CAL27 cells expressed HPV 16 in vitro only after transfection. RT-PCR from total RNA demonstrated that CAL27, HTB-32, and GH354 cells did not express HPV16 mRNA (A: lanes 1–3) but did express laminin-5 γ2-subunit, the positive control (A: lanes 4–6). RT-PCR confirmed transfection efficiency using HPV18-vector (B: lane 4), compared to HPV18-/HPV+ cell lines, HTB-32 and GH354 (B: lanes 3, 5); no cell lines expressed HPV16-specific mRNA (B: lanes 1, 2, 6). CAL27-HPV16-transfectants expressed HPV16-specific mRNA (C: lane 3) but not HPV18-mRNA (C: lane 5) and CAL27-HPV18 transfectants expressed HPV18-specific mRNA (C: lanes 4) but not HPV16 (C: lane 6). CAL27 controls expressed neither HPV16 nor HPV18 mRNA (C: lanes 1, 2). Densitometry measurements of relative endpoint RT-PCR band intensities for endogenous HPV (GH354) were compared to HPV18 controls (D). CAL27 HPV-transfectant mRNA levels were compared with positive controls (E).