For cancer patients with HIV, immunotherapy appears safe

A new category of immunotherapies called checkpoint inhibitors that has been highly effective against many different cancers appears safe to use in patients with both advanced malignancies and HIV, a population excluded from earlier trials of such therapies, according to an early-phase trial.

Study Principal Investigator, Dr. Thomas Uldrick of the HIV & AIDS Malignancy Branch at the National Cancer Institute, will present late breaking results from the first 17 patients on a phase I study of pembrolizumab in patients with HIV and advanced cancers Friday at the Society for Immunotherapy of Cancer’s annual meeting in National Harbor, Maryland. The ongoing, multi-site study is being conducted by the NCI-funded Cancer Immunotherapy Trials Network, which is headquartered at Fred Hutchinson Cancer Research Center.

Cancer has become the leading cause of death for people with HIV. But until now, they and their physicians have had little data to guide them on whether they can safely use powerful new anti-cancer drugs called immune checkpoint inhibitors.

“During the development of these drugs, people with HIV were routinely excluded from studies due to concerns that they would not tolerate these medications or perhaps not benefit from them because of their underlying HIV and associated immune dysfunction,” Uldrick said. “The most important first step was to show that this class of drug would be safe in cancer patients with HIV.”

Study participants — who were on standard antiretroviral therapy to control their HIV infections and had various cancers that had failed to respond to standard therapies — received pembrolizumab (Keytruda), known since 2015 as “the Jimmy Carter drug” after it swiftly beat back melanoma that had spread to the former president’s brain and liver.

Pembrolizumab belongs to a type of immunotherapy that blocks a braking system cancers use to tamp down the immune response. Checkpoint inhibitors have been extremely effective in some patients with advanced cancers otherwise thought untreatable. The treatments have received U.S. Food and Drug Administration approval for melanoma, lung cancer, head and neck cancer, Hodgkin’s lymphoma, and kidney and bladder cancers.

“These drugs are the backbone of cancer immunotherapy at present and have been shown to be effective in subsets of virtually every different kind of cancer,” said Fred Hutch immunotherapy researcher Dr. Martin “Mac” Cheever, who leads the Cancer Immunotherapy Trials Network and is senior author of the new study. “For patients with HIV who are using effective antiretroviral therapy and have cancers for which these drugs are approved, there’s no reason not to consider these drugs as standard therapy.”

HIV and cancer

From the earliest days of the AIDS pandemic, Kaposi sarcoma — a rarely seen cancer until then — was one of a trio of cancers known as AIDS-defining malignancies. It, non-Hodgkin lymphoma and, in women, cervical cancer, often signaled that a person’s HIV infection had progressed to full-blown AIDS. People did not die of AIDS, per se. They died of one of these cancers or of infections like pneumocystis pneumonia and toxoplasmosis that took advantage of a weakened immune system.

Since the advent of antiretroviral therapy for HIV in 1996, full-blown AIDS and AIDS deaths have dropped dramatically. But the association between HIV and cancer remains, and not just with the traditional AIDS-defining malignancies. A large study published in the journal Annals of Internal Medicine in 2015 found higher cancer incidence across the board in HIV patients, including lung cancer and Hodgkin lymphoma.

“Globally, more than 35 million people are infected with HIV, and cancer is the number one reason they are dying,” Uldrick said. “Establishing proven effective regimens to manage cancer in people with HIV is critically important.”

The ongoing study will enroll up to 36 patients, and there are plans to include more patients with Kaposi sarcoma, a cancer for which checkpoint inhibitors have not been studied. It is one of the leading causes of cancer deaths in sub-Saharan Africa — where HIV rates are high — and new treatments are sorely needed.

Further study in Kaposi sarcoma

Kaposi sarcoma is caused by the Kaposi sarcoma herpes virus (also known as human herpesvirus 8, or HHV-8) and most commonly appears as lesions on the skin. KSHV can also cause two other B-cell tumors, primary effusion lymphoma and a form of multicentric Castleman disease. Additionally, it can infect blood cells and spread through the bloodstream to infect other cells in the body, Uldrick said.

