Immunbiology of Tumors

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”)

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

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

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

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.)

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

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

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

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.

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

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

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

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

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

TAA Oncofetal antigens Differentialtion specific antigens (DSA)

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

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

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

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

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

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

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

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

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

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

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

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)

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

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

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

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)

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

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

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.

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