Friday, November 20, 2009

Taking Lessons from the CCR5Δ32 Mutation for Patient Treatment

I’m Lindsay Sween, and welcome to this installment of the AIDS Pandemic blog and podcast.

Human immunodeficiency virus type 1 (HIV-1) invades a CD4+ (T4) cell through the attachment of the viral protein gp120 to its primary cellular receptor, CD4, and to a transmembrane chemokine coreceptor, usually CCR5 or CXCR4. Agrawal et al. (2007) explain that the removal of 32 base pairs from the CCR5 gene results in the CCR5Δ32 mutation, which produces a shortened, nonfunctional protein that cannot act as a coreceptor due to the fact that it is no longer expressed on the cell membrane. Thus, individuals homozygous for the CCR5 mutation (also known as CCR5 -/- individuals) are extremely resistant to contracting HIV-1, while heterozygous people (aka CCR5+/- people) express fewer CCR5 proteins on the surface of their lymphocytes than wild type individuals, which slows the transition of HIV infection to AIDS. The CCR5Δ32 mutation confers HIV-1 resistance by two mechanisms: the mutated protein cannot be expressed on the lymphocyte surface, and it actively downregulates CXCR4 coreceptor production by causing the formation of heterodimers between CCR5 and CXCR4 proteins that then get trapped in the endoplasmic reticulum.

As explained by Nazari and Joshi (2008), individuals with the CCR5Δ32 mutation appear perfectly healthy in all other areas of their immune systems, which seems to indicate that the CCR5 chemokine receptor is not absolutely essential for immune function. Thus, with no selective pressure against the CCR5Δ32 mutation, Agrawal et al. (2007) report that Caucasians carry the mutation relatively frequently, with about 1% of individuals being homozygous for the mutated allele and approximately 10% of the population being heterozygous. Individuals of purely African or Asian descent, however, almost entirely lack the CCR5Δ32 mutation.

Figure 1. The CCR5Δ32 mutation results in a nonfunctional protein that cannot serve as a cell surface coreceptor for M-tropic (aka CCR5-tropic or R5) HIV viral isolates and, thus, confers some resistance to HIV-1 infection. The immune cells are still fully receptive to T-tropic (aka CXCR4-tropic or X4) viral isolates, which could bind to their coreceptor, CXCR4 (aka fusin), and transmit HIV-1 infection.
From: Samson, Michel. “Human immunodeficiency virus (HIV).” Access Science Online.

There is now a new antiretroviral drug called maraviroc, which was approved by the U.S. Food and Drug Administration U.S. Food and Drug Administration in August 2007 and mimics the natural CCR5Δ32 mutation by acting as an antagonist for the CCR5 receptor and preventing the viral envelope protein gp120 from binding to it. Lieberman-Blum et al. (2008) report the results of two Phase IIb/III clinical trials, MOTIVATE 1 and 2, in which the effects of treatment with 300 mg of maraviroc once or twice daily were compared to placebo treatment in patients who were already being treated with HAART and still had primarily R5 HIV-1 infection. Maraviroc was found to decrease viral load by a greater percentage than placebo. Of the patients receiving maraviroc once or twice daily, 43.2% and 45.5%, respectively, had virus particle counts of less than 50 copies per milliliter, as opposed to 16.7% of patients in the placebo group. After the 48 weeks of the studies, patients demonstrated average viral load reductions of -1.68 log10 copies/mL for the once daily group and -1.84 log10 copies/mL for the twice daily group compared to -0.78 log10 copies/mL for the control group.

Figure 2. Most patients given maraviroc once or twice daily had lower HIV-1 viral loads and higher CD4 cell counts at the end of 48 weeks and had a long time period until treatment failure than did patients taking placebo.
From: Gulick, R.M., Lalezari, J., Goodrich, J., Clumeck, N., DeJesus, E., Horban, A., Nadler, J.,
Clotet, B., Karlsson, A., Wohlfeiler, M., Montana, J.B., McHale, M., Sullivan, J., Ridgway, C., Felstead, S., Dunne, M.W., van der Ryst, E., Mayer, H. 2008. Maraviroc for Previously Treated Patients with R5 HIV-1 Infection. The New England Journal of Medicine 359: 1429-1441.

