Alterations of the immune system in thymic malignancies.

Normal thymic architecture is essential for the proper development of T-lymphocytes. Immature T-cell progenitors enter the thymus where through interactions with cortical and medullary thymic epithelial cells (TECs) they undergo positive and negative selection and become competent cells that do not react with self-antigens. This process requires normal thymic architecture, expression of major histocompatibility complex (MHC) class II, and normal expression of the autoimmune regulator (AIRE) gene. Thymomas are rare neoplasms of the TECs that often generate lymphocytes that mature into CD4+ and CD8+ T-lymphocytes. However, several abnormalities have been described in thymomas that may affect normal T-cell development: the tumor architecture is distorted, neoplastics expresses less MHC class II, most thymomas do not express AIRE, and production of T-regulator cells is decreased. Thymomas are associated with a variety of autoimmune disorders often linked to T-cell-mediated autoimmunity. Myasthenia gravis, the most common autoimmune disorder associated with thymoma patients, is present in 30% of patients with thymoma. Several theories attempt to explain the association of immune disorders with thymomas. These different theories are based on failure of positive and negative selection of T-lymphocytes and on autoimmunizing mechanisms in an AIRE-poor environment in the thymus. The finding that immunosurveillance against cancer may be impaired before the diagnosis of thymoma may challenge current theories and suggest a more complex defect in T-lymphocyte maturation. It is likely that a combination of mechanisms is responsible for immune disorders in patients with thymoma. More investigation is needed to clarify the basic mechanisms responsible for immune disorders in patients with thymoma.

Adoptive regulatory T-cell therapy protects against cerebral ischemia.

OBJECTIVE: Recent evidence suggests that functional deficiency in regulatory T cells (Tregs), an innate immunomodulator, exacerbates brain damage after cerebral ischemia. We therefore evaluated the effect of Treg transfer in rodent models of ischemic stroke and further investigated the mechanism underlying Treg-afforded neuroprotection. METHODS: We examined the therapeutic potential of Tregs and the mechanisms of neuroprotection in vivo in 2 rodent models of ischemic stroke and in vitro in Treg-neutrophil cocultures using a combined approach including cell-specific depletion, gene knockout mice, and bone marrow chimeras. RESULTS: Systemic administration of purified Tregs at 2, 6, or even 24 hours after middle cerebral artery occlusion resulted in a marked reduction of brain infarct and prolonged improvement of neurological functions lasting out to 4 weeks. Treg-afforded neuroprotection was accompanied by attenuated blood-brain barrier (BBB) disruption during early stages of ischemia, decreased cerebral inflammation, and reduced infiltration of peripheral inflammatory cells into the lesioned brain. Surprisingly, Tregs exerted early neuroprotection without penetrating into the brain parenchyma or inhibiting the activation of residential microglia. Rather, both in vivo and in vitro studies demonstrated that Tregs suppressed peripheral neutrophil-derived matrix metallopeptidase-9 production, thus preventing proteolytic damage of the BBB. In addition to its potent central neuroprotection, Treg treatment was shown to ameliorate poststroke lymphopenia, suggesting a beneficial effect on immune status. INTERPRETATION: Our study suggests that Treg adoptive therapy is a novel and potent cell-based therapy targeting poststroke inflammatory dysregulation and neurovascular disruption.