Single-cycle parainfluenza virus type 5 vectors for producing recombinant proteins, including a humanized anti-V5 tag antibody.

Parainfluenza virus type 5 (PIV5) can cause either persistent or acute/lytic infections in a wide range of mammalian tissue culture cells. Here, we have generated PIV5 fusion (F)-expressing helper cell lines that support the replication of F-deleted viruses. As proof of the principle that F-deleted single-cycle infectious viruses can be used as safe and efficient expression vectors, we have cloned and expressed a humanized (Hu) version of the mouse anti-V5 tag antibody (clone SV5-Pk1). We show that multiple different cell lines can be infected and express high levels of the Hu anti-V5 antibody, with Chinese hamster ovary cells expressing 20-50 mg l^-1 after 5 days when cells were grown to a density of ~1×10⁶ cells per millilitre at the time of infection. We suggest that PIV5-based vectors may be further developed to produce recombinant proteins both in vitro and in vivo.