Cancer, an intricate disease linked to genomic changes and influenced by both host and environmental interactions, is a significant worldwide health concern, causing over 8 million deaths each year.
Gene therapy, aiming to introduce and express genetic material in specific cells or tissues for therapeutic outcomes, presents several benefits over traditional treatments.
One key advantage is that it can be applied directly to the affected area, allowing for a high concentration of therapy without the risk of systemic side effects. Moreover, as most gene therapies require only a single application, they might be more cost-effective in the long term.
Gene Therapy for Cancer: A Broad Outline
In 1989, the US Food and Drug Administration (FDA) approved the first gene therapy protocol. This involved extracting tumor infiltrating lymphocytes from patients with advanced melanoma, modifying them ex vivo with a marker gene, expanding them in vitro, and then reintroducing them to the patients.
The first clinical trial using gene therapy for cancer treatment began the following year, with patients with advanced melanoma receiving tumor infiltrating lymphocytes that had been genetically altered ex vivo to express tumor necrosis factor.
An important turning point in the gene therapy field was marked by a study conducted by Cline and colleagues.
The significance of this study was not due to its outcome, which was unsuccessful, but because it had been conducted without obtaining the necessary permission from the Institutional Review Board at the University of California, Los Angeles (UCLA).
This case underscored the technical and ethical complexities inherent in human gene therapy, highlighting the need for greater understanding and stringent oversight.
Here are some ways in which gene therapy is being used or studied for the treatment of cancer:
- Replacing or repairing mutated genes: Some cancers are caused by DNA mutations that lead to the growth of tumors. Gene therapy can potentially replace these mutated genes with healthy copies or repair the mutations to stop the tumor from growing.
- Knocking out harmful genes: Some genes contribute to the progression of cancer when they are active. Gene therapy can be used to “knock out” these genes and stop them from functioning.
- Making cancer cells more visible to the immune system: Certain gene therapies aim to help the immune system better recognize and attack cancer cells. This can be done by introducing new genes into the body that help immune cells to identify and destroy cancer cells.
- Instructing cells to kill cancer: Some gene therapies involve introducing new genes that instruct cells to produce a specific protein that kills cancer cells. This method has been used in CAR-T cell therapy, which involves modifying T cells to produce a receptor that binds to a protein on cancer cells, causing the T cells to kill the cancer cells.
- Viral gene therapy: This method involves using viruses, modified so they cannot cause disease, to carry therapeutic genes into cancer cells. Oncolytic virotherapy is a type of gene therapy that uses viruses to infect and kill cancer cells.
- Using gene therapy to make traditional therapies more effective: Some researchers are studying ways to use gene therapy to make cancer cells more sensitive to chemotherapy or radiation therapy.
Some gene therapies have been approved for use, such as certain CAR-T cell therapies for leukemia and lymphoma, but these are not first-line treatments and are typically used only when other treatments have failed.
The field is advancing rapidly, and many clinical trials are underway to study new gene therapies for a variety of cancers.
However, there are still significant challenges to overcome, including the difficulty of delivering genes to cells, potential side effects and immune reactions, and the high cost of treatment.
Potential of Gene Therapy in Cancer Treatment
Gene therapy has been explored as a potential treatment for many types of cancer, including:
- Leukemia: In 2017, the U.S. Food and Drug Administration (FDA) approved the first gene therapy for use in the United States, a treatment for certain types of leukemia. Known as CAR-T cell therapy, this treatment involves modifying patients’ own immune cells to fight cancer.
- Lymphoma: Similar to leukemia, certain types of lymphoma have also been treated with CAR-T cell therapies.
- Breast cancer: Gene therapy for breast cancer is still mostly in the experimental stage, with researchers working on numerous approaches, including modifying immune cells, using viruses to kill cancer cells, and replacing or deactivating malfunctioning genes.
- Melanoma: Experimental gene therapies for melanoma include those that aim to bolster the immune system’s response to cancer cells and those that introduce genes into the body to directly attack the cancer or make it more susceptible to other treatments.
- Prostate cancer: Researchers are studying gene therapy as a possible way to treat prostate cancer, including trials that use viruses to deliver cancer-killing genes directly to prostate cancer cells.
- Lung cancer: Gene therapy is being tested in clinical trials for lung cancer. Some experimental treatments aim to repair or replace faulty genes in lung cancer cells, while others are designed to stimulate the immune system to better fight the disease.
In many of these cases, gene therapy is not a first-line treatment and is used only when other more established treatments have failed. It’s also important to note that while these therapies have shown promise, they are still considered experimental and are associated with significant risks and side effects.
Additionally, not all cancers are currently treatable with gene therapy. The effectiveness of gene therapy can vary greatly depending on the specific type of cancer, the patient’s individual health status, and other factors.
