Failure of anti-T-cell receptor Vβ antibodies to consistently identify a malignant T-cell clone in Sezary syndrome

Monoclonal antibodies (MAbs) reacting with the human T cell receptor (TCR) Vβ or Vα region have been shown to be almost as specific as a private idiotypic MAb in identifying T cell clones. When available, Vβ-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 Vβ gene families. The Vβ expression of peripheral blood lymphocytes from twenty- three consecutive patients with Sezary syndrome has been analyzed by reverse transcriptase (RT)-PCR. Ten patients had malignant T cell clones that expressed a TCR Vβ corresponding to a commercially available anti-Vβ antibody. Immunofluorescence staining with anti-Vβ MAbs showed a direct correlation with RT-PCR results in seven often 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-Vβ MAb. These three cases expressed a TCR Vβ from gene families containing a single member, ie, Vβ14, Vβ18, and Vβ20, 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 front two patients expressed a TCR using Vβ5.1-Dβ1.1 genes with different J-C segments. One patient's cells reacted with an anti-Vβ5.1 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.