Scientific Background
This section contains a compilation of selected publications that provide a basic scientific understanding of immunology and oncology as it relates to the mTEV technology.
CD28 costimulation at the immune synapse is an essential step for allowing the activation, proliferation and differentiation of T-cells into effector T cells. A deficiency of CD28 and/or CD80/86 (B7-1/2) proteins results is a weak or compromised costimulation, which drives tolerance, clonal anergy and apoptosis. Only when both antigen presentation (signal 1) and costimulation (signal 2) occurs can the T-cell become activated.
How important is combining priming and costimulation? Represented in the graph below, one can see the synergistic effects of having both antigen presentation (signal 1, CD3 = TCR) and costimulation (signal 2 = CD28) combined. Note that the activation of either TCR or CD28 alone is not enough to activate a T-cell.
What are Micro RNAs? Micro RNAs (miRNA's) are short non-coding RNAs generated within cancer cells and packaged into membranous nano-particle sized extracellular vesicle (TEV) that are released into the tumor microenvironment (TME). TEVs are then taken up (phagocytised) by dendritic cells (a key antigen presenting cell) where antigens are processed (cut) and presented onto their surface.
Once TEVs enters an antigen presenting cell, it releases its content. The miRNA binds specifically to the complementary messenger RNA sequence of key costimulatory proteins (CD28 and CD80), which then results in the inhibition of their protein production (i.e. expression). The cells lacking these essential proteins lose the costimulatory T-cell function.
What are Neoantigens?
Neoantigens are an important feature of cancer cells and help to stimulate anti-cancer immune responses.
Neoantigen definition
To understand neoantigens, we first need to define what an antigen is. Antigens are substances that induce the immune system to produce antibodies against that material (literally an antibody generator).1 Antigens are commonly abbreviated as Ag. Examples of neoantigens include proteins or sugar molecules (polysaccharides) located on the outside of cells.
Neoantigens are produced by tumor or cancer cells. Cancer cells accumulate many DNA mutations that can alter the structure of proteins, and the resulting neoantigens earn their name from the Greek neo, meaning “new”. Therefore, neoantigens are a class of tumor-specific antigens – they are absent from normal tissue. The resulting neoantigens are displayed by human leukocyte antigens (HLA) on the surface of cancer cells, helping to stimulate immune responses when immune cells – such as T cells – recognize the neoantigens as “non-self”, in a similar way to bacteria and viruses.
How do neoantigens arise?
The development of neoantigens is caused by non-synonymous mutations in tumor cells, i.e., a mutation that changes the amino acid sequence of a protein. Mutational events include point mutations (also known as single nucleotide polymorphisms; SNPs) and insertions or deletions (indels). Neoantigens can also be produced as a result of viral infection, alternative splicing or gene rearrangements.
Types of neoantigens
There are two main types of neoantigens – shared and personalized.
Shared neoantigens are:
- Caused by mutations that are commonly found in many different cancer patients.
- Derived from driver/hotspot mutations.
- More common in some cancer types than others.
- Not present in the normal human genome.
- Highly immunogenic.
- Promising for use as targets for “off-the-shelf” anti-cancer vaccines.
Personalized neoantigens are:
- Unique to the individual.
- Different from patient to patient.
- Arise from somatic mutations in tumor cells.
- Potential targets for personalized therapies.
EV Therapeutics can provide solutions for both shared (as an off-the-shelf vaccine) or personalized cancer vaccine.
Identifying neoantigens
Efficient and fast identification of neoantigens has been enabled by the advancement of next-generation sequencing technologies. These technologies have improved the identification of tumor-specific mutations in individual patients that give rise to neoantigens. This is achieved using techniques such as whole-exome or whole-genome sequencing, in which DNA or RNA is compared from paired tumor and non-tumor samples. Neoantigens are predicted using bioinformatics and computational algorithms.
The identification of neoantigens usually follows this sequence of events:
- List genomic mutations/alterations identified from next-generation sequencing of paired normal and tumor cells.
- Convert these into “neopeptides” of the appropriate length.
- Predict the binding affinity between neopeptides and HLA alleles specific to the patient using computational tools.
- Assess immunogenicity (the ability to generate an immune response) and validate T-cell responses against cancer cells.
Neoantigen-targeting therapies
Cancer therapies that target neoantigens are promising therapeutic prospects due to their tumor-specific nature, which means they are highly specific and have few off-target effects. Examples of neoantigen-targeting therapies include cancer vaccines and T-cell therapies. Cancer vaccines “train” immune cells within the body.
Neoantigens are associated with tumors with a high mutational load. These tumors typically have an abundance of tumor-infiltrating immune cells and can benefit from immunotherapy such as immune checkpoint inhibitors (ICIs). Such patients usually have a more favorable prognosis. For example, colorectal cancers (CRCs) with DNA mismatch repair deficiency (dMMR) are commonly hypermutated, have better patient outcomes than MMR-proficient tumors and the use of ICIs has been approved by the FDA in some of these cases , in approximately 15% of the patients.
Cancer vaccines
off-the-shelf therapeutic neoantigen vaccines are designed to produce a tumor-specific T-cell response against the neoantigen, typically to reduce the risk of “off-target” damage to non-tumor tissues. Additionally, immunological memory from neoantigen-based vaccines can provide long-term and persistent protection against tumor recurrence.
Antigen-presenting cells, such as dendritic cells, recognize neoantigens administered in the vaccine and present them to T cells, initiating an immune response. Neoantigens can either be delivered via extracellular vesicles like our mTEVs as proteins, or as DNA or RNA that code for the neoantigen and is translated into protein by the patients’ cells. Dendritic cell vaccines based on neoantigens involve taking a patient’s dendritic cells, exposing them to neoantigens (i.e. mTEV), then administering them back into the patient where they promote immune responses specific to the neoantigen.
references: https://www.technologynetworks.com/cancer-research/articles/what-are-neoantigens-372277
EV Therapeutics develops modified TEV (mTEV) by removing this key immunosuppresive miRNA, and keeps the diverse neoantigens available for MHCI processing and presentation on the APC. When mTEVs are systemically injected, they quickly reach the spleen and lymph nodes to engage with naiive dendritic cells and T cells allowing the rebuilding of the lost CD28 and CD80 proteins. The strong immune cell stimulation then causes the checkpoint inhibitor protein (PD-1 and PD-L1) to be expressed on the cell's surfaces, which helps to counter the strong T cell activation provided by the mTEVs. With the checkpoint inhibior protein expressed externally, the T cell is now ready to receive an anti-checkpoint inhibitor which bind and helps provide a sustained T cell activation that eventually leads to the killing of cancer cells.
Here's a detailed view of the transformation of CD 4+ and CD8+ T cells into Cytotoxic T cells (CTL) that trigger a series of events that eventually kill tumor cells.
To learn more about why CD28 costimulation is so important for
T cell activation please watch this video by Dr. John Looney from the Cleveland Clinic where he reviews T cell activation contributors, T cell antigen recognition, and T cell "braking."
Here's also another excellent tutorial titled "Check Point Inhibitors & Co-stimulatory Molecules in Immunology" by Dr. Kristeen Barker. Please subscribe to her channel. All her tutorials videos are great to watch!
This medical 3D animation shows the biogenesis and function of microRNAs within the cell.
Credit: http://www.katharinapetsche.com
