TLR4- and TRIF-dependent stimulation of B lymphocytes by peptide liposomes enables T cell-independent isotype switch in mice.

Immunoglobulin class switching from IgM to IgG in response to peptides is generally T cell-dependent and vaccination in T cell-deficient individuals is inefficient. We show that a vaccine consisting of a dense array of peptides on liposomes induced peptide-specific IgG responses totally independent of T-cell help. Independency was confirmed in mice lacking T cells and in mice deficient for MHC class II, CD40L, and CD28. The IgG titers were high, long-lived, and comparable with titers obtained in wild-type animals, and the antibody response was associated with germinal center formation, expression of activation-induced cytidine deaminase, and affinity maturation. The T cell-independent (TI) IgG response was strictly dependent on ligation of TLR4 receptors on B cells, and concomitant TLR4 and cognate B-cell receptor stimulation was required on a single-cell level. Surprisingly, the IgG class switch was mediated by TIR-domain-containing adapter inducing interferon-ß (TRIF), but not by MyD88. This study demonstrates that peptides can induce TI isotype switching when antigen and TLR ligand are assembled and appropriately presented directly to B lymphocytes. A TI vaccine could enable efficient prophylactic and therapeutic vaccination of patients with T-cell deficiencies and find application in diseases where induction of T-cell responses contraindicates vaccination, for example, in Alzheimer disease.

Sequence-independent control of peptide conformation in liposomal vaccines for targeting protein misfolding diseases.

Synthetic peptide immunogens that mimic the conformation of a target epitope of pathological relevance offer the possibility to precisely control the immune response specificity. Here, we performed conformational analyses using a panel of peptides in order to investigate the key parameters controlling their conformation upon integration into liposomal bilayers. These revealed that the peptide lipidation pattern, the lipid anchor chain length, and the liposome surface charge all significantly alter peptide conformation. Peptide aggregation could also be modulated post-liposome assembly by the addition of distinct small molecule ß-sheet breakers. Immunization of both mice and monkeys with a model liposomal vaccine containing ß-sheet aggregated lipopeptide (Palm1-15) induced polyclonal IgG antibodies that specifically recognized ß-sheet multimers over monomer or non-pathological native protein. The rational design of liposome-bound peptide immunogens with defined conformation opens up the possibility to generate vaccines against a range of protein misfolding diseases, such as Alzheimer disease.

Efficacy and safety of a liposome-based vaccine against protein Tau, assessed in tau.P301L mice that model tauopathy.

Progressive aggregation of protein Tau into oligomers and fibrils correlates with cognitive decline and synaptic dysfunction, leading to neurodegeneration in vulnerable brain regions in Alzheimer's disease. The unmet need of effective therapy for Alzheimer's disease, combined with problematic pharmacological approaches, led the field to explore immunotherapy, first against amyloid peptides and recently against protein Tau. Here we adapted the liposome-based amyloid vaccine that proved safe and efficacious, and incorporated a synthetic phosphorylated peptide to mimic the important phospho-epitope of protein Tau at residues pS396/pS404. We demonstrate that the liposome-based vaccine elicited, rapidly and robustly, specific antisera in wild-type mice and in Tau.P301L mice. Long-term vaccination proved to be safe, because it improved the clinical condition and reduced indices of tauopathy in the brain of the Tau.P301L mice, while no signs of neuro-inflammation or other adverse neurological effects were observed. The data corroborate the hypothesis that liposomes carrying phosphorylated peptides of protein Tau have considerable potential as safe and effective treatment against tauopathies, including Alzheimer's disease.