Iimmunity to tumors

Tumor ImmunologyTumor Immunology

NCI, Cairo UniversityNCI, Cairo University

CancerCancer Introduction Introduction

• Uncontrolled growth produces a tumor or Uncontrolled growth produces a tumor or neoplasm.neoplasm.

• A tumor that grows indefinitely and often A tumor that grows indefinitely and often spreads (metastasis) is called spreads (metastasis) is called malignantmalignant----also called cancer.also called cancer.

• A tumor that is not capable of indefinite A tumor that is not capable of indefinite growth----growth----benignbenign..

• Malignant---kills host.Malignant---kills host.• Benign---does not kill host.Benign---does not kill host.

Molecular Basis of Cancer

Uncontrolled cell growth

Proto-oncogenesTumor-suppressor genes

MutationsRadiationChemical (Carcinogen)Virus

Types of cancers based on etiologic agent• Chemically-induced tumorsChemically-induced tumors

– Each tumor induced by a carcinogen (e.g. benzopyrene) Each tumor induced by a carcinogen (e.g. benzopyrene) injected at various sites expresses a unique Ag.injected at various sites expresses a unique Ag.

– Thus difficult to develop vaccine.Thus difficult to develop vaccine.

• Virus-induced tumorsVirus-induced tumors– Tumors induced by same virus express same tumor Ag.Tumors induced by same virus express same tumor Ag.– Induce a strong immune response.Induce a strong immune response.

e.g. Gardasil vaccine – Human Papilloma Virus (HPV) e.g. Gardasil vaccine – Human Papilloma Virus (HPV) induced cervical cancerinduced cervical cancer

• UV-induced tumorsUV-induced tumors– UV radiation--->melanomasUV radiation--->melanomas– Highly tumorigenicHighly tumorigenic

Evidence for the role of immune system in tumor rejection

• Spontaneous regressionSpontaneous regression• Infiltration of tumors by lymphocytes and Infiltration of tumors by lymphocytes and

macrophagesmacrophages• Regression of metastases after removal of primary Regression of metastases after removal of primary

tumortumor• Regression after chemotherapyRegression after chemotherapy• Lymphocyte proliferation in draining lymph Lymphocyte proliferation in draining lymph

nodesnodes• Higher incidence of cancer after Higher incidence of cancer after

immunosuppression/immunodeficiency (AIDS, immunosuppression/immunodeficiency (AIDS, neonates, aged, transplant patients)neonates, aged, transplant patients)

Syngeneic(accepted)

Allogeneic(rejected)

Inbred: repeated brother-sister matings

Outbred:normal population

Xenogeneic(rejected)

Tumor Growth

Across SpeciesRat

Mouse

Tumors stimulate specific, adaptive immune responses

• Although tumor cells are Although tumor cells are derived from host cells, the derived from host cells, the tumors elicit tumors elicit immune responsesimmune responses. .

• They are surrounded by They are surrounded by mononuclear cell infiltrates mononuclear cell infiltrates composed of composed of T lymphocytesT lymphocytes, , natural killer (NK) cellsnatural killer (NK) cells, and , and macrophagesmacrophages..

• Activated lymphocytes and Activated lymphocytes and macrophages are present in macrophages are present in lymph nodes draininglymph nodes draining. .

• Lymphocytic infiltrates is Lymphocytic infiltrates is predictive of a predictive of a betterbetter prognosisprognosis. .

• Tumors can induce protective immune responsesTumors can induce protective immune responses. . • A sarcoma induced in an inbred mouse by chemical carcinogen A sarcoma induced in an inbred mouse by chemical carcinogen

methylcholanthrene (MCA).methylcholanthrene (MCA).• If tumor is excised and transplanted into other syngeneic mice, the If tumor is excised and transplanted into other syngeneic mice, the

tumor grows. tumor grows. • In contrastIn contrast, if the tumor is transplanted back into the original host, the , if the tumor is transplanted back into the original host, the

mouse mouse rejectsrejects the tumor. the tumor. • The same mouse that had become immune to its tumor is incapable of The same mouse that had become immune to its tumor is incapable of

rejecting MCA-induced tumors produced in other mice. rejecting MCA-induced tumors produced in other mice.

• Furthermore, T cells from the tumor-bearing animal can transfer Furthermore, T cells from the tumor-bearing animal can transfer protective immunity to the tumor to another tumor-free animal. protective immunity to the tumor to another tumor-free animal.

• Immune responses to tumors exhibit the defining characteristics of Immune responses to tumors exhibit the defining characteristics of adaptive immunityadaptive immunity, namely, , namely,

specificityspecificity, , memorymemory, , key role of T- key role of T- lymphocyteslymphocytes. .

Immune responses frequently fail to prevent the growth of tumors

• FirstFirst, tumor cells are derived from host cells and , tumor cells are derived from host cells and resemble normal cells in many respects. resemble normal cells in many respects.

• Therefore, most tumors tend to be Therefore, most tumors tend to be weakly weakly immunogenicimmunogenic. .

• Tumors that elicit Tumors that elicit strong immune responsesstrong immune responses include include those induced by oncogenic viruses. those induced by oncogenic viruses.

• Many Many spontaneous tumorsspontaneous tumors induce weak or even induce weak or even undetectable immunityundetectable immunity. .

• SecondSecond, the rapid growth and spread of tumors may , the rapid growth and spread of tumors may overwhelm the capacity of the immune system. overwhelm the capacity of the immune system.

• ThirdThird, many tumors have specialized mechanisms for , many tumors have specialized mechanisms for evading host immune responses. evading host immune responses.

