Quantitative Monitoring of Lineage-Specific Chimerism after Dual Hematopoietic Stem Cell Transplantation (Umbilical Cord Blood with Co-Infusion of Third Party Donor CD34+ Cells)

Background: Allogeneic umbilical cord blood (UCB) stem cell transplantation (SCT) shows some advantages (HLA matching requirements or availability) respect to SCT using other sources of matched unrelated donor (MUD) stem cells. However, it is correlated with slower engraftment, increasing risk of infections and early mortality. It has been recently shown that co-infusion of third party donor (TPD) CD34+ cells (dual SCT) is useful to speed up engraftment. Objective: To evaluate the usefulness of lineage-specific chimerism quantification in the management of this transplant setting. Patients and methods: 8 dual SCT (Tables 1, 2) in 7 patients (1 CML-BC, 2 AML-M2, 1 AML-M4, 1 ALL-Ph+, 1 biphen. ALL, 1 NHL). Chimerism was analyzed by STR-PCR (AmpFlSTR SGM Plus, Applied Biosystems; sensitivity 1%) and quantitative real-time PCR (qrt-PCR) of null alleles and insertion/deletion polymorphisms (Light Cycler, Roche; sensitivity 0,01%). Peripheral blood (PB) and leukocyte lineages (T cells, CD3+, and myeloid cells, CD15+), isolated by positive selection using automated immunomagnetic technology (AutoMACS, Miltenyi Biotec), were analyzed weekly. Bone marrow (BM) was analyzed at days +30, +100, +180 and +365). Results: 7/8 cases showed initially a high proportion of TPD cells in PB which were progressively replaced by UCB cells. UCB complete chimerism (UCB-CC, absence of recipient or TPD cells even in qrt-PCR assays) was acquired in a median of 22.5 days (range 18–39). In one patient, fully HLA-mismatched with the TPD, no TPD cells were observed after dual SCT. 4/8 cases showed recipient cells in PB after dual SCT during a median period of 12 days (range 4–18 days). In 3/8 cases, recipient cells were found after CC had been acquired, which allowed early diagnosis of 1 graft rejection and 2 relapses. T cells (CD3+) are mainly of UCB origin early after dual SCT and reach UCB-CC a median of 7 days (range 0–21) before PB. However, myeloid cells (CD15+) derive primarily from the TPD and reach CC together with PB. TPD cellularity favoured early engraftment (before UCB-CC took place) in 4 cases. In this context, only one important infectious complication (hepatosplenic tuberculosis) was observed, which resolved with the appropriate treatment. Conclusions: Lineage-specific chimerism quantification allowed a close monitoring of the dynamics of engraftment of cells of both donors which is of key importance in this SCT setting. Moreover, lineage-specific chimerism analysis was useful to diagnose one graft rejection and two relapses (the patient with NHL showed a ganglionar relapse in CC). Table 1. Transplantation characteristics. Table 2. Transplantation results. Median (range).