Induction of antigen specific CD4+ T cell responses by invariant chain based DNA vaccines

MHC II and the endocytic pathway: regulation by invariant chain

The major histocompatibility complex (MHC) class I and II molecules perform vital functions in innate and adaptive immune responses towards invading pathogens. MHC class I molecules load peptides in the endoplasmatic reticulum (ER) and display them to the T cell receptors (TcR) on CD8(+) T lymphocytes. MHC class II molecules (MHC II) acquire their peptides in endosomes and present these to the TcR on CD4+ T lymphocytes. They are vital for the generation of humoral immune responses. MHC II assembly in the ER and trafficking to endosomes is guided by a specialized MHC II chaperone termed the invariant chain (Ii). Ii self-associates into a trimer in the ER, this provides a scaffold for the assembly of three MHC II heterodimers and blocks their peptide binding grooves, thereby avoiding premature peptide binding. Ii then transports the nascent MHC II to more or less specialized compartment where they can load peptides derived from internalized pathogens.

In vivo hierarchy of individual T-cell epitope-specific helper T-cell subset against an intracellular bacterium

Cellular immunity is indispensable for efficient protection against intracellular bacterial infection. CD4+ and CD8+ T cells specific for a variety of antigenic peptides derived from particular bacteria are induced after the infection. T cells recognizing different antigenic peptides have been speculated to have different functions in terms of the protective immunity. We here induced individual CD4+ T cells specific for each antigenic peptide derived from Listeria monocytogenes independently with DNA vaccines using gene gun bombardment and compared the CD4+ T-cell populations for their ability on the specific protective immunity against lethal listerial challenge and analyzed their characteristics.

DNA vaccines encoding Ii-PADRE generates potent PADRE-specific CD4+ T-cell immune responses and enhances vaccine potency

It is now clear that CD4+ T cells play a crucial role in the generation of CD8+ T effector and memory T-cell immune responses. In this study, we enhanced the CD4+ T-cell immune responses in mice by constructing a DNA vaccine encoding an invariant (Ii) chain in which the class II-associated Ii peptide (CLIP) region is replaced with a CD4+ T-helper epitope, PADRE (Ii-PADRE) (invariant Pan HLA-DR reactive epitope). C57BL/6 mice vaccinated with DNA encoding Ii-PADRE showed significantly greater PADRE-specific CD4+ T-cell immune responses than mice vaccinated with DNA encoding the Ii chain alone (Ii DNA). More important, administration of DNA encoding human papillomavirus (HPV) E6 or E7 antigen with DNA encoding Ii-PADRE led to significantly stronger E6- or E7-specific CD8+ T-cell immune responses and more potent protective and therapeutic anti-tumor effects against an E6/E7-expressing tumor model in mice than administration of E6 or E7 DNA with Ii DNA. Overall, our data indicate that administration of DNA vaccines with Ii-PADRE DNA represents an effective approach to enhancing the generation of CD4+ T cells and eliciting stronger antigen-specific CD8+ T-cell immune responses. Therefore, this strategy may be expected to have significant potential for clinical translation.

HCV-NS3 Th1 minigene vaccine based on invariant chain CLIP genetic substitution enhances CD4+ Th1 cell responses in vivo

BACKGROUND

HCV is a major cause of chronic liver disease, cirrhosis, hepatocellular carcinoma and death of end-stage liver disease worldwide. Therapy regimen based on IFN-alpha combined with ribavirin can induce a sustained virological and biochemical response in 20-60% of treated patients depending on the HCV genotype, the virus load and the age of the patients. So the development of a preventive or a therapeutic vaccine is very desirable.

METHODS

Thirty female BALB/c mice of 6-8 weeks old were randomly divided into five groups of six each to receive injection with experimental vaccine (pHCV-NS3, pHCV-NS3-Th1) and experimental controls (saline, pCI-neo, pCI-neo-Ii), respectively. After the fifth immunization, humoral and cellular immune responses were estimated. The therapeutic efficacy was also evaluated with BALB/c mice carried tumor cells expressing HCV-NS3 protein.

