Steve Ziegler, Ph.D.

Dr. Ziegler is an immunologist and molecular biologist recognized for the discovery of FoxP3 as a critical regulator of Treg development and function. He has also been involved in the finding that, in humans, Tregs can be generated in vitro. His laboratory continues to explore ways to generate and manipulate Treg development and function through modulation of FoxP3.

The principal focus of the laboratory is the development and regulation of the immune system. They are taking a variety of approaches, ranging from a detailed molecular analysis of gene expression to the generation of animal models of human autoimmune disease.

1. FoxP3 and the control of CD4+CD25+ regulatory T cell development and function.

The forkhead-family transcription factor FoxP3 has been implicated in the development and function of CD4+CD25+ regulatory T cells (Tregs). In the mouse, FoxP3 expression is both necessary and sufficient for generating Tregs, while FoxP3 expression has been shown to correlate with Treg function in humans. His laboratory is taking several approaches to better understand the role of this protein.

1. Structure/function analysis of FoxP3. They have shown that FoxP3 functions as a transcriptional repressor, targeting composite NF-AT/AP-1 sites in cytokine gene promoters. They have taken advantage of mutations in the FoxP3 gene found in human patients with IPEX (Immune dysfunction/Polyendocrinopathy/Enteropathy/X-linked) syndrome to study the function of FoxP3. Using these mutations, as well as deletions, they have mapped the region responsible for NF-AT inhibition to the amino terminus of FoxP3. They are currently examining the mechanism of FoxP3-mediated NF-AT inhibition, and the role of this amino terminal domain of FoxP3 in this process
2. Regulators of FoxP3 expression and function. They are taking a genetic approach to determine factors that influence either FoxP3 expression or its function. For example, they have found that mice with targeted mutations in the IL-2 pathway lack Tregs, die young from an autoimmune lymphoproliferative disease, and lack FoxP3 expression. Breeding these mice with a mouse expressing a T cell-specific FoxP3 transgene rescues these mice and restores Treg function. They are taking similar approaches using mice lacking CTLA-4, STAT5, and whose T cells lack the ability to signal through the TGF-b pathway.
3. Consequences of ectopic FoxP3 expression. Previous work has shown that introduction of FoxP3 into conventional mouse T cells converts these T cells to a Treg-like phenotype. They have developed mice that express tetracycline-inducible FoxP3 transgenes in order to assess whether constant FoxP3 expression is needed for Treg function. They have just developed these mice, and preliminary data suggests that T cell phenotype correlates with expression of the inducible transgene. They are also using ectopic FoxP3 expression to 'convert' pathogenic T cells to regulatory T cells. They are utilizing animal models of type I diabetes for these experiments.
4. In vitro generation of human Tregs. Unlike the mouse, human CD4+CD25- T cells can be converted to CD25+ Tregs following in vitro stimulation. This acquisition of Treg-like function correlates with induction of FoxP3 expression. They have recently shown that antigen-specific Tregs can be generated in vitro, and that both naïve and memory CD4+CD25- T cells are capable of becoming Tregs. They are currently using this system to study the human FoxP3 promoter, as well as to ascertain the pathways that are involved in generating Tregs.

2. TSLP and allergic inflammation

They are also studying a cytokine called thymic stromal lymphopoietin (TSLP). TSLP is an IL-7-like cytokine that is expressed by epithelial cells in the lung, skin, gut, and thymus. The TSLP receptor complex is a heterodimer comprised of the TSLPR and IL-7Ra. The receptor is expressed primarily on monocytes and myeloid-derived dendritic cells, as well as on B cells. Recent work has shown that TSLP treatment of human dendritic cells has several outcomes, including increased survival, upregulation of co-stimulatory molecules, and the production of the Th2-attracting chemokines CCL17 and CCL22. When T cells are primed on TSLP-treated DC, they produce inflammatory cytokines when restimulated (IL-4, -5, -13, and TNFa, but no IL-10). In support of its role in allergic inflammation, keratinocytes from patients with atopic dermatitis produce high levels of TSLP, while keratinocytes from normal individuals do not.

They have begun to model human allergic diseases using transgenic mice that express TSLP at specific sites. Thus far they have mice that express an inducible TSLP transgene in the skin, and mice that express both constitutive and inducible TSLP transgene in the lung. In both cases the mice develop the corresponding disease when the transgene is expressed-atopic dermatitis in the skin and asthma in the lung. The diseases developed by these mice closely resemble their human counterparts. The approaches they are currently taking to further analyze these mice are outlined below.

1. In our model, TSLP initiates the inflammatory cascade that leads to eventual disease. To identify and characterize the downstream mediators of TSLP-induced disease the TSLP transgenic mice are being bred to a series of mice carrying targeted mutations in genes upregulated in the target tissue. For example, they are using Stat6 deficient mice to eliminate IL-4 and IL-13 signaling, and CCR4-, CCR2-, and CXCR2- deficient mice to inhibit the migration of specific cell subsets to the target tissue.
2. They are isolating specific cell subsets from the TSLP transgenic mice to test their ability to transfer disease in an adoptive transfer system.
3. They have established collaborations to screen lung samples from patients with a variety of inflammatory lung diseases for TSLP expression.
4. They have begun to examine the regulation of TSLP expression in epithelial cells. Interestingly, the cytokines that are at elevated levels in the TSLP transgenics, and also in humans with asthma or atopic dermatitis, induce TSLP expression. This suggests that TSLP not only initiates disease, but is also part of a feed-back loop to perpetuate disease. They have identified 3 regions upstream of the TSLP gene that appear to be involved in its regulation. They are currently characterizing these sequences.

Assistant: Matt Warren mwarren@benaroyaresearch.org