hf-HSV amplicon–mediated expression of CD40L leads to an up-regulation of endogenous CD80 (B7.1).

CLL cells were left untreated or were transduced with equivalent transduction units of hf-HSVlac or hf-HSVCD40L. Cell surface expression of B7.1 was assayed by fluorescence-activated cell sorting; representative flow diagrams for each treatment are shown. Cell number quantitation is represented on the y-axis, whereas the x-axis illustrates positive B7.1 staining. hf-HSVCD40L–infected CLL cells (heavy line, both panels) shows preferential up-regulation of B7.1 compared to uninfected CLL cells (A, shaded curve) or CLLs transduced with hf-HSVlac (B, shaded curve). Average percentages of CLL cells staining positive for CD80 for each treatment group were as follows: 3% for uninfected control CLL cells, 11% for hf-HSVlac–infected cells, and 62% for hf-HSVCD40L–infected cells. Data are representative of 4 different patient samples.