Peripheral T-cell lymphomas

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Abstract
The development of T cells from stem (progenitor) cells to effector cells results from a two-wave process of proliferation and differentiation. The cells of the first differentiation wave are the precursor T cells, and those of the second differentiation wave are peripheral T cells, hi the first differentiation wave, resting/circulating naive antigen-reactive T lymphocytes are produced which differ from each other in their antigen receptor-speci-ficity. In the second differentiation wave, those T lymphocytes multiply whose antigen receptors have found the corresponding antigen. Thus three major forms of differentiation can be distinguished in the peripheral T cells: (1) resting/circulating naive antigen-reactive T cells, (2) activated T cells, and (3) effector T cells and memory T cells. In addition, there are at least three major organ-restricted sublines of peripheral T cells, i.e., nodal T cells, mucosa-associated T cells, and skin-associated T cells. Thanks to the availability of markers for most of the above-mentioned T-cell sublines and differentiation forms, all these cellular forms can be associated with certain lymphoma types, i.e., lymphomas of T-cell type can be divided into categories of precursor T-cell lymphomas and peripheral T-cell lymphomas. The peripheral T-cell lymphomas can be subdivided into those derived from lymph nodal, mucosal, and cutaneous T cells. The gut mucosal T-cell lymphomas are associated with enteropathy. The lymph node, mucosal, and cutaneous T-cell lymphomas can be further subdivided into those in which all tumor cells are similar to recirculating resting (nonactivated) T cells, those in which some of the tumor cells resemble activated T cells, and those in which all tumor cells resemble activated T cells. The second group includes pleo-morphic T-cell lymphoma, Lennert's lymphoma, and angioimmunoblastic T-cell lymphoma, and the third group includes Ki-1+ (CD30+) anaplastic large-cell (ALC) lymphomas of T-cell type. The apparently constant associa-tion of Ki-1+ T-ALC lymphoma with the breakpoint 5q35 underlines the justification of its classification as a separate entity.