Discovering the HIV/AIDS Drug "Cocktail" in an Equation
David Ho is the Scientific Director & CEO of the Aaron Diamond AIDS Research Center. Ho’s laboratory has focused on the pathogenesis of HIV infection. Most recently, his group has made substantial strides in the development of vaccines for HIV, as well as in the development of innovative prevention strategies. Ho also serves as head of the China AIDS Initiative, an alliance of Chinese and international organizations dedicated to helping China accelerate its response to HIV/AIDS.
David Ho: In terms of the most important scientific discovery to come out of my group there was an acute moment, an eureka moment so to speak, and this was in 1994. By that time my colleagues and I had been immersed in AIDS research already and we realized that for any given patient with HIV infection his or her viral load or the amount of virus in the blood tends to remain rather constant over time. We had been thinking about that, why does it remain constant? And gradually we realized that it was a what we call a dynamic equilibrium, that is the amount of the virus being made is approximately equal to the amount of virus being cleared, so it was a steady state. And then the eureka moment came when we had the opportunity to administer new drugs to HIV-infected people. And within weeks of doing so we collected the data and it showed that viral load actually dropped precipitously. And of course that is a great outcome for the patient and for the doctor, but the question that we posed was "Why does it drop and why does it drop in that acute manner?"
This is where my quantitative background in physics applied; we realized that we could actually write that out mathematically in a straightforward differential equation that an AP high school student would be able to do. From there, fitting the data and doing the calculation we were able to come up with the idea. We were using the drugs to block virus infection and production and therefore the precipitous decline reflected the fact that the virus was constantly being cleared at a very rapid rate. So using that quantitative background we were able to calculate what the turnover of virus was all the time in a given infected person and that number turned out to be enormously large, so the virus was just replicating away at a rapid clip.
And from there we also knew that HIV changes every time it replicates, so high replication rate meant high error rate and therefore HIV was able to mutate very quickly. We could then do the additional calculation to show that if you treat this virus with one or two drugs at a time the virus is predictably going to mutate and escape from the action of the drugs. But at the same time we could also calculate what it would take to corner the virus so it’s not able to escape. Those calculations suggested to us that three or more drugs would do the trick. So we knew that by 1995 and launched a series of experiments in patients using what is now called a cocktail therapy of three drugs or more. And immediately within weeks we saw the good result. But we wanted to wait to see if the results could be sustained and it was only by middle of 1996 we realized that we were able to keep the virus below detection level for a good year and that opened up the door for what is called combination therapy today.
Question: When did you first know that you wanted to be a scientist?
David Ho: I’m not sure there was one moment that sparked my interest in math and sciences. I think as far as I could recall I have always had some interest in these areas. I certainly remember being a very curious child and perhaps that is a precursor to pursuing science, but I think there is also quite a bit of family influence that affected me gradually and that has to do with having a number of important family members who pursue science or engineering, including my father and a very important uncle. Their interest in technology and in sciences I think had a great deal of influence on my decision ultimately to pursue science.
Question: How intense was your early education in science and math?
David Ho: In terms of the math education in Taiwan, it was quite intense. So the math that I had learned by sixth grade served me pretty well until about eighth or ninth grade here in the U.S. In terms of science education we didn’t have that much formal science in Taiwan and I began to be exposed to that in the later years in middle school and of course in high school and so I think I was first grounded in math and then gradually shifted into the sciences. That is what I remember.
Question: How did your early education influence your career?
David Ho: My career did not go as planned. Initially as I said my interest was in physics, but through my college education I saw the coming of new biology and the promises of biomedical research, so I shifted my interest from physics to life sciences and ultimately went to medical school with the idea that I would somehow pursue medical research. And my real focus in medicine did not come until sometime later when I was doing my clinical training when I first encountered patients with what we now call AIDS and that sparked a real interest in me and I have pursued that kind of research ever since 1982.
Question: Why did you get interested in infectious diseases?
David Ho: I was initially interested in cardiology, but gradually I realized infections affect many, many people throughout the world and many of the infections are actually manageable or treatable and we can make an impact. In particular, I was interested in new infections that plague the world and when I was doing my medical training there were a number of new infections that emerged, including what we call Legionnaires’ disease and Lyme disease today. But as I was finishing medical training I encountered some of the earliest cases of HIV/AIDS and I realized that was a fascinating scientific challenge in terms of trying to understand what was the underlying cause, but I did not realize that it would become a major public health problem until sometime later.
Question: What were your initial thoughts when you saw some of the first cases of AIDS?
David Ho: I was doing my chief medical year as chief resident in internal medicine in the west side of Los Angeles when the very first case was a young homosexual man who presented to the hospital with a multitude of problems all of which suggest that his immune system was not functioning very well and that was curious to me because he was not getting any chemotherapy or radiation or any drugs that would suppress the immune system. It was immediately clear that we were looking at something new because such a case was never described in the textbooks. Then he was treated for his acute problems, but only to die a few weeks later. And then another case that was quite similar came in, and another and another. In rapid succession we had five such cases and it was too much of a coincidence to observe this. We realized that something was going on with a common theme and from their medical history it was pretty clear that it was a transmissible disease and the search was on to hunt down that microbe that was the underlying cause.
The pioneering HIV/AIDS researcher used high school math in creating a drug "cocktail" to combat the worldwide epidemic.
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