T gamma lymphocytosis and T cell chronic leukemias.

The T cell chronic leukemias encompass a broad spectrum of diseases involving mature post-thymic T cells. With the development of highly specific marker studies, clear patterns of immunophenotypic and functional characteristics of the involved cells have emerged. These studies, along with the development of molecular probes for the T cell receptor gene loci, have helped to elucidate the pathogenetic basis for the highly variable clinical course which has been described for patients with these disorders. The T gamma lymphocytosis syndrome has been identified as a benign chronic illness which is nevertheless usually a monoclonal neoplastic proliferation of large granular lymphocytes. These patients represent a distinct clinical entity characterized by splenomegaly, neutropenia, and peripheral blood lymphocytosis. The cells of TGLS are large granular lymphocytes and display many of the immunophenotypic and functional characteristics of NK and K cells. These cells have been implicated pathogenetically in the associated cytopenias seen in the illness, but a clear link has not been established. Although the lymphoproliferative manifestations of the disease are usually easily controlled with low-dose alkylating agents, therapy of the neutropenia has been relatively unsuccessful. Separating these patients from the rest of the spectrum of the T cell chronic leukemias has provided insight into the other disorders as well. It has established that T-CLL and T-PLL are, in fact, extremely rare. T-CLL is similar to its B cell counterpart, except that patients have a higher incidence of skin infiltration. Available data suggest that the prognosis in T-CLL is actually less variable, and somewhat worse, than generally believed when those patients were viewed in conjunction with the patients with the more benign TGLS. T-PLL is an extremely aggressive disease characterized by massive splenomegaly, lymphadenopathy, and skin infiltration. It is refractory to most forms of therapy. These illnesses are again phenotypically distinct from the retrovirus-associated ATLL. Most of the early cases of T-CLL reported from Japan were probably ATLL; this disease is characterized by pronounced splenomegaly, hepatomegaly, lymphadenopathy, and skin infiltration. It has an extremely aggressive natural history, and survival is usually less than 1 year from diagnosis. The rapid development of sophisticated immunologic and molecular techniques for analyzing T cell proliferations has allowed highly specific distinctions to be made among the cells of origin of the different T cell chronic leukemias. It is hoped that increased understanding of the immunologic and functional characteristics of these diverse T lymphoid populations will provide further insights which will have an impact on directed therapeutic interventions in the future.