Salmonella ‘can kill cancer’: How bacteria that cause food poisoning could be used to attack tumour cells 

The bacteria that cause food poisoning could be used to kill cancer, medical experts said yesterday.

A genetically-altered form of salmonella has been developed that will attack tumour cells but leave healthy cells alone.

The bugs are a leading cause of food poisoning in the UK each year.

It is the latest example of developments in a new field of cancer treatment called ‘bacteriotherapy’.

Experiments on mice using a modified version of salmonella reduced the size of cancer tumours, the American Association for the Advancement of Science annual meeting in Boston heard.

Genetically-modified salmonella could be used to destroy cancer cells while leaving healthy cells alone

Alterations made to the salmonella bug stopped it attacking and infiltrating into normal healthy cells. Instead it targeted cancer cells.

It was also engineered to create ‘flags’ that are recognised by the immune system, guiding the body’s defence system to target the cancerous tumours.

When injected into the bloodstream of mice with colon cancer, tumours exposed to the bacteria shrunk.

The development, led by Jin Hai Zheng from Chonnam University in South Korea and colleagues, was published in the AAAS journal Science Translational Medicine.

Dr Zheng said: ‘The engineered bacteria induced an effective antitumor immune response, successfully treating tumours in several different mouse models with no evidence of toxicity.’

The breakthrough was hailed by British researchers yesterday.

Kevin Harrington, professor of biological cancer therapies at the Institute of Cancer Research in London, said: ‘It has been known for some time that certain types of bacteria, including strains of salmonella, are able to grow in tumours but not in normal tissues.

Researchers called the new work by South Korean scientists ‘a fascinating new approach’

‘However, until now, attempts to use bacteria as anti-cancer therapies have had limited success, both in the laboratory and in the clinic.

‘The current work by Zheng and colleagues represents a fascinating new approach to using bacteria.

‘Instead of asking the bacteria to kill cancer cells directly, the researchers have genetically engineered salmonella so that it expresses a gene from a different bacterium and this triggers the immune system to mount an attack on the tumour.

‘The results show that this approach is effective against a range of tumour types with little or no toxicity in mice.’

Dr Catherine Pickworth, Cancer Research UK’s science information officer, added: ‘In this study the researchers injected the bacteria into the mice where it was delivered to the tumour through the blood, causing an immune reaction.

‘The bacteria fits like a lego piece onto the surface of immune cells. This starts a chain reaction inside the immune cells, causing them to release molecules that can kill cancer.’

Salmonella is the bacteria behind large numbers of cases of food poisoning

Dr Pickworth went on: ‘This study, carried out in mice, shows that bacteria can be used to trigger the immune system to attack cancer cells. The next steps will be to see if this method is safe and if it could be used to help patients.

‘We’re funding similar research using viruses to help the immune system recognise cancer cells as a threat so it can destroy them, opening potential new ways to treat the disease.’

Professor Paul Dyson, of Swansea University, who is also studying the use of salmonella in fighting cancer said one advantage is that ‘the salmonella are living factories for production of therapeutic molecules.

He added: ‘So long as the tumor persists, potentially the bacteria will continuously produce the therapeutic agents.

‘So we believe there is huge mileage in pursuing research into this type of treatment. Existing evidence indicates there would few or no side effects.’

Read more:

What’s new in cancer immunotherapy research?

What’s new in cancer immunotherapy research?

Immunotherapy is a very active area of cancer research. Many scientists and doctors around the world are studying new ways to use immunotherapy to treat cancer. Some of these are discussed here.

Newer monoclonal antibodies

Monoclonal antibodies (mAbs) have already become an important part of the treatment for many cancers. As researchers have learned more about what makes cancer cells different from normal cells, they have developed mAbs to exploit these differences. They have also developed newer forms of mAbs, attaching them to drugs or other substances to make them more powerful.

