A molecular threshold for effector CD8(+) T cell differentiation controlled by transcription factors Blimp-1 and T-bet.

T cell responses are guided by cytokines that induce transcriptional regulators, which ultimately control differentiation of effector and memory T cells. However, it is unknown how the activities of these molecular regulators are coordinated and integrated during the differentiation process. Using genetic approaches and transcriptional profiling of antigen-specific CD8(+) T cells, we reveal a common program of effector differentiation that is regulated by IL-2 and IL-12 signaling and the combined activities of the transcriptional regulators Blimp-1 and T-bet. The loss of both T-bet and Blimp-1 leads to abrogated cytotoxic function and ectopic IL-17 production in CD8(+) T cells. Overall, our data reveal two major overlapping pathways of effector differentiation governed by the availability of Blimp-1 and T-bet and suggest a model for cytokine-induced transcriptional changes that combine, quantitatively and qualitatively, to promote robust effector CD8(+) T cell differentiation.

The transcriptional regulators IRF4, BATF and IL-33 orchestrate development and maintenance of adipose tissue-resident regulatory T cells.

Foxp3(+) regulatory T (Treg) cells in visceral adipose tissue (VAT-Treg cells) are functionally specialized tissue-resident cells that prevent obesity-associated inflammation and preserve insulin sensitivity and glucose tolerance. Their development depends on the transcription factor PPAR-γ; however, the environmental cues required for their differentiation are unknown. Here we show that interleukin 33 (IL-33) signaling through the IL-33 receptor ST2 and myeloid differentiation factor MyD88 is essential for development and maintenance of VAT-Treg cells and sustains their transcriptional signature. Furthermore, the transcriptional regulators BATF and IRF4 were necessary for VAT-Treg differentiation through direct regulation of ST2 and PPAR-γ expression. IL-33 administration induced vigorous population expansion of VAT-Treg cells, which tightly correlated with improvements in metabolic parameters in obese mice. Human omental adipose tissue Treg cells also showed high ST2 expression, suggesting an evolutionarily conserved requirement for IL-33 in VAT-Treg cell homeostasis.

The transcription factor IRF4 is essential for TCR affinity-mediated metabolic programming and clonal expansion of T cells.

During immune responses, T cells are subject to clonal competition, which leads to the predominant expansion of high-affinity clones; however, there is little understanding of how this process is controlled. We found here that the transcription factor IRF4 was induced in a manner dependent on affinity for the T cell antigen receptor (TCR) and acted as a dose-dependent regulator of the metabolic function of activated T cells. IRF4 regulated the expression of key molecules required for the aerobic glycolysis of effector T cells and was essential for the clonal expansion and maintenance of effector function of antigen-specific CD8(+) T cells. Thus, IRF4 is an indispensable molecular 'rheostat' that 'translates' TCR affinity into the appropriate transcriptional programs that link metabolic function with the clonal selection and effector differentiation of T cells.

The transcription factors Blimp-1 and IRF4 jointly control the differentiation and function of effector regulatory T cells.

Regulatory T cells (T(reg) cells) are required for peripheral tolerance. Evidence indicates that T(reg) cells can adopt specialized differentiation programs in the periphery that are controlled by transcription factors usually associated with helper T cell differentiation. Here we demonstrate that expression of the transcription factor Blimp-1 defined a population of T(reg) cells that localized mainly to mucosal sites and produced IL-10. Blimp-1 was required for IL-10 production by these cells and for their tissue homeostasis. We provide evidence that the transcription factor IRF4, but not the transcription factor T-bet, was essential for Blimp-1 expression and for the differentiation of all effector T(reg) cells. Thus, our study defines a differentiation pathway that leads to the acquisition of T(reg) cell effector functions and requires both IRF4 and Blimp-1.

Identifying low-grade cellular rejection after heart transplantation in children by using gene expression profiling.

