CELL-SURFACE LOCALIZATION AND DENSITY OF THE TUMOR-ASSOCIATED VARIANTOF THE EPIDERMAL GROWTH-FACTOR RECEPTOR, EGFRVIII

The potential of therapeutic targeting of tumor cell surface epidermal growth factor receptors (EGFRs) by modified ligands or specific antib odies has been limited by the normal tissue distribution of the recept or. The identification and characterization of a variant of this recep tor, EGFR-vIII, which is not expressed in normal tissues but has been described in gliomas, non-small cell lung carcinomas, and breast carci nomas, has provided a highly specific, internalizing target for antibo dy-mediated approaches. To determine the feasibility of immunotargetin g EGFRvIII, we have assessed the qualitative distribution and quantita tive expression at both the population and cellular levels of EGFRvIII in 21 biopsy samples of human gliomas by indirect analytical and quan titative flow cytometry and by immunohistochemical assay of frozen and formalin-fixed tissue. Consistent with previous reports, 50% of gliom as tested (1 of 2 anaplastic astrocytomas, 7 of 12 glioblastoma multif orme, and 2 of 6 oligodendrogliomas) expressed EGFRvIII, as determined by a minimum of 2 separate assays. Minimum estimates of the proportio n of positive tumor cells in these populations ranged from 37-86%; in four of five cases in which quantitation of the EGFRvIII density, cell was performed, values of 2.7-6.8 X 10(5) were obtained with monoclona l antibody (mAb) L8A4 (EGFRvIII specific), levels consistent with succ essful in vivo immunotargeting. Confocal microscopic analysis confirme d that the subcellular localization of EGFRvIII was identical to that described for EGFR: predominant cell membrane expression, with some pe rinuclear distribution suggestive of localization to the Golgi region. Neither EGFR nor EGFRvIII was found within the nucleus. This study es tablishes for the first time that approximately 50% of human glioma bi opsies contain cell populations expressing a sufficient number of memb rane-expressed EGFRvIIIs to mediate specific: anti-EGFRvIII mAb locali zation. Coupled with previous demonstrations of the rapid internalizat ion of specific mAb-EGFRvIII complexes and the susceptibility of the t argeted cells to isotope or toxin-mediated cytotoxicity, this study es tablishes the validity of targeting EGFRvIII for therapy of mutant rec eptor-positive gliomas, breast carcinomas, and non-small cell lung car cinomas.