Retention of neutralising activity by recombinant anti-pneumolysin antibody fragments

The variable domains of a neutralising (prevents erythrocyte lysis) anti-pneumolysin monoclonal antibody have been cloned and expressed as functional protein in Escherichia coli. Purification of the anti-pneumolysin single-chain antibody fragment, via antibody-affinity or metal-chelate affinity chromatography, resulted in product that was predominantly in a dimeric or monomeric form, respectively. The dimeric single-chain antibody fragment showed a higher sensitivity and affinity for immobilised antigen in both ELISA and BIAcore studies. The dimeric single-chain antibody fragment was as effective at protecting erythrocytes from lysis as the parent monoclonal. The monomeric, low affinity single-chain antibody fragment, showed reduced neutralising potency. As antibiotic resistant Streptococcus pneumoniae strains continue to show an increasing word-wide distribution, recombinant, neutralising antibody fragments, may provide an additional class of molecules useful in the treatment of toxaemia.