Albert Einstein College of Medicine of Yeshiva University
Dr. Jacobs is also a professor of microbiology and immunology and of molecular genetics at Albert Einstein College of Medicine.
Tuberculosis and Herpes: Persistent Infections of Man
Bill Jacobs wanted to be an astronomer, but a genetic eye disease prevents him from seeing the stars. His other interest, biology, seemed out of the question because he didn't think he could memorize all those facts. So he decided to major in mathematics when he went to the University of Pittsburgh in 1974. He also became an equipment manager for the football team, as in his high school days, when he was unable to play sports. But traveling with the team took so much time that he escaped to Edinboro State University, where he was lucky enough to take a course in microbial genetics from Ellis Kline. "By isolating mutants of E. coli, you could tell whether the bug wanted to eat a cheeseburger or a hamburger," Jacobs explains. "I said, 'This is what I want to do.'" He now studies one of the world's most dangerous bugs: the one that causes tuberculosis.
Jacobs didn't know much biology when he began graduate studies at the University of Alabama in Birmingham in 1979. But his math training had taught him to think logically about problems in the lab. "And one of my great strengths," he says, "was that I was so ignorant about biology that I was not afraid to ask simple questions."
Rotating through several labs, he encountered Roy Curtiss III and Josephine Clark-Curtiss, who were beginning to study leprosy. "I decided I wanted to work on problems affecting people in the developing world," Jacobs recalls.
Leprosy studies are frustrating because Mycobacterium leprae, the causative agent, grows only in humans, mouse footpads, and nine-banded armadillos. Moreover, its growth is painfully slow. So during the 6 years leading to his Ph.D., Jacobs isolated M. leprae DNA from cells of armadillos that had been injected with biopsies from Korean lepers 2 years earlier. Meanwhile, he learned a lot of molecular biology. He also was introduced to bacteriophages (viruses that infect bacteria), which have become invaluable tools in his research.
Jacobs moved to Albert Einstein College of Medicine in 1985 to become a postdoc with Barry Bloom, who was studying a related bacterium, Mycobacterium tuberculosis. At that time, the molecular targets of the common TB drugs were unknown. Also, it was unclear why BCG (bacille Calmette-Guérin), the live vaccine that had been given to more than 3 billion people by that time, usually did not cause disease. "We didn't know these things because we couldn't do genetics," Jacobs says. "We had mutants, we could clone genes, but we couldn't put the mutated genes back." In fact, not many people had tried because you need the highest-level biosafety lab to work on TB, which now kills 2−3 million people each year.
In 1987, Jacobs set up his own lab at Albert Einstein, a stone's throw from a former TB sanatorium. Taking a down-to-earth approach, he began to isolate mycobacterial phages from the dirt in his backyard. The first was Bxb1, the "Bronx Bomber," which is now featured in 13 publications. But his phage collection has grown over the years, thanks to high school students in his summer Phage Phinders program. To everyone's surprise, a phage scooped out of the Bronx Zoo's zebra pen was found to contain a gene related to one involved in lupus, a human autoimmune disease. "The full function of that gene is unknown," Jacobs says. "But having an organism that we can study it in will help us find out what it does."
Graham Hatfull, Jacobs's long-time collaborator and an HHMI professor, has spearheaded the sequencing of these mycobacteriophages. "I used to think the Bronx Zoo was cool because of all the animals," Jacobs says. "What is cooler still is all the microbes in the animals." He even recruited his twin sister, a high school biology teacher, to the cause. She's helping Hatfull run a No Phage Left Behind program for high school students at the University of Pittsburgh.
Jacobs used these phages to genetically manipulate mycobacteria. In the mid-1980s, he joined a circular piece of DNA (a plasmid) from E. coli to DNA from a mycobacterial phage to make a genetic tool he named "the shuttle phasmid." Because this hybrid DNA can replicate itself as a plasmid in E. coli and as a phage in Mycobacterium, it can shuttle genes from one to the other, including genes that have been inserted into E. coli in the lab. In 1987, on the day his daughter was born, Jacobs reported in Nature that he had introduced foreign DNA into Mycobacterium for the first time. "The concept of this shuttle phasmid was very important," he says, "because it opened up the door to genetic studies." Investigators around the world now routinely use shuttle phasmids to knock out mycobacterial genes.