Antigens expressed on tumor cells

Major HistocompatabilityComplex antigens

TSTATATA

TSTA: unique to a tumor Play an important role in tumor rejection.TATA: shared by normal and tumor cells

Tumor-associated developmental Ag (TADA)Tumor-associated viral Ag (TAVA)

Tumor-specific transplantation AgTumor-associatedtransplantation Ag

• It is important to identify tumor antigens It is important to identify tumor antigens in humans because:in humans because:

1- They may be used as1- They may be used as components of components of tumor vaccines. tumor vaccines.

2- Antibodies and effector T cells2- Antibodies and effector T cells generated against these antigens may be generated against these antigens may be used forused for immunotherapy.immunotherapy.

Identification of Tumor AntigensIdentification of Tumor Antigens

• The identification of many antigens expressed The identification of many antigens expressed by:by:1- biochemical1- biochemical approachesapproaches2- Molecular genetic approaches. 2- Molecular genetic approaches.

• For tumor antigens recognized by For tumor antigens recognized by CD8+ CD8+ cytotoxiccytotoxic T lymphocytes (CTLs), cloned lines T lymphocytes (CTLs), cloned lines of of tumor-reactive CTLstumor-reactive CTLs from cancer patients from cancer patients are used as probes, to specifically identify the are used as probes, to specifically identify the relevant peptide antigens or the genes relevant peptide antigens or the genes encoding the peptides. encoding the peptides.

• For example, many For example, many cloned CTLcloned CTL lines lines specific for melanomas have been generated specific for melanomas have been generated from the from the T cells of patientsT cells of patients. .

• The T cells can be isolated from:The T cells can be isolated from:

- Peripheral blood- Peripheral blood. .

- Lymph nodes draining the tumor.- Lymph nodes draining the tumor.

- directly from removed tumor tissue. - directly from removed tumor tissue.

• These T cells can be stimulated to grow in These T cells can be stimulated to grow in vitro by vitro by coculture with the tumor cellscoculture with the tumor cells, and , and individual clones can be isolated. individual clones can be isolated.

• Because the T cells and the tumor are from the Because the T cells and the tumor are from the same individual, the major histocompatibility same individual, the major histocompatibility complex (MHC) restriction of the T cells matches complex (MHC) restriction of the T cells matches the MHC alleles expressed by the tumor.the MHC alleles expressed by the tumor.

• These tumor antigen–specific CTL clones have been used These tumor antigen–specific CTL clones have been used to detect responses to tumor-derived peptides or responses to detect responses to tumor-derived peptides or responses to proteins made by complementary DNA (cDNA) libraries to proteins made by complementary DNA (cDNA) libraries of the tumor. of the tumor.

• Such approaches were first used to identify human Such approaches were first used to identify human melanoma antigensmelanoma antigens that stimulated CTL responses in that stimulated CTL responses in patients with melanoma. patients with melanoma.

• The same methods have been used to identify antigens that The same methods have been used to identify antigens that are recognized by CD4+ helper cells, in which case the are recognized by CD4+ helper cells, in which case the probes are helper T cell clones derived from patients’ probes are helper T cell clones derived from patients’ CD4+ T cells. CD4+ T cells.

• A successful method for A successful method for identification of identification of tumor antigenstumor antigens that have stimulated humoral that have stimulated humoral immune responses in tumor patients is called immune responses in tumor patients is called the serologic analysis of recombinant cDNA the serologic analysis of recombinant cDNA expression expression (SEREX).(SEREX).

• In this method, expression libraries of cDNA In this method, expression libraries of cDNA derived from a patient’s tumor RNA are derived from a patient’s tumor RNA are transfected into a cell line, and assays are transfected into a cell line, and assays are performed to detect binding of the cancer performed to detect binding of the cancer patient’s serum immunoglobulins to the patient’s serum immunoglobulins to the transfected cells. transfected cells.

• In this way, In this way, gene sequencesgene sequences for targeted for targeted proteins are obtained.proteins are obtained.

Products of Mutated Genes• Oncogenes and mutated tumor suppressor genes produce Oncogenes and mutated tumor suppressor genes produce

proteins that differ from normal cellular proteins and are, proteins that differ from normal cellular proteins and are, therefore, recognized as tumor antigens.therefore, recognized as tumor antigens.

• Many tumors Many tumors express genesexpress genes whose products are whose products are required for required for malignant transformationmalignant transformation or for or for maintenance of the malignant phenotype. maintenance of the malignant phenotype.

• These genes are produced by These genes are produced by point mutationspoint mutations, , deletionsdeletions, , chromosomal translocationschromosomal translocations, or , or viral gene insertionsviral gene insertions affecting cellular proto oncogenes or tumor suppressor affecting cellular proto oncogenes or tumor suppressor genes. genes.

• The products of these oncogenes and altered tumor The products of these oncogenes and altered tumor suppressor genes are synthesized in the cytoplasm of the suppressor genes are synthesized in the cytoplasm of the tumor cells and may enter the tumor cells and may enter the class I antigen-processing class I antigen-processing pathway. pathway.

• These proteins may enter the These proteins may enter the class II antigen-processingclass II antigen-processing pathway in antigen-presenting cells (APCs) that have pathway in antigen-presenting cells (APCs) that have phagocytosed dead tumor cellsphagocytosed dead tumor cells. .

• Because these altered genes are not present in normal cells, Because these altered genes are not present in normal cells, peptides derived from them do peptides derived from them do not induce self-tolerancenot induce self-tolerance and may and may stimulate T cell responsesstimulate T cell responses in the host. in the host.

