The majority of vaccine candidates in clinical development are highly purified proteins and peptides relying on adjuvants to enhance and/or direct immune responses. Despite the acknowledged need for ...novel adjuvants, there are still very few adjuvants in licensed human vaccines. A vast number of adjuvants have been tested pre-clinically using different experimental conditions, rendering it impossible to directly compare their activity. We performed a head-to-head comparison of five different adjuvants Alum, MF59®, GLA-SE, IC31® and CAF01 in mice and combined these with antigens from M. tuberculosis, influenza, and chlamydia to test immune-profiles and efficacy in infection models using standardized protocols. Regardless of antigen, each adjuvant had a unique immunological signature suggesting that the adjuvants have potential for different disease targets. Alum increased antibody titers; MF59® induced strong antibody and IL-5 responses; GLA-SE induced antibodies and Th1; CAF01 showed a mixed Th1/Th17 profile and IC31® induced strong Th1 responses. MF59® and GLA-SE were strong inducers of influenza HI titers while CAF01, GLA-SE and IC31® enhanced protection to TB and chlamydia. Importantly, this is the first extensive attempt to categorize clinical-grade adjuvants based on their immune profiles and protective efficacy to inform a rational development of next generation vaccines for human use.
The majority of vaccine candidates in clinical development are highly purified proteins and peptides relying on adjuvants to enhance and/or direct immune responses. Despite the acknowledged need for ...novel adjuvants, there are still very few adjuvants in licensed human vaccines. A vast number of adjuvants have been tested pre-clinically using different experimental conditions, rendering it impossible to directly compare their activity. We performed a head-to-head comparison of five different adjuvants Alum, MF59 (R), GLA-SE, IC31 (R) and CAF01 in mice and combined these with antigens from M. tuberculosis, influenza, and chlamydia to test immune-profiles and efficacy in infection models using standardized protocols. Regardless of antigen, each adjuvant had a unique immunological signature suggesting that the adjuvants have potential for different disease targets. Alum increased antibody titers; MF59 (R) induced strong antibody and IL-5 responses; GLA-SE induced antibodies and Th1; CAF01 showed a mixed Th1/Th17 profile and IC31 (R) induced strong Th1 responses. MF59 (R) and GLA-SE were strong inducers of influenza HI titers while CAF01, GLA-SE and IC31 (R) enhanced protection to TB and chlamydia. Importantly, this is the first extensive attempt to categorize clinical-grade adjuvants based on their immune profiles and protective efficacy to inform a rational development of next generation vaccines for human use.
Infection with hepatitis C virus (HCV), a leading cause of chronic liver diseases, can associate with B lymphocyte proliferative disorders, such as mixed cryoglobulinemia and non-Hodgkin lymphoma. ...The major envelope protein of HCV (HCV-E2) binds, with high affinity CD81, a tetraspanin expressed on several cell types. Here, we show that engagement of CD81 on human B cells by a combination of HCV-E2 and an anti-CD81 mAb triggers the JNK pathway and leads to the preferential proliferation of the $na\ddot{i}ve$ (CD27-) B cell subset. In parallel, we have found that B lymphocytes from the great majority of chronic hepatitis C patients are activated and that $na\ddot{i}ve$ cells display a higher level of activation markers than memory (CD27+) B lymphocytes. Moreover, eradication of HCV infection by IFN therapy is associated with normalization of the activation-markers expression. We propose that CD81-mediated activation of B cells in vitro recapitulates the effects of HCV binding to B cell CD81 in vivo and that polyclonal proliferation of $na\ddot{i}ve$ B lymphocytes is a key initiating factor for the development of the HCV-associated B lymphocyte disorders.
A widely accepted model for regulation of the Lck tyrosine kinase is that it is activated by CD45-mediated dephosphorylation of its COOH-terminal negative regulatory tyrosine (Tyr505). Previous work ...from our laboratory, however, found that despite hyperphosphorylation of Tyr505, the activity of Lck from CD45- T cell lines was actually increased due to hyperphosphorylation of the positive regulatory tyrosine, residue 394. To avoid potential complications introduced by transformed cells, in this study we have characterized the effect of CD45 on Lck activity in normal cells. Lck in thymocytes from CD45-/- mice was hyperphosphorylated on tyrosine residues. Importantly, and in disagreement with the model that CD45 only activates Lck in vivo, the kinase activity of Lck from cells lacking CD45 was substantially increased. These results support a model in which CD45 dephosphorylates both Tyr505 and Tyr394, the net effect in normal thymocytes being a decrease in enzymatic activity.
