Avidity-Engineered CD3 Engaging DARPin ® Targeting Three Tumor Associated Antigens Induce Strong and Specific T Cell Dependent Killing of AML Cells with Potential for Improved Safety

AML is driven by leukemic stem cells (LSC) that resist conventional chemotherapies and remain unaffected in their niche, continually replenishing circulating blast cells. We postulated that an avidity-engineered CD3 engaging DARPin ® (Designed Ankyrin Repeat Protein) able to simultaneously target LSC-specific CD70 as well as CD123 and CD33 could allow highly efficient and specific T cell-mediated killing of AML LSCs and circulating blast cells while preserving a therapeutic window towards healthy cells. Moreover, this simultaneous targeting of three different tumor associated antigens (TAAs) has the potential to address tumor heterogeneity, allowing targeting of AML cells with different co-expression patterns and/or expression levels of each single TAA. To achieve this ambitious goal we used our DARPin ® platform to build a novel class of triple targeting CD3 engaging molecules.