In Vivo Efficacy of Measles Virus Fusion Protein-Derived Peptides Is Modulated by the Properties of Self-Assembly and Membrane Residence.

Measles virus (MV) infection is undergoing resurgence and remains one of the leading causes of death among young children worldwide despite the availability of an effective measles vaccine. MV infects its target cells by coordinated action of the MV hemagglutinin (H) and fusion (F) envelope glycoproteins; upon receptor engagement by H, the prefusion F undergoes a structural transition, extending and inserting into the target cell membrane and then refolding into a postfusion structure that fuses the viral and cell membranes. By interfering with this structural transition of F, peptides derived from the heptad repeat (HR) regions of F can inhibit MV infection at the entry stage. In previous work, we have generated potent MV fusion inhibitors by dimerizing the F-derived peptides and conjugating them to cholesterol. We have shown that prophylactic intranasal administration of our lead fusion inhibitor efficiently protects from MV infection in vivo We show here that peptides tagged with lipophilic moieties self-assemble into nanoparticles until they reach the target cells, where they are integrated into cell membranes. The self-assembly feature enhances biodistribution and the half-life of the peptides, while integration into the target cell membrane increases fusion inhibitor potency. These factors together modulate in vivo efficacy. The results suggest a new framework for developing effective fusion inhibitory peptides. IMPORTANCE: Measles virus (MV) infection causes an acute illness that may be associated with infection of the central nervous system (CNS) and severe neurological disease. No specific treatment is available. We have shown that fusion-inhibitory peptides delivered intranasally provide effective prophylaxis against MV infection. We show here that specific biophysical properties regulate the in vivo efficacy of MV F-derived peptides.

Heterologous prime-boost strategy to immunize very young infants against measles: pre-clinical studies in rhesus macaques.

Infants in developing countries are at high risk of developing severe clinical measles if they become infected during the "window of vulnerability" (age 4-9 months), when declining maternal antibodies do not protect against wild virus, yet impede successful immunization by attenuated measles vaccine. We developed two Sindbis replicon-based DNA vaccines expressing measles virus hemagglutinin and fusion protein with the goal of priming young infants to respond safely and effectively to subsequent boosting with attenuated measles vaccine. Intradermal prime with DNA vaccines by needle-free injection followed by aerosol or parenteral boost with licensed measles vaccine was well tolerated by juvenile and young infant rhesus macaques, and protected against clinical measles and viremia on wild-type virus challenge. A proteosome-measles vaccine administered alone (three doses) or as a boost following DNA vaccine priming was also safe and protective. These promising results pave the way for clinical trials to assess this prime-boost strategy.

Protection against measles virus-induced encephalitis by anti-mimotope antibodies: the role of antibody affinity.

Synthetic peptides mimicking a conformational B-cell epitope (M2) of the measles virus fusion protein (MVF) were used for the immunization of BALB/c mice and the anti-peptide and anti-virus antibody titers induced were compared. Of the panel of tested peptides, a chimeric peptide consisting of two copies of a T-helper epitope (residues 288-302 of MVF) and one copy of the mimotope M2 (TTM2) and a multiple antigen peptide with eight copies of M2 (MAP-M2) induced the highest titers of anti-M2 and anti-MV antibodies. Furthermore, peptides TTM2 and MAP-M2 induced antibodies with highest affinity for the mimotope and highest avidity for measles virus. Immunization with the MAP-M2 construct induced high titers of high-affinity anti-M2 antibody despite the absence of a T-helper epitope, and lymphocyte proliferation data suggest that the addition of M2 to the MAP resulted in the generation of a structure capable of stimulating T-cell help. Sera with anti-M2 reactivity were pooled according to affinity values for binding to M2, and high- and low-affinity pools were tested for their ability to prevent MV-induced encephalitis in a mouse model. The high-affinity serum pool conferred protection in 100% of mice, whereas the lower affinity pool conferred protection to only 50% of animals. These results indicate the potential of mimotopes for use as synthetic peptide immunogens and highlight the importance of designing vaccines to induce antibodies of high affinity.