Catalytic antibodies are immunoglobulins endowed with enzymatic properties. Discovered in the second part of the 1980s, the enthusiasm they initially aroused was counterbalanced by the difficulty of their production and their low catalytic rates. Nevertheless, improvements in expression systems and engineering technologies, combined with various studies suggesting that catalytic antibodies play a role in the immune system, have opened the way to new applications for these proteins. Herein we review catalytic antibodies from a biotechnological point of view, focusing our study on the different production methods, expression systems and their potential clinical applications dedicated to these proteins.

In the last decade polycistronic vectors have become essential tools for both basic science and gene therapy applications. In order to co-express heterologous polypeptides, different systems have been developed from Internal Ribosome Entry Site (IRES) based vectors to the use of the 2A peptide. Unfortunately, these methods are not fully suitable for the efficient and reproducible modulation of the ratio between the proteins of interest. Here we describe a novel bicistronic vector type based on the use of alternative splicing. By modifying the consensus sequence that governs splicing, we demonstrate that the ratio between the synthesized proteins could easily vary from 1 : 10 to 10 : 1. We have established this system with luciferase genes and we extended its application to the production of recombinant monoclonal antibodies. We have shown that these vectors could be used in several typical cell lines with similar efficiencies. We also present an adaptation of these vectors to hybrid alternative splicing/IRES constructs that allow a ratio-controlled expression of proteins of interest in stably transfected cell lines.

Catalytic antibodies are currently being investigated in order to understand their role under physio-pathological situations. To this end, the knowledge of structure-function relationships is of great interest. Recombinant scFv fragments are smaller and easier to genetically manipulate than whole antibodies, making them well suited for this kind of study. Nevertheless they are often described as proteins being laborious to produce. This paper describes a highly efficient method to produce large quantities of refolded soluble catalytic scFv. For the first time, the functionality of a refolded catalytic scFv displaying a β-lactamase activity has been validated by three approaches: (1) use of circular dichroism to ensure that the refolded had secondary structure consistent with a native scFv fold, (2) development of enzyme-linked immunosorbant assay and surface plasmon resonance (SPR) approaches for testing that the binding characteristics of an inhibitory peptide have been retained, and (3) proof of the subtle catalytic properties conservation through the development of a new sensitive catalytic assay using a fluorogenic substrate.