Mouse vaccination with dendritic cells loaded with prion protein peptides overcomes tolerance and delays scrapie.

Prion diseases are presumed to be caused by the accumulation in the brain of a pathological protein called prion protein (PrP) scrapie which results from the transconformation of cellular PrP, a ubiquitous glycoprotein expressed in all mammals. Since all isoforms of PrP are perceived as self by the host immune system, a major problem in designing efficient immunoprophylaxis or immunotherapy is to overcome tolerance. The present study was aimed at investigating whether bone-marrow-derived dendritic cells (DCs) loaded with peptides previously shown to be immunogenic in PrP-deficient mice, can overcome tolerance in PrP-proficient wild-type mice and protect them against scrapie. Results show that, in such mice, peptide-loaded DCs elicit both lymphokine release by T cells and antibody secretion against native cellular PrP. Repeated recalls with peptide-loaded DCs reduces the attack rate of 139A scrapie inoculated intraperitoneally and retards disease duration by 40 days. Most interestingly, survival time in individual mice appears to be correlated with the level of circulating antibody against native cellular PrP

Exacerbation of experimental autoimmune encephalomyelitis in prion protein (PrPc)-null mice: evidence for a critical role of the central nervous system

<p>Abstract</p> <p>Background</p> <p>The cellular prion protein (PrPc) is a host-encoded glycoprotein whose transconformation into PrP scrapie (PrPSc) initiates prion diseases. The role of PrPc in health is still obscure, but many candidate functions have been attributed to the protein, both in the immune and the nervous systems. Recent data show that experimental autoimmune encephalomyelitis (EAE) is worsened in mice lacking PrPc. Disease exacerbation has been attributed to T cells that would differentiate into more aggressive effectors when deprived of PrPc. However, alternative interpretations such as reduced resistance of neurons to autoimmune insult and exacerbated gliosis leading to neuronal deficits were not considered.</p> <p>Method</p> <p>To better discriminate the contribution of immune cells versus neural cells, reciprocal bone marrow chimeras with differential expression of PrPc in the lymphoid or in the central nervous system (CNS) were generated. Mice were subsequently challenged with MOG_35-55peptide and clinical disease as well as histopathology were compared in both groups. Furthermore, to test directly the T cell hypothesis, we compared the encephalitogenicity of adoptively transferred PrPc-deficient versus PrPc-sufficient, anti-MOG T cells.</p> <p>Results</p> <p>First, EAE exacerbation in PrPc-deficient mice was confirmed. Irradiation exacerbated EAE in all the chimeras and controls, but disease was more severe in mice with a PrPc-deleted CNS and a normal immune system than in the reciprocal construction. Moreover, there was no indication that anti-MOG responses were different in PrPc-sufficient and PrPc-deficient mice. Paradoxically, PrPc-deficient anti-MOG 2D2 T cells were less pathogenic than PrPc-expressing 2D2 T cells.</p> <p>Conclusions</p> <p>In view of the present data, it can be concluded that the origin of EAE exacerbation in PrPc-ablated mice resides in the absence of the prion protein in the CNS. Furthermore, the absence of PrPc on both neural and immune cells does not synergize for disease worsening. These conclusions highlight the critical role of PrPc in maintaining the integrity of the CNS in situations of stress, especially during a neuroinflammatory insult.</p

La protéine prion (son rôle dans la régulation de la réponse immune et sa valeur en tant que cible vaccinale)

Les maladies à prions sont des affections neurodégénératives fatales, caractérisées par une perte neuronale circonscrite au système nerveux central et liée à la présence d une protéine anormalement conformée, la PrPSc. Cette dernière provient de la conversion d une protéine membranaire, la PrPC. Pour un gène présent dans toutes les espèces, aucune anomalie n a été observée chez les souris Prnp-/-. La fonction de la PrPC demeure donc méconnue. La première partie de ce travail a consisté à évaluer l impact de la PrPC dans les interactions entre les lymphocytes T et les cellules dendritiques. La PrPC migre vers les zones de contact entres les cellules et joue un rôle sur les deux partenaires de la synapse. De plus, l absence de PrPC à la surface des cellules présentatrices ralentit la réponse proliférative des lymphocytes T in vivo. La deuxième partie de ce mémoire s inscrit dans le cadre de la recherche d approches prophylactiques et thérapeutiques contre les maladies à prions. Des lymphocytes T anti-PrP engendrés dans des souris Prnp-/- ont été injectés dans des receveuses histocompatibles Prnp+/+ ultérieurement infectées avec l agent de la tremblante. Les lymphocytes T transférés survivent et demeurent fonctionnels dans un environnement PrP+ ; les souris receveuses sont partiellement protégées contre l invasion par les prions et cette protection est indépendante de la production d anticorps. Les informations obtenues à l issue de ce travail constituent un préalable au développement de stratégies vaccinales chez l homme, dans les maladies à prions.PARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Th2-polarised PrP-specific transgenic T-cells confer partial protection against murine scrapie.