• Some patients with cancer have circulating CD4+ and Some patients with cancer have circulating CD4+ and CD8+ T cells that can respond to the products of mutated CD8+ T cells that can respond to the products of mutated oncogenes such as oncogenes such as Ras and Bcr/AblRas and Bcr/Abl proteins and mutated proteins and mutated tumor supressor genes such as tumor supressor genes such as p53p53..

• In animals, immunization with mutated Ras or p53 In animals, immunization with mutated Ras or p53 proteins induces CTLs and rejection responses against proteins induces CTLs and rejection responses against tumors expressing these mutants. tumors expressing these mutants.

• However, these proteins do not appear to be major targets However, these proteins do not appear to be major targets of tumor-specific CTLs in most patients with a variety of of tumor-specific CTLs in most patients with a variety of tumors.tumors.

• Tumor antigens may be produced by randomly Tumor antigens may be produced by randomly mutated genes whose products are not related to mutated genes whose products are not related to the malignant phenotypethe malignant phenotype..

• Tumor antigens that were defined by the Tumor antigens that were defined by the transplantation of carcinogen-induced transplantation of carcinogen-induced tumors, called tumors, called tumor-specific transplantation tumor-specific transplantation antigensantigens,,

• They are mutants of various host cellular They are mutants of various host cellular proteins. proteins.

• Studies established that different rodent Studies established that different rodent tumors, all tumors, all induced by the same carcinogeninduced by the same carcinogen, , expressed different transplantation antigens.expressed different transplantation antigens.

• The tumor antigens identified by such experiments are The tumor antigens identified by such experiments are peptides derived from peptides derived from mutated self proteinsmutated self proteins and presented in and presented in the form of peptide–class I MHC complexes capable of the form of peptide–class I MHC complexes capable of stimulating CTLsstimulating CTLs. .

• These antigens are extremely These antigens are extremely diversediverse because the carcinogens because the carcinogens that induce the tumors may that induce the tumors may randomly mutagenizerandomly mutagenize any host any host gene, and the class I MHC antigen presenting pathway can gene, and the class I MHC antigen presenting pathway can display peptides from any mutated cytosolic protein in each display peptides from any mutated cytosolic protein in each tumor. tumor.

• Mutated cellular proteinsMutated cellular proteins are found more frequently in are found more frequently in chemical carcinogenchemical carcinogen– or – or radiation-inducedradiation-induced animal tumors animal tumors than in spontaneous human cancers, probably because they than in spontaneous human cancers, probably because they mutagenize many cellular genes. mutagenize many cellular genes.

• However, because of the However, because of the intrinsic genomic instabilityintrinsic genomic instability of many of many cancers, a cancers, a wide variety of geneswide variety of genes may be mutated in tumor may be mutated in tumor cells. cells.

• Even if these mutations do not contribute to the malignant Even if these mutations do not contribute to the malignant phenotype, they may encode abnormal proteins that are phenotype, they may encode abnormal proteins that are recognized by the immune systemrecognized by the immune system..

Abnormally Expressed but Unmutated Cellular ProteinsAbnormally Expressed but Unmutated Cellular Proteins

• Tumor antigens that elicit immune responses Tumor antigens that elicit immune responses may be normal cellular proteins that are may be normal cellular proteins that are abnormally expressed in tumor cells.abnormally expressed in tumor cells.

• Many such antigens have been identified in Many such antigens have been identified in human tumors, such as melanomas, by the human tumors, such as melanomas, by the molecular cloningmolecular cloning of antigens that are of antigens that are recognized by T cells and antibodies from recognized by T cells and antibodies from tumor-bearing patientstumor-bearing patients..

• One of the surprises that emerged from these One of the surprises that emerged from these studies was that some tumor antigens are studies was that some tumor antigens are normal proteinsnormal proteins that are produced that are produced at low at low levels in normal cellslevels in normal cells and overexpressed in and overexpressed in tumor cells . tumor cells .

• One such antigen is One such antigen is tyrosinasetyrosinase, an enzyme , an enzyme involved in melanin biosynthesis that is involved in melanin biosynthesis that is expressed only in expressed only in normal melanocytesnormal melanocytes and and melanomasmelanomas..

• Both class I MHC–restricted CD8+ CTL Both class I MHC–restricted CD8+ CTL clones and class II MHC–restricted CD4+ clones and class II MHC–restricted CD4+ helper T cell clones from melanoma helper T cell clones from melanoma patients patients recognize peptides derived from recognize peptides derived from tyrosinase. tyrosinase.

• On face value, it is surprising that these On face value, it is surprising that these patients patients are able to respond to a normal self are able to respond to a normal self antigen. antigen.

• The likely explanation is that tyrosinase is The likely explanation is that tyrosinase is normally normally produced in such small amountsproduced in such small amounts and in so few cells that it is not recognized and in so few cells that it is not recognized by the immune system and by the immune system and fails to induce fails to induce tolerance. tolerance.

• Therefore, the increased amount produced Therefore, the increased amount produced by melanoma cells is able to elicit immune by melanoma cells is able to elicit immune responses.responses.

• The finding of tyrosinase-specific T cell The finding of tyrosinase-specific T cell responses in patients responses in patients raises the possibility raises the possibility that tyrosinase vaccinesthat tyrosinase vaccines may stimulate such may stimulate such responses to melanomas.responses to melanomas.

• Cancer/testis antigens are proteins expressed in gametes and trophoblasts and in many types of cancers but not in normal somatic tissues.

• The first cancer/testis antigens were identified by cloning genes from human melanomas that encoded cellular protein antigens recognized by melanoma-specific CTL clones derived from the melanoma-bearing patients.

• These were called MAGE proteins, and they were subsequently found to be expressed in other tumors in addition to melanomas, including carcinomas of the bladder, breast, skin, lung, and prostate and some sarcomas, as well as in normal testes.

