Dr. Stone’s group at the MGH has identified several new disease associations with IgG4-RD, including lymphoplasmacytic thoracic aortitis, eosinophilic angiocentric fibrosis, and Riedel’s thyroiditis, and identified the concept that IgG4-RD is a form of vasculitis. His group made the novel observation that B cell depletion leads to swift, targeted declines in serum IgG4 concentrations and dramatic clinical improvement, culminating in a New England Journal of Medicine publication in 2024 and the approval of an anti-CD19 approach to treatment this year – the first drug approved for the treatment of IgG4-RD.