The words genetically engineered supersoldier do nothing to help Bruce's paranoia. If anything, it heightens it, sharpens his attention to a fine point as he takes in every word. He has to agree that dead things should stay dead-- he's always taken a sour disposition toward his own presumed immortality, and uncomfortably tries to avoid thinking on it.

That Jim doesn't care if he doesn't have control of the extracted regeneration factor is what convinces Bruce. Letting Bruce keep unilateral control over something is a fast way to get him to agree.

"I'll keep a sample of the blood," he decides out loud, seeing the logic in Jim's concerns and not discounting it. "I'd rather not have the concentrated substance sitting around. It's too easily abused. But I can keep some blood on ice, and if it comes up later, let me know. If he shows up and starts with the extortion-- this is my area. I'm confident I can replicate it."

That's the most he'll promise. Bruce isn't keen on absolute commitments, but if those terms are acceptable, he has no problem with it.