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.
McGraw-Hill.
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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.

Preventing Mother to Child Transmission of HIV in Mwandi, Zambia- A Success

Welcome to this installment of the AIDS Pandemic, a podcast hosted by Dave Wessner of the Department of Biology at Davidson College. I am Sarah Bertram.

This past summer, I traveled to Mwandi, Zambia through a Davidson biology and pre-medical program. Mwandi is a predominantly Lozi village of about 7,000 people and the catchment area totals about 25,000 people. We spent 5 weeks in Africa, 3 of which were spent working in the Mwandi Mission Hospital, the Mwandi AIDS clinic, the Orphans and Vulnerable Children’s center, and the Mother and Child Health Center. We all went with a research topic to study that was based on some aspect of Mwandian life. I looked at Mwandi’s Prevention of Mother to Child Transmission of HIV, otherwise known as the PMTCT program, and its effectiveness over the past three years. Here, I will talk about my findings.

About out of every five pregnant women in Zambia is infected with HIV and without any prevention or treatment interventions, more than 300,000 babies would contract HIV from their mothers each year. Starting in 1999, many Zambian mission and government hospitals started PMTCT programs. The Mwandi PMTCT program was launched in 2005 by an American Pediatrician in conjunction with the Mwandi missionary who was going to serve as the leader of the program. The procedure for PMTCT at the Mwandi Mission Hospital is as follows: 1) discuss the PMTCT program and HIV/AIDS information during group antenatal care visits, 2) offer private pre-test counseling, 3) test the mother for HIV and CD4 counts and give her the results, and 4) offer post-test counseling and discuss further treatment and a re-test in three months. According to the hospital staff in Mwandi, HIV testing of any pregnant mother is required by law in Zambia.

If a woman tests positive, she is evaluated at the Pastoral Care Center for AIDS treatment. If she is considered a WHO stage IV or has multiple symptoms for WHO stage III, HAART treatment is usually started unless the woman chooses to undergo short-course treatment instead. Many of the HIV positive mothers choose to undergo HAART treatment because of its documented increased ability to treat HIV/AIDS symptoms and to lower the viral load by decreasing viral replication. The Mwandi hospital staff is good about giving options to the positive mothers and explaining each option and its risks and benefits. Due to the staff’s willingness to counsel and inform the HIV positive pregnant mothers of treatment options, a majority of these women decide to take part in a course of HIV/AIDS treatment in order to help themselves and to prevent the transmission of HIV to their babies.

Although record-keeping is sparse and sometimes hard to find and evaluate, some records for the PMTCT program proved helpful in evaluating the program’s success over the years. From March of 2005 to September of 2007 (before HIV testing was mandatory), 1,205 women attended an antenatal care appointment to sign up for the PMTCT program and of these 1,205 women, only 35 women or about 3% refused the HIV test. Of the 1,170 women who agreed to be tested, 24.4% tested positive for HIV. This statistic is quite high, but reflects the belief that about 1/3 to ¼ of Mwandi’s population is infected with HIV. Because the PMTCT program was in place, the HIV positive women were able to learn their status, get treatment, and prevent (for the most part) the transmission of HIV to their babies during pregnancy, delivery, and breastfeeding.

Mwandi’s PMTCT program has changed drug regimens in order to stay current with the most effective treatments. Originally, the program was based on a single dose of nevirapine given to the mother during delivery and to the baby right after birth. In April of 2006, the PMTCT program switched to a dual therapy involving both nevirapine and AZT for both mothers and babies. Starting in November of 2007, Mwandi updated its treatment regimen to the most current and effective triple therapy drug treatment. This drug therapy involves a mixture of AZT, 3TC, and NVP for the mother and baby. This new therapy has proven to be very effective and the PMTCT program workers approximate that transmission from mother-to-child rates have decreased to less than 10% and possibly even as low as 6% or 7%.

