Compositions and methods for inducing cell membrane wounding, cell permeabilization and cell killing are provided. The composition comprises a polyvalent agent that binds to a highly expressed cell surface antigen present on the surface of a cell. Preferably, the cell surface antigen is associated with the cytoskeleton of the cell. A preferred polyvalent agent is an IgM, and enhanced cell wounding and killing can be provided by the addition of a crosslinking agent. At sublethal concentrations in vivo, the cell wounding antibodies permeabilize cells and dramatically enhance response to chemotherapeutic agents, even in patients refractory to the chemotherapeutic agents.