Xiao Song Liu

The role of interferon γ in regulation of CD4+ T-cells and its clinical implications

Interferon gamma (IFNgamma) plays a central role in the immune response against infection and tumur immune surveillance. Its functions include not only activation of the host immune system to control microbial infections but also repression of autoimmune responses by turning on T-regulatory cells and increasing T effector cell apoptosis. Defects in IFNgamma and IFNgamma receptor genes have been associated with autoimmune diseases such as rheumatoid arthritis, type 1 diabetes and multiple sclerosis. However, treatment of autoimmune diseases by supplementing with IFNgamma has been satisfactory due to its broad biological effects. Instead, its target T-regulatory cells may be used for the clinical treatment of autoimmune diseases. Future study could also focus on promotion of the beneficial effects of IFNgamma and blocking those unwanted IFNgamma-induced activities.

Activation of dendritic cells by human papillomavirus-like particles through TLR4 and NF-κB-mediated signalling, moderated by TGF-β

Human papillomavirus‐like particles (HPV‐VLP) are a candidate vaccine for prevention of HPV infection, and also are a candidate for an immunogenic delivery system for incorporated antigen. VLP activate in vitro generated dendritic cells (DC) but not Langerhans cells (LC); however, the mechanism of this activation is unknown. We have shown that uptake and activation of DC by VLP involves proteoglycan receptors and can be inhibited by heparin. Heparin has been shown to activate DC by signalling through Toll‐like receptor 4 (TLR4) and nuclear factor (NF)‐κB. The pathway of DC activation by VLP was further investigated in the present study. Exposure to VLP induced costimulatory molecule expression, RelB translocation and IL‐10 production by DC but not by LC. The lack of LC activation was reversible when TGF‐β was removed from the LC medium. VLP‐induced induction of costimulatory molecule expression, RelB activation and cytokine secretion by DC was blocked by inhibition of NF‐κB activation, heparin or TLR4 mAb. The data provide evidence that HPV‐VLP signal DC through a pathway involving proteoglycan receptors, TLR4 and NF‐κB, and shed light on the mechanism by which VLP stimulate immunity in the absence of adjuvants in vivo. LC may resist activation in normal epithelium abundant in TGF‐β, but not in situations in which TGF‐β concentrations are reduced.

IL-10 Mediates Suppression of the CD8 T Cell IFN-γ. Response to a Novel Viral Epitope in a Primed Host

Priming to Ag can inhibit subsequent induction of an immune response to a new epitope incorporated into that Ag, a phenomenon referred to as original antigenic sin. In this study, we show that prior immunity to a virus capsid can inhibit subsequent induction of the IFN-γ effector T cell response to a novel CD8-restricted antigenic epitope associated with the virus capsid. Inhibition does not involve Ab to the virus capsid, as it is observed in animals lacking B cells. CD8-restricted virus-specific T cell responses are not required, as priming to virus without CTL induction is associated with inhibition. However, IL-10−/− mice, in contrast to IL-10+/+ mice, generate CD8 T cell and Ab responses to novel epitopes incorporated into a virus capsid, even when priming to the capsid has resulted in high titer Ab to the capsid. Furthermore, capsid-primed mice, unable to mount a response to a novel epitope in the capsid protein, are nevertheless able to respond to the same novel epitope delivered independently of the capsid. Thus, inhibition of responsiveness to a novel epitope in a virus-primed animal is a consequence of secretion of IL-10 in response to presented Ag, which inhibits local generation of new CD8 IFN-γ-secreting effector T cells. Induction of virus- or tumor Ag-specific CD8 effector T cells in the partially Ag-primed host may thus be facilitated by local neutralization of IL-10.

IFN-γ Promotes Generation of IL-10 Secreting CD4+ T Cells that Suppress Generation of CD8 Responses in an Antigen-Experienced Host

Ags characterizing tumors or chronic viral infection are generally presented to the host immune system before specific immunotherapy is initiated, and consequent generation of regulatory CD4+ T cells can inhibit induction of desired effector CD8 T cell responses. IL-10 produced in response to ongoing Ag exposure inhibits generation of CD8 T cells in an Ag-experienced host. We now show that this IL-10 is produced by Ag experienced CD4+ glucocorticoid-induced tumor necrosis factor receptor+ T cells that also secrete IFN-γ upon antigenic stimulation, that IL-10 secretion by these cells is enhanced through IFN-γ signaling, and, unexpectedly, that IFN-γ signaling is required for inhibition of generation of Ag-specific CD8 T cell responses in an Ag-experienced host. Systemic inhibition of both IL-10 and IFN-γ at the time of immunization may therefore facilitate induction of effective immunotherapeutic responses against tumor specific and viral Ags.

