a bio blog about genetics, genomics, and biotechnology
Posts Tagged ‘hiv’
Josh: This is a really neat idea. I’m guessing they would take CD8 cells from the patient, modify them, perhaps grow them in culture, and re-introduce them? I don’t think this is really going to be that practical in reality, and would probably be more expensive that taking anti-retrovirals.
HIV is a master of disguise, able to rapidly change its identity and hide undetected in infected cells. But now, in a long-standing collaborative research effort partially-funded by the Wellcome Trust, scientists from Oxford-based Adaptimmune Limited, in partnership with the Universities of Cardiff and Pennsylvania have engineered immune cells to act as “bionic assassins” that see through HIV’s many disguises.
The findings of the study, published online today in the journal Nature Medicine, may have important implications for developing new treatments for HIV and slowing – or even preventing – the onset of AIDS. Over 33 million people were estimated to be living with HIV worldwide in 2007. Although anti-retroviral drugs have been successful in delaying the onset of AIDS for several years, the drugs are expensive, have serious side effects and must be taken for life. No vaccine or cure yet exists and drug resistance is increasingly becoming a problem.
When viruses enter our bodies, they hijack the machinery of host cells in order to replicate and spread infection. When our body’s cells are infected with a virus they expose small parts of the virus on their surface, offering a “molecular fingerprint” called an epitope for killer T-cells from the immune system to identify. This triggers an immune response, eliminating the virus and any cells involved in its production.
As with other viruses, HIV enters the body and replicates itself rapidly. However, it also has the ability to mutate quickly, swiftly disguising its fingerprints to allow it to hide from killer T-cells.
“When the body mounts a new killer T-cell response to HIV, the virus can alter the molecular fingerprint that these cells are searching for in just a few days,” explains Professor Andy Sewell from Cardiff University, co-lead author of the study and long-term collaborator with Adaptimmune. “It’s impossible to track and destroy something that can disguise itself so readily. As soon as we saw over a decade ago how quickly the virus can evade the immune system we knew there would never be a conventional vaccine for HIV.”
Now, Professor Sewell and colleagues from Adaptimmune Ltd and the University of Pennsylvania School of Medicine have engineered and tested a killer T-cell receptor that is able to recognise all of the different disguises that HIV is known to have used to evade detection. The researchers attached this receptor to the killer T-cells to create genetically engineered “bionic assassins” able to destroy HIV-infected cells in culture.
“The T-cell receptor is nature’s way of scanning and removing infected cells – it is uniquely designed for the job but probably fails in HIV because of the tremendous capability of the virus to mutate,” says Dr Bent Jakobsen, co-lead author and Chief Scientific Officer at Adaptimmune Ltd, the company which owns the technology. “Now we have managed to engineer a receptor that is able to detect HIV’s key fingerprints and is able to clear HIV infection in the laboratory. If we can translate those results in the clinic, we could at last have a very powerful therapy on our hands.”
The researchers believe that HIV’s chameleon-like ability may still prevent the virus from being completely flushed out of the body. It could mutate and change its fingerprint further, hiding behind these new disguises and evading detection. However, each time the virus is forced to mutate to avoid detection by killer T-cells, it appears to become less powerful.
“In the face of our engineered assassin cells, the virus will either die or be forced to change its disguises again, weakening itself along the way,” says Professor Sewell. “We’d prefer the first option but I suspect we’ll see the latter. Even if we do only cripple the virus, this will still be a good outcome as it is likely to become a much slower target and be easier to pick off. Forcing the virus to a weaker state would likely reduce its capacity to transmit within the population and may help slow or even prevent the onset of AIDS in individuals.”
Pending regulatory approval, Professor Carl June and Dr James Riley from the University of Pennsylvania in Philadelphia will shortly begin clinical trials using the engineered killer T-cells.
