The Gaithersburg company is Maryland’s largest biotech, with $1.3 billion in revenues for 2006 and 2,500 employees, with about half in Maryland.

The deal comes just weeks after another Gaithersburg biotech, BioVeris Corp., announced it plans to sell most of its assets to Swiss drugmaker Roche for $600 million.

MedImmune may be best known for its nasal flu vaccine, called FluMist, but its biggest money-maker, by far, is Synagis, which helps prevent respiratory infections in babies.

The MedImmune deal is an indication of the recent maturity of Maryland biotechs into late clinical stages of drug candidates, according to industry observers.

‘‘Clearly, this is a threshold for our local industry, and paves the way for other companies to grow in a similar manner,” said John Holaday, co-founder and chairman of HarVest Bank of Maryland in Rockville and a founding partner of Montgomery Pacific Group.

Linda Powers, managing director of Toucan Capital in Bethesda, welcomed the news.

‘‘I think it is terrific,” Powers said. ‘‘It makes MedImmune that much more of a success story. I think it is a milestone for biotech in the region. Medimmune has been the big anchor and now for them to get a big buyout that completes the cycle and will bring a lot of attention to our region.”

‘‘The value of this company is clearly invested in its intellectual property, the employees and its facilities. MedImmune’s facilities here are state-of-the-art,” said David W. Edgerley, secretary of Maryland’s Department of Business and Economic Development and former head of economic development in Montgomery County.

A key provision of the purchase agreement is to ‘‘retain MedImmune employees and its culture,” said Emily Denney, an AstraZeneca spokeswoman, who did not elaborate.

MedImmune spokeswoman Jamie Lacey called the deal ‘‘great” for the company, the stockholders and ‘‘our patients.”

The agreement calls for David M. Mott, CEO of MedImmune, to assume a ‘‘high-level position” with AstraZeneca, reporting directly to CEO David Brennan, Denney said. She said James F. Young, MedImmune president of research and development, has also committed to remain with the company, as have other members of MedImmune’s senior management.

‘‘The potential to harness the combined skills and capabilities of MedImmune, AstraZeneca and [Cambridge Antibody Technology, recently purchased by AstraZeneca] and take our combined world-class biologics capabilities to the next level is very exciting and a challenge to which I am personally committed,” Mott said in a statement.

After the deal closes, AstraZeneca will provide MedImmune employees a ‘‘one-time retention grant,” stipulating salary and other compensation, Denney said.

MedImmune will keep its name and remain headquartered in Gaithersburg, Denney said. The company’s recent commitments to build manufacturing plants in Frederick was another key to the agreement, which is expected to close in June.

The company’s $250 million expansion project in Frederick, which will mean 250 additional employees — on top of the 216 there now — ‘‘as far as I know is still on track and moving forward,” said Richard Griffin, director of Frederick’s Office of Economic Development.

‘‘We’re looking forward to continue working with AstraZeneca on the expansion project. We’re working toward completing the construction phase,” Griffin said.

‘‘The manufacturing part of the package was very attractive to us,” Denney said. ‘‘Let me remind you that manufacturing biologics is a new area for us and this suggests that we want to retain the talent and value there.”

Heather Gramm, business development specialist for the city of Frederick, said the deal is a plus for the city.

‘‘We’re always happy when local companies become successful,” Gramm said. ‘‘We’ll have to wait and see what actually happens, but we expect the company to continue to grow and prosper.”

State and countyloans and grants

Less than five years ago, MedImmune broke ground on its 450,000-square-foot headquarters it recently completed in Gaithersburg. At the time, it was given a $5 million grant from Maryland’s Sunny Day Fund and a $500,000 loan from the Montgomery County Department of Economic Development.

MedImmune has received $11.8 million in state funds since 1996, according to James Henry, managing director for finance programs for DBED.

Henry said DBED is also working with a Maryland legislative committee for an additional $7.5 million loan for a multi-phase expansion of the company’s manufacturing plant in Frederick.

Besides the MedImmune and BioVeris deals, BioReliance, an early and prominent Maryland biotech, was involved in a recent acquisition. The company was purchased in 2004 by Invitrogen Corp. of San Diego, which this month sold the unit to Avista Capital Partners for $210 million.

‘‘The maturation of any life sciences company to the point where premiums are paid in recognition of value added is always a plus,” Holaday said.

‘‘Both BioReliance and MedImmune achieved that status by being acquired in lucrative relationships that hopefully will build on the momentum for Maryland life sciences companies,” he said.

The MedImmune sale comes after complaints from influential stockholders over what they perceived as MedImmune’s disappointing stock performance in the past year. The company announced on April 12 that it had retained Wall Street investment banking firm Goldman Sachs & Co. to help entertain suitors.

AstraZeneca — makers of the cholesterol drug Crestor and the stomach acid treatment Nexium — reported first-quarter sales of $6.97 billion, an increase of 13 percent over the same quarter in 2006. Revenues in 2006 were $26.48 billion.

The purchase of the Gaithersburg biotech would allow the giant British pharmaceutical company to accelerate its stated ambition of producing more biologics — drugs produced from living organisms.

Acquiring MedImmune is also the British company’s first entry into vaccine production, Denney said. MedImmune controls a patented technology used by Merck in its new vaccine against human papillomavirus, some strains of which can cause cervical cancer.

MedImmune is recognized as a leading producer of biologics, including FluMist, and is one of the world’s top 10 biopharmaceutical companies by equity. It has 45 research and development projects, including seven monoclonal antibody-based treatments and five vaccines in development.

MedImmune Inc.

Employees: 2,500 worldwide, about half in Maryland

CEO: David M. Mott

Founder: Wayne T. Hockmeyer in 1987 as Molecular Vaccines Inc.

Products on market: Synagis for infant lung infections; Ethyol to reduce toxic effects of cancer treatments; and nasal spray flu vaccine FluMist.

Revenues:$1,267.8 billion, 2006$1,243.9 billion, 2005

Net income (loss):$48.7 million, 2006$(16.6) million, 2005

Headquarters: Gaithersburg.

Other locations: Frederick, Pennsylvania, California, Kentucky, the United Kingdom, the Netherlands.

Bioscience Acquistions

Some recent deals involving Maryland bioscience companies:

April 2007: MedImmune Inc. of Gaithersburg to be acquired by AstraZeneca Plc of London for $15.2 billion.

April 2007: BioVeris Corp. of Gaithersburg announced selling most of its assets to Swiss drugmaker Roche for $600 million.

April 2007: The remaining unit of BioReliance sold to Avisita Capital Partners for $210 million by Invitrogen Corp. of San Diego, which had purchased BioReliance in Rockville in 2004.

June 2006: Celera Genomics of Rockville, a subsidiary of Applera of Norwalk, Conn., sold its small-molecule drug program to German pharmaceutical giant Schering AG for a potential $360 million.

September 2006: GeneDx Inc. of Gaithersburg purchased by Bio-Reference Laboratories of Elmwood Park, N.J., for $17 million.

September 2000: Life Technologies Inc. of Rockville purchased by Invitrogen for $400 million.