DEAR DOCTOR K >> I hear that doctors are trying to boost the immune system to help people fight cancer. Does that actually work?

DEAR READER >> Yes, this old, simple idea is beginning to work. The job of the immune system is to recognize when "foreign" things (such as microbes or chemicals) enter our bodies and eliminate them. Cancerous cells make substances that look foreign to the immune system. So, a person's immune system should be an ally in fighting cancer.

The problem is that in most people with cancer, the immune system response is just not strong enough to do much good. So medical scientists have been trying to boost the immune system's response. There are several different approaches:

• Checkpoint-Inhibitor Therapy: Unleashing the Immune Attack. When a cancer starts, immune system cells called T cells are naturally activated to attack it. However, the T cells then paradoxically produce "checkpoint" molecules that stop the T-cell attack. Scientists have created treatments called monoclonal antibodies that attach to and disable the checkpoint molecules. This unleashes the T-cell attack on the tumor.

This approach is showing real promise in several different types of cancer: melanoma, kidney cancer, one type of lung cancer, bladder cancer, Hodgkin lymphoma and certain types of colon cancers.


• Adoptive Cell Transfer: Finding and Boosting "Natural" Lymphocyte Attackers. When doctors remove a primary tumor, they often also find small numbers of T cells that are trying to attack the tumor cells. These few T cells can be greatly multiplied in number, and stimulated by certain natural immune system chemicals to be more aggressive attackers. This increased number of "angry" T cells are then returned to the cancer patient's body, where they travel to the tumor and attack it. This approach has been most effective against melanoma.

• CAR Cells and TCR Cells: Creating Lymphocyte Attackers. Doctors begin with a cancer patient's own T cells and modify them by inserting an element into them. That element recognizes and attaches to the patient's tumor cells and causes the T cells to attack the cancer cells. Large numbers of these cells are grown in the laboratory.

The element inserted into T cells to create CAR cells does not occur in nature. In contrast, a cancer patient does naturally make a few TCR cells — just not enough to stop the cancer. These few cells are removed from the body and made to multiply in the laboratory. Recently, 70 percent of children and young adults with a particular type of leukemia had dramatic improvement.

Dr. Komaroff is a physician and professor at Harvard Medical School.