The SCF-Moloney chimeric envelope binds to the SCF receptor, Kit. Binding assays were performed on both Kit-positive (HMC-1) and Kit-negative (Jurkat) human cell lines using unmodified Moloney and 4070A envelopes and the SCFXMo chimeric envelope. The fine line represents Moloney binding (negative control), the dashed line, 4070A binding (positive control), the thick line, SCFXMo binding, and the dotted line, SCFXMo binding in the presence of exogenous rHuSCF. SCFXMo binds only to the Kit-positive cell line and the binding is competitively inhibited by the addition of rHuSCF.