When the common house lizard is attacked - or feels threatened - it often drops its tail to distract the predator. It can afford to shed its tail because a new one grows in just a few days. Many other reptiles, amphibians and all sponges are able to regenerate damaged or severed body parts.

Unfortunately, mammals cannot do so.

But scientists at Calcutta University (CU) believe that may change. Learning from creatures who can regenerate lost body parts, they say they have been able to regenerate fully functional lungs in mice using human embryonic stem cells.

The mice used in the experiment had badly damaged lungs caused by fibrosis, a disease common in humans. Fibrosis stiffens the lungs, which are then unable to absorb oxygen.

"We were able to regenerate healthy lungs in the mice with human embryonic stem cells - cells that can develop into any type of tissue or organ - obtained from the placenta and umbilical cord," says Ena Ray Banerjee, head, immunobiology and regenerative medicine research, zoology department, CU.

The scientists will have to do trials on at least two other major animals - sheep and dogs because their lungs are similar to that of humans - before they get clearance for clinical trials for human beings. If those succeed, it will mark a major breakthrough in treating serious lung diseases such as chronic obstructive pulmonary disease, asthma, fibrosis, interstitial lung disease, pneumonia, tuberculosis, pulmonary arterial hypertension and cancer. Unfortunately, Ray Banerjee does not have the infrastructure to carry out the planned experiments on large animals and will have to outlicense it to another research team.

Lung diseases are on the rise in India, where pollution levels are alarmingly high. Apart from pollution, the use of tobacco and sedentary lifestyles have also caused a spike in the number of lung diseases. World Health Organization (WHO) reports state that about 11 per cent of deaths in India are caused by lung diseases, with around 142.09 people out of every lakh citizens dying of some form of lung ailment.

Studies widely available on the Internet show that 15 per cent of those inflicted with lung diseases also suffer from pulmonary fibrosis. Reports presented by the Indian Council of Medical Research state that around five per cent of men suffer from COPD.

For their experiment, Ray Banerjee and her team used vials of frozen human embryonic stem cells procured from the US, the UK, Bangalore and Mumbai. Once defrosted, the cells were kept in exactly the way they stay inside the human body.

"It had to be a sterile environment with a temperature not more than 37 degrees Celsius, with five per cent of carbon dioxide and a perfect pH balance," she explains.

The cells were replenished with the right amount of amino acids and glucose and administered antibiotics to prevent infections. But the one concern that the researchers had was the "pluripotent" nature of the embryonic stem cells. A "pluripotent" cell is able to multiply into any one of more than 200 types of cells, depending on the signals they get from the environment. It's here that the team led by Ray Banerjee came up with a new technology.

"We gave the cells a certain cocktail of signals which led to a cellular reprogramming in the cells, making them grow what is desired - nonciliated squamous epithelial cells," Ray Banerjee adds.

As the cells began to grow into lung tissue, they were placed at the base of the windpipe of the mice. "We tagged the cells with nanoparticles so that they reach where they are supposed to go and integrate seamlessly with minimal loss," she says.

The cells of the damaged lungs, she adds, accepted these new cells as their own, gradually replacing the damaged cells and regenerating the lungs completely.

The breathlessness that the mice exhibited in the initial stages eased in the next six months. When put on the plethysmograph - an instrument used to test a smoker's lungs - the lungs of the mice were found to be in excellent condition.

"It was as if the lungs were never diseased," she says.

"If a person has not stored his cord blood, we can theoretically regenerate lungs by extracting stem cells from bone marrow," Ray Banerjee says.

It will, however, be a while before people can rejoice. "This research, though it provides hope for the future, has a long way to go before being put into clinical use," says Dr Parthasarathi Bhattacharyya, pulmonologist, Institute of Pulmocare and Research, Calcutta.

He points out that there is need for finding alternatives to lung transplant. "In a populous country like ours, there could be millions with terminal lung disease, requiring lung transplantation. Right now, a few centres are struggling to set up regular lung transplant units, for there are many logistic and technical issues related to that," he says.

The CU team is now in the process of applying for a patent for these inducers or signals, which they have discovered. Earlier, Ray Banerjee, along with a clinician at the University of Washington School of Medicine, Seattle, had come up with a tissue engineering technique for generating lungs from stem cells. The study was published in the US-based journal PLoS One.