Johnson & Johnson (NYSE:JNJ) announced today that it entered into an agreement to purchase Momenta Pharmaceuticals (NSDQ:MNTA) for $6.5 billion.

New Brunswick, N.J.-based Johnson & Johnson will stump up the $6.5 billion in an all-cash transaction for the developer of novel therapies for immune-mediated diseases, according to a news release.

Momenta felt the full effect of the news of the acquisition breaking, as shares of MNTA were trading up 69.2% at $52.13 per share in late-afternoon trading today.

The acquisition is seen by Johnson & Johnson as an opportunity for its Janssen Pharmaceutical subsidiary to broaden its work in immune-mediated disease and drive growth through expansion into autoantibody-driven diseases.

Included in the acquisition are the full global rights to Momenta’s nipocalimab (M281) anti-FcRn antibody, for which Janssen plans to pursue indications across autoimmune diseases with unmet medical needs in maternal-fetal disorders, neuro-inflammatory disorders, rheumatology, dermatology and autoimmune hematology. Janssen expects many first-in-class indications for nipocalimab, with the potential for significant peak year sales that could exceed $1 billion.

Janssen will also acquire Momenta’s pipeline of clinical and pre-clinical assets and the company’s employees, along with nipocalimab. The company intends to retain Momenta’s Cambridge, Mass. facility to expand its footprint in the growing Boston medtech hub.

“This acquisition broadens Janssen’s leadership in autoimmune diseases and provides us with a major catalyst for sustained growth,” Johnson & Johnson executive VP & worldwide chairman of pharmaceuticals Jennifer Taubert said in the release. “Autoantibody-driven diseases are often serious, and patients are underserved by current treatment options. We’re excited by the opportunity to further advance patient care by combining Johnson & Johnson’s world-class R&D, commercial and supply chain capabilities with Momenta’s talented people, pipeline and deep expertise in this important area.”