Schematic representation of key constructs in this study encoding the FM derived from the Sindbis virus glycoprotein, lentiviral transfer vector FUGW, membrane-bound human/mouse chimeric antibody against CD20 (αCD20), and accessory proteins for surface expression of antibody (Igαβ). CMV: human cytomegalovirus immediate-early gene promoter; E3: leader peptide of Sindbis virus glycoprotein; E1: E1 protein of the Sindbis virus glycoprotein for mediating fusion; E2: E2 protein of the Sindbis virus glycoprotein for binding to viral receptor; HA tag: 10-amino acid epitope hemagglutinin sequences (MYPYDVPDYA); Ubi: human ubiquitin-C promoter; GFP: green fluorescent protein; WPRE: woodchuck regulatory element; LTR: long-terminal repeat; ΔU3: U3 region with deletion to disable the transcriptional activity of integrated viral LTR promoter; EF1α: human elongation factor 1α promoter; αCD20κ and αCD20λ: light chain and heavy chain of human/mouse chimeric antibody against CD20; TM: human antibody transmembrane domain; Igα and Igβ: human antibody accessory proteins Igα and Igβ. For the FM constructs (SINmu, SGN, SGM and AGM), the amino acid sequences at E1 226 region are shown. The sequence starts at amino acid 225 and ends with amino acid 234 of the wild-type E1 protein. Specific amino acids involved in generating new FMs are shown underlined in bold.