Isolation and characterization of malaria PfHRP2 specific V_NAR antibody fragments from immunized shark phage display...

Malaria rapid diagnostic tests (RDTs) represent an important antibody based immunoassay platform. Unfortunately, conventional monoclonal antibodies are subject to degradation shortening shelf lives of RDTs. The variable region of the receptor (V_NAR) from shark has a potential as alternative to monoclonal antibodies in RDTs due to high thermal stability.

In this study, new binders derived from shark V_NAR domains library were investigated. Following immunization of a wobbegong shark (Orectolobus ornatus) with three recombinant malaria biomarker proteins (PfHRP2, PfpLDH and Pvaldolase), a single domain antibody (sdAb) library was constructed from splenocytes. Target-specific V_NAR phage were isolated by panning. One specific clone was selected for expression in Escherichia coli expression system, and study of binding reactivity undertaken.

The primary V_NAR domain library possessed a titre of 1.16 × 10⁶ pfu/mL. DNA sequence analysis showed 82.5% of isolated fragments appearing to contain an in-frame sequence. After multiple rounds of biopanning, a highly dominant clone specific to PfHRP2 was identified and selected for protein production in an E. coli expression system. Biological characterization showed the recombinant protein expressed in periplasmic has better detection sensitivity than that of cytoplasmic proteins. Assays of binding activity indicated that its reactivity was inferior to the positive control mAb C1-13.

Target-specific bacteriophage V_NARs were successfully isolated after a series of immunization, demonstrating that phage display technology is a useful tool for selection of antigen binders. Generation of new binding reagents such as V_NAR antibodies that specifically recognize the malaria biomarkers represents an appealing approach to improve the performance of RDTs.