Immunology Flashcards
Summarise the evidence for the importance of tumour surveillance by the immune system.
Spontaneous immune response against tumour-expressed antigen results in auto-immune disease
breast cancer patient can have CDR2 = cerebellum degeneration related antigen 2
Patient has made antibodies against this (tumour immunity) which can pass blood-brain barrier to neurone (autoimmune neurological disease) into brain
Explaining symptoms of severe vertigo, unintelligible speech, truncates and appendicular ataxia (abnormal movements) —> paraneoplastic cerebellar degeneration (PCD)
Elimination of Purkinje cells by tumour-induced auto-immune response 9auto antibodies) causes PCD; humoural anti-tumour response
- At least certain tumours can express antigens that are absent from (or not detectable in) corresponding normal tissues.
- The immune system can, in principle, detect such abnormally expressed antigens and, as a result, launch an attack against the tumour.
- In certain cases, this may result in auto-immune destruction of normal somatic tissues.
Circumstantial evidence for immune control of tumours in humans:
- Autopsies of accident victims have shown that many adults have microscopic colonies of cancer cells, with no symptoms of disease. Immune control?
- Patients treated for melanoma, after many years apparently free of disease, have been used as donors of organs for transplantation. Transplant recipients have developed tumours. Donor had developed ‘immunity’ to the melanoma, but the transplant recipients had no such ‘immunity’.
- Deliberate immunosuppression (e.g. in transplantation) increases risk of malignancy
- Men have twice as great chance of dying from malignant cancer as do women (women typically mount stronger immune responses)
Concept of tumour ‘immunosurveillance’: malignant cells are generally controlled by the action of the immune system.
Immunotherapy tries to enhance immune responses to cancer.
Explain the cancer-immunity cycle.
T cells: alpha, beta T cell receptor, MHC restricted - I and II
B cells: B cell receptor (antibody), vast range of molecules e.g. virus neutralisation
Cancer-immunity cycle
1) release of cancer cell antigens (cancer cell death)
2) cancer antigen presentation (dendritic cells/APCs)
3) priming and activation (APCs and T cells) - present to recirculating T cells
4) trafficking of T cells to tumours (CTLs)
5) infiltration of T cells into tumours (CTLs, endothelial cells), TIL - tumour infiltrating leukocytes
6) recognition of cancer cells by T cells (CTLs, cancer cells)
7) killing of cancer cells —> 1)
At each stage there are molecules which activate/regulate lymphocytes e.g. IL-10 (inhibitory) TNF-alpha (stimulatory)
Immune selection pressure - tumour cells can lose MHC so T cells cant recognise so escape and have advantage + grow
1)Initiation of cancer usually results from multiple sporadic events over time
-irradiation
-chemical mutagens
-spontaneous errors during DNA replication
-tumour virus-induced changes in genome
Cause induction of mutations in cellular DNA
2)Aberrant regulation of apoptosis and cell cycle results in tumour growth
3)tumour growth (eventually) results in inflammatory signals
4)recruitment of innate immunity: dendritic cells, macrophages, natural killer cells
5) and subsequent recruitment of adaptive antigen-specific immunity in draining lymph node
Requirements for activation of an adaptive anti-tumour immune response 1. Local inflammation in the tumour (“danger signal”) 2. Expression and recognition of tumour antigens
Problems in 1 = it takes the tumour a while to cause local inflammation
Problems in 2 = antigenic differences between normal and tumour cells can be very subtle e.g. small number of point mutations
If requirements for ‘spontaneous’ activation of the adaptive anti-tumour response are not met e.g. immune system suppressed, can we ‘teach’ the adaptive immune system to selectively detect and destroy tumour cells?
Cancer Immunotherapy
- Potential alternative/supplement to conventional therapies (surgery, chemotherapy, radiotherapy)
- Which antigens should be targeted?
Explain how immune responses to tumours have similarities with those to virus infected cells.
