Sure, broccoli fights cancer. But tobacco?

When scientists at Stanford University looked around for a good way to grow a cancer vaccine, they realized they could do no better than the plant that has caused more cancers than you can count. They were not trying to develop a cancer vaccine such as Gardasil, which gives the body immunity against an infectious agent (in this case, the papillomavirus) that can trigger cancer (in this case, cervical). That's all well and good, but the true grail is a therapeutic vaccine, one that would prompt the body’s immune system to attack cancer cells and only cancer cells, or that would consist of antibodies that do so.

The theory rests on the fact that the surface of malignant cells are studded with molecules that can prime the immune system’s T cells, for instance, to attack the cancer cells, or act as homing signals that lure antibodies to munch up and destroy the cells.

A bunch of such cancer vaccines are in development, but they face a serious problem. Everyone is likely to need a different vaccine, because everyone's cancer cells are probably slightly different on the molecular level. Growing the antibodies according to the usual recipe means using animal cells, which is expensive (thousands of dollars per patient), time consuming (months) and possibly risky (they might contain viruses or other contaminants that are not exactly what you want to inject into cancer patients). So biologist Ronald Levy of Stanford University and colleagues decided to investigate plants as vaccine factories.

This evening, they are announcing in the advance online issue of the Proceedings of the National Academy of Sciences that they have grown an injectable cancer vaccine in genetically-engineered plants, tested it in 16 cancer patients and found it to be safe (tests of whether it works come next).

Fully aware of the irony here, Levy and his team used tobacco plants to grow the vaccine, which would act against follicular B-cell lymphoma. This chronic, incurable form of non-Hodgkin’s lymphoma strikes some 16,000 people in the United States each year. For all its horrors, however, follicular B-cell lymphoma just may be tailor-made for a cancer vaccine: all of the malignant cells are the descendants of a single bad actor and have an identical molecule on their surface. But the molecular signature of one patient’s cancer cells is slightly different from every other patient’s; hence the need for potentially expensive personalized vaccines.

The scientists therefore spliced the DNA for the molecular sequences of the antibodies from each of the 16 patients into tobacco cells. The DNA triggered production of antibodies in the tobacco plants’ leaves which were tailor-made for each patient’s lymphoma cells. The scientists ground up the leaves and isolated the antibodies, injecting them into each patient.

The patients’ immune systems got cracking: 70 percent of the patients developed an immune response to the plant-produced vaccine, and 47 percent produced a response specific to the antigen.