Also to be presented Friday is the death of one patient later in the study who had Kaposi sarcoma. The death is still being evaluated but was likely due to dissemination of KSHV. Uldrick and Cheever said review of the case suggests the patient had a history of symptomatic KSHV viremia, and the study has been changed to exclude such patients in the future and provide specific guidelines for management should new symptomatic KSHV viremia be observed.

Six other study participants with Kaposi sarcoma or primary effusion lymphoma have been treated on this study. None has experienced similar problems, and some have benefitted from therapy, Uldrick said.

“We do not believe that this takes away from the safety message in patients with HIV and other, better studied cancers,” Uldrick said. “However, more experience is clearly needed in treating KSHV-associated diseases with checkpoint inhibitors.”

A passion to ‘change the culture’

Although the NCI has recommended including people with HIV in immunotherapy clinical trials for a decade, virtually every industry-sponsored study over the last five years excluded them, according to a review by Uldrick and others published in the Journal of Clinical Oncology. Uldrick believes that reluctance to include people with HIV in cancer immunotherapy studies dates back to a time when patients were still dying of opportunistic infections and antiretroviral therapies were more toxic than they are today.

As a physician-scientist who focuses on immunology, virology and cancer, Uldrick became frustrated with the lack of data.

“The culture was slow to change,” he said. “It was preventing the advance of appropriate clinical therapies.”

Dr. Holbrook Kohrt, a Stanford oncologist and researcher, shared that frustration. Kohrt instigated the current clinical trial, according to Cheever, driven by his boyhood experience being one of only two hemophiliacs in a special summer camp who did not die of AIDS. (The genetic disorder impairs the blood’s clotting ability and requires infusions of lifesaving clotting factor, which at that time was made from the pooled blood of tens of thousands of donors. Before a test was developed to detect HIV in blood, about half the hemophiliacs in the United States died of AIDS from infected clotting factor.)

“Holbrook had three patients early on with malignancies that he thought would benefit from [checkpoint inhibitors] and could not get access to the drug because they had HIV,” Cheever said. “He was passionate about this study because he was a passionate individual and physician. But he was also influenced by his experience as someone with hemophilia who lost so many peers to HIV.”

Kohrt died in 2016 from complications of hemophilia. He is named as an author of the study.

“He would have predicted these results,” Cheever said.

Getting out the message

The ongoing study is now being conducted at eight sites, each of which includes physician-researchers with expertise in both cancer and HIV. A majority of the early patients were enrolled on the trial through Uldrick’s group at the NCI Intramural Research Program in Bethesda, Maryland.

Uldrick will continue to lead the study after he leaves the NCI to become deputy head of Fred Hutch Global Oncology on Dec. 1.

He and Cheever are hoping that these early results lead to additional studies of checkpoint inhibitors in people with HIV and malignancies, especially those cancers that are more prevalent in people with HIV such as Kaposi sarcoma and cancers caused by another virus, human papillomavirus, such as cervical cancer.

In the meantime, the researchers intend to talk about their findings at multiple scientific communities so that people with HIV and their physicians become aware of the data.

“We’d recommend that patients with HIV and malignancy be considered for this therapy if it’s approved for their particular cancer,” Uldrick said.

Zika Virus Protein Mapped to Speed Search for Cure

A recently-published study shows how Indiana University scientists are speeding the path to new treatments for the Zika virus, an infectious disease linked to birth defects in infants in South and Central America and the United States.

Cheng Kao, a professor in the IU Bloomington College of Arts and Sciences‘ Department of Molecular and Cellular Biochemistry, has mapped a key protein that causes the virus to reproduce and spread.