Possibly the most enticing aspect of the PMTCT program for pregnant women is the free formula feeding program provided to HIV-negative babies of HIV-positive mothers. Breastfeeding is the most common type of mother-to-child HIV transmission, so by providing free formula for those babies who test negative (after 6 weeks of age), the worry of transmission by breastfeeding can be alleviated. Currently there are over 100 babies receiving infant formula and most, but not all, are HIV-negative babies of HIV-positive mothers who participated in the PMTCT program. The program has never resulted in a case of child dysentery, a common negative outcome of formula feeding programs, which is often a result of incorrectly boiled water used to make the formula. This clean record is a result of the care and attention put forth into teaching the mothers how to correctly make the formula and clean the bottles.

Compared to many other Sub-Saharan African PMTCT programs, Mwandi’s program is doing a very good job of keeping the program advancing, as far as the number of women being treated and the updates to newer forms of drug therapies. The program could however still make larger strides in incorporating more women from far out in the catchment area and by possibly providing more rural village outreaches for the sole purpose of PMTCT.

Opportunistic Infections in Developing Nations: A World Away

In the United States and other developed nations, for many people, AIDS has become a manageable disease. With adequate care and lots of medication, HIV positive individuals can live with relatively few serious complications for a long time. In the US, 71% of HIV-infected individuals have at least started HAART therapy, decreasing deaths per infected individuals per year from 30/100 to 5/100 since the 1980’s. In developed nations, however, HIV positive individuals do not have the luxury of adequate care. In areas like Africa where the burden of disease is highest, HIV positive individuals must face an array of opportunistic infections as their CD4 counts dip lower and lower.

Because these opportunistic infections are generally localized to areas where HAART is not available, it is both hard for us to understand the difficulties in treatment and to determine which infections are endemic to what populations. For example, MAC (for Mycobacterium avium complex) is a common, life-threatening opportunistic infection in Asia causing a significant portion of AIDS-related mortalities. In Africa, however, MAC is rare. In addition, tuberculosis is a particularly life-threatening coinfection that is particularly common in many developing areas, especially Sub-Saharan Africa and Asia. Many opportunistic infections in these nations have developed resistance to the drugs typically used to treat them. Determining which disease populations have resistance to what medications can be exceptionally difficult given how isolated some of these areas are.

The HIV/IDS prevalence is highest in sub-Saharan Africa

The most reputable source for information like this is undoubtedly the World Health Organization. The WHO publishes information on the geography, morbidity, symptoms and treatment of various opportunistic infections for different nations and settings. While it is hard to determine where exactly the WHO gets their sources for information from developing nations, it is clear that they get their information from all parts of the globe. However, it is also hard to pick apart the complicated interactions of HIV and opportunistic infections in a multitude of settings, and even harder when there are additional complicating factors such as malnutrition, social unrest, and a lack of medical infrastructure for reporting treatment schemes. Many times, the WHO provides useful information about the scope of opportunistic infections in developing nations, but they often miss the deeper and more individual issues that a given region may have. If first-line drugs for opportunistic infections are not available in these developing areas (due to oppressively high costs or restrictive storage conditions), the WHO lacks vital information on how to cope.

The availability of antiretrovirals in lowest in sub-Saharan Africa

While it is not the fault of the WHO that there is a dearth of useable information for medical workers in low-resource environments, it is clear that there is a lack of necessary medical care in these nations that perpetuates a cycle of poverty and illness and that millions of HIV-positive individuals are dying as a result of a lack of ARVs. In a situation where prohibitively high costs of necessary drugs prevents individuals from being treated for HIV, we need to focus more on preventative efforts and HIV prophylaxis in the form of vaccines or microbicides. In this sense, the US and other developed nations are providing a massive amount of resources in trying to find a vaccine and developing useful microbicides to prevent HIV infection from happening in the first place. Because of the massive amount of people infected in areas that lack the resources to treat them, the disease needs to be treated when it is least expensive to do so. While it is hard to know what the future holds for those with HIV in developing nations, it is sure that we need to develop better ways of treating opportunistic infections and preventing the development of AIDS from HIV.

