466. Comprehensive Analyses of Diverse Lentiviral and Retroviral Vectors for Post-Entry Restriction by TRIM5α and Implications for Gene Therapy

Abstract

We analyzed HIV-1, FIV, EIAV, N-MLV and NB-(i.e., Moloney)- MLV vectors for post-entry restriction by human (Ref1) and monkey (Lv1) activities and by the respective species-specific TRIM5α proteins that mediate them. RT-normalized preparations were compared. FIV, EIAV and HIV-1 vector infectivity varied widely but concordantly in numerous non-primate mammalian cell lines. In contrast, in diverse human and monkey cells, relative restriction of FIV and EIAV compared to HIV-1 varied from none to substantial, with the greatest nonprimate vector infectivity deficits observed in human T cell lines. Using permissive (restriction factor-lacking) non-primate cells engineered to express human or rhesus TRIM5α, we compared restricted (HIV-1, FIV, EIAV, and N-MLV) and unrestricted (NB-MLV) retroviruses across wide ranges of viral inputs. EIAV, FIV and N-MLV vectors were restricted by rhesus and human TRIM5α, while HIV was only significantly restricted by the rhesus allele and NB-MLV was unrestricted. For FIV, human TRIM5α was less restricting than rhesus TRIM5α, while EIAV was approximately equivalently restricted by both alleles. N-MLV was much more proportionately restricted than FIV or EIAV by human TRIM5α. Rhesus and human TRIM5α proteins restricted in a saturable manner, since endogenous and introduced TRIM5α restrictions could be titrated by co-transduction with FIV, HIV-1 or EIAV virus-like particles. We achieved stable RNAi knockdown of endogenous rhesus TRIM5α in FrhK4 cells, which released the Lv1 restriction, resulting in marked increases in all lentiviral vector infectivities while having no effect on negative control NB-MLV. Interestingly, in canine cells but not feline cells, human TRIM5α supported minimal restriction of FIV compared to significant restriction of EIAV, a phenomenon which is under ongoing mechanistic investigation. We conclude that human and rhesus TRIM5α proteins restrict both FIV and EIAV vectors, with the degree of restriction in different human cell lines varying from none to substantial. Human T cells are more susceptible to transduction by HIV vector than either non-primate vector. Stable knockdown of rhesus TRIM5α releases LV1 restrictions. Differential restrictions in canine cells raise the possibility that these proteins may not function autonomously or that a canine factor may interfere. Further development of lentiviral vector gene therapy will benefit from informed appraisal of the consequences of Ref1/human TRIM5α restriction, which may be advantageous or disadvantageous depending on the particular application.