Researchers at Georgetown University Medical Center (GUMC) have successfully tested a genetic strategy designed to improve treatment of human infections caused by the yeast Candida albicans, ranging from diaper rash, vaginitis, oral infections (or thrush which is common in HIV/AIDS patients), as well as invasive, blood-borne and life-threatening diseases.Their findings confirm that inhibiting a key protein could provide a new drug target against the yeast, which inhabits the mucous membranes of most humans. The research was presented today at the 48th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy/46th Annual Meeting of the Infectious Diseases Society of America (ICAAC/IDSA) in Washington, DC.

“This is a genetically intelligent approach to target identification and drug design,” says the study’s lead author, Richard Calderone, PhD, professor and chair of the department of microbiology and immunology and co-director of the PhD program in the global infectious disease program at GUMC.

“Candida infections are often treatable, however, in patients that are immunocompromised following cancer chemotherapy, bone marrow transplantation, or surgery, diagnosis is often delayed, postponing therapy,” he says. “Also when drug-resistant yeast pathogens cause the infection, clinical management of the patient becomes a problem.”

Candida invasive, blood-borne infections are the fourth most common hospital-acquired infection in the United States, costing the healthcare system about $1.8 billion each year, Calderone says.

“More drug resistance is being seen clinically, so there is significant room for improvement in the therapies used today,” he says

This study continues research in which Calderone and his colleagues identified a protein, the product of the Ssk1 gene that Candida needs to infect its host. To date, this protein has not been found in humans or in animals, which means it could be “targeted” with a novel drug without producing toxicity because such an agent should only attack the fungus.

The researchers found that if the Ssk1 gene is deleted from Candida albicans, the “triazole” drugs that are now used to treat these diseases are much more effective in the laboratory. “This allows the triazole drugs to do their job,” Calderone says. “We propose that this finding might lead to other, possibly more effective, treatment options.”

In this study, the researchers used a gene microarray analysis to further understand what knocking out the Ssk1 gene does to the organism, and they discovered that the gene is critical to the pathogenic nature of the fungi.

What this means is that an Ssk1 inhibitor might work in synergy with a triazole or perhaps as an effective stand-alone drug to treat Candida infections, the researchers say. If it works in Candida, it may have broader activity in other pathogens because Ssk1p is found in other fungi.

“Using the genome of the organism to find genes to target is a logical approach to drug design,” he says. The researchers are now working with other groups to find the right agent to target the Ssk1protein.

A new study looking at unprotected intercourse within gay couples when each partner has established HIV-infection found a correlation between anti-HIV immune response and sexual activity.

Study results showed that individuals who had regular unprotected receptive anal intercourse with partners with significant levels of HIV in their blood showed a stronger anti-HIV immune response. In addition, the magnitude of anti-HIV specific immune response correlated with their exposure to HIV through sex.

Published in the October 24th, 2008 issue of PLoS Pathogens, the study paper is authored by a research team from UCSF and the Gladstone Institute for Virology and Immunology.

The researchers found no evidence of systemic superinfection (re-infection with another strain of HIV) in the receptive partners, whose virus had been successfully suppressed through antiretroviral therapy for at least five months. In a comparison group of HIV-infected couples in which both partners’ viruses had been suppressed by therapy, researchers did not find the same strength of immune responses correlations or the same correlations with sexual exposure.

“We found HIV-specific immune responses in the treatment-suppressed partners that correlated with the level and route of exposure. The individuals with no detectable virus who were on antiretroviral therapy and who were exposed to HIV through receptive intercourse with a partner with detectable virus, had the stronger anti-HIV immune responses in comparison to individuals exposed to partners whose virus was also suppressed by antiretroviral therapy, where no effect was seen,” said study lead author, Christian B. Willberg, PhD, post-doctoral fellow in the UCSF Division of Experimental Medicine.

Notwithstanding the intriguing HIV specific findings, the findings also reveal an important general mechanism occurring in infectious diseases.

“We found that immune responses to chronic viral infections are influenced not only by the chronic infection existing in an individual or host, but also by exposures to exogenous virus from outside the individual or host,” said study co-senior author, Douglas F. Nixon, MD, PhD, professor of medicine in the UCSF Division of Experimental Medicine.

The investigators were unable to determine from these findings whether there is any benefit from this type of repeated exposure to HIV—i.e., a type of therapeutic vaccination for HIV-infected patients with suppressed virus. Some HIV patients on antiretroviral regimens lose many of their HIV-specific immune responses over time due to the successful suppression of viral replication by therapy.

“Indeed, our hypothesis had been that in the context of these waning anti-HIV responses among the suppressed partners and the expected level of exposure from repeated unprotected receptive intercourse, we would find evidence of superinfection. While we did not find systemic super-infection, we cannot exclude limited or localized superinfections in the gut. And, antiretroviral therapy may have been the factor that prevented superinfection in these patients,” said study co-senior author Robert M. Grant, MD, MPH, senior investigator at the Gladstone Institute of Virology and Immunology and associate professor of medicine at UCSF.

