PRINCETON, N.J. -- Sisters Sam and Alex Kimura are living the life on a year-long cross-country road trip. But theirs is no post-college fling - it is, in fact, a medical mission.

Five years ago, Sam was a healthy high school athlete. Now, she copes with severe aplastic anemia -- a rare blood disorder in which the bone marrow does not make enough blood cells for the body. A bone marrow transplant, to replace diseased cells with healthy ones, is the only cure.

Sam Kimura, left, with her sister Alex KIMURA SISTERS

"As a 22-year-old, you know, you want to have your whole life stretched out ahead of you and that you have limitless possibilities," said Sam with tears in her eyes. "But it's hard knowing that I might not have that."

Big sister Alex hoped to be the hero -- but was not a suitable match. As Sam's name lingered, for years, on the National Bone Marrow Registry, the sisters decided to take action.

Sam and Alex traded in their cars, bought a tricked-out van and plotted a route through all 50 states.

The plan was to find a donor for Sam. But along the way, they realized something.

"There are thousands of patients every year that are in the same position -- that can't find a donor -- but there are millions and millions of people in this country that just aren't signed up yet, they could be the cure for all these patients," said Alex.

Now their goal is to swab DNA from 50,000 cheeks thousand cheeks and getting those people on the registry. Along with the non-profit Delete Blood Cancer, the sisters have hosted "donor jams" at student unions, rock concerts, brew pubs -- even just curbside. CBS News met the sisters at an event hosted by MedStar Georgetown University Hospital where donors expressed their appreciation for their work.

Sam and Alex hold a flag promoting their cross country mission to find bone marrow donors KIMURA SISTERS

So far, there' been no match yet for Sam. But they have discovered 33 DNA matches that have led to five possible life-saving donations.

The sisters are also trying to remove the stigma of donating bone marrow by educating people about the process. They say the most common method of donation is peripheral blood stem cell donation (PBSC). PBSC involves several hours of having your blood run through an IV to a machine that circulates the blood and separates stem cells. It looks a lot like giving blood and is considered a simple procedure.

For Sam, living out of a van is grueling. She's already weak from the 30 pills a day that control her disorder. But for Alex, the worst part is the constant rejection: hundreds of eyes that simply look past or through her little sister.

Sam and Alex stand in front of the van they use to travel cross country in a mission to raise awareness for bone marrow transplants CBS News

"It keeps me up at night and it gets me up in the morning because we have to, we have to find a match for her," said Alex.

Despite those disappointments, there are now more than 8,000 people who have "swabbed up." So down the road they roll, two sisters convinced that one special hero may be just around the bend.

Learn more about Alex and Sam's mission by visiting: http://www.sharingamericasmarrow.com/ andhttp://www.deletebloodcancer.org/en