Limited Availability of Non-Caucasian Stem Cell Donors: A Growing Problem?

• A Korean patient within my clinic was diagnosed with high-risk myelodysplastic syndrome. Stem cell transplant was the only chance for cure. Unfortunately, her sibling wasn’t a match, and no matches were located in the American donor registry either. There were 2 matches found in the Asian donor registry, but both were unavailable.
• A recent media article described a woman of Indian descent with leukemia who could not find a donor for a life-saving bone marrow transplant.¹

Prerna Mewawalla, MD

In the instance of the first patient, the search for a donor continues. In the instance of the second, the tragedy of this woman’s death could have very well been averted.¹

What are stem cell transplants and when are they used?

Hematopoietic stem cell transplantation (HSCT) is a procedure performed to help restore hematopoietic stem cells, cells that normally divide or mature into white or red blood cells, and platelets that have been destroyed by chemotherapy or radiation treatment. HSCT is performed most commonly for certain types of blood and bone marrow cancers. To restore the cells, the procedure includes the use of peripheral blood, bone marrow, or umbilical cord tissue.² For certain types of cancer, it is the only hope for cure. Unlike patients undergoing solid organ transplants, those undergoing HSCT have to be matched for DNA, specifically for human leukocyte antigen (HLA) types on chromosome 6.³

The relationship between ethnicity and available donor matches

Historically, it has been observed that patients are more likely to match their HLA type with another person within the same ethnic group. The number of HLA types seen among one ethnic group may vary significantly from that seen in another ethnic group. While there are no substantial studies to provide statistics, it is widely believed that Caucasians have fewer HLA types compared with other ethnicities. Therefore, Caucasians are more likely to locate a donor match than patients from other ethnicities (eg, Asians, Indians, Hispanics, African Americans). This gap is further exacerbated due to a low number of donors among non-Caucasian ethnicities.⁴

In the United States, the 2012 National Marrow Donor Program (NMDP) registry reported that 63% of adult donors were Caucasian, 27% were of a minority group, and 10% reported unknown race/ethnicity. The likelihood of finding a matched unrelated donor for a Caucasian is 93%, and a mere 66% to 82% among minorities, depending on the ethnicity. African Americans are the least likely to find a match.⁵

According to the National Cord Blood Program, African Americans make up only 12% of the US population. There would have to be 3 times more African Americans than Caucasians in a bone marrow donor registry to have the same likelihood of finding a match.⁶

Other factors that limit transplants in minorities

Additionally, in India, where the current population is roughly 1.2 billion,⁷ only about 45,000 people have signed up as bone marrow donors.⁸ Comparative figures from the US NMDP indicate over 10 million donors. About 1 in 300 will be selected as a best possible donor.⁹In addition to the fact that minorities are at a disadvantage for stem cell transplants because there are fewer people to match with, other factors further limit the number of stem cell transplants in minority groups.

Religious beliefs, myths, and a lack of awareness often discourage people from donating.^10,11

Among the many prevailing myths, there is the myth that stem cell donation is a painful procedure accompanied by several side effects. In many countries, blood donation is considered painful and/or harmful.^10,11 Based on my experience, patients do not like the idea of invasive needles being pushed into their bone for bone marrow. However, they are not aware that stem cells can also be donated by peripheral blood, just as in platelet donation.

Additionally, many cultures throughout the world do not emphasize the importance of public charity. Such acts of service are typically saved for family and friends.¹⁰

Cord blood transplants expand among minority groups

Although there are a limited number of stem cell transplants among minority groups, there has been an increase in the proportion of cord blood transplants. For example, the NMDP recently reported that 44% of transplants in minority groups were cord blood transplants.⁵ During a cord blood transplant procedure, a partial match is acceptable. However, cord blood transplants are more complicated, as the number of cells is much lower. A cord blood transplant also has a longer lead time for engraftment, which may result in an increased incidence of infections and complications.¹²

Addressing unmet needs

To address the challenge of the limited availability of stem cell donors in non-Caucasians, it is vital that we increase awareness through more campaigns that are targeted specifically to minorities. These campaigns should be publicized in areas where specific minority groups dwell.

At an international level, the myths regarding stem cell transplantation need to be addressed by informing the general public that donations can be collected through peripheral blood, just as in platelet donation, and not through the bone. An increase in the absolute number of patients who register worldwide increases the chance of minority patients in the United States finding a match. Even 1 extra life saved can make these actions, although challenging, worthwhile.

References

1. Malhotra A. Stanford professor dies as donor hunt fails. The Wall Street Journal. Published October 30, 2013.
2. Bone marrow transplantation and peripheral blood stem cell transplantation. Nation Cancer Institute website. http://www .cancer.gov/cancertopics/factsheet/Therapy/bone-marrow-transplant/print. Published August 12, 2013. Accessed January 2, 2014.
3. Shiina T, Inoko H, Kulski JK. An update of the HLA genomic region, locus information and disease associations: 2004. Tissue Antigens. 2004;64(6):631-649.
4. Setterholm M. Using HLA allele and haplotype associations: guess who. World Marrow Donor Association [presentation].
5. National Marrow Donor Program. HCT presentation slides. Be The Match website. https://www.bethematchclinical.org/Resources-and-Education/HCT-Presentation-Slides. Accessed January 2, 2014.
6. Why is cord blood important for ethnic minorities? National Cord Blood Program website. http://www.nationalcordblood program.org/qa/what_is_significance.html. Accessed January 2, 2014.
7. India’s population 2013. IndiaOnlinePages.com website. http://www.indiaonlinepages.com/population/india-current-population.html. Accessed January 2, 2014.
8. Datri brings together the donor and recipient of India’s first successful unrelated Blood Stem Cell transplant facilitated by an Indian Registry. ICTPost.com website. http://ictpost .com/health-directory/?p=775. Published November 26, 2013. Accessed January 2, 2014.
9. National Marrow Donor Program. National Marrow Donor Program and Be The Match key messages, facts & figures. Be The Match website. http://bethematch.org/News/Facts_and_Figures_%28PDF%29/. Updated January 2013. Accessed January 2, 2014.
10. Switzer GE, Bruce JG, Myaskovsky L, et al. Race and ethnicity in decisions about unrelated hematopoietic stem cell donation. Blood. 2013;121(8):1469-1476.
11. Office of Inspector General. National Marrow Donor Program progress in minority recruitment. Report OEI-01-95-00120. Published December 1996.
12. Moretta A, Maccario R, Fagioli F, et al. Analysis of immune reconstitution in children undergoing cord blood transplantation. Exp Hematol. 2001;29(3):371-379.