Table 1

Viral vector properties and clinical implications on efficacy and safety

Adeno-associated virusAdenovirusSimple retrovirusLentivirusHerpes virus
Transgene carrying capacity<5 kb<8 kb8 kb9 kb30–40 kb
Integration into host genomeNoNoYesYesNo
Target cell populationMitotic and quiescent cellsMitotic and quiescent cellsMitoticMitotic and quiescent cellsMitotic and quiescent cells
Transgene expression durationLong term
(in quiescent cells)
Short termLong termLong termLife-long
ImmunogenicityModerateHighLowLowHigh
Insertional oncogenesis riskLowLowVery highModerateLow
Oncolytic potentialNoYesNoNoYes
Risk of human pathogenicity*NegligiblePossible but low riskHighHighPossible but low risk
Comments on clinical utilityOnly vector to be approved and licenced for clinical use in neurological disease†Reduced utility in patients due to significant immunotoxic effectsReduced utility in patients due to significant oncogenetic potentialEx vivo strategies used due to reduced penetrance of BBB in adultsEffective in malignant brain tumours secondary to oncolytic potential
  • Transgene expression duration: short term=days to weeks, long term=months to years, lifelong=occurs in sensory neurons of peripheral nervous system after herpes simplex-based viruses establishes latency in dorsal root ganglion.

  • *Pathogenicity after emergence of viral replication ability in vivo.

  • †Food and Drug Administration approval of AVXS-101 in 2019 for treatment of spinal muscular atrophy.

  • BBB, blood–brain barrier.