The company says the first patient, who has been told of the hold placed on the trial, "continues to do well since their implant in September 2013".
Living Cell Technologies, established in 2003, is the company which developed encapsulated pig pancreas cells into a promising treatment for type 1 diabetes. The so-called Diabecell has been trialled in humans at Middlemore Hospital and at health centres in Russia and Argentina.
The company's managing director, Andrea Grant, said gaps in the data on the efficacy of the "NTcell" brain therapy in a rat trial were discovered when data was being compiled into "a more formal regulatory format".
The results claiming the effectiveness of the therapy in rats were published in a medical journal in 2011 but the publication is now being withdrawn because they cannot be verified from the company's source data. The data is is also being withdrawn from regulatory documentation.
However, Dr Grant said there was no suggestion from these developments that the one patient treated so far had been put at risk.
"It's only the efficacy data from the rat study that we can't recapitulate. All the safety data ... is complete and we have every confidence in that."
In addition, the therapy had been trialled in monkeys, producing "quite impressive efficacy. Within two weeks, we saw improvements in limb and cognitive symptoms in a Parkinson's model. That study was done by a contract research organisation so we have a much higher degree of confidence in the monkey studies. Monkeys are much more predictive of human outcomes than rats are."
A similar check of the monkey-trial data was almost finished and so far "everything is in order". Until that check was complete, "it was our decision to take the path of utmost patient safety - the lowest risk - and put patient recruitment on hold and make sure everything is in order before we start again".
She said the gaps in the rat-trial data dated from 2007 to 2009, when the company was "relatively immature and wouldn't necessarily have had the right processes and procedures in place in terms of record-keeping. As of today, our record keeping is international best practice; this would be unlikely to happen again."
Records from the diabetes programme had been audited and no concerns had arisen.
NTcell
What is the therapy?
Named NTcell, the experimental therapy is made of particular pig cells that are encapsulated with a special coating to prevent their destruction by the human immune system, without the need for immune-suppression drugs.
What type of cells are they?
They are from the choroid plexus, a support structure in the brain. The choroid plexus helps to produce cerebrospinal fluid and nerve growth factors that protect against nerve cell death. The aim is to induce regeneration of nerve cells that produce the nerve-transmitter substance dopamine. A deficiency of dopamine is the cause of Parkinson's disease.
How is therapy delivered?
A small hole is drilled through the skull and a tube is inserted deep into the brain. A plastic tube is fed through the outer tube and clusters of cells are pushed into the brain.
Are there other uses for it?
The biotech company developing the therapy is investigating whether it could help treat strokes and Huntington's disease.
