Simultaneous quantification of recent thymic T-cell and bone marrow B-cell emigrants in patients with primary immunodeficiency undergone to stem cell transplantation

A major problem in the field of stem cell transplantation is the difficulty to monitor the efficacy of immune reconstitution. By modifying the widely used method of measuring T-cell receptor excision circles (TRECs) and the recently proposed kappa-deleting recombination excision circles (KRECs) assay, we set up a duplex Real-Time PCR that allowed the simultaneous quantification of newly produced T and B cells in children with primary immunodeficiency undergone to transplantation. We found that lymphocyte recovery involves the mobilization of both new T and B cells from production and maturation sites, and that the increase of TRECs and KRECs can be or strictly associated or independent one from the other. Some patients showed a “lymphocyte rebound” which is followed by a progressive decrease of newly produced T and B lymphocytes starting about 2 years after transplantation. In other patients, TRECs and KRECs number remained very low for the entire period of study.