For more information on the global context of the AIDS pandemic, please visit:
Avert.org
WHO

Testing and Treatment of HIV/AIDS in Children

According to a 2006 UNAIDS/WHO AIDS Epidemic Update, there are approximately 39.5 million people living with HIV/AIDS throughout the world. Of those infected, 2.3 million are aged 15 or younger. Approximately 90% of children infected with HIV acquire the virus perinatally, meaning it is transmitted from a mother to her child during pregnancy, labor, delivery or through breastfeeding. According to the CDC, the prevalence of mother-to-child transmission of AIDS in the US has dropped significantly due to effective testing of pregnant women and treatment of those found to be infected; in resource poor settings, however, the testing and treatment of infected women is far less common. In 2005, the UNAIDS/WHO AIDS Epidemic Update found that only 9% of pregnant women in resource poor countries were offered any sort of prevention services, leading to a higher prevalence of pediatric HIV/AIDS infection in less developed countries. As the prevalence of women of childbearing age who are infected with HIV increases in resource poor settings, it can be expected that the number of babies infected from mother-to-child transmission will likewise increase.

Children infected with HIV/AIDS are confronted with an extremely high rate of illness and death. The World Health Organization has found that because of their unique metabolic and immunologic circumstances, HIV progresses rapidly in children, with an estimated one third of infants dying by the time they reach their first birthday and half dying by their second birthday. Although in most developed countries identification and treatment of HIV infected babies is quite successful, which allows those children to lead healthier and longer lives, the situation is quite different in resource poor countries where testing, much less treatment of infants and children is relatively unavailable. To begin with, testing may be unavailable to individuals in developing countries due to the distance, expense and impracticality of reaching those hospitals and clinics that provide testing. Even when testing is locally available, parents may be unwilling to test their babies for fear of stigma and prejudice associated with an HIV positive status. Furthermore, testing of infants in developing countries can require far more time than in developed countries. PCR tests are among the fastest and most effective ways to diagnose infants as they can be done within 48 hours of birth and results are available to the mother within 6 weeks of the completion of the test. PCR tests are rarely accessible and prohibitively expensive in resource poor settings where antibody tests are the norm. These antibody tests only begin to give accurate results 18 months after birth, and so babies in developing countries are oftentimes diagnosed far later than in developed countries, if they are diagnosed at all.

Aside from the difficulties in testing infants and children for HIV in resource poor settings, there continues to be a dearth of treatment for children found to be positive for the virus. Although both prophylaxis and HAART or highly active antiretroviral therapy can be extremely effective in treating HIV/AIDS and preventing opportunistic infections in children, the unique difficulties associated with treating children in resource poor settings mean that these therapies are widely underused. UNAIDS found in 2006 that “an estimated 380,000 children died of AIDS-related causes” and that, “the vast majority of these deaths could have been prevented either by treating opportunistic infections or providing HAART.” Similarly, a UNAIDS/WHO report found that nearly 90% of children who could benefit from ARV treatments are not currently receiving it. This lack of treatment can be attributed to several factors.

