Figure 1.

Proposed strategy to increase the selectivity of antibody-mediated effector function for target cells with elevated antigen expression using mixtures of engineered antibodies. (a) Wild-type trastuzumab, which has high affinity for its antigen (HER2), binds strongly to cells with either high (HER2⁺⁺⁺) or low (HER2⁺) levels of antigen, and is expected to mediate relatively high effector function in both cases. This is expected to result in a relatively low effector function ratio for cells with high HER2 levels versus those with low HER2 levels. (b) An engineered version of trastuzumab, namely a high avidity low affinity (HALA) variant, is expected to bind strongly to HER2⁺⁺⁺ cells and weakly to HER2⁺ cells. This is expected to result in an increase in the effector function ratio, which is primarily due to reduced effector function on HER2⁺ cells. (c) A mixture of the HALA antibody and an effectorless version of trastuzumab that has high HER2 affinity but little affinity for activating FcγRs – referred to as a blocking antibody – is expected to result in a high selectivity with moderate effector function. (d) A mixture of the Fc-enhanced HALA antibody and the blocking antibody is expected to result in high effector function and high selectivity. This is posited to be due to both the accumulation of the 1) Fc-enhanced HALA antibody in the synapses involving HER2⁺⁺⁺ cells, which would lead to high effector function, and 2) effectorless (high affinity) trastuzumab antibody in the synapses involving HER2⁺ cells, which would lead to high selectivity. Together, the mixture of the Fc-enhanced HALA antibody and effectorless, high-affinity blocking antibody is expected to lead to both high selectivity and high effector function.