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Response​ to Tagraxofusp in Blastic Plasmacytoid Dendritic Cell Neoplasm

Tagraxofusp is a CD123-targeted therapy comprised of a recombinant human interleukin-3 (IL-3) fused to a truncated diphtheria toxin (DT) payload. It is the first approved treatment specifically for patients with Blastic Plasmacytoid Dendritic Cell Neoplasm (BPDCN). In order to identify biomarkers of response, bone marrow samples from 12 BPDCN patients who were treated with tagraxofusp in the pivotal phase II trial (NCT02113982) were profiled longitudinally using gene panel and/or single-cell RNA sequencing. Durable responders had either wildtype or missense TET2 mutations while transient and non-responders had at least one truncating TET2 mutation. Those who had progression at any one point during the treatment course (transient responders) and non-responders had enrichment of the chemokines CCL3, CCL4, and CCL5. Residual tumor cells following tagraxofusp treatment were identified in all patients, whose resistance may be due to their lower levels of TXNRD1 possibly preventing the potentiation of tagraxofusp. Thus, response to tagraxofusp may be related to culmination of intrinsic TET2 mutations, levels of TXNRD1, and extrinsic effects of chemokines within bone marrow.