• Subsequent to identification of the MAGE genes, several other unrelated gene families have been identified that encode melanoma antigens recognized by CTL clones derived from melanoma patients.

• Like the MAGE proteins, these other melanoma antigens are silent in most normal tissues, except the testes or trophoblasts in the placenta, but they are expressed in a variety of malignant tumors.

• There are now more than 40 different cancer/testis antigen families identified.

• Half are encoded by genes on the X chromosome• The rest are encoded by genes distributed

throughout the genome.• Although some cancer/testis antigens have been

shown to regulate transcription or translation of other genes, the functions of most of these proteins are unknown.

• In general, they are not required for the malignant phenotype of the cells, and their sequences are identical to the corresponding genes in normal cells; that is, they are not mutated.

• Several X-linked cancer/testis antigens are currently being used in tumor vaccine trials.

Antigens of Oncogenic Viruses• The products of oncogenic viruses function as tumor antigens

and elicit specific T cell responses that may serve to eradicate the tumors.

• DNA viruses are implicated in the development of a variety of DNA viruses are implicated in the development of a variety of tumors in humans and experimental animals. tumors in humans and experimental animals.

• Epstein-Barr virus (EBV).Epstein-Barr virus (EBV). • Human papillomavirus (HPV).Human papillomavirus (HPV). • Papovaviruses.Papovaviruses.• In these DNA virus–induced tumors, virus-encoded protein In these DNA virus–induced tumors, virus-encoded protein

antigens are found in the antigens are found in the nucleusnucleus, , cytoplasmcytoplasm, or , or plasma plasma membranemembrane of the tumor cells. of the tumor cells.

• These endogenously synthesized proteins can be processed, These endogenously synthesized proteins can be processed, and complexes of processed viral peptides with class I MHC and complexes of processed viral peptides with class I MHC molecules may be expressed on the tumor cell surface.molecules may be expressed on the tumor cell surface.

• Because the viral peptides are foreign antigens, these tumors Because the viral peptides are foreign antigens, these tumors are among the are among the most immunogenic tumors known.most immunogenic tumors known.

• The ability of The ability of adaptive immunityadaptive immunity to prevent the to prevent the growth of DNA virus–induced tumors has been growth of DNA virus–induced tumors has been established by many observations. established by many observations.

• These tumors are frequent in These tumors are frequent in immunosuppressedimmunosuppressed::• 1- Allograft recipients receiving 1- Allograft recipients receiving immunosuppressive immunosuppressive

therapytherapy and and • 2- Acquired immunodeficiency syndrome 2- Acquired immunodeficiency syndrome (AIDS)(AIDS). .

• ExperimentsExperiments have shown that animals may be have shown that animals may be specifically immunized against DNA virus–induced specifically immunized against DNA virus–induced tumors and will tumors and will reject transplants of these tumors. reject transplants of these tumors.

• virus-encoded tumor antigens are not virus-encoded tumor antigens are not uniqueunique for each tumor but are for each tumor but are shared by all shared by all tumors induced by the same type of virustumors induced by the same type of virus. .

• A A competent immune systemcompetent immune system plays a role in plays a role in surveillance against virus-induced tumors surveillance against virus-induced tumors because of its ability to recognize and because of its ability to recognize and kill kill virus-infected cells. virus-infected cells.

• In fact, the concept of In fact, the concept of immune surveillanceimmune surveillance against tumors is better established for against tumors is better established for DNA virus–induced tumorsDNA virus–induced tumors than for any than for any other type of tumor.other type of tumor.

• The realization that immune responses against viruses The realization that immune responses against viruses protect individuals from virus-induced cancers has led protect individuals from virus-induced cancers has led to the development of to the development of vaccinesvaccines against oncogenic against oncogenic viruses.viruses.

• A A vaccine against HPVvaccine against HPV is now in use, which has the is now in use, which has the potential to reduce the incidence of potential to reduce the incidence of cervical cancercervical cancer. .

• The vaccine is composed of recombinant HPV The vaccine is composed of recombinant HPV capsid capsid proteinsproteins from the most common oncogenic strains of from the most common oncogenic strains of HPV, which form HPV, which form virus-like particles free of viral virus-like particles free of viral genome. genome.

• Vaccination against Vaccination against hepatitis B virushepatitis B virus is also reducing is also reducing the incidence of the incidence of liver cancerliver cancer. .

• The virus is The virus is not oncogenicnot oncogenic, but it promotes the , but it promotes the development of liver cancer by inducing chronic development of liver cancer by inducing chronic inflammation (inflammation (risk factor for cancer development).risk factor for cancer development).

• RNA tumor virusesRNA tumor viruses (retroviruses) are important causes of (retroviruses) are important causes of tumors in animals.tumors in animals.

• Retroviral oncogene products theoretically have the same Retroviral oncogene products theoretically have the same potential antigenic properties as mutated cellular oncogenes.potential antigenic properties as mutated cellular oncogenes.

• Humoral and cell mediated immune responses to retroviral Humoral and cell mediated immune responses to retroviral gene products on tumor cells can be observed experimentally. gene products on tumor cells can be observed experimentally.

• The only well-defined human retrovirus that is known to cause The only well-defined human retrovirus that is known to cause tumors is human T cell lymphotropic virus 1 (HTLV-1), the tumors is human T cell lymphotropic virus 1 (HTLV-1), the etiologic agent of adult T cell leukemia/lymphoma (ATL), a etiologic agent of adult T cell leukemia/lymphoma (ATL), a malignant tumor of CD4+ T cells. malignant tumor of CD4+ T cells.

