Death Benefit by Robin Cook Page B

differentiated mature cell.”
    “Right on,” Yamamoto said. “An example is a bone marrow stem that can become an adult blood cell. These cells are often called adult stem cells. What’s a pluripotent stem cell?”
    Lesley spoke up: “A stem cell that can turn into any of the three hundred or so types of cells that make up the body of a multicellular organism like a human.”
    “Right on again. You guys are making this easy for me.”
    Pia felt a wave of impatience wash over her. She was eager to see the organ bath unit. Had it been up to her, she would have preferred to forgo any review session.
    “Up until four or five years ago, how were pluripotent stem cells obtained?”
    “From blastocysts.” Pia spoke up by reflex. She wanted this little talk over with.
    “Right,” Yamamoto said. “Blastocysts from fertilized eggs, meaning very early-stage embryos. Why was that a problem that led to serious delays in stem cell research?”
    “Because it offended conservatively minded people,” Pia said. “Particularly here in the United States, limitations were placed on what could and could not be done in stem cell research with government funds.”
    “Well said,” Yamamoto commented. “Here’s a harder question. Let’s say that the research on embryonic stem cells had been allowed to proceed unimpeded. Can anyone say what the major problem would have been if the research had advanced to a point of using the stem cells to treat patients?”
    None of the students moved.
    “Let me give you a hint,” Yamamoto said. “I’m referring to an immunological problem.”
    “Rejection!” Lesley called out, her eyes lighting up.
    “Exactly. Rejection, meaning that any use of such embryological stem cells would have elicited some degree of rejection reaction. Some techniques would have reduced this problem but not completely eliminated it.”
    All three students nodded. Everything that Yamamoto was saying they had heard before. “Now, can anyone define ‘induced pluripotent stem cells’ in contrast to embryological stem cells? These are the cells that Dr. Rothman and I have been working with exclusively.”
    “They are pluripotent stem cells made from mature cells, usually a fibroblast and not egg cells,” Pia explained. “They are ‘induced’ by particular proteins to revert back from being a mature fibroblast to being a stem cell.”
    “Exactly,” Yamamoto said. “And isn’t it a marvel that it works? For a long time one of the tenets of biological science was that cellular differentiation was a one-way street, meaning the process could never revert. But people should have known that this particular tenet was false. After all, it was known that certain animals could regrow body parts, like starfish and salamanders. Also cancer should have been a hint that the process of differentiation could go in the opposite direction, as many cancers are composed of immature cells that arise in organs populated by mature cells.”
    Pia found herself glancing at her watch and sitting up straighter in her seat. She wanted to speed up the review session but didn’t know how. She inwardly groaned when Lesley piped up with a question: “How exactly are the cells changed back from mature to immature?”
    “The same way that everything else is accomplished in the cell,” Yamamoto said. “By switching on and off genes. Remember, every eukaryotic cell—that is, a cell with a nucleus—contains a copy of an organism’s entire genome. Meaning that every nucleated cell has all the information necessary not only to build itself but to build the entire body. How this works is a process called gene expression, meaning the turning on and off of genes in a kind of molecular ballet. I know you learned all this in your genetics courses in college and during your first two years here at Columbia. Anyway, cellular maturation proceeds by a sequential switching on and off of the appropriate genes. It used to be thought that genes