By using MRI to detect magnetic probes of tiny iron oxide particles, an international research team for the first time has successfully tracked immune-stimulating cells implanted into cancer patients for treatment purposes.
"In four of the eight patients, MRI revealed that the implanted cells weren't where they needed to be to be effective for treatment," says Jeff Bulte, Ph.D., an associate professor of radiology at Hopkins' Institute for Cell Engineering who developed methods to optimally label cells with the clinically approved iron oxide particles.
This new application of the probes -- already clinically approved for MRI scanning of the liver -- could dramatically improve efforts to test and use cellular therapies such as vaccines to treat cancer or prevent its recurrence or stem cells to repair damaged organs, say the researchers.
Bulte and a team of Dutch researchers used MRI and a magnetic probe approved by both European and U.S. agencies to locate therapeutic cells injected into eight melanoma patients.
"Our results show that the MRI-based technique was more accurate than tracking the cells using radioactivity and that ultrasound failed to accurately guide injection of the cells into lymph nodes in half of the patients," says Bulte, an author on the report, which appears in the November issue of Nature Biotechnology.
The cells used in the current study, so-called dendritic cells, are the immune system's own "most wanted posters" because they take up and display foreign proteins that tell the immune system's fighters what cells to look for and destroy.
Since the mid-1990s, clinical trials have been testing dendritic cells to see whether they can stimulate the immune system to kill cancer cells. In these trials, dendritic cells from patients are exposed to proteins from the patients' cancer cells and then returned to the patients.
However, some of the clinical trials of such "cancer vaccines" have been disappointing, with some patients responding very well but others not at all. A critical issue behind each patient's success on the treatment, however, is whether the cells get to the lymph nodes, where the immune system's fighters are normally "trained" by dendritic cells. Until now, there's been no accurate way to know where the cells end up.
It's thought, but not proven, that the best way to get the cells where they need to be is to inject them directly into the lymph nodes that drain the area containing a tumor. Currently, doctors use ultrasound to guide the needle, and dendritic cells carrying a radioactive tag are sometimes used to try to double-check the cells' final resting place.
However, in this study, the Dutch team discovered that using MRI and iron oxide particles was able to track the cells' location much more accurately than the radioactive tracking method and provided anatomic detail simultaneously -- structural detail not possible by tracking radioactivity.