"Even highly aggressive forms of malignancy with extremely large tumors were eradicated," Zheng Cui, M.D., Ph.D., and colleagues reported in this week's on-line edition of Proceedings of the National Academy of Sciences.
The transplanted white blood cells not only killed existing cancers, but also protected normal mice from what should have been lethal doses of highly aggressive new cancers.
"This is the very first time that this exceptionally aggressive type of cancer was treated successfully," said Cui. "Never before has this been done with any other therapy."
The original studies on the cancer-resistant mice -- reported in 2003 -- showed that such resistance could be inherited, which had implications for inheritance of resistance in humans, said Mark C. Willingham, M.D., a pathologist and co-investigator.
Moreover, preliminary studies show that the white blood cells also kill "endogenous" cancers -- cancers that spring up naturally in the body's own cells.
Cui and Willingham said the research produced many other surprises. For one thing, if a virulent tumor was planted in a normal mouse's back, and the transplanted white blood cells were injected into the mouse's abdomen, the cells still found the cancer without harming normal cells. The kind of cancer didn't seem to matter.
A single injection of cancer-resistant macrophages offered long-term protection for the entire lifespan of the recipient mouse, something very unexpected, they said.
"The potency and selectivity for cancer cells are so high that, if we learned the mechanism, it would give us hope that this would work in humans," said Cui. "This would suggest that cancer cells send out a signal, but normal white blood cells can't find them."
Cui said the findings "suggest a cancer-host relationship that may point in a new therapeutic direction in which adverse side effects of treatment are minimal."
Discover magazine had a follow up in its August issue. They are finding that some people are cancer resistant. They are going to try to perform tests to see if transplanted white blood cells from cancer resistant people can help those with cancer. They have a blood test to identify cancer resistant mice without trying to give them cancer. The plan is to use such a blood test to find cancer resistant people. Cui points out that it could take years to find the gene, and many more to develop and test drugs that target it. In the meantime, his team has begun to test blood samples from healthy people, and have found a wide range of cancer-killing activity in humans. Cui says he would like to pursue both the conventional and unconventional approaches. "We think there might actually be a possibility we could do it without knowing the mechanism," he says, "but of course by knowing the mechanism you could devise many other options, so if one thing doesn't work then you can also find different ways using the same concept. So we think both directions are important."
if the cell-donation approach were to work in people, it would not need to go through a long FDA approval process. "All the delivery mechanisms are already in place and all the ethical regulations for that direction are already in place. So if we can identify cancer-resistant humans then they could start treating them tomorrow if someone wants to pay for it."