Blood, 15 May 2001, Vol. 97, No. 10, pp. 2921-2921
Young is better if enough
For patients without an HLA-identical sibling donor,
alternative sources of stem cells are partially HLA-matched relatives, matched unrelated volunteers, or unrelated cord blood. In this issue, 2 articles compare the outcome of unrelated cord blood and marrow
transplantation in children.
Barker and colleagues (page 2957) report on a retrospective,
single-center study of unrelated cord blood or marrow transplants in
children with various diseases. While engraftment of granulocytes and
platelets was slower with cord blood, survival was similar with either
cord blood or marrow. Survival after cord blood transplantation in this
series appears better than in larger series. Rocha and colleagues (page
2962) report on a multicenter retrospective study of unrelated cord
blood or marrow transplants for children with leukemia. Cord blood led
to slower engraftment of granulocytes and platelets, and higher
mortality, which occurred during the first 100 days. Relapse was
similar after cord blood or marrow transplantation. Despite a higher
degree of HLA incompatibility, cord blood was associated with less
acute and chronic GVHD than was marrow. The median interval from the
last leukemia remission induction to transplantation was 30 days
shorter with cord blood than with marrow. Because patients with acute
leukemia may deteriorate and die while waiting for transplantation, the
survival gain from a shorter wait for a cord blood graft could
partially offset the increased mortality after transplantation. The
data from the 2 studies support the conclusion that transplantation of
partially matched cord blood is effective treatment for children
without a suitably matched unrelated marrow donor.
Transplantations in children have shown that HLA-identical sibling cord
blood is associated with less GVHD and same survival compared to
HLA-identical sibling marrow, suggesting that cord blood T-cell
naïveté protects from severe GVHD and that HLA matching
criteria for selection of unrelated cord blood may be relaxed. Almost
all unrelated cord blood transplants, performed thanks to more than
65 000 units available globally, are mismatched for one or more HLA
alleles. What constitutes an acceptable mismatched cord blood remains
undefined. Slow engraftment and graft failures are the predominant
hurdles that limit success of cord blood transplantation in children
and even more in adults. HLA mismatching and low cell dose are risk
factors for slow engraftment and graft loss. Therefore, new strategies
for suppression of the host immune response across HLA disparity and,
perhaps, stem cell expansion will be necessary for broadening the
utilization of cord blood transplants.
Claudio Anasetti
Fred Hutchinson Cancer Research Center
