Immune Regulation, Tolerance, and Autoimmunity 1 Immune Regulation, Tolerance, and Autoimmunity Mark S. Anderson, MD, PhD UCSF

Disclosures Research support from Juno Therapeutics Consultant for Sanofi

Lecture outline Principles of immune regulation Self-tolerance; mechanisms of central and peripheral tolerance Inhibitory receptors of T cells Treg’s and IL-2

The immunological equilibrium: balancing lymphocyte activation and control 3 Activation Effector T cells Tolerance Regulatory T cells Normal: reactions against pathogens Inflammatory disease, e.g. reactions against self Controlled response to pathogens No response to self

Central and peripheral tolerance to self The principal fate of lymphocytes that recognize self antigens in the generative organs is death (deletion), BUT: Some B cells may change their specificity (called “receptor editing”) Some T cells may differentiate into regulatory (suppressor) T lymphocytes Abbas, Lichtman and Pillai. Cellular and Molecular Immunology, 7th edition, 2011 c Elsevier

Consequences of self antigen recognition in thymus Abbas, Lichtman and Pillai. Cellular and Molecular Immunology, 7th edition, 2011 c Elsevier

What self antigens are seen in the thymus? Ubiquitous cell-associated and circulating proteins The thymus has a special mechanism for displaying peripheral tissue antigens in thymic medullary epithelial cells, where they signal self-reactive thymocytes for death

Consequences of AIRE mutation Human disease: autoimmune polyendocrinopathy with candidiasis and ectodermal dysplasia (APECED), also called autoimmune polyendocrine syndrome (APS-1) Associated gene identified by positional cloning, named AIRE (“autoimmune regulator”) Mouse knockout: autoantibodies against multiple endocrine organs, retina Failure to express many self antigens in the thymus --> failure of negative selection

Deletion of self-reactive T cells in the thymus: how are self antigens expressed in the thymus? Abbas, Lichtman and Pillai. Cellular and Molecular Immunology, 8th edition, 2014 AIRE (autoimmune regulator) is a regulator of gene transcription that stimulates thymic expression of many self antigens which are largely restricted to peripheral tissues

NOD.Aire GW/+ mice develop peripheral neuropathy (CIDP) Sciatic Nerve

Peripheral T cell tolerance Abbas, Lichtman and Pillai. Basic Immunology, 4th edition, 2014

12 T cell anergy Abbas, Lichtman and Pillai. Cellular and Molecular Immunology, 7th edition, 2011 c Elsevier

CTLA-4 competitively inhibits B7-CD28 engagement APC APC B7 B7 CTLA-4 CD28 T Cell T cell (activated T cell or Treg) Costimulation  T cell activation CTLA-4 blocks and removes B7  lack of costimulation  T cell inhibition

The B7:CD28 families Abbas, Lichtman and Pillai. Cellular and Molecular Immunology, 8th edition, 2014

Major functions of selected B7-CD28 family members CD28-B7: initiation of immune responses ICOS-ICOS-L: T cell help in germinal center reactions (antibody responses) CTLA-4-B7: inhibits early T cell responses in lymphoid organs PD-1:PD-L1,2: inhibits effector T cell responses in peripheral tissues Activation Inhibition

Blocking CTLA-4 promotes tumor rejection: CTLA-4 limits immune responses to tumors Administration of antibody that blocks CTLA-4 in tumor-bearing mouse leads to tumor regression

The PD-1 inhibitory pathway PD-1 recognizes two widely expressed ligands (PD-L1, PD-L2) Knockout of PD-1 leads to autoimmune disease (less severe than CTLA-4-KO) Role of PD-1 in T cell suppression in chronic infections, tumors?

T cell “exhaustion” in chronic viral infections Memory T cells: enhanced antiviral responses Effector T cells Naïve CD8+ T cells Acute infection: clearance of virus Virus Chronic infection: persistence of virus Exhausted T cells: inability to respond to virus (expression of inhibitory receptors, e.g. CTLA-4, PD-1)

Actions of PD-1 PD-1 attenuates TCR signaling in responding T cells Limits harmful consequences of chronic stimulation with persistent antigen (self, tumors, chronic viral infections) Greater role in CD8 than in CD4 T cells Also expressed on follicular helper T cells; function?

