Harnessing HIV for Good

As a graduate student at the Weizmann Institute in 1967, Inder Verma set out to study mitochondrial RNA from animal cells. At the time, culturing cells was a challenge. "We had to go to the butcher to get blood, then separate serum to grow cells," he recalls. But Verma soon faced an even bigger problem. "In Israel, there were a lot of orange orchards, and they had a lot of fungi," he explains. "So every plate had this gigantic green fungus on it." Undaunted, Verma ground up all the material at hand and purified mitochondrial RNA - from the fungus. "It was a great piece of luck," says Verma, now at the Salk Institute for Biological Studies in La Jolla, Calif. No one had ever studied the properties of fungal mitochondrial RNA. "It was a very successful PhD. I had lots and lots of papers."

But more than luck, the story illustrates something about Verma's approach to science. "First, it calls into question his sterile technique," jokes former Verma postdoc Robert Marr of the Rosalind Franklin University of Medicine and Science in Chicago. Second, it reflects his tenacity. "He took lemons and made lemonade."

Even more importantly, the experience reflects Verma's ability to remain flexible in the face of unexpected results. "Inevitably there's some sort of weird surprise that comes out of every experiment," notes Fred Gage, Verma's colleague and collaborator at the Salk Institute. One type of scientist will ignore the anomaly; another will pursue it. "A third type says, 'Let me look at the options and make a judgment about which avenue is potentially most important to me,'" says Gage. "That person has to have the confidence to discriminate between staying the course and chasing a new finding that might lead in a direction that's more important."

Photograph by Marc L. Lieberman/Salk Institute

That fungus not only led Verma in important new directions, but also essentially launched his career. Backed by his impressive publication record, Verma landed a postdoctoral position with David Baltimore (who'd just moved to Massachusetts Institute of Technology) to work on reverse transcriptase (RT). Again, his career took an unexpected turn when one morning in the early 1970s, a visiting professor from Moscow mentioned that the globin mRNA he'd isolated could not be labeled at its 5' end. The researcher hypothesized that his failure to be able to modify the globin message was due to blockage of the 5' end by a stretch of polyA.

The observation got Verma wondering: was there really a string of As on the front end of mRNA? Back in the early '70s, no one knew the answer. But Verma realized he could use RT to find out. If he incubated the mRNA with an oligo dT primer and there were a polyA stretch at the 5' end, all he'd need to add to the reaction would be TTP, because RT would transcribe only the 5' end. "We did the experiment that afternoon," says Verma. And the results were clear: globin mRNA does not have a polyA cap at its 5' end. Verma had to add all four trinucleotides along with his oligo dT primer to get the reaction to go-suggesting that globin mRNA harbors a polyA sequence, but not at the 5' end. With these experiments, Verma not only determined that globin mRNA has a 3' polyA tail, but he became the first person to synthesize a full-length cDNA from an RNA message. The results not only confirmed that globin mRNA has a 3' polyA tail, but also Verma became the first person to synthesize a full-length cDNA from an RNA message. "Inder is very likely to do the kind of experiment that has elegance written all over it," notes David Livingston of the Dana-Farber Cancer Institute in Boston. "With an economy of experimentation, he's often able to derive a maximum of insight."

That elegant experiment, along with Verma's other accomplishments, paved his way to a faculty position at the Salk Institute at age 26. "It was really exciting to come to California," he says. "It was so different from Boston: Everybody was outside. There was sun. You could walk around in your shorts" - conditions that Verma takes advantage of to this day. "Inder is always in shorts," laughs postdoc Gerald Pao. "If you see him wearing long pants, you know something big is going on."

As a young investigator at Salk, Verma turned his attentions to cancer. In short order, his team discovered the retroviral oncogenes mos and fos, sorted out the connection between fos and jun, and in the 1980's began to explore how these genes can transform cells. And, he also started thinking about their packaging. If a retrovirus can inject these genes into mammalian cells, why not harness that ability to deliver therapeutic genes - for insulin, growth factor, Factors VIII and IX - to patients with diabetes, growth factor deficiencies, or hemophilia? And so the concept of gene therapy was born in the late 1980's.

But Verma wasn't satisfied yet. Retroviruses are not an ideal gene-therapy vector in that most don't infect nondividing cells such as those in liver, lung, and especially brain. For that capability, Verma turned to HIV. "HIV has learned to introduce genes in cells that are not dividing," he says. The question then became: "How can we hijack HIV's good properties to do the same for us without causing disease?" By eliminating HIV's ability to replicate (a feat accomplished in the mid '90's), Verma and his colleagues generated a vector that's now used worldwide for gene delivery.

Everyone in the 25-person Verma lab exploits these lentiviral HIV vectors in one way or another. In collaboration with the Gage group and with Eliezer Masliah and his lab at the University of California, San Diego, Marr used the system to administer genes that destroy or prevent the formation of the beta amyloid plaques that riddle the brains of people with Alzheimer disease. With the help of the lentiviral vector, in 2003 the researchers introduced the gene for neprilysin, an enzyme that digests amyloid peptide, into the brains of mice engineered to develop plaques. The treatment reduced the amount of neurodegeneration seen in these animals.

An even more promising therapy, says Marr, uses the lentiviral system to deliver an siRNA that knocks out the gene for β-secretase, an enzyme that helps drive the formation of the amyloid plaques. This therapy decreased plaque production and also slowed the cognitive decline experienced by these transgenic mice in a study published last year. "Inder thinks unconventionally," says Marr. Many people would have thought it "crazy to use HIV as a therapy tool," he says. "But it worked out very well. It's a landmark technological development."

The inspiration for the neprilysin study came from a tidbit that Gage heard at a meeting in Japan about the enzyme degrading β amyloid in the brain. Verma's pursuit of the project is a testament to his ability to use his connectedness to do good science, says Gerald Fink of the Whitehead Institute in Cambridge, Mass. "Inder always has his ear to the ground," says Fink. "He seems to know what's going on not only in the published literature and in unpublished work, but almost in the imagined work in everyone's lab."

Verma continues to focus heavily on cancer. Several people in his lab are exploring the role that NF-ΚB plays in inflammation and malignancy, and he and his colleagues are also attempting to unravel the activities of BRCA1 and BRCA2. In one study published in 2000, Verma's team found that BRCA1 associates with the molecular machinery responsible for repressing transcription. More recently, Verma's lab has found that BRCA1 appears to be involved in controlling proper brain development. Mice lacking BRCA1 in their neuroprogenitor cells were born with a cerebral cortex one-third the size of their unaltered peers. What's more, their brains showed a total lack of organization - a trait that, interestingly, resembles the undifferentiated appearance of cancer. The animals, Verma hopes, will shed light on how the brain is formed and how BRCA1 regulates differentiation.

Although he's still engaged by experimentation, Verma no longer works at the bench. "I'm the most useless person in the lab," he says. "I open doors when someone has two hands full."