And I'm wondering if our Data Science in Africa Initiative might be getting the data that we could actually answer that question. So, Diane Rausch, I hope you're listening. Maybe we can figure that one out.

Back to you, Serena. So, that's on Prep. What about the general group of folks dealing with HIV in one way, shape, or form and COVID outcomes?

DR. SPUDICH: Yeah, I think that's an area of controversy. So, I'll say there have been a number of studies that have looked at major outcomes, such as death or severe COVID-19 disease in people living with HIV. And they've been actually not necessarily agreeing with one another.

So some of the studies have suggested that people with HIV are at higher risk of death or severe outcomes. But then some very large studies and a big meta-analysis that was published this year really said that actually in terms of the severe outcomes, end points, there's no difference in people who were living with HIV. Of course, you can imagine that it depends completely on the background of what you're talking about when you say people living with HIV. Are these people with CD-4 counts, off of treatment, who already have a lot of immune dysfunction, or a lot of comorbidities?

So, those are complicated studies to interpret. I think what we're really interested in is whether or not the second hit of COVID in somebody with well-suppressed HIV who's doing pretty well is going to instigate any kind of different trajectory of either cognitive or mental health.

DR. GORDON: Yeah, I was wondering about that in particular.

DR. SPUDICH: And in fact, NIMH had just funded us in a new project that is based in our cohort in Thailand. The design of the study is predicated on this idea that when you have before COVID and after COVID data, you can make the most sense of what's happening in the brain. And in that cohort, we have individuals who have serial MRI's, serial lumbar punctures, serial cognitive and mental health testing, and we have really complete information about who acquired COVID.
So, in that cohort, we're going to look at these more subtle end points about immune trajectories, but also looking specifically at the cognitive and mental health outcomes in people who had COVID or who did not.

DR. GORDON: So, now moving full on into the COVID, can you say something about how long the COVID virus lives in the body and whether there are any implications for treating long haulers with COVID?

DR. SPUDICH: That's the $64 million question.

DR. GORDON: Let's talk about the brain and the brain effects. But obviously is it going to be dependent on the COVID virus being in the body? Or maybe that's not it with long-COVID, it doesn't need the virus to be around.

DR. SPUDICH: Yeah. I think that that's a really important question. Generally, most of the data suggests that when you're just looking for PCR evidence of viral replication, within two or three weeks it's usually no longer detectable in the nasopharynx, the places that we usually find virus.

DR. GORDON: Of course, HIV is not detectable in people suppressed, but we know the virus is there. Right? It's latent in cells.

DR. SPUDICH: That's right. And so, that's one major difference in our understanding of how these viruses operate in the body, in the sense that HIV takes its genetic material and integrates it into the host genome. And it basically uses the host machinery to replicate itself through the nucleus.

Whereas as far as we understand, SARS-CoV-2 just uses cytoplasm machinery to make more of itself, and never integrates its genome into the host. So, we don't think it's a chronic infection that stays long term in the body. However, of course, with the concern of long-COVID, there has been a hunt for residual virus, either reservoirs where actually the virus could fully replicate and be released and cause ongoing problems, or potentially - and I think the data so far only really supports potentially the latter - that there are fragments of virus sitting around in the body, viral proteins that may be stimulating the immune system and causing some of these longer-term problems.

And there's been some data suggesting that viral proteins can be found in the gut. A recent study identified one particular part of the viral protein in the blood in people who are having long-COVID symptoms. And of course, a big question is, are there viral fragments or proteins detected in the brain. But I don't think there's convincing evidence yet that this is something that's ongoing, despite the fact that I have many patients who come and say I want Paxlovid for my long-COVID.

DR. GORDON: I know there are a number of studies looking at long-COVID right now. Many of them funded by NIH and many of which you're not necessarily involved in. But there are a couple questions pertaining to the issue of long-COVID I thought I'd throw at you, and you can answer them, or you can say, you know what, that's not really my area.

So, one of them has to do with prevention, whether, for example, Paxlovid or other medications that people are using early in the course, whether that reduces the likelihood of neuropsychiatric symptoms in the long-COVID period or even maybe not even long-COVID, but maybe acute. And then the second one is whether there are any clinical trials underway involving immunotherapy in COVID. You can expand that out if you'd like, just to talk generally about what's going on in these studies right now and what you may be involved in in particular.

DR. SPUDICH: Yeah, well, I think I can answer both of those questions. There was very recently, I think earlier this week, there was a nice paper published by a group that's in St Louis at the VA where they looked at a very, very large datasets of individuals in the VA system who received Paxlovid during acute COVID. Of course, they were getting Paxlovid for certain indications. So, it does bias the sample somewhat because there are certain reasons people are given Paxlovid or offered Paxlovid during acute COVID.

But what they found is there was a slightly lower risk of long-COVID symptoms, and the neuro-psych symptoms were part of the group that seemed to have a lower rate after receiving acute Paxlovid therapy.