The ability of a T cell to be activated is critically regulated by the number of TCRs expressed on the plasma membrane. Cell surface TCR expression is influenced by dynamic processes such as ...synthesis and transport of newly assembled receptors, endocytosis of surface TCR, and recycling to the plasma membrane of internalized receptors. In this study, the internalization of fluorescently labeled anti-TCR Abs was used to analyze constitutive endocytosis of TCRs on T cells, and to investigate the role of the zeta-chain in this process. We found that cell surface TCRs lacking zeta were endocytosed more rapidly than completely assembled receptors, and that reexpression of full-length zeta led to a dose-dependent decrease in the rate of TCR internalization. Rapid TCR internalization was also observed with CD4(+)CD8(+) thymocytes from zeta-deficient mice, whereas TCR internalization on thymocytes from CD3-delta deficient animals was slow, similar to that of wild-type thymocytes. This identifies a specific role for zeta in the regulation of constitutive receptor internalization. Furthermore, chimeric zeta molecules containing non-native intracellular amino acid sequences also led to high levels of TCR expression and reduced TCR cycling. These effects were dependent solely on the length of the intracellular tail, ruling out a role for intracellular zeta-specific interactions with other molecules as a mechanism for regulating TCR internalization. Rather, these findings strongly support a model in which the zeta-chain stabilizes TCR residency on the cell surface, and functions to maintain cell surface receptor expression by sterically blocking internalization sequences in other TCR components.
Small changes in the complex between a peptide and a molecule of the major histocompatibilty complex generate ligands able to partially activate (partial agonist) or even inhibit (antagonist) T-cell ...functions. T-cell receptor engagement of antagonist complex results in a partial $\zeta $ chain phosphorylation without activation of the associated ZAP-70 kinase. Herein we show that, despite a strong inhibition of both inositol phospholipid hydrolysis and extracellular regulated kinase activation, exposure of a T-cell clone to increasing antagonist concentrations increased the activity of the CD4-Lck kinase. Addition of anti-CD4 antibody to culture medium prevented inhibitory effects induced by antagonist ligand. We propose that CD4-Lck activation triggered by antagonist complexes may act in a dominant negative mode, thus overriding stimulatory signals coming from agonist ligand. These findings identify a new T-cell signaling profile that may explain the ability of some T-cell receptor variant ligands to inhibit specific biological activities or trigger alternative activation programs.
Bispecific antibodies binding to the TCR/CD3 complex and to a tumor‐associated surface molecule can be used to target cytotoxic T lymphocytes against tumor cells. We reasoned that high‐affinity ...binding to CD3 may reduce the efficiency of T cell stimulation and target the bispecific reagent to T cells rather than to tumor cells in vivo. We therefore mutated a bispecific single‐chain antibody (BscAb) directed to human CD3 and EpCAM to generate variants that bind to CD3 with higher or lower affinity. When compared to the wild‐type molecule, a mutant with increased binding to CD3 showed lower capacity to target T cells against an EpCAM+ tumour. In contrast, mutants with decreased binding to CD3, in spite of rapid dissociation, efficiently triggered T cell activation and cytotoxicity, especially when present on tumor cells at low copy number. These results are consistent with the TCR serial triggering model and suggest that BscAb with extremely low affinityfor the TCR‐CD3 complex could be exploited therapeutically because of their preferential localization to tumor cells.
The mechanism by which TCR expression is regulated was explored by expressing a constitutively active form of the tyrosine kinase Lck (Lck
505F) in T cells. Expression of Lck
505F down-regulated TCR ...levels, an effect that was even more pronounced in CD45
− T cells, in which the activity of this tyrosine kinase is further enhanced. Cells expressing Lck
505F synthesized all TCR subunits, but lysosomal degradation of assembled receptors was enhanced. TCRs were rapidly internalized and degraded after removal of a tyrosine kinase inhibitor that had permitted cell surface expression. Finally, TCR levels on thymocytes were increased by an Lck inhibitor, and activation- but not phorbol ester–induced internalization of TCRs on Jurkat cells was prevented by inhibition or loss of Lck. These studies identify a regulated nonreceptor tyrosine kinase–mediated pathway for targeting cell surface receptors for lysosomal degradation.
How does the CD45 tyrosine phosphatase regulate Src-family kinase activity
in vivo? Here, Jonathan Ashwell and Ugo D'Oro discuss evidence that, contrary to the widely accepted model, CD45 can ...actually inhibit the activity of some Src-family kinases by dephosphorylating the positive regulatory tyrosine in the activation loop of the catalytic region.
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