Spodoptera frugiperda 9 cells

Spodoptera frugiperda 9 (Sf9) cells (Invitrogen) were cultured in SFX insect medium (HyClone, GE healthcare life science) supplemented with 1% fetal bovine serum (HyClone). Trichoplusia ni (Tn) cells (High Five) were maintained in Serum-free insect cell culture medium at 27°C. Bacmid BAC10:KO₁₆₂₉ (Zhao et al., 2003 (link)) and Bac563-5 T (Zhang et al., 2021 (link)) were propagated in E. coli strain HS996. Plasmids pTriEx-GFP, pTriEx-OD-Fc and pTriEx-Fluc were stored in our laboratory (Zhang et al., 2021 (link)).

AcHERV-triHPV was produced using a Bac-to-Bac baculovirus expression system (Invitrogen, CA, USA) according to the manufacturer’s instructions [12 (link)]. Briefly, the recombinant baculovirus was constructed to encode a codon-optimized envelope gene of human endogenous retrovirus (HERV; GenBank accession number NM014590; GenScript Corp., Piscataway, NJ, USA) and sequences of the three HPV genes, 16L1, 18 L1, and 58 L1 (kindly supplied by Dr. Schiller, National Cancer Institute, National Institutes of Health, USA) under the control of the human elongation factor1α promoter. Spodoptera frugiperda 9 (Sf9) cells were from Invitrogen (Catalog No. 11496–015), and cultured at 28°C in Sf-900 II medium (Invitrogen) supplemented with 100 units/ml of Gibco antibiotic-antimycotic (Invitrogen). AcHERV-triHPV was amplified by propagation in Sf9 cells and purified by first centrifuging at 2,000×g at 4°C for 10 minutes to remove virus-infected cell debris. Thereafter, supernatants were overlaid on a 30% sucrose cushion and centrifuged at 35,000 rpm at 4°C for 1.5 hour in a 50.2Ti rotor (Beckman Coulter Inc., CA, USA). The pellet was re-suspended in phosphate-buffered saline (PBS; Invitrogen) and used for immunization.

The bacmid BAC10:KO1629, which contains an AcMNPV genome, was maintained in E. coli strain HS996 cells as previously described [6 ]. Spodoptera frugiperda 9 (Sf9) cells (Invitrogen) were cultured in T25 Flasks or 6-well plates at 27 °C in SFX insect medium (HyClone, GE healthcare life science) containing 1% fetal bovine serum (HyClone).