Proliferative fraction and DNA content are lower in B-cell non-Hodgkin's lymphomas with the t(14;18).

The t(14;18), which juxtaposes the immunoglobulin enhancer region from chromosome 14 to the bcl-2 gene on chromosome 18, is a recurrent cytogenetic abnormality in the majority of follicular lymphomas (FL). This translocation results in overexpression of bcl-2, which increases cellular life span of the mutated cells by decreasing apoptosis. The t(14;18) also occurs in a subgroup of diffuse large cell lymphomas (DLCL), and current thought is that the majority of these represent transformation of FL. Low grade FL are characterized by low proliferation, and diploid/peridiploid DNA content. In this study, we compared proliferative activity (PF) and DNA content (DI) in FL containing the t(14;18) to DLCL with and without the t(14;18). The mean PF and DI were lower in the NHL containing t(14;18) irregardless of histologic subtype. We conclude that increased life span due to the presence of t(14;18) provides the conditions for accumulation of a different set of mutations as compared to those NHL developing from mutations in more rapidly proliferating precursors. This has implications for prognosis of patients with DLCL depending upon the presence or absence of t(14;18).

Comparison of DNA content in non-Hodgkin's lymphoma as measured by flow cytometry and cytogenetics.

Specific cytogenetic changes such as t(14;18) and t(8;14) are associated with specific histologic subtypes of non-Hodgkin's lymphoma (NHL) and may predict disease outcome. Nonspecific cytogenetic changes include other structural rearrangements or numerical changes such as monosomies and trisomies, which may cause changes in total cellular DNA content. In many solid tumors, the presence of abnormal DNA content may be predictive of clinical behavior. NHL biopsies, however, contain normal (diploid) as well as abnormal cells, and DNA changes in the peridiploid range are detectable by cytogenetic analysis, but not consistently by flow cytometry. In the present study, we performed flow cytometric and cytogenetic analysis of DNA on biopsies from 129 patients with non-Hodgkin's lymphoma (NHL). Cytogenetic studies were successful on 88 (68%) of the samples. There was 55% concordance between flow cytometric and cytogenetic techniques in detecting aneuploid DNA content, with the majority of discrepancies occurring in the peridiploid range. We also detected six samples which were aneuploid by flow cytometry, but diploid by cytogenetics. We suggest that a reasonable approach to determine DNA content, as it relates to prediction of outcome in NHL, would be to combine data from both of these techniques and analyze the results in terms of ranges of DNA rather than by categorizing as diploid versus aneuploid.

Effect of 6-hydroxydopamine on murine hematopoietic stem cells: enhanced cytotoxicity on megakaryocyte colony forming units.

We examined the effect of catecholaminergic neurotoxin 6-hydroxydopamine (6-OHDA) on murine committed megakaryocyte progenitor cells, the megakaryocyte-colony forming unit (CFU-Meg). More mature cells of the megakaryocyte series have the capacity for active uptake of catecholamines, and we speculated that the CFU-Meg would also take up 6-OHDA and be selectively killed. CFU-Meg were much more sensitive to the effects of this agent than were granulocyte-macrophage colony forming units (CFU-GM) or spleen-colony forming units. Co-incubation with catalase, which would destroy hydrogen peroxide generated extracellularly by the autoxidation of 6-OHDA, ablated 6-OHDA toxicity towards CFU-GM, but also significantly reduced the effect on CFU-Meg. Mazindol, a selective dopamine uptake inhibitor did not alter 6-OHDA effect on either CFU-Meg or CFU-GM. Finally, CFU-Meg were no more sensitive to incubation with hydrogen peroxide than were CFU-GM. These data suggest that CFU-Meg, unlike their more mature progeny, do not actively concentrate 6-OHDA, and the excess toxicity of this agent towards CFU-Meg is probably due to increased sensitivity to autoxidation products of 6-OHDA, other than hydrogen peroxide, generated extracellularly.

Low proliferative activity is associated with a favorable prognosis in peripheral T-cell lymphoma.

Peripheral T-cell lymphoma (PTCL) consists of a diverse group of post-thymic tumors bearing a mature T-cell phenotype and, excluding mycosis fungoides, comprises approximately 10-20% of the non-Hodgkin's lymphomas in the United States. This category of non-Hodgkin's lymphomas exhibits considerable morphological, immunological, and clinical diversity and is generally considered to be a high-grade malignancy. In the present study, paraffin-embedded biopsy specimens of lymph nodes from 31 patients with PTCL who were treated with curative intent were evaluated by flow cytometry for DNA ploidy and proliferative activity (PA). DNA ploidy was not predictive of the clinical outcome. However, low PA, defined by less than or equal to 10% of cells in S + G2M phase of cell cycle, was associated with a favorable prognosis. Patients with tumors having low PA had a significantly higher complete remission rate (100%) as compared to those with high PA (55%; P less than 0.02), and the predicted actuarial 4-year survival of those with low PA was 85% versus only 50% for those with high PA (P less than 0.04). This is the first report of the effects of PA and DNA ploidy in patients with PTCL who were treated with curative intent. Additional studies of similar patients are needed to confirm these findings.