“Mapping this protein provides us the ability to reproduce a key part of the Zika virus in a lab,” Kao said. “This means we can quickly analyze existing drugs and other compounds that can disrupt the spread of the virus. Drugs to target the Zika virus will almost certainly involve this protein.”

The World Health Organization reports that more than 1 million people in 52 countries and territories in the Americas have been infected with the Zika virus since 2015. The disease has also been confirmed to cause microcephaly in more than 2,700 infants born to women infected with the virus while pregnant. Symptoms include neurological disorders and a head that is significantly smaller than normal.

The virus is also transmissible through sexual activity and can trigger an autoimmune disease in adults called Guillain-Barre syndrome.

The IU-led study, conducted in collaboration with Texas A&M University, revealed the structure of the Zika virus protein NS5, which contains two enzymes needed for the virus to replicate and spread. The first enzyme reduces the body’s ability to mount an immune response against infection. The other enzyme helps “kick off” the replication process.

“We need to do everything we can to find effective drugs against the Zika virus, as changes in travel and climate have caused more tropical diseases to move into new parts of the globe,” said Kao, who has also spent 15 years studying the virus that causes hepatitis C.

“We’ve learned a lot of lessons about how to fight this class of virus through previous work on hepatitis C, as well as other work on the HIV/AIDS virus,” he added.

In addition, Kao said, the study showed that the Zika virus protein is similar in structure to proteins from viruses that cause dengue fever, West Nile virus, Japanese encephalitis virus and hepatitis C, which prompted the team to test several compounds that combat those diseases. The team also tested other compounds to disrupt the virus’s replication.

“Drugs approved to treat hepatitis C and compounds in development to treat other viral diseases are prime candidates to use against the Zika virus,” Kao said. “We’re continuing to work with industry partners to screen compounds for effectiveness against the NS5 protein.”

Other IU Bloomington authors on the study were Guanghui Yi and Yin-Chih Chuang in the Department of Molecular and Cellular Biochemistry and Robert C. Vaughan in the Department of Biology. Additional authors were Baoyu Zhao and Pingwei Li of Texas A&M University and Banumathi Sankaran at Lawrence Berkeley National Laboratory.

The method used to reproduce the virus protein in the lab is the subject of a U.S. patent application filed by the IU Research and Technology Corp.

The study appears in the journal Nature Communications. It was supported in part by the Johnson Center for Innovation and Translational Research at IU Bloomington.

How Prenatal Maternal Infections May Affect Genetic Factors in Autism Spectrum Disorder

Researchers find activation of maternal immune system during pregnancy disrupts expression of key genes and processes associated with autism and prenatal brain development

For some infections, such as Zika, the virus passes through the placenta and directly attacks the fetus. For others, such as the H1N1 influenza, the virus induces maternal immune activation (MIA) by triggering a woman’s immune system during pregnancy. Both Zika and MIA mechanisms may lead to potentially disastrous neurological repercussions for the unborn child, such as microcephaly (an undersized, underdeveloped brain and head) in the case of Zika or cortical abnormalities with excess numbers of neurons, patches of disorganized cortex, synapse mal-development and early brain overgrowth in some cases of MIA.

Large population-based studies suggest MIA caused by infection during pregnancy are also associated with small increases in risk for psychiatric disorders, including autism spectrum disorder (ASD). In a new study published today in Molecular Psychiatry, researchers at the University of California San Diego School of Medicine, University of Cyprus and Stanford University map the complex biological cascade caused by MIA: the expression of multiple genes involved in autism are turned up or down by MIA, affecting key aspects of prenatal brain development that may increase risk for atypical development later in life.

“We provide novel evidence that supports the link between prenatal infections and biology known to be important in the development of autism,” said senior author Tiziano Pramparo, PhD, associate research scientist at the Autism Center of Excellence at UC San Diego School of Medicine. “There are different routes of importance. We highlight a specific pathway that seems to be key in driving downstream early abnormal brain development.”

