Table 1.

Summary of gene transfer technologies. AAV: adeno-associated virus; ASO: antisense oligonucleotides; siRNAs: small interfering RNAs; CRISPR/Cas9: Clustered Regularly Interspaced Short Palindromic Repeats; NHEJ: nonhomologous end-joining

APPROACH	TECHNOLOGY	STRENGTHS	WEAKNESSES	POTENTIAL THERAPEUTIC TARGETS
Overexpression	AAV	Safe for use in humans Nonreplicating Low risk of insertional mutagenesis Noncytotoxic, modest immune response Efficient transduction of dividing and nondividing cells Strong and sustained transgene expression for months to years	Limited packaging capacity ~4.9 kb Artificial expression cassettes do not preserve endogenous regulation High frequency of neutralizing antibodies to AAV capsids in humans T-cell responses to capsid managed with immunosuppression	Pursued LPL LDLR Possible LCAT APOE APOC2 APOA1 LIPA LIPC LDLRAP1 GPIHBP1
Knockdown	ASOs	Efficient knockdown by RNAse H recruitment or translation blocking Splicing modulation by targeting pre-mRNA Chemically modified for improved liver uptake Efficient long-term silencing with weekly or biweekly administration Subcutaneous injection	Chemical modifications needed to increase nuclease resistance and half-life Possibility of sequence-related off-targets Potential class effects depending on modifications Mild skin reactions	Pursued APOB APOC3 ANGPTL3 LPA Possible PCSK9
	siRNA	Efficient knockdown by RNAi machinery Long-term silencing can be achieved Chemically modified for direct liver uptake Can also be effective at lower doses via lipid nanoparticle delivery	Possibility of sequence-related off-targets Potential class effects depending on modifications Some formulations require intravenous injection	Pursued PCSK9 Possible APOB APOC3 ANGPTL3 LPA
Genome editing	CRISPR/Cas9	Ease of design and customization High NHEJ-mediated editing efficiency Multiplex genome editing capacity Correct gene dosage Preservation of regulatory elements One-time treatment Permanent correction to patient's own DNA	Potential off-target activity that requires careful testing Potential unintended consequences at the DSB site (i.e., large insertions/deletions) Low efficiency of HDR-mediated gene correction (restricted to dividing cells) Potential immune response against Cas9-expressing cells	Possible APOB APOC3 ANGPTL3 PCSK9 LPA