FILE PHOTO: A sign is seen at an AstraZeneca site in Macclesfield, central England May 19, 2014. REUTERS/Phil Noble

LONDON (Reuters) - AstraZeneca AZN.L has taken another step to refocus on priority drugs by selling U.S. rights to a treatment for infant lung infections to Swedish Orphan Biovitrum SOBIV.ST for an upfront fee of $1.5 billion.

Around 130 AstraZeneca staff will transfer to Sobi as the Swedish company, widely known as Sobi, takes over marketing of the treatment Synagis in the United States.

The move is a significant commercial boost for rare diseases specialist Sobi, giving it a substantially increased U.S. footprint and expanding its business in immunology, and its shares jumped more than 6 percent.

“The addition of Synagis will become an important catalyst for Sobi’s future development and will form a powerful platform for growth in rare diseases,” said Chief Executive Guido Oelkers.

For AstraZeneca, whose stock gained 0.7 percent, it marks another step to streamline operations as it turns increasingly to a new batch of drugs - notably against cancer - to drive future growth.

Just last week AstraZeneca sold three older drugs for asthma and rhinitis to a small Swiss company for at least $350 million.

Sobi also gets the right to participate in AstraZeneca's share of U.S. profits and losses in a follow-on drug for respiratory syncytial virus, called MEDI8897, which AstraZeneca is developing with Sanofi SASY.PA, the companies said.

AstraZeneca will receive $1 billion in cash and $500 million in Sobi shares, equal to a stake of 8 percent in the Swedish group.

The British drugmaker is also entitled to further contingent payments. It will get up to $470 million in sales-related payments for Synagis, a $175 million milestone when MEDI8897 is filed for U.S. approval, and other potential payments related to the new drug of up to $170 million.