But this is the first-known case of a brain tumor caused by a brain stem cell therapy, according to the report-a phenomenon scientists have predicted in the pages of Scientific American and elsewhere.

In others, such as Britain, the brain's stem is regarded as the crucial part. In this case simpler tests can be applied, such as whether a patient's pupils react to light.

Brown's case paves a path for constructing a permanent cure for HIV through genetically-engineered stem cells.