• Although Although immune responses specific for HTLV-1–encoded immune responses specific for HTLV-1–encoded antigens have been demonstratedantigens have been demonstrated in individuals infected with in individuals infected with the virus, the virus, it is not clear whether they play any role in it is not clear whether they play any role in protective immunityprotective immunity against the development of tumors. against the development of tumors.

• Furthermore, patients with ATL are often profoundly Furthermore, patients with ATL are often profoundly immunosuppressed, probably because the virus infects CD4+ T immunosuppressed, probably because the virus infects CD4+ T cells and induces functional abnormalities in these cellscells and induces functional abnormalities in these cells.

Oncofetal Antigens• Oncofetal antigens are proteins that are expressed at high levels Oncofetal antigens are proteins that are expressed at high levels

in cancer cells and in normal developing fetal but not adult in cancer cells and in normal developing fetal but not adult tissues.tissues.

• The genes encoding these proteins are The genes encoding these proteins are silenced during silenced during developmentdevelopment and and derepressed with malignant transformationderepressed with malignant transformation. .

• Oncofetal antigens are provide Oncofetal antigens are provide markers that aid in tumor markers that aid in tumor diagnosis. diagnosis.

• It has become clear that their expression in adults is It has become clear that their expression in adults is not not limited to tumorslimited to tumors. .

• The proteins are increased in tissues and in the circulation in The proteins are increased in tissues and in the circulation in various various inflammatory conditionsinflammatory conditions and are found in small and are found in small quantities even in normal tissues. quantities even in normal tissues.

• There is There is no evidenceno evidence that oncofetal antigens are important that oncofetal antigens are important inducers or inducers or targets of anti-tumor immunitytargets of anti-tumor immunity. .

• CEA (CD66) is a highly CEA (CD66) is a highly glycosylated membrane proteinglycosylated membrane protein• Member of the immunoglobulin (Ig) superfamily.Member of the immunoglobulin (Ig) superfamily.• Functions as an intercellular adhesion molecule. Functions as an intercellular adhesion molecule. • CEA expression is CEA expression is normally high normally high during the during the first two first two

trimesterstrimesters of gestation in cells of the gut, pancreas, and liver. of gestation in cells of the gut, pancreas, and liver. • Low expression is seen in normal adult colonic mucosa and Low expression is seen in normal adult colonic mucosa and

the lactating breast.the lactating breast.• CEA expression is CEA expression is increasedincreased in in carcinomascarcinomas of the colon, of the colon,

pancreas, stomach, and breast, and serum levels are pancreas, stomach, and breast, and serum levels are increased in these patients. increased in these patients.

• The level of serum CEA is The level of serum CEA is used to monitor the persistence or used to monitor the persistence or recurrence of the tumors after treatmentrecurrence of the tumors after treatment. .

• CEA can also be elevated in the setting of non-neoplastic CEA can also be elevated in the setting of non-neoplastic diseases, such as diseases, such as chronic inflammatory conditions of the chronic inflammatory conditions of the bowel or liver.bowel or liver.

• AFP is a circulating AFP is a circulating glycoproteinglycoprotein normally synthesized and normally synthesized and secreted in fetal life by the yolk sac and liver. secreted in fetal life by the yolk sac and liver.

• FetalFetal serum concentrations can be serum concentrations can be as high as 2 to 3 mg/mLas high as 2 to 3 mg/mL, , the protein is the protein is replaced by albumin in adult replaced by albumin in adult , and only low , and only low levels are present in serum.levels are present in serum.

• Serum levels of AFP can be significantly elevated in Serum levels of AFP can be significantly elevated in hepatocellular carcinoma, germ cell tumors, and, occasionally, hepatocellular carcinoma, germ cell tumors, and, occasionally, gastric and pancreatic cancers. gastric and pancreatic cancers.

• An elevated serum AFP level is a useful indicator of An elevated serum AFP level is a useful indicator of advanced advanced liver or germ cell tumorsliver or germ cell tumors or of recurrence of these tumors. or of recurrence of these tumors.

• Detection of AFP in tissue sections by Detection of AFP in tissue sections by immunohistochemical immunohistochemical techniquestechniques can help in the pathologic identification of tumor can help in the pathologic identification of tumor cells. cells.

• The diagnostic value of AFP as a tumor marker is limited by The diagnostic value of AFP as a tumor marker is limited by the fact that elevated serum levels are also found in the fact that elevated serum levels are also found in non-non-neoplastic diseases, such as cirrhosis of the liver.neoplastic diseases, such as cirrhosis of the liver.

Altered Glycolipid and Glycoprotein Antigens

• Tumors express higher than normal levels or Tumors express higher than normal levels or abnormal abnormal forms of surface glycoproteins and glycolipidsforms of surface glycoproteins and glycolipids, which may be , which may be diagnostic markers and targets for therapy. diagnostic markers and targets for therapy.

• These altered molecules include These altered molecules include gangliosidesgangliosides, , blood group blood group antigensantigens, and , and mucinsmucins. .

• Altered cell surface properties that result from abnormal Altered cell surface properties that result from abnormal glycolipid and glycoprotein synthesis leads to tissue invasion glycolipid and glycoprotein synthesis leads to tissue invasion and metastatic behavior. and metastatic behavior.

• Many Many antibodiesantibodies have been raised in animals that have been raised in animals that recognize recognize the carbohydrate groups or peptide cores of these moleculesthe carbohydrate groups or peptide cores of these molecules..

• Although most of the epitopes recognized by these antibodies Although most of the epitopes recognized by these antibodies are not specifically expressed on tumors, they are present at are not specifically expressed on tumors, they are present at higher levels on cancer cells than on normal cells. higher levels on cancer cells than on normal cells.

