(Reuters) -Danish drugmaker Novo Nordisk and Omeros ( OMER ) have signed a licensing deal worth up to $2.1 billion for the U.S.-based company's experimental drug, which is being developed for rare blood and kidney disorders, they said on Wednesday.

As part of the agreement, Novo gains exclusive global rights to develop and commercialize Omeros' ( OMER ) drug zaltenibart, designed to inhibit MASP-3 - a protein that acts as a key activator of the alternative pathway of complement.

The complement pathway is a system of proteins in the blood that enhances the immune system's ability to fight infections.

Omeros ( OMER ) is eligible to receive up to a total of $2.1 billion, including $340 million upfront and near-term milestone payments.

The company had said in March it began enrollment for late-stage trials studying the drug for paroxysmal nocturnal hemoglobinuria (PNH), a rare blood disorder in which part of the immune system attacks and damages the red blood cells and platelets.

Zaltenibart has shown several potential advantages over other alternative pathway inhibitors currently in development or on the market, the companies said.

The drug was safe and well tolerated in the trials.

After the deal closes, expected in the fourth quarter of 2025, Novo aims to start a global program for zaltenibart in PNH and explore development in a range of other rare blood and kidney disorders.

Omeros ( OMER ) remains focused on securing approval for its other experimental drug, narsoplimab, this quarter.

The company is pursuing approval for narsoplimab in the U.S. and in Europe to treat transplant-associated thrombotic microangiopathy, a complication that can arise after hematopoietic cell transplantation.

Omeros ( OMER ) also retains certain rights to its preclinical MASP-3 programs unrelated to zaltenibart, including the ability to develop and commercialize small-molecule MASP-3 inhibitors with limited indication restrictions.