Pfizer Inc said it had acquired privately held gene therapy developer Bamboo Therapeutics Inc in a deal worth up to $645 million to boost its presence in the treatment of rare diseases.

Research into gene therapy, which aims to insert corrective genes into malfunctioning cells, goes back a quarter of a century but the field has experienced multiple setbacks and been plagued by safety concerns.

However, the discovery of better ways to carry replacement genes into cells is building optimism.

The U.S. Food and Drug Administration has yet to approve any gene therapies but Europe has approved two a treatment from GlaxoSmithKline for a rare immune disorder in babies and one from uni Qure NV for a serious blood condition.

Genetic material can be delivered to the cells by a variety of means, most frequently using a viral vector.

Bamboo was formed in 2014 to advance the work of Dr. Richard Jude Samulski, who is considered a pioneer in the field after he became the first to realise the potential of using adeno associated virus's (AAV) as a vehicle to replace a defective gene with a healthy gene.

Through the acquisition, Pfizer will gain access to Bamboo's experimental gene therapies for rare diseases such as Duchenne Muscular Dystrophy (DMD), giant axonal neuropathy (GAN), Friedreich ataxia (FA) and Canavan disease.

Focused on neurological and neuromuscular diseases, Bamboo's drugs are still in the preclinical or early stages of development. Pfizer is paying the Chapel Hill, North Carolina-based company $150 million upfront, and Bamboo stands to make $495 million in milestone payments.

Pfizer has been investing in gene therapies touted as a one-time cure for intractable and expensive to treat diseases in recent years.

In 2014, the drugmaker entered into a collaboration with Philadelphia based Spark Therapeutics Inc to develop SPK-9001, a gene therapy for hemophilia B.

Earlier this year, Pfizer signed a collaboration and license agreement with Emeryville, California-based 4D Molecular Therapeutics to develop targeted vectors for cardiac disease.

Other big drugmakers have made similar investments. Bristol-Myers Squibb Co has a tie-up with uniQure to develop gene therapies for heart diseases, while Celgene Corp has teamed up with bluebird bio Inc for cancer.