I find it interesting and reassuring that medicine is now turning to trying to fix our own defense systems in order to cure certain diseases rather than giving a strong drug (or a combination of drugs) that will kill the “bad” cells along with many of the good ones, and therefore making us weak and often experiencing side effects, for which there is a need for more drugs, and so on….
One of these defense or “balance maintenance” systems that has gotten a lot of attention recently is the huge and immensely varied bacterial “cosmos” we have in our guts called “microbiome” (see my previous post on this subject).
But the subject of this post is immunotherapy, a result of research conducted in the “cancer immunology” field, which is a type of cancer treatment designed to boost the body's natural defenses to attack and eliminate tumors. In order for our immune system to defend us from viruses and bacteria, it first has to “recognize” parts of these organisms. The parts that are recognized are “antigens” which are “seen” by our “antibodies”; these antigens are usually located on the surface of the invading organisms. A helpful way to think about antigen-antibody interactions is that of a key and its lock, where the antigen is the key that fits in the antibody lock as shown in the figure where the antibody is bound to the cell surface antigen. Cancer cells on the other hand are our own cells, although abnormal. They are not necessarily recognized by our immune system, and they then proliferate rapidly to form tumors due to specific mutations in these cells that make them divide in an uncontrolled and faster way compared to normal cells in the same parts of our bodies (tissues).
There are different types of immunotherapies being used or developed to treat specific cancers. They essentially consist of helping the immune system recognize these cancer cells and strengthen the immune response to hopefully ensure tumor reduction and/or elimination.
One of these defense or “balance maintenance” systems that has gotten a lot of attention recently is the huge and immensely varied bacterial “cosmos” we have in our guts called “microbiome” (see my previous post on this subject).
But the subject of this post is immunotherapy, a result of research conducted in the “cancer immunology” field, which is a type of cancer treatment designed to boost the body's natural defenses to attack and eliminate tumors. In order for our immune system to defend us from viruses and bacteria, it first has to “recognize” parts of these organisms. The parts that are recognized are “antigens” which are “seen” by our “antibodies”; these antigens are usually located on the surface of the invading organisms. A helpful way to think about antigen-antibody interactions is that of a key and its lock, where the antigen is the key that fits in the antibody lock as shown in the figure where the antibody is bound to the cell surface antigen. Cancer cells on the other hand are our own cells, although abnormal. They are not necessarily recognized by our immune system, and they then proliferate rapidly to form tumors due to specific mutations in these cells that make them divide in an uncontrolled and faster way compared to normal cells in the same parts of our bodies (tissues).
There are different types of immunotherapies being used or developed to treat specific cancers. They essentially consist of helping the immune system recognize these cancer cells and strengthen the immune response to hopefully ensure tumor reduction and/or elimination.
One type of immunotherapy currently used consists of blocking the ability of certain immune “checkpoint” proteins that normally keep immune responses at a low level. Some tumors can use these proteins to suppress immune responses against them. This checkpoint blocking immunotherapy results in an increased ability to destroy cancer cells. Several such inhibitors have been approved by the FDA (see table below) for advanced melanoma treatment, and others are in development.
Therapeutic antibodies is another type of immunotherapy, consisting of antibodies that are made in the laboratory to destroy cancer cells. Antibody–drug conjugates (ADCs) have been approved by the FDA for treatment of different cancers (see table below). The drug that is linked to the antibody is usually a toxic substance or poison that enters and kills the tumor cell after this one is recognized by the antibody part of the antibody-drug “hybrid”. Other therapeutic antibodies that are not conjugated to a toxic substance make cancer cells commit suicide (apoptosis) when they bind to them via different mechanisms, also triggering destruction of tumor cells by immune action known as “cytotoxicity”. There are also FDA-approved antibodies in this category (see table below) as well as some non-antibody immune conjugates linked to cancer-killing drugs which act in the same way.
A very promising experimental form of immunotherapy called adoptive cell transfer (ACT) has been applied in small clinical trials on patients with very advanced cancers, mainly blood cancers. Some patients have shown complete remission lasting several years. This approach is based on extraction of patient’s cells that are involved in immune recognition of cancer cells, then these cells are grown to large amounts, “activated” to attack tumor cells or sometimes they are genetically modified to do so, and finally they are infused back into the patient so they can do their anti-cancer job.
Another immunotherapy approach is the use of cancer treatment vaccines which are usually made from a patient’s own tumor cells, or immune cells which are manipulated/activated in the laboratory to react against tumor cells and then given back to the patient. One such vaccine has been FDA-approved for treatment of metastatic prostate cancer in men (although it does not cure the cancer, it has been shown to extend the life of patients by several months; see table below) and other candidate vaccines are being tested to treat forms of brain, breast, and lung cancer.
Table: Immunotherapies for which there are FDA-approved drugs
Another immunotherapy approach is the use of cancer treatment vaccines which are usually made from a patient’s own tumor cells, or immune cells which are manipulated/activated in the laboratory to react against tumor cells and then given back to the patient. One such vaccine has been FDA-approved for treatment of metastatic prostate cancer in men (although it does not cure the cancer, it has been shown to extend the life of patients by several months; see table below) and other candidate vaccines are being tested to treat forms of brain, breast, and lung cancer.
Table: Immunotherapies for which there are FDA-approved drugs
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