Andrew Badley, M.D., works at both ends of the broad avenue that makes Mayo Clinic research available to patients. At one end, he treats patients with HIV infection, and patients with infections after transplantation. At the other, he wends his way through HIV's cellular killing fields searching for ways to stop the virus from wielding its murder weapon.

"Many infections cause disease by killing a variety of cells in your body," says Dr. Badley. "In the majority of HIV cases the virus causes a certain subset of lymphocytes to die. Our research focuses on understanding the mechanisms by which that happens."

In 1994, when Dr. Badley began studying cell death in HIV, scientists recognized only one method that the virus used to kill T cells—it breached the cell and replicated causing the cell to explode. Since then it is the HIV field that has exploded. Dr. Badley recently edited the first book on how HIV kills T cells—it contains 28 chapters concerning the methods used by the virus to kill cells.

"Studying HIV is complex and difficult," says Dr. Badley. "You can test an HIV patient and see that their cells are dying but, since HIV is known to kill in many different ways, you can only find out which of those stimuli is responsible by taking one molecule at a time and investigating how specific inhibitors change the process."

Collision Course: A Man and a Virus on Opposing Missions

Dr. Badley is attempting to describe the role of a particular protein—HIV protease—in the killing process. Dr. Badley's group has demonstrated that protease expression inside a cell can independently cause cell death. The next step is to track the molecular pathways involved in the death of those cells with an eye to constructing roadblocks on the pathways, thus preventing cell death.

"It's early days yet but we have good evidence that HIV protease can kill, and good evidence that it kills through a classical caspase-dependent pathway," says Dr. Badley. "We have some early evidence to suggest the location of the cleavage site within procaspase 8. Now we're taking that new cleavage fragment and trying to figure out how it activates the signaling pathways."

Caspases are a family of enzymes that cause cell death by essentially digesting structures within the cell's cytoplasm. Procaspase 8 is the particular caspase that interacts with protease. HIV protease controls the cleavage of proteins required to generate viral particles. The site where this occurs is called a cleavage site.

Dr. Badley's group has furthered the understanding of classical viral genetics through their discoveries.

"In studies done in other labs, mice that were induced to overproduce HIV protease in specific organs, developed tissue injury," explains Dr Badley. "We think the death process of the organ is due to the caspase 8-dependent cell death pathway."

The Protease Roadblock: A Promising Therapy for Other Diseases

For eight years, Dr. Badley has been investigating HIV protease inhibitors—a class of HIV drugs that interrupt the ability of HIV to reproduce. He hypothesizes that the drugs could have intrinsic effects on cell survival, even in cells that are not infected with HIV.

"It's one of the things I'm passionate about," says Dr. Badley. "We've been able to show that they can block cell death signaling pathways whether HIV is involved or not. So that raises the possibility of using this class of drugs as therapeutic agents for non-HIV disease states."

Based upon their observation that protease inhibitors block apoptosis, Dr. Badley is collaborating with experts in diseases characterized by excessive apoptosis.

"We've looked at it in mouse models of liver and neurological disease and sepsis," says Dr. Badley. "Our animal studies suggest that protease inhibitors can have benefits in all of these disease states."

Sepsis spreads through excessive apoptosis of lymphatic cells. When in vitro studies demonstrated that protease inhibitors prevent apoptosis, Dr. Badley collaborated with James Steckelberg, M.D., and a colleague from the University of Ottawa, Canada to study their effect on animal models. Their research (FASEB J. 2004 Aug; 18(11):1185-91) demonstrated the potential for protease inhibitors as a candidate for treating sepsis in humans because of its action of inhibiting apoptosis in vital organs.

"In the animal model, we can improve survival from 20 percent to 70 percent," reports Dr. Badley. "By comparison, the only licensed agent for treatment of sepsis in humans reduces mortality by only six percent and is much more expensive."

Critical care specialists, Rolf Hubmayr, M.D. and Bekele Affessa, M.D., are collaborating with Dr. Badley in a clinical trial to determine the effect of protease inhibitors in sepsis—a leading cause of death in intensive care units.

Dr. Badley is also collaborating with liver disease expert Gregory Gores, M.D., who is researching the role of death receptors in liver cell apoptosis, and with Stacey Vlahakis, M.D., who researches how HIV and hepatitis C virus interact in causing liver disease.

Dr. Badley and his Canadian collaborators came a step closer to the development of protease inhibitors as a treatment for some non-HIV diseases in a recent paper (Journal of Clinical Investigation, July 1st, 2005). Their study evaluated apoptotic changes in a variety of animal models.

