In vivo selection of CD4⁺ T cells transduced with a gamma-retroviral vector expressing a single-chain intrabody targeting HIV-1 tat

We evaluated the potential of an anti-human immunodeficiency virus (HIV) Tat intrabody (intracellular antibody) to promote the survival of CD4 ⁺ cells after chimeric simian immunodeficiency virus (SIV)/HIV (SHIV) infection in rhesus macaques. Following optimization of stimulation and transduction conditions, purified CD4⁺ T cells were transduced with GaLV-pseudotyped retroviral vectors expressing either an anti-HIV-1 Tat or a control single-chain intrabody. Ex vivo intrabody-gene marking was highly efficient, averaging four copies per CD4⁺ cell. Upon reinfusion of engineered autologous CD4⁺ cells into two macaques, high levels of gene marking (peak of 0.6% and 6.8% of peripheral blood mononuclear cells (PBMCs) and 0.3% or 2.2% of the lymph node cells) were detected in vivo. One week post cell infusion, animals were challenged with SHIV 89.6p and the ability of the anti-HIV Tat intrabody to promote cell survival was evaluated. The frequency of genetically modified CD4⁺ T cells progressively decreased, concurrent with loss of CD4⁺ cells and elevated viral loads in both animals. However, CD4⁺ T cells expressing the therapeutic anti-Tat intrabody exhibited a relative survival advantage over an 8-and 21-week period compared with CD4⁺ cells expressing a control intrabody. In one animal, this survival benefit of anti-Tat transduced cells was associated with a reduction in viral load. Overall, these results indicate that a retrovirus-mediated anti-Tat intrabody provided significant levels of gene marking in PBMCs and peripheral tissues and increased relative survival of transduced cells in vivo.