A young paraplegic woman who underwent spinal stem cell therapy developed a growth in her back made up of nasal cells eight years later.

The team from the University of Iowa Hospitals and Clinics that removed and investigated the growth has reported the anomaly in a paper published in the Journal of Neurosurgery: Spine. Although the case is a rare occurrence (the first of its kind, that we know of) the authors admit this may simply be because patients that undergo therapy are not monitored long enough, and either way it provides ample evidence attesting to our lack of understanding around programming and controlling stem cell proliferation and differentiation post-transplant.

Human trials for this type of therapy are still at the very early stages, but animal trials have had some promising results. Several different types of cells have been experimented with for implantation including schwann cells (these surround nerves and sometimes grow on the spinal cord post-injury), foetal neural cells (with successes in rat studies) andnasal olfactory ensheathing cells (these are extracted from the lining of the nose and were the ones used in this particular case study).

The patient in question was just 18 years old when she suffered an injury during a car accident. She had been paraplegic for three years when she opted to undergo surgery, implanting olfactory mucosal cells into the injury site. These cells originate in the roof of the nasal cavity and have the ability to take on the characteristics of other cells in the body because they are partially made up of progenitor cells (adult stem cells). They also contain olfactory ensheathing cells, often used in spinal cord therapy trials. This is all despite, as the authors note, the fact that: "the ability of these cell types to differentiate into organised neural tissue in humans or support new neural growth in humans in the setting of spinal cord injury is unclear."

The location of the transplantation was not divulged in the Spine paper, but the New Scientist reports that it was carried out as part of an early stage trial in the Hospital de Egas Moniz in Lisbon, Portugal. In a paper, the Lisbon team revealed that out of 20 candidates, 11 regained some sensation and one person's paralysis actually worsened.

The woman's therapy did not flag up any issues at the time of implantation, but eight years down the line she complained of worsening back pain that had already been ongoing for a year. Scans at the University of Iowa Hospitals and Clinics revealed a mass, thick like mucus and surrounded by fibrous walls, on the spinal cord, at the site of the cell implantation. The investigators explain that the mass was made up "mostly of cysts lined by respiratory epithelium, submucosal glands with goblet cells, and intervening nerve twigs". Nasal elements were growing.

The mass was pressing against the spinal cord, causing the patient discomfort and threatening her spine. When it was extracted, the team could confirm it came from the neural stem-like cells implanted eight years earlier, because the cysts contained a network of non-functioning nerves that were separate from the spine (suggesting they were new) and bone.

"The presence of these nerves within the mass indicates the capacity of olfactory mucosa to support nerve fibre regeneration or new nerve formation," write the team.

In total, the mass was made up of two major parts, measuring 1.4 x 0.8 x 0.7 cm and 1.6 x 1.3 x 0.7 cm. When they were removed, the patient's pain immediately subsided.

These kinds of trials have been ongoing for years, but the fears have been that stem cells -- which have the ability to turn into any cell in the body if programmed to -- could just as easily mutate into something that is not intended, and create tumours in the long term.

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Stem cell therapy caused nasal tumour on paraplegic's back