In many resource poor settings, antiretroviral treatment may simply be unavailable. Those countries where the HIV/AIDS burden is greatest such as in Sub-Saharan Africa are oftentimes the least able to provide treatment, and so a lack of resources oftentimes translates into a lack of prophylaxis and/or antiretrovirals. Prophylaxis has been found to be extremely effective in staving off opportunistic infections in HIV positive children and is useful in delaying the need for HAART in pediatric populations. Although prophylactic drugs are widely available and relatively cheap, a UNAIDS/WHO study has found that currently nearly 4 million children who could benefit from such treatment are not receiving it. This is probably the result of lack of available treatment sites and infrastructure in resource poor settings. This dearth of available treatment translates to ARVs as well as prophylactic treatments. Even in areas where adult ARV treatment is present, there is rarely a comparable pediatric treatment site. This is due to the fact that suitable pediatric drug formulations are oftentimes prohibitively expensive and impractical. Little research had been conducted in the area of pediatric dosages because in the developed world effective mother to child prevention had limited the need for pediatric ARVs. Because so few drugs are available in pediatric dosages, and those that are available tend to be far more expensive than those made for adults, most caregivers in resource poor settings are limited to providing either expensive and unpleasant tasting syrup formulas or cutting and crushing adult tablets to provide ARVs for their pediatric patients. Crushing the pills provides an inexact measure of the amount of medication that is administered. Since under dosage can result in resistance of the virus to the drugs, and over dosage can result in amplified side-effects, the lack of correct dosages inherent in using adult drugs for pediatric patients means this mode of drug administration is far from ideal.

Important steps have been taken to begin to provide better treatment for pediatric AIDS patients. In August of 2007 the US Food and Drug Administration (FDA) approved a special tablet for children with HIV that combines three antiretroviral drugs into one pill. The tablet can be dissolved in water for ease of administration which is required only twice a day. The drug is produced by the manufacturer Cipla Limited, a generic pharmaceutical company based in India. Though unapproved for use in the US, the drug has been authorized for use in developing countries where the need and demand is greatest. Despite the enormous implications for successful treatment of pediatric AIDS that this drug will bring, there are still substantial obstacles to be overcome before pediatric care and treatment of AIDS is fully complete. Mother-to-child transmission must be diminished in resource poor settings. In situations where prevention of mother-to-child transmission is not achieved, suitable infrastructure for administration of prophylactic and antiretroviral drugs to pediatric patients must be established. Movements and groups such as the “Stop AIDS in Children” campaign are working towards prevention of mother-to-child transmission and improvement of treatment for infected children. With support of both developed and resource poor countries, the relatively ignored problem of HIV/AIDS in children can be successfully addressed.

Until next time, this is Dominique Maietta for the AIDS Pandemic Podcast.

VIRIP: A new anti-HIV compound?

Welcome to this installment of The AIDS Pandemic. I’m Dave Wessner.

Could our own bodies be producing potent inhibitors of HIV? According to research published in today’s issue of Cell, the answer may be ‘Yes.’ And these interesting findings eventually may lead to the development of new anti-retroviral drugs.

Since the isolation of HIV in 1983, numerous naturally occurring human factors have been postulated to have anti-HIV properties. Today, a group of researchers in Germany have added another factor to this list. By studying hundreds of small molecules isolated from human blood, the researchers identified a short peptide, or protein fragment, that effectively blocked HIV from infecting cells. Termed Virus-Inhibitory Peptide, or VIRIP, this peptide represents a small piece of a larger protein normally found in our blood – alpha1-anti-trypsin.

To demonstrate the inhibitory effects of VIRIP, the researchers infected cell lines with HIV-1, added VIRIP to the cells, and then determined how many additional cells subsequently became infected. VIRIP decreased the infection rate in a dose-dependent manner. In other words, when higher concentrations of VIRIP were used, the effect was greater. The effect also was very specific for HIV; the peptide did not block the infectivity of other types of viruses. Interestingly, the researchers showed that if they altered the VIRIP peptide slightly, it’s inhibitory properties increased dramatically. Finally, VIRIP was equally effective against strains of HIV that were resistant to other anti-retroviral drugs, yet resistance to VIRIP was not observed.

Mechanistically, it appears that VIRIP blocks HIV infection by binding to the viral protein gp41 and preventing fusion between the viral envelope and the cell membrane. An existing drug, T20, or Fuzeon, works in a similar manner.

The path from an initial discovery like this and a marketable drug is a long and winding path, filled with potholes. Promising candidate molecules rarely become FDA-approved drugs. So, the odds are against VIRIP. But, based on this report, it’s certainly worth keeping our eye on it.

Until next time, I’m Dave Wessner.