3. tumor immunology Taradi 3Interactive immunology
Oncology
Oncology is the branch of medicine
(biology) that deals with tumors.
Tumor, which means swelling,
neoplasm which means new growth
and cancer which means spreading in
the menner of a crab are synonym.
Cancer cells are altered self-cells that
have escaped normal growth regulating
mechanisms.
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Prevalence
Current estimates project that one person
in three will develop cancer, and that one
in five will die from it.
Cancer is the second-ranking cause of
death, led only by cardiovascular disease.
Cancer is largely a disease of older
people.
5. tumor immunology Taradi 5Interactive immunology
Origin of the tumour
In most tissues of a mature organism, a
balance is maintained between cell
renewal and cell death.
Occasionally, though, cells arise that no
longer respond to normal growth-control
mechanisms.
These cells give rise to clones of cells
that can expand to a considerable size,
producing a tumour, or neoplasm.
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Benign and Malignant Tumour
A tumour that grows incapsulated and does not
invade the healthy surrounding tissue is benign.
A tumour that grows uncontrolled invasive,
progressive, destructive and that exhibit
metastasis is malignant.
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Classification of tumours
Malignant tumours or cancers are classified
according to the embryonic origin of the tissue
from which the tumour is derived.
– Carcinomas are tumors that arise from endodermal or
ectodermal tissues such as skin or the epithelial
lining of internal organs and glands.
– Sarcomas arise from mesodermal connective tissues
such as bone, fat, and cartilage.
– Leukemia, lymphoma and myeloma are malignant
tumors of hematopoietic cells of the bone marrow.
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The Clonal origin of tumour
Tumour is a clon of cells.
Tumours are monoclonal
at the time of initiation.
Most tumours exhibit
genomic instability such
that additional genetic
abnormalities accumulate
during the course of the
disease and frequently
correlate with clinical
aggressiveness.
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The Characteristics of Transformed Cells
Altered antigen expression (mutant antigens, virally controled antigens, loss of MHC
class I expresion)
Altered surface charge
Altered surface carbohydrate expression
Altered nuclear/cytoplasmic ratio
Altered and variable nuclear morphology (pleomorphism)
Altered nuclear staining (hyperchromasia)
Altered DNA content (aneuploidy)
Molecular alterations in key regulatory genes (expression of normally silent genes)
Molecules related to metastatic potential (CD44)
Reduced requirements for growth factors (or serum) when grown in vitro
Growth at very low cell densities in vitro
Loss of contact inhibition (ie. still proliferate at high densities)
Growth in an anchorage independent manner
Immortality: ie. do not show senescence after 70 rounds of division (ie. they exceed
Hayflick limit)
Tumourigenesis in animal models
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Induction of Cancer: A Multistep Process
The development
from a normal cell
to a cancerous cell
is usually a
multistep process
of clonal evolution
driven by a series
of somatic
mutations that
progressively
convert the cell
from
– normal growth to a
– precancerous state
and finally into a
– cancerous state.
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Tumour growth and metastasis
(d) The malignant tumor metastasizes by generating small
clusters of cancer cells that dislodge from the tumor and
are carried by the blood or lymph to other sites in the
body.
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Tumour Heterogeneity
Tumours are generally composed of subpopulations of cells that
are heterogeneous for many characteristics such as:
– morphology,
– karyotype,
– antigenicity,
– immunogenicity,
– biochemical properties,
– growth rate,
– metastatic potential,
– sensitivity to chemotherapeutic agents,
– sensitivity to radiation etc.
The leading hypothesis for the origin of tumour subpopulations is
the genetic and epigenetic instability of cancer cells.
Tumour heterogeneity is a fundamental property of cancer and has
important biological and clinical consequences among which
augmentation of tumour progression and development of
resistance to treatment are most crucial for the host.
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The Cell Cycle
Representative
schematic of the two
major checkpoint of the
cell cycle.
Immortality is acquired at
chromosome’s ends.
One characteristic of
DNA replication is that
the ends of linear DNA
molecules are
progressively shortened
at each round of
replication of normal
cells, but not in tumour
cells.
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Cancer-Associated Genes
Cancer associated genes can be
divided into three categories:
– Genes that induce cellular proliferation
• Growth factors
• Growth-factor receptors
• Signal transducers
• Transcription factors
– Tumour-suppressor genes
• Rb, suppressor of retinoblastoma
• P53 encodes a nuclear phosphoprotein
– Genes that regulate programmed cell
death
• bcl - 2, an anti-apoptosis gene
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Oncogenes and Cancer Induction
Proto-oncogenes encode
proteins involved in
control of normal cellular
growth.
