Mutations in calreticulin (mutCALR) are the second most common drivers of myeloproliferative neoplasms (MPNs) and yet, the current therapeutic landscape lacks a selective agent for mutCALR-expressing MPNs. Here we show that the monoclonal antibody INCA033989 selectively targets mutCALR-positive cells. INCA033989 antagonized mutCALR-driven signaling and proliferation in engineered cell lines and primary CD34+ cells from patients with MPN. No antibody binding or functional activity was observed …