Stemline on Thursday had to report that another patient died from capillary lead syndrome (CLS) after receiving SL-401, the company’s CD-123 targeting antibody drug conjugate. There had already been two deaths caused by CLS during the lead in of the BPDCN trial. As a result Stemline adjusted the study protocol including a more rigorous monitoring. It is assumed that CLS is caused by the diphtheria toxin element of the drug but a final assessment if the incident is still outstanding. Stemline reports that the study is not on hold due to the incident.
As with all study events, the Company has and will continue to report the data to the FDA in accordance with the study protocol and applicable regulations. Stemline plans to provide a clinical and safety update on this cohort when the cohort and data are complete. The pivotal Phase 2 trial with SL-401 in BPDCN is currently ongoing, patient enrollment is ahead of schedule, and patients continue to receive SL-401 in the trial. Our timelines for study completion and BLA submission remain on track.
It is not clear if SL-401 can make it through the clinic as a treatment for BPDCN. The prospects for the drug in other hematological malignancies like AML or even in autoimmune diseases are however not so bright anymore.