“Our work adds to growing evidence that prenatal development is an important window for understanding key biology of relevance to neurodevelopmental conditions like autism,” added lead author Michael Lombardo, PhD, at the University of Cyprus. “MIA is an environmental route of influence on fundamental biological processes important for brain development. The influence it exerts overlaps with key processes known to be important in how the brain in autism develops.”

Pramparo said the effects are not caused by the infectious agents themselves — virus or bacterium — but from the maternal immune response itself. “Although the mechanisms are not entirely known, it has to do with the cascade of altered events regulating production and function of neurons, their synapses and how they arrange themselves in the brain that are triggered when a mother’s immune system is activated.”

For example, increased levels of maternal cytokines (small signaling molecules driven by the immune response) may directly or indirectly alter gene expression in the fetus’ brain.

“These up- and down-regulated genes may lead to an excess or reduction in the normal amounts of proteins required for normal brain development,” Pramparo said. “Importantly, we have found that MIA-induced effects involve both single genes and pathways (many genes working in a coordinated way to serve some dedicated biological purpose) essential for early fetal neurodevelopment.” Among the large number of genes whose activity is altered by the maternal immune response, are a few that, when mutated, are thought to cause more genetic forms of autism in a small subset of all ASD toddlers.

Pramparo suggested the findings have multiple clinical implications.

“In general, the more we know and understand about a disrupted mechanism, the higher the chance of finding amenable targets for potential therapeutic intervention or for informing how to prevent such risk from occurring in the first place.”

Another implication, he said, is the potential to define the effects and clinical phenotypes based upon the underlying mechanisms: genetic, environmental or both.

“The MIA effects are transient but very potent during fetal development and perhaps even more potent than the effects induced by certain types of mutations in single gene forms of autism. Also, depending on when MIA occurs during gestation, the clinical characteristics may vary. The finding of MIA affecting the expression genes known to be important in autism supports the hypothesis that a genetic-by-environment interaction may lead to amplified effects at the clinical level. For example, more severe cases of autism.”

Cytomegalovirus Infection Relies On Human RNA-Binding Protein

Viruses hijack the molecular machinery in human cells to survive and replicate, often damaging those host cells in the process. Researchers at the University of California San Diego School of Medicine discovered that, for cytomegalovirus (CMV), this process relies on a human protein called CPEB1. The study, published October 24 inNature Structural and Molecular Biology, provides a potential new target for the development of CMV therapies.

“We found that CPEB1, one of a family of hundreds of RNA-binding proteins in the human genome, is important for establishing productive cytomegalovirus infections,” said senior author Gene Yeo, PhD, professor of cellular and molecular medicine at UC San Diego School of Medicine.

CMV is a virus that infects more than half of all adults by age 40, and stays for life. Most infected people are not aware that they have CMV because it rarely causes symptoms. However, CMV can cause serious health problems for people with compromised immune systems, or babies infected with the virus before birth. There are currently no treatments or vaccines for CMV.

In human cells, RNA is the genetic material that carries instructions from the DNA in a cell’s nucleus out to the cytoplasm, where molecular machinery uses those instructions to build proteins. CPEB1 is a human protein that normally binds RNAs that are destined to be translated into proteins.

Yeo’s team discovered that CPEB1 levels increase dramatically in human cells infected by CMV. Using genomics technologies, the researchers also found that increased CPEB1 levels in CMV-infected cells leads to abnormal processing of RNAs encoding thousands of human genes. In addition, they were surprised to find that CPEB1 was necessary for proper processing of viral RNAs. Without the host CPEB1 protein, viral RNA did not mature properly and the virus was weakened.

CMV-infected human cells undergo abnormal changes and produce more virus, which ultimately infects other cells. In collaboration with Deborah Spector, PhD, Distinguished Professor at UC San Diego School of Medicine and Skaggs School of Pharmacy and Pharmaceutical Sciences, the team went on to show that suppressing CPEB1 levels during CMV infection reversed these harmful cellular changes and reduced viral production tenfold.

