By David N. Leff

Annual influenza vaccination is highly recommended, especially for high-risk groups, in particular the elderly. Flu shots are cheap, often free. Yet surprisingly few people take advantage of immunization against the virus of influenza.

"The percentage of flu vaccine used is quite low," observed vaccinologist De-chu Tang, at the University of Alabama, Birmingham, "because most people don't want to go to a clinic to get a shot."

He and his colleagues in the university's gene therapy program are perfecting a technique to get around this needle-shyness. They call it "democratic vaccination."

Tang is lead author of a brief article in the current issue of Nature, dated Aug. 21, 1997, titled: "Vaccination onto bare skin."

Its rationale, which they are now putting to the test, Tang told BioWorld Today, "makes biological sense, because skin is the border, the natural barrier, between the host and its environment. That's where all the immune surveillance mechanisms are."

Despite this fact, he pointed out, "Medical personnel have been injecting vaccines underneath the epidermis for many, many years, bypassing the border where the tissue is most immunocompetent."

Tang and his co-authors now show that a single drop of an antigen gene sequence coupled to an adenoviral vector, deposited on a mouse's skin, can deliver immunity in the same ballpark as an injection by needle.

Mice Wake Up Vaccinated

The team put 25 mice to sleep under a light anesthetic, so they would hold still during the experimental procedure. Then they shaved a patch of their abdomen and removed hair stubble and exfoliating cornified epithelium with an over the counter depilatory cream.

Onto this denuded skin surface the Alabamans pipetted recombinant adenovirus vectors encoding the human carcinoembryonic antigen (CEA) gene, in 10 to 50 microliters of buffer fluid. By the time the animals woke up, 30 to 60 minutes later, the outermost layer of their epidermis had absorbed this gene delivery package.

"With CEA," Tang said, "it worked amazingly well, in fact, better than conventional injection."

Specifically, 24 of the 25 vaccinated rodents (96 percent) produced antibody to the CEA after one month, as assayed by serum from tail-bleeds.

A second trial, which delivered the gene for human granulocyte macrophage colony-stimulating factor (GM-CSF), yielded antibody in six of 14 mice (43 percent). "They are possibly less immunogenically potent," Tang suggested, "than CEA." However, sera from three kinds of controls — collected before treatment, from untreated animals and an irrelevant gene, all failed to react with the GM-CSF proteins.

With a view toward human trials, and because adenoviruses provoke immune reactions, Tang and his group are "working up plasmid-DNA vectors right now in [Escherichia] coli host cells, independent of adenovirus. Plasmids are cheaper to produce than viral vectors," he pointed out, "though their expression efficiency is lower than the virals." But, he observed, "People would probably favor plasmids, because they'd think of them as being non-infectious, unlike a virus."

He continued: "In addition, the low efficiency might not matter, because all we need to do is express the antigen in immune cells of the skin. We're testing those hypotheses right now."

The university has already filed a patent application on the technology.

The Alabama vaccinologists envision their bare-skin immunization as "increasing the percentage of vaccination greatly" — hence, "democratic."

Tang foresees "a vaccine kit sold over the counter, to be applied by individuals without medical training or the equivalent. Virtually, housewives will be able to vaccinate their children at home. Also," he pointed out, "it would be very useful for developing countries. They don't have enough vaccines anyhow."

He plans to begin with an influenza vaccine, "because the flu vaccine is already available. Merck has come out with a nuclear protein, which can protect people against a wide variety of flu-virus strains."

"We were the first," Tang pointed out, "to develop a DNA vaccine, as we reported in Nature in 1992 (356:152-154). Today it's a big research field," he observed. "Every vaccine lab is now trying to try DNA vaccines and protein vaccines."

But initial human trials of the bare-skin vaccination are a year or two in the future, Tang predicted, because "the standard procedure for getting an IND [investigational new drug] permit means we have to go over a mountain of paperwork. That's something we can't change. But as soon as FDA turns on the green light, we think the experiment can proceed very quickly."

Needle-Shy Cattle Are Candidates For Skin Shots

But casual conversation with some farmer friends has opened up a possible unexpected escape hatch for Tang and his team.

"Some people in the animal industry," he recounted, "have told us that it's very difficult to inject vaccines into cattle. It takes a very special skill and a lot of effort to give them a shot. So they wondered if we could develop a bovine skin vaccine, to be administered on the back of the ear. That would reduce the cost to industry."

Tang surmised that it would also reduce his paperwork, "because cattle regulations, I am sure, are less stringent than for human vaccines." He foresees a collaboration with farmers "in which we'd provide the technique; they'd provide the disease models."

Meanwhile, Tang concluded, "We are open to collaboration. Anybody who has a disease model they think would be appropriate for applying this technology, please contact us." *