Control of acute myeloid leukemia by a trifunctional NKp46-CD16a-NK cell engager targeting CD123.

CD123, the alpha chain of the IL-3 receptor, is an attractive target for acute myeloid leukemia (AML) treatment. However, cytotoxic antibodies or T cell engagers targeting CD123 had insufficient efficacy or safety in clinical trials. We show that expression of CD64, the high-affinity receptor for human IgG, on AML blasts confers resistance to anti-CD123 antibody-dependent cell cytotoxicity (ADCC) in vitro. We engineer a trifunctional natural killer cell engager (NKCE) that targets CD123 on AML blasts and NKp46 and CD16a on NK cells (CD123-NKCE). CD123-NKCE has potent antitumor activity against primary AML blasts regardless of CD64 expression and induces NK cell activation and cytokine secretion only in the presence of AML cells. Its antitumor activity in a mouse CD123+ tumor model exceeds that of the benchmark ADCC-enhanced antibody. In nonhuman primates, it had prolonged pharmacodynamic effects, depleting CD123+ cells for more than 10 days with no signs of toxicity and very low inflammatory cytokine induction over a large dose range. These results support clinical development of CD123-NKCE.

Leukocyte Elastase Inhibitor, the precursor of L-DNase II, inhibits apoptosis by interfering with caspase-8 activation.

LEI (Leukocyte Elastase Inhibitor), the precursor of the pro-apoptotic molecule L-DNase II, belongs to the ovalbumin subgroup of serpins. Several serpins can inhibit apoptosis: the viral serpin Crm A inhibits Fas or TNFalpha-induced apoptosis, and overexpression of PAI-2 or PI-9 protects cells from TNFalpha or granzyme B induced apoptosis. We have previously shown that LEI overexpression protects cells from etoposide-induced apoptosis. The molecular reason of this anti-apoptotic activity is now investigated. We show that, in BHK-21 and HeLa cells, LEI anti-protease activity is essential for its anti-apoptotic effect. The protease inhibited is cathepsin D, released from the lysosome during etoposide treatment. Cathepsin D enhances caspase activity in the cell by cleaving procaspase-8 and LEI overexpression slows down this cleavage, protecting cells from apoptosis. This let us presume that high expression of LEI in tumor cells may reduce the efficiency of etoposide as a chemotherapeutic agent.