It is interesting to note that the idea of using PCs or PRs emerged from an early observation where ΔF508 CFTR, a single phenylalanine deletion mutant found in more than 85% of cystic fibrosis alleles was functional when expressed in Xenopus oocyte grown at room temperature (Drumm et al., 1991). This evidence concerns the gene CFTR and cystic fibrosis.