VATICAN CITY (AP) — The Vatican has canceled a stem cell research conference whose speaker lineup included scientists whose work involves human embryonic stem cells, a practice opposed by church teaching.

The Pontifical Academy for Life had organized the "Responsible Stem Cells Research Congress" for April 25-28 at the Vatican. But its website said that because so few participants had signed up, the event was canceled.

A Vatican spokesman, the Rev. Ciro Benedettini, quoted on Tuesday from an Academy memo blaming "organizational, logistical and economic factors."

"Unfortunately, the scarce number of sponsors and registrations would have adversely affected the positive outcome of the meetings, and therefore this prompted the organizers to take the necessary steps to cancel the conference," the Academy website's said.

Academy officials couldn't immediately be reached about media reports that the speaker lineup irked scientists opposing embryonic research, while others declined invitations for fear of lack of open discussion.

Among the invited speakers was Alan Trounson, president of the California Institute for Regenerative Medicine, the state stem cell agency based in San Francisco.

"I am disappointed that the decision was made to cancel the conference because it offered the opportunity for a constructive dialogue on all types of stem cell research," Trounson said in a statement released by the institute.

"Open dialogue can enhance the field as a whole and accelerate our efforts to provide new therapies for patients in need," said Trounson, an Australian.