RESULTS

Specific antibodies to HCV-NS3 could be detected only in pHCV-NS3 immunized group. The antibody titers reach up to 1/1024. For CD4(+) Th cell proliferation assay, only the pHCV-NS3 and pHCV-NS3-Th1 treated groups were positive according to absorbance assayed at 450nm. The absorbance of the pHCV-NS3-Th1 treated group was significant higher than that of pHCV-NS3 treated group (P<0.01, 0.002). Only the pHCV-NS3-Th1 immunized group produced detectable IFN-gamma, the concentration was 33.65pg/ml. For IL-4 detection, only pHCV-NS3 immunized group produced tiny IL-4 cytokine, the concentration was 4.55pg/ml. pHCV-NS3 and pHCV-NS3-Th1 immunized mice showed significantly lower tumorigenesis rate and higher survival rate compared to experimental controls, but no significant differences were observed in our experiment between the two vaccine immunized groups.

CONCLUSIONS

Minigene vaccine based on invariant chain CLIP genetic substitution might be a potential candidate for HCV therapeutic vaccine development. The results might also have some inspiring significance for the therapeutic vaccine development against other chronic infectious diseases and tumor.

Target HCV NS3 CD4+ Th1 epitope to major histocompatibility complex class II pathway

A hepatitis C virus (HCV) plasmid vaccine was constructed, based on class II-associated invariant chain peptide (CLIP) substitution which endogenously targets HCV non-structure protein 3 (NS3) CD4+ T helper 1(Th1) epitope (1248AA-1261AA) to major histocompatibility complex (MHC) class II antigen. The in vitro expression results demonstrated that the vaccine was expressed efficiently in COS-7 cell line. The expressed protein could co-localize in endo-membrane system with BALB/c mouse MHC class II molecule I-Ad. The recombinant invariant chain molecule could aggregate with BALB/c mouse I-Ad molecule and form the theoretical nonomer structure in the COS-7 cell line. The assembled molecules migrate to the cell surface by exocytosis. This has implications for HCV vaccine development.

Genetic approaches for the induction of a CD4+ T cell response in cancer immunotherapy

Recently, it has become more and more obvious that not only CD8+ cytotoxic T lymphocytes, but also CD4+ T helper cells are required for the induction of an optimal, long-lasting anti-tumor immune response. CD4+ T helper cells, and in particular IFN-gamma-secreting type 1 T helper cells, have been shown to fulfill a critical function in the mounting of a cancer-specific response. Consequently, targeting antigens into MHC class II molecules would greatly enhance the efficacy of an anti-cancer vaccine. The dissection of the MHC class II presentation pathway has paved the way for rational approaches to achieve this goal: novel systems have been developed to genetically manipulate the MHC class II presentation pathway. First, different genetic approaches have been used for the delivery of known epitopes into the MHC class II processing pathway or directly onto the peptide-binding groove of the MHC molecules. Second, several strategies exist for the targeting of whole tumor antigens, containing both MHC class I and class II restricted epitopes, to the MHC class II processing pathway. We review these data and describe how this knowledge is currently applied in vaccine development.

Targeting plasmid-encoded proteins to the antigen presentation pathways

The antigen presentation pathways constitute a fulcrum on which adaptive immunity is balanced, and their manipulation should allow us to induce designer immune responses. The ease and rapidity with which DNA vaccines can be constructed and altered make them ideal candidates with which to test the various targeting strategies that have been conceived to date. These approaches and the mechanisms that may (or may not) underlie their success are reviewed in this article.

