Table 2.

Overview of donor DNA templates for HDR and their key features.

Template Type	Key Modifications	Suitable Applications	HDR Increase	Limitations
Viral Templates	Capsid engineering [67]	T cells, HSCs, and in vivo editing	Between ~3 and ~25-fold	Integration risk; immune response [70,71]
	Synthetic RNA-targeting sequences [69]
ssODNs	Chemically modified (phosphorothioate) [82,83]	Point or small mutations; T cells, HEK293T, K562, and HSCs	~21% HDR	Limited capacity for large insertions
	Retron systems and transcription-coupled systems [85,86]		Between ~15% and ~60% HDR
cssDNA	High stability; reduced degradation; minimizes off-target integration [91,92]	Precise small edits; iPSCs and T cells	Between ~20% and ~70% HDR	Limited capacity for large insertions
Plasmid Templates	Synthetic RNA-targeting sequences [93,94,95]	Large insertions in immortalized cell lines	Between ~10% and ~30% HDR	Cytotoxicity at high concentrations [96,97]
Linear dsDNA	TEG or RNA::DNA hybrids [98]	Large insertions with homology arms (200–800 bp), can be used in primary cells, γδ-T cells, and NK cells	~80% HDR	Cytotoxicity; random integration risks [96,97]
	Doggybone DNA [99]
	Target sequences (tCTS) [100]		Between ~15% and ~30% HDR
	Biotinylation [101]		~80%

HDR efficiency reported in the table is context-dependent and varies based on donor template type, cell type, and delivery strategy. Viral vectors such as AAV demonstrate high HDR enhancement but pose risks of immune responses and genomic integration. Chemically modified ssODNs enable precise small edits, while cssDNA offers improved stability. Linear dsDNA with hybrid modifications or biotinylation can reach high HDR but may introduce cytotoxicity and random integrations. Plasmid-based repair templates support large insertions but show variable efficiency and potential toxicity at high concentrations.