Nanobody-Based high-performance immunosorbent for selective beta 2-microglobulin purification from blood.

Removing β2-microglobulin (β2M) from blood circulation is considered to be the most effective method to delay the occurrence of dialysis-related amyloidosis (DRA). The ideal extracorporeal β2M removal system should be cost-effective, highly specific and having a high capacity. However, the traditional technologies based on size exclusion do not have an adequate specificity, and alternative immunosorbents have limited applications due to low capacity and their high cost. Nanobodies (Nbs), the smallest functional recombinant antibody fragments, offer several advantages to overcome these obstacles. In this study, an anti-β2M Nb with a C-terminal thiol-tag was successfully prepared from E. coli for site-directed and oriented immobilization and usage as capture ligand in a β2M-selective immunosorbent. The prepared immunosorbent showed a high binding capacity of up to 7 mg β2M per mL resin, which is 17 times higher than that of previous studies using single-chain variable antibody fragments (scFv). Furthermore, an exceptional high specificity has been demonstrated as other human serum proteins were not adsorbed during dynamic adsorption experiments. About 80% of the original binding capacity of the immunosorbent was restored after four consecutive easy regenerations, whereas 90% of the original capacity was retained after 1-month storage of the resin. Moreover, the mathematical model fitted very well the in vitro perfusion. The results with this pioneering immunosorbent confirm its possible clinical application and is expected to reach the required clinical effect of immunoadsorption therapy. STATEMENT OF SIGNIFICANCE: Dialysis-related amyloidosis (DRA), associated with the accumulation of β2-microglobulin (β2M), is a serious complication of end-stage kidney disease. Removing β2M from blood circulation by extracorporeal blood purification is considered to be the most effective method to delay the occurrence of DRA. However, the existing methods are incapable to eliminate sufficient quantities of β2M from circulation, either because of lack of specificity, high cost or for low capacity. In this manuscript, we provide a practical and economic immunosorbent based on anti-β2M nanobody for DRA. The prepared immunosorbent was reusable and storable, and demonstrated high specificity and realized a high binding capacity of up to 7 mg β2M per mL resin, which is 17 times higher than that of the previous studies.