Bardet‐Biedl syndrome (BBS) is a recessive genetic disease causing multiple organ anomalies. Most patients carry mutations in genes encoding for the subunits of the BBSome, an octameric ciliary transport complex, or accessory proteins involved in the BBSome assembly or function. BBS proteins have been extensively studied using in vitro, cellular, and animal models. However, the molecular functions of particular BBS proteins and the etiology of the BBS symptoms are still largely elusive. In this study, we applied a meta‐analysis approach to study the genotype‐phenotype association in humans using our database of all reported BBS patients. The analysis revealed that the identity of the causative gene and the character of the mutation partially predict the clinical outcome of the disease. Besides their potential use for clinical prognosis, our analysis revealed functional differences of particular BBS genes in humans. Core BBSome subunits BBS2, BBS7, and BBS9 manifest as more critical for the function and development of kidneys than peripheral subunits BBS1, BBS4, and BBS8/TTC8, suggesting that incomplete BBSome retains residual function at least in the kidney.

The development of thymic regulatory T cells (Treg) is mediated by Aire-regulated selfantigen presentation on medullary thymic epithelial cells (mTECs) and dendritic cells (DCs), but the cooperation between these cells is still poorly understood. Here we show that signaling through Toll-like receptors (TLR) expressed on mTECs regulates the production of specific chemokines and other genes associated with post-Aire mTEC development. Using single-cell RNA-sequencing, we identify a new thymic CD14 + Sirpα + population of monocytederived dendritic cells (CD14 + moDC) that are enriched in the thymic medulla and effectively acquire mTEC-derived antigens in response to the above chemokines. Consistently, the cellularity of CD14 + moDC is diminished in mice with MyD88-deficient TECs, in which the frequency and functionality of thymic CD25 + Foxp3 + Tregs are decreased, leading to aggravated mouse experimental colitis. Thus, our findings describe a TLR-dependent function of mTECs for the recruitment of CD14 + moDC, the generation of Tregs, and thereby the establishment of central tolerance.

Regulatory T cells (Tregs) play a key role in the peripheral self‐tolerance and preventing autoimmunity. While classical CD4+ Foxp3+ Tregs are well established, their CD8+ counterparts are still controversial in many aspects including their phenotypic identity and their mechanisms of suppression. Because of these controversies and because of only a limited number of studies documenting the immunoregulatory function of CD8+ Tregs in vivo, the concept of CD8+ Tregs is still not unanimously accepted. We propose that any T‐cell subset considered as true regulatory must be distinguishable from other cell types and must suppress in vivo immune responses via a known mechanism. In this article, we revisit the concept of CD8+ Tregs by focusing on the characterization of individual CD8+ T‐cell subsets with proposed regulatory capacity separately. Therefore, we review the phenotype and function of CD8+ FOXP3+ T cells, CD8+ CD122+ T cells, CD8+ CD28low/− T cells, CD8+ CD45RClow T cells, T cells expressing CD8αα homodimer and Qa‐1‐restricted CD8+ T cells to show whether there is sufficient evidence to establish these subsets as bona fide Tregs. Based on the intrinsic ability of CD8+ Treg subsets to promote immune tolerance in animal models, we elaborate on their potential use in clinics.

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