WASHINGTON, June 4 (Xinhua) -- Researchers at the Stanford University School of Medicine converted human immune cells in blood directly into functional neurons in the laboratory in about three weeks.

The dramatic transformation does not require the cells to first enter a state called pluripotency but instead occurs through a more direct process called transdifferentiation, according to a study published on Monday in the Proceedings of the National Academy of Sciences.

The conversion occurred with relatively high efficiency, generating as many as 50,000 neurons from 1 milliliter of blood, and it could be achieved with fresh or previously frozen and stored blood samples.

"Blood is one of the easiest biological samples to obtain," said Marius Wernig, associate professor of pathology and a member of Stanford University's Institute for Stem Cell Biology and Regenerative Medicine.

"This technique is a breakthrough that opens the possibility to learn about complex disease processes by studying large numbers of patients," said Wernig, the paper's senior author.

For those with autism or schizophrenia, many hundreds of individual, patient-specific samples are needed in order to suss out the relative contributions of dozens or more disease-associated mutations.

"Generating induced pluripotent stem (iPS) cells from large numbers of patients is expensive and laborious," Wernig said. "The prospect of generating iPS cells from hundreds of patients is daunting and would require automation of the complex reprogramming process."

The transdifferentiation technique was first developed in Wernig's laboratory in 2010 when he and his colleagues showed that they could convert mouse skin cells into mouse neurons without first inducing the cells to become pluripotent, a developmentally flexible stage from which the cells can become nearly any type of tissue.

They went on to show the technique could also be used on human skin and liver cells.

Although it's possible to directly convert skin cells to neurons, the biopsied skin cells first have to be grown in the laboratory for a period of time until their numbers increase, a process likely to introduce genetic mutations not found in the person from whom the cells were obtained.

In the new study, Wernig and his colleague focused on highly specialized immune cells called T cells that circulate in the blood.

T cells protect us from disease by recognizing and killing infected or cancerous cells. In contrast, neurons are long and skinny cells capable of conducting electrical impulses along their length and passing them from cell to cell.

But despite the cells' vastly different shapes, locations and biological missions, the researchers found it unexpectedly easy to complete their quest.

"It's kind of shocking how simple it is to convert T cells into functional neurons in just a few days," Wernig said.

According to the study, the resulting human neurons aren't perfect, lacking the ability to form mature synapses, or connections, with one another, but they are able to carry out the main fundamental functions of neurons.

Wernig and his colleague are hopeful they will be able to further optimize the technique in the future. In the meantime, they've started to collect blood samples from children with autism.