Boston biotech Vertex is the leading developer of cystic fibrosis medicines. Its four approved drugs can treat most patients. Trikafta, the one most recently approved in the U.S., raised the percentage of people with cystic fibrosis who are eligible for a Vertex product from 50% to 90%, a major achievement.

But the remaining 10%, whose disease is caused by so-called nonsense mutations, don’t benefit as much and are left without effective options.

Boehringer’s acquisition of the lentiviral gene therapy is aimed at that group, which the company describes as the “immediate target” of its development plans.

The therapy, which is still in preclinical testing, is envisioned as an inhalable treatment, rather than one injected intravenously. Known as BI 3720931, it is designed to selectively introduce a healthy CFTR gene into the relevant cells.

The partnership between Boehringer and its partners in the U.K. was first established in 2018. Tuesday’s announcement gives the Germany company exclusive global rights to develop, manufacture, register, and commercialize the gene therapy.

According to a Boehringer executive, the therapy has demonstrated “high gene transfer efficiency in pre-clinical models.”