February 9, 2009
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There's nothing like hearing the results of studies directly from those who actually conducted the research. In this interview, you'll meet two of these impressive HIV researchers and read their explanation of the studies they presented at CROI 2009. After their explanation, they will answer several questions from the audience.
Prameet Sheth: I'm Prameet Sheth from the University of Toronto. Our study was looking at the impact of HAART [highly active antiretroviral therapy] on HIV RNA levels in the seminal plasma.1 We know that effective HAART reduces HIV RNA levels in blood to below the limit of detection. However, the impact that it has on semen HIV RNA levels is much less clear.
We enrolled two cohorts: One cohort was of HIV-infected men that were therapy-naive, just prior to HAART initiation. We followed them prospectively, every two weeks for the first month and then every month out to six months, while on HAART. The second cohort consisted of HIV-infected men that had been on long-term suppressive HAART, which we classified as being somebody that was on suppressive HAART for at least four years and had an undetectable viral load in blood for at least four years. We measured HIV RNA levels in blood as well as seminal plasma.
As our follow-up in this arm was only to six months, we looked in our second group of elitely treated men. In this cohort, we found that out of the 13 individuals that had been completely suppressed for over four years, four of them actually had isolated semen HIV shedding episodes.
What our study shows is that, even though HAART will be able to reduce sexual transmission of HIV on a population level, there is still an individual risk that exists despite long-term HAART.
Anne-Genevieve Marcelin, Pharm.D., Ph.D.
Anne-Genevieve Marcelin: We have had very similar results in France. Recently, the Swiss Federal Commission for HIV/AIDS stated that a seropositive individual with no other sexually transmitted diseases [STDs], who is on antiretroviral treatment and who has an undetectable HIV-1 plasma viral load below 40 copies/mL for at least six months, does not sexually transmit HIV. Indeed, studies have shown that there is a strong relationship between HIV plasma viral load and heterosexual transmission rates. However, HIV plasma viral load might not always reflect HIV replication levels in semen and some factors could increase the risk of transmission, such as incomplete adherence or other STDs.
The aim of our study was to evaluate the residual HIV RNA shedding in semen from patients who were enrolled in an assisted reproductive technology program in France.2 This program started in 2002 in a center for serodiscordant couples to help them conceive while avoiding the risk of HIV transmission and to treat infertility. So 145 HIV-infected men in this multi-disciplinary assisted reproductive technology program at the Pitie-Salpetriere Hospital in France provided 264 paired samples of blood and semen between January 2002 and January 2008. We quantified HIV RNA in blood and in seminal plasma using a Roche assay. The majority of samples were concordant, with approximately 85% with undetectable HIV RNA in both seminal plasma and in blood. But 5% of patients had detectable HIV RNA in seminal plasma, although their blood viral load was undetectable.
All these patients were on stable HAART, had an undetectable HIV RNA for at least six months and had none of the other STDs that were systematically screened for in the program, thus corresponding to the three study criteria. Although effective antiretroviral therapy is likely to substantially reduce HIV transmission at the population level, residual HIV RNA shedding can occur, suggesting that a small, residual risk of transmission is still possible during unprotected sexual intercourse. We think that this result should be taken into account in public health messages, underlining that the risk of HIV transmission in the presence of effective treatment is low, but not zero.
Reporter #1: Do you have any idea what is going on in the compartment and why there would not be full suppression? Have you looked for drug resistance that's isolated to the genital compartment versus plasma? Do you think that it might have to do with drug penetration to the genital compartment?
Anne-Genevieve Marcelin: Yes, we looked at that. For the patients who were discordant in the blood and in the semen, we tried to amplify the virus to see if there was any drug resistance, but we did not find any drug resistance in the seminal compartment. We did not succeed in amplifying all the cases, because the viral load was quite low. But when amplification was possible, we did not find any drug resistance.
Some patients were treated with antiretrovirals that have good penetration in the seminal compartment, such as indinavir [IDV, Crixivan], 3TC [lamivudine, Epivir] and tenofovir [TDF, Viread], so this does not seem to be related to a specific treatment. We have few cases and it's difficult to come to a conclusion, but I think it would be interesting to make larger studies to evaluate the impact of the diffusion of antiretrovirals to see if they have any effect on the residual shedding of HIV in seminal plasma.
