Intestinal organoids
Intestinal organoids are derived from rectal biopsies of individual patients. The biopsied cells form three dimensional structure of epithelial cells in vitro. As these intestinal cells have CFTR channels, in cells with functioning CFTR, the addition of forskolin will open the CFTR channels allowing for water uptake and the organoid will swell. As would be expected, in the absence of a modulator, the organoid will not exhibit forskolin-induced swelling If a modulator is present and effective, organoid swelling will be observed. Researchers have used organoids to test the effects of modulators on individual patients. Organoids include the specific cells of a patient in a three dimensional in vitro model, which can potentially be compared to the patient’s individual clinical improvements with a specific modulator therapy. There have been two studies using organoids to study CFTR modulators in 2020. One group, mentioned above in the LCI endpoint section, studied the effectiveness of iva and compared the clinical and in vitroorganoid endpoints18. In the randomized placebo-controlled, crossover study of 38 subjects (37 completed), with either the 3849+10kbCT or D1152H mutation, intestinal organoids cultures were successfully established in 29 out of 33 biopsies, but only 25 intestinal organoid cultures met quality control standards. Swelling of organoids (indicating appropriate action of iva) occurred in 23 out of 25 patients, but there was no correlation (using Pearson correlation analysis) between the degree of clinical improvement (sweat chloride, LCI, FEV1pp) and the degree of swelling of the organoids for these subjects with the D1152H or 3849+10kbCT mutation. Of note, the clinical improvements were small and measured over an 8 week period. In a separate study of patients with the A455E mutation, based on in vitro organoid data, 20 pwCF over age 12 were included in a randomized trial of lum/iva in the Netherlands with cross-over design for 8 weeks20. With lum/iva, FEV1pp did not change significantly (0.1%). CFQ-R respiratory domain increased by 3.5 points, but this is not considered clinically significant. Sweat chloride decreased significantly by -7.8mmol/L, p=0.004, but this again may not show a biochemically relevant change, as the decreases in sweat chloride have been much greater with even lum/iva in F508del homozygotes, on the order of 20mmol/L. In vitro organoid response was seen but not correlated with sweat chloride or FEV1pp20, similar to the above findings. Both authors conclude that the use of organoids are of potential benefit to identify modulator responsive mutations, but may not predict the degree of response the patient will have in terms of clinical parameters like FEV1pp or sweat chloride18,20. One researcher postulated that a correlation between intestinal organoids and clinical phenotypes may not exist, as the clinical phenotypes took years to establish and may not be fully reversed by CFTR modulators, or may be impacted by other non-CFTR dependent factors21. It will be interesting to see the use of intestinal organoids for CFTR modulator research in the future.