Enhanced intracellular stability of sFv-Fc fusion intrabodies.

The ability of intracellular antibodies (intrabodies) to block the function of a target protein can be dependent on the stability of the single-chain antibody (sFv) when expressed in the intracellular environment. Low-affinity sFvs capable of reaching high steady-state levels can be more effective modulators of target proteins than high-affinity, unstable sFvs. In an effort to enhance the intracellular stability of sFvs when expressed as intrabodies, we have generated novel sFv-Fc fusion intrabodies. Fusion of the native sFv sequence with the entire heavy chain constant region fragment of IgG results in decreased turnover of the intrabody and enhanced steady-state accumulation of sFv-Fc protein, while maintaining the ability to target intrabody expression to sub-cellular compartments. Here, we describe the rationale and design for this strategy using two anti-cyclin E sFvs constructed for use as intrabodies.