1. Immunbiology of Tumors

2. Tumor cells are considered as “parasites” of the body
They are formed also in healthy subjects but anti-tumor control mechanism eliminate them
Tumor cells escape control with
- fast proliferation
- mutations
- high diversity (“mini evolution”)

3. Inducers of malignant transformation of cells
chemical carcinogens e.g. tar
physical carcinogens e.g. UV or X-ray
viral - both DNA or RNA viruses

4. Oncogens
gene coding a protein which can induce malignant transformation - viral or v-onc (they are only exons)
proto-oncogens - are present and function in physiologically intact cells - cellular or c-onc (they are exons or introns)
these genes are well-conserved structures
their main function is: to modulate proliferation or apoptosis

5. Neoplastic transformation
genetic alterations
environmental factors
expression of new, non-self cell surface antigens
the non-self antigens are detected by the immune system

6. Potential sources of tumor antigens
Category Example
Oncogene product muation in RAS codon 12 (pancr. cc.)
bcr/abl protein (chr. myeloid leukemia)
Embryonic proteins MAGE family (melanoma, breast cc.)
Viral proteins Epstein-Barr virus (Hodgkin’s lymph.)
Hepatitis B (hepaticellular cc.)
Tissue spec. antigen Tyrosinase (melanoma)
Mutant tu. suppressor prot. p53 (several cc.)
Idiotypic epitopes T-cell receptor idiotypes (T-cell lymph.)

7. Formation of Tumor Specific Antigens
effect of mutagen
mRNA
protein
MHC
changed peptide

8. Tumor antigens Tumor specific antigens (TSA)
expressed by tumor cells only
Tumor associated antigens (TAA)
expressed by tumor cells and some normal cells, too

9. Characterization of TSA (1)
expression of TSA is induced by chemical carcinogens or X-rays.
somatic mutations result TSA
each carcinogen can induce unique or specific class of TSA

10. Characterization of TSA (2)
T-cell receptors recognize peptides bound to the antigen - binding to the binding cleft of MHC molecules
TSA that evoke cytotoxic T cell response are derived from peptides uniquely synthesized by tumor cells and expressed on the surface of MHC I.

11. Normal cell
Normal cytoplasmic
protein
Peptide fragment
MHC I antigen
CD8+ T cell
CD8+ T cell
CD8+ T cell

12. Responses elicited by tumor cells
Antigen-specific effects
on the tumor cell
Escape mechanisms
Immunologic tolerance
Apoptosis of tumor cells
METASTASIS, DEATH
SURVIVAL

13. Antigen-specific effect of Tc cells
MHC I.
TCRa Tc
Tumor cell
TCRb
CD8
TNFb
FasL
Fas
APOPTOSIS
APOPTOSIS

14. Mechanisms by which TSAs are derived
Peptides without structural motives for binding to MHC molecules of the host
Mutation in gene encoding converting proteins that convert the peptide to a form binding to MHC and displayed az TSA on cell surface

15. MAGE-1 - embryonal protein,
40% melanomas
express MAGE-1
(melanoma antigen-encoding gene)
20% breast ca.
30% lung small cell ca.
MAGE embryonal protein,
expression is de-repressed in tumors
- present also in some normal cells e.g. testis

16. TAA
Oncofetal antigens
Differentialtion specific antigens (DSA)

17. Oncofetal antigens
normally expressed during a specific phase of enbryogenesis
they are practically in mature, differentiated tuissues
they are not immunogenic
they do not possess functional role in tumor immunity
Their significance: they are diagnostic and prognostic markers
serum cc. correlates with tumor mass, level of differentiation and response to therapy

18. Ideal tumor markers specific for the type of the tumor
released only in response to tumor
results proportional to tumor mass
quantitatively reflects to tumor response
elevated even with low tumor burden

19. Carcinoembryonic antigen (CEA)
discovered in extracts of adenocc. of colon
a group of heterogeneous glycoproteins - M.W. 200 kD
normally present in embryonic and fetal digestive tissues
detected by RIA or immunoenzymatic technique
elevated (over 5 ng/ml) in gastrointestinal, breast, pancreas, lung tu. and alcoholic cirrhosis, inflammations

20. Alpha-fetoprotein (AFP)
increased in hepatocellular cc. and malignant teratomas
serum levels are increased in metastatic tumors in liver and acute hepatitis

22. Prognostic roles of tumor markers† † †
1000
Se AFP ng/ml
100
chemotherapy - no response
chemotherapy - response
surgery with regrowth or metastasis
surgery

23. In experimental model TSA assessed by:
ability to resist a live tumor implant following the immunization with tumor cells
ability to resist when the model is infused with sensitized T cells from a syngeneic donor
in vitro demonstration of tumor cell destruction by cytotoxic T cells gained from a tumor immunized animal

