Proteins and Their Derived Peptides as Carriers in a Conjugate Vaccine forStreptococcus pneumoniae: Self-Heat Shock Protein 60 and Tetanus Toxoid

Abstract

We induced T cell help for vaccination against Streptococcus pneumoniae (Pn) using self and foreign peptides and their source proteins conjugated to the capsular polysaccharide (CPS) of type 4 Pn; the carriers were self-heat shock protein 60 (HSP60) and tetanus toxoid (TT). We measured the production of IgG Abs to the CPS and the carriers, and tested resistance to challenge with highly lethal amounts of Pn injected i.p. (LD50 × 103–106). We now report that vaccination protects old and young mice from bacterial challenge; however, there were significant differences in vaccine efficacy based on the carrier. Self-HSP60 peptide p458m was more effective than the whole HSP60 molecule and was equally effective compared with TT. Both p458m and TT were more protective than the TT-derived peptide p30 after a single vaccination. However, peptide p30 was effective in more MHC genotypes than was p458m. Unlike other vaccines, protection conferred by p458m was not related to the amount of anti-CPS Ab: mice that produced very little Ab were still protected from highly lethal doses of bacteria (LD50 × 105–106). Furthermore, unlike the other carriers, there was no Ab response to the p458m carrier. Thus, peptides, self as well as foreign, can provide T cell help that differs functionally from that provided by the whole parent protein.

Pneumococcal Capsular Polysaccharide Is Immunogenic When Present on the Surface of Macrophages and Dendritic Cells: TLR4 Signaling Induced by a Conjugate Vaccine or by Lipopolysaccharide Is Conducive

“…9 that some of the mice vaccinated with BMDC produced very little or no detectible IgG or IgM Abs, but were, nevertheless, protected against the challenge. We have previously reported that some mice vaccinated with the PS4-p458 conjugate made very little detectible Ab, yet were still resistant to supralethal S. pneumoniae challenge (14). Similarly, RAW cells pulsed with PS4 induced protection to 100 ϫ LD 50 bacteria for 3 mo, but no IgG or IgM Ab could be detected in the sera of the injected mice by a variety of assay systems (data not shown).…”

“…The conjugates were made as previously described (14). Briefly, PS4 was dissolved in double-distilled water (5 mg/ml) and was activated with 0.1 ml of cyanogen bromide (20 mg/ml in acetone) in the presence of 30 mM triethylamine (Sigma-Aldrich) in acetone (pH 7).…”

“…We used the hsp60 peptide as a carrier because healthy humans mount a natural T cell response to hsp60 epitopes (18). Indeed, the p458 peptide conjugated to pneumococcal CPS type 4 (PS4)-p458 could induce protection in mice against a supralethal S. pneumoniae challenge (14,15). Protection was associated with PS4-specific IgG Ab in most but not in all the mice, a T cell response to the p458 carrier and long-term memory.…”

Biomarker vaccines

“…20 For these reasons, I and my colleagues have developed conjugate vaccines based on combining a specific pathogen epitope with a peptide epitope of the mammalian HSP60 molecule. We have used a peptide of self-HSP60, termed p458, to formulate subunit vaccines by conjugating p458 to various pathogen virulence molecules such as the capsular polysaccharides (CPS) of Salmonella, 21 Pneumococcus 22 or Meningococcus types C and B. 23 Some bacterial HSP60 peptides too are agonists for effective innate receptors, and can also serve in effective conjugate vaccines; the phenomenon is not limited to self.…”

“…1). Note that these conjugate vaccines are effective without the need for added adjuvant, [21][22][23] a factor that adds to safety. The detailed results can be seen in the publications.…”