A nationwide dearth of research monkeys has forced vaccine researchers at Harvard to scale back their studies, potentially compromising their rate of discovery, according to scientists.

The supply of research monkeys has been increasingly unable to meet the rapidly increasing demand over the past few years, making large-scale primate research projects difficult to organize and expensive to maintain.

And so many researchers have had to curtail their work to focus on more limited and specific questions than they might otherwise address.

“We have to design the experiments very carefully because of the lack of monkeys and their cost,” said Harvard Medical School (HMS) Associate Professor Judy Lieberman, who is part of a group researching an oral AIDS vaccine. “Because of that, they don’t answer all the questions you might have.”

HMS researcher R. Paul Johnson is conducting a study on how various vaccines affect the localization of T-cells to mucosal surfaces—an path of inquiry important in discovering a successful vaccine for mucosally-centered diseases such as AIDS. He planned his research to employ about 10 monkeys—enough to answer only one sort of question.

“I’ll be able to accomplish over the next three to five years the research I’m planning to do, but I think its more a case that the experiments have not been designed optimally because of the shortage,” he said. “As a result, we’re having to address these questions piecemeal.”

More test subjects would have allowed him to undertake a more comprehensive, multivariate study of vaccine effectiveness, he said.

The shortage centers on rhesus macaque monkeys, which are used in more than half of primate research projects across the nation, according to Ronald C. Desrosiers, who directs of the New England Primate Research Center (NEPRC), which is part of HMS. Researchers favor rhesus monkeys for disease treatments tests because of their biological similarity to humans.

“You can get some guidance from small animals like mice, but experience has shown that attributes don’t transfer well,” Lieberman explained. Before applying research to humans, most disease treatment researchers refine their work through primate study.

Her project, planned on a larger scale than Johnson’s, requires 86 monkeys at the Yerkes Regional Primate Research Center in Atlanta, Ga. But the study attempts only to determine whether test vaccines effective in preventing the virus.

Should she and her colleagues wish to explore their results even a bit further—such as to determine whether the test vaccines also offer effective treatment—they would need more monkeys, she explained.

Acquiring the necessary number of animals would be exceedingly difficult in the face of the shortage and the price increase it has yielded.

Rhesus monkeys presently cost $5,000 each to purchase, she said, and care during research contributes considerably to the overall cost of a primate study. Purchasing the dozens of monkeys for her present study would not have been possible without a hefty research grant, she said.

Finding such funding—and acquiring animals in a tight market—has stymied several similar studies, she said.

“It’s a very common problem for people who are developing new therapies and new vaccine,” she said. “It’s a combination of the availability of the animals plus the high cost of the experiments.”