Recent thymic emigrants as the bridge between thymoma and autoimmune diseases

The thymus represents the major site of the production and generation of T cells expressing alphabeta-type T-cell antigen receptors. Age-related involution may affect the ability of the thymus to reconstitute T cells expressing CD4 cell-surface antigens that are lost during HIV infection; this effect has been seen after chemotherapy and bone-marrow transplantation. Adult HIV-infected patients treated with highly active antiretroviral therapy (HAART) show a progressive increase in their number of naive CD4-positive T cells. These cells could arise through expansion of existing naive T cells in the periphery or through thymic production of new naive T cells. Here we quantify thymic output by measuring the excisional DNA products of TCR-gene rearrangement. We find that, although thymic function declines with age, substantial output is maintained into late adulthood. HIV infection leads to a decrease in thymic function that can be measured in the peripheral blood and lymphoid tissues. In adults treated with HAART, there is a rapid and sustained increase in thymic output in most subjects. These results indicate that the adult thymus can contribute to immune reconstitution following HAART.

In recent years, the understanding of regulatory T cell (Treg cell) biology has expanded considerably. Key observations have challenged the traditional definition of Treg cells and have provided insight into the underlying mechanisms responsible for the development of autoimmune diseases, with new therapeutic strategies that improve disease outcome. This Review summarizes the newer concepts of Treg cell instability, Treg cell plasticity and tissue-specific Treg cells, and their relationship to autoimmunity. Those three main concepts have changed the understanding of Treg cell biology: how they interact with other immune and non-immune cells; their functions in specific tissues; and the implications of this for the pathogenesis of autoimmune diseases.

Thymoma is a rare malignancy of unknown etiology. The author examined patterns in thymoma incidence in the US general population using data from Surveillance, Epidemiology, and End Results (SEER) cancer registries. Prior studies concerning the risk of additional malignancies in thymoma patients were reviewed. Based on cancer registry data, the overall incidence of thymoma in the US is 0.13 per 100,000 person-years. Thymoma is exceedingly uncommon in children and young adults, rises in incidence in middle age, and peaks in the seventh decade of life. Thymoma incidence is especially high among Asians and Pacific Islanders in the US. While several studies based at single treatment centers have suggested that thymoma patients have a broadly increased risk for other malignancies, follow up data from US cancer registries support a more limited spectrum of cancer risk. In particular, thymoma patients have a subsequently elevated risk for developing B-cell non-Hodgkin's lymphoma. Based on limited data, thymoma patients may also have an elevated risk for developing soft tissue sarcomas. Thymoma is a rare malignancy. The excess risk for non-Hodgkin's lymphoma is consistent with an effect of immune disturbance arising from the thymoma or its treatment. While descriptive epidemiologic data may yield clues to the etiology of thymoma, large multi-center case-control studies will be required to formally evaluate environmental and genetic risk factors.