Thymic hormones in cancer diagnostics and treatment

The thymus is an endocrine organ. A unified, physiological concept of humor al regulation of the immune response emerged in the last three decades. The thymus is the primary major site of production of immunocompetent T-lympho cytes from their haematopoietic stem cells. The thymus provides a superior humoral microenvironment for the development of immunocompetent T-lymphocyt es. Although yolk sac derived pre-T stem cells enter the thymus using a hom ing receptor, the immigration process requires also secretion of a peptide, called thymotaxin by the cells of the reticulo-epithelial (RE) network. Th is complex process requires direct cell to cell, receptor based interaction s, as well as in situ paracrine information via the numerous cytokines and thymic hormones produced by the RE cells of thymic microenvironment. Thymic hormones induce in situ T-lymphocyte marker differentiation, expression an d functions. These polypeptide hormones have also been shown by means of im munocytochemistry to localise in the RE cells of the thymic cellular microe nvironment. Based on the complexity of the intrathymic maturation sequence of T-lymphocytes and the increasing numbers of T-lymphocyte subpopulations that are being identified, it would be surprising if a single thymic humora l factor could control all of the molecular steps and cell populations invo lved. Rather, it would appear that the control of intrathymic T-lymphocyte maturation and functional maturation involves a complex number of thymic-sp ecific factors and other molecules that rigidly control the intermediary st eps in the differentiation process. Thymosin fraction 5 (TF5) and its compo nent polypeptides influence a variety of lymphocyte properties including cy clic nucleotide levels, migration inhibitory factor production, T-dependent antibody production and expression of certain surface maturation/different iation markers. Recently, thymic hormones, mostly thymosins have been emplo yed not only in neoplasms' early detection but also in clinical trials to s trengthen the effects of immunomodulators in immunodeficiencies, autoimmune diseases and neoplastic malignancies. Combined chemoimmunotherapeutical an tineoplastic treatment seems to be useful. Generally, haematopoietic toxici ty of every chemotherapeutical clinical trial can be reduced significantly by the immunotherapy, compared to 50% in patients treated with chemotherapy alone.