Detection of minimal residual disease by polymerase chain reaction in patients with different hematologic diseases treated by bone marrow transplantation

Morphology of the bone marrow after stem cell transplantation

In many haematological conditions the only curative option is stem cell (SCT) or bone marrow (BM) transplantation. Little information exists about BM morphology following non-ablative engraftment. During the pretransplantation period and depending on the kind of pretreatment, there may be hypoplasia, residual disease and varying degrees of fibrosis. In the post-transplantation period, after 1-3 weeks of transfusion-dependent pancytopenia, the first signs of successful engraftment are indicated by the recurrence of neutrophils, monocytes and erythrocytes in the peripheral blood. In the BM there is slow regeneration of erythropoiesis, followed by the other lineages of haematopoiesis and increase in reticulin fibres or even a resolution of fibrosis. Diagnostic problems arise when neoplastic lympho- or haematopoiesis are maintained following transplantation. Moreover, there may be a significant graft versus tumour response reaction or an already relapsing disease needing aggressive treatment. On the other hand, a conspicuous dyshaematopoiesis should not be mistaken as representing a myelodysplastic syndrome. The presence of granulomas being treatment-related or a manifestation of intercurrent granulomatous disease has to be considered. More advanced knowledge of the histological features of regenerating BM will certainly aid the recognition of relapsing disease and is needed for the adequate reporting of post-transplant alterations associated with a successful or failing engraftment.

Mixed chimerism of erythro- and megakaryopoiesis following allogeneic bone marrow transplantation

Until now, studies on mixed chimerism (MCh) after allogeneic bone marrow transplantation (BMT) have predominantly focused on the B- and T-lymphocyte population, but not on distinct myeloid cell lineages like nucleated erythroid precursors and megakaryocytes. To evaluate the lineage-restricted MCh more explicitly in 10 patients with chronic myelogenous leukemia (CML), a quantitative analysis was performed on bone marrow biopsies following a sex-mismatched host/donor constellation. Techniques included immunophenotyping (antiglycophorin C, CD61) for the identification of erythro- and megakaryopoiesis and a simultaneously conducted genotyping with x- and y-chromosome-specific DNA probes. Normal bone marrow and specimens taken before BMT served as controls. Contrasting a total gender-dependent sex-typing in the latter samples in the early and late posttransplant period (up to 586 days), 3-9% erythroid precursors and about 16% megakaryocytes revealed a host-type origin. This significantly higher number of host megakaryocytes is explained by their polyploidy generating an increased probability to detect positive signals at a certain section level of the corresponding biopsies. A striking conversion of MCh to a recipient cell type was found in leukemic relapse with a more than 90% host-derived erythroid and megakaryocytic cell population in 4 patients approximately 643 days after BMT.

Comparative Study of FISH, PCR and Cytogenetics on 25 Patients Submitted to Bone Marrow Transplantation (BMT) for Chronic Myelogenous Leukemia (CML); Which Tests can we Use in Routine Analysis Post BMT?

Chronic Myeloid Leukaemia (CML) shows an excellent response to allogeneic bone marrow transplantation (BMT) with a 60-80% long term disease free survival in recipients of unmanipulate marrow. The most frequent cause of treatment failure is leukaemic relapse, due to the re-emergence of malignant recipient clones. Clinical and haematological relapse is usually preceded by molecular evidence of relapse. Early detection of molecular relapse may allow intervention with immunotherapy such as donor lymphocyte infusions (DLI). This study was undertaken to compare results from two centres who employ either Fluorescent In Situ Hybridisation (FISH) or polymerase chain reaction (PCR) analysis of DNA polymorphisms as their routine method of detecting residual host cells following BMT for CML in order to establish (1) if these methods are equivalent for routine laboratory use in reporting of chimaerism results to the referring clinician, and (2) if these methods are beneficial for indicating new and early therapeutic strategies. FISH analyses for the X and Y chromosomes (in sex mismatched patients) and/or FISH for BCR and ABL loci were compared with short tandem repeat PCR (STR-PCR) and conventional karyotyping in serial analyses in 25 patients submitted to BMT for Philadelphia positive (Ph) CML. Comparison of all results on samples assessed between 1 and 13 years post BMT indicated that FISH and PCR, performed on the same bone marrow samples displayed similar results in more than 90% of patients in first 3 years after BMT which increased to a concordance rate of 100% in long term survivors. In contrast, comparison of FISH or PCR versus cytogenetic analysis indicated a low concordance rate, with less than 50% of samples showing similar results during all the follow-up period. Eighty percent of recipients (22 patients) had evidence of mixed chimaerism following BMT (initial level of positivity 1-6% recipient cells) during the follow-up period. This low percentage of recipient cells remained stable in 7 patients, while 9 patients reverted to a donor profile. All 16 patients are in haematological remission. In addition the 3 patients with complete donor chimaerism remain in remission. In the remaining 6 patients, a progressive increase in recipient cells occurred (progressive mixed chimaerism, PMC), and was followed by haematological relapse. We conclude that FISH and PCR can be used to monitor CML patients post BMT and transient or stable low level mixed chimaerism is not associated with leukaemia relapse, but PMC is predictive of imminent relapse and its detection may help to illucidate the timing of early intervention with donor lymphocyte infusion.