• It is a target for It is a target for cancer therapycancer therapy with specific antibodies. with specific antibodies.

• Gangliosides, including GM2, GD2, and GD3, are Gangliosides, including GM2, GD2, and GD3, are glycolipidsglycolipids expressed at high levels in expressed at high levels in neuroblastomas, melanomas, and many sarcomas. neuroblastomas, melanomas, and many sarcomas.

• They are an They are an attractive target for tumor-specific attractive target for tumor-specific therapiestherapies such as antibody therapy. such as antibody therapy.

• Clinical trials of Clinical trials of anti-ganglioside antibodiesanti-ganglioside antibodies and and immunization with immunization with ganglioside vaccinesganglioside vaccines are under are under way in patients with melanoma. way in patients with melanoma.

• Mucins are high molecular- weight glycoproteins Mucins are high molecular- weight glycoproteins containing numerous O-linked carbohydrate side containing numerous O-linked carbohydrate side chains on a core polypeptide.chains on a core polypeptide.

• Tumors often have Tumors often have dysregulated expressiondysregulated expression of the of the enzymes that synthesize these carbohydrate side enzymes that synthesize these carbohydrate side chains, which leads to the appearance of tumor-chains, which leads to the appearance of tumor-specific epitopes on the carbohydrate side chains specific epitopes on the carbohydrate side chains or on the abnormally exposed polypeptide core. or on the abnormally exposed polypeptide core.

• Mucins including Mucins including CA-125 and CA-19-9CA-125 and CA-19-9, expressed on , expressed on ovarian carcinomas, and ovarian carcinomas, and MUC-1MUC-1, expressed on , expressed on breast carcinomas. breast carcinomas.

• MUC-1 is an MUC-1 is an integral membrane proteinintegral membrane protein that is that is normally expressed only on the apical surface of normally expressed only on the apical surface of breast ductal epithelium, a breast ductal epithelium, a site that is relatively site that is relatively sequestered from the immune system. sequestered from the immune system.

• In ductal carcinomas of the breast, however, the In ductal carcinomas of the breast, however, the molecule is expressed in an non polarized fashion molecule is expressed in an non polarized fashion and contains new, tumor-specific carbohydrate and and contains new, tumor-specific carbohydrate and peptide epitopes detectable by mouse monoclonal peptide epitopes detectable by mouse monoclonal antibodies. antibodies.

• The peptide epitopes induce The peptide epitopes induce both antibody and Tboth antibody and T cell cell responses in cancer patients.responses in cancer patients.

• Efforts are under way to develop Efforts are under way to develop vaccines vaccines containing containing immunogenic forms of MUC-1 epitopes.immunogenic forms of MUC-1 epitopes.

Tissue-Specific Differentiation AntigensTissue-Specific Differentiation Antigens

• Tumors may express molecules that are Tumors may express molecules that are present only on the normal cells of origin and present only on the normal cells of origin and not on cells from other tissues.not on cells from other tissues.

• These antigens are called differentiation These antigens are called differentiation antigens because they are antigens because they are specificspecific for for particular lineages or particular lineages or differentiation stagesdifferentiation stages of various cell types. of various cell types.

• Their importance is as potential Their importance is as potential targets for targets for immunotherapyimmunotherapy and for identification of and for identification of the tissue of origin of tumors.the tissue of origin of tumors.

• For example, several melanoma antigens that are targets of For example, several melanoma antigens that are targets of CTLs in patients are melanocyte differentiation antigens, such CTLs in patients are melanocyte differentiation antigens, such as as tyrosinasetyrosinase. .

• CD10CD10 (previously called common acute lymphoblastic (previously called common acute lymphoblastic leukemia antigen, or CALLA) and leukemia antigen, or CALLA) and CD20 in CD20 in Lymphomas. Lymphomas.

• Antibodies against these molecules are used for tumor Antibodies against these molecules are used for tumor immunotherapy; the most successful immunotherapy for non-immunotherapy; the most successful immunotherapy for non-Hodgkin’s B cell lymphomas is an anti-CD20 antibody Hodgkin’s B cell lymphomas is an anti-CD20 antibody (rituximab). (rituximab).

• The idiotypic determinants of the surface Ig of a clonal B cell The idiotypic determinants of the surface Ig of a clonal B cell population are markers for that B cell clone because all other population are markers for that B cell clone because all other B cells express different idiotypes. B cells express different idiotypes.

• Therefore, the Therefore, the Ig idiotypeIg idiotype is a highly specific tumor antigen is a highly specific tumor antigen for B cell lymphomas and leukemias. for B cell lymphomas and leukemias.

• These differentiation antigens are normal self molecules, and These differentiation antigens are normal self molecules, and therefore they therefore they do not usually induce strong immunedo not usually induce strong immune responses responses in tumor bearing hosts.in tumor bearing hosts.

IMMUNE RESPONSES TO TUMORS

• The effector mechanisms of both innate and The effector mechanisms of both innate and adaptive immunity have been shown to kill adaptive immunity have been shown to kill tumor cells. tumor cells.

• Immunologists work on which of these Immunologists work on which of these mechanisms may contribute to mechanisms may contribute to

• 1- 1- protection against tumorsprotection against tumors

• 2- to 2- to enhanceenhance these these effector mechanisms in effector mechanisms in ways that are tumor specific. ways that are tumor specific.

Innate Immune Responses to Tumors

• Some of the early research on Some of the early research on functions of effector cells of the functions of effector cells of the innate immune system, including innate immune system, including NK cellsNK cells and and macrophagesmacrophages, focused , focused on the ability of these cells to kill on the ability of these cells to kill cultured tumor cells.cultured tumor cells.

