Stories about: AIDS

Our T-cells have been hiding something: Another way to kill bacteria

Listeria intracellular bacteria infection T-cell immunity granzymes granulysins
Listeria bacteria on a plate. The biology of HIV/AIDS suggests T-cells have a hitherto unrecognized way of killing pathogens like these.

The immune system, despite its immense complexity, really has only a few ways to kill bacteria:

  • Neutrophils and macrophages can capture and digest extracellular bacteria (ones that live free in tissues and the bloodstream).
  • Peptides (protein fragments) can punch holes in bacterial membranes or cross the membranes to disrupt bacterial processes.
  • T-cells can kill cells infected by intracellular bacteria (ones that take up residence within cells).

It’s this last mechanism that I want you to pay attention to. The conventional wisdom has long held that T-cells can only kill intracellular bacteria indirectly by eliminating the cells they’ve infected. But a paper by Judy Lieberman, MD, PhD, of Boston Children’s Hospital’s Program in Cellular and Molecular Medicine, reveals that T-cells have a hitherto unnoticed way of directly killing intracellular bacteria And she only found it because of HIV/AIDS.

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First reported cure of a baby infected with HIV

HIV (green dots) budding from a white blood cell. (CDC)

AIDS and HIV have been with us for more than 30 years. In that time, millions have died and millions more have been able to keep the virus at bay with a cocktail of medications called highly active antiretroviral therapy, or HAART.

But of those millions, only one person has reportedly been cured. As of this week, that number may now be two.

A team of researchers at Johns Hopkins University Medical School reported at last weekend’s Conference on Retroviruses and Opportunistic Infections the case of a child believed to be born HIV-positive and who, by all available tests, is no longer carrying active virus in the blood.

The key, according to their report, was aggressive and near immediate HAART treatment, starting before the child was 30 hours old and continuing until she was a year and a half old.

“This finding is hopeful but requires further study,” says Sandra Burchett, MD, MSc, clinical director of our Division of Infectious Diseases and director of the Children’s Hospital AIDS Program. “We all agree that treating babies infected with HIV as soon as possible maintains a healthy immune system; what we do not know is when, if ever, it is safe to stop HAART. Treating adults early after infection is not curative, but it may be that babies are somehow different.

“It is critically important, though,” she cautions, “for children, youth and young adults with HIV who are on HAART now to keep taking their medications, not stop on their own to see if they too are cured.”

Some question, though, whether the child was ever actually infected. Her doctors started therapy so early because her mother had uncontrolled HIV, putting the child at extremely high risk of developing the infection herself.

The only other patient reportedly ever cured of HIV is a man named Timothy Ray Brown. In 2006, Brown received a bone marrow transplant for leukemia, but with a twist: the marrow donor had been chosen for harboring a rare genetic mutation that conferred resistance to HIV. According to a paper published in the New England Journal of Medicine in 2009, Brown has been off HAART treatment since 2007 with little to no sign of infection.

Want to learn more? Click here to read an online Q&A with Burchett hosted by The Guardian on March 5.

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HIV prevention: Could fatty particles protect women worldwide from AIDS?

These hollow particles seemed to work with minimal tweaking.

HIV vaccines are in their infancy, and effective microbicides to prevent sexual transmission of HIV still don’t exist. Women, making up nearly half of the world’s 33 million HIV cases, are especially in need of protection. Here’s a new possible way for women to protect themselves before sex: an applicator filled with specially formulated fatty particles called liposomes.

The tiny spheres measure 4 microns in diameter, not visible without a microscope, and consist of a double outer layer of lipids (fats) and hollow centers. They’re relatively easy and cheap to engineer, and thus present a viable option for developing countries, where the cost of anti-HIV drugs, while falling, still bars access for most people.

In tests reported online this month in the journal Biomaterials, liposomes inhibited HIV infection in cell culture and appeared safe in female mice when given intravaginally.

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Building an active barrier against HIV: Topical RNAi

A painting at the U.N. shows a condom over the world to limit the spread of HIV/AIDS. But what if we could find a longer-lasting, more reliable topical treatment? (Photo: Island Nimbus/Flickr)

This month marks an anniversary that no one wants to see: 30 years since the first paper describing what we know now as HIV/AIDS.

Over those three decades, more than 30 million people worldwide have died from the disease. We have learned a great deal – how HIV is passed from person to person, how long it circulated among humans before it was recognized, how to control it with antiretroviral drugs. Yet HIV still spreads: An additional 2.6 million people were infected with it in 2009 alone. Safe sex practices like condom use provide an effective barrier against passage of the virus, but don’t affect HIV’s ability to gain a foothold should the barrier fail.

Judy Lieberman and Lee Adam Wheeler want to move prevention beyond one-time physical blockades to longer-lasting, more reliable molecular resistance. “The current model of HIV transmission holds that the virus is localized to the genital tract for about a week,” says Lieberman, “which could provide a window of opportunity to intervene and prevent the infection from establishing itself throughout the body.”

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Blowing HIV’s cover

HIV-1 budding (in green) from a cultured lymphocyte. (Courtesy CDC)

HIV is unique among viruses in many ways. Here’s another: upon breaking into a cell, it erases evidence of its presence by exploiting a natural cellular “cleanup” mechanism. It thereby manages to dodge the innate immune system, the body’s first line of attack against invaders.

Investigators Judy Lieberman and Nan Yan, of the Program in Cellular and Molecular Medicine and the Immune Disease Institute, worked out how HIV does this and put together a counter-attack: disabling this cleanup mechanism.

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