Long-term study of chimaerism in bone marrow transplantation recipients for severe aplastic anaemia

A systematic approach to molecular quantitative determination of mixed chimaerism following allogeneic bone marrow transplantation: an analysis of its applicability in a group of patients with severe aplastic anaemia

Mixed chimaerism (MC) following allogeneic bone marrow transplantation (allo-BMT) is defined as the persistent cohabitation of haematopoietic cells from recipients and donors. Its kinetics, clinical implications and more efficient laboratory approaches for MC detection are the object of ongoing research in view of the possibility of developing useful markers. Here we describe a sequential analysis of chimaerism using variable number of tandem repeat (VNTR) polymerase chain reaction (PCR) followed by quantitative, fluorescent labelled, short tandem repeat (STR) PCR. A set of four, highly discriminative VNTR and four STR markers was used to assess chimaerism. Sensitivity and regression analysis indicated that this approach was reliable for routine application in a single BMT centre. We studied 12 patients with severe aplastic anaemia (SAA) who had received allo-BMT, and had been conditioned with cyclosphosphamide (Cy) with or without anti-thymocyte globulin (ATG). We found a 50% prevalence of MC in the whole group, with levels between 4% and 37% of recipient cells. A sustained stable MC pattern after BMT was characteristic of the Cy-only conditioned patients but was also recorded in one patient treated with the Cy + ATG regime who showed a sustained MC pattern over a period of 24 months post-BMT. In none of our patients, MC was associated with an increased risk of graft rejection in a median follow-up of 39.5 months.

Minimal residual disease post-bone marrow transplantation for hemato-oncological diseases

The detection of minimal residual disease (MRD), which is important in cancer treatment, gained special significance in bone marrow transplantation (BMT-) due to the possibility not just to detect but recently also to prevent, treat and reinduce remission in patients that relapsed post-BMT by immunotherapy. The various modern techniques of MRD detection are described including cytogenetics, analysis of restriction fragment length polymorphism, variable number of tandem repeats by Southern Blot or polymerase chain reaction (PCR), microsatellite sequences, PCR amplification products of the Y chromosome or the Amelogenin gene, quantitative PCR and fluorescence in situ hybridization. The role of MRD detection in refinement of indications for BMT, autografting, prediction of relapse, adoptive immunotherapy, mixed chimerism in nonmalignant diseases and in solid organ transplantation is discussed.

Studies on hemopoietic chimerism following allogeneic bone marrow transplantation in the molecular biology era

Donor hematopoiesis or donor chimerism in the host following allogeneic bone marrow transplantation (BMT) has appeared crucial to the engraftment process. However, as molecular techniques exploiting neutral variation in human genetic material have been used in the study of chimerism, the detection of residual host cells or mixed hemopoietic chimerism has indicated that donor chimerism is not obligatory following BMT. This review focuses on the detection and significance of mixed chimerism (MC) in patients transplanted for both malignant and non-malignant hemopoietic disease and attempts to tease out the contribution of MC to engraftment, leukemia relapse, graft rejection and long-term disease-free survival.

Evaluation of mixed chimerism by two-step polymerase chain reaction amplification of hypervariable region MCT118 after allogeneic bone marrow transplantation

We assessed the origin of peripheral blood cells and bone marrow cells of 92 samples obtained from 19 patients after allo BMT by two-step polymerase chain reaction (PCR) amplification of MCT118, one of the variable number of tandem repeat regions (VNTR) which has a different length in 19 of 32 sibling pairs examined, that can detect the DNA pattern of a minor cell population of only 1% without using radioisotopes. Mixed chimerism (MC) was detected in the hematopoietic cells of four patients. Two patients who showed progressive MC developed relapse of leukemia 3 months and 4 months after the detection of MC, and two patients died with bone marrow hypoplasia 61 days and 7 months after BMT. These data suggest the clinical importance of analyzing the correlation of MC and clinical complications after BMT by this method, which can be used to monitor MC in about two thirds of allo BMT patients with an adequate sensitivity.

Partial engraftment of donor bone marrow cells associated with long-term remission of haemophagocytic lymphohistiocytosis

We used polymerase chain reaction amplification of minisatellite sequences or of a Y chromosome-specific sequence and Southern blotting to analyse long-term engraftment (12-82 months) after bone marrow transplantation (BMT) for familial haemophagocytic lymphohistiocytosis (FHL). Six children aged from 1 to 18 months were transplanted with bone marrow from an HLA-identical sibling in five cases and from an HLA-nonidentical related donor (one mismatched HLA antigen) in one. The conditioning regiment included VP 16-213 (900 mg/m2), busulfan (16 mg/kg), cyclophosphamide (200 mg/kg) and, in one case, aracytine (2 g/m2). Four patients are alive without therapy more than 3 years after BMT; the other two relapsed 1 year after BMT. DNA was extracted from separated polymorphonuclear cells and mononuclear cells, as well as from separated E+ and E- cells in one case and CD16+ (natural killer) and CD16- cells in two cases. Engraftment was partial in the four long-term survivors. Recipient cells were largely predominant in three of them as well as in one of the patients who relapsed (the donor also developed FHL 18 months after BMT). E+, E-, CD16+ and CD16- cells presented the same pattern of chimaerism. Engraftment failed to occur in the patient who received an HLA-nonidentical bone marrow. These results indicate that partial engraftment is compatible with long-term remission of FHL and that the presence of a small proportion of cells of donor origin can prevent FHL-related lymphocyte and macrophage activation.

Short-term study of chimaerism after bone marrow transplantation for severe aplastic anaemia

Chimaerism was studied early (2 weeks to 3 months) during haematopoietic reconstitution after bone marrow transplantation in 18 severe aplastic anaemia patients (acquired SAA: 14 patients; Fanconi anaemia: four patients). Fourteen patients received marrow from an identical sibling donor, one from the phenoidentical father and three from a matched unrelated donor. Peripheral blood cell DNA was first analysed by Southern blotting with a multilocus minisatellite probe (33.6.3) or a Y chromosome specific probe (pHY2.1). For all 14 patients grafted with a genotypically identical sibling donor, the post-graft DNA profile strictly matched the respective donor profile (minisatellite probe) or disclosed the Y chromosome specific band in the case of female patients grafted with a male donor. In contrast, for the one patient grafted in a mismatched situation and for two out of three patients grafted with a matched unrelated donor, the results indicated autologous bone marrow recovery. This difference between patients grafted with an identical sibling donor and those grafted in other situations is statistically significant (P less than 0.01). The 15 patients with circulating cells of donor origin were then studied by polymerase chain reaction amplification of the DNA samples. The three male patients with a female donor were studied by amplification of a Y chromosome specific sequence (DYZ1), allowing the detection of one male cell in 10(4) female cells. In all three cases, residual male nucleated cells were detected. The analysis was performed by amplification of the 33.6.3 minisatellite sequence for the 12 remaining patients. No residual recipient cells were detected within the sensitivity limit of the method which is 1% in that case. This suggests that detection of residual host cells depends on the sensitivity of the technique used.