CTNS and cystinosis: In this regard, Iglesias et al.47 have shown that coculture of fibroblasts and proximal tubular cells from cystinosis patients with BMMSC-derived Exos resulted in a dose-dependent decrease in cellular cystine levels because BMMSC-derived Exos contain cystinosin, a cystine efflux channel in the lysosomal membrane.