Malignant lymphoma of plasmacytoid T-cells. Morphologic and immunologic studies characterizing a special type of T-cell.

In 1958, a medium-sized cell was recognized in human lymph nodes and found to occur in clusters in about one out of every 10 cases of reactive hyperplasia. At first, it was interpreted as a lymphoblast. Later, electron-microscopic investigations revealed that the cell contained abundant rough endoplasmic reticulum and was apparently restricted to T-regions of lymph nodes. Recently, it was possible to analyze a malignant lymphoma uniformly composed of such cells with a panel of monoclonal antibodies. The cells proved to be Leu-1+, OKT4+, Leu-3a+, HLA-DR+, and weakly reactive with VIL-A1 (antibody to common ALL antigen) and clone F8-11-13, but negative for OKT3, OKT11, OKT8, cytoplasmic immunoglobulin, common B-cell antigen, and C3b receptors. Short-term, in vitro cultures of lymphoma cells showed weak responses to phytohemagglutinin and Interleukin 2 (IL2), but no IL2 production. Lymphoma cells had a low spontaneous proliferation rate (about 2% Ki-67+ cells). In view of these findings, the term "plasma-cytoid T-cell" is proposed. A functional relationship between these cells and the myeloid system was suggested because the patient developed a myelomonocytic leukemia 3 months after the diagnosis of malignant lymphoma was made.