Inadvertent germline modification and novel gene therapies

Gene therapy is on the rise. Major successes have been achieved and fifteen gene therapy treatments have now been approved for the European market. Current gene therapies are based on viral vectors derived from lenti- and retroviruses and adeno-associated viruses (AAV). These genetically modified (GM) viruses can be administered directly to a patient or used to modify cells taken from the patient, after which the cells are returned to the patient.

In gene therapy, only somatic cells are modified. Modification of germ cells is prohibited due to ethical and safety concerns. The risk of inadvertent germline modification when using viral vectors is considered to be absent. The vectors appear to be unable to cross the germline barrier: viral DNA can be detected in the semen of patients and laboratory animals, but the vector is in the fluid or the lymphocytes and not in the sperm cells.

Meanwhile, other forms of gene therapy are developed at a rapid pace. The first CRISPR-Cas gene therapy has now been approved and RNA applications are expected shortly. Many of the new gene therapies are no longer based on viral vectors.

However, the use of these non-viral ‘gene delivery’ systems raises questions about whether they could cross the germline barrier. It is known that germ cells and somatic cells in the gonads communicate with each other via so-called gap junction connections, endocytosis and extracellular vesicles. These transport nutrients, hormones, proteins and small RNAs to the germ cells. Since extracellular vesicles can reach germ cells and transfer their contents, the possibility cannot yet be ruled out that, for example, a lipid nanoparticle with a CRISPR/Cas construct could also do this.

This research project will inventory the latest knowledge on germline transport and non-viral delivery systems. It will also examine the data on unintended germline modification in animal experiments and in clinical studies performed in humans. Using these data, an attempt will be made to analyse the possible chance of unintended germline modification. In addition, an attempt will be made to gain insight into the requirements of other authorities regarding preclinical data on germline transmission before proceeding to ‘first in human’ studies.

The present project is a collaboration with the Central Committee on Research Involving Human Subjects (CCMO)