T cells can see inside cells and can recognise tumour-specific antigens
Peptide sample on surface from inside cell
MHC I/II ‘Display’ contents of cell for surveillance by T cells: infection, carcinogenesis
Tumour-specific antigens Viral proteins: -Epstein Barr Virus (EBV) -Human Papillomavirus (HPV) Mutated cellular proteins: -TGF-beta receptor III
Cancers of viral origin
Opportunistic malignancies: Immunosuppression
• EBV-positive lymphoma: Post-transplant immunosuppression
• HHV8-positive Kaposi sarcoma: HIV
Also in immunocompetent individuals:
• HTLV1-associated leukaemia/lymphoma
• HepB virus- and HepC virus-associated hepatocellular carcinoma
• Human papilloma virus-positive genital tumours
Tumour cells express viral antigens
Cervical cancer is induced and maintained by the E6 and E7 oncoproteins of HPV - oncoproteins cause deregulation of cell cycle and abbarent cell growth
E6 and E7 are intracellular antigens
Can target antigens for preventive HPV vaccination
Surface proteins incorporated into virus-like particles (VLPs) - no DNA so can’t cause cancer
Relation between consequences of cervical HPV infection and HPV-specific T cell immunity
In majority, HPV16 infection:
strong immunity —> clearance HPV-infection, immunological memory
In minority, HPV16 infection:
Immune failure —> cervical neoplasia, 50%: no immunity; 50%: non-functional immunity
Can use preventative vaccination before immune failure and therapeutic vaccination after neoplasia
Explain the concept of tumour-associated antigens giving named examples, and explain how they differ from tumour-specific antigens.
Tumour-associated antigens (TAA) are normal cellular proteins which are aberrantly expressed (timing, location or quantity) - wrong time, place, amount
Because they are normal self proteins, for an immune response to occur tolerance (delete auto-reactive lymphocytes) may need to be overcome.
Tumour-associated antigens: ectopically expressed auto-antigens
- Cancer-testes antigens (developmental antigens): Silent in normal adult tissues except male germ cells (some expressed in placenta).
e. g. MAGE family: Melanoma associated antigens. Identified in melanoma also expressed in other tumours.
Human epidermal growth factor receptor 2 (HER2): overexpressed in some breast carcinomas Mucin 1 (MUC-1): membrane-associated glycoprotein, overexpressed in very many cancers Carcinoembryonic antigen (CEA): normally only expressed in foetus/embryo, but overexpressed in a wide range of carcinomas PROSTATE: prostate-specific antigen (PSA) prostate-specific membrane antigen (PSMA) prostatic acid phosphatase (PAP)
Tolerance induction by negative selection in the thymus: central tolerance
Self-MHC-restricted, self-tolerant but some may be autoreactive cells
Tumour-associated antigens: differentiation (i.e. lineage-specific) auto-antigens
Melanocyte / melanoma – differentiation antigens e.g. tyrosinase (melanin production): poor self- tolerance - autoimmune reactivity against normal cells.
Local auto-immune depigmentation in melanoma patients
Immunotherapy against melanoma in mice is accompanied by auto-immune skin depigmentation (vitiligo)
Targeting of tumour-associated auto-antigens for T cell-mediated immunotherapy of cancer
Two major problems:
1. Auto-immune responses against normal tissues
2. Immunological tolerance
-Normal tolerance to auto-antigens
-Tumour-induced tolerance
Summarise approaches being used and developed for tumour immunotherapy, including antibody-based therapy, tumour vaccination and immune checkpoint blockade.
