It comes down to the number three. Strokes are the third most prevalent cause of death in the United States, but the best currently available medicine, tPA, must be administered within three hours of the onset of treatment.

After that stroke patients have only rehab and positive thinking.

But if all goes well, a potential treatment in the first phase of safety trials could change all that.

Dr. Sean Savitz, an associate professor of neurology at the University of Texas-Houston Medical School, is in the early phases of a study implanting bone marrow cells — including stem cells — into the brain up to 72 hours after stroke symptoms emerge.

In a typical stroke, a blood vessel is blocked, depriving a specific area of the brain glucose and oxygen, and causing brain cells in that region to die.

While other doctors focus on protoneurons in hopes of healing or replacing damaged or dead cells, Savitz focuses on the regions directly around the core stroke-affected area that are damaged after the stroke by inflammation, harvesting the marrow cells and administering them via IV.

"The cells end up in different places — some in the liver, some go to the kidneys, but a substantial number do make it to the brain," Savitz says, referencing studies previously done on animals. "We aren't exactly sure why or how, but the brain seems to give off a homing signal saying, 'Hey I'm up here! I need some resources!"

Savitz's background propelled him towards this research. Not only was his father a neurologist, but his undergraduate thesis at Harvard focused on cell death and as a resident in Boston he ended up working unexpectedly on a study using fetal porcine cells as a stroke therapy.

"I knew I wanted to be in neuroscience and I wanted to devote myself to a career in an area where the condition was highly prevalent and very limited in the way of new therapies," Savitz says. "I wanted to go into an area where there was a huge public health concern where I could go in and make a contribution to finding a therapy."

"It seemed like it all came together with stroke. Stroke is so common, but trying to find new therapies is very challenging and it requires laboratory work to really understand the mechanisms behind how the brain tissue is responding under the conditions of the stroke. Not just the cells dying, so to speak, but what happens afterwards."

The safety/efficacy study was implemented for the first time in April 2009, and has found a total of 10 patients that fit the criteria to undergo the experimental treatment. Though Savitz is not at liberty to discuss the results so far, the study has received an additional grant from the National Institute of health to take on more cases past the originally planned 10.

By the end of 2011 Savitz would like to have 30 patients treated, and is hoping to work with other Med Center hospitals to transfer stroke patients who were admitted too late to receive tPA or did not respond to it.

"I never thought of coming to Houston, being from the Northeast, but I was really glad we took the chance to visit and check out the city and the hospital," Savitz says. "In addition to having the largest stroke center in the country, everything here is set up for success. There are so many hurdles in a project like this, and I never would have been able to do it without the help and the mentoring and everything already being in place."