TCR-INDEPENDENT CD28-MEDIATED GENE-EXPRESSION IN PERIPHERAL-BLOOD LYMPHOCYTES FROM DONORS CHRONICALLY INFECTED WITH HIV-1

Complete activation of peripheral blood T cells requires both T-cell r eceptor (TCR) stimulation and CD28 costimulation. Signalling pathways associated specifically with CD28 are not well understood, however, be cause ligation of CD28 in the absence of TCR stimulation does not give rise to cellular responses in normal cells. In peripheral blood lymph ocytes (PBL) from donors chronically infected with human immunodeficie ncy virus-1 (HIV-1), CD28 can induce viral replication through an alte rnative pathway that does not require TCR ligation. We have exploited this observation to study CD28-mediated signal transduction using reve rse transcriptase-mediated polymerase chain reaction (RT-PCR) to ampli fy viral RNA. Independent ligation of CD28 on donor PBL induced expres sion of the HIV-1 tat gene but not the interleukin-2 (IL-2) gene. Vira l induction did not occur following pretreatment of cells with actinom ycin D, suggesting it was mediated through transcriptional activation of the viral long terminal repeat (LTR). rat was induced in the presen ce of the protein kinase C inhibitor H-7, but was inhibited by cyclosp orin A. Our results demonstrate that CD28 is linked directly to specif ic signalling pathways leading to de novo induction of genes in PBL.