Commensal Microbes and Hair Follicle Morphogenesis Coordinately Drive Treg Migration into Neonatal Skin.

Regulatory T cells (Tregs) are required to establish immune tolerance to commensal microbes. Tregs accumulate abruptly in the skin during a defined window of postnatal tissue development. However, the mechanisms mediating Treg migration to neonatal skin are unknown. Here we show that hair follicle (HF) development facilitates the accumulation of Tregs in neonatal skin and that upon skin entry these cells localize to HFs, a primary reservoir for skin commensals. Further, germ-free neonates had reduced skin Tregs indicating that commensal microbes augment Treg accumulation. We identified Ccl20 as a HF-derived, microbiota-dependent chemokine and found its receptor, Ccr6, to be preferentially expressed by Tregs in neonatal skin. The Ccl20-Ccr6 pathway mediated Treg migration in vitro and in vivo. Thus, HF morphogenesis, commensal microbe colonization, and local chemokine production work in concert to recruit Tregs into neonatal skin, thereby establishing this tissue Treg niche early in life.

Tumor immune profiling predicts response to anti-PD-1 therapy in human melanoma.

BACKGROUND: Immune checkpoint blockade is revolutionizing therapy for advanced cancer, but many patients do not respond to treatment. The identification of robust biomarkers that predict clinical response to specific checkpoint inhibitors is critical in order to stratify patients and to rationally select combinations in the context of an expanding array of therapeutic options. METHODS: We performed multiparameter flow cytometry on freshly isolated metastatic melanoma samples from 2 cohorts of 20 patients each prior to treatment and correlated the subsequent clinical response with the tumor immune phenotype. RESULTS: Increasing fractions of programmed cell death 1 high/cytotoxic T lymphocyte-associated protein 4 high (PD-1hiCTLA-4hi) cells within the tumor-infiltrating CD8+ T cell subset strongly correlated with response to therapy (RR) and progression-free survival (PFS). Functional analysis of these cells revealed a partially exhausted T cell phenotype. Assessment of metastatic lesions during anti-PD-1 therapy demonstrated a release of T cell exhaustion, as measured by an accumulation of highly activated CD8+ T cells within tumors, with no effect on Tregs. CONCLUSIONS: Our data suggest that the relative abundance of partially exhausted tumor-infiltrating CD8+ T cells predicts response to anti-PD-1 therapy. This information can be used to appropriately select patients with a high likelihood of achieving a clinical response to PD-1 pathway inhibition. FUNDING: This work was funded by a generous gift provided by Inga-Lill and David Amoroso as well as a generous gift provided by Stephen Juelsgaard and Lori Cook.

Plaque-based sub-blistering dosimetry: Reaching PASI-75 after two treatments with 308-nm excimer laser in a generalized psoriasis patient.

BACKGROUND: Generalized UVB phototherapy has been established as an effective and safe treatment for chronic plaque-type psoriasis for decades and in recent years, targeted 308-nm excimer laser has emerged as an equally safe and more effective treatment option. While traditional dosimetry for laser has been determined either through minimal erythema dose (MED) or a combination of the patient's Fitzpatrick skin type and the level of plaque induration, we have developed "Plaque-based Sub-blistering Dosimtery" based on observations that administering anywhere from 8 to 16 multiples of MED to psoriatic plaques has resulted in clearance after one treatment with longer remission rates than the traditional dosing protocol. CASE REPORT: The authors describe a case in which a patient achieved PASI 75 following only two treatments with 308 nm excimer laser using this new protocol. Biopsies taken before and after treatment reveal a dramatic decrease in CD4+T cells as well as TNF-alpha- and IL-2-producing T cells. CONCLUSION: This case demonstrates using a more aggressive dosing protocol determined by plaque testing is well-tolerated and can lead to excellent clearance with minimal side effects and comorbidity.

Memory regulatory T cells reside in human skin.

Regulatory T cells (Tregs), which are characterized by expression of the transcription factor Foxp3, are a dynamic and heterogeneous population of cells that control immune responses and prevent autoimmunity. We recently identified a subset of Tregs in murine skin with properties typical of memory cells and defined this population as memory Tregs (mTregs). Due to the importance of these cells in regulating tissue inflammation in mice, we analyzed this cell population in humans and found that almost all Tregs in normal skin had an activated memory phenotype. Compared with mTregs in peripheral blood, cutaneous mTregs had unique cell surface marker expression and cytokine production. In normal human skin, mTregs preferentially localized to hair follicles and were more abundant in skin with high hair density. Sequence comparison of TCRs from conventional memory T helper cells and mTregs isolated from skin revealed little homology between the two cell populations, suggesting that they recognize different antigens. Under steady-state conditions, mTregs were nonmigratory and relatively unresponsive; however, in inflamed skin from psoriasis patients, mTregs expanded, were highly proliferative, and produced low levels of IL-17. Taken together, these results identify a subset of Tregs that stably resides in human skin and suggest that these cells are qualitatively defective in inflammatory skin disease.

Xenogeneic graft-versus-host-disease in NOD-scid IL-2Rγnull mice display a T-effector memory phenotype.

The occurrence of Graft-versus-Host Disease (GvHD) is a prevalent and potentially lethal complication that develops following hematopoietic stem cell transplantation. Humanized mouse models of xenogeneic-GvHD based upon immunodeficient strains injected with human peripheral blood mononuclear cells (PBMC; "Hu-PBMC mice") are important tools to study human immune function in vivo. The recent introduction of targeted deletions at the interleukin-2 common gamma chain (IL-2Rγ(null)), notably the NOD-scid IL-2Rγ(null) (NSG) and BALB/c-Rag2(null) IL-2Rγ(null) (BRG) mice, has led to improved human cell engraftment. Despite their widespread use, a comprehensive characterisation of engraftment and GvHD development in the Hu-PBMC NSG and BRG models has never been performed in parallel. We compared engrafted human lymphocyte populations in the peripheral blood, spleens, lymph nodes and bone marrow of these mice. Kinetics of engraftment differed between the two strains, in particular a significantly faster expansion of the human CD45(+) compartment and higher engraftment levels of CD3(+) T-cells were observed in NSG mice, which may explain the faster rate of GvHD development in this model. The pathogenesis of human GvHD involves anti-host effector cell reactivity and cutaneous tissue infiltration. Despite this, the presence of T-cell subsets and tissue homing markers has only recently been characterised in the peripheral blood of patients and has never been properly defined in Hu-PBMC models of GvHD. Engrafted human cells in NSG mice shows a prevalence of tissue homing cells with a T-effector memory (T(EM)) phenotype and high levels of cutaneous lymphocyte antigen (CLA) expression. Characterization of Hu-PBMC mice provides a strong preclinical platform for the application of novel immunotherapies targeting T(EM)-cell driven GvHD.