Recombination of replicon and helper RNAs and the emergence of propagation-competent vectors upon Sindbis virus vector production

Abstract

Sindbis vectors have shown remarkable antitumor efficacy and tumor-targeting capacity in animal models and hold promise for cancer therapy. Different packaging systems are used to produce propagation-incompetent Sindbis vectors. However, the vectors produced using either DH-BB single helper RNA or split helper RNA can spread in permissive cell cultures. We investigated the mechanisms of vector spreading and show, here, that recombination occurs between the replicon and DH-BB helper RNA, leading to formation of the full-length virus genome. Split helper RNA may not completely prevent wild-type reversion, although the frequency is greatly reduced. Contrary to propagation of Sindbis DH-BB vectors, Sindbis split helper vectors were frequently able to spread without cytopathic effect (CPE), a feature that was linked to wild-type reversion. Our results support the hypothesis that the non-cytopathic local spreading constantly observed with Sindbis split helper vector results from unspecific packaging of helper RNAs into vector particles and co-infection with particles containing replicon and helper RNAs. Several malignant cell lines with defective interferon responses were found to be permissive for non-cytopathic spreading of the Sindbis split helper vector. Interferon-α suppressed the spreading providing a possible option to control the vector.

Replicating viral vector platform exploits alarmin signals for potent CD8+ T cell-mediated tumour immunotherapy

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“…2a–d ) should enable industrial exploitation. During scale-up in batch production, but also upon administration to vaccinees, rearranged genomes with a fitness gain are readily selected 32 56 , compromising product safety as well as efficacy 29 30 . Accordingly, stable transgene expression and attenuation of artLCMV, together with the simplicity and rapidity of vector generation, represent critical assets for clinical translation and the vector's exploitation in personalized medicine approaches 57 .…”

Virally vectored vaccine delivery: medical needs, mechanisms, advantages and challenges

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