BETHESDA, Md. (TheStreet) -- Northwest Biotherapeutics (NWBO) remains unable to screen new brain tumor patients for an ongoing phase III study, said CEO Linda Powers, speaking Wednesday at a cancer conference in London.

Powers offered no explanation for why federal health regulators placed the phase III study of Northwest Bio's brain tumor vaccine DCVax-L on a temporary hold, which prevents the company from screening new patients.

"We're currently on hold for screening, but we will be hopefully not too much longer," said Powers.

Northwest Bio confirmed the suspension of patient screening on Aug. 21 and said "certain information" would be submitted to regulators within a couple of weeks. On Wednesday, almost four weeks later, Powers didn't say if Northwest Bio had yet followed through on the information submission.

Slightly more than 300 out of a required 348 brain tumor patients are currently enrolled in the DCVax-L study, Powers said.

DCVax-L is a patient-specific vaccine designed to train immune cells to identify and kill brain tumor cells. Northwest Bio started the DCVax-L study in 2005 but numerous changes and setbacks over the years have delayed its completion.

Powers spoke Wednesday at a cancer immunotherapy conference in London which Northwest Bio paid to sponsor.

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