Minimal Disease Detection and Confirmation in Hematologic Malignancies: Combining Cell Sorting with Clonality Profiling

Detection of monoclonal IGH rearrangements in circulating cells from healthy first-degree relatives of patients with multiple myeloma

Multiple myeloma (MM) is characterized by abnormal proliferation of clonal plasma cells or monoclonal plasmacytosis, resulting in accumulation of clonal immunoglobulins. Monoclonal gammopathy of unknown significance (MGUS) is considered a premorbid stage for developing MM. Studies have shown an increased risk of MGUS in first-degree relatives of patients with MM. Detection of immunoglobulin heavy chain gene (IGH) rearrangement provides a useful tool for assessing clonality. The aim of this study was to determine clonality in peripheral blood samples from 61 healthy first-degree relatives of MM probands by sorting circulating lymphocytes and detection of the IGH rearrangements in these cells. We detected 16 out of 61 (26.2%) relatives with monoclonal complete and incomplete IGH rearrangements; only three of them showed elevated monoclonal immunoglobulin in the serum protein electrophoresis. We conclude that this strategy is able to identify efficiently clonality in peripheral blood samples from first-degree relatives of patients with MM, who have a non-negligible risk of developing MGUS or other plasma cell dyscrasias.

Cell sorting in cancer research--diminishing degree of cell heterogeneity

Increasing evidence of intratumor heterogeneity and its augmentation due to selective pressure of microenvironment and recent achievements in cancer therapeutics lead to the need to investigate and track the tumor subclonal structure. Cell sorting of heterogeneous subpopulations of tumor and tumor-associated cells has been a long established strategy in cancer research. Advancement in lasers, computer technology and optics has led to a new generation of flow cytometers and cell sorters capable of high-speed processing of single cell suspensions. Over the last several years cell sorting was used in combination with molecular biological methods, imaging and proteomics to characterize primary and metastatic cancer cell populations, minimal residual disease and single tumor cells. It was the principal method for identification and characterization of cancer stem cells. Analysis of single cancer cells may improve early detection of tumors, monitoring of circulating tumor cells, evaluation of intratumor heterogeneity and chemotherapeutic treatments. The aim of this review is to provide an overview of major cell sorting applications and approaches with new prospective developments such as microfluidics and microchip technologies.

Detection of genomic abnormalities in multiple myeloma: the application of FISH analysis in combination with various plasma cell enrichment techniques

Multiple myeloma (MM) is a hematopoietic neoplasm characterized by malignant plasma cells (PCs) that accumulate in the bone marrow. A number of different genomic abnormalities are associated with MM; however, detection of these by fluorescence in situ hybridization (FISH) can be limited by the percentage of PCs in the specimen. In this study, we tested 20 bone marrow specimens with known MM and a low concentration of monoclonal PCs for the presence of genomic abnormalities using FISH in combination with various PC enrichment techniques: magnetic cell sorting, targeted manual scoring, and automated image analysis. In addition, flow cytometric cell sorting of PCs in combination with FISH analysis was also tested for minimal residual disease applications. Different parameters were evaluated when assessing the detection efficiency of each approach. FISH results are highly dependent on the chosen enrichment method. We describe the evaluation of different techniques applicable for various laboratory settings and specimen parameters.

DNA ploidy analysis as an adjunct for the detection of relapse in B-lineage acute lymphoblastic leukemia

Detection of relapse in acute lymphoblastic leukemia (ALL) is essential for proper management. However, immunophenotypic detection of relapse by flow cytometry in B-lineage ALL can be confounded by several factors, including lack of a unique immunophenotype and modulation of aberrant phenotypes after treatment. We hypothesized that flow cytometric DNA ploidy analysis may detect relapse in aneuploid ALL cases that might be missed by flow immunophenotyping. We retrospectively studied ALL cases at our institution between 1991 and 2003 (n = 114). Aneuploid populations were present at diagnosis in 32% of all patients. Sixty-five percent of all patients had "normal" leukemic immunophenotypes, defined as being similar to normal precursor B-cells, while 35% had "aberrant" immunophenotypes with myeloid or T antigen co-expression. In ALL cases that were originally aneuploid, follow-up ploidy-analysis detected relapsed disease in all cases which were also detected by flow immunophenotyping, suggesting that ploidy analysis is highly sensitive for detecting ALL relapse. However, in 5 cases in which the diagnosis of relapse could not be reliably made by flow immunophenotyping, ploidy analysis successfully detected aneuploid cells, i.e., relapse, in all five; these included 3 patients with normal and 2 with aberrant original immunophenotypes. These results suggest that it may be beneficial to perform ploidy analysis as an adjunct to flow immunophenotyping in following patients with B-lineage ALL who demonstrate aneuploidy at diagnosis.