Breaking Immune Tolerance to the Prion Protein Using Prion Protein Peptides Plus Oligodeoxynucleotide-CpG in Mice

Abstract

The absence of a detectable immune response during transmissible spongiform encephalopathies is likely due to the fact that the essential component of infectious agents, the prion protein (PrP), is a self Ag expressed on the surface of many cells of the host. To overcome self-tolerance to PrP, we used 30-mer PrP peptides previously shown to be immunogenic in Prnp−/− mice, together with CFA or CpG-oligodeoxynucleotides (CpG) in IFA. Generation of anti-PrP T and B cell responses was analyzed in the spleen, lymph nodes, and serum of immunized C57BL/6 wild-type mice. Immunization with PrP peptides emulsified in CFA did not trigger an immune response to PrP. When CpG were used, vaccination with peptides P143–172 and P158–187 generated IFN-γ-secreting splenic T cells, and only P158–187 significantly stimulated IL-4-secreting T cells. Both peptides induced few Ab-producing B cells, and low and variable serum Ab titers. In contrast, immunization with peptide P98–127 did not induce significant levels of T cell responses but elicited specific peptide Abs. T cell epitope mapping, performed using 15-mer peptides covering PrP segment 142–182, revealed that an immunogenic motif lies between positions 156 and 172. These results demonstrate that T and B cell repertoires against PrP can be stimulated in C57BL/6 when adjuvant of the innate immunity such as CpG, but not CFA, is added to PrP peptides, and that the pattern of immune responses varies according to the epitope.

Humoral immune response to native eukaryotic prion protein correlates with anti-prion protection

“…Therefore, the presence of anti-native PrP C titers appears to correlate with the capability to interfere with prion pathogenesis, and anti-native PrP C antibodies may represent an indispensable precondition for preventing prion diseases. These findings may explain the very modest effects of active PrP immunization attempts on prion pathogenesis that have been reported by others (14) and should lead to a critical reassessment of the value of immunization protocols, leading to immune responses whose affinity to native PrP C has not been investigated (13)(14)(15)(16)(17)(18)28).…”

“…However, host tolerance to endogenous PrP C remains a major obstacle to devising active immunization regimens. Nevertheless, several recent studies suggest that the induction of anti-PrP antibodies in WT mice is in principle feasible (13)(14)(15)(16)(17)(18). Although anti-PrP Ig titers could be measured in most of these studies, the titers were rather low.…”

Adoptive Transfer of T Lymphocytes Sensitized against the Prion Protein Attenuates Prion Invasion in Scrapie-Infected Mice

“…Ab binding to native PrPc was measured by indirect immunofluorescence, as described previously (45,50,55), on a stably transfected EL4 T cell clone activated overnight with anti-CD3 Ab (clone 2C11 at 10 g/ml) to maximize cell surface PrPc. Cells, blocked first for Fc receptors, were incubated for 20 min with serum dilutions at 1/10, 1/50, and 1/100, washed in FACS buffer, and revealed for 20 min with clone Mark1, a FITC-conjugated rat anti-mouse -chain Ab.…”

Anti-prion activity generated by a novel vaccine formulation

“…The most comparable study by Schwarz et al [12] required six 50 g peptide-KLH immunizations to generate antibody titers as measured by ELISA of 1/1500. Use of an adjuvant using CpG oligodeoxynucleotides to boost immune response to free prion peptides has been reported as a successful strategy to overcome immune tolerance [11]. A comparison of the antibody levels generated using the CpG adjuvant and free prion peptide approach to this study suggests that both higher antibody titers and less animal to animal immune response variability were obtained using BCP and the AdjuvacTM formulation described herein.…”