By Sneha S K and Kamal Choudhury

Aug 15 (Reuters) - The U.S. Food and Drug Administration

has approved Precigen's ( PGEN ) immunotherapy to treat adults

with a rare respiratory disease, making it the first treatment

for the condition to receive the health regulator's nod.

The therapy, Papzimeos, was approved to treat recurrent

respiratory papillomatosis (RRP) - a condition that causes

growth of wart-like tumors in the respiratory tract due to human

papillomavirus (HPV) infection.

RRP can be fatal as there is no cure and the current

standard-of-care is repeated surgeries. A distinguishing aspect

of this disease is the tendency for the growth to return even

after removing them through surgical procedures.

"Everybody is anxiously awaiting a new treatment for this

disease. The patients are and the surgeons are. There's nothing

more frustrating than doing a surgery and then having the

patient come back six months later," said Simon Best, associate

professor of Otolaryngology at Johns Hopkins Hospital.

Precigen ( PGEN ) estimates about 27,000 adult RRP patients in the

U.S. It did not immediately respond to a Reuters request for

comment on the treatment's pricing.

"There is so much hope in the community right now, the

common theme is we may finally be able to say no more surgery,"

said Kim McClellan, president of the Recurrent Respiratory

Papillomatosis Foundation. McClellan herself was diagnosed with

RRP at the age of five and has since then had more than 250

surgeries.

The approval was based on an early-to-mid-stage study data

that showed 51% of patients required no surgeries in the 12

months after the treatment.

"Randomized trials are not always needed to approve medical

products and this approval is proof of that philosophy," said

Vinay Prasad, who recently returned to the FDA to oversee

vaccine, gene therapy and blood product regulation.

Papzimeos is designed to stimulate an immune response

against cells infected with HPV types 6 and 11 - the strains

that cause the disease.

J.P.Morgan analysts estimate peak sales for the drug in the

U.S. to be about $250 million.