“We hope to begin testing the treatment on patients with advanced HIV infection next year,” says Professor June. “If the therapy in that group proves successful, we will treat patients with early stage well-controlled HIV infection. The goal of these studies is to establish whether the engineered killer T cells are safe, and to identify a range of doses of the cells that can be safely administered.”
“The AIDS virus evades human immunity in all it infects,” says Professor Rodney Phillips, from the University of Oxford, where the collaborative research effort first began in 2003. “Until now no-one has been able to clear the virus naturally. Immune cells modified in the laboratory in this way provide a test as to whether we can enhance the natural response in a useful and safe way to clear infected cells. If successful the technology could be applied to other infectious agents.”
The researchers are now exploring using engineered receptors on killer T-cells as a way of improving immune responses to cancer.
Source: Wellcome Trust
Control of HIV-1 immune escape by CD8 T cells expressing enhanced T-cell receptor. Angel Varela-Rohena, Peter E Molloy, Steven M Dunn, Yi Li, Megan M Suhoski, Richard G Carroll, Anita Milicic, Tara Mahon, Deborah H Sutton, Bruno Laugel, Ruth Moysey, Brian J Cameron, Annelise Vuidepot, Marco A Purbhoo, David K Cole, Rodney E Phillips, Carl H June, Bent K Jakobsen, Andrew K Sewell & James L Riley. Nature Medicine. 09 November 2008; | doi:10.1038/nm.1779
Josh: I wrote about this same enzyme earlier in the year, but this is a new paper on it. The earlier study reported the NMR structure of the enzyme, but this study focused on the X-ray crystal structure. The authors note “In the X-ray structure, these APOBEC3G active-site loops [that are directly involved in substrate binding] form a continuous ‘substrate groove’ around the active centre. The orientation of this putative substrate groove differs markedly (by 90 degrees) from the groove predicted by the NMR structure”.
Humans have a built-in weapon against HIV, but until recently no one knew how to unlock its potential.
A study published online by the journal Nature reveals the atomic structure of this weapon – an enzyme known as APOBEC-3G – and suggests new directions for drug development.
APOBEC-3G is present in every human cell. It is capable of stopping HIV at the first step of replication, when the retrovirus transcribes its RNA into viral DNA.
The study’s authors, led by Xiaojiang Chen of the University of Southern California, were able to show the atomic structure of the active portion of APOBEC-3G.
The discovery suggests how and where the enzyme binds to the viral DNA, mutating and destroying it.
“We understand how this enzyme can interact with DNA,” said Chen, a professor of molecular and computational biology at USC. “This understanding provides a platform for designing anti-HIV drugs.”
If APOBEC-3G works so well, why do people get AIDS? Because the HIV virus has evolved to encode the protein Vif, known as a “virulence factor,” that blocks APOBEC-3G.
With APOBEC-3G out of the way, the RNA of the HIV virus can be successfully transcribed to viral DNA, an essential step for infection and for producing many more HIV viruses.
Chen said his group’s research offers important clues on where Vif binds to APOBEC-3G. The knowledge could be used to design drugs that would prevent Vif from binding and allow APOBEC-3G to do its job, Chen said.
That would unlock humans’ innate ability to fight HIV.
“We were born with it, and it’s there waiting,” Chen said.
In addition to fighting HIV, APOBEC-3G can inhibit the Hepatitis B virus. Other members of the APOBEC family serve important roles in antibody maturation, fat metabolism and heart development.
Mapping the structure of APOBEC-3G at the atomic level is a goal that “has been sought after worldwide because of its significance,” Chen said.
Source: University of Southern California
Crystal structure of the anti-viral APOBEC3G catalytic domain and functional implications. Lauren G. Holden, Courtney Prochnow, Y. Paul Chang, Ronda Bransteitter, Linda Chelico, Udayaditya Sen, Raymond C. Stevens, Myron F. Goodman & Xiaojiang S. Chen. Nature. Advance online publication. 12 October 2008
The life expectancy for patients with human immunodeficiency virus (HIV) has increased by more than 13 years since the late 1990s thanks to advancements in antiretroviral therapy, according to researchers at the University of Alabama at Birmingham (UAB) and Simon Fraser University in Vancouver, British Columbia.
