Fab dimers of antitumor immunoglobulins as covalent carriers of daunomycin.

Fab dimers were prepared by pepsin digestion from the immunoglobulin fraction of a rabbit antiserum towards the Yac Moloney virus lymphoma cells. Daunomycin was attatched to these (Fab)2 by covalent binding. The resultant conjugates exerted pharmacological toxic activity and specificity towards Yac target cells similar to that observed previously with conjugates of intact anti-Yac IgG. The activity was manifested both in vitro by inhibition of RNA synthesis and by the effect of reduction of the growth of the tumor cells in vivo after short exposure to the conjugates. The potential advantage of using an IgG molecule devoid of its Fc portion is discussed.