So, again, it's a retrospective study. People weren't randomized to getting Paxlovid. So, there might be other features in there that led people to potentially have lower risk of long-COVID. But it sort of goes along with the hypothesis. It's a little similar to our acute HIV studies. Maybe if you control the virus at some level during acute infection, you may be able to stop or ameliorate some of the processes that kick off long term problems.

And again, in that study, some people did get long-COVID who received Paxlovid, but the risk was lower. So, I think that's an important answer to the first part of your question.

The second part of your question is about immunotherapies. And it's an enormous area of focus. So, if you look on for COVID studies, there are many, many studies that are ongoing, worldwide looking at different pathways, JAK pathways, all sorts of just general immune suppressants, immune modulators looking at different approaches.

It's challenging because in fact I don't think there is really convincing evidence yet that when we're looking at people with long-COVID, that they even have, for example, generalized inflammation. It still has not been completely shown. It doesn't mean that they have a normal immune response. And I think some of the really detailed phenotyping and the types of single cell studies that are happening are revealing that there are some potential abnormalities, but the challenges are manifold.

One is that, again, you can't group everybody with long-COVID and try to study them all the same way, because clearly there are different organ systems involved, there are different degrees of things involved and there's a lot of overlap with other conditions. And so, trying to do a clinical intervention trial, you have to really select the right group to study.

And the other thing is, I think there's probably myriad causes of long-COVID. Some may be persistent inflammation, maybe in some cases it's autoimmunity. I haven't even mentioned vascular dysfunction, but microvascular dysfunction, it looks like part of the pathway in acute COVID.

And so, these trials are getting started mostly because there's such an immense pressure to try to intervene. Also, with the hope that studying the biology during the interventional trials will be revealing. And I think that's reasonable. But it's difficult to really figure out exactly, if a patient in front of you step into a clinical trial, which one, what's the right thing to do?

DR. GORDON: Well, there's certainly a lot of equipoise in our hypotheses around what is going to be effective in helping people. So, those of you who are out there with long-COVID think about a clinical trial. Let's get you into one and see if we can't figure out what to do for people who are continuing to be infected. We're still getting more COVID infections. We're still getting more cases of long-COVID. Let's see what we can learn to help people, because there are significant psychiatric symptoms in the context of long-COVID. And so, it's really important voice.

Thank you so much, Serena, for joining us today and answering all these amazing questions. A lot more questions on the science that I'd love to be able to get to, but we're almost out of time. I wonder if before you go, we have just a few minutes left, whether you might offer some pearls of wisdom to early career scientists or others interested in studying this interface. To me, it's a fascinating one between infection and the brain and mental health and cognition.

Anyway, what might make you say to an early career scientist interested in this particular aspect of science?

DR. SPUDICH: I think the main thing is that it's actually really fun to study an intersection that's been understudied, partly because it just means there's so many questions. It also means that you can learn from both fields. I actually spend most of my time going to infectious disease and immunology meetings and less than neuro and psych meetings. And I've learned most of what I think about in terms of the infectious effects in the brain from the people who are doing systemic studies and thinking about, how does that translate into what we know about the brain.

Of course, the cool thing about that is that you kind of can take from both. You can use the tools that people have developed to study the brain, but apply it with the knowledge that you have from the other field.

I also think that from a clinical standpoint, when you take care of or you try to study diseases that fall in these interfaces, you really have the sense that you're doing something that people really need. And I thought that over and over again, taking care of people with HIV and doing studies on people's HIV over the years. People say, this is something that I just don't have an answer to and there's not good information. And of course, that's been 1,000 times even more in the last two and a half years with this long-COVID issue and with COVID, is that people really are desperate for answers. And so, it really feels stimulating to work in an area that's so understudied.

The other thing I would just say is that I think these clinical disciplines are the research disciplines that we've thought about all these years. Those are just silos that are based on sort of training pathways or the sort of dogma of how we used to think about things. But the fact that I'm here - I'm a neurologist, but almost all my funding has been from NIMH. It's artificial to say that something is the brain, something is psychiatry versus neurology.

In the same way the brain is part of an organ of a whole body. And I think that's part of the way I've always thought about the effect of infections. It's not just in this compartment and it's really connected. I think that's kind of a new approach that I think most people are now taking and thinking about, but trying to integrate studies of the brain and the mind in studies of the whole body, I think is that cross-disciplinary area that's really fun and exciting.

DR. GORDON: Well, thank you very much. Thanks for all the science you've done. Thanks for explaining it so patiently to us today and sharing your experiences along the way. And thank you all in the audience for joining us and look forward to seeing you at our next Director's Innovation Speaker event.

And again, this this presentation will be archived on our website in just a few weeks, so please feel free to share it around. Thanks again, Serena, for joining us.

DR. SPUDICH: Thank you for the honor. It was wonderful. Thanks so much!