Genetic engineering and cancer treatment are advancing rapidly, driven by CRISPR and immunotherapy. CRISPR technology provides a way to precisely edit the genetic code of living organisms, while immunotherapy uses the body’s own immune system to combat diseases. A specific application of CRISPR, known as CRISPR screening, is accelerating the development of new immunotherapies for diseases like cancer.
Understanding CRISPR Screens
CRISPR-Cas9 is often described as “genetic scissors” for its ability to make precise cuts in DNA, allowing scientists to alter gene function. Building on this, CRISPR screens are large-scale experiments that let researchers systematically test the function of thousands of genes at once. The process begins by creating a library of cells where each has had a single gene modified by the CRISPR system. This modification can turn a gene off (knockout) or alter its activity through CRISPR activation (CRISPRa) and CRISPR interference (CRISPRi).
Once this library is established, it is subjected to a selective pressure, such as exposure to a drug. Scientists then observe which cells survive and use next-generation sequencing to identify the specific gene that was altered in them. This determines the gene’s role in the observed outcome. This high-throughput method allows for an unbiased survey of the genome to find genes involved in a particular biological process and identify novel targets for drug development.
A Primer on Immunotherapy
Immunotherapy is a treatment that uses the body’s immune system to fight diseases, especially cancer. It enhances the ability of immune cells to recognize and eliminate harmful cells, such as malignant tumors. While the immune system can distinguish between healthy and abnormal cells, cancer often develops ways to evade this surveillance.
There are several major types of immunotherapy:
- Immune checkpoint inhibitors are drugs that release the brakes on the immune system by blocking natural checkpoints, like PD-1/PD-L1, that cancer cells exploit to suppress an immune attack.
- CAR T-cell therapy is a form of adoptive cell transfer where a patient’s T-cells are collected, genetically engineered to produce cancer-recognizing chimeric antigen receptors (CARs), and then infused back into the patient.
- Therapeutic vaccines are designed to stimulate a targeted immune response against cancer cells.
- Cytokine therapies use immune-signaling proteins to boost overall immune activity.
The ability of immunotherapy to create a lasting “memory” in the immune system gives it an advantage over other therapies.
Unlocking Immunotherapy Potential with CRISPR Screens
The combination of CRISPR screens and immunotherapy research provides a powerful engine for discovery. Scientists use these genetic screens to probe the complex interactions between cancer cells and the immune system. This approach accelerates the identification of new targets and helps researchers understand why some treatments fail, paving the way for more effective therapeutic strategies.
A primary application is identifying gene targets that make cancer cells more vulnerable to immune attack. For instance, by co-culturing a library of gene-edited cancer cells with immune T-cells, researchers can see which cancer cells are eliminated. This process pinpoints genes whose removal makes cancer susceptible to the immune system, providing a roadmap for new drugs.
CRISPR screens also uncover the genetic drivers of resistance to existing immunotherapies. By screening cancer cells that survive treatment with a checkpoint inhibitor, scientists can identify the genes responsible for their resilience. These screens can also be applied directly to immune cells to find genes that enhance their cancer-killing capabilities, leading to more potent cell-based therapies.
Breakthroughs from CRISPR Screening in Immunotherapy
The application of CRISPR screens in immuno-oncology has yielded significant breakthroughs, uncovering information about how cancer evades the immune system. These discoveries are providing a blueprint for the next generation of immunotherapies. The screens have been effective at identifying regulators of pathways that control how tumors are recognized and attacked by immune cells.
One area of discovery is the identification of new immune checkpoint molecules beyond the well-known PD-1 and CTLA-4. These targets offer fresh avenues for developing drugs that release the immune system’s brakes in new ways. For example, a CRISPR screen identified the gene APLNR; when lost in cancer cells, this gene helps them resist T-cell attacks, marking it as a potential therapeutic target.
Screens have also clarified mechanisms of resistance to current treatments. Research confirmed that genes in the interferon-gamma signaling pathway are often involved when tumors become resistant to T-cell killing. Additionally, screens in T-cells have identified genes like DHX37 as negative regulators of T-cell function, as deleting this gene enhanced the ability of T-cells to attack tumors.
These genetic studies have uncovered many genes not previously suspected of playing a role in the tumor-immune interaction. This expanded list of potential targets is now being explored to develop more effective treatments for a wider range of patients. The insights gained are helping to build a more complete picture of the dialogue between cancer cells and the immune system.
Translating Discoveries into Treatments
Identifying a gene through a CRISPR screen is an early step. The potential target must first be validated by confirming the finding in more complex settings, like animal models that mimic the human tumor microenvironment.
Once validated, the next phase is developing a drug or therapy, such as a small molecule, antibody, or gene therapy approach. This candidate must then undergo extensive preclinical testing for safety and efficacy before being considered for human trials, a process that is both time-consuming and resource-intensive.
Translating these discoveries into clinical treatments faces challenges, as modulating the immune system can cause adverse events. For therapies involving genetic modification of a patient’s cells, like CAR T-cell therapy, ensuring safe delivery of the edits is a priority. Despite these hurdles, early clinical trials using CRISPR-edited immune cells have shown the approach is feasible and relatively safe, accelerating the development of new immunotherapies.