Syncytins enable novel possibilities to transduce human or mouse primary B cells and to achieve well-toleratedin vivogene transfer

Abstract

One Sentence Summary: Syncytins are fusogenic cellular proteins that can pseudotype lentiviral gene transfer vector particles, achieving efficient gene transfer into primary quiescent B cells and reducing the in vivo immunogenicity of the particles following systemic administration. AbstractSyncytins are cellular transmembrane glycoproteins with fusogenic and immunosuppressive properties that are encoded by endogenous retroviral envelope sequences in mammalian genomes. Based on their properties, syncytins may be useful to pseudotype lentiviral gene transfer vectors (LV) and to obtain well-tolerated in vivo gene delivery but their cellular targets are unknown in this context. We pseudotyped LV with human or murine syncytins. Such LV-Syn particles were infectious in vitro but required a transduction additive, as do other retroviral envelope LV pseudotypes. In these conditions, LV-Syn remarkably transduced quiescent human or murine primary B cells at high level in vitro including naïve blood B cells or B cell precursors from murine bone marrow. Transduced human B cells could be expanded in culture and were functional. Human or murine T cells were transduced less efficiently than B cells, in agreement with lower levels of syncytin receptors on T cells compared to B cells. Well-tolerated in vivo gene transfer was possible without additive, as demonstrated with murine syncytin Amediated gene delivery in C57BL/6 mice. A single intravenous injection of LV-SynA vector to mice led to stable gene transfer into spleen germinal center B cells. LV-SynA were also intrinsically less immunogenic than LV-VSVG, leading to low antibody responses against the vector capsid. This is the first evidence of interactions between syncytins and B cells, providing novel opportunities for B cell genetic engineering and for well-tolerated gene transfer in vivo. The findings also suggest that some immunosuppressive properties of syncytins could be mediated by B cells.word count : 250

Mammalian retrovirus-like protein PEG10 packages its own mRNA and can be pseudotyped for mRNA delivery

“…Pseudotyped particles were incubated with tail-tip fibroblasts from loxP-tdTomato reporter mice, a cell type that we have found amenable to transduction by these fusogens. Based on previous reports, we added the transduction enhancer vectofusin-1 to the supernatant for MmSYNA and MmSYNB particles to enhance in vitro transduction ( 25 ). In these primary cells, both VSVg and MmSYNA enabled SEND-mediated functional transfer of Mm.cargo(Cre), whereas MmSYNB did not (Fig.…”

Delivering mRNAs to mouse tissues using the SEND system

“…This is based on the following experiments and observations reported by others. Prior reports demonstrate that SynA and SynBpseudotyped lentiviral vectors could be transfected into primary mouse splenocytes with relatively high efficiencies whereas lentiviral delivery to murine spleen in vivo was only moderately efficient 17 that was below the detection threshold of our experimental methods. Further, the receptor for SynA, lymphocyte antigen 6 family member E (Ly6e), is highly expressed in murine spleen (in addition to liver, lung, and placenta) and mediates cell-cell fusion upon binding with SynA, [18][19][20] which suggests that fusogens like SynA and SynB could be involved in SEND-VLP phenomenon in spleen but again our experiments may not have been sensitive enough to detect it.…”

“…This is based on the following experiments and observations reported by others. Prior reports demonstrate that SynA and SynB-pseudotyped lentiviral vectors could be transfected into primary mouse splenocytes with relatively high efficiencies whereas lentiviral delivery to murine spleen in vivo was only moderately efficient 17 . The absence of transduction in spleen cells in our experiments with SynA or SynB was possibly because the effect of VLPs (unlike lentiviral vectors) was too weak for detection.…”