1) Antibody-based therapy
2) Therapeutic vaccination
3) Immune checkpoint blockade
4) Adoptive transfer of immune cells
5) Combinations of 1) to 4) above
Monoclonal antibody-based therapy
-“Naked” - just antibody by itself e.g. Trastuzumab (Herceptin) - humanised antibody - anti HER2, anti CD20 (B cell lymphoma), anti CD52 (“) and anti EGFR
(colon cancer)
-“conjugated”- radioactive, drug-linked
Radioactive particle: e.g. Ibritumomab tioxetan (Zevalin), anti CD20 linked to yttriym-90
Drug: e.g. trastuzumab emtansine (Kadcyla) anti HER2 linked to cytotoxic drug
-“bi-specific” antibodies - genetically engineered so both arms not symmetrical; genetically engineered to combine 2 specificities e.g. anti CD3 and anti CD19 (Blinatumomab approved for use in patients with B cell tumours)
Issue is cost because all monoclonal antibodies are expensive
Therapeutic cancer vaccination
•There is one FDA approved vaccine to treat cancer (also licensed for sale in the UK, but not NICE approved):
•Provenge® (sipuleucel-T) for advanced prostate cancer
•Patient’s own WBC are treated with a fusion protein between prostatic acid phosphatase (PAP) and the cytokine GM-CSF
•Stimulates DC maturation and enhances PAP-specific T cell responses and then put back into patient
Personalised tumour-specific cancer vaccines: WES = whole genome sequencing, compare sequences between cells, stimulation of adaptive mine responses against mutant proteins - EXPENSIVE
Immune checkpoint blockade
•Rather than directly stimulate responses, this
approach seeks to reduce/remove negative regulatory controls of existing T cell responses
•Targets CTLA-4 and PD-1 pathways:
• CTLA-4 is expressed on activated and regulatory T cells, binds to CD80/86 (costimulatory molecules on APC)
• PD-1 is expressed on activated T cells, binds to PD-L1/L2 (complex expression patterns, may be upregulated on tumours)
• e.g. Ipilimumab (anti CTLA-4), Nivolumab (anti PD-1), antagonistic antibodies
Monoclonal antibodies used to block these interactions
(No need for details or names, removing negative regulation —> autoimmune)
Adoptive transfer of cells (ACT)
T ell source from human, can be genetically engineered and is then made into culture (stimulated by cytokines), expansion occurs and re-infusion into patient
-Tumour may be removed by surgery.
-Extract the TILs and then multiple the number of TILs and reinfuse the TILs into the patient.
o They can be expanding with use of cytokines as well.
o Genetic engineering techniques can also be used to express chimeric antigen receptors (CARs) (see below).
CARS: part of antibody which binds to antigen is linked together with linker, fused to transmembrane part of T cell receptor —> binds to antigen recognises which activates T cells —> insert into patient so T cell activated whenever in contact
Explain which organs are transplanted and why they’re transplanted.
Organs are transplanted when they are
failing or have failed, or for reconstruction
• Life-saving– other life-supportive methods have reached end of their use:
- liver
- heart (LVAD – left ventricular assist device)
- small bowel (TPN - total parenteral nutrition)
• Life-enhancing – other life-supportive methods less good
-Kidney – dialysis
-Pancreas – in selected cases, tx better than insulin injections
– organ not vital but improved quality of life: cornea, reconstructive surgery
Why do organs fail?
• Cornea – degenerative disease, infections, trauma
• Skin/composite – burns, trauma, infections, tumours
• Bone marrow – tumours, hereditary diseases • Kidney – diabetes, hypertension, glomerulonephritis, hereditary conditions
• Liver – cirrhosis (viral hepatitis, alcohol, auto-immune, hereditary conditions), acute liver failure (paracetamol)
• Heart – coronary artery or valve disease,
cardiomyopathy (viral, alcohol), congenital defects
• Lungs – chronic obstructive pulmonary disease (COPD)/emphysema (smoking, environmental), interstitial fibrosis/interstitial lung disease (idiopathic, autoimmune,
environmental), cystic fibrosis (hereditary), pulmonary hypertension
• Pancreas – type I diabetes
• Small bowel – mainly children (“short gut”); volvulus, gastroschisis, necrotising enteritis related to prematurity (in adults - Crohn’s, vascular disease, cancer)
Explain the types of transplantation.
Autografts: within the same individual e.g. stem cells
Isografts: between genetically identical individuals of the same species
Allografts: between different individuals of the same species
• Solid organs (kidney, liver, heart, lung, pancreas)
• Small bowel
• Free cells (bone marrow, pancreas islets)
• Temporary: blood, skin (burns)
• Privileged sites: cornea
• Framework: bone, cartilage, tendons, nerves • Composite: hands, face, larynx
Types of donor: deceased donor, living donor (bone marrow, kidney, liver ; genetically related or unrelated (spouse, altruistic)
Xenografts: between individuals of different species e.g. heart valves (pig/cow), skin
Prosthetic graft: plastic, metal
Explain deceased donors.
