title: On technological and immunological benefits of multivalent single-injection microsphere vaccines.
abstract: OBJECTIVE
  With the aim of developing multivalent vaccines for single-injection, we examined the feasibility of combining antigens in biodegradable microspheres. Such vaccines are expected to improve vaccination coverage by reducing the number of vaccination sessions required to generate immunity.
  
  
  METHODS
  Mono- and multivalent vaccines of Haemophilus influenzae type b (Hib) conjugate, diphtheria toxoid (DT), tetanus toxoid (TT), and pertussis toxin (PT) in poly (lactic acid) and poly(lactic-coglycolic acid) microspheres were prepared by spray drying, and the influence of coencapsulated antigens and excipients on antigen loading, release, and stability was examined. Two tetravalent formulations were tested in guinea pigs.
  
  
  RESULTS
  Monovalent Hib and PT vaccines showed loading efficiencies of 10% (Hib) and 30% (PT) in both polymers. The loading efficiencies increased upon addition of trehalose and, even more, when the antigens were coencapsulated in di- and trivalent combinations. Highest loading efficiencies (> 80%) were achieved with trivalent formulations (DT + PT + Hib) that also contained coencapsulated albumin. The percentage of antigen released during 24 h of incubation was typically 10-40% and decreased as loading efficiency increased. Enzyme-linked immunosorbent assay (ELISA) data revealed that TT, DT, and PT remained antigenic throughout the encapsulation and subsequent release processes. Finally, all antigens maintained their immunogenicity, since strong and sustained antibody responses were elicited after a single injection of tetravalent microsphere vaccines (DT + TT + PT + Hib) in guinea pigs.
  
  
  CONCLUSIONS
  This study reveals technologic benefit as well as an immunological potential of multivalent single-injection microsphere vaccines. The results support our hypothesis that coencapsulation of several antigens may intrinsically improve entrapment of antigenic and immunogenic antigen probably by virtue of increased protein concentration during microencapsulation leading to mutual stabilization of the components.
authors.affiliation: Institute of Pharmaceutical Sciences, ETH Zurich, Switzerland.
authors.forename: Gérard
authors.initials: G
authors.lastname: Boehm
authors.forename: Marisa
authors.initials: M
authors.lastname: Peyre
authors.forename: Dorothea
authors.initials: D
authors.lastname: Sesardic
authors.forename: Rachel J
authors.initials: RJ
authors.lastname: Huskisson
authors.forename: Fatme
authors.initials: F
authors.lastname: Mawas
authors.forename: Alexandra
authors.initials: A
authors.lastname: Douglas
authors.forename: Dorothy
authors.initials: D
authors.lastname: Xing
authors.forename: Hans P
authors.initials: HP
authors.lastname: Merkle
authors.forename: Bruno
authors.initials: B
authors.lastname: Gander
authors.forename: Pål
authors.initials: P
authors.lastname: Johansen
mesh_terms: D000818:Animals; D005260:Female; D006168:Guinea Pigs; D007279:Injections, Subcutaneous; D008863:Microspheres; D014612:Vaccines / Q000008:administration & dosage* / Q000276:immunology*
chemical_list: D014612:Vaccines