Dynamics of antibody transport and internalization

By following the interaction of labelled anti-tumor antibodies with target cells, it was found that in most systems cross-linking of externally bound antibody by anti-IgG leads to nearly complete internalization, whereas excess unlabelled antibody induces fast release of radioactivity from the cell. Uptake in tumor tissue did not depend on presentation of antigen at the cell surface, as demonstrated with antibody RA96 directed against an intra- and inter-cellular antigen. With respect to permeation into solid tissue, autoradiography revealed highly non-homogeneous distribution of intact IgG, while antibody fragments tended to show a more homogeneous penetration. Small spontaneous metastases showed markedly higher accumulation than large tumor processes.