The mode and duration of anti-CD28 costimulation determine resistance to infection by macrophage-tropic strains of human immunodeficiency virus type 1 in vitro

We have investigated the ability of anti-CD28 antibody costimulation to ind uce resistance to macrophage (M)-tropic strains of human immunodeficiency v irus type 1 (HIV-1) in vitro. Our results confirm the observations of Levin e et al. (15) that stimulation of CD4 T cells with anti-CD3/anti-CD28 antib odies coimmobilized on magnetic beads renders the cells resistant to infect ion by M-tropic strains of HIV-1. The resistance was strongest when the bea ds were left in the cultures throughout the experiment. In contrast, stimul ation of CD4 T cells with the same antibodies immobilized on the surface of plastic culture dishes failed to induce resistance and resulted in high le vels of p24 production. This was true even if the cells were passaged conti nuously on freshly coated plates. If the beads were removed after initial s timulation, p24 production increased over time and produced a result interm ediate to the other forms of stimulation. For beads-in, beads-out, and one- time plate stimulated cultures, resistance to infection correlated with dow n-regulation of CCR5 expression at the cell surface and with increased prod uction of beta-chemokines. However, cultures of CD4 T cells continuously pa ssaged on anti-CD3/anti-CD28-coated plates produced large amounts of p24 de spite decreased levels of CCR5 expression and increasing production of beta -chemokines. Expression of the T-cell activation markers CD25 and CD69 and production of gamma interferon further supported the differences in plate v ersus bead stimulation. Our results explain the apparent contradiction betw een the ability of anti-CD28 antibody costimulation to induce resistance to HIV infection when presented on magnetic beads and the increased ability t o recover virus from the cells of HIV-positive donors who are on highly act ive antiretroviral therapy when cells are stimulated by anti-CD3/anti-CD28 immobilized on plastic dishes.