FUNCTIONAL PHAGE DISPLAY OF CILIARY NEUROTROPHIC FACTOR

We report the display of human ciliary neurotrophic factor (hCNTF), a survival factor for neuronal cells belonging to the alpha-helical cyto kine superfamily, on the surface of the filamentous bacteriophage fd. The hCNTF cDNA was fused to a DNA sequence encoding the C-terminal dom ain of pIII, a minor coat protein exposed at one end of fd. Gene fusio ns were cloned into a plasmid containing the ColE1 plasmid and fd orig ins of replication, and were packaged into phagemid particles upon sup erinfection with M13KO7 helper phage. The resulting fusion phage bound specifically to anti-CNTF antibodies and to the recombinant soluble C NTF alpha-receptor Moreover, phage-displayed hCNTF was found to posses s biological activity at concentrations comparable to those of the sol uble cytokine. These results demonstrate that CNTF can be displayed on phage in a correctly folded and functionally active form. Binding of fusion phage to immobilized CNTF alpha-receptor and subsequent elution at low pH resulted in affinity purification of CNTF-displaying virion s. Utilization of this technology should enable the selection of high- affinity variants from libraries of CNTF mutants displayed on phage.