Immunotherapy: T-cell therapy in Cancer

• Need for novel approaches in cancer

  • 375,000 new cancer cases every year in the UK, which is around 1,000 per day
  • Every two minutes someone in the UK is diagnosed with cancer.
  • Projections suggest that this might rise to ~506,000 new cases of cancer per year in the UK by 2038-2040.
  • One of the three leading causes of death (others: infectious disease and cardiovascular disease)
  • ~167,000 cancer deaths in the UK every year
  • Development of new approaches to treatment is urgently required
• Immunotherapy: a breakthrough in cancer therapy

  • Successful treatment requires removal/destruction of all malignant cells without killing the patient
  • One strategy for achieving this is immunotherapy
  • Aim to harness the ability of the immune system to recognize and eliminate cancer cells
  • Combination with surgery or chemotherapy to reduce tumour load
  • Multiple Immunotherapies are already licensed in the clinics

  1. IL-2 Therapy
  2. Checkpoint Blockade
  3. CAR-T cell therapy

  • Many more are in development and clinical trials
• T-cells can mediate tumour rejection


  • The figure illustrates key experiments which demonstrated immunity to tumours in inbred mouse strains (i.e. host and tumour is matched for their MHC type).
  • The majority of transplantable tumours grow progressively and kill the mice.
  • Mice immunized with irradiated tumour and challenged with viable cells of the same tumour can reject that tumour.
  • These protective effects are not seen in T-cell deficient mice.
  • Therefore, tumours express tumour rejection antigens that become targets for the T-cell response mediating tumour rejection.

  
• Tumours may be controlled by the immune response but can subsequently acquire the ability to ‘escape’


  Three phases of tumour growth:

  1. elimination phase (immune surveillance): recognition and destruction of tumour cells
  2. equilibrium phase: tumours undergo changes or mutations that enhance survival (cancer immunoediting shapes the properties of the surviving tumour cells)
  3. escape phase: tumour escapes from the immune response and grows out of control

  
• Challenges that must be overcome: strategies that tumours use to avoid immune recognition

  
• T-cell recognition and destruction of cancer cells

  • CD8 cells can recognize and kill cancer cells directly
  • CD4 T cells have a role in the activation of CD8 cytotoxic T cells and the establishment of memory.
  • CD4 T cells may also kill tumour cells via cytokines e.g. TNF-a.
  • Tumour rejection is usually mediating by CD8 T-cells
  • T-cell immunotherapy approaches are often focused on the use of CD8 T-cells but can involve use of CD8 and CD4 T-cells
  • Approaches are also in development that utilise gd T-cells, MAIT cells and Natural Killer (NK) cells
• How do CD8 T-cells recognize their targets?


  • Tumour transformed cells represent a challenge to the immune system as abnormal proteins are buried within the cell
  • To overcome this: abnormal proteins are processed and presented at the cell surface in association with MHCI molecules.
  • CD8 T-cells recognise small peptide fragments (8-13 amino acids long) presented in the context of MHCI molecules at the target cell surface.

  
• Two receptors for peptide-MHCI

  • Recognition of pMHCI involves two receptors: TCR and CD8
  • TCR and CD8 bind to different sites on the MHCI molecule
  • A single MHCI can be bound simultaneously by TCR and CD8
  • T-cells recognize small peptide fragments complexed with MHC molecules presented at the target cell surface

  TCR: pMHCI recognition

  CD8: enhances sensitivity

  One ligand: Two receptors

  2 key interactions involved

  
• Tumour antigens recognized by T-cells form the basis of T-cell cancer immunotherapies


  • Identifying candidate tumour antigens is challenging
  • Tumour antigens are often present on normal tissue i.e. self-antigens
  • Therefore, targeting them can cause damage to normal tissue e.g. vitiligo has been observed when T-cell therapy is used to target melanoma
  • In addition, the TCRs specific to tumour epitopes can be very low affinity (as high affinity TCRs that recognize self-peptides are eliminated during thymic selection)

  
• Goal of Immunotherapy for cancer

  To harness and enhance the ability of the immune system to recognize and destroy cancer cells:

  • Cancer vaccination (Prof. Wuelfing’s Lecture)
  • Adoptive transfer therapy
  • Genetic engineering of T-cells (TCRs, high affinity CD8 and CARs)
  • Use of soluble TCRs as a treatment for cancer