Overcoming Original Antigenic Sin to Generate New CD8 T Cell IFN-γ Responses in an Antigen-Experienced Host

The failure to mount effective immunity to virus variants in a previously virus-infected host is known as original antigenic sin. We have previously shown that prior immunity to a virus capsid protein inhibits induction by immunization of an IFN-γ CD8+ T cell response to an epitope linked to the capsid protein. We now demonstrate that capsid protein-primed CD4+ T cells secrete IL-10 in response to capsid protein presented by dendritic cells, and deviate CD8+ T cells responding to a linked MHC class I-restricted epitope to reduce IFN-γ production. Neutralizing IL-10 while delivering further linked epitope, either in vitro or in vivo, restores induction by immunization of an Ag-specific IFN-γ response to the epitope. This finding demonstrates a strategy for overcoming inhibition of MHC class I epitopes upon immunization of a host already primed to Ag, which may facilitate immunotherapy for chronic viral infection or cancer.

Paucity of functional CTL epitopes in the E7 oncoprotein of cervical cancer associated human papillomavirus type 16

Many specific antiviral and antitumour immune responses have been attributed to the protective effects of antigen‐specific CD8+ cytotoxic T lymphocytes (CTL). Recognition of virus infected or tumour cells by CTL requires presentation of at least one peptide epitope from a virus or tumour‐specific antigen by the relevant MHC Class I molecule. Viral genes with mutations which remove CTL epitopes may thus be favoured for survival. Human cervical cancers are caused by papillomavirus infection, and these cancers consistently express the E7 protein of the oncogenic papillomavirus. We therefore investigated the MHC Class I restricted T cell epitopes of the human papillomavirus type 16 E7 oncoprotein using mice of five different genetic backgrounds, and an IFN‐γ ELISPOT assay, to determine the frequency with which MHC Class I epitopes might be expected in this small oncoprotein (98 amino acids). No MHC Class I restricted responses were detected in E7 immunized BALB/c (H‐2d), CBA/CaH (H‐2 k), FVB/N (H‐2q) or A2KbH2b human HLA2.1 transgenic mice. In C57BL/6 J (H‐2b) mice, a previously identified single antigenic epitope was detected. Therefore, we conclude that there is a paucity of MHC Class I restricted T cell epitopes in HPV16 E7 protein because of its small size. This might be advantageous to the virus. Furthermore here we present a quick and easy method to exhaustively determine CD8 T cell epitopes in proteins using a unique set of overlapping 8, 9 and 10 mer synthetic peptides.

Route of administration of chimeric BPV1 VLP determines the character of the induced immune responses.

To examine the mucosal immune response to papillomavirus virus‐like particles (PV‐VLP), mice were immunized with VLP intrarectally (i.r.), intravaginally (i.va.) or intramuscularly (i.m.) without adjuvant. PV‐VLP were assembled with chimeric BPV‐1 L1 proteins incorporating sequence from HIV‐1 gp120, either the V3 loop or a shorter peptide incorporating a known CTL epitope (HIVP18I10). Antibody specific for BPV‐1 VLP and P18 peptide was detected in serum following i.m., but not i.r. or i.va. immunization. Denatured VLP induced a much reduced immune response when compared with native VLP. Immune responses following mucosal administration of VLP were generally weaker than following systemic administration. VLP specific IgA was higher in intestine washes following i.r. than i.va. immunization, and higher in vaginal washes following i.m. than i.r. or i.va. immunization. No differences in specific antibody responses were seen between animals immunized with BPV‐1 P18 VLP or with BPV‐1 V3 VLP. Cytotoxic T lymphocyte precursors specific for the P18 CTL epitope were recovered from the spleen following i.m., i.va. or i.r. immunization with P18 VLP, and were similarly detected in Peyers patches following i.m. or i.r. immunization. Thus, mucosal or systemic immunization with PV VLP induces mucosal CTL responses and this may be important for vaccines for mucosal infection with human papillomaviruses and for other viruses.