To determine the roles of membrane associated IFITM3 in BCR-signalling in B-cell malignancies we expressed N-terminal BirA-IFITM3-Y20E fusion or BirA-EV control in patient derived B-ALL cells (PDX2) and Jeko1 Mantle cell lymphoma (MCL) cells. Additionally to examine the role of PIP3 binding residues in the conserved intracellular loop region a K83A/K104A mutated form of IFITM3-Y20E-BirA fusion and compared with basic patch unmutated.