Prameet Sheth: We also sequenced virus from the seminal compartment and we did not find any drug resistance present. We also measured levels of antiretroviral drugs in both blood plasma and seminal plasma and, as she indicated, we did see quite a differential in the penetration of drugs. Again, 3TC was present in seminal plasma a 100-fold higher than it was in blood, but we were able to still get isolated semen HIV shedding in these individuals. So, it was not related to -- at least that we could find -- the concentration of antiretroviral drugs or the drug regimen that people were on.
Reporter #2: We know there is shedding here, but could you talk about the clinical significance or relevance of it? Is it at such a level where there is significant risk of transmission, or is this more of an academic exercise to know that it's occurring?
Prameet Sheth: We don't actually know what level is needed to transmit. What we did do was, in the individual that was shedding the highest amount of HIV RNA, which in our case was 16,000 copies/mL, we isolated his virus and we used it to see if we could, in fact, activate CD4+ cells in vitro. We found that it could, so in this individual, the virus was infectious. We did look into whether the individual had been noncompliant [with his antiretroviral regimen], but his viral load in blood stayed undetectable. So I would argue that it is infectious, although we don't know what level of virus is required for infection to occur.
Reporter #2: I know a much more difficult type of work to do would be to find out whether there is any correlation between blips in plasma and changes in semen.
Prameet Sheth: That would be quite difficult. [Laughs.]
Reporter #3: I'm wondering if you were able to characterize patients who shed more than others. Did you have specific people in your relatively small patient cohorts who were more likely to show ongoing isolated blips of viral shedding? Or was it more distributed across your patient population?
Anne-Genevieve Marcelin: At this time, we have not identified factors that are associated with intermittent shedding, but we're working on that in our cohort. We are accumulating some samples and clinical data to see if we can find some factors.
Prameet Sheth: We looked at several clinical factors: CD4 count, blood viral load, as well as herpes serostatus. We thought these may be predictive of individuals that would go on to shed HIV in semen in an isolated fashion. None of these factors were actually associated. The only predictor that we were able to find was that individuals who were shedding on average, I think, eight-fold higher HIV RNA in semen prior to therapy initiation were more likely to be isolated semen shedders versus those that had a lower viral load in semen. That was the only thing, and obviously that [sort of information is] not readily available to clinicians.
Reporter #4: How intermittent is "intermittent" [shedding]?
Prameet Sheth: That depended. There were some people in whom there was just one case where we saw isolated semen HIV shedding. [By contrast,] we have one participant in our study that was what we call a sustained isolated semen shedder: This individual, after starting therapy, very quickly suppressed in blood; I think within four weeks of starting HAART he was completely undetectable in blood. But we were always able to detect semen HIV RNA in this individual, and that was for seven visits while on HAART out to six months.
Reporter #5: Is it fair to say that, taken together, these two studies explode the Swiss contention that HAART completely prevents sexual transmission?
Anne-Genevieve Marcelin: I think our results show that we cannot be completely affirmative when saying that if the viral load in blood is completely undetectable, there is no transmission. There is a residual risk.
Reporter #5: So in other words, the Swiss statement is wrong? Come on, let's nail this down.
Anne-Genevieve Marcelin: At the population level, it's right. In individual cases, it's wrong.
Reporter #6: You said, at least in one study, that top viral load was 16,000. What was the overall range in your studies? What was the mean? What was the distribution of viral load amongst the shedders?
Prameet Sheth: We had 12 individuals that were shedding when their blood viral load was undetectable. Three out of the 12 were actually high-level shedders, which we defined as having a semen viral load over 5,000 copies/mL. Of the three, we chose the one with the highest level to do our in vitro infection assays, just to hedge our bets. Sorry, I don't remember the raw numbers offhand.
Anne-Genevieve Marcelin: For our study, among the seven patients who had HIV detectable in the seminal plasma, the viral load ranged from 2,050 copies/mL to 1,200 copies/mL.
Reporter #6: And were there any cases of transmission in the people you were working with?
Anne-Genevieve Marcelin: No.
This transcript has been edited for clarity.
No comments have been made.
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