ABSTRACT
A major problem in achieving effective immunotargeting is the poor tumor-toblood activity ratio which rarely reaches values sufficiently high to give effective radioimmunotherapy (RIT) or permit accurate diagnostic radioimmunoimaging (RII). This is of particular importance in RIT, where the toxic effect of conjugates on critical organs (marrow) is normally a limiting factor due to high absorbed doses from the relatively long circulation time of intact monoclonal antibodies (MAbs). Although MAb fragments such as Fab or F(ab′)2 are cleared more rapidly from the blood and penetrate more easily into solid tumors than the intact antibodies, most MAb fragments do not accumulate sufficiently in tumors to achieve the desired therapeutic effect (1).
