12 December 2017

Using CRISPR/Cas9 to outsmart cancer

Dorit Verhoeven

Our immune system has the difficult job of maintaining peace within our body. It must distinguish normal cells from foreign pathogens and (pre)malignant cells and only becomes active when needed. This can be done by checkpoints, certain molecules on cells that let our immune system know when to turn ‘on’ and ‘off’. Our T-cells display proteins (PD-1 for programmed cell death protein 1, and CTLA-4 for cytotoxic T-lymphocyte associated protein 4) that act as an ‘off’ signal, by which T-cell function is regulated.

As a medical student starting down a research path, I know that questions regarding health are big and complex.

Cancers have an escape mechanism

Cancers have the sneaky ability to exploit this off-switch for their own use, and turn it against us. You see, many cancer cells display the ligands of PD-1 and CTLA-4. Our immune system recognizes these ligands and is then turned off. And in fact, for some cancer patients, these signals actually indicate a worsening of their prognosis. Thus, an immune checkpoint that maintains the balance within our immune system may become the very thing that accelerates a patient’s chances of dying from cancer.

This conundrum intrigues me. As a medical student starting down a research path, I know that questions regarding health are big and complex. And in order to even begin to answer these questions, we need to find answers to smaller questions first. This is what makes research so exciting for me in our fight against cancer.

Immunotherapy tries to combat cancer

Immunotherapy uses a patient’s own immune system to treat cancer, by boosting the ‘on’ signals and silencing the ‘off’ signals. PD-1 and CTLA-4 are currently the primary targets in immunotherapy. The concept of immunotherapy has been around for more than a century and most recently, has gained traction with several FDA approved treatments for several types of cancer including melanoma and non-small-cell lung cancer.

Immunotherapy drugs interfere with the PD-1 and CTLA-4 checkpoints in T-cells, enabling the immune system to properly recognize and kill cancer cells. This type of treatment is called immune-checkpoint blockade and sounds like a one-fits-all treatment for cancer. Unfortunately, not all cancer cells display the ligands of PD-1 and CTLA-4; thus, not all patients respond. Because of this, we’re using a one-fits-one (also known as personalized medicine) approach looking for other protein receptors that have functions similar to PD-1.  

Improving immunotherapy approaches

To do this, we’re studying patients with Primary Immunodeficiency Diseases (PID), who are at higher risk for certain types of cancers, primarily pediatric lymphoma. PID is a group of more than 300 diseases caused by defects in the immune system and affects 1 out of every 1200 people. Most PID are caused by single gene mutations, and most are inherited. Unfortunately, symptoms are broad and varied, and it may be years before a patient is accurately diagnosed.

We have identified a group of genes in children with PID that can be associated with an increased risk of subsequent lymphoma development. These genes code for receptors involved in T-cell function. Although genetic manipulation of primary T-cells has been challenging, we’re using CRISPR/Cas9 now to make T-cells that lack a specific receptor. Once we have our modified T-cells, we’ll co-culture them with cancer cells to evaluate the ‘on’ and ‘off’ capacity of these receptors.

If we see an increased immune response by the T-cells (meaning that if there is no off-switch because the receptor is missing), we’ll know that a particular receptor may be an alternative to PD-1. The outcome of our results may uncover new drug targets, and enable us to make immunotherapy more broadly applicable in pediatric patients.

Dorit Verhoeven
Summa student
Group: Marianne Boes, PhD
WKZ/UMC Utrecht