치료적용을 위한 인간 T 세포 특이적인 siRNA 전달체 개발에 관한 연구

Abstract

Since the discovery of RNA interference (RNAi), the cellular mechanism responsible for gene silencing, many studies have exploited the RNAi pathway as therapy for incurable disease such as cancers, genetic diseases, or viral infections like HIV-1. However, siRNAs, the mediators of RNAi, have limitations as in vivo drug candidates because of (i) poor stability making them difficult to be delivered to living tissues particularly through the blood stream (ii) inability to be effectively delivered across cell membranes in the absence of a transfection reagent (iii) inability of most siRNA transfection reagents to penetrate cell membranes of many primary cells. Of the immune cells, Primary T cells, a major target of the human immunodeficiency virus-1 (HIV-1), are known to be especially resistant to uptake of nucleic acids by transfecion. In vivo siRNA delivery will be hugely facilitated through the use of a targeting molecule to guide siRNA to the specific target cells and a vehicle to protect siRNA from the nucleases in the serum as well as to deliver it across cell membranes. For my thesis, I have explorer the use of the CD7 molecule as a target receptor which is expressed exclusively and at high levels on the surface of the majority of human T cells as it is rapidly internalized after binding with antibodies or agonists by endocytosis. Hence, I have selected a CD7-specific single chain antibody (scFvCD7) as a T-cell targeting moiety. As siRNA carrier, I have explored the use of nona-arginine (9R), which consists of the oligomer in its d-form as it is a highly positively charged peptide with the ability to bind siRNA with cell transduction properties. Thus, 9R was conjugated to the C-terminal end of scFvCD7 generating scFvCD7-9R for T cell specific siRNA delivery. To test the silencing effects of siRNA delivered to T cells by scFvCD7-9R in vivo, we used a model of HIV-infected humanized mice. NOD/SCIDIL2rγ-/- mice reconstituted with human lymphocytes (Hu-PBL mouse model) were infected with HIV. Delivery of three kinds of siRNA targeting two viral genes (vif and tat) and a host gene (CCR5) successfully inhibited the replication of HIV and the numbers of CD4+ T cells in peripheral blood were maintained at normal level. This suggests that scFvCD7-9R is promising for siRNA delivery to human T cells, suppressing HIV replication in a humanized mouse model. To minimize the possible immunogenicity due to the murine originated amino acid sequence in variable region of scFvCD7, humanized anti CD7 single chain antibody (HzscFvCD7) was generated by recombinant PCR. HzscFvCD7-9R also delivered siRNA into T cells on humanized mice and induced specific gene silencing with low immunogenicity suggesting the potential of HzscFvCD7-9R for therapeutic application to human.