Improved survival has led to a nearly 40 percent drop in AIDS deaths among 43,355 HIV-positive study participants in Europe and North America, bolstering the call for improved anti-HIV efforts worldwide, the study authors said.
The study is published in the British medical journal The Lancet. It was compiled by The Antiretroviral Therapy Cohort Collaboration, which includes UAB, Simon Fraser University and more than a dozen other research sites around the world. … Continue Reading »
In a world first, a University of Melbourne study has shown that topical estrogen could help prevent HIV infection by blocking entry of the virus into the human penis.
[editor's note] (Andrew): The only reason I’m not scrubbing this trash study off my website is to mock it.
First, there is no clinical application. Rather than a CONDOM, which costs nothing, works immediately, is everywhere, works for everyone, has no side effects, and prevents every STD up to and including pregnancy itself by almost 100%, I’m supposed to sagely ponder rubbing female hormones on my penis to “toughen it up” by “15%” which might increase my resistance to HIV a week later? And this is suggested as viable solution for AIDS control in countries with pervasive cultural taboos about the penis? Total, absolute bullshit.
Second, the sample size of this study is: TWO. Yes, two. Ok, eight if you include the foreskin donors. And the study only tested keratin coverage and presented some untested hypotheses regarding a couple tangential studies as conclusions regarding HIV prevention.
But good news for readers, because I’m awarding a Think Gene coffee mug to the first reader who forwards me a spam email hawking topical oestrogen as an “all natural” penis cream to “u last longr.”
The study to be published in PLoS ONE journal today reveals that application of estrogen to the human penis increased the thickness of the natural keratin layer on the skin, which could prevent HIV from infecting the male.
The epithelium of the human penis is richly supplied with estrogen receptors suggesting it could respond to topical estrogen.
Dr Andrew Pask from the Department of Zoology at the University of Melbourne analyzed the tissue samples from 12 foreskins and made the discovery.
“This suggested that estrogen could induce a thickening of the keratin layer of the foreskin epidermis in the same way as it acts in the vagina,” said Dr Pask.
“Keratin on our skin acts a barrier to viral infection. We hope to be able to enhance this protection with the use of a naturally occurring, weak estrogen,” said Professor Roger Short of the Faculty of Medicine, Dentistry and Health Sciences who lead the research.
To confirm its effect, topical estrogen was applied to the human foreskin for a two week trial. This resulted in a rapid and substantial increase in keratin thickness.
“We have found a new avenue to possibly prevent HIV infection of the penis.”
HIV is one of the greatest health crises the world has ever seen, and affects over 40 million people worldwide.
Source: The University of Melbourne
Kevin: HIV is on the rise around the world and a treatment such as this could have impact where condoms are not socially acceptable because of adverse societal influence. Estrogen on the penis would be fine, and while it’s nothing like condoms for preventing HIV (and anti-retrovirals at your local free HIV drug stand) this could mean something in terms of harm reduction.
Pask AJ, McInnes KJ, Webb DR, Short RV (2008) Topical Oestrogen Keratinises The Human Foreskin and May Help Prevent HIV Infection. PLoS ONE 3(6): e2308. doi:10.1371/journal.pone.0002308
A team of scientists at Cold Spring Harbor Laboratory (CSHL) has discovered new details about how a simian strain of the AIDS virus replicates. The findings are significant because they suggest new strategies to prevent replication, and because they are applicable to human strains of the virus, which, despite the persistent efforts of scientists over two decades, can only be slowed by drug treatments but neither cured nor prevented.
Jacek Skowronski, Ph.D., CHSL associate professor, led a team that studied a virulent strain of simian immune-deficiency (SIV) virus called SIVsm/mac, named for two species of monkeys in which it occurs, sooty mangabeys and macaques. The team included members of Dr. Skowronski’s CSHL lab and researchers at Stowers Institute for Medical Research in Kansas City, Missouri, and the Skirball Institute of Biomolecular Medicine in New York City.
