MHC class 1 expression is lost in CLL cells transduced with helper virus–containing amplicon stocks but not with helper virus–free stocks.

CLL cells were isolated from human subjects and were left untreated (A) or were transduced with equivalent transduction units of hf-HSVB7.1 (B) or HSVB7.1 (C). Cell surface expression of B7.1 and MHC class I was assayed by fluorescence-activated cell sorting, and representative flow diagrams for each treatment are shown. The y-axis illustrates positive B7.1 staining increasing from bottom to top, and the x-axis illustrates positive MHC class I staining increasing in intensity from left to right. Transduction with HSVB7.1 results in loss of MHC class I positivity in a significant proportion of B7.1-expressing cells (C), whereas cells infected with hf-HSVB7.1 maintain cell surface expression of both B7.1 and MHC class I. Data are representative of 1 of 4 different samples.