“CPEB1 was previously shown to play a role in neuronal development and function, but this involvement in active viral infections is unexpected,” said first author Ranjan Batra, PhD, a postdoctoral fellow in Yeo’s lab. “This discovery has important implications for many viral infections.”

Yeo said the next steps are to determine the therapeutic value of inhibiting CPEB1 in CMV infections and identify other RNA-binding proteins that may be important in other viral infections.

Neurodevelopmental Model Of Zika May Provide Rapid Answers

A newly published study from researchers working in collaboration with the Regenerative Bioscience Center at the University of Georgia demonstrates fetal death and brain damage in early chick embryos similar to microcephaly—a rare birth defect linked to the Zika virus, now alarming health experts worldwide.

The team, led by Forrest Goodfellow, a graduate student in the UGA College of Agricultural and Environmental Sciences, developed a neurodevelopmental chick model that could mimic the effects of Zika on the first trimester. Historically, chick embryos have been extensively used as a model for human biology.

Early last spring, Goodfellow began inoculating chick embryos with a virus strain originally sourced from the Zika outbreak epicenter.

“We wanted a complete animal model, closely to that of a human, which would recapitulate the microcephaly phenotype,” said Goodfellow, who recently presented the findings at the Southern Translational Education and Research (STaR) Conference.

The RBC team, which included Melinda Brindley, an assistant professor of virology in the College of Veterinary Medicine, and Qun Zhao, associate professor of physics in the Franklin College of Arts and Sciences, suggests that the chick embryo provides a useful model to study the effects of Zika, in part because of its significant similarity to human fetal neurodevelopment and rapid embryonic process.

“Now we can look quickly, at greater numbers, to take a closer look at a multitude of different strains and possibly identify the critical window of susceptibility for Zika virus-induced birth defects,” said Brindley. “With this approach, we can continue to further design and test therapeutic efficacy.”
The challenge today is unpredictable disease outbreaks and how to ramp up process and production of therapeutic antibodies in preparation. Having an active pathogen threat like Zika that can jump across continents reinforces the need for therapeutic innovation.

Early stage chick embryos are readily available and low in cost, Goodfellow explained. Development within the egg (in ovo) provides an environment that can be easily accessed by high-speed automation. Poultry automation in the Southeast is impressive, and the industry is now using robotic technology, Goodfellow said.

“With egg injection automation and embryo viability technology, we could test tens of thousands of potential therapeutic compounds in a single day,” he said.
Since 2011, under the mentorship of Steven Stice, a Georgia Research Alliance Eminent Scholar and director of the Regenerative Bioscience Center, Goodfellow has worked extensively with eggs and chickens. In a previous project with Stice and Zhao, the team developed a unique approach of marrying stem cell biology and MRI to track and label neural stem cells.

“We knew we could look at the brain structure, shape and size with MRI, but what we captured was evidence that the infection caused MRI-visible damage, and the total brain volume was substantially smaller,” said Stice, faculty lead and principal investigator of the study. “From this finding, our data provides a rationale for targeting future therapeutic compounds in treating early-stage microcephaly to stop or slow the progress of the disease.”

UMN researchers find distinct differences in structure, features of retroviruses

In the most comprehensive study of its kind, researchers in the Institute for Molecular Virology and School of Dentistry at the University of Minnesota report that most types of retroviruses have distinct, non-identical virus structures.

Researchers analyzed seven different retroviruses including two types of HIV as well as HTLV-1, a virus that causes T-cell leukemia. They also examined retroviruses that infect birds, mice, chimpanzees and fish, that can cause cancer or immunodeficiency.

“Each kind of retrovirus has distinct structural features and each assembles virus particles differently,” said Louis Mansky, Ph.D., director of the Institute for Molecular Virology, who is also a member of the Masonic Cancer Center. “Most researchers assume that all retroviruses are just like HIV, but they’re not. We cannot take a one-size-fits-all approach when studying retroviruses and discovering new strategies for antiviral treatments or vaccines.”

