pathology lecture

1. Tumor immunology
Integrating
Immunity’s Roles in Cancer
Suppression and Promotion
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2. Objectives
• Answer the question, how the immune system
affects cancer development & progression?
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3. Modern concepts in carcinogenesis

4. Modern concepts in carcinogenesis
• viral etiology
• mutated onco-proteins
• over-expression normal antigens
• generation of antigen specific immune
responses
• sophisticated mechanisms
– triggering of multiple pathways
• impairment of T cell anti-tumor responses

5. Variable intermediaries
• Tregs
• pDC
• suppressor macrophages
• MDSC
– regulate T cell responses
– bioavailability of L-arg

6. Alterations of Immune Response in
cancer
• dysfunctional immune response
– loss of DTH
• “blocking antibodies”
• suppressor factors
• suppressor macrophages
• development of characteristic opportunistic
infections?
– T cell responses against bacterial and/or chemical
antigens

7. ability of Tumors to suppress T responses?
• failure of immunotherapy
– loss of T cell responses
• vaccine trials demonstrated progression of
tumors
– robust T cell response
• cellular and molecular models
– T cell anergy

8. discovery of several mechanisms
• role of immunoregulatory molecules in APC
– B7.1, B7.2, B7-H1 & B7-H4
• development of Tregs
• tumor-induced accumulation of MDSCs
• initiators of suppression
– tumor cells
– APCs(DCs & Ms)
– MDSC

9. Tumor cells?
• tumor cells produce
 VEGF
 G-CSF
 GM-CSF
• arrested differentiation of myeloid cells
– block T cell responses
• IL-10, TGF-β & PGE2
• accumulation of immature myeloid cells
– head & neck, breast, and lung cancer

10. mechanisms by which T cells become
suppressed
• multiple, but discrete changes in expression of
– CD3ζ (H2O2)
– tyrosine kinases p56lck, p59fyn
– upregulate Jak-3
– translocate NFkBp65
• diminished ability to mobilize Ca++
• decreased tyrosine phosphorylation
renal cell carcinoma, melanoma, Hodgkin’s disease,
ovarian cancer, colon carcinoma, & cervical cancer

11. CD3ζ
• oxygen scavengers radicals (H2O2)
• increased number of activated neutrophils
• pancreatic & breast cancer
– chronic stimulation of T cells by specific antigens

12. Metabolism of L-Arg by Myeloid Cells
• L-Arg substrate for
– NOS1, NOS2, & NOS3
– Arginase I and II
– Arginine: glycine amidinotransferase (AGLT)
– L-Arg decarboxylase (ADC)
• dietary L-Arg is taken up by intestinal
epithelial cells
• transported via y+ system of cationic amino
acid transporters (CAT)

13. Raber et al., 2012

14. expression of arginase I and NOS2
• in murine macrophages
– differentially regulated
• Th1 & Th2 cytokines
– IFN-γ up-regulates NOS2 exclusively
– IL-4, IL-10 and IL-13 induce arginase I
• arginase II
– mitochondrial isoform
– modulation by Th1 or Th2 cytokines?

