L17 - immunotherapy T-cell therapy and cancer

• why do we need novel approaches to cancer?

  every 2 minutes someone in UK diagnosed with cancer

  375000 new cancer cases every year in UK - rise to 506000 by 2038

  one of leading causes of death

  development new approaches to treatment urgently required
• what does immunotherapy aim to do?

  remove or destroy all the malignant cells without killing the patient with no or minimum collateral damage
• immunotherapies aim to harness the ability of the immune system to recognise and eliminate cancer cells
• can use immunotherapy in combination with?

  surgery or chemotherapy to reduce tumour load
• multiple immunotherapies already licensed in clinics:

  IL-2 therapy

  checkpoint blockade

  CAR-T cell therapy

  many more in development and clinical trials
• t-cells can mediate tumour rejection using mouse models


  demonstrated immune system does have ability to recognise and kill cancer cells.

  • using inbred mouse strains - host and tumour matched for their MHC type
  • majority transplantable tumours grow progressively and kill the mice
  • mice immunized with irradiated tumour and challenged with viable cells of same tumour - can reject the tumour
  • these protective effects not seen in T-cell deficient mice
  • therefore tumours express tumour rejection antigens that become targets for T-cell response mediating tumour rejection
• tumours can be controlled by immune response but can subsequently acquire the ability to escape

  3 phases of tumour growth

  1. elimination phase
  2. equilibrium phase
  3. escape phase
• elimination phase (immune surveillance)

  recognition and destruction of tumour cells

  immune response that can recognise and keep from getting out of control - CD8 + CD4 T-cells as well as others like NK
• equilibrium phase

  tumours undergo changes or mutations that enhance survival

  variant tumour cells arise that are more resistant to being killed, over time variety of different tumour variants develop

  (cancer immunoediting shapes the properties of the surviving tumour cells)
• escape phase

  tumour escapes from the immune response and grows/proliferates out of control
• the immune response has to overcome lots of challenges to effectively control cancer - important when developing new strategies
• challenges that must be overcome - strategies that tumours use to avoid immune recognition

  mechanisms by which tumours avoid immune recognition

  • low immunogenicity
  • tumour treated as self antigen
  • antigenic modulation
  • tumour-induced immune suppression
  • tumour-induced privileged site
• solid tumours can create immunosuppressive environments by various different mechanisms
• low immunogenicity

  downregulate MHC1 molecules - not presenting tumour antigens well

  • no peptide:MHC ligand
  • no adhesion molecules
  • no co-stimulatory molecules
• tumour treated as self antigen

  tumour treated like self tissue, tumour antigens taken up and resented by APCs and presented without co-stimulation - tolerisation of T-cells
• antigenic modulation

  antibody against tumour cell-surface antigens can induce endocytosis and degradation of the antigen

  immune selection of antigen-loss variants
• tumour-induced immune suppression

  factors secreted by tumour cells inhibit T-cells directly.

  induction of regulatory T-cells by tumours

  Tregs dampen immune responses within tumours

  checkpoint inhibitor pathways - express PDL1 - engage with PD1 on various immune cells, secretion various factors eg IL10 immunosuppressive cytokine
• tumour-induced privileged site

  factors eg collagen secreted by tumour cells create physical barrier to immune symptoms
• T-cell recognition and destruction of cancer cells

  CD8 can recognise and kill cancer cells directly

  CD4 role in activation of CD8 cytotoxic T cells and establishment of memory

  CD4 may also kill tumour cells via cytokines eg TNF-a

  tumour rejection - mediating by CD8

  T-cell immunotherapy approaches focused on use of CD8 but can involve use CD8 and CD4

  approaches also in development that utilise delta-gamma T-cells, MAIT and NK
• how do CD8 T-cells recognise their targets?

  tumour transformed cells represent challenge to immune system as abnormal proteins buried within cell

  overcome this: abnormal proteins processed and presented at cell surface in association with MHC1 molecules

  CD8 recognise small peptide fragments (8-13 amino acids long) presented in context MHC1 molecules at target cell surface

  • due to MHC1 processing pathway - proteosome chewing up proteins into little peptides that go into ER and loaded onto MHC1 then move to cell surface and presented at cell surface
• recognition pMHC1 involves 2 receptors - TCR and CD8


  TCR and CD8 bond to different sites on MHC1 molecule

  single MHC1 can be bound simultaneously by TCR and CD8
• TCR = T-cell receptor


  pMHC1 recognition

  determines the antigen specificity of the cell - binds partly to the peptide and MHC
• CD8 - co-receptor

  binds to different part MHC

  plays role in enhancing antigen sensitivity
• lots of scope for engineering 2 different receptors and getting different effects and outcomes in immune therapy
• T-cells recognise small peptide fragments complexed with MHC molecules presented at target cell surface
• Tumour antigens recognized by T-cells form the basis of T-cell cancer immunotherapies

  identifying candidate tumour antigens = challenging

  tumour antigens often present on normal tissue eg self-antigens -individuals can have neoantigens associated with their tumours - need a more personalised approach to identify antigens

  therefore targeting them can cause damage to normal tissue eg vitiligo - T-cell therapy used for melanoma

  TCRs specific to tumour epitopes can be very low affinity - as high affinity TCRs that recognise self-peptides are eliminated during thymic selection
• naturally occurring TCR to tumour antigen can be low affinity = poor T-cell response
• goal of immunotherapy for cancer

  to harness and enhance the ability of the immune system to recognise and destroy cancer cells

  • cancer vaccination
  • adoptive transfer therapy
  • genetic engineering of T-cells
  • use of soluble TCRs as treatment for cancer
• adoptive T-cell therapy

  treatment used to help immune system fight diseases eg cancer and infections with certain viruses.

