What it takes to make an organ

In the first stop on our tour, which begins on the ground level of the biotech's office, Krentz opens a door into a dark, echoing room, and flips a switch. Over the next minute or two, as the lights slowly become hot and flicker on, the darkness retreats and it becomes clear that I'm on a metal catwalk, crisscrossed above and below by tubes of all shapes and sizes. "This is sort of the hidden side of manufacturing," he says.

All of this tubing reaches down into the cleanest rooms in the facility, where workers manipulate the progenitor bladder cells. Once a room is declared clean, entering for maintenance becomes an issue, so the company constructed a level above, where they can maintain the tubing that keeps the air within the cleanest rooms free of particles and other contaminants. (The closest I get to the cleanest area, on another visit, is a glimpse through a set of three double doors containing narrow windows of a man dressed in hat, gown, goggles and mask moving in and out of view, mopping the floor.) Finding a facility with such high ceilings was key, says CFO Gary Sender, since it allows technicians to access clean rooms from above. "It enabled us to build a building within a building," he says.

Tengion doesn't expect to begin using the facility, housed in the basement of their suburban office park, to produce human bladders until the end of 2008 (when, if all goes well, the Phase III clinical trial would begin), so there aren't many people around. The facility has that still-new smell of rubber. As we walk around, the sound of our shoes squeaking on the slick floor, Krentz and Sender point out which largely empty rooms will eventually do what. There's the gowning room, where workers will take off their street clothes and don full scrubs; the scaffold prep room, where they will store the architecture that molds the sheets of bladder cells into a functioning organ; the incubator room, where rows of still-empty containers the shape of small refrigerators will hold the progenitor cells while they expand. In many rooms, the black-topped tables and benches are largely empty. Some of the incubators have thin red and blue wires streaming out of them, a sign they are being tested. Here and there, I see a lone computer, turned off.

To keep one room cleaner than the others, Krentz and his team do a delicate job they call balancing, which uses positive pressure to prevent less-clean air from neighboring rooms from seeping into a clean room. The formula changes depending on how clean the room is supposed to be, relative to those adjacent to it. Balancing is an "art," Krentz says: Once, at a previous job, he postponed a task until the contractor he trusted most to balance the pressure was available. In this facility, everything moves in one direction: Used tools, waste, all take a specific path through the grid to avoid contaminating a clean area. To test the equipment, workers are handling animal and cadaver cells, practicing for show time.

If all goes well, the company has left room to expand. Next to the 2,800-square meter space they're slowly bringing to life is another area within the same building, just as big, still floor-to-ceiling full of office furniture.