Johnson & Johnson agreed to buy Momenta Pharmaceuticals Inc. for about $6.5 billion to expand in treatments for autoimmune diseases.

The deal involves an all-cash tender offer of $52.50 per Momenta share, J&J said in a statement. The offer is 70% more than the target’s closing price on Tuesday. The Cambridge, Massachusetts-based company’s shares had gained about 56% this year.

The transaction will help its Janssen Pharmaceutical unit broaden its leadership in immune-mediated diseases, J&J said, and includes full global rights to Momenta’s experimental drug nipocalimab. Momenta received positive news on the drug in June when it hit its main goal in a phase 2 trial as a treatment for myasthenia gravis, an autoimmune neuromuscular disorder.

The purchase follows French drugmaker Sanofi’s deal earlier this week to acquire U.S. biotech company Principia Biopharma Inc. for about $3.4 billion. That all-cash agreement gave Sanofi treatments for multiple sclerosis and a range of autoimmune disorders.

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