Table 2.

The Rate of Production of HSV-tk^- Cells in EJ-30 Clones with Telomeric or Interstitial Integration Sites.

Cell Clone	HSV-tk-*	neo+/HSV-tk-*
Telomeric
A3	1.3x10-4	1.6x10-6
B3	1.3x10-4	6.9x10-7
Interstitial†
B1–2	3.4x10-6	<10-7
E1	5.1x10-7	<10-7
F1	9.2x10-7	4.1x10-7

^*The rate of production of HSV-tk^- or neo⁺/HSV-tk^- cells was determined from the frequency of colonies resistant to ganciclovir or G418 and ganciclovir, respectively (see Materials and Methods section).

^†Clones used for analysis of interstitial integration sites lacked diffuse bands but had an intact HSV-tk gene, as demonstrated by Southern blot analysis and sensitivity to ganciclovir.