24. Host immune response to tumor Experimental
Colony inhibition of tumors by sensitized lymphocytes
Tumor extracts induce lymphocyte blast tratnsformation
Lymphocyte-enhanced cytotoxicity
Macrophage-enhanced phagocytosis

25. Host immune response to tumors Clinical
Spontaneous regression
Regression of tu. - sublethal doses of chemotherapy
Regression of metastasis - resection of primary tumor
Mononuclear cell infiltration
High incidence of tu. after clinical immunospureassion
High incidence of tu in immunodeficiency
Increased incidence of tu. in aging

26. Cellular effectors that mediate immunity (1)
Cytotoxic T-Ly - protective role against virus- associated neoplasms (e.g. EBV)
NK-Ly - capable to destroy tumor cells w\o prior sensitization
Only tu. cells w\o MHC are lysed: NK-Ly recognize carbohydrate components of the membrane by NKR-P1 rec. BUT Ly49 rec. recognize MHC I. and blocks NK-Ly activity
(This is the first-line of defense.)
Activation with IL-2: NK Ly lyse a variety of tu.
T Ly
Complementary anti-tumor mechanisms
NK Ly

27. Cellular effectors that mediate immunity (2)
Macrophages (activated) possess selective cytotoxicity against tumor cells
T Ly
NK Ly collaborate in anti-tumor reactivity
Macrophages
(e.g. INF-g secreted by T and NK Ly activator of macrophages. Production of reactive oxygen, or secretioon of TNF-a)
Humoral mechanisms: activation of complement
induction of ADCC by NK Ly

28. Cellular effectors of antitumor immunity
IL-2
CTL
NK Ly
Peptide
TC-rec.
NK-rec.
MHC I
Antigen
IgG
INF-g
TNF-a
Fc-rec.
Macrophage
NK Ly

29. Effector Mechanisms in Tumor Immunity
Humoral:
opsonisation and phagocytosis
complement mediated lysis
loss of cell adhesion (antibody dependent)
Cellular:
T Ly
Antibody-dependent cytotoxicity
NK Ly
Lymphokine-activated killer (LAK) cells
Macrophages (also activated by lymphokines)

30. Immuno Surveillance
In 5% with congenital immunodeficiencies develop cancer (200x rate)
In immunsuppressed patients (80x rate)
AIDS, lymphomas, chronic infectious mononucleosis or malignant lymphomas

31. Escape of Tumors
Continuous shedding of tumor antigens - solubile antigens
Reults: - impossible to detect selectively these cells
- only NK-Ly can detect these cells, BUT they are not present everywhere

32. Effects of NK on the target cells
Killer inhibitory receptor = KIR; Killer activator receptor = KAR
KIR
KAR +
target
MHC I
KAR
KIR + -
NK-Ly
NO apoptosis
Apoptosis

33. More Escape Mechanisms from Immuno Surveillance
selective outgrowth of antigen negative variants
loss or reduced expression of HLA antigens
no costimulation - no sensitization- anergic T Ly - apoptosis of T Ly
expression of local inhibitory molecules (TNF- b or Fas ligand
immunosuppression (chemicals, radiation, TGF-b)

34. Immunologic activation and tolerance
Viral infection
Cancer V
Danger signals
(GM-CSF, TNF-a)
Antigen uptake by
activated APC
T cell V V
Costimulatory signal
(B7, Il-12)
T cell
T cell
Tumor-specific T cells become
tolerant
Virus-specific T cells become
activated

35. Failure of Immune Response to Tumor
Some tumors arise in areas not accessible to the effector cells (e.g. eye, CNS)
Antigenic modulation - antigens of tumor cells may undergo several changes
Blocking factors - immune complexes or cytophilic antibodies can mask tumor antigens or prevent binding by effector cells or lytic antibodies

36. Prospects for Immunotherapy to generate antitumor responses (1) 1890 Wiliam Coley: bacterial extracts to activate general immunity
Tumor cell vaccines - there are T cells directed against the tumor - their number could be increased with autologous or allogeneic tumor cells (the replication is prevented by irradiation)
Immunization with tumor-specific peptides - only for tumors for which TAA have been cloned and peptides synthesised
Cytokine therapy - increasing the levels of some cytokines (IL-2, IFN, GM-CSF, IL-7, IL-12)
Problems: short life-time, toxicity, non-specific cytokines.

37. Prospects for Immunotherapy to generate antitumor responses (2)
Monoclonal antibodies - used to deliver immunotoxins. radioisotopes, drugs. Bivalent antibodies recognize both T cells and TAA - they guide T cell to the tumor.
Gene therapy - combines the concepts of “tumor cell vaccines” and “cytokine therapy” by expressing genes coding for cytokines, costimulatory molecules or MHC.
Adoptive immunotherapy - with antitumor cells, tumor infiltrating lymphocytes (TIL) or lymphokine-activated killer (LAK) cells.
Problems: growing the large number of cells required, loss of antigene specificity for T cells, altered homing pattern