Regulation of DNA fragmentation in a CD28-transfected murine T-cell hybridoma by B7.1- or B7.2-expressing cells. DWT6.11 cells were seeded for 8 hours in a 24-well plate in the presence or absence of CD3 MoAb and/or of L cells expressing a transfected B7.1 cDNA (LB7.1) or B7.2 cDNA (LB7.2), as indicated. After this incubation period, DNA was extracted and analyzed on a 1% agarose gel containing ethidium bromide. Lane 1, untreated cells; lane 2, anti-CD3; lanes 3 to 6, LB7.1 cells alone at the DWT6.11:LB7.1 cell ratio 2:1, 4:1, 10:1, and 20:1, respectively; lanes 7 to 10, plus anti-CD3; lane 11 to 14, LB7.2 cells alone at the DWT6.11:LB7.2 cell ratio 2:1, 4:1, 10:1, and 20:1, respectively; and lanes 15 to 18, plus anti-CD3.