The concept here is engineering stem cells so they differentiate into body cells that target, go after and kill “bad” cells, such as cells infected with HIV or cancer cells. It is a fairly new approach. Since stem cells have an uncanny ability to be welcomed in the body and get around in it, they potentially make very attractive seek-and-destroy cells.
A December 8 2009 Science Daily story Stem Cells Can Be Engineered to Kill HIV, Scientists Show is a this-week example. “Researchers from the UCLA AIDS Institute and colleagues have for the first time demonstrated that human blood stem cells can be engineered into cells that can target and kill HIV-infected cells –. Taking CD8 cytotoxic T lymphocytes — the “killer” T cells that help fight infection — from an HIV-infected individual, the researchers identified the molecule known as the T-cell receptor, which guides the T cell in recognizing and killing HIV-infected cells. These cells, while able to destroy HIV-infected cells, do not exist in enough quantities to clear the virus from the body. So the researchers cloned the receptor and genetically engineered human blood stem cells, then placed the stem cells into human thymus tissue that had been implanted in mice, allowing them to study the reaction in a living organism. — The engineered stem cells developed into a large population of mature, multifunctional HIV-specific CD8 cells that could specifically target cells containing HIV proteins. The researchers also found that HIV-specific T-cell receptors have to be matched to an individual in much the same way that an organ is matched to a transplant patient. — The next step is to test this strategy in a more advanced model to determine if it would work in the human body –“This approach could be used to combat a variety of chronic viral diseases,” said Zack, who is also a professor of microbiology, immunology and molecular genetics (at UCLA). “It’s like a genetic vaccine.””
A May 2009 Science Daily story Adult Stem Cells From Bone Marrow Made To Kill Metastatic Lung Cancer Cells In Mice describes another example. “Researchers in London have demonstrated the ability of adult stem cells from bone marrow (mesenchymal stem cells, or MSCs) to deliver a cancer-killing protein to tumors. — The genetically engineered stem cells are able to home to the cancer cells, both in culture and in mouse models, and deliver TNF-related apoptosis-inducing ligand (TRAIL), destroying the tumor cells while sparing normal cells.” This story was covered in the blog entry Trojan-horse stem cells might offer an important new cancer therapy. And, regarding the payload TRAIL, see the blog entry On the TRAIL of a selective cancer treatment.
A 2005 Science Daily story Researchers Use Human Embryonic Stem Cells To Kill Cancer Cells described an earlier related development. In this case, human embryonic stem cells were coaxed to differentiate into NK (natural killer) cells. “Natural killer cells (or NK cells) are a type of cytotoxic lymphocyte that constitute a major component of the innate immune system. NK cells play a major role in the rejection of tumors and cells infected by viruses. The cells kill by releasing small cytoplasmic granules of proteins called perforin and granzyme that cause the target cell to die by apoptosis(ref).”
A related but not quite terminator-cell approach is described in an October 2009 Science Daily story The Stem Cells Which ‘Fool Immune System’ May Provide Vaccination For Cancer. In this case “Scientists from the United States and China have revealed the potential for human stem cells to provide a vaccination against colon cancer, reports a study published in Stem Cells. — “This finding potentially opens up a new paradigm for cancer vaccine research,” said Dr. Zihai Li. “Cancer and stem cells share many molecular and biological features. By immunizing the host with stem cells, we are able to ‘fool’ the immune system to believe that cancer cells are present and thus to initiate a tumor-combating immune program –‘ .The team vaccinated laboratory mice with human embryonic stem (hES) cells and discovered a consistent immune response against colon cancer cells. The team witnessed dramatic decline in tumor growth within the immunized mice. This revealed that immunized mice could generate a strong anti-tumour response through the application of hES cells.”
These four stem-cell approaches to disease immunization or cure show potential promise but each is still in an early stage of development and is yet to be tested in humans. I would guess that 8-15 years will be required for any of them to become part of clinical practice.