Like versions of the virus that occur in humans, SIV viral particles, or virions, are composed of a few fundamental parts. At their heart are two identical but separate strands of RNA surrounded by a protective envelope of roughly 2,000 proteins called a capsid.
This tiny, conical capsule, in turn, is surrounded by multiple defensive rings, somewhat like the walls of a medieval city. Immediately surrounding it is a protective protein shell, or matrix, and beyond it a formidable double-walled viral envelope. Poking through the outer envelope are the viral equivalent of grappling hooks, protein molecules designed to lock onto receptors on the surface of the unfortunate cell that the virus will attach to and then invade.
Viruses Hijack Living Cells to Reproduce
Viruses, unlike cells, are not living things. They must penetrate a living cell and commandeer its internal machineries in order to reproduce. HIV and its simian cousin SIV are members of a viral subspecies called retroviruses that invert the usual reproductive procedure. Their genetic raw material is not DNA but rather RNA, and before they can begin to replicate, they must first convert their RNA into DNA, using a special enzyme that they encode, called reverse transcriptase.
Once its RNA has been reverse-transcribed into DNA, the virion, having invaded a cell whose genetic material consists of DNA, can shed its protein coat and immediately proceed to integrate its newly converted DNA — containing 9 genes — into the host cell’s DNA. In this way the virion effectively hijacks the cell and reproduces itself whenever the cell reproduces.
Dr. Skowronski has devoted years to the study of various molecular factors — think of them as assistants — that immune-deficiency viruses employ to perform a range of essential tasks. The idea behind his approach is to understand with great precision all of the details of the processes by which the virus lives and propagates, as a means of identifying points of vulnerability, where drugs might be inserted to foul up the works.
In the research just completed, results of which appeared in PLoS Pathogens on May 9, Skowronski and his team focused on a so-called accessory protein called Vpx (Viral protein x). Prior studies had shown that Vpx was produced by simian, as well as a subset of human, immunodeficiency viruses, and was somehow active at the heart of their reproductive processes in a subset of immune cells called macrophages. The question was how, and to what effect.
How Vpx Enables the Virus to Replicate
Macrophages are central players in the mammalian immune system. Immune-deficiency viruses are devastating because they specifically seek out, invade, and commandeer the machinery of these particular cells — macrophages, dendritic cells, helper T-cells — which protect the mammalian system from foreign invaders.
Skowronski and colleagues knew from prior work that Vpx was a key enabler: it somehow facilitated an “early event” in the viral life cycle that helped the virus invade macrophage target cells. Recent studies had further shown that Vpx proteins in both monkey and human viruses promoted the process of reverse transcription that underlies the conversion of viral RNA to DNA.
In their study, which consisted of several steps, the CSHL team showed that when the vpx gene (the gene that encodes the Vpx protein) was deliberately deleted, the virus went about reverse transcription “very inefficiently.”
“This suggests that the Vpx protein is key to the process by which the virus infects macrophages,” Dr. Skowronski comments, “and further, that it seems to be acting either before and/or during the reverse transcription process.” This new view of Vpx’s role contrasts with a prior hypothesis that it was involved in the transporting of genetic material that had already undergone reverse transcription.
The team’s experiments revealed that the Vpx protein in the SIVmac virus binds to a complex of three cellular proteins that in turn engage a molecular machinery involved in the degradation of proteins. Thus, the team revealed for the first time not only that Vpx interacted with this system — called the ubiquitin-dependent proteosomal protein degradation mechanism — but also identified precisely the way it does so, via a series of intermediate steps.
“The net result,” says Dr. Skowronski, “is that we show how Vpx enables efficient reverse transcription in the simian virus, and in so doing, overcomes an innate block that otherwise prevents viral replication.”
