Cross-disciplinary research stirs new challenges into the study of the structure, function and systems biology of complement

Display of the Albumin-Binding Domain in the Envelope Improves Lentiviral Vector Bioavailability

Vesicular stomatitis virus G glycoprotein (VSVg) is extensively used for retroviral and lentiviral vector (LV) pseudotyping. However, VSVg pseudotyped vectors are serum inactivated, blocking the in vivo gene delivery. Several strategies have been employed to prevent complement inactivation, including chemical and genetic envelope modifications. This study employed the streptococcal albumin-binding domain (ABD) to generate a construct to express ABD as a glycosylphosphatidylinositol-anchored protein. LV particles bearing ABD are able to bind bovine and human serum albumin in vitro. Neither the lentiviral vector production titer nor the in vitro transduction was affected by the ABD display. The study demonstrated that ABD-bearing LVs are protected from human complement inactivation. More importantly, intravenous administration demonstrated that the presence of ABD significantly reduces lentivector sequestration in liver and bone-marrow cells. Therefore, the use of ABD represents an improvement for in vivo gene therapy applications. The results strongly point to ABD display as a universal strategy to increase the in vivo efficacy of different viral vectors.

The role of complement in inflammatory diseases from behind the scenes into the spotlight

Our understanding of the biology of the complement system has undergone a drastic metamorphosis since its original discovery. This system, which was traditionally primarily described as a "complement" to humoral immunity, is now perceived as a central constituent of innate immunity, defending the host against pathogens, coordinating various events during inflammation, and bridging innate and adaptive immune responses. Complement is an assembly of proteins found in the blood and body fluids and on cell surfaces. Soluble complement components form the proteolytic cascade, whose activation leads to the generation of complement effectors that target various cells involved in the immune response. Membrane-bound receptors and regulators transmit signals from complement effectors to target cells and limit complement activation to the surfaces of pathogens and damaged or activated host cells. The multiple interconnections among complement proteins, immune cells, and mediators provide an excellent mechanism to protect the organism against infections and support the repair of damaged tissues. However, disturbances in this "defense machinery" contribute to the pathogenesis of various diseases. The role of complement in various inflammatory disorders is multifaceted; for example, the activation of complement can significantly contribute to inflammation-mediated tissue damage, whereas inherited or acquired complement deficiencies highly favor the development of autoimmunity.