• DBD – donor after brain stem death
– majority of organ donors
– brain injury has caused death before terminal apnoea has resulted in cardiac arrest and circulatory standstill
– E.g. Intracranial haemorrhage; road traffic accident
– Circulation established through resuscitation
– Confirm death using neurological criteria
– Harvest organs and cool to minimise ischaemic damage
• DCD – donor after circulatory death
– death is diagnosed and confirmed using cardio-respiratory criteria; 5 minutes observation of irreversible cardiorespiratory
arrest
– Controlled: generally patients with catastrophic brain injuries who
while not fulfilling the neurological criteria for death have injuries of such severity as to justify withdrawal of life-sustaining
cardiorespiratory treatments on the grounds of best interests
– [Uncontrolled: no or unsuccessful resuscitation]
– Longer period of warm ischaemia time
Neurological criteria of death
• irremediable structural brain damage of KNOWN cause
• apnoeic coma NOT due to
– cardiovascular instability
– depressant drugs
– metabolic or endocrine disturbance
– hypothermia
– neuromuscular blockers
• demonstrate absence of brain stem reflexes
– Pupillary reflex absent (light)
– Corneal reflex absent (touch)
– Ocular vestibular reflex (no eye movements with cold caloric test)
– Motor response cranial nerves (to orbital pressure)
– Cough and gag reflex
– Lastly - Apnoea test: no respiratory movements on disconnection from
ventilator (with PaCO2 >50 mmHg)
• Exclude: – viral infection (HIV, HBV, HCV) – malignancy – drug abuse, overdose or poison – disease of the transplanted organ • Removed organs rapidly cooled and perfused – absolute maximum cold ischaemia time for kidney 60h (ideally <24h) – much shorter for other organs
Explain transplant allocation guidelines.
What strategies can increased transplantation activity?
• Transplant selection: listing (waiting list) at a transplant centre after multidisciplinary assessment
• Transplant allocation: how organs are allocated as they become available
• NHSBT (NHS Blood and Transplant)
– Provision of a reliable, efficient supply of blood, organs and associated services to the NHS
– Establishes rules for organ allocation and monitors allocation
• Equity – what is fair?
– Time on waiting list
– Super-urgent transplant - imminent death (liver, heart)
– What else?
• Efficiency – what is the best use for the organ in terms of patients survival and graft survival?
Organ allocation: kidney • 5 tiers of patients depending on – paediatric or adult – Highly sensitised or not - if rarer HLA, easily reject so they’re placed on top of list if match found • 7 elements – Waiting time – HLA match and age combined – Donor-recipient age difference – Location of patient relative to donor – HLA-DR homozygosity – HLA-B homozygosity – Blood group match
Strategies
1. deceased donation
– Marginal donors – DCD, elderly, co-morbidities - can be used if age matched patients
2. living donation
– transplantation across tissue compatibility barriers
– Exchange programmes: organ swaps for better tissue matching
3. The future?
– Xenotransplantation
– Stem cell research
Explain ABO blood group in the immunology of transplantation.
Explain HLA in the immunology of transplantation.
• A and B proteins with carbohydrate chains on red blood cells but also endothelial lining of
blood vessels in transplanted organ
• Naturally occurring anti-AB antibodies
If patient is blood group A, Circulating, pre-formed, recipient anti-B antibody binds to B blood group antigens on donor endothelium = antibody-mediated rejection, micro circulation will be full of thrombi and inflammatory molecules
ABO-incompatible transplantation
• Remove the antibodies in the recipient ( plasma exchange) • Good outcomes (even if the antibody comes back) • Kidney, heart, liver
HLA (human leukocyte antigens)
- Discovered after first failed attempts at human transplantation
- Cell surface proteins
- Highly variable portion
- Variability of HLA molecules important in defense against infections and neoplasia
- Foreign proteins are presented to immune cells in the context of HLA molecules recognised by the immune cells as “self” = on antigen presenting cells
• Class I (A,B,C)– expressed on all cells
• Class II (DR, DQ, DP) – expressed antigen-
presenting cells but also can be upregulated on other cells
• Highly polymorphic – lots of alleles for each
locus (for example: A1, A2, …, A341… etc.)
• Each individual has most often 2 types for each HLA molecule (for example: A3 and A21)
Have peptide binding groove
Highly polymorphic HLAs have stronger immune response
Higher chance of match if family used
- Exposure to foreign HLA molecules results in an immune reaction to the foreign epitopes
- The immune reaction can cause immune graft damage and failure = rejection
Explain transplant rejection.
