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Deleterious mutations in genes involved in the Fas apoptosis pathway lead to Autoimmune Lymphoproliferative Syndrome (ALPS). Demonstration of an apoptosis defect is critical for the diagnosis and study of ALPS. The traditional in vitro apoptosis assay, however, requires a week of experimental procedures. Here, we show that defects in Fas-induced apoptosis in PBMCs can be evaluated directly ex vivo using multicolor flow cytometry to analyze the apoptosis of effector memory T cells, a Fas-sensitive subset of PBMCs. This method allowed us to sensitively quantify defective apoptosis in ALPS patients within a few hours. Some ALPS patients (ALPS-sFAS) without germline mutations have somatic mutations in Fas specifically in double-negative αβ T cells (DNTs), an unusual lymphocyte population that is characteristically expanded in ALPS. Since DNTs have been notoriously difficult to culture, defective apoptosis has not been previously demonstrated for ALPS-sFAS patients. Using our novel ex vivo apoptosis assay, we measured Fas-induced apoptosis of DNTs for the first time and found that ALPS-sFAS patients had significant apoptosis defects in these cells compared to healthy controls. Hence, this rapid apoptosis assay can expedite the diagnosis of new ALPS patients, including those with somatic mutations, and facilitate clinical and molecular investigation of these diseases. [ABSTRACT FROM AUTHOR]

In this issue of Immunity, ablate expression of the death receptor Fas in T cells, B cells, and DC. Fas deficiency in any of these lineages is sufficient to break self-tolerance. [Copyright &y& Elsevier]

Adoptive cell transfer (ACT) of purified naive, stem cell memory, and central memory T cell subsets results in superior persistence and antitumor immunity compared with ACT of populations containing more-differentiated effector memory and effector T cells. Despite a clear advantage of the less-differentiated populations, the majority of ACT trials utilize unfractionated T cell subsets. Here, we have challenged the notion that the mere presence of less-differentiated T cells in starting populations used to generate therapeutic T cells is sufficient to convey their desirable attributes. Using both mouse and human cells, we identified a T cell-T cell interaction whereby antigen-experienced subsets directly promote the phenotypic, functional, and metabolic differentiation of naive T cells. This process led to the loss of less-differentiated T cell subsets and resulted in impaired cellular persistence and tumor regression in mouse models following ACT. The T memory-induced conversion of naive T cells was mediated by a nonapoptotic Fas signal, resulting in Akt-driven cellular differentiation. Thus, induction of Fas signaling enhanced T cell differentiation and impaired antitumor immunity, while Fas signaling blockade preserved the antitumor efficacy of naive cells within mixed populations. These findings reveal that T cell subsets can synchronize their differentiation state in a process similar to quorum sensing in unicellular organisms and suggest that disruption of this quorum-like behavior among T cells has potential to enhance T cell-based immunotherapies. [ABSTRACT FROM AUTHOR]

Bcl-3 is an atypical member of the IκB family and modulates gene expression via interaction with p50/NF-KBl or p52/NF-KB2 homodimers. We report in the present study that Bcl-3 is required in dendritic cells (DCs) to assure effective priming of CD4 and CD8 T cells. Lack of Bcl-3 in bone marrow-derived DCs blunted their ability to expand and promote effector functions of T cells upon Ag/adjuvant challenge in vitro and after adoptive transfers in vivo. Importantly, the critical role of Bcl-3 for priming of T cells was exposed upon Ag/adjuvant challenge of mice specifically ablated of Bcl-3 in DCs. Furthermore, Bcl-3 in endogenous DCs was necessary for contact hypersensitivity responses. Bcl-3 modestly aided maturation of DCs, but most consequentially, Bcl-3 promoted their survival, partially inhibiting expression of several antiapoptotic genes. Loss of Bcl-3 accelerated apoptosis of bone marrow-derived DCs during Ag presentation to T cells, and DC survival was markedly impaired in the context of inflammatory conditions in mice specifically lacking Bcl-3 in these cells. Conversely, selective overexpression of Bcl-3 in DCs extended their lifespan in vitro and in vivo, correlating with increased capacity to prime T cells. These results expose a previously unidentified function for Bcl-3 in DC survival and the generation of adaptive immunity. [ABSTRACT FROM AUTHOR]