  
• Adoptive T-cell therapy


  A treatment used to help the immune system fight diseases, such as cancer and infections with certain viruses. T cells are collected from a patient and grown in the laboratory. This increases the number of T cells that are able to kill cancer cells or fight infections. These T cells are given back to the patient to help the immune system fight disease
• Adoptive TIL therapy

  TIL = Tumour Infiltrating Lymphocytes

  
• Adoptive TIL therapy


  • Figure shows clinical regression in patients with metastatic melanoma with T-cell transfer therapy
  • Lymphodepletion prior to administration, administration with high dose IL-2 and/or enriching for neoantigen specific TILs - improved response to TIL therapy.
  • Objective and complete response rates of up to 40% and 15% in melanoma
  • Response rates depend on approach used – scope for improvement
  • Promise in other settings too e.g. cervical, lung, breast and colorectal
  • Currently not licensed for use in clinics, multiple clinical trials are ongoing

  
• Genetic Engineering of T-cells to enhance their activity

  1. Isolate T-cells from blood & culture in vitro with cytokines e.g. IL-2, Il-7, IL-15, IL-21.
  2. T-cells are genetically modified using vectors that encode receptors (TCR, CD8, CAR), or molecules that enhance response to cancer cells.
  3. Most common vectors = g-retroviruses and lentiviruses engineered to be replication incompetent by the removal of genes that encode vital proteins.
  4. Genes of interest are incorporated in the genome of T-cells.
  5. 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 that they express TCR genes from tumour specific T-cells.
• Genetic Engineering of T-cells to express cancer specific TCRs

  +ve

  1. Large number of cancer-specific CD8 T-cells generated in short span of time
  2. increase affinity of the TCR enhances activity of the cancer specific T-cells

  -ve

  1. Must identify a suitable MHCI restricted tumour rejection antigen
  2. Must isolate a tumour specific TCR
  3. Increasing the affinity of TCR may result in some loss of specificity and/or creation of new specificities
  4. Mis-pairing with the endogenous TCRs: loss of activity or dangerous new specificities.
  5. Restricted by specific MHCI: can only use in subset of patients.
• Genetic Engineering of T-cells to express cancer specific CARs

  CAR = Chimeric Antigen ReceptorvOperate in a non-MHCI restricted manner

  Extracellular domain is a single chain antibody

  Several different generations which vary in their cytoplasmic domains:

  1st: contains intracellular CD3z

  2nd: intracellular CD3z and a co-stimulatory domain e.g. CD28 or 4-1BB

  3rd: intracellular CD3z  and two co-stimulatory domains

  4th: include ‘armoured’ CAR T-cells, cytokine expressing CAR T-cells etc.

  
• Genetic Engineering of T-cells to express cancer specific CARs

  
• CAR-T cell therapy: clinical outcomes and FDA approval

  
• CAR-T cell therapy: adverse events and challenges


  Side Effects:

  • Cytokine Release Syndrome (CRS):
  • Mediated by IL-1 and IL-6.
  • Symptoms: Fever, hypertension, systemic issues.
  • Treatment: Tocilizumab (anti-IL-6 antibody).
  • On-target, off-tumor toxicity:
  • Autoimmune response against normal cells sharing tumor antigens.
  • Leads to normal B cell depletion.
  • Immune Effector Cell-associated Neurotoxicity Syndrome (ICANS)
  • Post CAR T-cell therapy infections

  Challenges:

  • High manufacturing cost
  • Ineffectiveness against solid tumors
  • Need for an off switch
• Genetic Engineering of T-cells continued........

  
• Using soluble versions of TCRs


  •ImmTacs are a soluble therapy which combines a high affinity TCR fused with a stimulatory anti-CD8 antibody fragment

  This results in the redirection of T-cells to kill tumour cells

  •Side Effects: cytokine mediated events (T-cell activation), skin-related events (GP-100+ melanocytes, rash, pyrexia and pruritis

  
• Checkpoint Inhibitors: a breakthrough in human cancer treatment


  T-cell Inhibition in Tumor Microenvironment:

  • T-cells express co-inhibitory receptors: PD-1, CTLA4, TIM3, Lag3, TIGIT.

  Checkpoint Inhibitors:

  • Monoclonal antibodies blocking PD-1 and CTLA-4 treat metastatic melanoma.
  • Notable clinical responses, but ~60% non-responders highlight need for further research.
  • Also used in treating lung cancers and other types.

  Combination Therapies:

  • Interest in combining checkpoint inhibitors with T-cell therapy (e.g., TIL therapy).
  • These receptors prevent T-cell activation and cancer cell destruction.