- Most common cause of graft failure
- Diagnosis = histological examination of a graft biopsy
- Treatment = immunosuppressive drugs
- hyperacute reaction = immediate rejection
- acute rejection = weeks after transplantation
- chronic rejection = several years, slow deterioration of function
- T cell mediated rejection
- antibody-mediated rejection
T-cell mediated rejection
1) lymphocytic interstitial infiltration
2) ruptured tubular basement membrane
3) tubulitis
1) graft infiltration by alloreactive CD4+ cells
2) cytotoxic T cells - release of toxins to kill target e.g. granzyme B, punch holes in target cells e.g. perforin, apoptotic cell death e.g. FasL
3) macrophages
- phagocytosis
- release of proteolysis enzymes
- production of cytokines
- production of oxygen radicals and nitrogen radicals
Antibody-mediated rejection
- antibody against graft HLA and AB antigen
- antibodies arise: pre-transplantation (sensitised - naturally have antibodies e.g. pregnancy, blood transfusion, previous transplant), post-transplantation (de novo)
Antibody activates complement and macrophages
Intravascular inflammation in interstitium and tubules e.g. glomerularitis
Describe post transplant monitoring for rejection.
• Deteriorating graft function
– Kidney transplant: Rise in creatinine, fluid retention,hypertension
– Liver transplant: Rise in LFTs, coagulopathy – Lung transplant: breathlessness, pulmonary infiltrate
• Subclinical
– Kidney
– Heart (no good test for dysfunction, regular biopsies)
• Prevention of rejection – maximise HLA compatibility – Life-long immunosuppressive drugs • Treatment of rejection – more drugs…
Immunosuppressive drugs
• Targeting T cell activation and proliferation e.g. azathioprine targets cell cycle, anti-CD52 mAb depletes T cells - apoptosis, cyclosporine - targets calcineurin which involves in downstream T cell activation
• Targeting B cell activation and proliferation
, and antibody production e.g. anti-CD20 depletes B cells, Bortezomib (proteosome inhibitor) - depletes plasma cells; drugs can also target complement activation
Standard immunosuppressive regime
• Pre-transplantation - Induction agent (T-cell depletion or cytokine blockade)
• From time of implantation - Base-line immunosuppression
– Signal transduction blockade, usually a CNI inhibitor: Tacrolimus or Cyclosporin; sometimes mTOR inhibitor (Rapamycin)
– Antiproliferative agent: MMF or Azathioprine – Corticosteroids
• If needed - Treatment of episodes of acute rejection
– T-cell mediated: steroids, anti-T cell agents
– Antibody-mediated: IVIG, plasma exchange, anti-CD20, anti-
complement
Describe problems associated with post-translation immunosuppression.
Post transplantation infections
• Increased risk for conventional infections
– Bacterial, viral, fungal
• Opportunistic infections – normally relatively harmless infectious agents give severe infections because of immune compromise
– Cytomegalovirus
– BK virus
– Pneumocytis carinii (jirovecii)
Post transplantation malignancy • Skin cancer • Post transplant lymphoproliferative disorder – Epstein Barr virus driven • others
Infection
tumours
Drug toxicity are consequences of immunosuppression
Explain appropriate immune reactions and appropriate immune tolerance.
Appropriate immune responses occur to foreign harmful agents such as viruses, bacteria, fungi, parasites
- Required to eliminate pathogens
- May be concomitant tissue damage as a side effect, but as long as pathogen is eliminated quickly will be minimal and repaired easily
Involves antigen recognition by cells of the
immune system and antibody production
Appropriate immune tolerance occurs to
self, and to foreign harmless proteins:
-Food, pollens, other plant proteins, animal proteins, commensal bacteria
Involves antigen recognition and generation
of regulatory T cells and regulatory
(blocking) antibody (IgG4) production
-Antigen recognition in context of “danger” signals leads to immune reactivity, absence of “danger” to tolerance
Described hypersensitivity reactions and its classification.
Hypersensitivity reactions occur when immune responses are mounted against:
- harmless foreign antigens (allergy, contact hypersensitivity)
- autoantignes (autoimmune diseases)
- alloantigens (serum sickness, transfusion reactions, graft rejection)
Classified by Gell and Coombs:
- Type I: immediate hypersensitivity
- Type II: antibody-dependent cytotoxicity
- Type III: immune complex mediated
- Type IV: delayed cell mediated
Many diseases involve a mixture of types
