Bone in a bottle

Bone in a bottle
Mar 5th 2009 From The Economist print edition
Tissue engineering: Attempts to grow artificial bone marrow in the laboratory have failed—but now a new approach is showing promise
GROWING human cells in a laboratory is easy. Making those cells arrange themselves into something that resembles human flesh is, alas, rather more difficult. So-called tissue engineers have mastered the arts of making artificial skin and bladders, and they recently managed to cook up a windpipe for a patient whose existing one was blocked. But more complicated organs elude them. Nor has anyone managed to grow bone marrow.
At first sight, that is surprising. The soft and squishy marrow inside bones does not look like a highly structured tissue, but apparently it is. This does not matter for transplants: if marrow cells are moved from one bone to another they quickly make themselves at home. But it matters for research. Bone marrow plays an important role in the immune system and in bodily rejuvenation. Stem cells that originate within the marrow generate various sorts of infection-fighting blood cells and help repair damaged organs. But many anticancer and antiviral drugs are toxic to marrow. That leaves patients taking them susceptible to disease and premature ageing. Experiments intended to investigate this toxicity using mice have proved unsatisfactory. Nicholas Kotov of the University of Michigan in Ann Arbor and his colleagues have therefore been trying to grow human marrow artificially.
When they started their research, Dr Kotov and his team knew that the stem cells from which marrow is derived grow naturally in specialised pores within bone. These pores are lined by a mixture of connective-tissue cells, bone cells and fat cells, which collaborate to nurture the stem cells. The researchers also knew that the cells in this lining send chemical signals to one another and to the stem cells they touch. This suggests that a stem cell’s fate may depend on its surroundings in three dimensions, rather than the two dimensions of the bottom of a Petri dish—the type of vessel in which cell cultures are traditionally grown. If correct, this would explain why attempts to grow marrow in Petri dishes have failed.