The analysis was conducted on three splicing mutations 711+5G->A, 1898+3A->G e c.2657+5G>A that affect respectively exons 5, 13, and 16. In vitro analysis with minigene assays identifies for each mutation a panel of active ExSpeU1s. Focus was directed to study expecially c.2657+5G>A mutation. Lentiviral mediated delivery of ExSpeU1s molecules showed the 16 exon splicing correction, that produced rescue of normal CFTR protein. These results highlight the potential therapeutic efficacy of ExSpeU1s delivered by lentiviral to correct this mutation and pave the way for a mutation-specific therapy in CF splicing defects.