Producing antibodies directed against a surface antigen of a drug-resistant form of a native tumor comprises immunizing animals with a cell homogenate, suspension or lysate derived from the resistant tumor and selecting antibodies that recognize the resistant tumor but not the native tumor. Independent claims are also included for: (1) a monoclonal antibody (I) produced as above； (2) a murine hybridoma capable of secreting (I)； (3) nucleic acid (II) coding for (I) or hybridizing with a sequence coding for a complementarity-determining region, light chain or heavy chain of (I)； (4) vector containing (II)； (5) host cell containing the vector； (6) nonhuman transgenic animal comprising a cell transformed with the vector； (7) producing (I) by culturing a cell as above； (8) identifying therapeutic or diagnostic targets involved in drug resistance by producing an antibody as above and identifying the protein recognized by the antibody. ACTIVITY : Cytostatic. MECHANISM OF ACTION : Passive immunization.
