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RNA interference (RNAi) is a potent and specific gene silencing mechanism that utilizes small -double-stranded RNA intermediates (small interfering RNAs or siRNAs) to target homologous mRNA sequences for degradation. The therapeutic potential of RNAi for HIV infection has been demonstrated in many studies. However, successful clinical application of RNAi is contingent on developing practical strategies to deliver siRNA to the desired target cells and tissues. Recently, there has been significant progress towards developing reagents that selectively deliver exogenous siRNA to immune cells that are targeted by HIV or involved in viral pathogenesis, such as T cells, macrophages, and dendritic cells. Here, we describe details of two antibody-based strategies for systemic delivery of siRNA either specifically to T cells via the CD7 receptor or to multiple immune cell types via LFA-1, present on all leukocytes.

Dendritic cells (DCs) are potent antigen-presenting cells that play a critical role in the activation of T cells. RNA interference (RNAi)-mediated silencing of negative immunoregulatory molecules expressed by DCs may provide a strategy to enhance the potency of DC-based vaccines and immunotherapy. Ablation of suppressor of cytokine signaling-1 (SOCS-1) in antigen-presenting cells has been shown to enhance cellular immune response in mice. Here, we used a previously reported DC-targeting approach to deliver small interfering RNA (siRNA) against SOCS-1 to human myeloid-derived DCs (MDDCs). SOCS1-silencing in MDDCs resulted in enhanced cytokine responses to lipopolysaccharide (LPS) and a strong mixed-lymphocyte reaction. Moreover, only DCs treated with SOCS-1 siRNA, and not controls, elicited strong primary in vitro responses to well-characterized HLA-A*0201-restricted Melan-A/MART-1 and human immunodeficiency virus (HIV) Gag epitopes in naive CD8(+) T cells from healthy donors. Finally, stimulation of CD8(+) T cells from HIV-seropositive subjects with SOCS1-silenced DCs resulted in an augmented polyfunctional cytotoxic T-lymphocyte (CTL) response, suggesting that SOCS-1 silencing can restore functionally compromised T cells in HIV infection. Collectively, these results demonstrate the feasibility of DC3-9dR-mediated manipulation of DC function to enhance DC immunogenicity for potential vaccine or immunotherapeutic applications.