Bush's HHS secretary, Tommy Thompson, is a panelist at the conference and told reporters Tuesday that science had moved beyond destroying embryos.
"Why destroy an embryo?" Thompson asked. "We are in a new science of adult stem cells that are pluripotent," or able to differentiate into other tissues.
Another speaker at the conference starting Wednesday is Sharon Porter, who was diagnosed with systemic scleroderma, a chronic connective tissue disorder that leads to a hardening of the skin and internal organs.
There is no cure, but three years ago she underwent a treatment to reboot her immune system: Adult stem cells were removed from her body, her immune system was destroyed and the stem cells were re-injected to build a new immune system.
"It changed my life," Porter told reporters. "It brought me back to where I was before I was diagnosed."
Vatican officials acknowledged the unusual nature of the partnership between the Roman Catholic Church and a publicly-traded, for-profit biotech company.
But the Rev. Tomasz Trafny, head of the science department in the Vatican's culture office, said NeoStem's research and mission corresponded with the Vatican's concerns to both promote research exclusively on adult stem cells, and broaden understanding about its uses to the wider public.
"It's not just an event but an itinerary of projects," he said of the collaboration.