BackgroundThymus transplantation is a promising strategy for the treatment of athymic complete DiGeorge syndrome (cDGS).MethodsTwelve patients with cDGS underwent transplantation with allogeneic cultured thymus.ObjectiveWe sought to confirm and extend the results previously obtained in a single center.ResultsTwo patients died of pre-existing viral infections without having thymopoiesis, and 1 late death occurred from autoimmune thrombocytopenia. One infant had septic shock shortly after transplantation, resulting in graft loss and the need for a second transplant. Evidence of thymopoiesis developed from 5 to 6 months after transplantation in 10 patients. Median circulating naive CD4 counts were 44 × 106/L (range, 11-440 × 106/L) and 200 × 106/L (range, 5-310 × 106/L) at 12 and 24 months after transplantation and T-cell receptor excision circles were 2,238/106 T cells (range, 320-8,807/106 T cells) and 4,184/106 T cells (range, 1,582-24,596/106 T cells). Counts did not usually reach normal levels for age, but patients were able to clear pre-existing infections and those acquired later. At a median of 49 months (range, 22-80 months), 8 have ceased prophylactic antimicrobials, and 5 have ceased immunoglobulin replacement. Histologic confirmation of thymopoiesis was seen in 7 of 11 patients undergoing biopsy of transplanted tissue, including 5 showing full maturation through to the terminal stage of Hassall body formation. Autoimmune regulator expression was also demonstrated. Autoimmune complications were seen in 7 of 12 patients. In 2 patients early transient autoimmune hemolysis settled after treatment and did not recur. The other 5 experienced ongoing autoimmune problems, including thyroiditis (3), hemolysis (1), thrombocytopenia (4), and neutropenia (1).ConclusionsThis study confirms the previous reports that thymus transplantation can reconstitute T cells in patients with cDGS but with frequent autoimmune complications in survivors.

Genome-wide association studies into complex immune-mediated diseases have indicated that many genetic factors, each with individual low risk, contribute to overall disease. It is therefore timely and important to characterise how immune responses may be subtly modified by tissue context. Here we explore the role of tissue-derived molecules in influencing the function of T-cells, which, due to their migratory nature, come into contact with many different microenvironments through their lifespan. Hedgehog (Hh) proteins act as secreted morphogens, providing concentration-dependent positional and temporal cell-fate specification in solid tissues. Hh signalling is required for embryogenesis and is important in postnatal tissue renewal and in malignancy. However, the function of Hh in dynamic, fluid systems such as in mammalian immunity is largely unknown. Here we show that Hh-dependent transcription in T-cells promoted Th2 transcriptional programs and differentiation, exacerbating allergic pathology. Interestingly, expression of Sonic Hedgehog (Shh) increased in lung epithelial cells following the induction of allergic disease, and lung T-cells upregulated Hh-target gene expression, indicating that T-cells respond to locally-secreted Hh ligands in vivo. We show that Il4, the key Th2 cytokine, is a novel transcriptional target of Hh signals in T-cells, providing one mechanism for the role of Hh in Th differentiation. We propose that Hh, secreted from inflamed, remodelling or malignant tissue can modulate local T-cell function. Our data present an unexpected and novel role for tissue-derived morphogens in the regulation of fluid immune responses, with implications for allergy and tumour responses, suggesting new uses for anti-Hh therapeutics.

Hedgehog proteins signal for differentiation, survival and proliferation of the earliest thymocyte progenitors, but their functions at later stages of thymocyte development and in peripheral T-cell function are controversial. Here we show that repression of Hedgehog (Hh) pathway activation in T-lineage cells, by expression of a transgenic repressor form of Gli2 (Gli2DeltaC2), increased T-cell differentiation and activation in response to TCR signalling. Expression of the Gli2DeltaC2 transgene increased differentiation from CD4(+)CD8(+) to single positive thymocyte, and increased peripheral T cell populations. Gli2DeltaC2 T-cells were hyper-responsive to activation by ligation of CD3 and CD28: they expressed cell surface activation markers CD69 and CD25 more quickly, and proliferated more than wild-type T-cells. These data show that Hedgehog pathway activation in thymocytes and T-cells negatively regulates TCR-dependent differentiation and proliferation. Thus, as negative regulators of TCR-dependent events, Hh proteins provide an environmental influence on T-cell fate.

Thymus-derived Foxp3 ؉ natural regulatory CD4 T cells (nTregs) prevent autoimmunity through control of pathogenic, autoreactive T cells and other immune effector cells. Using T cell receptor (TCR) transgenic models, diversity within this lineage has been found to be similar to that of conventional CD4 T cells. To determine whether balanced TCR diversity may be perturbed in autoimmunity, we have analyzed receptor composition in C57BL/6 and autoimmune non-obese diabetic (NOD) mice. The natural regulatory and conventional CD4 repertoires of C57BL/6 had similar diversities. Despite the apparently normal thymic development of the NOD nTreg lineage, TCR diversity within the selected repertoire was markedly restricted. Detailed analysis of TCR␣ and -␤ chain composition is consistent with positive selection into the natural regulatory lineage being under stringent audition for interaction with MHC class II/self-peptide. The NOD MHC region, including the unique H2-A g7 class II molecule, partly accounts for the reduction in diversity, but additional NOD genetic contribution(s) are required for complete repertoire compaction. Mechanistic links between MHC, autoimmunity, and nTreg diversity identified in this study are discussed.diabetes ͉ NOD mice ͉ TCR repertoire ͉ thymic selection A utoimmune insulin-dependent diabetes mellitus culminates in destruction of the insulin-producing ␤ cells of the islets of Langerhans. The genetic basis of disease susceptibility is complex, with the strongest association being encoded by the MHC class II region in human and the non-obese diabetic (NOD) mouse strain. In NOD mice, T cells play an essential role in disease pathogenesis and, through the activity of regulatory T cells (Tregs), control of disease progression. Foxp3-expressing natural Tregs (nTregs), arising in the thymus, play a crucial role in suppressing the pathogenic effects of self-reactive T cells. NOD mice have been reported to be relatively deficient in nTregs (1), although more recent evaluation of thymic production, export, and peripheral levels of nTregs did not find significant differences between NOD and nonautoimmune strains (2). More generally accepted is an age-dependent waning of Treg function apparent from adoptive transfer studies and in vitro assay of suppressive activity (3, 4). Multiple mechanisms, including an age-related decline of active, membrane-bound TGF-␤ (5), IL-2 insufficiency (6), defective antigen presentation (7), and resistance of conventional CD4 T cells to regulation (8) may contribute to the compromised function of peripheral NOD nTreg cells.Although thymic production of nTregs is not obviously aberrant, other aspects of T cell development and repertoire selection in NOD mice are anomalous. The TCR␤ checkpoint, which drives early thymocyte proliferation and differentiation, is partially independent of ␤ chain expression (9), and CD8 ϩ , CD4 ϩ (DP) thymocytes have a low activation threshold (10). NOD mice exhibit partial resistance to clonal deletion of autoreactive thymocytes involving failure...