Genome editing for clinically relevant mutations in genetic diseases and cancer

The present thesis concerns of two sections. The first one focuses on the application of Cluster Regularly Interspaced Short Palindromic Repeats (CRISPR) system as a tool for precise genome targeting and genome editing; the association between specific endonuclease and RNA guides complementary to the DNA target allows its targeting with single-nucleotide precision. CRISPR/Cas is able to perform Double-Strand Breaks (DSBs) at a target site which are soon repaired by cellular repairing mechanism, non-homologous end joining (NHEJ) or homology-directed repair (HDR). The first part of my project aims to explore and demonstrate the efficacy of a personalized therapeutic approach based on the CRISPR/Cas9 technology associated with adeno-associated viral vectors (AAVs)s, a mutation-specific gene therapy to restore mutated genes in genetic diseases to their original sequence trough the HDR-mediated correction. I developed an mCherry/EGFP reporter cassette where the reporter gene bears a mutation-specific target. It connects the mCherry and the EGFP (out of frame) coding sequences. Due to a frameshift, the reactivation of the EGFP allows the visualization of cells in which Cas9 had targeted the mutation-specific sequence leading to the production of Indels. I worked to edit mutations involved in specific genetic diseases such as mutations in FOXG1 or in MECP2, which are responsible for Rett syndrome, in the IQSEC2 gene that causes an intellectual disability clinically related to the Rett syndrome and in COL4A3 and COL4A5 causing Alport syndrome. In the second part of my study, I worked on developing a gene editing system aims to selective targeting to cancer cells while preserving the genetic integrity of normal cells. To this aim, I plan to exploit microhomology-mediated end joining (MMEJ) through Cas12a, an RNA-directed endonuclease that causes double-strand breaks with staggered ends, to insert in-frame the Herpes Simplex Virus –Thymidine Kinase suicide gene to trigger cell death. I designed and developed a construct to target a patient-specific single nucleotide variant within a coding sequence of the TP53 gene, from a patient with Chronic Lymphocytic Leukemia characterized by clonal expansion of clones bearing this TP53 mutation. I am able to detect the proper integration of the suicide gene sequence by analyzing the treated cells by fluorescence-activated cell sorting (FACS). Indeed, a green fluorescent protein (EGFP) sequence is linked to the TK by a 2A peptide system, thus green fluorescent cells are also the one expressing for the TK gene. The second section of my thesis concerns the COVID-19 pandemic global crisis and the need to understand how best to study and treat COVID-19. A key focus is sharing and analyzing data to learn about the genetic determinants of COVID-19 susceptibility, severity, and outcomes. In particular, my work has been focused on the TLR7 gene that has been involved as an important pattern recognition receptor for the ssRNA of SARS-CoV-2. We demonstrate that rare loss-of-function variants in the TLR7 gene in young men with severe COVID-19 and with no prior history of major chronic diseases were associated with impaired TLR7 signaling and type I and II IFN responses.