By implication, this suggests a strategy by which a future drug might interfere with the reproductive machinery of the virus to prevent or limit is ability to spread. “There are no guarantees, of course, that such an approach will work,” Dr. Skowronski says, “but unless we understand molecular mechanisms such as this one that empower this remarkable virus, we are not likely to devise a means of stopping it.”
Source: Cold Spring Harbor Laboratory
“Lentiviral Vpx accessory factor targets VprBP/DCAF1 substrate adaptor for Cullin 4 E3 ubiquitin ligase to enable macrophage infection”. Smita Srivastava, Selene K. Swanson, Nicolas Manel, Laurence Florens, Michael P. Washburn, Jacek Skowronski. PLoS Pathogens. May 9, 2008.
I just skimmed the paper, but it seems that the protein prevents an E3 ubiquitin ligase from targetting the viral proteins for degredation by the proteasome. This will definitely be a drug target in the future. I think the “cure” for HIV will be a cocktail of medications that all target different parts in the viral replication and infection pathway.
A potential new therapeutic use for anti-HIV drugs known as protease inhibitors has been suggested by a team of researchers from Harvard Medical School, Boston, and Inserm U848, France, as a result of their work in a mouse model of retinal detachment.
An important cause of vision loss in many diseases of the eye is the death (by a process known as apoptosis) of nerve cells in the eye (known as photoreceptors) after retinal detachment. In the study, administration of HIV protease inhibitors by mouth markedly decreased photoreceptor apoptosis in the mouse model of retinal detachment. Mechanistic analysis in mouse retinal cell cultures and in mice expressing decreased amounts of specific proteins established that the HIV protease inhibitors disrupted two molecular pathways that cause apoptotic cell death, both of which affect the cell compartments known as mitochondria. As the same apoptotic cell death–inducing pathways were shown to be activated in human retinas after retinal detachment, the authors suggest that although the HIV protease inhibitors cannot reattach the retina, they might be of clinical benefit through their ability to prevent the photoreceptor apoptosis that has a central role in vision loss after retinal detachment.
Source: Journal of Clinical Investigation
HIV protease inhibitors provide neuroprotection through inhibition of mitochondrial apoptosis in mice. Toshio Hisatomi, Toru Nakazawa, Kousuke Noda, Lama Almulki, Shinsuke Miyahara, Shintaro Nakao, Yasuhiro Ito, Haicheng She, Riichiro Kohno, Norman Michaud, Tatsuro Ishibashi, Ali Hafezi-Moghadam, Andrew D. Badley, Guido Kroemer, and Joan W. Miller. The Journal of Clinical Investigation.
It makes me uneasy to disrupt apoptosis this way, as it could also contribute to cancer. However, certainly it would help in cases of retinal detachment. Perhaps there is a way to localize it to the retina.
A new study reveals the genetic identity of human immunodeficiency virus (HIV), the version responsible for sexual transmission, in unprecedented detail.
The finding provides important clues in the ongoing search for an effective HIV/AIDS vaccine, said researchers at the University of Alabama at Birmingham (UAB). The UAB team found that among billions of HIV variants only a few lead to sexual transmission.
Earlier studies have shown that a ‘bottleneck’ effect occurs where few versions of the virus lead to infection while many variants are present in the blood. The UAB study is the first to use genetic analysis and mathematical modeling to identify precisely those viruses responsible for HIV transmission. … Continue Reading »
Researchers have developed what they believe is the first new mechanism in nearly 20 years for inhibiting a common target used to treat all HIV patients, which could eventually lead to a new class of AIDS drugs.
Researchers at the University of Michigan used computer models to develop the inhibiting compound, and then confirmed in the lab that the compound does indeed inhibit HIV protease, which is an established target for AIDS treatment. The protease is necessary to replicate the virus, says Heather Carlson, U-M professor of medicinal chemistry in the College of Pharmacy, and principal investigator of the study. … Continue Reading »