Immunotherapy is a type of cancer treatment that uses the body's own immune system to fight cancer. It is a promising new treatment option, but it doesn't always work. A new study from the University of California, San Francisco (UCSF) explains why certain immunotherapies don't always work as predicted.

The study, published in the journal Nature Medicine, found that some tumors can produce a molecule called TGF-beta, which can suppress the immune system. This means that even if an immunotherapy drug is able to activate the immune system, the TGF-beta produced by the tumor can prevent the immune system from killing the cancer cells.

"Our study provides a new explanation for why certain immunotherapies don't always work," said Dr. Robert Schreiber, director of the UCSF Helen Diller Family Comprehensive Cancer Center and senior author of the study. "By understanding the role of TGF-beta in suppressing the immune system, we can develop new strategies to overcome this resistance."

The study also found that a combination of immunotherapy drugs can be effective in overcoming TGF-beta-mediated resistance. The researchers found that a combination of an anti-TGF-beta antibody and an anti-PD-1 antibody was able to activate the immune system and kill cancer cells in mice.

"This study suggests that combining immunotherapy drugs with drugs that target TGF-beta could be an effective new strategy for treating cancer," said Dr. Schreiber. "We are currently conducting clinical trials to test this combination therapy in patients with cancer."

Immunotherapy is a promising new treatment option for cancer, but it doesn't always work. The study from UCSF provides a new explanation for why certain immunotherapies don't always work and suggests a new strategy for overcoming this resistance.