Further Evaluation of Soluble CD4 as an Anti-HIV Type 1 Gene Therapy: Demonstration of Protection of Primary Human Peripheral Blood Lymphocytes from Infection by HIV Type 1

We previously reported on the construction of retroviral vectors that produce a secreted form of the HIV-1 receptor, T cell antigen CD4 (Morgan et al., AIDS Res Hum Retroviruses 1990;6:183-191). In this article we test the ability of these sCD4-expressing retroviral vectors to protect human T-cell lines or primary T cells from HIV-1 infection. To demonstrate that protection from HIV-1 infection is mediated by the soluble nature of this protein, two coculture protection experiments were conducted. In these experiments, sCD4-expressing retroviral vectors were used to engineer mouse NIH 3T3 cells. In one coculture experiment the human SupT1 cell line was added directly to the culture of sCD4-producing NIH 3T3 cells, and in another experiment the two cell types were separated physically by a semipermeable membrane. In both coculture configurations, the T cell line was protected from HIV-1 challenge as measured by syncytium formation and indirect immunofluorescent assays. In addition, the SupT1 line was directly engineered with sCD4-expressing retroviral vectors and shown to be protected from HIV-1 challenge. As a prelude to further preclinical studies, we tested the ability of retroviral vectors to transduce primary human peripheral blood lymphocytes (PBLs). Conditions used to stimulate T cell growth resulted in significant shifts in the CD4/CD8 cell in favor of CD8 cells. Retroviral-mediated gene transfer under these conditions resulted in low levels of gene transfer (<5%). By applying appropriate selection conditions, cell populations that are 30-50% gene containing can be obtained. Challenge of sCD4-engineered bulk PBLs with HIV-1 demonstrates a 50-75% inhibition in HIV-1 production. HIV-1 challenge of a coculture of sCD4-engineered CD8 PBLs with the SupTl T cells showed diminished HIV-1 infection of the SupT1 cell line, again suggesting the ability of sCD4-engineered cells to protect unengineered HIV-1 target cells in solution.