Scientists have declared success in translating retinal cone cells, vital for colour vision, into blind mice.
Four years ago, the same research team transplanted rod cells, used in night vision.
The hope for restoring vision in the blind is that transplantable cells which mature into rods or cones can be derived from human embryonic stem cells (hESCs), which can grow into any of the body's tissues.
They selected cells with activity in a gene called cone rod homeobox which commits cells to becoming rods or cones, reports New Scientist.
Treatment was given to mice engineered to mimic a form of childhood blindness called Leber's congenital amaurosis.
The team injected 200,000 isolated cells into each eye, in a space between the layer of light-sensitive cells - engineered to be damaged in the recipient mice - at the rear of the retina and a supporting epithelial cell layer above.
Within 21 days, the new cells settled into the photoreceptor layer and grew into rods and cones.
"This is very exciting work and it would be a huge medical breakthrough to be able to restore lost photoreceptors in patients who are blind," says Robert Lanza, chief scientific officer at Advanced Cell Technology, a company in Worcester, Massachusetts, which in 2004 successfully turned hESCs into retinal cells.
"But it's important to point out that this is very early-stage work, and incorporation of the cells into the retina doesn't mean that they're functional, which is of course the ultimate goal."
The report has been published in the Journal Human Molecular Genetics.