Induction of broadly neutralizing antibodies against measles virus mutants using a polyepitope vaccine strategy

Chimeric molecules expressing multiple copies of the loop-forming hemagglutinin noose epitope (designated as "L"; aa386-400), a protective B cell epitope of the measles virus were generated by recombinant technology. The recombinant polyepitope [L₄T₄]₂ combining two sets of four repeats of the L epitope and with two sets of four repeats of the human promiscuous T cell epitope of tetanus toxoid ("T", tt830-844) was produced in transgenic carrot plants. After intraperitoneal immunization of mice with plant membrane extract, sera neutralized all wild-type viruses. In a modified plaque reduction neutralization assay based on CD150-transfected Vero cells anti-[L₄T ₄]₂ sera neutralized all field isolates, irrespective of mutations in the L epitope. Even viruses with a mutation in the contact residues of a neutralizing L-specific monoclonal antibody or two mutations in other positions of the epitope were equally sensitive to neutralization. These results suggest that the multiple copies of the L epitope fold into different conformations that induce a repertoire of B cells diverse enough to overcome the genetic diversity of field viruses.