In the last four months, the Food and Drug Administration approved more gene therapies for inherited diseases than it had in the five years previous, a flurry of activity that’s lifted a beleaguered sector of the biotechnology industry.

In August and September, the regulator cleared treatments for a severe form of the blood condition beta thalassemia as well as for a childhood brain disease, both developed by Bluebird bio. And in November, partners CSL and UniQure won an FDA OK for Hemgenix, their therapy for hemophilia B.

All three are the product of many years of research. In developing them, their makers have played a large role in pushing the gene therapy field from promising proof-of-concept experiments to convincing late-stage clinical trials.

Yet as the pipeline of gene therapies in testing has grown, the challenges have too. Concerns over safety have resurfaced, prompting the FDA to move cautiously, while companies have struggled to size up their manufacturing in preparation for commercialization.

The field’s recent difficulties have made the approvals from Bluebird, CSL and UniQure meaningful beyond those companies’ walls.

“We’ve had to cross this desert for years,” said Geoff MacKay, CEO of a gene therapy biotech called Avrobio, in a recent interview. “For those of us who have been in the field for a decade plus, this is an incredible period of time.”

New hurdles await. The three gene therapies each cost several million dollars, posing barriers to patient access and testing an insurance system not set up for one-time medicines with potentially long-lasting benefit. Other developers will be watching to see how the market responds.