Immunotherapy can trigger the immune system to fight cancer in different ways.
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Immunotherapy available now
On the surface of T-cells are proteins called “checkpoints” that stop the immune system from attacking cancer cells.
Drugs called checkpoint inhibitors block certain proteins so the T-cells can recognise and destroy cancer cells.
The checkpoint inhibitors that are currently available can block the following proteins:
- Programmed death-1 (PD-1)
- Programmed death-ligand 1 (PD-L1)
- Cytotoxic T-lymphocyte-associated antigen (CTLA-4).
Checkpoint inhibitors are now the most widely used form of immunotherapy. The types currently subsidised by the Australian Government through the Pharmaceutical Benefits Scheme (PBS) include pembrolizumab (Keytruda), nivolumab (Opdivo) and ipilimumab (Yervoy). These drugs are approved and reimbursed for people with advanced melanoma. Nivolumab has recently been approved and will soon be reimbursed for kidney and lung cancers.
They are also being tested for other cancers, and may soon be approved and reimbursed for cancers of the head and neck, and bladder.
Some treatments have been used to stimulate the immune system so it reactivates and attacks the cancer.
- In non-muscle-invasive bladder cancer, the vaccine Bacillus Calmette-Guérin (BCG) is given into the bladder through a catheter to stimulate a person’s immune system to stop or delay bladder cancer coming back or becoming invasive.
- In some types of skin cancers, a cream called imiquimod is applied directly to the affected area to stimulate a local immune response.
Immunotherapy in clinical trials
Adoptive cell transfer
This boosts the ability of the body’s T-cells to fight cancer.
Chimeric antigen receptor (CAR) T-cell therapy is a type of adoptive cell transfer that is showing benefits for some people with some types of leukaemia and lymphoma.
First, T-cells are removed from the blood and a new gene is introduced into the cells to enable them to recognise cancer. The T-cells are then returned to the blood by an intravenous drip (infusion). The altered T-cells multiply and trigger a number of immune responses that attack the cancer cells.
Cytokines (immune hormones)
These are proteins made by white blood cells that stimulate the immune system.
The two main types of cytokines that have been used to treat cancer are interferons, which help the immune system to slow the growth of cancer cells, and interleukins, which stimulate anti-cancer T-cells.
Interferons were once used at high doses to help people with melanoma and kidney cancer, but they were found to be toxic. They are currently being trialled at lower doses and given with checkpoint inhibitors. If these trials are successful, interferons may be used to treat cancer in the future.
These viruses directly infect tumour cells and cause an immune response against the infected cells.
Other immune treatments
Vaccines help train the immune system to prevent cancer. There are prevention and treatment vaccines, but treatment vaccines have not been successful.
The human papillomavirus (HPV) vaccine is used to prevent cervical cancer, and it is hoped it will also prevent penile and anal cancers and some cancers of the head and neck. Vaccines against hepatitis B and hepatitis C viruses help prevent liver cancer.