15. Tumor immunology
Integrating
Immunity’s Roles in Cancer
Suppression and Promotion
15

16. Immunity’s Roles in Cancer Suppression &
Promotion
• immune system plays a dual role in cancer:
– suppress tumor growth
• by destroying cancer cells or inhibiting their
outgrowth
– promote tumor progression
• by selecting for tumor cells that are more fit to
survive in an immunocompetent host
• by establishing conditions within tumor
microenvironment that facilitate tumor outgrowth
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17. Tumor immunology
• Can immune system control cancer?
– subject of debate for over a century
• Paul Ehrlich (1900)
“that cancer would be quite common in long-
lived organisms if not for the protective effects
of immunity”
• How?? 50 yrs
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18. cancer immunosurveillance hypothesis
• Burnet and Thomas
– adaptive immunity was responsible for preventing
cancer development in immunocompetent hosts
• Stutman challenged this hypothesis
– similar susceptibility of immunocompetent &
nude mice
• largely abandoned
• why cancer immunosurveillance could not
possibly occur?
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19. cancer immunosurveillance hypothesis
• “danger signals” in tumor cells?
• ignorance or tolerance to a developing tumor
• persistent activation of innate, pro-
inflammatory arm of immunity
– facilitate cellular transformation & promote
cancer outgrowth
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20. cancer immunosurveillance hypothesis
• improved mouse models of immunodeficiency on
pure genetic backgrounds
– reassess role of immunity in cancer control
• rekindled immunosurveillance hypothesis:
– IFN inducing rejection of transplanted tumor cells
– mice lacking either IFN responsiveness
• lacking either IFN R or STAT1 transcription or adaptive
immunity [RAG2−/−]
– more susceptible to carcinogen induced & spontaneous primary
tumor formation
“the immune system can function as an extrinsic
tumor suppressor”
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21. Immunity’s Roles in Cancer
• 3 distinct roles in preventing cancer:
protects host against viral infection
suppresses virus-induced tumors
it prevents establishment of an inflammatory
environment
• tumorigenesis
• by eliminating pathogens & prompt resolution of
inflammation
 it eliminates tumor cells in certain tissues
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22. Tumor Antigens & Cancer Immunosurveillance
• fundamental tenet of tumor immunology in
general & of cancer immunosurveillance
– cancer cells express antigens
• differentiate them from their non-transformed
counterparts
• mice immunized with chemically induced
tumors
– protected against subsequent re-challenge with
same tumor
– “transplantation rejection antigens”
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23. Tumor Antigens
• molecular studies revealed that these antigens
were
– products of mutated cellular genes
– aberrantly expressed normal genes
– genes encoding viral proteins
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24. Tumor Antigens
• human tumor antigens include:
– differentiation antigens (melanocyte
differentiation)
– mutational antigens (such as p53)
– over expressed cellular antigens (such as HER-2)
– viral antigens (such as HPV proteins)
– cancer/testis (CT) antigens
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25. The Cancer Immunoediting Hypothesis
• The discovery in 2001
“the immune system controls not only tumor
quantity but also tumor quality
(immunogenicity)”
• prompted a major revision of cancer
immunosurveillance hypothesis
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27. The Cancer Immunoediting Hypothesis
• the immune system not only protects host
against tumor formation but also shapes
tumor immunogenicity is basis of cancer
immunoediting hypothesis
• stresses dual host-protective & tumor-
promoting actions of immunity on developing
tumors
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28. The Cancer Immunoediting Hypothesis
• cancer immunoediting process
• in its most complex embodiment, proceeds
sequentially through 3 distinct phases:
– “elimination”
– “equilibrium”
– “escape”
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29. The Cancer Immunoediting Hypothesis
• in some cases tumor cells may directly enter
into either equilibrium or escape phases
• external factors may influence directionality of
flow:
– environmental stress
– immune system deterioration accompanying aging
– immunotherapeutic intervention on tumor cell
outgrowth in human cancer patients
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31. Elimination pahse
• transformed cells
– develop after failure of intrinsic tumor suppressor
mechanism
– initiate stromal remodeling which results in local
tissue disruption
– recognized as a danger signal by cells of innate
immune system
• NK cells, NKT, γδ T cells & macrophages
• interaction of these cells triggers extrinsic tumor
suppressive mechanism:
– generation of IFN-γ and ILs by NK cells and macrophages
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32. Elimination phase
• INF-γ activates
– antiproliferative, proapoptotic & angiostatic
processes
– lead to death of a significant number of tumor
cells
• Macrophages by production of ROS & RNI
• NK cell via TRAIL or perforin dependent
mechanisms
– together kill the residual tumor cells
32

33. Elimination phase
• killing generates tumor antigens which
activate DCs recruited at the tumor site
• DC capture tumor antigens & migrate to LNs
– activate naïve Th1 CD4+ T cells
– CD8+ cytotoxic lymphocytes (CTL)
– tumor specific CD4+ and CD8+ T cells
• migrate to tumor site to kill viable antigen positive
tumor cells
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34. Elimination phase
• CD4+ T cells produce IL-2
– keeps tumor specific CD8+ T cells activated
• CD8+ T cells recognize
• kill the tumor cells directly
– by IFN-γ dependent mechanisms of cell cycle
inhibition, apoptosis, and angiostasis
– by induction of macrophage tumoricidal
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36. Does the Equilibrium Phase Really Exist?
• explain the period of immune dormancy
experienced
• phenomenon of relapse seen in many cancers
after one to two decades of remission
• immune system controlling, but not
eliminating
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37. Evidences to equilibrium phase of cancer
• occurrence of minimal residual disease (MRD)
in leukemia and some solid malignancies lends
further support to equilibrium hypothesis
• MRD
– small number of malignant cells remain in body
below threshold of conventional morphologic or
cytogenetic recognition
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38. Evidences to equilibrium phase of cancer
• preneoplastic conditions like monoclonal
gammopathy of undetermined significance
(MGUS)
• existence of an immune response to
premalignant MGUS cells that eventually
progress to multiple myeloma (MM)
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39. What are the Mechanisms Involved in
Equilibrium?
• solely maintained by adaptive immunity in
contrast to the other two phases
– significant reduction in tumor progression in case
of infiltration of tumor by the T lymphocytes
– extent of involvement of CD4+CD25+Foxp3+ T
cells or Treg???
– role of cytokines like IFN-γ and TNF has also been
suggested by some studies
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40. Evidences to equilibrium phase of cancer
• immunogenicity of cancer cells also varies
during the three stages
– more immunogenic in equilibrium phase
• Where do they hide?
– reside in “niches” made up of specialized vascular
bed of endothelial cells, associated stromal cells of
mesenchymal origin & extracellular matrix
components
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42. How does Tumor Evade Equilibrium?
• by complex interplay of cancer cells, the
cytokines and the immune cells
• the tumor
– sheds all its antigens & other molecules which
immune cells use for their recognition i.e. MHC,
NKG2D
– tumor cells which in turn induce CTLA-4
– immuno suppresive state is accentuate by
secretion of cytokines like TGF-β and IL-10
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