Human Genome Sciences

(HGSI)

said Tuesday the

Food and Drug Administration

had granted it exclusive U.S marketing rights for seven years for the drug,

BlyS

, which is used to treat Common Variable Immunodeficiency.

The drug, currently used in human clinical trials, has received the FDA's orphan drug designation, which, in addition to granting exclusive marketing rights, allows the company to apply for research funding, tax credits and a waiver from the FDA's application user fee, the company said.

The designation has previously been associated with biopharmaceuticals such as

Avonex

for multiple sclerosis.

Common Variable Immunodeficiency is one of a group of disorders that are characterized by increased susceptibility to infection. BLyS is a protein made by the human body that stimulates the production of antibodies that help defend the body against viruses and bacteria. BLyS is currently in an on-going Phase I clinical study.

Shares of Human Genome Sciences fell $2.44, or 4.4%, to $53.38 in recent

Nasdaq

trading.