Variable CD7 expression on T cells in the leukemic phase of cutaneous T cell lymphoma (Sézary syndrome).

CD7, a molecule normally expressed on 90% of normal CD4+ T cells, is often deficient on the malignant T cells of cutaneous T cell lymphoma. To investigate the clinical and biologic implications of CD7 expression, blood lymphocytes from 42 patients with the leukemic phase of cutaneous T cell lymphoma (CD4/CD8 ratio of 10 or more with evidence of a T cell clone in the blood) were analyzed for level of expression of CD7 by flow cytometry. CD7 expression by cells did not clearly segregate into two distinct subgroups that are either CD7 positive or CD7 negative as generally thought; however, nine of 17 patients with a predominantly CD4+CD7+ tumor population on early studies became CD4+CD7- over time whereas the converse situation was not observed. In addition, of three patients with evidence of large tumor cells in the blood coexisting with smaller cells, discordant CD7 expression was observed in one instance. In lymph node specimens, the percentage of cells expressing CD7 and other T cell markers did not correlate with histologic evidence of involvement. CD7 expression on blood lymphocytes also did not correlate with patients' survival nor to serum IgE levels or blood eosinophil counts, a finding suggesting that this marker does not identify functional cell subsets that produce serum interleukin-4 or -5, respectively. We speculate that the level of CD7 expression on malignant T cells may be the effect of sustained antigen stimulation in vivo analogous to what has been proposed to occur with normal T cells during aging.

Distinct epitopes on the T8 molecule are differentially involved in cytotoxic T cell function.

The present report attempts to determine if there are distinct epitopes on the T8 molecule that are involved in class I-restricted cytotoxic T lymphocyte (CTL) function. A panel of 9 monoclonal antibodies (OKT8A,B,C,E,F,G,H,I, and OKT5) was produced and all antibodies were shown to bind to the T8 molecule. This panel of antibodies was employed to characterize the distribution of distinct epitopes on the T8 molecule and to block the activity of class I-specific influenza virus-immune and allo-immune CTL effector function. Significant differences in the ability of the anti-T8 antibodies to block CTL function were observed: OKT8C and T8F blocked best (49 and 55% respectively); OKT8A,E,G,H,I, and OKT5 blocked less well (24-31%); and OKT8B blocked marginally (11%). There was no correlation between the capacity of the antibodies to block CTL function and their heavy chain isotype. Competitive binding of the different OKT8 antibodies to the cell surface and differential trypsin sensitivity of the epitopes recognized by the antibodies indicated that OKT8C and T8F were located on topographically distinct regions of the T8 molecule. These results indicate that specific epitopes on the T8 molecule are involved in CTL function, and that there could be more than one functional site on the molecule.

Failure of anti-T-cell receptor V beta antibodies to consistently identify a malignant T-cell clone in Sézary syndrome.

Monoclonal antibodies (MAbs) reacting with the human T cell receptor (TCR) V beta or V alpha region have been shown to be almost as specific as a private idiotypic MAb in identifying T cell clones. When available, V beta-specific MAbs offer the ease of immunofluorescence analysis to identify and quantitate expanded malignant or nonmalignant T cell populations without requiring polymerase chain reaction (PCR) technology to evaluate expression of V beta gene families. The V beta expression of peripheral blood lymphocytes from twenty-three consecutive patients with Sézary syndrome has been analyzed by reverse transcriptase (RT)-PCR. Ten patients had malignant T cell clones that expressed a TCR V beta corresponding to a commercially available anti-V beta antibody. Immunofluorescence staining with anti-V beta MAbs showed a direct correlation with RT-PCR results in seven of ten patients. No false positive reactivity was noted on immunofluorescence staining with any MAb. Cells from three patients, however, did not react with the corresponding anti-V beta MAb. These three cases expressed a TCR V beta from gene families containing a single member, ie, V beta 14, V beta 18, and V beta 20, yet MAbs reported to be specific for these regions failed to react with the T cell clone from these patients. Sequencing of the PCR product in these cases confirmed the RT-PCR results. Cells from two patients expressed a TCR using V beta 5.1-D beta 1.1 genes with different J-C segments. One patient's cells reacted with an anti-V beta 5.1 MAb (LC4) whereas the other patient's cells bound one-tenth the amount of this same MAb. These results indicate that currently available anti-TCR V region MAbs may not react consistently with T cell clones expressing the corresponding V region or may react with a low affinity making detection difficult. Differences in the J-C junction or in CDR3 may influence the binding of these MAbs. Until the false negative rate is reduced and the fine specificity and affinity of these MAbs is better characterized, both PCR and MAb studies will be required to reliably identify and quantitate clonal T cell populations.