p53 loss and point mutations are associated with suppression of apoptosis and progression of CML into myeloid blastic crisis

A longitudinal investigation using fluorescence in situ hybridization (FISH) analysis, PCR-SSCP, and in situ detection of apoptosis by the terminal deoxynucleotidyl Transferase (TdT) method was carried out on 13 chronic myelogenous leukemia (CML) patients to study the p53 gene behavior and the apoptotic process during the course of the disease. At diagnosis, FISH showed no loss of the p53 gene on interphase nuclei, and no point mutation was detected by polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) and sequencing. During the disease course, FISH analysis showed a significative loss of allele (LOA) rate for the p53 gene in eight patients that in seven cases was associated with a suppression of apoptotic process and the progressive expansion of the p53+/p53- clone. DNA sequencing showed in two of these eight patients a point mutation on the other allele, consisting in the formation of a stop codon in one case, and in a frameshift mutation in the other. Six patients had a myeloid blastic crisis (BC), five a lymphoid BC, and the other two an erythroid and an undifferentiated BC, respectively. All patients with myeloid BC and the one with undifferentiated BC disclosed a progressive expansion of the clone with p53 loss that was associated with a significant reduction in apoptosis. On the contrary in the 5 patients with lymphoid BC no significant p53 LOA rate was observed during the course of the disease. In these patients apoptotic process also persisted in the acute phase although in a lower rate as compared to CP.

Detection of residual host cells in sex-mismatched bone marrow transplantation in various hematological diseases by fluorescence in situ hybridization

Thirty-eight sex-mismatched bone marrow transplantation patients with various hematological diseases were followed-up using fluorescence in situ hybridization. Probes specific for various translocations, the X chromosome (DXZ1) and the whole Y chromosome (WCP Y), were used to assess successful engraftment and residual host cells. The combination of translocation and WCP Y probes enabled the identification of host and donor cells in addition to the identification of malignant vs. normal cells in the transplant recipient. Fifteen patients were sequentially followed up. The results obtained using the combination of translocation plus WCP Y probes were more reliable than those with DXZ1 plus WCP Y probes, or the translocation probe alone, especially when the percentage of residual leukemic cells detected by the translocation probe alone was around the cut-off level.

Retrospective investigation of hematopoietic chimerism after BMT by PCR amplification of hypervariable DNA regions

We report on nine patients submitted to BMT with sex-matched donors and investigated by means of PCR amplification of the VNTRs ApoB, D1S80, DXS52, and D17S5. In all cases it was possible to detect a polymorphism able to distinguish between donor and patient cells, thus allowing us to recognize the presence of complete or mixed chimerism. In eight patients PCR analysis showed a complete chimerism during the entire follow-up. Only one of these patients relapsed, while the others are alive and without any sign of relapse 56.2 months (mean) after BMT. Mixed chimerism was detected in only one patient, who relapsed 3 months after this finding. These results confirm the usefulness of the study of PCR-amplified VNTRs in the assessment of marrow engraftment after BMT, mostly in sex-matched transplants where, in the absence of specific chromosome rearrangements, cytogenetic or FISH analysis cannot be used.

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.

Detection of minimal residual disease after sex-mismatch bone marrow transplantation in chronic myelogenous leukemia by fluorescence in situ hybridization

Detection of minimal residual disease is one of the major goals in bone marrow transplantation. We used a fluorescence in-situ hybridization technique to detect residual Philadelphia-chromosome positive cells in chronic myelogenous leukemia (CML) patients after sex-mismatch BMT. We analyzed the level of detection using probes for the BCR/ABL fusion product by comparison with results obtained with probes for the Y and X sex chromosomes. Detection of sex-mismatch chromosomes was significantly higher than that of the BCR/ABL translocation. In contrast, a higher specificity of residual tumor cell detection by the BCR/ABL probe was demonstrated because most of the sex-mismatch cells detected by FISH had a normal karyotype. Tumor-specific markers probes are thus superior and more accurate than sex-mismatch probes for detection of MRD in CML patients after BMT.