P4P: We are here this morning with Dr. Charles Rice from Rockefeller University, and Dr. Rice has been doing some very interesting work in HCV and co-infection issues. Doctor, I went to your presentation this morning. Could you explain some of the exciting events that have happened in the last year here that have got you up there on the plenary this morning?
Dr. Rice: Well, certainly they are not all events that occurred in my lab, but I think this is a blossoming field. I think that there are a number of things that have been going on, not just basic studies to find out more about how Hepatitis C virus replicates, but I think for the field in general 2003 was an exciting year because we saw some of the first HCV-specific antiviral drugs actually move into Hepatitis C-infected patients in clinical trials. Certainly one of the most exciting pieces of work was from Boehringer Ingelheim in their protease inhibitor that they reported in Nature last fall where two-day administration of this very potent viral protease inhibitor lead to 2 to 3 log drop in the viral load of these people. So I think it's exciting to see basic science actually yield something that works in vivo.1 Now it's still a very early phase in terms of therapeutic development, and in fact that compound has run into some toxicity issues, but I think it at least tells us that it's possible, and we can hope that there are going to be good compounds in the pipeline. So that's one of the areas.
Dr. Rice: Yes. One of the things we've been struggling with, with Hepatitis C, is the inability to replicate the virus in the laboratory. This has been a long road that has taken more than 10 years, and we're still not there yet. But I think some advances have been made in terms of being able to mimic the intracellular events and amplification of the viral nucleic acid of the viral RNA that Hepatitis C virus uses. This is called the replicon system. Basically, replicons are self-amplifying and replicating RNAs that will do their thing in cells that are permissive for replication. In the last several years it's been possible to do that in certain human hepatoma cell lines. Most of the machinery that people that are focusing their attention on for antiviral development or for basic studies is encoded in these subgenomic replicons, so the protease, polymerase, conserved RNA elements that are important for selective amplification of viral genome are all represented in this replication system. It's been a very important breakthrough both for basic studies and for drug development. There are a continuing number of improvements to this system. I guess one of the things that we've learned, though, is that coaxing these RNAs to replicate in cells -- and this has been the work of a number of groups around the world -- has not yet yielded a complete infectious cycle for the virus. There still seems to be some block in cell culture at the level of assembly or release of infectious particles. So some of the elegant work that's been done with HIV looking at, as you heard yesterday, TSG101 involvement in budding of HIV, we haven't been able to study those processes for HCV. So the quest still continues to get a complete and robust replication cycle in cell culture.
P4P: Do you see possibilities here with developments in this last year with research tools, such as the RNAi, where do you see research going in terms of development in the coming years in terms of being able to reproduce in the lab an entire life cycle for HCV?
Dr. Rice: I think one of the exciting aspects in molecular virology and in mammalian cell biology has been the recognition that RNA interference actually isn't just working in plants and nematodes and flies, but is also works in mammalian cells. That gives us a tool that allows us to explore cellular factors that may be important for virus replication in a way that we couldn't do before. As a research tool, RNAi (RNA interference) is proving to be extremely useful for Hepatitis C, HIV, and for other research efforts. The other exciting thing about RNAi is that it does have the potential of being a therapeutic, I guess as you heard last year from work from the Lieberman lab. We don't know how it's going to work as an antiviral, but certainly the proof of concept experiments in cell culture have been done. You can eradicate functional HCV RNA from this in vitro cell culture replicon system. How difficult it's going to be to deliver si-RNAs or the RNA interference signal to target HCV RNA to every infected cell or potentially every infectable cell in a person, is another matter. That's probably going to keep the companies that are working on this technology busy for some time, but I think it's an exciting possibility because, the platform is so general that if it works you can apply it to a number of different viral RNA sequence targets, you can target very highly conserved portions of the viral genome that would be difficult for the virus to escape from, so a very, very exciting new technology.
P4P: Do you see that moving into primate models anytime soon?
Dr. Rice: People have certainly been talking about that. I guess what we've seen so far have been the cell culture and smaller animal model experiments. The challenge always in moving into primate models is the amount of material that you need to achieve the same dosing. But I think people will give it a try in primate models fairly soon. That may be lead by the SHIV models, for retrovirus control rather than Hepatitis C in chimpanzees. We have two potential kinds of animal models that we can use for Hepatitis C. One is the chimpanzee, which as you know these animals are limited and expensive, so it's difficult to do experiments that involve large numbers of animals. And there are some chimeric2 mouse models, where they have human liver that is engrafted into an immunodeficient mouse rendering them susceptible to Hepatitis C virus infections. It may be that, at least in terms of HCV in vivo, those would be the first kinds of models that will be tested.
P4P: That would be kind of like perhaps stemming off of Dr. Lieberman's work last year with her mouse models?
Dr. Rice: Right. But I think one of things that's going to have to be done is to figure a less invasive way of getting good delivery of the si-RNAs3 to cells, rather than hydrodynamic injection.
P4P: On developing a vaccine ... it's going to be very difficult, in the same fashion that it's going to be very difficult for HIV-vaccine development, because there are so many variants of HCV. Where do you see progress at this point? Would you be willing to go out on a limb and say there might be a possibility of a therapeutic vaccine that may be efficacious to X-percent in X-time?
