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A monoclonal antibody OKT 9 which detects a determinant expressed by a variety of proliferating cell types has been recently developed. This antibody was used in conjunction with the immunoperoxidase technique to study the cutaneous lymphoid infiltrates of nine patients with mycosis fungoides, one patient with lymphomatoid papulosis, two patients with Sézary syndrome, and ten patients with large plaque atrophic parapsoriasis (a condition which may terminate in overt mycosis fungoides.) OKT 9 reactive cells were identified in all cases of mycosis fungoides examined, in one case of lymphomatoid papulosis, one of two cases of Sézary syndrome, and one of ten cases of large plaque atrophic parapsoriasis. These results suggest that further studies using OKT 9 should be performed to assess whether OKT 9 reactivity may be used as a prognostic marker in cutaneous lymphomas and prelymphomas.

A monoclonal antibody (OKT10), which was developed recently, reacts with pro-thymocytes, T cell acute lymphoblastic leukemia (ALL) cells, cells in normal bone marrow (including plasma cells), and activated T cells. Tissues from patients with cutaneous T cell lymphoma were studied for the presence of OKT10-reactive cells with the use of an indirect immunoperoxidase technic. OKT10-reactive cells were identified in three of eight cases of mycosis fungoides, one of two cases of Sézary syndrome, with an equivocal reaction in one of ten cases of large-plaque parapsoriasis and in one of seven positive patch tests (allergic contact dermatitis). The biologic and possible clinical implications are discussed.

In situ immunologic phenotyping of the cutaneous lymphoid infiltrates of five cases of mycosis fungoides (MF) was performed. This was done by the immunoperoxidase technic using monoclonal antibodies directed against normally expressed by mature peripheral T cells and T cells subsets. A significant proportion of the infiltrates reacted with peripheral T cell antibodies. In addition, "helper" predominance was demonstrated. However, cells reacting positively with "suppressor" antibodies were also demonstrated in three cases, indicating immunologic heterogeneity of the infiltrates. The presence of a significant component of the infiltrates yielding an equivocal or negative reaction with the mature T cell antibodies, especially in the infiltrates of one case which had a fatal outcome, suggests further heterogeneity with the presence of immature cells. Future investigation with monoclonal antibodies directed against immature T cell differentiation antigens will be of interest.

Infiltrates of five cases of mycosis fungoides (MF) were studied for the presence of cells reactive with a monoclonal antibody, OKT 6, which detects an antigen present on relatively immature thymocytes and Langerhans cells. In situ immunohistochemical staining was used for their demonstration. OKT 6-reactive cells formed a definite component of the dermal infiltrates of all patients examined. In three patients who showed numerous Pautrier microabscesses on routine histologic examination, OKT 6-positive cells were found to form a component of these abscesses. OKT 6-reactive cells have also recently been shown to be present in varying numbers in the dermal infiltrates of large plaque (atrophic) parapsoriasis (LPAP), a condition which may terminate in MF. The significance of these findings is discussed.

The T cell nature of mycosis fungoides and Sézary syndrome was established a decade ago. The recent advent of monoclonal antibodies to T cells and other lymphoid subpopulations has resulted in an explosion of knowledge on the biology of this group of disorders. These reagents have increased our knowledge on thymic differentiation status, pathogenesis, the phenotype of premalignant vs malignant lymphocytic infiltrates, the identification of other previously unrecognized cells within lymphomas, and the phenotype of circulating vs skin lymphocytes. Therapeutic applications may result. These new developments are discussed.

Experimental work on animal models suggests that various lymphoid subpopulations (K/NK, lymphocytes, macrophages, T-cells) may play a role in immunity against neoplasia, including lymphomas. The incidence and possible role of these cells in spontaneously occurring human tumors is less clear. The prevalence of these lymphoid subpopulations was studied in 60 cutaneous biopsy specimens using in situ immunocytochemistry. Monoclonal HNK-1 (Leu 7), which detects human granular lymphocytes with K/NK function, was used to detect K/NK lymphocytes; macrophages were identified by diffuse cytoplasmic esterase activity; T-cells were identified using monoclonal antibodies OKT3 and Leu 1. HNK-1+ lymphocytes, esterase-positive macrophages, and infiltrating T-cells were identified in varying numbers in the cases studied. The demonstration of HNK-1+ lymphocytes, macrophages, and T-lymphocytes in cutaneous lymphoma lesions is of potential therapeutic application. Whatever the naturally occurring role of these immune cells, it is possible that they may be manipulated pharmacologically for the benefit of the patient.

The development of monoclonal antibodies to T cells at various stages of differentiation, B cells and histiocytes, suggests that these reagents may be of use in the diagnosis and categorization of cutaneous lymphomas. The findings to date in skin and blood are discussed.