Immunoglobulin gene rearrangement in plasma cell dyscrasias: detection of small clonal cell populations in peripheral blood and bone marrow

Ancillary techniques in bone marrow pathology: molecular diagnostics on bone marrow trephine biopsies

Pathologic examination of trephine bone marrow (BM) biopsies plays a central role in the diagnosis and staging of haematological neoplasms and other disorders affecting haematopoiesis. Haematopathology has been profoundly influenced by the advent of molecular genetic techniques suitable for paraffin-embedded tissues, and certain applications, such as the determination of B- and T-cell clonality, belong to its standard diagnostic repertoire. Many of these molecular tests can be performed successfully with nucleic acids extracted from BM trephine biopsies, if some technical aspects specific to this template source such as various fixation and decalcification procedures are taken into consideration. The current indications for molecular BM diagnostics range from the confirmation of lymphoma involvement with gene rearrangement analysis, demonstration of tumor-specific translocations in lymphoid and chronic myeloproliferative disorders along to the detection of microorganisms or marrow involvement by soft tissue sarcomas. The availability of quantitative polymerase chain reaction techniques for the investigation of allelic imbalances and gene expression levels in paraffin-embedded material also open new avenues for research and advanced diagnostics. The molecular detection of minimal residual disease in haematological neoplasms, especially in the context of new treatment strategies, will provide future challenges. This article summarizes the current state of the art in molecular diagnostics applied to paraffin-embedded BM biopsies.

Mobilisation of tumour cells along with CD34+ cells to peripheral blood in multiple myeloma

BACKGROUND

Cells belonging to the malignant clone are found in the peripheral blood in myeloma patients. In order to minimise the content of tumour cells in the stem cell product it is crucial to perform stem cell harvest at a time when tumour cells in the peripheral blood are at a minimum.

OBJECTIVE

The aim of the study was to compare the mobilisation kinetics of normal CD34+ cells and myeloma plasma cells during mobilisation with either G-CSF alone or high-dose cyclophosphamide (HDCy) plus G-CSF.

DESIGN AND METHODS

Morning blood samples were drawn each day during mobilisation from start of G-CSF or HDCy and to the end of leukapheresis, and were analysed by flow cytometry for content of CD34+ cells and myeloma plasma cells (CD38+ + CD45-). Tumour cells were also estimated by a patient-specific real-time polymerase chain reaction (PCR) method based on the 5' nuclease TaqMan technology.

RESULTS

Flow cytometry data from 16 patients showed concomitant mobilisation of CD34+ cells and myeloma plasma cells. Seven patients were mobilised twice; first with G-CSF alone and then with HDCy plus G-CSF. There was no difference between the two mobilisation regimens regarding tumour cell mobilisation kinetics. Real-time PCR was performed in one patient and confirmed the mobilisation of tumour cells at the time when CD34+ blood cells were at a maximum.

CONCLUSIONS

Tumour cells are mobilised to the peripheral blood at the same time as CD34+ cells in multiple myeloma patients after priming with both G-CSF alone and HDCy in combination with G-CSF.

Longitudinal analysis of circulating myeloma cells detected by allele specific mRNA in situ hybridization

Individual myeloma cells in the peripheral blood of 7 patients with multiple myeloma were detected by mRNA in situ hybridization (ISH) using biotinylated antisense oligonucleotide probes to non-germline sequences of the CDR3 region of the immunoglobulin heavy chain gene. Peripheral blood samples from these patients were studied over a period of 2-3 years. The number of circulating myeloma cells varied from 0.1-23% of the mononuclear cell population. Longitudinal studies showed that the highest number of circulating myeloma cells were present during escape phase and thus the percentage of mRNA ISH+ cells correlated with the clinical state of the patient. This technique is the most accurate means of monitoring and quantitating individual myeloma cells in the peripheral blood of patients with myeloma and provides insight into the relevance of circulating myeloma cells.

Serial studies of peripheral blood myeloma cells in patients with multiple myeloma: when is the optimal time for stem cell harvest?

This study serially quantitated monoclonal plasma cells (PC) in the peripheral blood (PB) of 33 patients with multiple myeloma (MM) at diagnosis, after therapy, and at relapse using a sensitive immunofluorescence technique. The goal was to learn which disease phase is best for harvesting PB stem cells free of monoclonal PC. In 24 chemotherapy responders, 88% (21/24) had circulating PC at diagnosis; after therapy, 63% (15/24) had none, 33% (8/24) had < 3 x 10(6)/L, and only one had > or = 3 x 10(6)/L. In nine cases who failed to respond to initial chemotherapy, 89% (8/9) had high levels (> or = 3 x 10(6)/L) of circulating PC at diagnosis that remained high after therapy. In the relapse phase, 88% (21/24) had circulating PC and 63% (15/24) had high numbers. This study demonstrates that the PB is least likely to have circulating monoclonal PC during the period after successful chemotherapy. Patients who fail to respond to initial chemotherapy or are in relapse are likely to have tumor cells in the PB.

Idiotypic oligonucleotide probes to detect myeloma cells by mRNA in situ hybridization

An mRNA in situ hybridization (ISH) method which used non-radioactive idiotypic oligonucleotide probes has been used to detect malignant cells in the bone marrow and peripheral blood of patients with multiple myeloma. For each of two patients with multiple myeloma a pair of biotinylated antisense oligonucleotide probes (18-22mer) was prepared from non-germline sequences of the rear-ranged immunoglobulin heavy chain (IgH) gene. These oligonucleotide sequences were not homologous with any previously published sequence. The probes from each patient were specific as shown by a failure to hybridize to any cells from six other myeloma patients and four normal individuals. Specific staining of IgH gene mRNA occurred only when the myeloma cells and the sequence of the probe used were from the same patient. Using simultaneous fluorescent immunocytochemistry it was shown that more than 95% of the ISH-positive cells expressed the malignant light chain in their cytoplasm. ISH positive cells were found in 1-4% of the peripheral blood mononuclear fraction of these two patients. These studies show that idiotypic oligonucleotide IgH gene probes can be used to identify individual cells belonging to the malignant clone and offer the possibility of developing innovative tumour-specific therapeutic procedures using antisense technology for patients with myeloma.

Detection of monoclonal plasma cells in the peripheral blood stem cell harvests of patients with multiple myeloma

We evaluated the harvest product from 47 patients undergoing peripheral blood (BP) stem cell collections for monoclonal plasma cells (PC) using a sensitive immunofluorescence technique. 60% (28/47) had documented tumour cells in the apheresis product. The 32 patients in plateau had a mean of 1.62 x 10(6) PC/l v 74.64 x 10(6) in 15 relapsed patients (P < 0.01). 32% (6/19) of patients without any tumour cells in the initial sample had them detected on a subsequent apheresis sample. In four cases (all treated with GM-CSF) small numbers of tumour cells were detected initially but became undetectable on a subsequent sample.