The conversion of proto-
oncogenes to oncogenes
is one of the key steps in
the induction of most
human cancer.
This conversion may
result from mutation in an
oncogene, its
translocation, or its
amplification.
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Chromosome translocations
In the past 30 years, molecular
pathology (which includes chemistry,
biochemistry, molecular biology,
molecular virology, molecular
genetics, epigenetics, genomics,
proteomics, and other molecular-
based approaches) has identified
some key alterations that are required
for cellular transformation and
malignancy.
Chromosome translocations are
common in lymphoproliferative
disorders.
A hallmark of human chronic myeloid
leukaemia is a 9;22 chromosome
translocation that generates the so-
called ‘Phyladelphia chromosome’.
'Phyladelphia chromosome'
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Gene expression profiles
Schematic
representation of the
test technology used
to determine the
expression status of
the 70 gene profile or
signature that is
indicative of a poor
prognosis.
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Tumour antigens
The tumour antigens recognized by
human T cells fall into one of four major
categories:
– Antigens encoded by genes specifically
expressed by tumors
– Antigens encoded by variant forms of normal
genes that have been altered by mutation
– Antigens normally expressed only at certain
stages of differentiation or only by certain
differentiation lineages
– Antigens that are overexpressed in particular
tumors
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Tumour Antigens
Tumour cells display
– tumour-specific antigens (TSA) and the more
common
– tumour-associated antigens (TAA).
Tumour-specific antigens are unique to tumour
cells and do not occur on normal cells in the
body.
Tumour-associated antigens, which are not
unique to tumour cells, may be proteins that are
expressed on normal cells during fetal
development, but that normally are not
expressed in the adult.
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Tumour Transplantation Antigens
Two types of tumour transplantation
antigens have been identified on tumour
cells:
– tumour-specific transplantation antigens
(TSTAs)
– and tumour-associated transplantation antigens
(TATAs).
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Oncogenes and Cancer Induction
Conversion of proto-
oncogenes into
oncogenes can involve
– mutation, resulting in
production of
qualitatively different
gene products, or
– DNA amplification or
– translocation, resulting
in increased or
decreased expression of
gene products.
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Virally controlled antigens
After infection
with
oncogenic
viruses, they
express genes
homologous
with cellular
oncogens
which encode
factors
affecting
growth and
cell division.
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The Immune Response to Tumours
Immune surveillance against strongly
immunogenic tumours
– Cell-mediated responses to tumours
– Humoral responses to tumours
Immunological escape of tumours
– Immunological unresponsiveness
– Immunoselection (“sneaking through”)
– Antigen modulation
– Immunological enhancement and blocking antibody
– Circulating antigen, immune complex
– Shedding of antigens (“antgenic smokescreen”)
– Immunologically privileged sites
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Immune Response to Tumours
The immune
response to
tumors
includes
– CTL-mediated
lysis,
– NK-cell
activity,
– macrophage-
mediated
tumor
destruction,
and
– destruction
mediated by
ADCC.
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Tumor Evasion of the Immune System
Tumors may evade the immune
response by
– modulating their tumor antigens
– reducing their expression of class I MHC
molecules
– antibody-mediated or immune complex-
mediated inhibition of CTL activity.
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Vaccination Strategies
Key elements in the design of strategies
for vaccination against cancer are:
– the identification of significant tumour
antigens by genetic or biochemical
approaches
– the development of strategies for the effective
presentation of tumour antigens and
– the generation of activated populations of
helper or cytotoxic T cells.
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Therapy with transfection
Use of transfected
tumor cells for cancer
immunotherapy.
Tumor cells
transfected with the
B7 gene express the
co-stimulatory B7
molecule, enabling
them to provide both
activating signal (1)
and co-stimulatory
signal (2) to CTL
Cancer is a diverse collection of diseases that are caused by abnormal and invasive cell proliferation.
Cancer is one of the leading causes of death in humans with most cancer deaths resulting from local invasion and distant metastases of tumour cells. Treatment of the cancer at this stage of the progression of the disease has of course clear limitations. What is urgently needed is a detailed examination of all possibilities that might result in the reversal of the proliferation of cancer cells so that a much more efficient therapeutic regimen could be designed for cancer patients.
_ _ _ This days the cancer occur frekvently than in earlier periods. Whay? The life expectancy and the average age of population are increasing.
