Background and design: To accurately assess tumor burden in cutaneous T-cell lymphoma as well as to determine the number of residual normal circulating T cells, it is necessary to accurately distinguish malignant cells. Because cutaneous T-cell lymphoma cells regularly display many normal phenotypic markers of T cells (CD2+, CD3+, CD4+) these surface proteins have been of limited value. We have used a set of monoclonal antibodies with specificity for those T-cell receptor proteins containing variable regions on the beta chain to distinguish normal from malignant T cells in patients with cutaneous T-cell lymphoma.
Results: The results revealed an unanticipated and profound expansion of the malignant cell populations (59% to 87% of blood T cells) in six patients with total T-cell counts in the normal or near normal range. By subtracting the percentages of malignant T cells, identified in this manner, from the total T-cell counts, we found that the residual normal T-cell compartments were small (0 to 0.155 x 10(9)/L) in four of the six patients. Sézary cell counts by peripheral blood smear analysis by routine light microscopy underestimated the number of malignant T cells. Markedly elevated CD4/CD8 ratios (10 to 90) occurred in all cases, reflecting expansion of the CD4+ malignant population and parallel reduction of the normal residual CD8+ subset.
Conclusions: Patients with erythrodermic cutaneous T-cell lymphoma often have markedly depressed levels of normal blood T cells, to the range seen in advanced acquired immunodeficiency syndrome, and absolute numbers of malignant cells substantially exceed those recognized with less sensitive techniques.