Mansky’s team looked at the behavior of retrovirus Gag proteins, which drive retrovirus particle formation. Once the virus enters a cell, reverse transcriptase converts the viral RNA to DNA, which subsequently creates the Gag protein.

Understanding the nature of Gag protein interactions with one another and how the structures form will help scientists better understand how and why the virus works. It will also help identify ways to target the virus and prevent it from infecting a cell in the first place.

The study examined virus-like particle size, cellular distribution and basic morphological features through three distinct microscopy techniques.

The team noted that:

– HIV-1 and HIV-2 have Gag proteins that assemble retrovirus-like particles with distinct structures and sizes, which implies that differences exist in how the two HIV types form new virus particles. – HIV and HTLV-1 particles are quite distinct from one another in appearance, which also suggests fundamental differences in virus particle assembly.

“We found significant differences among the retroviruses,” said Jessica Martin, senior Ph.D. student in the Department of Pharmacology and lead author on the study. “A parallel comparative study evaluating retroviral Gag proteins and virus particle intermediates of this size and scope has never been done before.”

The team was surprised to find that one of the retroviruses, walleye dermal sarcoma virus (WDSV), did not readily produce virus particles.The disease can affect anything from 1-30 percent of walleye in a population, depending on the location. This research could help aquatic scientists better understand how to control the disease.

“Our study helps to highlight the importance of serendipity of basic science research,” Mansky said. “We set out to learn more about the differences among two important human retroviruses, namely HIV and HTLV, which we did, but our findings also shed light on important differences among all kinds of retroviruses that could inform not only the treatment of human viral diseases but could also impact aquatic health in fisheries.”

The study findings will help serve as a foundation for studying differences among retroviruses, including HIV.

“The scientific community can build off of our findings to develop new antiviral treatments, and hopefully determine how to stop these viruses from causing deadly diseases in humans such as cancer and AIDS,” Mansky said.

A New Way to Nip AIDS in the Bud

When new AIDS virus particles bud from an infected cell, an enzyme named protease activates to help the viruses mature and infect more cells. That’s why modern AIDS drugs control the disease by inhibiting protease.

Now, University of Utah researchers found a way to turn protease into a double-edged sword: They showed that if they delay the budding of new HIV particles, protease itself will destroy the virus instead of helping it spread. They say that might lead, in about a decade, to new kinds of AIDS drugs with fewer side effects.

“We could use the power of the protease itself to destroy the virus,” says virologist Saveez Saffarian, an associate professor of physics and astronomy at the University of Utah and senior author of the study released today by PLOS Pathogens, an online journal published by the Public Library of Science.

So-called cocktails or mixtures of protease inhibitors emerged in the 1990s and turned acquired immune deficiency syndrome into a chronic, manageable disease for people who can afford the medicines. But side effects include fat redistribution in the body, diarrhea, nausea, rash, stomach pain, liver toxicity, headache, diabetes and fever.

“They have secondary effects that hurt patients,” says Mourad Bendjennat, a research assistant professor of physics and astronomy and the study’s first author. “And the virus becomes resistant to the inhibitors. That’s why they use cocktails.”

Bendjennat adds that by discovering the molecular mechanism in which protease interacts with HIV, “we are developing a new approach that we believe may be very efficient in treating the spread of HIV.”

However, he and Saffarian emphasize the research is basic, and that it will be a decade before more research might develop the approach into news AIDS treatments.

Figuring out the role of protease in HIV budding

Inside a cell infected by HIV, new virus particles are constructed largely with a protein named Gag. Protease enzymes are incorporated into new viral particles as they are built, and are thought to be activated after the new particles “bud” out of infected cell and then break off from it.