Researchers are also studying other ways of making monoclonal antibodies safer and more effective. For example, because mAbs are proteins, they can actually make the body’s immune system react against them. This can lead to side effects, as well as destroying the mAbs. Newer forms of mAbs are less likely to cause immune reactions. Researchers are also looking to see if using only parts of antibodies can make these drugs work better.

Another new approach is to combine parts of two antibodies together (known as a bispecific antibody). One part attaches to a cancer cell, while the other attaches to an immune cell, bringing the two together and leading to an immune response.

New types of mAbs are now being studied for use against many types of cancer. For information on newer treatments for a particular type of cancer, please see our information on that type of cancer.

Treatments that target immune system checkpoints

As mentioned in Immune checkpoint inhibitors to treat cancer, the immune system has checkpoint proteins (such as PD-1 and CTLA-4) that help keep it from attacking other normal cells in the body. Cancer cells sometimes take advantage of these checkpoints to avoid being attacked by the immune system.

Targeting these checkpoints is quickly becoming an important part of the treatment for some cancers, including melanoma and non-small cell lung cancer. Researchers have also found promising early results against a number of other cancer types. Unlike most other cancer drugs, these checkpoint inhibitors seem to be helpful against many different types of cancer.

Only a handful of these treatments have been approved for use so far, but many others are now being studied in clinical trials.

A newer approach being studied is to combine treatments that have different targets (such as nivolumab, which targets PD-1, and ipilimumab, which targets CTLA-4) to see if this might work better. In melanoma, this combined approach has been shown to work better than using either treatment alone, but the combination also comes with an increased risk of serious side effects.

Other studies are looking at combining checkpoint inhibitors with other types of drugs used to treat cancer.

Newer cancer vaccines

Vaccines are not yet a major type of treatment for cancer. Researchers have been trying to develop vaccines to fight cancer for decades, but this has proven to be harder than was first thought. As researchers have learned over the years, the immune system is very complex. It has also become clear that cancer cells have different ways of eluding the immune system, which makes creating effective vaccines difficult.

Researchers are using the knowledge gained in recent years to improve how they develop cancer vaccines. For example, vaccines are now often given along with other substances (called adjuvants) that help boost the body’s immune response, which might help the vaccines work better.

Researchers are also studying the best way to give vaccines, looking to see if they work better when used alone or with other types of cancer treatments.

Types of cancer vaccines

Many different types of vaccines are now being studied to treat a variety of cancers.

Tumor cell vaccines: These vaccines are made from actual cancer cells that have been removed from the patient during surgery. The cells are altered (and killed) in the lab to make them more likely to be attacked by the immune system and then injected back into the patient. The patient’s immune system then attacks these cells and any similar cells still in the body.

Most tumor cell vaccines are autologous, meaning the vaccine is made from killed tumor cells taken from the same person in whom they will later be used. Other vaccines are allogeneic, meaning the cells for the vaccine come from someone other than the patient being treated. Allogeneic vaccines are easier to make than autologous vaccines, but it’s not yet clear if one type works better than the other.

Antigen vaccines: These vaccines boost the immune system by using only one antigen (or a few), rather than whole tumor cells. The antigens are usually proteins or pieces of proteins called peptides.

Antigen vaccines can be specific for a certain type of cancer, but they are not made for a specific patient like autologous tumor cell vaccines are.

Dendritic cell vaccines: These vaccines have shown the most success so far in treating cancer. Sipuleucel-T (Provenge), which is approved for the treatment of advanced prostate cancer, is an example of a dendritic cell vaccine.

Dendritic cells are special immune cells in the body that help the immune system recognize cancer cells. They break down cancer cells into smaller pieces (including antigens), and then hold out these antigens so other immune cells called T cells can see them. The T cells then start an immune reaction against any cells in the body that contain these antigens.

Dendritic cell vaccines are made from the person in whom they will be used. The process used to create this type of vaccine (known as an autologous vaccine) is complex and expensive. Doctors remove some immune cells from the patient’s blood and expose them in the lab to cancer cells or cancer antigens, as well as to other chemicals that turn the immune cells into dendritic cells and help them grow. The dendritic cells are then injected back into the patient, where they should cause an immune response to cancer cells in the body.