"We are pleased with the results of our experiments with animal models of disease states that are associated with excessive apoptosis," says Dr. Badley. "Our data supports the good news that treatment with these drugs prevents rather than delays death—and it does so without toxicity. In addition, the knowledge that we gained about the mechanisms involved in the process will help us move this potential treatment to a level where it can help patients."

What Can We Learn From HIV Survivors?

One of the curiosities of HIV is that five or more percent of patients have Longterm Non-progressive HIV. In other words, they live with the replicating virus but don't die from it. In the course of many years of studying how HIV infection causes cells to die, Dr. Badley's group suspected that this subset of patients had abnormalities of the programmed cell death response. They decided to look closely at a Vpr gene associated with the HIV virus because it was known to play a role in apoptosis.

Dr. Badley's lab engineered HIV virus and tested two versions—the normal, or wild type Vpr and the mutated Vpr. Then they infected cultured cells grown in laboratory glassware with the two strains and noted that the mutated virus did not kill as well as the wild type.

"We tested the hypothesis and found that this subset of patients have a mutation on the Vpr gene that impairs the cell-killing mechanism of the HIV virus and preserves the T cells."

Their study (Journal of Clinical Investigation, 2003) compared survival rates of T cells in mice treated with Vpr containing the mutation and those treated with normal Vpr. The mutant-Vpr mice suffered significantly less T-cell death. That left them with greater T cell reserves for fighting the opportunistic infections. By comparison, mice treated with normal Vpr had reduced T cell number--a characteristic of AIDS.

Dr. Badley hypothesizes that a greater understanding of the role of the mutant gene and its products could lead to new AIDS therapies, and that developing Vpr inhibitors might reduce immune-system cell death.

Novel treatment approaches and strategies toward HIV disease are tested in Mayo's multi-disciplinary HIV clinic. Members of the HIV Clinic conduct clinical trials for new drugs as standard therapy or for people who have developed resistance to the standard therapy.

TRAILing the Holy Grail of HIV Research

Being able to selectively kill cells that harbor HIV is one of the holy grails of HIV research. Dr. Badley's group took a giant step when, in 2001, they accomplished the feat in a test tube. The experiment used a cloned apoptosis-inducing protein called TRAIL (TNF-related apoptosis-inducing ligand). In the study, which took place in Dr. Badley's native Canada, investigators took cells from HIV patients and exposed them to TRAIL in a test tube. The results were rewarding—cells that contained HIV died while HIV-negative cells lived.

The usual next step in the research process is animal testing. However, the progression to animal studies is difficult to accomplish because there are no good animal models for HIV. Macaque monkeys infected with a fusion virus between simian immunodeficiency virus (SIV) and HIV are useful but prohibitively expensive. Dr. Badley is collaborating with Peter Wettstein, Ph.D. on developing a mouse model that has no immune system. Such a model could be implanted with human lymphocytes and infected with HIV.

Hard Work—Rich Rewards

Dr. Badley is quick to point out that research success requires a dedicated and motivated team of students, fellows, technicians, and research associates.

"I am fortunate to be able to work with very talented and hardworking lab mates," says Dr. Badley. "Our lab successes are the result of group effort."

While Dr. Badley knows that being a researcher means long hours including nights and weekends, he is easily energized by the rare "wow, we-might-have-stumbled-onto-something moments."

"There's safe research and then there's let's-go-out-on-a-limb research," he says. "Good days are absolutely wonderful—you've learned something and you're a step ahead of where you were. But every potential breakthrough is followed up repeat experiments with added controls and you have to have both luck and funding to get results."

Related Research

Basic cancer researcher, Scott Kaufmann, M.D., Ph.D., who studies the mechanism by which anticancer agents induce apoptosis in susceptible cancer cells, is collaborating with Dr. Badley on a new immunotherapeutic approach for HIV.

Liver and GI investigator, Nicholas LaRusso, M.D. and Dr. Badley share an interest in how particular micro-organisms cause host-cell damage. While Dr. Badley is interested in HIV and lymphocytes, Dr. LaRusso has a particular interest in the role of an organism called Cryptosporidium parvum in promoting apoptosis in bile duct cells.

Eric Poeschla, M.D., uses his background as an infectious disease specialist to develop gene therapy vectors from retroviruses—basic research that also furthers the understanding of HIV virology.