Eleven drugmakers led by Pfizer and Novartis have set aside a combined $2 billion to invest in gene therapy manufacturing since 2018, according to a Reuters analysis, in a drive to better control production of the world’s priciest medicines.

The full scope of Novartis’ $500 million plan, revealed to Reuters in an interview with the company’s gene therapy chief, has not been previously disclosed. It is second only to Pfizer, which has allocated $600 million to build its own gene therapy manufacturing plants, according to filings and interviews with industry executives.

Gene therapies aim to correct certain diseases by replacing the missing or mutated version of a gene found in a patient’s cells with healthy copies. With the potential to cure devastating illnesses in a single dose, drugmakers say they justify prices well above $1 million per patient.

The senior vice president of Pfizer’s global gene therapy business, acknowledged drugmakers take a “leap of faith” when they make big capital investment outlays for treatments before they have been approved or, in some cases, even produced data demonstrating a benefit. The rewards are potentially great, however.

Gene therapy is one of the hottest areas of drug research and, given the life-changing possibilities, the FDA is helping to speed treatments to market. It has approved two so far, including Novartis’s Zolgensma treatment for a rare muscular disorder priced at $2 million, and expects 40 new gene therapies to reach the U.S. market by 2022.

There are currently several hundred under development by around 30 drugmakers for conditions from hemophilia to Duchenne muscular dystrophy and sickle cell anemia.

The proliferation of these treatments is pushing the limits of the industry’s existing manufacturing capacity. Developers of gene therapies that need to outsource manufacturing face wait times of about 18 months to get a production slot, company executives told Reuters. They are also charged fees to reserve space that run into millions of dollars, more than double the cost of a few years ago, according to gene therapy developer RegenxBio.

As a result, companies including bluebird bio, PTC Therapeutics and Krystal Biotech are also investing in gene therapy manufacturing, according to a Reuters analysis of public filings and executive interviews. They follow Biomarin Pharmaceutical Inc, developer of a gene therapy for hemophilia, which constructed one of the industry’s largest manufacturing facilities in 2017.

The FDA is keeping a close eye on standards. This comes amid the agency’s disclosure in August that it is investigating alleged data manipulation by former executives at Novartis’ AveXis unit.