- axl, a transforming gene isolated from primary human myeloid leukemia cells, encodes a novel receptor tyrosine kinase. O'Bryan, J.P., Frye, R.A., Cogswell, P.C., Neubauer, A., Kitch, B., Prokop, C., Espinosa, R., Le Beau, M.M., Earp, H.S., Liu, E.T. Mol. Cell. Biol. (1991)