Newly updated guidelines can inform the selection of adult donors and cord blood units for allogeneic hematopoietic stem cell transplant.
The evidence-based guidelines suggest high-resolution human leukocyte antigen (HLA) matching and donor age are important when selecting adult donors, while HLA matching, cell dose, and banking practices should be considered when selecting cord blood units.
The guidelines were developed by the National Marrow Donor Program (NMDP) and Center for International Blood and Marrow Transplant Research (CIBMTR) and were recently published in Blood.
Adult donors
The guidelines recommend high-resolution HLA typing for adult donors and patients. This means typing for HLA-A, -B, -C, and -DRB1, at minimum. Typing at other loci – DPB1, DQB1, DRB3/4/5, DQA1, and DPA1 – is “optional but often helpful.”
An 8/8 HLA-matched donor is considered optimal. If only 7/8-matched donors are available, select a donor with a single allele mismatched at the patient’s homozygous locus if possible, and select an HLA-C*03:03 mismatch over an HLA-C*03:04 mismatch where applicable.
For both 8/8- and 7/8-matched donors, try to avoid mismatches at DQB1 and DRB3/4/5, and select DPB1 mismatches based on the DPB1 T-cell epitope algorithm. Mismatches of allotypes targeted by donor-specific HLA antibodies (DSA), including DQA1 and DPA1, should be avoided.
The guidelines recommend pursuing multiple donors because not all potential donors will be available. Younger donors should be prioritized over older donors. Other factors – such as sex or cytomegalovirus serostatus – should not affect donor selection.
Cord blood
For cord blood donations, testing attached segment identity is mandatory, red blood cell–replete units are not recommended, and both unit cryovolume and year of cryopreservation should be taken into consideration. The guidelines note that “some expert centers” favor red blood cell–depleted units with a postcryopreservation volume of about 25 ml/bag, and units banked more recently “may be linked to optimal banking practices.”
The guidelines recommend a minimum of eight high-resolution HLA typing for cord blood units and patients. A 4/6 match (HLA-A, -B, -DRB1) is acceptable, as is a 4/8 match (HLA-A, -B, -C, and -DRB1) or greater. In the case of a double-unit transplant, there is no need to match the units to each other.
“DSA must be considered on a case-by-case basis,” according to the guidelines. The patient’s diagnosis, prior immunosuppressive therapy, planned conditioning regimen, and DSA number/titer/specificity/complement fixation should be taken into consideration. DSA-targeted units should be avoided in patients with nonmalignant conditions and used with caution in patients with hematologic malignancies.
For single–cord blood units, the total nucleated cell dose should be at least 2.5 x 107/kg, and the number of CD34+ cells should be at least 1.5 x 105/kg. For double-unit transplants, the total nucleated cell dose should be at least 1.5 x 107/kg for each unit, and the number of CD34+ cells should be at least 1.0 x 105/kg for each unit.
The guidelines note that additional research is needed to inform how to balance cell dose against HLA match. However, cell dose should often take priority over HLA match for adults and larger pediatric patients, and HLA match can take priority in children, smaller adults, or patients with common HLA typing who have multiple units with a high cell dose.
The guidelines’ authors reported relationships with MolMed, NexImmune, AbbVie, Bellicum, Incyte, Medigene, Merck, Nektar, Novartis, Servier, Miltenyi, and the U.S. government/military.
SOURCE: Dehn J et al. Blood. 2019 Jul 10. doi: 10.1182/blood.2019001212.