1. Immune Regulation, Tolerance, and Autoimmunity1
Immune Regulation, Tolerance, and Autoimmunity
Mark S. Anderson, MD, PhD
UCSF

2. Disclosures Research support from Juno Therapeutics
Consultant for Sanofi

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

4. The immunological equilibrium: balancing lymphocyte activation and control3
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

5. 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

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

7. 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

8. 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

9. 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

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

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

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

13. 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

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

15. 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

16. 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

17. 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?

18. 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)

19. 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?

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

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

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

23. Risks of blocking CTLA-4 or PD-123
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

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

25. 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

26. 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

27. 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

28. 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

29. 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)

30. Functions of Interleukin-2: the dogma

31. 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

32. 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

33. Differential effects of IL-2 on Teff vs Treg

35. Pathogenesis of autoimmunity

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

37. 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

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