The particles start to bud from the host cell in a saclike container called a vesicle, the neck of which eventually separates from the outer membrane of the infected cell. “Once the particles are released, the proteases are activated and the particles transform into mature HIV, which is infectious,” Saffarian says.

“There is an internal mechanism that dictates activation of the protease, which is not well understood,” he adds. “We found that if we slow the budding process, the protease activates while the HIV particle is still connected to the outer membrane of host [infected] cell. As a result, it chews out all the proteins inside the budding HIV particle, and those essential enzymes and proteins leak back into the host cell. The particle continues to bud out and release from the cell, but it is not infectious anymore because it doesn’t have the enzymes it needs to mature.”

Budding HIV needs ESCRTs

The scientists found they could slow HIV particles from budding out of cells by interfering with how they interact with proteins named ESCRTs (pronounced “escorts”), or “endosomal sorting complexes required for transport.”

ESCRTs are involved in helping pinch off budding HIV particles – essentially cutting them from the infected host cell.

Saffarian says scientific dogma long has held “that messing up the interactions of the virus with ESCRTs results in budding HIV particles permanently getting stuck on the host cell membrane instead of releasing.” Bendjennat says several studies in recent years indicated that the particles do get released, casting some doubt on the long held dogma.

The new study’s significance “is about the molecular mechanism: When the ESCRT machinery is altered, there is production of viruslike particles that are noninfectious,” he says. “This study explains the molecular mechanism of that.”

“We found HIV still releases even when early ESCRT interactions are intentionally compromised, however, with a delay,” Saffarian says. “They are stuck for a while and then they release. And by being stuck for a while, they lose their internal enzymes due to early protease activation and lose their infectivity.”

Bendjennat says by delaying virus budding and speeding “when the protease gets activated, we are now capable of using it to make new released viruses noninfectious”

How the research was done

The experiments used human skin cells grown in tissue culture. It already was known that new HIV particles assemble the same way whether the infected host cell is a skin cell, certain other cells or the T-cell white blood cell infected by the virus to cause AIDS. The experiments involved both live HIV and so-called viruslike particles.

Bendjennat and Saffarian genetically engineered mutant Gag proteins. A single HIV particle is made of some 2,000 Gag proteins and 120 copies of proteins known as Gag-Pol, as well as genetic information in the form of RNA. Pol includes protease, reverse transcriptase and integrase – the proteins HIV uses to replicate.

The mutant Gag proteins were designed to interact abnormally with two different ESCRT proteins, named ALIX and Tsg101.

A new HIV particle normally takes five minutes to release from an infected cell.

When the researchers interfered with ALIX, release was delayed 75 minutes, reducing by half the infectivity of the new virus particle. When the scientists interfered with Tsg101, release was delayed 10 hours and new HIV particles were not infectious.

The scientists also showed that how fast an HIV particle releases from an infected cell depends on how much enzyme cargo it carries in the form of Pol proteins. By interfering with ESCRT proteins during virus-release experiments with viruslike particles made only of Gag protein but none of the normal Pol enzymes, the 75-minute delay shrank to only 20 minutes, and the 10-hour delay shrank to only 50 minutes.

“When the cargo is large, the virus particle needs more help from the ESCRTs to release on a timely fashion,” Saffarian says.

Because HIV carries a large cargo, it depends on ESCRTs to release from an infected cell, so ESCRTs are good targets for drugs to delay release and let HIV proteases leak back into the host cell, making new HIV particles noninfectious, he says.

Bendjennat says other researchers already are looking for drugs to block ESCRT proteins in a way that would prevent the “neck” of the budding HIV particle from pinching off or closing, thus keeping it connected to the infected cell. But he says the same ESCRTs are needed for cell survival, so such drugs would be toxic.

Instead, the new study suggests the right approach is to use low-potency ESCRT-inhibiting drugs that delay HIV release instead of blocking it, rendering it noninfectious with fewer toxic side effects, he adds.