The study involved 49 HIV-infected gay men from the San Francisco Positive Partners Program study—a cohort of couples in which both partners are HIV-positive that began enrolling participants in 2000. Viral suppression in this study meant viral loads less than 50 copies. Among those participants whose virus had not been suppressed, the lowest viral load was 9,420 copies.

The team that designed this study benefited from its unique multidisciplinary composition. Immunologists working with social researchers were able to design a study that managed to distinguish between different levels of viral suppression and different patterns of sexual contacts and correlate the immunological aspects with the behavioral variables.

“We call the interaction between these two scientific communities together: ’social immunology’. It may be true that patterns of social activities shape immune responses generally, as we observed for people with HIV having contact with other HIV infected persons. Obviously more study is needed and we would like to see whether social immunology will continue to offer important insights,” said Grant.

“While we have not found a case of superinfection in our cohort of chronically infected HIV couples, a handful of cases of superinfection verified by linkage to a known partner’s virus have been reported in chronically infected HIV patients. It is also important to stress, these findings do not address the negative consequences of acquiring other sexually transmitted diseases through engaging in unprotected sex or the potentially positive consequences that unprotected sex may have in partnerships where both individuals are HIV-positive,” said study co-author, J. Jeff McConnell, MA, director of the Positive Partners study at the Gladstone Institute for Virology and Immunology.

Among many global health challenges, infectious diseases remain among the most problematic, accounting for about one quarter of all deaths globally, and nearly two-thirds of deaths in sub-Saharan Africa. Dr. Fauci will discuss progress–and remaining challenges–in the fight against major infectious causes of death and disability such as HIV/AIDS, malaria, tuberculosis and drug-resistant microbes. He also will discuss how conceptual and technological progress in fields such as genomics and nanotechnology has invigorated infectious disease research. These advances also are contributing to exciting studies on the ecology of human disease, including the Human Microbiome Project, which is exploring how the billions of bacteria that inhabit our bodies contribute to health and illness.

Other NIAID scientists are scheduled to present findings during the four-day meeting as well. The range of topics covered reflects the broad scope of NIAID’s research efforts aimed at better understanding, treating and preventing infectious and immune-mediated diseases.

• Noroviruses, the highly contagious viruses that cause the episodes of acute gastroenteritis also known as winter vomiting disease (Kim Green, Ph.D.)
• The role of gut-dwelling commensal bacteria in producing the symptoms of Crohn’s disease, a chronic inflammatory disease of the intestines (Warren Strober, M.D.)
• Antibiotic-resistant bacterial infections caused by Staphylococcus epidermidis (Michael Otto, Ph.D.) and Staphylococcus aureus (Frank DeLeo, Ph.D.)
• Finding ways to treat primary immunodeficiencies, inherited conditions in which immune function is impaired (Steve Holland, M.D.)
• Containing Ebola virus, for which there is currently no vaccine or specific treatment (Gary Nabel, M.D., Ph.D.)

A surprising interaction may enable development of new HIV treatment strategies by exploiting infection with multiple pathogens.  The research, published by Cell Press in the September 11th issue of the journal Cell Host and Microbe, demonstrates that a drug commonly used to treat herpes directly suppresses HIV in coinfected tissues and thus may be beneficial for patients infected with both viruses.

Commonly, individuals infected with HIV are infected also with other microbes.  Infection with human herpesvirus (HHV), especially with herpes simplex virus-2 (HSV-2), is often associated with HIV.  These HHV infections may be either active or dormant, but HIV infection makes HHV reactivation more likely.

For many years, acyclovir (ACV), a well-studied drug, has been used safely to treat HHV in humans.  “HHV has a unique ability to phosphorylate ACV to activate it, making the drug quite specific for HHV and, for the same reason, relatively non-active against other viruses, including HIV,” offers senior study author Dr. Leonid Margolis from the National Institute of Health.  Nevertheless, some patients coinfected with HIV and HSV-2 exhibit lower HIV levels after ACV treatment.

“We decided to investigate this phenomenon experimentally using small blocks of human tissues” says Dr. Margolis.  “Drs.  Andrea Lisco and Christophe Vanpouille who performed this work in my laboratory found that although ACV doesn’t inhibit HIV in ’sterile’ cell lines, it does, surprisingly, suppress HIV in tissues that carry no HSV-2 but various other HHVs.”  In collaboration with a prominent AIDS researcher Dr. Raymond Schinazi from Emory University and Dr. Matthias Gotte from McGill University, the researchers found that phosphorylated ACV that is formed in HHV-infected cells directly inhibits the HIV-1 reverse transcriptase (RT), thus preventing HIV from copying itself.

