conjugates were significantly more effective in inhibiting 

 specific tumor cell processes. These conjugates represent 

 a considerable improvement over those previously discussed 

 in that their synthesis is a result of the interaction of 

 a single reactive group on daunomycin with the immunoglo- 

 bulin. This results in well defined covalent conjugates 

 that retain the targeting specificity of the immunoglobulin. 

 The primary disadvantage to their use as chemotherapeutic 

 agents is that they interact with DNA rather than a critical 

 enzyme required for macromolecular replication, transcrip- 

 tion or translation and would thus require much larger doses 

 to achieve a given cytotoxic effect. This presents a signi- 

 ficant problem in view of the fact that the inhibitors will 

 act on normal as well as neoplastic cells with potentially 

 detrimental side effects. 



Conjugates of diphtheria toxin and immunoglobulins 

 directed against cell surface antigens have proven to be 

 selective as well as effectively cytotoxic. When coupled 

 to immunoglobulin with specificity directed against mumps 

 virus infected monkey kidney cells, the diphtheria toxin 

 conjugates were selectively toxic to virally infected 

 cultures (Moolten and Cooperband, 1970). Other conjugates 

 of diphtheria toxin and anti-DNP antibodies exhibited selec- 

 tive toxicity in vivo against hapten (DNP) coated tumor 

 cells in hamsters (Moolten et al., 1972). Hamster lymphoma 

 growth was effectively suppressed by conjugates of diph- 

 theria toxin and antibodies prepared against SV-40 