As would be predicted by the absence of adverse health problems in individuals lacking functional CCR5 receptors due to the CCR5Δ32 mutation, maraviroc produced few severe side effects for the immune system by blocking the CCR5 surface protein. According to Lieberman-Blum et al. (2008), 21 of 426 (4.9%) individuals taking maraviroc and 11 of 209 (5.3%) individuals taking placebo had poor health outcomes that lead them to stop taking their medication and quit the trials. Most patients (92.3%) reported at least one side effect, which included upper respiratory illness, cough, fever, and abdominal pain. The primary concern with the use of antiretroviral drugs that block the CCR5 receptor is that the HIV virus will evolve into X4 or R5X4 variants that will then evade the drug’s action. For the individuals who were not benefitted by maraviroc, 54.4% of the once-daily patients and 55.2% of the twice-daily patients demonstrated virus that had changed from the R5 strains to either X4 or R5X4 strains. When the researchers performed phylogenetic analyses of the viral envelope proteins in these strains, however, they found that the new X4 or R5X4 strains had developed from preexisting viral particles of these strains that had been missed in the screening process before the beginning of the drug trials and had not resulted from R5 mutation during the course of drug treatment. Thus, these clinical trials suggest that maraviroc could be a good possibility for “salvage therapy” for those HIV+ individuals who have experienced treatment failures in the current categories of HIV/AIDS medications. More studies are still needed, however, to determine the long-term effects of antagonizing the CCR5 receptor.

The CCR5Δ32 genetic mutation and the recent research investigating it and its therapeutic implications are very relevant topics given the fact that the HIV/AIDS pandemic is one of the greatest public health concerns in the world, especially in developing nations. As cited in Lieberman-Blum et al. (2008), the Joint United Nations Programme on HIV/AIDS and the World Heath Organization report that as of 2007 33.2 million people worldwide were HIV+, and 2.5 million of those cases were new infections. In addition, the virus’s high mutation rate makes viral resistance to current antiretroviral medications a growing problem for disease treatment. The research into the CCR5Δ32 mutation aided scientists in developing the new class of antiretroviral drugs known as CCR5 antagonists. Furthermore, most new infections of HIV-1 are caused by R5 (also known as CCR5-tropic or macrophage-tropic) viral isolates. Thus, gene therapy involving the complete downregulation of CCR5 by the CCR5Δ32 mutation inserted into cells via viral vectors could one day prevent transmission of HIV by removing the coreceptor in the semen-receiving individual. Through the CCR5Δ32 mutation, evolution and natural selection may have unwittingly supplied we humans with a very powerful weapon in the fight against the HIV/AIDS pandemic.

For more information, please see:

Agrawal, L., Jin, Q., Altenburg, J., Meyer, L., Tubiana, R., Theodorou, I., Alkhatib, G. 2007. CCR5Δ32 Protein Expression and Stability Are Critical for Resistance to Human Immunodeficiency Virus Type 1 In Vivo. Journal of Virology 81: 8041-8049.

Lieberman-Blum, S.S., Fung, H.B., Bandres, J.C. 2008. Maraviroc: A CCR5-Receptor Antagonist for the Treatment of HIV-1 Infection. Clinical Therapeutics 30: 1228-1250.

Nazari, R., Joshi, S. 2008. CCR5 as Target for HIV-1 Gene Therapy. Current Gene Therapy 8: 264-272.

Wednesday, November 11, 2009

The Search for an HIV vaccine

I'm Paige Bates and this is The AIDS Pandemic

The RV144 study was a phase III HIV vaccine trial conducted by the US Army and Thai government over seven years on 16,402 volunteers—all HIV negative men and women between the ages of 18 and 30 in parts of Thailand. For ethical reasons, all participants were taught HIV prevention behaviors, given condoms, and promised lifelong antiretroviral treatment if they contracted HIV. Half of the volunteers were given a prime-boost vaccine regimen and half received placebo vaccinations. The prime-boost approach utilizes Sanofi Pasteur’s ALVAC-HIV vaccine as a prime and AIDSVAX (originally made by Genentech) as a boost. ALVAC-HIV is comprised of a canarypox virus with three HIV genes grafted onto it. AIDSVAX contains a recombinant gp120 protein found on the surface of HIV. These vaccinations were combined because one was designed to create antibodies and the other to alert white blood cells. These vaccinations were focused on the two strains of HIV commonly found in Thailand, but it is unclear whether this regimen would have any benefit elsewhere in the world. The participants were regularly tested for HIV for three years following the completion of the vaccine regimen. In September, the companies and agencies which implemented and funded the trial announced in a press release and interviews that new HIV infections were observed in 74 of the 8,198 people who received the placebo, but in only 51 of the 8,187 given the vaccine. They claimed that this was a statistically significant 31.2% reduction in infection. However, the vaccine did not reduce levels of HIV activity in those who became infected and did not appear to produce any neutralizing antibodies.

