2seventy Bio Pauses Pediatric Blood Cancer Trial After Patient Death, Stock Plunges

2seventy Bio Inc TSVT announced that the Phase 1 trial of the PLAT-08 study of SC-DARIC33 in Acute Myeloid Leukemia (AML), has been paused by Seattle Children's, the company's partner and the regulatory sponsor of the study. 

The pause was instituted as part of the clinical study protocol stopping rules in response to a recent Grade 5 (fatal) serious adverse event (SAE) and was followed by the required notification to the U.S. Food & Drug Administration (FDA). 

The root cause of this SAE and its potential relationship to the study drug is under investigation.

The SAE occurred in the first patient treated at the second dose level in the Phase 1 trial.

Last month, 2seventy Bio announced late-breaking results from the ongoing Phase 1 PLAT-08 trial at the American Society of Gene & Cell Therapy (ASGCT) Annual Meeting.

Results of preliminary correlative analysis from the PLAT-08 study show rapamycin-regulated in vivo expansion and activation of SC-DARIC33 T cells and concurrent anti-CD33 activity.

Enhanced anti-acute myeloid leukemia (AML) potency was obtained with the combination of regulated IL-15 production and rapamycin-controlled DARIC33 activation.

Price Action: TSVT shares are down 11.90% at $10.40 on the last check Wednesday.