The role of multivalency in antibody mediated liposome targeting

We have investigated the role of multivalency in immunoliposome binding to cells displaying different amounts of surface antigen using k liposomes with increasing numbers of palmitoyl anti-H2K^k antibodies incorporated into the bilayer. The application of increasing numbers of palmitoyl antibody causes a regular increase in immunoliposome binding to mouse L-929 cells, beyond an apparent threshold of 12 Ab/liposome. RDM-4 lymphoma cells were treated with proteinase k to generate a series of cells with various amounts of H2K^k antigen. Binding percent of immunoliposomes was related to the number of antigens displayed by RDM-4 cell. Again, increasing liposome binding was observed with increasing number of antibody molecules per liposome. However, the ratio of binding of the high-antigen-density cells to that of the low-antigen-density cells was higher with immunoliposomes of lower antibody density than the ones with higher antibody density. This result suggests that for a better discrimination between cells differing in antigen density, liposomes with lower, but above threshold, number of antibody molecules per liposome may be more useful than those with a larger number of antibody molecules.