Alexion Pharmaceuticals Inc. has completed its acquisition of Syntimmune.

The Boston-based company announced the completion of the deal Friday. Syntimmune is a clinical-stage biotechnology company developing antibody therapeutics targeting the neonatal Fc receptor (FcRn).

“We’ve made significant progress rebuilding our pipeline this year, and the acquisition of Syntimmune is another critical step in continuing to expand and diversify our portfolio,” Ludwig Hantson, Ph.D. and CEO of Alexion, said in a statement. “We’re very excited to continue the development of SYNT001, which we believe holds great promise in transforming patient care across a number of rare IgG-mediated diseases. We are rapidly advancing the current development programs and look forward to beginning two pivotal programs next year, including one in warm autoimmune hemolytic anemia.”

Under the terms of the previously announced agreement, Alexion will acquire Syntimmune for an upfront payment of $400 million, with the potential for additional milestone-dependent payments of up to $800 million for a total value of up to $1.2 billion.

The transaction is expected to close in this quarter and Alexion intends to finance the acquisition through cash on hand.

Alexion announced at the end of 2017 that it would move its headquarters from New Haven to Boston, bringing 400 corporate and research jobs and filling the remaining office and lab space in Boston’s Seaport District. The company did, however, retain approximately 450 jobs in its New Haven office, primarily in its R&D, clinical supply and quality teams, nurse case management and enterprise business services.