Vector-based vaccines: These vaccines use special delivery systems (called vectors) to make them more effective. They aren’t really a separate category of vaccine; for example, there are vector-based antigen vaccines.

Vectors are special viruses, bacteria, yeast cells, or other structures that can be used to get antigens into the body. The vectors are often germs that have been altered to make sure they can no longer cause disease.

Vectors can be helpful in making vaccines for a number of reasons. First, they can be used to deliver more than one cancer antigen at a time, which might make the body’s immune system more likely to mount a response. Second, vectors such as viruses and bacteria might trigger their own immune responses from the body, which could help make the overall immune response even stronger. Finally, these vaccines might be easier and less expensive to make than some other vaccines.

Some common cancers in which vaccines are being tested

Some of the more common types of cancer in which vaccines are now being studied include:

  • Brain tumors (especially glioblastoma)
  • Breast cancer
  • Cervical cancer
  • Colorectal cancer
  • Kidney cancer
  • Lung cancer
  • Lymphoma
  • Melanoma
  • Pancreas cancer
  • Prostate cancer

This is not a complete list – vaccines are being studied in other types of cancer as well. For information on newer treatments for a particular type of cancer, please see our information on that type of cancer.

Oncolytic viruses

Viruses are a type of germ that can infect and kill cells. Some viruses can be altered in the lab so that they infect and kill mainly cancer cells. These are known as oncolytic viruses. Along with killing the cells directly, the viruses can also alert the immune system to attack the cancer cells.

An example is talimogene laherparepvec (Imlygic), which is an oncolytic virus that has been modified to make GM-CSF, a protein that boosts the immune response. This virus can be used to treat melanomas in the skin or lymph nodes that can’t be removed with surgery. It is injected directly into the tumors, typically every 2 weeks. This treatment can sometimes shrink these tumors, but it has not been shown to shrink tumors in other parts of the body.

Other ways to boost the immune system

Some other forms of immunotherapy are being studied to try to boost specific parts of the immune system. These types of treatments show a lot of promise, but they are complex and so far are available only through clinical trials being done at major medical centers.

Chimeric antigen receptor (CAR) T-cell therapy

This is a promising new way to get immune cells called T cells to fight cancer. For this technique, T cells are removed from the patient’s blood and genetically altered in the lab to have specific antigen receptors (called chimeric antigen receptors, or CARs) on their surface. These receptors will attach to proteins on the surface of cancer cells. The T cells are then multiplied in the lab and infused back into the patient’s blood, where they can now seek out the cancer cells and launch a precise immune attack against them.

This technique has shown very encouraging results in early clinical trials against some advanced, hard-to-treat types of leukemias and lymphomas. In many people the cancer could no longer be detected after treatment, although it’s not yet clear if these people have been cured.

Some people have had serious side effects from this treatment, including very high fevers and dangerously low blood pressure in the days after it’s given. Doctors are learning how to manage these side effects.

Doctors are still improving how they make the T cells and are learning the best ways to use them. They are also studying whether this treatment will work for other types of cancer. CAR T-cell therapy is only available in clinical trials at this time.

Tumor-infiltrating lymphocytes and interleukin-2 (IL-2)

Researchers have found immune system cells deep inside some tumors and have named these cells tumor-infiltrating lymphocytes (TILs). These T cells can be removed from tumor samples taken from patients and multiplied in the lab by treating them with IL-2. When injected back into the patient, these cells can be active cancer fighters.

Treatments using TILs are being tested in clinical trials in people with melanoma, kidney cancer, ovarian cancer, and other cancers. Early studies of this approach by researchers from the National Cancer Institute have been promising, but its use may be limited because doctors might not be able to get TILs from all patients.

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Last Medical Review: July 23, 2015 Last Revised: August 8, 2016

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