Johnson & Johnson is acquiring Momenta Pharmaceuticals in a $6.5 billion deal that brings the pharma giant a slate of experimental autoimmune disease therapies, including a potential blockbuster antibody drug in late-stage development for a rare type of anemia. Momenta develops treatments for diseases driven by autoantibodies – antibodies produced by the immune system that spark dozens of rare autoimmune disorders. The Cambridge, Massachusetts-based biotech’s lead drug candidate, nipocalimab, is in a pivotal clinical trial testing it in warm autoimmune hemolytic anemia…