NEUTRALIZATION SENSITIVITY OF CELL-CULTURE PASSAGED SIMIAN IMMUNODEFICIENCY VIRUS

CEMx174- and C8166-45-based cell lines which contain a secreted alkali ne phosphatase (SEAP) reporter gene under the control of a tat-respons ive promoter derived from either SIVmac239 or HIV-1(NL4-3) were constr ucted. Basal levels of SEAP activity from these cell lines were low bu t were greatly stimulated upon transfection of tat expression plasmids . Infection of these cell lines with simian immunodeficiency virus (SI S? or human immunodeficiency virus type 1 (HIV-1) resulted in a dramat ic increase in SEAP production within 48 to 72 h that directly correla ted with the amount of infecting virus. When combined,vith chemilumine scent measurement of SEAP activity in the cell-free supernatant, these cells formed the basis of a rapid, sensitive, and quantitative assay for SIV and HIV infectivity and neutralization. Eight of eight primary isolates of HIV-I that were tested induced readily measurable SEAP ac tivity in this system. While serum neutralization of cloned STVmac239 was difficult to detect with other assays, neutralization of SIVmac239 was readily detected at low titers with this new assay system. The ne utralization sensitivities of two stocks of SIVmac251 with different c ell culture passage histories were tested by using sera from SIV-infec ted monkeys. The primary stock of SIVmac251 had been passaged only twi ce through primary cultures of rhesus monkey peripheral blood mononucl ear cells, while the laboratory-adapted stock had been extensively pas saged through the MT4 immortalized T-cell line. The primary stock of S IVmac251 was much more resistant to neutralization by a battery of pol y clonal sera from SIV-infected monkeys than was the laboratory-adapte d virus. Thus, SIVmac appears to be similar to HIV-1 in that extensive laboratory passage through T-cell lines resulted in a virus that is m uch more sensitive to serum neutralization.