Tutorial 4: Synthetic immune niches & immunoengineering Flashcards
Explain what antigenicity and immunogenicity is and highlight the difference between these 2 terms.
Antigenicity= the ability to bind a antibody to an antigen (ability to present antigen). Immunogenicity= the ability to elicit an immune reaction. An immunogenicity material is always antigenicity, but an antigenicity is not always immunogenicity. Presenting antigen by itself is not sufficient to mount an immunological response.
Dendritic cells are important regulators of activation or tolerance of the immune system. List the 3 signals by which dendritic cells activate T cells after encountering an antigen. Name the specific molecules involved for each signal.
Binding to a antigen that is specific for that type of T cell. Antigen presentation on the MHC-class II receptor to the T cell receptor.
Co-stimulatory via either CD40-CD40L (DC-CD4+ Th cell) or CD80/CD86-CD28 (DC-CD8+ cytotoxic T cell).
Cytokines. They cytokines determine to what type of T helper cell it will be activated. Either paracrine or via trans-presentation on the cell-membrane.
Activation of T cells by antigen-presenting cells such as dendritic cells takes place in the immunological synapse that is formed between the cells. Artificial antigen-presenting cells mimic the action of dendritic cells in order to therapeutically activate or suppress the immune system. An example of an artificial antigen-presenting cell is a synthetic nanoworm. Briefly explain (2-3 sentences) why the worm-like shape of a nanoworm makes them particularly effective in creating a strong immunological synapse with a T cell.
The immunological synapse is a physical connection between the cells. In order to have a strong synapse, the receptors and ligands on the cells rearrange themselves into a favorable configuration after initial binding. The flexible shape of a nanoworm allows such a rearrangement of the receptors.
List 4 different ways by which dendritic cells can induce peripheral tolerance.
- Ignorance: antigen is not presented by DC.
- Anergy: antigen is presented but DC receptors bind to inhibitory receptors on the T-cells, such as
CTLA-4 or PD-1 (the ‘are you sure?‘ buttons). - Phenotype skewing: by secreting anti-inflammatory cytokines DCs can induce an inhibitory
phenotype in the T cells, despite the presence of antigen and co-stimulation. - Apoptosis: DC activates Fas receptor on T cell (the self-destruct button).
One way to induce tolerance is by targeting trained immunity in innate immune cells, such as macrophages. Trained immunity is in a way the memory of the innate immune system. Briefly explain (3-4 sentences) the molecular mechanism of trained immunity and the fundamental functional difference between trained immunity of the innate immune system and the memory of the adaptive immune system.
Trained immunity functions via epigenetic modifications, meaning the conformation of DNA wrapping
around histones is changed but not the DNA sequence. After encountering a pathogen, the histones
move apart to enable gene activation. Once the threat is resolved, the DNA does not entirely go back
to its original confirmation, which means that the cell will respond differently (fast and more intense of
slower and less intense) the second time it encounters a pathogen. The main functional difference with adaptive immune memory is that trained immunity is not specific to a certain pathogen/antigen, unlike
the adaptive immune memory.
List 4 different forms of immunotherapy and briefly (2-3 sentences) explain their modes of action.
- Cytokine therapy like IFN-alpha or IL2. IL-2 boosts the survival, proliferation and activation of T
cells. - Blocking inhibitory signaling pathways in T cells. Immune checkpoint therapy. Monoclonal
antibodies blocking co-inhibitory receptors (checkpoints) on T cells. In this way the tumor can no
longer steer the T cells in apoptosis making them susceptible to T cell mediated killing. - Adoptive cell transfer. Increasing the number of effector T cells by adoptively transfer T cells in the
patient. Here t cells can be isolated from blood or tumor of the patient, expanded and selected for
specificity ex vivo and subsequently be administered to the patient. - Vaccination with tumor antigen. For example dendritic cell vaccination. In this therapy DC are
activated and loaded with tumor antigen after which they will be administered to the patient. In
the patient the DCs will travel to the lymph node to train and activate tumor specific T cells.
Although very successful in a small (<20%) percentage of treated patients, current cancer
immunotherapeutic strategies also have some drawbacks. What is the major drawback?
Most therapeutic interventions rely on systemic administration. This results in:
- Widespread aspecific immune activation due to systemic exposure
- Low local concentration of immune stimulants
- Cell survival and persistence is reduced
- Cellular localization at tumour site is hampered
- Sometimes severe adverse effects and toxicity related to the treatment
List 2 advantages of scaffold-based immunological
cancer therapies over systemic treatments.
Scaffolds offer a local protective environment for the cells and can be locally injected. The advantage
of this is that they are much more efficient, so:
1. High local concentration of activated immune cells with sustained activity
2. By having the scaffold close to the tumor, it is possible to not only promote the activation of T cells but also to modify the immune-inhibiting microenvironment that is created by the tumor
(for example by locally releasing pro-inflammatory cytokines).
As an alternative to scaffold-based vaccines, there are synthetic immune niches that are specifically targeted at myeloid-suppressor cells in the tumor. Briefly explain how these types of synthetic immune niches work and name at least 2 important aspects for their application.
A tumor contains many endogenous innate immune cells, such as tumor-associated macrophages, that are programmed by the tumor to be immunosuppressive. So, instead of activating specific T cells, such synthetic immune niches are designed to switch the phenotype of these innate immune cells in the tumor. Typically this means that the immune niche is loaded with some form of pro-inflammatory signals to reprogram the immune cells in the tumor to an activated phenotype.
2 important aspects:
- A scaffold needs to act locally, so it needs to be injectable or locally implantable (e.g. via self-assembly).
- And because it targets non-specific immune cells, it is very important that the scaffold targets the cells in the tumor only, and does not activate innate immune cells in the rest of the body.
