Relationship between antigen density and immunotherapeutic response elicited by monoclonal antibodies against solid tumors.

The relationship between the level of cell surface antigen expression and solid tumor immunotherapy with monoclonal antibody (MoAb) was evaluated. Two MoAb's that were shown effective in the passive therapy of breast carcinomas of human origin, established and growing in female Swiss nude mice, were used for these studies. Several groups of tumors were produced from cell cultures of different passages; each cell culture possessed a distinct target antigen level. Results from immunotherapy experiments demonstrated that the amount of tumor reduction response after MoAb therapy was proportional to the antigen density at the cell surface. Analysis of these data indicated a theoretical improbability of a single MoAb treatment being able to completely eradicate solid tumors and may necessitate the use of multiple MoAb's to circumvent this problem.