It is recognized that chimerism following hematopoietic stem cell transplantation (HSCT) is a dynamic process. The aims of this study were to describe the evolution of chimerism in children with non-malignant diseases who underwent allogeneic HSCT, and to analyze the risk factors influencing chimerism status.
101 HSCTs were performed in 85 patients with non-malignant diseases. The donor was unrelated in 62.4% of HSCTs. Reduced intensity conditioning (RIC) regimen was administered in 48.5% of patients. Acute Graft-versus-Host Disease (a-GvHD) occurred in 51.7%, and chronic GvHD (c-GvHD) in 39.7% of patients. Analysis of chimerism was performed through amplification of nine specific short tandem repeats (STRs) by polymerase chain reaction (PCR) at engraftment and 1, 6 and 12 months after HSCT.
Upon first evaluation, complete chimerism (CC) was detected in 34.7% and mixed chimerism (MC) in 55.4%, while graft failure occurred in 9.9% of patients. Severe a-GvHD was associated with CC (P=0.031). The last chimerism evaluation showed CC in 72.1%, stable mixed chimerism (SMC) in 12.8% and progressive mixed chimerism (PMC) in 3.5%. CC was associated with a higher incidence of a-GvHD (P=0.016) and c-GvHD (P=0.022), while the reduced-intensity conditioning regimen was associated with graft failure (P=0.026). One- and 3-year overall survival (OS) was 87.4% and 80.5% respectively, with a lower OS at 3 years in patients with CC compared to those with MC (P=0.008).
Acute and chronic GvHD represent factors favoring CC, thus close, careful follow-up of chimerism is recommended in patients affected by non-malignant disease.