  T-cells collected from patient and grown in lab

  this increases number of T-cells that can kill cancer cells or fight infections

  these T-cells given back to patient to help the immune system fight disease
• TIL

  tumour infiltrating lymphocytes
• adoptive TIL therapy method

  method

  1. surgical resection of solid tumour - lots of T-cells - TILs
  2. fragmentation of tumour
  3. initial expansion
  4. rapid expansion protocol (REP)
  5. ex vivo analyses and quality control
  6. infusion product - infused back into patient
  7. treatment

  patients also get various treatment prior or in combo with TIL therapy eg high docile T-cells, or lymphocyte depletion before infusion so T-cells easier to divide and establish in patient
• adoptive TIL therapy cont.

  TIL works in some patients but not all - can improve response through various things

  eg. lymphodepletion prior to administration - high docile IL-2 and/or enriching for neoantigen specific TILs

  in melanoma - objective rate = 40%, complete rate = 15%, promise in other settings like cervical, lung and breast

  currently not licensed for use in clinics, multiple clinical trials ongoing
• genetic engineering T-cells to enhance their activity

  generally the approach used

  • isolate T-cells from blood and culture in vitro with cytokines eg IL-2, IL-7, IL-15 to stimulate them
  • T-cells genetically modified using vectors that encode receptors (TCR, CD8, CAR) or molecules that enhance response to cancer cells
  • most common vectors = gamma-retroviruses and lentiviruses engineered to be replication incompetent by removal of genes that encode vital proteins
  • genes of interest incorporated in genome of T-cells
  • safety concerns: generation of replication-competent viruses
• genetic engineering of T-cells to express cancer specific TCRs

  tumour-reactive T-cells can be generated by genetically engineering blood derived T-cells so they express TCR genes from tumour specific T-cells
• advantages genetic engineeringTCRs

  Can generate large numbers of cancer-specific CD8 T-cells in a very short space of time e.g. against MAGE and NY-ESO-1 - naturally occurring TCR to cancer antigens can be low affinity = poor T-cell activation

  Strategies to increase the affinity of the TCR can enhance the activity of the cancer specific T-cells e.g. amino acid substitutions in the TCR CDR regions.
• disadvantages genetic engineeringTCRs

  Must identify suitable MHC1 restricted tumour rejection antigen

  Must isolate tumour specific TCR - can be challenging

  Increase affinity of TCR - some loss of specificity and/or creation new specificities e.g. MAGE-A3 specific TCR - could recognize epitope from Titin (muscle protein) -> cardiac toxicity and death - damage to normal tissues

  Mis-pairing with endogenous TCRs: loss of activity or dangerous new specificities.

  Restricted by specific MHCI so can only be used in subset of patients (e.g. HLA A*0201). One way to circumvent this - use

  CARs instead
• genetic engineering of T-cells to express cancer specific CARs

  CAR = chimeric antigen receptor

  • operate in non-MHC1 restricted manner - anybody can use
  • extracellular domain is a single chain antibody
  • several different generations which vary in their cytoplasmic domains

  Take t-cells from blood and engineer using retroviral or lentiviral vectors to express these CARs and then infuse them back into the patient - recognise and kill cancer cell hopefully
• generations chimeric antigen receptor

  1st - contains single intracellular CD3 zeta chain

  2nd - intracellular CD3 zeta and co-stimulatory domain eg CD28

  3rd - intracellular CD3 zeta and 2 co-stimulatory domains

  4th - armoured CAR T-cells, cytokine expressing CAR T-cells etc
• CAR T-cell therapy method

  patient's T-cells separated from rest of blood and sent to lab

  viral vector delivers CAR - encoding gene into T-cells

  T-cells now express CAR on their surfaces and known as CAR T-cells

  CAR T-cells multiplied and put back into patient's bloodstream

  CAR T-cells identify cancer cells with target antigens and kill them
• CAR T-cell therapy - clinical outcomes and FDA approval


  6 FDA approved for B cell malignancies and multiple myeloma

  Kymriah received FDA approval on Aug 30th, 2017, for the treatment of paediatric and young adult Acute Lymphoblastic Leukaemia (ALL)

  adverse events and challenges:

  • cytokine release syndrome - mediated by cytokines released by T-cell - treated with anti-IL6 receptor antibody Tocilizumab