HLA matching affects clinical outcome of adult patients undergoing haematopoietic SCT from unrelated donors: A study from the Gruppo Italiano Trapianto di Midollo Osseo and Italian Bone Marrow Donor Registry

The importance of HLA donor-recipient matching in unrelated haematopoietic SCT (HSCT) is the subject of debate. In this retrospective study, we analyzed 805 adult patients from the Italian Registry receiving HSCT for a haematological malignancy from January 1999 to June 2006 and correlated the degree of HLA matching with transplant outcome. All patient-donor pairs had high-resolution typing at HLA-A, -B, -C, -DRB1 and -DQB1. There was a significantly higher risk of overall mortality, non-relapse mortality, graft failure and acute GVHD (aGVHD) for patients receiving HSCT from an unrelated donor with one or more low- or high-resolution mismatch/es (Mm/s). When only a single HLA Mm is present (9/10 matched pairs), mortality risk is higher than among 10/10 matched pairs in patients transplanted with acute leukaemia in the first CR ('early' patients) but not in the other patients (advanced patients): HR = 1.69, 95% CI = 0.94-3.02, P = 0.08; HR = 1.03, 95% CI = 0.80-1.32, P = 0.82, for early and advanced patients, respectively. These results confirm that the advantage of a 10/10 match has a greater effect in early patients, thus suggesting that a 9/10 matched donor can be chosen in patients with advanced disease lacking a rapidly available 10/10 matched one.