Evaluation of Lymphoid-Specific Enhancer Addition or Substitution in a Basic Retrovirus Vector

Abstract

Two novel retroviral vectors bearing lymphoid-specific enhancers were tested for improved expression of human adenosine deaminase (hADA) in tissue culture cells and in mouse bone marrow transplant recipients. These vectors carried either an added human T-cell receptor α-chain enhancer (ΔN2TADA) or a substitution of the Moloney long terminal repeat (LTR) enhancer with the murine immunoglobulin μ heavy-chain first intron enhancer (ΔN2μADA). Each vector was produced at a titer of approximately 10⁶ infectious units/ml and efficiently transduced hADA into murine fibroblast and myeloma cells in culture. No quantitative difference in expression was observed between the enhancer modified vectors and the basic retrovirus vector (ΔN2ADA). In addition, each vector efficiently conferred hADA expression in lymphoid, myeloid, and erythroid cells of long-term transplanted mice. The majority of the transduced-marrow recipients demonstrated expression of the human enzyme for 4–8 months with each of the three vectors.

Overview summary

It is known that a retroviral vector will be transcribed to a different extent depending on the type of target cell that the vector is in. This variability in expression is because a vector's regulatory sequences (i.e., its enhancer and promoter) are composed of a number of binding sites for a number of different protein regulatory factors. The efficiency of expression depends on the balance of positive and negative regulatory factors that recognize these binding sites in any given cell type. Moore et al. attempt to develop a vector that is more efficient in lymphoid cells by adding or substituting lymphoid elements in the enhancer region.