Evaluation of P2X7 Receptor Function in Tumor Contexts Using rAAV Vector and Nanobodies (AAVnano).

Adenosine triphosphate (ATP) represents a danger signal that accumulates in injured tissues, in inflammatory sites, and in the tumor microenvironment. Extracellular ATP is known to signal through plasma membrane receptors of the P2Y and P2X families. Among the P2X receptors, P2X7 has attracted increasing interest in the field of inflammation as well as in cancer. P2X7 is expressed by immune cells and by most malignant tumor cells where it plays a crucial yet complex role that remains to be clarified. P2X7 activity has been associated with production and release of pro-inflammatory cytokines, modulation of the activity and survival of immune cells, and the stimulation of proliferation and migratory properties of tumor cells. Hence, P2X7 plays an intricate role in the tumor microenvironment combining beneficial and detrimental effects that need to be further investigated. For this, we developed a novel methodology termed AAVnano based on the use of Adeno-associated viral vectors (AAV) encoding nanobodies targeting P2X7. We discuss here the advantages of this tool to study the different functions of P2X7 in cancer and other pathophysiological contexts.

Nanobody-Enhanced Targeting of AAV Gene Therapy Vectors.

A limiting factor for the use of adeno-associated viruses (AAVs) as vectors in gene therapy is the broad tropism of AAV serotypes, i.e., the parallel infection of several cell types. Nanobodies are single immunoglobulin variable domains from heavy chain antibodies that naturally occur in camelids. Their small size and high solubility allow easy reformatting into fusion proteins. Herein we show that a membrane protein-specific nanobody can be inserted into a surface loop of the VP1 capsid protein of AAV2. Using three structurally distinct membrane proteins-a multispan ion channel, a single-span transmembrane protein, and a glycosylphosphatidylinositol (GPI)-anchored ectoenzyme-we show that this strategy can dramatically enhance the transduction of specific target cells by recombinant AAV2. Moreover, we show that the nanobody-VP1 fusion of AAV2 can be incorporated into the capsids of AAV1, AAV8, and AAV9 and thereby effectively redirect the target specificity of other AAV serotypes. Nanobody-mediated targeting provides a highly efficient AAV targeting strategy that is likely to open up new avenues for genetic engineering of cells.

Selection of nanobodies that block the enzymatic and cytotoxic activities of the binary Clostridium difficile toxin CDT.

The spore-forming gut bacterium Clostridium difficile is the leading cause of antibiotic-associated diarrhea in hospitalized patients. The major virulence factors are two large glucosylating cytotoxins. Hypervirulent strains (e.g. ribotype 027) with higher morbidity and mortality additionally produce the binary CDT toxin (Clostridium difficile transferase) that ADP-ribosylates actin and induces microtubule-based cell protrusions. Nanobodies are robust single domain antibodies derived from camelid heavy chain antibodies. Here we report the generation of functional nanobodies against the enzymatic CDTa and the heptameric receptor binding subunit CDTb. The nanobodies were obtained from a variable-domain repertoire library isolated from llamas immunized with recombinant CDTa or CDTb. Five CDTa-specific nanobodies blocked CDTa-mediated ADP-ribosylation of actin. Three CDTa-specific and two CDTb-specific nanobodies neutralized the cytotoxicity of CDTa+b. These nanobodies hold promise as new tools for research, diagnosis and therapy of C. difficile associated disease.