These results not only help to explain the response to ACV seen in patients coinfected with HSV-2 and HIV, but also suggest that ACV may be used against HIV in patients infected with various other HHVs, including the low-pathogenic and ubiquitous HHV-6 and HHV-7.  Moreover, in collaboration with Drs.  Balzarini from Catholic University of Leuven and McGuigan from Cardiff University, Dr. Margolis and his team demonstrated that new strategies for development of novel HIV inhibitors based on ACV structure can now be developed.  “We provide definitive experimental evidence of inhibition of HIV-1 RT activity by phosphorylated ACV and demonstrate that ACV phosphorylation occurring in human tissues infected by various HHVs transforms this widely-used inexpensive anti-herpes drug into a direct HIV inhibitor,” concludes Dr. Margolis.

Yeast fungus cells that kill thousands of AIDS patients every year escape detection by our bodies’ defences by hiding inside our own defence cells, and hitch a ride through our systems before attacking and spreading, scientists heard today (Tuesday 9 September 2008) at the Society for General Microbiology’s Autumn meeting being held this week at Trinity College, Dublin.

Cells of the Cryptococcus yeast responsible for one of the three most life-threatening infections that commonly attack HIV infected patients, causing cryptococcal meningitis, are using a previously unknown way to avoid detection, according to scientists from the University of Birmingham, UK.

“We have shown that these airborne yeast cells can hide inside our bodies’ own white blood cells, called macrophages, and then use them as vehicles to travel around inside our bodies, using them just like a bus,” said Miss Hansong Ma of the University of Birmingham.  “The yeast cells then escape from inside the macrophages when they arrive at the right destination – but importantly, they do this without killing the macrophage, which would trigger alarm bells.”

When a host’s cells are invaded by bacteria, fungi or viruses the invaders usually use the opportunity to multiply inside the cells and escape by bursting out, killing the host and releasing thousands of copies of the pathogen to attack other cells.  The death of the host cell releases debris and by-products which usually triggers our bodies into mounting an immune response, causing inflammation.

“This new method of remaining inside the host cells means that the pathogen can spread more efficiently round our bodies and is protected from the natural defences in our bloodstream that would normally kill the yeast or other invader,” said Hansong Ma.  “Yeast cells avoid killing or damaging the macrophages.  They leave by a method that we call ‘vomocytosis’; the yeast cells are acting like spies rather than terrorists, and go unnoticed, giving them more time to establish an infection.”

Although the use of antiretroviral drugs is cutting the number of AIDS patients with Cryptococcus infections there is still a major epidemic in Southeast Asia and Africa.  Up to 30% of AIDS patients there are infected, and up to 44% will die from the disease within 8 weeks.  Even in the USA or European countries like France where antiretroviral drug treatments are readily available, one in ten infected patients will die.

“We badly need to better understand the interaction between hosts, viruses and attacking pathogens like the yeast fungus to help us find new drug targets and so design new ways to treat these patients,” said Hansong Ma.

“We used time-lapse microscope photography to identify this new escape mechanism, and watched the yeast cells escaping into the fluid surrounding cells or, remarkably, directly into other host cells through cell-to-cell transmission, continuing to avoid detection by using this extremely rapid vomocytosis,” said Hansong Ma.  “Worryingly, this enables the cryptococci to avoid antifungal drugs and other treatments as well as our normal immune system, and may allow the yeast to become latent, achieving a long-term infectious state which could then be spread even further, to other individuals, without anyone realising.”

Soon after an individual becomes infected with HIV the virus infects cells in the brain and spinal cord (the central nervous system [CNS]).  Although this causes no immediate problems, during the late-stages of disease it can cause dementia and encephalitis (acute inflammation of the brain that can cause death).  Monkeys infected with a relative of HIV (SIV) also sometimes develop CNS damage and provide a good model of CNS disease in individuals infected with HIV.  Insight into the mechanisms of CNS damage in SIV-infected monkeys has now been provided by a team of researchers at The Scripps Research Institute, La Jolla, who developed an approach to identify molecular changes in the fluid bathing the CNS (the CSF).  The researchers, who were led by Howard Fox and Gary Siuzdak, hope that similar approaches could be used to provide new information about other neurodegenerative and neuropsychiatric disorders.

In the study, an approach known as global metabolomics was used to assess the levels of molecules known as metabolites in the CSF before and after SIV-induced encephalitis was manifest.  The level of a number of metabolites, including some known as fatty acids and phospholipids, was observed to increase during infection.  Consistent with this, a protein known to be important in the generation of fatty acids was found to be increased in the brain of monkeys with SIV-induced encephalitis.  Further studies will be required to determine the precise role of the increased level of each metabolite, but it should be noted that many of them are known to induce receptor signaling and thereby might be able to further modulate CNS function.