Clinical Effectiveness of Gene Therapy for Cancer
Gene therapy is being tested to treat cancer in several ways, like using special techniques to make cancer cells self-destruct, getting the immune system to work better, or stopping the blood supply to tumors. However, not many of these techniques have been used in real patients yet.
The protein was inserted into the tumor with the help of a special virus. Although this technique didn’t cause serious side effects, it didn’t help reduce the size of the tumors either.
But another experiment with p53 had better results. The therapy, called Gendicine, used a harmless virus to deliver the p53 protein into cancer cells.
The first gene therapy to be approved for use, Gendicine showed promising results in a test with 12 patients who had a type of throat cancer. None of the patients’ tumors came back in the five years after they were treated.
Another approved gene therapy product is Oncorine. This therapy uses a virus that can only multiply in cancer cells, causing them to burst and die. This is helpful in treating solid tumors. Another similar therapy, ONYX-015, didn’t get approved because it didn’t show beneficial effects in clinical trials.
Both Oncorine and ONYX-015 were tested in several types of cancer, like brain, head and neck, pancreas, and ovarian cancers. They generally didn’t cause serious side effects, but some patients had fever, pain at the injection site, nausea, hair loss, lower white blood cell counts, and flu-like symptoms.
In order to improve the effectiveness of these virus-based therapies, scientists are adding other proteins to the viruses.
For example, Onco VEXGM-CSF is a therapy that uses a virus and an additional protein to fight cancer. Early tests showed that it was safe and could have an effect on tumors in patients with skin cancer or tumors just under the skin.
Gene Therapy to Boost the Immune System to Fight Cancer
Immunotherapy, a way to help the body’s immune system fight cancer, is a hot topic. The idea is to make cancer cells more visible to the immune system. But, there are some problems, like the immune system’s natural tendency to ignore cancer cells and the fact that cancer can make the body less able to fight it off.
Scientists have been studying how to genetically engineer immune cells, called T cells, to make them better at fighting cancer.
One method is to put a special receptor on T cells that can recognize cancer cells. For example, a team of researchers led by Morgan did this using a receptor that can spot a marker on melanoma, a type of skin cancer.
They tested this on 15 patients and found that the engineered T cells stayed in their bodies for at least two months. Two of the patients even had their tumors shrink.
In another study, scientists used a receptor that can recognize a marker found on many different types of cancer. This also led to a positive response in patients, showing that this approach could be a good way to treat cancer.
Another way to make T cells better at fighting cancer is to put a fake receptor, called a CAR, on them. This has been very successful in treating blood cancers.
There are other ways to boost the immune system too. For instance, Herman and others tested a therapy that uses a harmless virus to deliver a gene that can stimulate the immune system. They tested this in patients with advanced pancreatic cancer, but it didn’t improve their survival.
On the other hand, another study tested a similar therapy in patients with bladder cancer. They found that the therapy made the immune system more active and reduced the number of cancer cells.
In a different study, scientists tested a therapy that uses a virus to deliver a gene that can stimulate the immune system. They tested this in 11 patients with different types of cancer, but unfortunately, all of them had their disease get worse within four months.
Is Gene Therapy Safe?
Gene therapy uses viruses, which can sometimes trigger unwanted immune responses because our bodies may have already encountered and built defenses against these viruses.
When the virus used in gene therapy enters the body, it triggers a response from our immune system. Our bodies react differently to different types of viruses. In a long-term study, two different types of the same virus were tested, and one caused only mild symptoms while the other caused moderate to severe symptoms.
While we don’t have a lot of long-term safety data on gene therapy in humans, the short-term results look promising. The side effects have generally been mild and not serious.
Scientists have been trying to improve the safety of gene therapy in several ways.
- One way is to make the gene therapy more targeted, meaning it only affects the cells it’s supposed to. Right now, one of the problems with gene therapy is that it sometimes affects the wrong cells. Better targeting would also make gene therapy more effective and safer.
- Another topic scientists are studying is how our immune system responds to gene therapy. They’re looking at how the immune system reacts to the gene therapy and the proteins it makes. We know that some people already have antibodies against the viruses used in gene therapy, which can make the therapy less effective.
- Scientists have tried modifying the viruses used in gene therapy to improve its specificity and effectiveness. But this comes with its own challenges, like lower production rates of the viruses and difficulties in getting the viruses into cells.
- Scientists have also tried using specific promoters, which control when and where the gene therapy is active. For example, they’ve used promoters that are only active in areas with low oxygen levels, like in stroke, heart disease, and cancer.
One risk with gene therapy is that it can accidentally cause cancer by inserting its genes into the wrong spot in our DNA. Scientists are working on ways to target the insertion of these genes to specific spots to avoid this risk.
It’s important to remember that even though gene therapy can potentially cause genetic changes, so can traditional cancer treatments like radiation and chemotherapy. And, just like with these traditional treatments, the goal with gene therapy is to minimize these risks as much as possible.