A series of breakthroughs followed, including the isolation in 1990 of a mutant of rapidly growing (and therefore research-friendly) strain of Mycobacterium that was amenable to genetic manipulation, the expression of foreign proteins in BCG in 1991, and the incorporation of a luciferase gene into Mycobacterium in 1992. Luciferase is the firefly enzyme that generates bursts of light. By using the shuttle phasmid to transfer the gene into Mycobacterium, Jacobs developed a clever way to rapidly screen antimicrobial drugs. Luminescence indicates that Mycobacterium is still alive, whereas no luminescence shows that a drug has done its job.
One of Jacobs's most important findings was published in Science in 1994, when his group identified the target for isoniazid (one of the most highly prescribed drugs in the history of the world) and a related TB drug, ethionamide. They discovered that mutating a gene called inhA (needed for an early step in the synthesis of mycolic acid, a distinguishing feature of mycobacteria) made Mycobacterium resistant to isoniazid and ethionamide. Genetics made it possible to determine that these drugs must be activated by an enzyme before they target InhA. "We should be able to make drugs that target InhA without requiring activation," Jacobs says. "And we have some candidates already."
Collaboration with Jim Sacchettini, a crystallographer at Texas A&M; University, uncovered an unprecedented mechanism of drug action by demonstrating that isoniazid must covalently attach to a cofactor to become active. Sacchettini also determined the crystal structure of InhA protein and how it is bound by the cofactor attached to isoniazid. Therefore, researchers can now look for compounds that bind in a similar way. Subsequent genetic studies by the Jacobs group have shown that inactivating InhA halts the synthesis of mycolic acids, which can have as many as 80 carbon atoms. Because these acids are essential components of the mycobacterial cell wall, the cells burst open and die. By isolating a diverse set of mutants with defects in enzymes that modify mycolic acids, the Jacobs group has demonstrated that specific additions to these acids are essential for full virulence. Moreover, the recent isolation of a mutant whose mycolic acids have shorter than normal carbon chains has helped explain the basis for the key diagnostic test used to identify mycobacteria for the last 125 years.
Although isoniazid can kill 99.9 percent of M. tuberculosis in the first few days of therapy, the remaining organisms persist in the body, requiring patients to take a four-drug cocktail for at least six months. "Much of my passion now is to figure out a better way to kill these resistant bugs," Jacobs says. With Hatfull, he has created mycobacterial mutants that appear to have lost their drug resistance. One of these mutants was made in 2005 by integrating the Bronx Bomber into the bacterium's DNA. "We have to figure out what these hunkered-down bacteria are," Jacobs says. "At the end of the day, it will require genetics, genetics, and genetics."
Genetic studies in 2003 finally revealed the nature of BCG. When the researchers relieved Mycobacterium of the piece of DNA that BCG lacks, the bacterium could no longer secrete a protein that lyses cells. It was therefore less able to invade lung tissue. This explains why it is relatively safe to use live, weakened bacteria as a TB vaccine. However, BCG, which was isolated from cows in 1904 and introduced in 1922, consists of multiple strains of M. bovis. Jacobs wants to devise a safer and more effective vaccine, using attenuated M. tuberculosis. His group is currently experimenting with mutants that are unable to modulate the immune system and that have proved safer than BCG in immunocompromised mice. And compared with BCG, other mutants created by Jacobs and his collaborators have done a better job of priming the immune system and improving the survival of TB-infected mice.
Now that Jacobs can manipulate mycobacterial DNA at will, he's ready for new challenges. In 2006, Jacobs, Hatfull, and David Fidock (then at Albert Einstein) used the Bronx Bomber to improve genetic systems of Plasmodium, which causes malaria. One of Jacobs's major goals is to create a multipurpose vaccine by putting genes from Plasmodium and HIV into M. tuberculosis. Jacobs and Bloom conceived this idea in 1987, when Jacobs was a postdoc.
As Jacobs launches his malarial genetics program, improving global health is still very much on his mind. In fact, his office door displays a quote by Margaret Mead, whom he met when he was in the ninth grade: "Never doubt that a small group of dedicated people can change the world. Indeed, it is the only thing that ever has."