In vitro and in vivo targeting of radiolabeled monovalent and divalent haptens with dual specificity monoclonal antibody conjugates: enhanced divalent hapten affinity for cell-bound antibody conjugate.

A method of pretargeted immunolocalization of a mouse cell subset, using dual specificity monoclonal antibody conjugates and labeled divalent haptens, is described. Conjugates were prepared by coupling F(ab')2 fragments of an antibody specific for the allelic mouse B cell antigen Lyb8.2, to Fab' fragments of an anti-2,4-dinitrophenyl antibody. Divalent and monovalent haptens were obtained by coupling dinitrophenyl to peptides or to diethylene-triamine-pentaacetic acid. In vitro, divalent haptens bind with higher affinity to mouse spleen lymphocyte-bound than to excess soluble conjugate (affinity enhancement). In vivo, localization of 125I- or 111In-labeled divalent haptens in mouse spleen is much higher than that of the monovalent analogs. Thus, using divalent haptens, a new kind of specificity to target cells was achieved, suggesting that affinity enhancement may improve target to background ratios in radioimmunoscintigraphy.