Several hurdles must be overcome in order to achieve efficient and safe immunotherapy against conformational neurodegenerative diseases. In prion diseases, the main difficulty is that the prion protein is tolerated as a self protein, which prevents powerful immune responses. Passive antibody therapy is effective only during early, asymptomatic disease, well before diagnosis is made. If efficient immunotherapy of prion diseases is to be achieved, it is crucial to understand precisely how immune tolerance against the prion protein can be overcome and which effector pathways may delay disease progression. To this end, we generated a transgenic mouse that expresses the ß-chain of a T cell receptor recognizing a PrP epitope presented by the class II major histocompatibility complex. The fact that the constraint is applied to only one TCR chain allows adaptation of the other chain according to the presence or absence of tolerogenic PrP. We first show that transgene-bearing T cells, pairing with rearranged α-chains conferring anti-PrP specificity, are systematically eliminated during ontogeny in PrP+ mice, suggesting that precursors with good functional avidity are rare in a normal individual. Second, we show that transgene-bearing T cells with anti-PrP specificity are not suppressed when transferred into PrP+ recipients and proliferate more extensively in a prion-infected host. Finally, such T cells provide protection through a cell-mediated pathway involving IL-4 production. These findings support the idea that cell-mediated immunity in neurodegenerative conditions may not be necessarily detrimental and may even contribute, when properly controlled, to the resolution of pathological processes

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

There is to date no effective way of preventing or curing neurodegenerative diseases such as Alzheimer disease or transmissible spongiform encephalopathies. The idea of treating those conditions by immunological approaches has progressively emerged over the last ten years. Encouraging results have been reported in Alzheimer disease and in peripheral forms of mouse prion diseases following passive injection of Abs or active immunization against the peptides or proteins presumably at the origin of those disorders. Still, major difficulties persist due to some characteristics of those conditions such as slow evolution, brain location, uncertainties regarding precise pathogenic pathways, and, above all, the fact that the target Ag is self, meaning that it is poorly immunogenic and potentially harmful if tolerance was transgressed. To analyze some of those difficulties, we are developing adoptive cell transfer approaches. In this study, lymphocytes sensitized against the prion protein in nontolerant Prnp mice were transferred into histocompatible wild-type recipients which were partly or totally devoid of their own lymphocytes. Under such conditions, we found that the engrafted T lymphocytes resisted peripheral tolerance, remained reactive for several months against epitopes of the prion protein, and significantly attenuated the progression of prions in secondary lymphoid organs with subsequent delay in the evolution of the neurological disease. Interestingly, those protective T lymphocytes secreted lymphokines and migrated more readily into the host CNS but did not appear to be engaged in cooperation with host B cells for Ab production

Variable HIV peptide stability in human cytosol is critical to epitope presentation and immune escape

Induction of virus-specific CD8+ T cell responses is critical for the success of vaccines against chronic viral infections. Despite the large number of potential MHC-I–restricted epitopes located in viral proteins, MHC-I–restricted epitope generation is inefficient, and factors defining the production and presentation of MHC-I–restricted viral epitopes are poorly understood. Here, we have demonstrated that the half-lives of HIV-derived peptides in cytosol from primary human cells were highly variable and sequence dependent, and significantly affected the efficiency of cell recognition by CD8+ T cells. Furthermore, multiple clinical isolates of HLA-associated HIV epitope variants displayed reduced half-lives relative to consensus sequence. This decreased cytosolic peptide stability diminished epitope presentation and CTL recognition, illustrating a mechanism of immune escape. Chaperone complexes including Hsp90 and histone deacetylase HDAC6 enhanced peptide stability by transient protection from peptidase degradation. Based on empirical results with 166 peptides, we developed a computational approach utilizing a sequence-based algorithm to estimate the cytosolic stability of antigenic peptides. Our results identify sequence motifs able to alter the amount of peptide available for loading onto MHC-I, suggesting potential new strategies to modulate epitope production from vaccine immunogens