Th17 and Treg in RA Seong Wook Kang Division of Rheumatology Department of Internal Medicine Chnungnam National University School of Medicine

Rheumatoid Arthritis

Rheumatoid Arthritis (RA) A symmetric polyarticular arthritis Primarily affects the small joints of the hands and feet Inflammation in the synovium Pannus invades and destroys local articular structures

Normal Synovium

Pathogenesis of RA

Role of T cells in RA Prominent T-cell infiltrate in RA synovium Genetic similarities between RA patients –specific human leukocyte antigen (HLA)-DR genes - HLA DR4, DR14 and DR1 Shared epitope –the third hypervariable region of DR β chains, especially amino acids 70 through 74

HLA Class II Molecule

Maturation of lymphocytes

Routes of antigen entry

Activation of naive and effector T cells by antigen from thymus

Phases of T cell responses Activated T cells deliver signals back to the APCs, further enhancing their ability to activate T cells

 SIGNALS FOR T LYMPHOCYTE ACTIVATION Proliferation of T lymphocytes and differentiation into effector and memory cells require – Antigen recognition –Costimulation –Cytokines that are produced by the T cells themselves and by APCs and other cells

Differentiation of CD4 + T Cells into T H 1, T H 2, and T H 17 Effector Cells

Old versus new models of Th cell development

Th17 cells A novel lineage of CD4 + effector T helper (Th) cells which produce IL-17 –Murine models of autoimmunity: experimental autoimmune encephalomyelitis (EAE) and collagen-induced arthritis (CIA) Mediated by Th1 response (?): ablated by Ab for IL-12p40 IL-23 shares with IL-12p40 –IL-12: p40 and p35 –IL-23: p40 and p19 IL-23, not IL-12 is critically linked to autoimmunity in these models IL-23 polarized cells express genes associated chronic inflammation, such as IL-17A, IL-17F, IL-6, TNF-a, and proinflammatory chemokines

Main activities attributed to Th17 cells

Diseases associated with Th17

Possible role of Th17 cells in RA IL-17 and IL-23p19 were found in sera, synovial fluid, and synovial biopsies of most patients with RA Increased expression of CC chemokine ligand 20 in the inflamed joints of patients with RA –CCL20 : able to bind CCR6 expressing Th17 cells Increased number of Th17 cells were observed in the peripheral blood and the SF of RA patients

Role of Th17 cells in RA

Helper T cell (Th) subgroups

Autoimmunity and Tolerance Breakdown of self-tolerance: autoimmune disease –T cell compartment of the immune system can react with a variety of antigens Equipped with receptors that are able to interact with self–antigens Auto-reactive T cell: potentially dangerous by initiating autoimmune responses Protective immune responses need to be stopped or down-regulated –When the body-invading agent has been neutralized –Intensity or chronicity may become dangerous for the body Regulatory mechanisms are required –Thymic clonal deletion: apoptotic cell death (central tolerance) –Induction of anergy: functional inactivation –Activation-induced cell death –Suppression by regulatory lymphocytes: Role of FOXP3 + regulatory T cells (T reg )

T cells suppressing immune responses Described early 1970s by Gershon and Kondo In mid-1990s, Sakaguchi identified a subset of CD4 + CD25 + T cells critical for preventing autoimmunity –when CD4 + T cells depleted of CD25 + T cells from normal mice were transferred into syngeneic athymic nude mice, multiorgan autoimmune disease was induced –Prevented by co-transfer of CD4 + CD25 + T cells Sakaguchi S. J Immunol 1995

Discovery of FOXP3 FOXP3 (forkhead family transcription factor) –A critical regulator of T reg development, function, and homeostasis FOXP3 + T cells, most of which are CD4 + CD25 + –suppress activation, proliferation and effector functions of immune cells including CD4 + and CD8 + T cells, NK cells, NKT cells, B cells and APCs –central in the prevention of autoimmune disease, allergy, and maintenance of allograft tolerance

FOXP3 + regulatory T cells in human immune system T reg expressing FOXP3 are indispensable for the maintenance of self tolerance and immune homeostasis Genetic mutations in FOXP3 develop a severe, fatal systemic autoimmune disorder –IPEX (Immune dysregulation Polyendocrinopathy Enteropathy X-linked) syndrome Enlargement of lymphoid organ, insulin-dependent diabetes, eczema, food allergy and concomitant infection

Regulatory T cells Many cell types have been shown to possess the capacity to regulate immune responses –CD4 + CD25 high regulatory T cells (“T regs ”), CD4 + Tr1 cells, CD4 + Th3 cells, CD8 + CD28 − T cells, CD4 − CD8 − T cells and NKT cells

Characteristics of regulatory T cells

Natural regulatory T cells (nT reg ) vs. Induced T reg (iT reg ) Natural regulatory T cells (nT reg ): Thymic-derived –One of the best-characterized subsets of immune regulatory cells is the CD4 + CD25 +/high T regs –FOXP3 appears to have emerged as the definitive marker for such T regs Induced T reg (iT reg ) –More recent studies have shown that FOXP3 may also be induced in CD4 + FOXP3 – T cells in vivo during some immune responses

Thymic and Peripheral Generation of FOXP3 + T reg Cells

Mechanisms of FOXP3 + T reg cell mediated suppression (direct)

Mechanisms of FOXP3 + T reg cell mediated suppression (indirect)

T regs in autoimmune diseases No difference in the frequency of CD4 + CD25 + T regs but reduced suppressive activity –Multiple sclerosis –Myasthenia gravis –Type 1 diabetes –Rheumatoid arthritis Decrease in CD4 + CD25 + T regs frequency in peripheral blood –SLE –Kawasaki disease –Autoimmune lymphoproliferative syndrome

T regs in human RA T regs in patients with RA appear to be present in normal numbers and to exhibit all of the features of Tregs, not only in phenotype but also in their suppression of T cell proliferation. Circulating T regs isolated from patients with active RA are unable to suppress the release of pro-inflammatory cytokines by activated T cells and monocytes Reversal of T reg -suppressive defect by successful anti-TNF treatment

T regs and inflammation in RA The frequency of T regs was much greater in the synovial fluid than in peripheral blood –The inflammatory milieu increases the number of T reg cells in the inflamed joint, but impairs their function –TNFα in SF of RA abrogate the suppressive activity of CD4 + CD25 + T regs Balance between T regs and pathogenic T h 17 cells at the site of inflammation –TGFβ and IL-6 secretion in rheumatoid synovium

Reciprocal generation of T reg and T h 17 cells

T regs can convert to T h 17 cells T reg and T h 17 cells may differentiate from the same precursor T cells –The balance of TGFβ and IL-6 might determine the differentiation of T reg / T h 17 cells The propensity of Tregs to convert to T h 17 cells in the context of pro-inflammatory stimuli –FOXP3 + CD4 + T cells can express RORγt and has the capacity to produce IL-17

Balance between Th17 and Treg

Therapeutic potential of T regs In vivo expansion of CD4 + CD25 + T regs –Anti-CD3 monoclonal Ab (type I DM) –CD28 superagonist Ex vivo generation of CD4 + CD25 + T regs –Adoptive cell Therapy

Clinical applications of T regs Adoptive cell Therapy

Cellular therapy in RA T regs may convert to pathogenic cells in human RA Strategies for expansion and isolation of highly pure FOXP3 + T regs to be used in cellular therapy

Summary A role for Th17 in RA –Inflammation –Cartilage destruction –Bone erosion T regs have a key role in immune homeostasis –Important functions in suppressing unwanted inflammatory responses toward self-antigens Great potential to use these cells in a therapeutic regimen for the treatment of autoimmune diseases