Kinetics of chimerism during the early post-transplant period in pediatric patients with malignant and non-malignant hematologic disorders: implications for timely detection of engraftment, graft failure and rejection

Abstract

The monitoring of chimerism by PCR has become a routine diagnostic approach in patients after allogeneic bone marrow or peripheral blood stem cell transplantation. Nevertheless, a temporal correlation between molecular and hematologic assessment of engraftment has not been clearly established. To address this issue, and to determine the potential clinical implications of early kinetics of mixed chimerism, we have investigated 66 allogeneic stem cell transplantations (SCTs) in 58 pediatric patients suffering from different types of leukemia (n = 44) or non-malignant hematologic disorders (n = 14) by close molecular monitoring during the first days and weeks after transplantation. Patient-and donor-derived hematopoiesis were assessed at 1-to 3-day intervals in peripheral blood samples by PCR analysis of highly polymorphic microsatellite loci (STR-PCR). Detection of an increasing, and ultimately dominant donor-specific allelic pattern, which we defined as molecular engraftment, preceded hematologic engraftment by a median of 7 days (range 1-17 days) in all patients investigated. PCR analyses during the first days after transplantation facilitated detection of molecular engraftment according to the above definition by day +14 (range day +2 to day +14), thus permitting prediction of successful engraftment (upper limit of the two-sided confidence interval p o = 6%) while the peripheral leukocyte counts were mostly below 200/l. In three cases, however, the criteria for molecular engraftment were not fulfilled by day +14. These patients also failed to show hematologic engraftment, and required a second transplantation. Close monitoring by STR-PCR showed that graft rejection and autologous recovery can occur early and with very rapid dynamics. Molecular analysis of specific leukocyte subsets isolated by flow-sorting enabled sensitive assessment of changes in the pattern of chimerism which had escaped detection in assays using whole white blood cell (WBC) samples. This approach facilitated the identification of expanding or decreasing recipient cells, and permitted early detection of impending rejection or relapse. Moreover, monitoring of the dynamics of chimerism allowed rapid assessment of the response to therapy. Our observations provide support for the concept of initiating genotype analyses early after SCT and monitoring at rather short intervals to permit timely evaluation of clinically relevant processes, and to provide a basis for early implementation of treatment.

How and when should we monitor chimerism after allogeneic stem cell transplantation?

“…The rapid development of complete chimerism in NK and T cells seems to play an important role in achieving sustained engraftment especially in patients who were treated with a dose reduced conditioning regimen. [64][65][66][67] …”

Expansion of donor-reactive host T cells in primary graft failure after allogeneic hematopoietic SCT following reduced-intensity conditioning

“…[10][11][12][13][14][15] An increase in number of residual host T cells is associated with graft rejection in pediatric allogeneic transplantation. 16 HLA-C mismatch with NK epitope mismatching in the rejection direction are associated with higher rates of graft rejection after HLAmismatched transplantation. 17,18 Positive serum crossmatch is predictive for graft failure in HLA-mismatched allogeneic SCT.…”

Monthly prospective analysis of hematopoietic chimerism after allogeneic hematopoietic cell transplantation

“…poietic cell transplantation Assays of hematopoietic chimerism (HpC) in patients who have undergone allogeneic hematopoietic cell transplantation (HCT) may provide physicians with valuable information regarding the status of transplanted hematopoietic grafts, [1][2][3][4][5] as well as providing information about the clinical course of the patients. Several methods can be used to assay HpC.…”

“…Polymerase chain reaction (PCR)-based procedures utilizing the amplification of polymorphic DNA sequences, such as short tandem repeats (STRs) or variable number of tandem repeats, are used widely because they are sensitive, require a small amount of sample, and are not dependent upon a sex mismatch. [1][2][3][4] It is, however, yet to be determined how to apply these techniques in the care of patients after allogeneic HCT, especially with regard to optimal timing and scheduling of the tests, and also in the interpretation of the results.…”