Strong evidence supports that CNS-specific CD4+ T cells are central to the pathogenesis of multiple sclerosis and experimental autoimmune encephalomyelitis (EAE). Using a model of spontaneous EAE, we demonstrated that myelin basic protein (MBP)-specific CD4+ T cells up-regulate activation markers in the CNS-draining cervical lymph nodes at a time when there is no T cell activation anywhere else, including the CNS, and before the appearance of clinical signs. In spontaneous EAE, the number of MBP-specific T cell numbers does not build up gradually in the CNS; instead, a swift migration of IFN-γ-producing T cells into the CNS takes place ~24 h before the onset of neurological signs of EAE. Surgical excision of the cervical lymph nodes in healthy pre-EAE transgenic mice delayed the onset of EAE and resulted in a less severe disease. In EAE induced by immunization with MBP/CFA, a similar activation of T cells in the draining lymph nodes of the injection site precedes the disease. Taken together, our results suggest that peripheral activation of T cells in draining lymph nodes is an early event in the development of EAE, which paves the way for the initial burst of IFN-γ-producing CD4+ T cell into the CNS.

Cutaneous T cell lymphoma (CTCL) is a heterogeneous group of mature T cell neoplasms characterized by the accumulation of clonal malignant CD4+ T cells in the skin. The most common variant of CTCL, Mycosis Fungoides, is confined to the skin in early stages but can be accompanied by extracutaneous dissemination of malignant T cells to the blood and lymph nodes in advanced stages of disease. Sézary Syndrome, a leukemic form of disease is characterized by significant blood involvement. Little is known about the transcriptional and genomic relationship between skin and blood residing malignant T cells in CTCL. To identify and interrogate malignant clones in matched skin and blood from leukemic MF and SS patients, we combine T cell receptor clonotyping, with quantification of gene expression and cell surface markers at the single cell level. Our data reveals clonal evolution at a transcriptional and genetic level within the malignant populations of individual patients. We highlight highly consistent transcriptional signatures delineating skin-derived and blood-derived malignant T cells. Analysis of these two populations suggests that environmental cues, along with genetic aberrations, contribute to transcriptional profiles of malignant T cells. Our findings indicate that the skin microenvironment in CTCL promotes a transcriptional response supporting rapid malignant expansion, as opposed to the quiescent state observed in the blood, potentially influencing efficacy of therapies. These results provide insight into tissue-specific characteristics of cancerous cells and underscore the need to address the patients' individual malignant profiles at the time of therapy to eliminate all sub-clones.

Spontaneous experimental autoimmune encephalomyelitis (EAE) develops in 100% of mice harboring a monoclonal myelin basic protein (MBP)-specific CD4+ alphabeta T-cell repertoire. Monoclonality of the alphabeta T-cell repertoire can be achieved by crossing MBP-specific T-cell receptor (TCR) transgenic mice with either RAG-/- mice or TCR alpha-/-/TCR beta-/- double knockout mice. Spontaneous EAE can be prevented by a single administration of purified CD4+ splenocytes or thymocytes obtained from wild-type syngeneic mice. The regulatory T cells (T-reg) that protect from spontaneous EAE need not express the CD25 marker, as effective protection can be attained with populations depleted of CD25+ T cells. Although the specificity of the regulatory T cells is important for their generation or regulatory function, T cells that protect from spontaneous EAE can have a diverse TCR alpha and beta chain composition. T-reg cells expand poorly in vivo, and appear to be long lived. Finally, precursors for T-reg are present in fetal liver as well as in the bone marrow of aging mice. We propose that protection of healthy individuals from autoimmune diseases involves several layers of regulation, which consist of CD4+CD25+ regulatory T cells, CD4+CD25- T-reg cells, and anti-TCR T cells, with each layer potentially operating at different stages of T-helper cell-mediated immune responses.

Notch signaling is essential for the development of T cell progenitors through the interaction of NOTCH1 receptor on their surface with the ligand, Delta-like 4 (DLL4), which is expressed by the thymic epithelial cells. Notch signaling is quickly shut down once the cells pass β-selection, and CD4/CD8 double positive (DP) cells are unresponsive to Notch. Over the past two decades a number of papers reported that over-activation of Notch signaling causes T cell acute lymphoblastic leukemia (T-ALL), a cancer that prominently features circulating monoclonal CD4/CD8 double positive T cells in different mouse models. However, the possible outcomes of Notch over-activation at different stages of T cell development are unknown, and the fine timing of Notch signaling that results in T-ALL is poorly understood. Here we report, by using a murine model that ectopically expresses DLL4 on developing T cells, that the T-ALL onset is highly dependent on a sustained Notch activity throughout the DP stage, which induces additional mutations to further boost the signaling. In contrast, a shorter period of Notch activation that terminates at the DP stage causes a polyclonal, non-transmissible lymphoproliferative disorder that is also lethal. These observations resolved the discrepancy of previous papers on DLL4 driven hematological diseases in mice, and show the critical importance of the timing and duration of Notch activity.

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