Checkpoint blockade for cancer immunotherapy e.g. ipilimumab Ribas A. N Engl J Med 2012;366:2517-2519.

Checkpoint blockade for cancer immunotherapy e.g. ipilimumab e.g. nivolumab, pembrolizumab Ribas A. N Engl J Med 2012;366:2517-2519.

Risks of blocking CTLA-4 or PD-1 Blocking a mechanism of self-tolerance leads to:

Risks of blocking CTLA-4 or PD-1 23 Risks of blocking CTLA-4 or PD-1 Blocking a mechanism of self-tolerance leads to: Autoimmune reactions (a new cottage industry for clinicians?) Colitis and dermatitis are common Vitiligo, Endocrinopathies, hepatitis less common but described Severity of adverse effects has to be balanced against potential for treating serious cancers Less severe with anti-PD1 antibody

Regulatory T cells Abbas, Lichtman and Pillai. Cellular and Molecular Immunology, 8th edition, 2014, Elsevier

Properties of regulatory T cells Phenotype: CD4+, high IL-2 receptor (CD25), low IL-7 receptor, Foxp3 transcription factor; other markers Essential features of stable Tregs: Foxp3 expression: requires demethylated non-coding CNS2 sequence in promoter CD25 (IL-2Ra) expression: IL-2 is a necessary survival factor CTLA-4 expression: required for suppressive function of most Tregs (Inability to produce IL-2) Take home messages

The significance of Foxp3+ Tregs Genetic evidence: Foxp3 mutations --> autoimmune disease (IPEX); in mice, disease can be corrected by providing normal Foxp3+ cells Do defects in Foxp3+ Tregs or resistance to Treg-mediated suppression contribute to common autoimmune diseases? Inconsistent and variable data

Mechanisms of action of Foxp3+ Tregs CTLA-4 on Tregs removes B7 on APCs, reduces CD28 engagement and T cell activation Genetic deletion of CTLA-4 in Foxp3+ cells results in severe systemic autoimmunity and lymphoproliferation Inhibitory cytokines produced by Tregs (TGF-b, IL-10, others?) suppress immune responses (DCs, Macs, T cells) IL-10 deletion in Foxp3+ cells results in colitis IL-10 is also produced by Foxp3- cells Consumption of IL-2

Regulatory T cells Explosion of information about the generation, properties, functions and significance of these cells Will cellular therapy with ex vivo expanded Treg become a reality? Therapeutic goal: induction or activation of Treg in immune diseases Take home messages

The therapeutic potential of regulatory T lymphocytes Cell transfer of autologous Tregs to suppress immune responses Grow up patient’s Tregs ex vivo Ongoing clinical trials in graft rejection, T1D show it is safe In one study of liver Tx, single infusion of Tregs resulted in tolerance (withdrawal of immunosuppression) in 7/10 patients (vs ~10% historically)

Functions of Interleukin-2: the dogma

The unexpected biology of IL-2 Interleukin-2 is the prototypic T cell growth factor (TCGF), required for initiating clonal expansion of T cells in response to antigen BUT: knockout of IL-2 or the a or b chain of the IL-2R results not in immune deficiency but in systemic autoimmunity and lymphoproliferation

Dual roles of IL-2 in T cell responses Surprising conclusion from knockout mice: the non-redundant function of IL-2 is in controlling immune responses Take home messages

Differential effects of IL-2 on Teff vs Treg

Pathogenesis of autoimmunity

Therapy of immune disorders: rational approaches target lymphocyte activation and subsequent inflammation

Autoimmune diseases Experimental models are revealing pathways of immune regulation But experimental animals are often inadequate models of human diseases Improving technologies for human genetic and phenotypic analyses are enabling studies of patients Challenges: Defining which mechanisms of immune tolerance fail in different autoimmune diseases Using this knowledge to develop therapies Take home messages

The landscape of T cell activating and inhibitory receptors: More to come? TIGIT