NKNK• NK cells kill many types of tumor cells, especially cells that NK cells kill many types of tumor cells, especially cells that

have reduced class I MHC expression and express ligands for have reduced class I MHC expression and express ligands for NK cell activating receptors. NK cell activating receptors.

• NK cells can kill NK cells can kill virally infected cellsvirally infected cells and certain and certain tumor celltumor cell lines. lines.

• NK cells also respond to the absence of class I MHC NK cells also respond to the absence of class I MHC molecules because the molecules because the recognitionrecognition of class I MHC molecules of class I MHC molecules delivers delivers inhibitory signals to NK cellsinhibitory signals to NK cells. .

• Some tumors lose expression of class I MHC molecules that Some tumors lose expression of class I MHC molecules that makes the tumors good targets for NK cells. makes the tumors good targets for NK cells.

• Some tumors also express Some tumors also express MIC-A, MIC-B, and ULBMIC-A, MIC-B, and ULB, which , which are ligands for the NKG2D activating receptor on NK cells.are ligands for the NKG2D activating receptor on NK cells.

• In addition, NK cells can be targeted to In addition, NK cells can be targeted to IgG antibody– IgG antibody– coated tumor cells by Fc receptorscoated tumor cells by Fc receptors (FcγRIII or CD16). (FcγRIII or CD16).

• The tumoricidal capacity of NK cells is increased by The tumoricidal capacity of NK cells is increased by cytokines, cytokines, (IL-γ(IL-γ), ), IL-15IL-15, and , and IL-12IL-12, with stimulation , with stimulation of NK cell activity. of NK cell activity.

• IL-2–activated NK cells, called lymphokine-activated IL-2–activated NK cells, called lymphokine-activated killer killer (LAK) cells(LAK) cells, are derived by culture of , are derived by culture of peripheral bloodperipheral blood cells or cells or tumor infiltrating tumor infiltrating lymphocyteslymphocytes from tumor patients with high doses of from tumor patients with high doses of IL-2.IL-2.

• These cells are more potent killers of tumors than are These cells are more potent killers of tumors than are un activated NK cells. un activated NK cells.

• T cell–deficient miceT cell–deficient mice do not have a high incidence of do not have a high incidence of spontaneous tumors, and this is attributed to the spontaneous tumors, and this is attributed to the presence of presence of normal numbers of NK cellsnormal numbers of NK cells that serve an that serve an immune surveillance function. immune surveillance function.

• Deficiencies of NK cells leads to an increased Deficiencies of NK cells leads to an increased incidence of EBV-associated lymphomas.incidence of EBV-associated lymphomas.

Macrophages• Macrophages are capable of both inhibiting and promoting the growth and Macrophages are capable of both inhibiting and promoting the growth and

spread of cancers, depending on their activation state.spread of cancers, depending on their activation state. • Classically activated M1 macrophages, display various anti-tumor Classically activated M1 macrophages, display various anti-tumor

functions.functions.• Possible mechanisms include direct recognition of some surface antigens Possible mechanisms include direct recognition of some surface antigens

of tumor cells and activation of macrophages by IFN-γ produced by of tumor cells and activation of macrophages by IFN-γ produced by tumor-specific T cells. tumor-specific T cells.

• M1M1 macrophages can kill tumor cells by the release of lysosomal macrophages can kill tumor cells by the release of lysosomal enzymes, reactive oxygen species, and nitric oxide. enzymes, reactive oxygen species, and nitric oxide.

• M1 macrophagesM1 macrophages also produce the cytokine tumor necrosis factor also produce the cytokine tumor necrosis factor (TNF),(TNF), which is as an agent that can kill tumors mainly by inducing thrombosis which is as an agent that can kill tumors mainly by inducing thrombosis in tumor blood vessels. in tumor blood vessels.

• In contrast, In contrast, M2 macrophagesM2 macrophages may contribute to tumor progression. may contribute to tumor progression. • These cells secrete vascular endothelial growth factor (VEGF), These cells secrete vascular endothelial growth factor (VEGF),

transforming growth factor-β (TGF-β), and other soluble factors that transforming growth factor-β (TGF-β), and other soluble factors that promote tumor angiogenesis. promote tumor angiogenesis.

Adaptive Immune Responses to Adaptive Immune Responses to TumorsTumors

• Tumors elicit both T cell–mediated and Tumors elicit both T cell–mediated and humoral immune responses. humoral immune responses.

• T cells are the principal mediators of T cells are the principal mediators of antitumor immunity. antitumor immunity.

• This realization has led to considerable This realization has led to considerable efforts to enhance T cell responses for the efforts to enhance T cell responses for the immunotherapy of cancers.immunotherapy of cancers.

T LymphocytesT Lymphocytes• The principal mechanism of adaptive tumor immunity is killing of tumor The principal mechanism of adaptive tumor immunity is killing of tumor

cells by CD8+ CTLs.cells by CD8+ CTLs. • The ability of CTLs to provide effective anti-tumor immunity is seen in The ability of CTLs to provide effective anti-tumor immunity is seen in

animal experimentsanimal experiments using using carcinogen inducedcarcinogen induced and and DNA virus–induced DNA virus–induced tumorstumors. .

• CTLs may perform a surveillance function by recognizing and killing CTLs may perform a surveillance function by recognizing and killing potentially malignant cells that express peptides which are derived from potentially malignant cells that express peptides which are derived from tumor antigens and are presented in tumor antigens and are presented in association with class I MHC association with class I MHC molecules.molecules.

