John L. LaMattina, former president of Pfizer's global research and development, said the company had oncology research sites in three states until a 2006 reorganization slimmed the number to one, in California.

"Oncology research for AstraZeneca is at least partially handled at MedImmune," said LaMattina, now senior partner at PureTech, a venture creation firm in Boston. "Will Pfizer decide to keep that group intact … or will they want to consolidate on the West Coast? I don't know. They could decide to keep both groups. But there will be project overlap."

Albert Wertheimer, a pharmacy economics professor at Temple University in Philadelphia, thinks MedImmune would be pretty safe. Its pipeline is a future "cash cow," he said, and Pfizer couldn't continue that work elsewhere easily because leaders there have less experience running a biotech firm.

But Pfizer does have a history of buying companies for the products and laying off much of the workforce, he said. When Pfizer struck a deal to buy Wyeth in 2009, its announced plans to lay off nearly 20,000 workers — 15 percent of the combined workforce.

"Pfizer has been just relentless in taking whatever piece they really want and then just getting rid of the rest," Wertheimer said.

And Pfizer's jobs pledge to the United Kingdom — that 20 percent of its global research and development jobs would be based in that country for at least five years — makes some nervous that the ax will swing more widely in the United States.

"I'm not sitting here saying that we can become more efficient without some reduction in jobs," Read acknowledged to British leaders, according to the Guardian newspaper. "We'll be more efficient by some reduction in jobs. What I can't tell you is how much or how many or where."

Rep. John Delaney, a Democrat whose district includes both AstraZeneca facilities, was among the congressional members who sent a letter to Pfizer on Monday. His staffers have heard from anxious MedImmune employees.

"People are concerned," he said. "MedImmune is an incredibly important company."

He said he's also troubled that the deal is driven in part by Pfizer's desire to reincorporate as a British company and avoid the United States' higher tax rate, a tactic known as inversion. Delaney, a former banker, thinks the deal wouldn't be so attractive to Pfizer if the U.S. didn't require companies to pay the full rate on money earned — and taxed — overseas.

"Pfizer probably has lots of good reasons to buy AstraZeneca from a strategic standpoint, but they'd be using an inversion technique … because our tax code is flawed," he said.

'Affected us in many ways'

At least some closed Pfizer research facilities in other states are seeing reuse. But the replacement doesn't always bring as many jobs as were lost, or the same types of positions. And it can take years.

In South Brunswick, N.J., the 450-employee research center Pfizer shut after its 2009 purchase of Wyeth is being renovated to become a data center.

"It's a lot of high-tech guys managing this, but I think you're only talking 50 to 100 people," said Bernard Hvozdovic, South Brunswick's township manager. "Now they're talking about bringing in a customer-service thing separately; they're talking about more jobs there."

In Chazy, N.Y., local officials saved a former Wyeth research facility from demolition two years ago after it was closed by Pfizer. It too is in renovations now. A container-liner manufacturer agreed to move 22 jobs there, leaving lots of space on the 55-acre property for other companies the town hopes will come.

The 300-employee research lab was the largest employer in the town of 4,300, and its loss sent ripples through the community, said Town Supervisor Mark R. Henry. People moved. The school lost students. Tax collections took a hit.

"It's affected us in many ways," he said.

Ann Arbor, Mich., lost a much bigger operation — Pfizer's 2,100-worker global research facility. The announcement in 2007 came as a shock, said Skip Simms, senior vice president at Ann Arbor SPARK, that region's economic development organization.

The community jumped into action.

Groups helped Pfizer employees start their own companies, connected others with jobs and transformed one of the buildings into a life sciences incubator — now full. The University of Michigan bought the rest of the campus. And Pfizer equipment, donated to Ann Arbor SPARK, is in the hands of local startups.

"We just needed to make lemonade," Simms said. "And we did."

In Maryland, officials would much rather skip the lemons. They want to hold on to the biotech that's a key part of a sector they have such high hopes for.

"Sometimes we feel that the state has invested huge amounts in research but that we've failed to turn those research discoveries into products," BioMaryland's Britz said. "MedImmune is an example of a company where that has occurred."