Schematic demonstration of IT AAV gene delivery. In the cortex of a thymus, thymocytes develop from CD4/CD8 double-negative 1 (DN1, early T-cell precursor) to CD4/CD8 double-positive (DP) stage, and these immature thymocytes have double-strand breaks (DSBs) created by RAG enzymes in TCR genes during TCR V(D)J recombination. AAV vectors enter thymocytes through receptor-mediated endocytosis, and the released AAV and transgene DNA in the nucleus is integrated into TCR genes close to the DSBs. The thymocytes with unsuccessful TCR formation owing to the AAV transgene integration will die. The transduced thymocytes with a functional TCR will undergo the selection process, and the positively selected thymocytes will develop into CD4 or CD8 single-positive (SP4 or SP8) T cells in the medulla and eventually be released into the peripheral lymphoid tissue.