The postulated tri-cell complex model suggesting interactions that led to the induction of tumor immunity and improved tumor cell destruction by intact bsAb.

The use of mouse IgG2a × rat IgG2b intact bsAb leads to the simultaneous recruitment of tumor cells, T cells, and Fcγ-receptor⁺ accessory cells. The formation of this complex induces the activation of different classes of effector cells, resulting in excellent antitumor activity. The stimulation of accessory cells is demonstrated by the production of cytokines such as IL-1, IL-6, IL-12, and the DC-specific cytokine DC-CK1.5Activated accessory cells, particularly professional antigen-presenting cells such as DCs or activated macrophages mediate costimulatory signals, eg, via CD40-CD40L to T cells that are necessary to prevent T-cell anergy. Furthermore, tumor material is phagocytosed,14 processed, and presented by professional antigen-presenting cells after activation by bsAb—an important prerequisite for the induction of antitumor immunity. The tri-cell complex is only a model and should not implicate a 1:1:1 ratio of the 3 involved cell types.