In Italy, approximately 30% of people with CF carry mutations that still lack a tailored treatment with CFTR modulator and are therefore defined as “orphan mutations”. Some of these mutations are uncharacterized and have unknown sensitivity to modulators, while for others there is already evidence that they can be rescued.
Possible differences among individuals with CF in their response to drugs as well as the increasing number of CFTR modulators that are in preclinical or clinical development highlight the need for relevant, predictive models for testing CF therapies.
Researchers collected nasal epithelial cells from about 200 people with CF carrying orphan mutations and from about 20 individuals without CF (including some parents of CF patients).
The cells were grown in the laboratory to increase their number and then allowed to form a sort of “epithelial avatars” that mimic patients’ airways.
The epithelial avatars were treated with combinations of modulators and then analyzed using several techniques: they measured chloride ions flow through the epithelium to evaluate CFTR activity, separated cell proteins to see if CFTR was present as an immature (lighter) or mature (heavier) form and, in some cases, analyzed the mRNA, used by the cell as a template to produce CFTR protein.
These tests allowed researchers to gain insights into the molecular and functional mechanisms by which orphan mutations cause CFTR loss of function and to understand if modulators can rescue mutations’ defects.
This study demonstrated that the G1244E mutation alters CFTR function in multiple ways not rescuable by a potentiator alone; it also showed that the G85E mutation rescue by Kaftrio is partial but it can be improved by adding a preclinical modulator. Finally, it allowed researchers to obtain mechanistic insights into the processing and rescue of the N1303K mutation, which differs from F508del: thanks to these observations, a compound (in therapeutic use) that could be useful as a co-treatment for N1303K and other variants was identified.
This work demonstrates that nasal cells derived from people with CF are one of the best models to study the effect of CFTR mutations. Since they replicate in a laboratory dish all the features of people’s airways, these cells are crucial to investigating and predicting the individual cell response to CFTR-modulating drugs.