Endomyocardial biopsy (EMB) remains the gold standard for detecting rejection after heart transplantation but is costly and invasive. This study aims to distinguish no rejection (0R) from low-grade rejection (1R/2R) after heart transplantation in children by using global gene expression profiling in blood. A total of 106 blood samples with corresponding EMB from 18 children who underwent heart transplantation from 2011 to 2014 were analyzed (18 baseline/pretransplantation samples, 88 EMB samples). Corresponding rejection grades for each blood sample were 0R in 39% (34/88), 1R in 51% (45/88), and 2R in 10% (9/88). mRNA from each sample was sequenced. Differential expression analysis was performed at the gene level. A k-nearest neighbor (kNN) analysis was applied to the most differentially expressed (DE) genes to identify rejection after transplantation. Mean age at transplantation was 10.0 ± 5.4 yr. Expression of B cell and T cell receptor sequences was used to measure the effect of posttransplantation immunosuppression. Follow-up samples had lower levels of immunoglobulin gene families compared with pretransplantation ( P < 3E-5) (lower numbers of activated B cells). T cell receptor alpha and beta gene families had decreased expression in 0R samples compared with pretransplantation ( P < 4E-5) but recovered to near baseline levels in 1R/2R samples. kNN using the most DE gene (MKS1) and k = 9 nearest neighbors correctly identified 83% (73/88) of 1R/2R compared with 0R by leave-one-out cross validation. Using a genomic approach we can distinguish low-grade cellular allograft rejection (1R/2R) from no rejection (0R) after heart transplantation in children despite a wide age range.

Blimp-1 transcription factor is required for the differentiation of effector CD8(+) T cells and memory responses.

In response to viral infection, naive CD8(+) T cells proliferate and differentiate into cytotoxic and cytokine-producing effector cells. Here we showed that the transcription factor Blimp-1, a crucial regulator of plasma cell differentiation, was required for CD8(+) T cells to differentiate into functional killer T cells in response to influenza virus. Blimp-1 was not essential for the generation of memory T cells but was crucial for their efficient recall response upon reinfection. Antigen-specific Blimp-1-deficient CD8(+) T cells failed to appropriately regulate the transcriptional program essential for killer T cell responses and showed impaired migration to the site of infection. This study identifies Blimp-1 as a master regulator of the terminal differentiation of CD8(+) effector T cells and uncovers a conservation of the pathways that regulate the terminal differentiation of T and B cells.

Id2 expression delineates differential checkpoints in the genetic program of CD8α+ and CD103+ dendritic cell lineages.

Dendritic cells (DCs) have critical roles in the induction of the adaptive immune response. The transcription factors Id2, Batf3 and Irf-8 are required for many aspects of murine DC differentiation including development of CD8α(+) and CD103(+) DCs. How they regulate DC subset specification is not completely understood. Using an Id2-GFP reporter system, we show that Id2 is broadly expressed in all cDC subsets with the highest expression in CD103(+) and CD8α(+) lineages. Notably, CD103(+) DCs were the only DC able to constitutively cross-present cell-associated antigens in vitro. Irf-8 deficiency affected loss of development of virtually all conventional DCs (cDCs) while Batf3 deficiency resulted in the development of Sirp-α(-) DCs that had impaired survival. Exposure to GM-CSF during differentiation induced expression of CD103 in Id2-GFP(+) DCs. It did not restore cross-presenting capacity to Batf3(-/-) or CD103(-)Sirp-α(-)DCs in vitro. Thus, Irf-8 and Batf3 regulate distinct stages in DC differentiation during the development of cDCs. Genetic mapping DC subset differentiation using Id2-GFP may have broad implications in understanding the interplay of DC subsets during protective and pathological immune responses.

Blimp1: driving terminal differentiation to a T.

B lymphocyte maturation-induced protein-1 (Blimp1) is a transcriptional repressor expressed in diverse cell types. In the adaptive immune system, Blimp1 is expressed in lymphocytes that have undergone effector differentiation. Blimp1 is a master regulator of plasma cell differentiation and plays important roles in controlling T cell homeostasis and effector differentiation. Blimp1 can be induced by a variety of cytokines including IL-2, IL-4, IL-12, and IL-21 in addition to TCR and co-stimulatory signals. Blimp1-deficient mice develop spontaneous inflammatory disease mediated by infiltration of activated T cells into tissues. During immune responses Blimp1 is required for the differentiation of plasma cells as well as short-lived CD8(+) cytotoxic T cells. Mounting evidence suggests that Blimp1 plays a common role in the terminal differentiation of multiple cell subsets.