Purine analogs in lymphoproliferative disorders

The functional phenotype of the primitive plasma cell in patients with multiple myeloma correlates with the clinical state

The malignant plasma cells from patients with multiple myeloma display considerable phenotypic heterogeneity. All plasma cells express high intensity CD38 (CD38++), cytoplasmic immunoglobulin and either kappa or lambda light chains. Subpopulations of mature (CD45-), immature (CD45+) and primitive (CD45++, CD19+) plasma cells can be defined but little is known about the functional differences and clinical significance of these subpopulations. Three colour flow cytometry and permeabilisation was used to determine the expression of functionally important antigens in plasma cell subpopulations. These antigens included the labelling index (LI, bromodeoxyuridine), number of nucleoside transporter per cell, p-glycoprotein (JSB-1), and oncoprotein expression (c-myc, c-fos, c-neu, bcl-2, p-ras, p53m, p-53w, and Rb). In progressive disease there was an increase in the absolute number but not the percentage of CD45++ plasma cells. There was a significant difference in the mean LI of the CD38++, CD45++ population in progressive disease compared with stable disease (9.2% vs 2.2%; z = 19.9, p < 0.001). The LI of CD45++ cells ranged up to 45% and provided a better correlation with disease status than the LI of the total cell population. Any increase in nucleoside transporters or p-glycoprotein expression was almost entirely attributable to an increase in the primitive plasma cell population. In 96% (n = 28) of samples from patients in progressive disease there was at least one abnormality in the functional phenotype of the primitive plasma cells. This is in contrast with 44% of samples from patients in stable disease (n = 58). These studies suggest that the functional phenotype of the primitive plasma cell determines the clinical phenotype of patients with myeloma.

The biological therapy of acute and chronic leukemia

With the increasing knowledge of the mechanisms of immune-mediated cytotoxicity, immunotherapeutic strategies are rapidly being incorporated into chemotherapy treatment schemes for acute and chronic leukemias. This includes the use of mAbs, immunotoxins, tumor-specific T cells, and, most recently, vaccines. Much of the new information is derived from bone marrow transplant data, where immune enhancement from IL-2 and donor T-cell infusions are being studied. Trials using humanized mAbs that permit prolonged and repeated dosing will allow better evaluation of the effectiveness of mAb therapy. More sophisticated molecular tests have been developed, allowing the detection of minimal residual disease to a greater degree. It is likely that biological and immunological therapy of leukemia will have its greatest impact here.

Low-grade lymphomas: new entities and treatment concepts

Therapy for patients with low-grade lymphomas has never been standardized. Recently, new entities have been described which are included in the REAL classification, and whether these entities should be regarded as separate diseases is not yet clear. Regardless, three new developments in the management of patients with low-grade lymphomas deserve special attention for treatment programs in the future. First, it appears that patients with stage I, II, and III low-grade lymphomas may enjoy very prolonged disease-free intervals after treatment with combination chemotherapy and radiation therapy programs. Although investigators disagree on prognostic factors, new features, such as beta 2-microglobulin appear to predict results better than any other feature, and future studies should address this prognostic factor in assessing their results. Second, for patients with advanced stage disease, administration of interferon as maintenance therapy prolongs the disease-free interval, and use of this drug should be further investigated. Finally, molecular studies using PCR for bcl-2 may be clinically relevant in detecting residual disease in patients with follicular lymphomas, and future studies should focus on the value of eliminating the residual disease from blood and marrow.

Adaptation of the TdT assay for semi-quantitative flow cytometric detection of DNA strand breaks

The enzyme Terminal Deoxynucleotidyl Transferase (TdT) is a DNA polymerase which can be used to label DNA strand breaks by the incorporation of a labelled nucleotide followed by a fluorescent detection step. The amount of label incorporated can then be assessed by flow cytometry. The mechanism of action of TdT, however, will allow the addition of varying numbers of nucleotides to the free 3' termini produced by DNA strand breaks. The substitution of Digoxigenin (DIG) labelled dideoxy-nucleotides for labelled deoxy-nucleotides in the TdT assay will limit the addition of label to a DNA break to a single nucleotide, thus ensuring a direct relationship between an increase in DNA strand breaks and an increase in fluorescence. We have used this adaptation of the TdT Assay to evaluate DNA damage incurred in lymphocytes, from patients with Chronic Lymphocytic Leukaemia (CLL), on exposure to UV irradiation and apoptosis-inducing drugs, fludarabine and 2-Chloro-2'-deoxyadenosine (2-CdA). This technique may give a good indication of the susceptibility of CLL patients to apoptosis inducing drugs, and hence an indication of the likely response to these therapies.