A narrative review of in utero gene therapy: advances, challenges, and future considerations

Abstract

The field of in utero gene therapy (IUGT) represents a crossroad of technologic advancements and medical ethical boundaries. Several strategies have been developed for IUGT focusing on either modifying endogenous genes, replacing missing genes, or modifying gene transcription products. The list of candidate diseases such as hemoglobinopathies, cystic fibrosis, lysosomal storage disorders continues to grow with new strategies being developed as our understanding of their respective underlying molecular pathogenesis increases. Treatment in utero has several distinct advantages to postnatal treatment. Biologic and physiologic phenomena enable the delivery of a higher effective dose, generation of immune tolerance, and the prevention of phenotypic onset for genetic diseases. Therapeutic technology for IUGT including CRISPR-Cas9 systems, zinc finger nucleases (ZFN), and peptide nucleic acids (PNAs) has already shown promise in animal models and early postnatal clinical trials. While the ability to detect fetal diagnoses has dramatically improved with developments in ultrasound and next-generation sequencing, treatment options remain experimental, with several translational gaps remaining prior to implementation in the clinical realm. Complicating this issue, the potential diseases targeted by this approach are often debilitating and would otherwise prove fatal if not treated in some manner. The leap from small animals to large animals, and subsequently, to humans will require further vigorous testing of safety and efficacy.

Keywords: Fetal therapies; gene editing; genetic therapy; prenatal diagnosis.

Figure 1

Lentiviral transduction of cells resulting in either episomal expression or integration into the host genome.

Figure 2

CRISPR-Cas9 system demonstrating the creation of double-stranded break in DNA followed by either NHEJ generating Indels or HDR with insertion of donor DNA. Cas9, CRISPR associated protein 9; sgRNA, single guide RNA; Indel, insertion/deletion; NHEJ, nonhomologous end joining; HDR, homology directed repair.

Figure 3

Structure and mechanism of gene therapy using PNA to promote homology directed repair. (A) Peptide nucleic acid (PNA) backbone demonstrating electrical neutrality; (B) PNA forming triple helical structure triggering homology directed repair with donor DNA.