Het gebruik van rectale organoïden voor diagnostiek en gepersonaliseerde geneeskunde bij mucoviscidose

In recent decades, cystic fibrosis (CF) has evolved from a devastating disease with a dire prognosis to a chronic but manageable disease in most cases. However, challenges still remain in the treatment and diagnosis of CF. In most cases, a diagnosis of CF is straightforward: the combination of a clinical presentation with either a high sweat chloride concentration (SCC) or identification of 2 CF-causing CFTR variants is sufficient. When the SCC is intermediate and the CFTR genotype undefined, the diagnosis remains inconclusive. Nasal potential difference (NPD) and intestinal current measurement (ICM) are advised for these cases. However, these physiological CFTR assays are not readily available and not feasible in most healthcare settings. Further complicating CF diagnostics are the newborns labelled 'cystic fibrosis screen positive, inconclusive diagnosis' (CFSPID) and the wider range of CFTR-related disorders (CFTR-RD), as well as the large number of CFTR variants of unknown significance. With the advent of CFTR modulators, efficacy of therapy in CF has increased dramatically. Their mode of action is specific to the molecular defect in the CFTR protein, and thus the genotype. Recording drug response in the patient's own tissue could predict treatment efficacy and thus aid in tailoring treatment. Recent years have seen an increasing use of rectal organoids in CF research. These are grown from stem cells obtained through a rectal biopsy and consist of an epithelial monolayer surrounding a central lumen. Chloride transport and consequent water movement into the lumen is mediated by CFTR. Organoid swelling is thus a measure of CFTR function, either at baseline or when modulated with compounds. Cultures can be expanded indefinitely for use in experiments or biobanking. In this project, the potential of organoids to fill in the gaps in CF research was explored. Rectal organoid morphology analysis (ROMA) was developed as a new physiological CFTR assay based on quantification of morphological differences between organoids from subjects with and without CF, showing complete discrimination between these two groups. For those with an inconclusive diagnosis, ROMA provided additional information with diagnostic classification in 75% of cases. ROMA can be performed at all ages, the image analysis has been standardised and is largely automated, and analysis can be centralised. Rectal organoids can also be used to predict response to modulator therapies and to help in characterisation of CFTR variants, as they have the benefit of stably retaining all of the individual's genetic and epigenetic background. A case series is presented including a person with CF (PwCF) with an unusually mild phenotype for the CFTR genotype. By measuring ROMA indices and organoid swelling in response to treatment, the complex CFTR allele carried by this PwCF was further characterised, in turn informing treatment allowing for a personalised medicine approach. Organoids have thus proven their potential in diagnostics, personalised medicine, and CFTR variant characterisation. Future work on ROMA will focus on inclusion of more equivocal cases, including CFTR-RD and CFSPID. ROMA could also be used to more accurately predict responses to treatments, especially in PwCF carrying CFTR variants with high residual function.