Nanobody mediated targeting of lentiviral vectors to dendritic cells: implications for cancer immunotherapy.

Nanobody mediated targeting of lentiviral vectors to dendritic cells: implications for cancer immunotherapy

Lentiviral vectors (LVs) encoding tumour antigens are ideal candidates for anti-cancer vaccination, since they deliver the transgene as well as activation stimuli to dendritic cells (DCs) in situ. A critical step to improve LV safety while retaining its efficacy is to avoid off-target transduction. We developed the nanobody display technology to target LVs to DCs (and macrophages). This innovative approach exploits the budding mechanism of LVs to incorporate a nanobody and a binding-defective but fusion-competent form of VSV.G in the viral envelope. Four nanobodies were used: BCII10, DC2.1, DC1.8 and R3_13. These were shown to bind to beta-lactamase, DCs and macrophages of mouse and human origin, mouse DCs and human DCs respectively. We first generated producer cell lines stably expressing a membrane bound form of these nanobodies to produce high titer LVs. Next selective transduction in situ of conventional DCs (DC1.8) or the latter, plsasmacytoid DCs and macrophages (DC2.1) was shown upon intranodal administration of targeted LVs in C57BL/6 mice. Importantly, selective transduction of human lymph node-derived myeloid DCs (R3_13), or these, plasmacytoid DCs and macrophages (DC2.) was demonstrated in vitro. Using the mouse model, we further demonstrated in vitro that targeted LVs induce less TNF-alfa production by DCs than broad tropism LVs. Consequently the transgene-specific CD8+ T cell response was less pronounced. This can be partially explained by the lack of TLR2 activation by targeted LVs. Nevertheless, targeted LVs induced a robust transgene-specific CD8+ T cell response in vivo, demonstrating their potential as an off-the-self vaccine.