Flow cytometric clonal excess analysis of peripheral blood, routine handling, and pitfalls in interpretation

Multiplex polymerase chain reaction on FTA cards vs. flow cytometry for B-lymphocyte clonality

BACKGROUND

Two-colour flow cytometry was compared with multiplex PCR with capillary electrophoresis for clonality determination in specific categories of B-cell lymphoma. FTA cards were evaluated for preserving DNA from node imprints and expediting molecular analysis.

METHODS

A single-tube multiplex PCR targeted IGH and lymphoma-specific translocations in DNA extracted from 180 frozen lymphoid tissues and DNA bound to FTA cards from 192 fresh tissues and 137 aspirates. PCR results were compared with flow cytometry in the extracted and aspirated samples.

RESULTS

Overall, single-tube multiplex PCR sensitivity was equivalent in the sample groups (intergroup range 79%-91%). False negatives were associated with tumour origin in the follicle centre. Multiplex PCR and flow cytometry were equally sensitive and together detected 98% of B-cell lymphomas. Additional two-tube targeting of IGK suggested an overall molecular sensitivity >90%. False positive (pseudoclonal) single-tube multiplex PCR was associated with necrosis and sparse lymphocytes.

CONCLUSIONS

Multiplex PCR using template DNA bound to an FTA card effectively detects B-lymphocyte clonality, obviates DNA extraction and refrigeration, and can be used without diminished sensitivity in fine needle aspirates or node imprints as a replacement for or complement to flow cytometry at any point in the diagnostic work-up.

Light chain-restricted autoantibodies in chronic idiopathic thrombocytopenic purpura, but no evidence for circulating clone B-lymphocytes

In chronic idiopathic thrombocytopenic purpura (ITP) platelet destruction is caused by antibodies directed against platelet membrane glycoproteins (GP), and the predominant autoantigens are known to be GPIb/IX and GPIIb/IIIa. In a recent study we reported that these antibodies frequently had a restricted light chain phenotype, thereby supporting a clonal origin. Similar findings and the presence of clonal B-cell populations in immune thrombocytopenias have been reported by others. In the present study we further explored the hypothesis of clonal B-cell expansions in chronic ITP. Twenty patients with chronic ITP were investigated. Antibodies were detected with an ELISA (MAIPA) specific for GPIb/IX and GPIIb/IIIa; circulating clonal B lymphocytes were assessed by flow-cytometric (FACS) clonal-excess analysis and by analyzing Ig-gene rearrangements (CDR3) with the PCR technique. Nine patients displayed a GP-specific antibody restricted to either kappa or lambda phenotype. However, FACS analysis and Ig-gene rearrangement studies did not disclose any circulating clonal B-cell population. Considering the sensitivity of the FACs analysis and Ig-gene rearrangement for detection of clonal B-cell populations, the hypothesis of clonally derived autoantibodies in ITP is still valid. Most probably, the clonal B-cell expansion responsible for the production of autoantibodies in ITP, if present, is below the detection limit for the techniques employed.

Absence of minimal residual disease detectable by FACS, Southern blot or PCR in patients with chronic lymphocytic leukaemia treated with fludarabine

We report the results of assessment of minimal residual disease in four patients with chronic lymphocytic leukaemia, who achieved clinical and haematological complete response following treatment with fludarabine. Patients were assessed both before and after treatment by immunophenotyping, DNA electrophoresis, Southern blotting and PCR amplification to detect immunoglobulin gene rearrangements. Immediately after treatment, no patient had disease detectable by any method and there was evidence of recovery of normal B-cells. No patient has yet shown evidence of clinical or haematological relapse (follow-up 59-142 weeks). Two patients remain in immunophenotypic and molecular remission at 141 and 59 weeks. These methods have allowed more sensitive definition of elimination of residual disease, with PCR demonstrating the capacity to detect disease recurrence before any other evidence is available.

Blood lymphocyte clonal excess in advanced non-Hodgkin's lymphoma. Relation to clinical data and prognosis

BACKGROUND

Increasingly sensitive methods, based on the monoclonal nature of NHL, are used to detect tumour spread and remaining disease. Since the lymphomas are thought to arise due to successive genetic changes, clonal cells in different compartments do not necessarily represent the same disease despite a common clonal origin.

PATIENTS AND METHODS

In 179 patients with advanced NHL, clonal cells in peripheral blood were identified by light chain restriction analysed in flow cytometry, i.e. clonal excess (CE) analysis.

RESULTS

CE was more common in low grade NHL (52%) than in high grade NHL (21%). In patients with a normal lymphocyte count CE was found in 23%. CE was significantly correlated to small cell histology and bone marrow involvement. In high grade NHL CE in peripheral blood was more common in those with discordant small or mixed cell involvement of the bone marrow. CE was significantly related to failure to achieve remission in both histologic subgroups. Survival was not influenced by CE in low grade NHL but in high grade NHL. In multivariate analyses however, CE did not emerge as an independent risk factor but age, B-symptoms and LDH were the major factors.

CONCLUSIONS

The utility of blood CE analyses in clinical praxis has still to be settled and the prognostic value of CE per se seem limited in the current perspective. The existence of CE in high grade NHL might be a clue of different biology as compared to de novo high grade NHL.