Source: Wall Street Journal, September 25, 2009

In the 1980s, top officials embarrassed themselves by predicting an HIV vaccine in five years. Reminiscent of these overly optimistic declarations, the backers of the RV144 trial claimed that “we now have evidence that a safe and effective HIV vaccine is possible.” In the first wave of press subsequent to the initial press release and interviews, many reputable news sources, such as the San Francisco Chronicle, New York Times, NPR radio and BBC news, suggested that these results were highly encouraging, and some even went so far as to suggest that this regimen might be the forerunner or basis for a usable vaccine in the near future. The LA Times suggested that these findings would “energize and redirect” the HIV vaccine field. Many articles quoted Dr. Anthony S. Fauci, the director of the National Institute of Allergy and Infectious Disease which largely funded the $100 million dollar study, as saying “I don’t want to use a word like breakthrough, but I don’t think that there’s any doubt that this is a very important result.” The Wall Street Journal suggested that this finding could be the second “big game changer in AIDS research since the mid 1990’s” with the advent of drug cocktails. Many articles later qualified with the cautionary statement that much more research is necessary before the vaccine could be available to the public. Phrases urging the public to be “cautious” but “hopeful” and describing the results as “modest” yet “encouraging” rang throughout the media and press releases.

However, only days later, the LA Times wrote “By Thursday afternoon, the initial wave of euphoria had given way to the recognition that many vexing questions will have to be answered before researchers can produce a vaccine that will reliably shield people from HIV.” Experts predicted that it would require two to three years of research to unravel how and why the vaccine regimen worked, and then an additional five to ten years to produce a vaccine that was ready to test in people. The fact that this still overly optimistic statement was a step back from the “initial euphoria” shows the extent of the preliminary sensationalism. The media reported that the researchers would now compare the blood of those who were vaccinated and resisted infection, and those who did not in order to determine whether the regimen stimulated antibodies or other protective molecules against HIV infection. In an article entitled “If AIDS went the way of smallpox,” a New York Times reporter recognized many problems with the initial reports including that many headlines in the first 24 hours after the press release read “One Third Protected,” while in reality the margin of success was “razor thin.” In addition, even the experts overseeing the trial could not explain why blending two failed vaccines suddenly resulted in “working” vaccine. Finally, this article recognized the financial difficulties surrounding a regimen that requires six shots over the span of months resulting in minimal protection. While this might be practical in rich countries, AIDS generally burdens the poorest nations in this world. Only one article mentioned that some researchers were suggesting that the apparent reduction in infections might be a statistical fluke due to the small number of HIV infections observed. Throughout all articles, there were minimal reminders to keep vigilance about prevention, testing, and the necessity to utilize current retroviral care.

Source: Wall Street Journal, October 12, 2009

In 2004, there was so much skepticism about this trial that 22 top AIDS researchers published an editorial in Science magazine suggesting it was a waste of money. Five years later, the organizations which conducted the trial announced in a press release that there has been significant protection, before making the scientific data available to peer review. When the full details of the study were released on October 20th at a meeting in Paris, the statistic frailty of the study was revealed. The vaccine was not shown to protect people at the highest risk of HIV infection. As The Washington Post noted on October 21st, when the results are analyzed using alternate methods, the protection is no longer statistically significant. For example, when only the people who received all six injections are counted, the trend towards protection is no longer significant. This raises many questions. What are the societal implications of the press surrounding this vaccine? If this vaccine doesn’t have much, if any, effect, what is the societal consequence of the data being overstated? The possibility of a public backlash against vaccination efforts wouldn’t be too hard to imagine. In fact, Gregg Gonsalves, an AIDS activist, remarked that, “When this was rolled out a couple of weeks ago, it was terribly hyped by the investigators. Some people think that you have to dangle the slimmest morsels of hope in front of the general public in order to keep them interested in an AIDS vaccine. But I think that damages the credibility of the effort.” The extent to which these results might represent a breakthrough can only be determined after the mechanism behind the possible conferred immunity is discovered. As Gonsalves points out, the over-exaggeration of the success in the media will likely hurt the results of the study if they prove to be less remarkable than originally stated. Furthermore, this study raises a general question about scientific results: is it appropriate to have news press releases before data is available for full review by scientific peers?

While this trial may not have been the scientific breakthrough that it was praised as, at the very least, this tremendous study is an example of international and interagency collaboration in conducting a large-scale vaccine trial, including the Thai and US governments, private companies such as Sanofi Pasteur, and non-profit organizations such as Global Solutions for Infectious Diseases (GSID). In this regard, it provides incredible hope for HIV vaccine efforts in the future.

For more information, please see these articles.
US Military Research Program in Thailand

BBC news coverage of RV144

The Wall Street Journal: Data Call ito Question HIV Study Results