Eric Langhoff, a young Danish doctor who had been trained by Ralph Steinman, joined my laboratory to work on this problem. Within a short period of time we were able to demonstrate that dendretic macrophages were highly efficient carriers of HIV. The virus sticks tightly to these cells and is carried across the mucosal membrane to nearby lymph nodes. The dendretic cells educate other immune cells by touching them with their long diaphanous membranes. This is how the virus reaches the susceptible immune cells, called CDA or T cells. Now inside the body, it begins the infection.

In the course of this work I learned much about these unusual cells. I learned they could be taught to educate the immune system outside the body. This could be done by exposing purified dendretic cells to a foreign substance and then reintroducing them back into the body. No other cells had this ability.

This observation triggered another thought. Might it be possible to train purified dendretic cells to recognize cancer cells? If so, then reintroduction of these cells might train the body's own immune system to attack the cancer itself.

At the time I was a consultant to a venture capital company, Healthcare Ventures. I presented the outline of this idea and they agreed to provide $5 million to fund a new company to explore this new approach to anti-cancer therapy. As often happens, I was not alone with this idea. While attending a scientific conference in Holland, I met two physicians scientists from Stanford, Sam Strober and Ed Engelmann. They had independently come up with the same idea and were in the early stages of starting a similar company. We joined forces, and Activated Cell Therapy, Inc., was born.

It is now 20 years on. The company experienced many ups and downs. It moved from California to Washington near Seattle. New financing was needed. Other venture capital companies provided additional funding. The original management was replaced. The name was changed to Dendreon. The company raised money from the public markets. I moved on to genomics research, and Sam and Ed's role as advisors ended. But the vision remained. The scientists, doctors and management at Dendreon persisted despite skepticism and initial rejection by the FDA.

The treatment is now approved. This small step in cancer treatment for men with advanced prostate cancer provides new hope for all those with cancer. We have begun to realize the dream of harnessing the power of the immune system to fight cancer. The road to here has been long and circuitous, but the path ahead is clear.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.