Dual-targeting CD33/CD123 NANOBODY® T cell engager with potent anti-AML activity and good safety profile.

Novel therapies are needed for effective treatment of Acute Myeloid Leukemia (AML). Relapse is common and salvage treatment with cytotoxic chemotherapy is rarely curative. CD123 and CD33, two clinically validated targets in AML, are jointly expressed on blasts and leukemic stem cells in >95% of AML patients. However, their expression is heterogenous between subclones and between patients which may impact the efficacy of single-targeting agents in certain patient populations. We present here a dual- targeting CD33/CD123 NANOBODY® T-cell engager (CD33/CD123-TCE) that was designed to decrease the risk of relapse from possible single antigen-negative clones and to increase coverage within and across patients. CD33/CD123-TCE killed AML tumor cells expressing one or both antigens in vitro. Compared to single-targeting control compounds, CD33/CD123-TCE conferred equal or better ex vivo killing of AML blasts in most primary AML samples tested, suggesting a broader effectiveness across patients. In a disseminated cell line-derived xenograft (CDX) mouse model of AML, CD33/CD123-TCE cleared cancer cells in long bones and in soft tissues. As cytokine release syndrome is a well-documented adverse effect of TCE, the compound was tested in a cytokine release assay and shown to induce less cytokines compared to a CD123 single-targeting control. In an exploratory single-dose non-human primate study, CD33/CD123-TCE revealed a favorable PK profile. Depletion of CD123 and CD33 expressing cells was observed, without signs of cytokine release syndrome nor clinical signs of toxicity. Taken together, the CD33/CD123 dual-targeting NANOBODY® TCE exhibits potent and safe anti-AML activity and promises a broad patient coverage.