Shares in Cytori Therapeutics dropped as much as 30% after it emerged the US biotech was forced to call time out on two trials assessing its experimental stem cell therapy in heart failure patients.

The San Diego-based group said enrolment in the ATHENA and ATHENA II trials is now on “clinical hold” following a safety review of reported “cerebrovascular events” in three patients.

Two of these patients were fully recovered “within a short period of time” and the third patient “has had substantial resolution of symptoms,” the firm stressed.

Also, the events had not been previously reported in other cardiovascular trials and appear to be related in part to the medical co-morbidities in the treated population and the complex nature of the procedures involved in the trial, it noted.

ATHENA and ATHENA II are randomised, double-blind, placebo controlled studies designed to evaluate the safety and feasibility of adipose-derived regenerative cells (ADRCs) in heart failure patients with ischaemic heart disease already receiving maximal therapy with no options for revascularisation. 

The procedure involves a fat harvest through small volume liposuction, cardiac catheterisation, electromechanical mapping of the heart to determine where to inject ADRCs (or placebo), the actual ADRC (or placebo) injection and related data collection and monitoring activities.

The firm said it continues to work with the FDA, an independent Data Monitoring Committee (DMC), trial investigators and external expert consultants to understand adverse events and carefully define adjustments to the protocol to minimise risks to patients and improve the benefit to risk profile of the study.