Carcinoma - Epithelial tissue cancers. Smooth linings of inner & outer surfaces of body. Sarcoma - Connective tissue involvement, bone, cartilage, and muscle. Leukemia - Cancers arising in the blood, stem cells in bone marrow. Lymphoma - Cancer of the lymphatic system. Carcinomas account for about 85% of all cancers. Another 10% are Sarcomas and Leukemias. Carcinoma rates increase with age. Sarcoma , which accounts for about 2% of cancers, has a constant rate across the lifespan
Tumour instability can lead to resistance of the cancer cells to new target-based therapeutics.
As eukaryotic cells divide, the protective ends of the linear chromosomes, the telomeres, gradually shorten with each cell division. When a critical telomere length is reached, the cells are signalled into senescence, an irreversible state of quiescence. Thus, telomere length has emerged as a replicative clock within each population of cells and the tissues and organs they form in vitro. Consequently telomere length has become accepted as a biomarker for biological ageing in vivo .
Representative schematic of the two major checkpoint of the cell cycle and involvement of some of the major tumor suppressor gene products. The ATM and ATR kinases are involved in the signaling of DNA damage. These kinases phosphorylate a number of downstream mediators, including p53and Chk (Checkpoint kinases 1 and 2). Phosphorylation of p53activates this transcription factor that in turn promotes synthesis of p21WAF, which inhibits the cyclin/CDK complexes, thus activating the G1/S checkpoint. If DNA damage cannot be repaired, p53promote s apoptosis. p53is also involved in the establishment of the G2/M checkpoint. The tumor suppressor p16INK4A is involved in inhibition of CDKs, thus contributing to the G1/S checkpoint. The checkpoint kinases halt the cell cycle by phosphorylating (thus inactivating) cdc25 protein family members. Cdc25 are phosphatases that activated cdc2 complexed with cyclin B. The latter complex is the mytosis-promoting factor (MPF), which is the complex that regulates cell entry into the Mphase Immortality is acquired at chromosomes’ ends The ends of all eucaryotes’ chromosome are organized into structures termed telomeres. One characteristic of DNA replication is that the ends of linear DNA molecules are progressively shortened at each round of replication because DNA polymerase uses RNA primers that are degraded after elongation, a phenomenon known as ‘end replication problem’ Therefore, telomeres work as a cellular hour glass that determines how many replication rounds a cell can afford. The protein component of telomerase (TERT, the reverse transcriptase) is not expressed (or expressed at insufficient levels) in most somatic cells. For this reason, somatic cells cannot restore the length of telomeres during cell proliferation and undergo replicative senescence and crisis. As a result of mutations, or of viral infection in certain cells (Foddis et al., 2002), tumor cells regain sufficient amounts of TERT expression and thus can proliferate indefinitely.
Immune cells in the tumour microenvironment not only fail to mount an effective anti-tumour immune response, but also interact intimately with the transformed cells to promote oncogenesis actively. Signal transducer and activator of transcription 3 (STAT3), which is a point of convergence for numerous oncogenic signalling pathways, is constitutively activated both in tumour cells and in immune cells in the tumour microenvironment. Constitutively activated STAT3 inhibits the expression of mediators necessary for immune activation against tumour cells. Furthermore, STAT3 activity promotes the production of immunosuppressive factors that activate STAT3 in diverse immune-cell subsets, altering gene-expression programmes and, thereby, restraining anti-tumour immune responses. As such, STAT3 propagates several levels of crosstalk between tumour cells and their immunological microenvironment, leading to tumour-induced immunosuppression. Consequently, STAT3 has emerged as a promising target for cancer immunotherapy.
- - - Different mechanisms generate tumor-specific transplantation antigens (TSTAs) and tumor-associated transplantation antigens (TATAs). The latter are more common.
- The immune response may play a role in selecting for tumor cells expressing lower levels of class I MHC molecules by preferentially eliminating those cells expressing high levels of class I molecules. With time, malignant tumor cells may express progressively fewer MHC molecules and thus escape CTL-mediated destruction.
Most of the recent advances in cancer immunotherapy have involved the identification and targeting of key molecular drivers of the disease process. Antibodies can target toxins or radioactive isotopes to the tumor-cell surface.
As a result of the combined signals, the CTL differentiate into effector CTLs, which can mediate tumor destruction. In effect, the transfected tumor cell acts as an antigen-presenting cell. (b) Transfection of tumor cells with the gene encoding GM-CSF allows the tumor cells to secrete high levels of GM-CSF. This cytokine will activate dendritic cells in the vicinity of the tumor, enabling the dendritic cells to present tumor antigens to both TH cells and CTL-Ps.