• The role of immune surveillance in preventing common, The role of immune surveillance in preventing common, non virally non virally induced tumorsinduced tumors remains remains controversialcontroversial because the frequency of such because the frequency of such tumors in T cell– deficient people is not clearly greater than the frequency tumors in T cell– deficient people is not clearly greater than the frequency in immunocompetent individuals. in immunocompetent individuals.

• The prognosis of some types of human tumors is better when more CTLs The prognosis of some types of human tumors is better when more CTLs are present. are present.

• Mononuclear cells derived from the inflammatory infiltrate in human solid Mononuclear cells derived from the inflammatory infiltrate in human solid tumors, called tumors, called tumor-infiltrating lymphocytes (TILs),tumor-infiltrating lymphocytes (TILs), contain CTLs with contain CTLs with the capacity to kill the tumor from which they were derived.the capacity to kill the tumor from which they were derived.

• CD8+ T cell responses specific for tumor antigens CD8+ T cell responses specific for tumor antigens may require cross-presentation of the tumor may require cross-presentation of the tumor antigens by dendritic cells.antigens by dendritic cells.

• Most tumor cells are Most tumor cells are not derived from APCsnot derived from APCs and and do do not express the costimulatorsnot express the costimulators needed to initiate needed to initiate T cell responses or the class II MHC molecules T cell responses or the class II MHC molecules needed to needed to stimulate helper Tstimulate helper T cells that promote the cells that promote the differentiation of CD8+ Tdifferentiation of CD8+ T cells. cells.

• Tumor cells or their antigens are ingested by host Tumor cells or their antigens are ingested by host APCs, particularly APCs, particularly dendritic cellsdendritic cells, and tumor , and tumor antigens are processed antigens are processed inside the APCsinside the APCs. .

• Peptides derived from these antigens are then Peptides derived from these antigens are then displayed bound to class I MHC molecules for displayed bound to class I MHC molecules for recognition by CD8+ T cells. recognition by CD8+ T cells.

Dendritic Cells• Highly potent antigen processing and Highly potent antigen processing and

presenting cellspresenting cells

• Prime an Immune ResponsePrime an Immune Response

• Pulse with tumor Ags or gene transferPulse with tumor Ags or gene transfer

Cl II Cl I

• The APCs express costimulators that provide the signals The APCs express costimulators that provide the signals needed for differentiation of CD8+ T cells into anti-tumor needed for differentiation of CD8+ T cells into anti-tumor CTLs, and the APCs express class II MHC molecules that CTLs, and the APCs express class II MHC molecules that may present internalized tumor antigens and activate may present internalized tumor antigens and activate CD4+ helper T cells as well CD4+ helper T cells as well (cross-presentation).(cross-presentation).

• Once effector CTLs are generated, they are able to Once effector CTLs are generated, they are able to recognize and killrecognize and kill the tumor cells without a requirement the tumor cells without a requirement for costimulation. for costimulation.

• A practical application of the concept of cross-priming: A practical application of the concept of cross-priming: 1- Grow dendritic cells from a patient with cancer1- Grow dendritic cells from a patient with cancer, , 2- incubate the APCs with the cells or antigens from that 2- incubate the APCs with the cells or antigens from that patient’s tumor. patient’s tumor. 3- Use these antigen-pulsed APCs 3- Use these antigen-pulsed APCs as vaccinesas vaccines to stimulate to stimulate anti-tumor T cell responses.anti-tumor T cell responses.

Activation of naïve T cells

Signal I

Signal II

Effector T cells: killers

T cells

Tumor

Cross Presentation of Tumor Antigens

• The importance of CD4+ helper T cells in tumor The importance of CD4+ helper T cells in tumor immunity is immunity is less clearless clear. .

• CD4+ cells may play a role in anti-tumor immune CD4+ cells may play a role in anti-tumor immune responses by responses by providing cytokinesproviding cytokines for effective CTL for effective CTL development. development.

• Helper T cells specific for tumor antigens may Helper T cells specific for tumor antigens may secrete cytokinessecrete cytokines, such as , such as TNFTNF and and IFN-γIFN-γ, that can , that can increase tumor cell class I MHC expression and increase tumor cell class I MHC expression and sensitivity to lysis by CTLs. sensitivity to lysis by CTLs.

• IFN-γIFN-γ may also activate may also activate macrophagesmacrophages to kill tumor to kill tumor cells. cells.

• Increased incidence of tumors in knockout mice Increased incidence of tumors in knockout mice lacking this cytokine, the IFN-γ receptorlacking this cytokine, the IFN-γ receptor, or , or components of the IFN-γ receptor signaling cascade.components of the IFN-γ receptor signaling cascade.

AntibodiesAntibodies• Tumor-bearing hosts may produce antibodies against various Tumor-bearing hosts may produce antibodies against various

tumor antigens. tumor antigens. • Patients with EBV associated lymphomas have serum Patients with EBV associated lymphomas have serum

antibodies against EBV-encoded antigens expressed on the antibodies against EBV-encoded antigens expressed on the surface of the lymphoma cells. surface of the lymphoma cells.

• Antibodies may kill tumor cells by Antibodies may kill tumor cells by • 1- activating complement1- activating complement or by or by • 2- antibody-dependent cell mediated cytotoxicity.2- antibody-dependent cell mediated cytotoxicity.

(Fc receptor–bearing MQ or NK cells mediate the killing). (Fc receptor–bearing MQ or NK cells mediate the killing). • There is There is little evidence for effective humoral immune little evidence for effective humoral immune

responses against tumorsresponses against tumors..• Some effective therapeutic anti-tumor antibodies that are Some effective therapeutic anti-tumor antibodies that are

passively administered to patients work by ADCC.passively administered to patients work by ADCC.