TABLE 5.

Relative susceptibility of human adherent cell lines to infection by PERV-NIH-2° pseudotypes

Origin	Cell line	% Controla	[3H]TTP incorporated (cpm)b	Signal by RT-PCRc
Clear cell kidney carcinoma	CaKi-1	0	NDd	ND
Cervical adenocarcinoma	HeLa	1	ND	ND
Osteosarcoma	HOS	3.6	ND	ND
Hepatoblastoma	HepG2	90	6,201	+
Fibrosarcoma	HT1080	39	1,237	+
Colorectal adenocarcinoma	CaCO-2	ND	Bkgd	+

^aResults were normalized to the infectivity titer observed on 293 cells exposed to the same PERV-NIH-2° pseudotype-containing supernatant (see Materials and Methods). Titers on 293 cells varied from 500 to 3,000 BFU/ml in different experiments. In the case where 0 is reported, no β-galactosidase-positive cells were observed after exposure of 30,000 to 40,000 cells to 1.0 ml of virus-containing supernatant. 

^bValues shown are for cell supernatant from cultures maintained for 8 weeks, determined in an RT assay performed as previously described (18), with background values subtracted. The background value is obtained from a matched uninfected control assayed at the same time point as the culture exposed to virus. If the value observed for the virus-exposed culture is <2-fold greater than the background value, it is reported as Bkgd. 

^cThe 8-week cell supernatant was examined for presence of viral RNA by RT-PCR as described in Materials and Methods. 

^dND, not determined.