CD8+ Cell Suppressor Effect on In Vitro Expression of HIV-1

Abstract

Peripheral blood mononuclear cells (PBMCs) from a panel of nine HIV-1 infected patients with well characterized patterns of virus isolation were used to evaluate the efficacy of virus isolation from enriched T-helper (CD4+) cells and to investigate the influence of T-suppressor (CD8+) cells on in vitro HIV-1 expression. Three patients were selected and grouped into each of three categories defined by the virus isolation rates obtained from their PBMCs co-cultured with mitogen induced actively replicating normal human PBMCs: a) high virus isolation category (89-99% isolation with 1 x 10^5 PBMCs), b) intermediate virus isolation category (50-75% isolation with 1 x 10^5 PBMCs), c) low virus isolation category (2-12% isolation with 1 x 10^5 PBMCs). Throughout these studies, PBMCs from patients in both the high and intermediate isolation categories yielded similar virus isolation rates to those obtained historically when the normal donor PBMCs (feeder cells, also referred to as target cells due to their CD4+ cell content) were actively replicating at the time of co-culture initiation. The isolation rate, however, dropped significantly (P<0.01) when feeder PBMCs were added to patient PBMCs and then activated mitogenically. Virus isolation from cultured patient PBMCs, without supplemental target cells, was generally unsuccessful; only two patients in the high virus isolation category yielded virus under these conditions. In contrast, HIV-1 was readily isolated from CD4+ cell enriched cultures and, in most cases, virus was generally more efficiently isolated from CD4+ cells than from co-cultures of patient PBMCs and donor target cells. Compared to their unseparated PBMC co-cultures with target cells, overall virus isolation from CD4+ cell enriched cultures from the high and intermediate virus isolation groups were enhanced 1.6-fold and 3.8-fold, respectively. Reconstitution of CD4+ cell enriched cultures with autologous CD8+ cells, however, significantly reduced virus isolation. This reduction varied somewhat between patients and was dependent on the number of CD8+ cells used in the reconstitution. With all patients who released virus in vitro, virus expression was totally suppressed at a CD8+ to CD4+ cell ratio equal to one. These data provide evidence supporting the thesis that CD8+ cells play a major regulatory role in HIV-1 expression and the spread of infection.