New Delhi, Sept. 11: A team of Indian scientists has developed and successfully tested in hamsters and mice a candidate vaccine against kala azar, an infection caused by a parasite against which there is no regulator-approved vaccine available now.
The team from institutions in Calcutta, New Delhi, and Patna today announced their vaccine provided “complete protection” to laboratory hamsters and mice from a virulent strain of the parasite, Leishmania donovani.
While several drugs are currently used to treat kala azar, or leishmaniasis, scientists have been looking for vaccines because some of the drugs are at times toxic. The parasite has also acquired drug resistance.
Amitabha Mukhopadhyay at the National Institute of Immunology, New Delhi, and his colleagues have now devised a vaccine that is aimed at interfering with the functions of a key protein molecule called haemoglobin-receptor that is essential for the parasite’s survival.
The results of their experimental study on animals were published today in the US journal Science Translational Medicine.
“This haemoglobin-receptor protein on the parasite serves two essential functions,” said Mukhopadhyay. “It binds to haemoglobin in human blood to extract one of its components called haeme, and it functions as an enzyme important for the parasite’s survival.”
The researchers designed and put together a sequence of appropriate genetic material to serve as a DNA vaccine that would target the haemoglobin-receptor and used it to immunise laboratory hamsters and mice.
“The vaccine appears to stimulate all arms of the animals’ immune system,” Mukhopadhyay said. The immunised animals remained free of infection during the full experimental period of eight months.
Immunologist Syamal Roy and his colleagues at the Indian Institute of Chemical Biology, Calcutta, collaborated in the study by performing experiments on the animals.
Another immunologist, Sanjiva Bimal at the Rajendra Memorial Research Institute of Medical Sciences in Patna, sent blood samples of patients of kala azar to Mukhopadhyay for studies to determine whether after they infection they had acquired antibodies against the haemoglobin receptor.
Their studies also showed that the vaccine suppresses disease-promoting chemicals. But the scientists caution that it is still unclear whether DNA vaccines are safe for human use because of possible interaction of the DNA with human genetic material.
But a large number of other DNA vaccines for other diseases are already under evaluation in human clinical trials. Mukhopadhyay said the vaccine would need to undergo further studies on animals before it could be declared as ready for safety and efficacy studies in humans.