Primary graft failure, but not relapse, may be identified by early chimerism following double cord unit transplantation.

Abstract Umbilical cord blood transplantation (UCBT) has increased access to potentially curative therapy for patients with life-threatening disorders of the bone marrow and immune system. The introduction of reduced intensity conditioning (RIC) regimens and double cord unit infusions (DUCBT) has broadened the applicability of UCBT to more frail or larger recipients. The kinetics of chimerism following RIC DUCBT and their clinical utility are poorly understood. The RIC CBT trial reported here sought to prospectively evaluate the role of lineage specific chimerism following DUCBT in adult patients with haematological malignancies in the UK. Fifty-eightpatients with a median age of 52 years were recruited, with an overall and progression free survival of 59% (95%CI 45% to 71%) and 52%(95%CI 39% to 64%) respectively at 2 years. Nonrelapse mortality was 4% (95% CI 1% to 13%) at day 100 and the relapse rate was 31% (95%CI 21% to 45%) at 1 year. Peripheral blood lineage specific chimerism was feasible from day 7 post-transplant onwards. Five patterns of chimerism were observed including i) complete single unit dominance (39 patients), ii) sustained donor-donor mixed chimerism (3 patients), iii) sustained donor-recipient mixed chimerism (5 patients), iv) dominance reversion (1 patient) and v) primary graft failure (4 patients). The RIC CBT trial enabled adult patients with high-riskhematological malignancies to safely access UCBT in the UK and provided novel insights into the kinetics of donor and recipient chimerism following RIC DUCBT which are clinically relevant. (Clinical Trials.gov identifier: NCT00959231; EudraCT identifier: 2004-003845-41).