Dr. Rice: I probably wouldn't want to go out on that limb, because I know it's been sawed off before. (Laughter.) I think that vaccination for Hepatitis C, even prophylactic vaccination, is going to be challenging just because of the immense variability that exists and the cleverness of this virus in avoiding the immune response. That said, I think conceptually for Hepatitis C, I think development of vaccine is going to be much easier than it is for HIV. First of all, it is an RNA-only life cycle, it doesn't integrate, and we have examples of people that have spontaneously cleared the virus, and we also have examples where people really show a sustained virologic response to treatment -- as far as we can tell, elimination of the virus after it was there. So that means that this virus can be eliminated under the right circumstances. That's a big difference between HIV and HCV. Another thing is that the vaccine for Hepatitis C doesn't have to provide sterilizing immunity, doesn't have to prevent infection, as long as it prevents the progression to chronic infection. So again, even if you didn't have a perfect vaccine, so that you go no infection at all, if you had a vaccine that gave the immune system a head start, gave it the help it needed to clear the virus in most cases, that will be sufficient for HCV. So conceptually it's easier. Practically, I think we're still a little ways away. I wouldn't want to predict how long it will take to develop the vaccine because there are still a lot of basic principles about how this virus interacts with the immune system that we do not understand at all. And that's true for a prophylactic vaccine. When you're talking about a therapeutic vaccine, there really aren't too many examples of successful therapeutic vaccines but, this is a very important goal in Hepatitis C with 150 million or so people that are chronically infected and not all of them are probably going to be in a situation where they can afford the best antiviral therapy as it comes along. Having a therapeutic vaccine would be of tremendous importance, and in fact we don't really even know what the defects are in chronic infection with Hepatitis C, because it doesn't cause a generalized immunodeficiency. It seems to be something which is more specific to the regulation of HCV itself, and so it's probably going to be important to even think about boosting the immune response in the context of antiviral therapy in order to achieve eradication, because people who are chronically infected somehow can't eliminate the virus. Even if you have a perfect combination of polymerase inhibitor and a protease inhibitor where you could stop replication and have no possibility of drug resistant variants emerging, there's still the issue of whether or not the immune system is present in a chronically infected individual to mop up what's left and get rid of the virus. So, this is an area of very active research in Hepatitis C. It's a very complicated and exciting area. I'm cautiously optimistic about vaccine development for Hepatitis C.
P4P: One thing I know a lot of folks are not aware of ... I saw in your presentation this morning that you estimate 2 percent of the world's population are infected, which is close to 200 million people ... I don't think many people realize the extent of this other pandemic. Being that it takes so long for someone to progress to 3rd Stage where you're developing CA in the liver, etc., what's the prognosis here, vis-á-vis the AIDS pandemic?
Dr. Rice: I think that you've hit the nail on the head in a sense. Even though there are more people that are infected with Hepatitis C, the predictability of disease progression has been a frustration for both the clinicians and their patients. We don't know why some people progress to cirrhosis and liver failure and other people may have some inflammation in the liver and trace amounts of scarring, but they're fine. They lead an otherwise healthy and normal life. So I think that's one reason why the epidemic has not achieved the dramatic public recognition that it perhaps deserves. That's the reality of it. I think in terms of ... for those of us working in the field the fact that it is a slow progressive disease means that people have a little bit more time in some cases to decide what kind of treatment options they're going to choose, and these are continuing, improving, and evolving as science and clinical research marches forward. People are becoming aware of it, but you're right; there are a number of misconceptions ... if you say viral hepatitis, most people think more about Hepatitis A, a food-borne fecal-oral transmission route, rather than Hepatitis C, because that's a dramatic acute usually resolving infection, whereas Hepatitis C is silent but potentially deadly in the long term.
P4P: In terms of clearing the virus, are there particular clades4 that are more easily cleared by the host compared to other clades of the virus?
Dr. Rice: In terms of natural infections with Hepatitis C, in terms of looking at the frequency of acute resolvers versus chronics, there's not a big difference between the different HCV -- we call them genotypes5 and subtypes within a genotype, there are six of these. So, in terms of the ability of the immune system to control the virus, not a big difference. Now, in terms of the outcome of treatment, there is a big difference, and that's really right now the only biological difference that we have between these different HCV genotypes. Genotype-1, which is the most common genotype in the U.S., Europe and Japan, is unfortunately the most difficult one to treat. With the current therapy, which is pegylated interferon and ribavirin, for genotype-1 only about half of those treated are able to eliminate the virus. That's defined as absence of detectable HCV RNA at the end of treatment and then also 6 months later. Genotypes-2 and -3 are much more easily treated, and the current treatment for those is probably 85-90% successful.
P4P: Doctor Rice, I want to thank you so much for your time here this morning. It's been a pleasure and an enlightenment for me, because I'm kind of rusty on the HCV stuff, so I really appreciate it. On behalf of the folks that can't be here, I'd like to say thank you for them also.
Dr. Rice: Thank you very much for having me. It's been a pleasure.
Back to the Winter 2003/2004 issue of Positives for Positives.
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