A New Option For Some Patients in Need of Stem Cell Transplant
There has now been enough research for the safety and efficacy of haploidentical transplants that we can offer the procedure to all of our patients who qualify.Christopher Lowrey, MD
Until recently, patients with various blood cancers and disorders such as leukemia, lymphoma, multiple myeloma, and sickle cell anemia who required a stem cell transplant, were dependent upon finding a donor who was a close enough human leukocyte antigen(HLA) tissue type match. HLA proteins are found on all cells of our body and are our immune system’s way of differentiating between our own cells and infectious cells, or cells from another body. If the HLA match between a donor and recipient is not close enough, the donor immune system recognizes the mismatch, and will attack the recipient’s tissues in a process known as graft versus host disease (GVHD). Other complications can include the recipient’s complete rejection of the transplanted cells. Recent medical advances have allowed for an increase in the potential donor pool without increased risk for complications.
In the Beginning
The concept of stem cell transplants began in the 1950s as a result of atomic bomb studies. Due to excessive radiation exposure, bomb survivors who were far enough away that the explosion didn’t kill them ended up dying as a result of complications from low blood counts (anemia) in their bone marrow. Researchers suggested that those affected by bone marrow failure could be treated with healthy marrow from a normal donor. Researchers were able to successfully perform marrow transplants in genetically identical mouse models. However, in human trials, the donor cells, unless from an identical twin, attacked the recipient cells resulting in patients dying from GVHD. Trials were put on hold to allow researchers to further study HLA and drugs to prevent GVHD. By the late 1970s, the necessity of a near-100 percent HLA match was realized, transplants were able to be performed with greater success rates, and the practice of stem cell transplants gained in popularity.
Finding a Match
Even with these scientific advancements, the chances of patients with malignant blood diseases finding a suitable donor still presented a challenge. For patients with siblings, each sibling is a possible one in four chance of being a match. Unrelated marrow registries were formed in the 1980s and today contain stem cells from tens of millions of donors around the world. People of Caucasian ethnicity have about an 80 percent chance of finding an unrelated donor match, as that’s what makes up most of the specimens in the bank. The chance decreases for ethnic minority populations, and outside of the United States.
For people who need a stem cell transplant but do not have a closely HLA-matched related or unrelated donor, recent medical advances have made possible the use of a partial or half (haplo) matched donor who is usually a 50 percent match to the recipient. This means that almost all patients who need a bone marrow transplant will now be able to find a donor, as almost everyone has at least one haploidentical relative. Biological parents and children will always be a half match for each other. An added advantage is that relatives are more likely to donate stem cells much more quickly than unrelated volunteer donors, thus allowing life-saving transplants to happen sooner.
Haplo Transplants are Here
A 50 percent match poses a concern because there is a high risk of GVHD. The key to a successful haploidentical transplant, is four to five days after transplant to give a very high dose of cyclophosphamide, a common chemotherapy drug used to treat various types of cancers. The cyclophosphamide kills certain donor immune cells that would otherwise cause GVHD. “It’s such a simple solution with a drug that has already been available for decades to treat other forms of cancer,” explains Christopher Lowrey, MD, chief of the Division of Hematology at Norris Cotton Cancer Center. The cyclophosphamide prevents the donor cells from becoming activated and attacking the recipient’s tissues. Because of the cyclophosphamide treatment, data show that complications of a haploidentical transplant, such as GVHD, rejection of the graft and slow recovery of the immune system appear not to be increased compared to transplants using full HLA-matched related or unrelated donors.
“There has now been enough research for the safety and efficacy of haploidentical transplants that we can offer the procedure to all of our patients who qualify” says Dr. Lowrey, who also points out that these procedures are becoming more widespread and mainstream. “Data on GVHD, rejection, mortality and overall survival compared to results from full match transplants shows that a partial match is just as good.”
Until now, patients who qualify for haploidentical transplants had to be transferred to a medical center that performed these procedures. Now, significantly fewer patients will need to be referred out or turned away for lack of a donor. Haploidentical transplants will be performed by the same established team within the Cancer Center’s trusted Blood and Marrow Transplant Program. Recovery time, which is proving to take about the same amount of time as a traditional full-match transplant, can also take place here at 1 West, the Cancer Center’s inpatient unit, all within the comfort and familiarity our patients have come to expect.