Spleen focus-forming virus long terminal repeat (SFFV LTR) promoter
Retroviral LTR promoter derived from spleen focus-forming virus (SFFV) that drives strong constitutive transcription in hematopoietic stem cells, progenitors, and differentiated blood lineages. Used as an internal promoter in gammaretroviral and lentiviral vectors for hematopoietic gene transfer and gene therapy.
Origin: Spleen focus-forming virus LTR, used as an internal vector promoter
Characteristics
Retroviral LTR promoter with a strong U3 enhancer/promoter region. Incorporated as an internal promoter into a VSV-G-pseudotyped HIV-1 lentiviral vector with WPRE and cPPT, it drove transduction of over 80% of human cord blood CD34+ cells with stable long-term transgene expression in NOD/SCID-repopulating myeloid, lymphoid, and progenitor lineages after a single 24-hour transduction exposure. Enhancer activity is dense and promiscuous, activating a range of downstream minimal promoters.
Applications: Used as the internal promoter in gammaretroviral and lentiviral vectors for gene marking and transgene expression in human CD34+ hematopoietic stem and progenitor cells, engrafted lymphoid, myeloid, and progenitor lineages in NOD/SCID xenograft models, and murine hematopoietic gene transfer studies.
Limitations: In lentiviral (but not gammaretroviral) vectors, the SFFV promoter becomes extensively methylated (>90% of CpGs) during in vivo hematopoietic differentiation after bone marrow transplantation, with transgene-positive cells falling from 5.4-17.6% at 4 weeks to 0.0-0.6% by 36 weeks post-transplant. Its strong, promiscuous enhancer also raises genotoxic/insertional-mutagenesis risk relative to weaker cellular promoters such as PGK or EFS, an important consideration for clinical gene therapy vector design.