Cytotoxic T-Lymphocyte-, and Helper T-Lymphocyte-Oriented DNA Vaccination

DNA vaccines have advantages over other types of vaccines in that they can induce strong cellular immune responses, namely cytotoxic T lymphocytes (CTL) and helper T lymphocytes (Th). DNA vaccines are therefore considered a promising alternative to attenuated live vaccines in the field of infectious diseases. So far, various DNA vaccines have been generated and tried to induce a particular cellular immune response by virtue of recombinant DNA technology. DNA vaccines have been designed for efficient transcription and translation of target genes by a variety of strategies. Also, various DNA vaccine strategies for induction of specific CTL and Th have been reported by taking into consideration antigen presentation pathways and the strategies have been shown to be effective to elicit particular T-cell responses. In this paper, we have reviewed these strategies, including our study on epitope-specific T-cell induction by DNA vaccination against Listeria monocytogenes infection. From this review, it has been surmised that, to induce strong immune responses by DNA vaccines, the immunization route and the immunization regimen, such as heterologous "prime-boost" regimen, should also be considered.

DNA fragments of the human 60-kDa heat shock protein (HSP60) vaccinate against adjuvant arthritis: identification of a regulatory HSP60 peptide

Adjuvant arthritis (AA) is induced by immunizing Lewis rats with Mycobacterium tuberculosis suspended in adjuvant. The mycobacterial 65-kDa heat shock protein (HSP65) contains at least one epitope associated with the pathogenesis of AA: T cell clones that recognize an epitope formed by aa 180-188 of HSP65 react with self-cartilage and can adoptively transfer AA. Nevertheless, vaccination with HSP65 or some of its T cell epitopes can prevent AA by a mechanism that seems to involve cross-reactivity with the self-60-kDa HSP60. We recently demonstrated that DNA vaccination with the human hsp60 gene can inhibit AA. In the present work, we searched for regulatory epitopes using DNA vaccination with HSP60 gene fragments. We now report that specific HSP60 DNA fragments can serve as effective vaccines. Using overlapping HSP60 peptides, we identified a regulatory peptide (Hu3) that was specifically recognized by the T cells of DNA-vaccinated rats. Vaccination with Hu3, or transfer of splenocytes from Hu3-vaccinated rats, inhibited the development of AA. Vaccination with the mycobacterial homologue of Hu3 had no effect. Effective DNA or peptide vaccination was associated with enhanced T cell proliferation to a variety of disease-associated Ags, along with a Th2/3-like shift (down-regulation of IFN-gamma secretion and enhanced secretion of IL-10 and/or tumor growth factor beta1) in response to peptide Mt176-190 (the 180-188 epitope of HSP65). The regulatory response to HSP60 or its Hu3 epitope included both Th1 (IFN-gamma) and Th2/3 (IL-10/tumor growth factor beta1) secretors. These results show that regulatory mechanisms can be activated by immunization with relevant self-HSP60 epitopes.

Induction of protective immunity to Listeria monocytogenes by immunization with plasmid DNA expressing a helper T-cell epitope that replaces the class II-associated invariant chain peptide of the invariant chain

Listeria epitope-specific helper T (Th) cells were able to be primed and induced in vivo by immunization with a plasmid carrying an invariant chain (Ii) gene whose class II-associated invariant chain peptide (CLIP) region was replaced by a Listeria Th epitope. Immunization of C3H/He mice with an Ii-LLO 215-226 plasmid induced specific interferon-gamma- and interleukin 2-producing Th cells and conferred significant protective immunity against listerial infection.

DNA fusion vaccines against B-cell tumors

DNA vaccination is currently being explored as a potential strategy for combatting cancer. However, tumor antigens are often weak and the immune system of patients may be compromised. For B-cell tumors, immunoglobulin idiotypic antigens provide defined targets but are poorly immunogenic. Fusion of a sequence derived from tetanus toxin to the genes encoding idiotypic determinants has proved highly effective in activating protective anti-tumor immunity. DNA fusion vaccines containing immuno-enhancing sequences can augment and direct immune attack on a range of target antigens. Gene-based fusion vaccines offer ease of manipulation and flexible design to activate effective attack on cancer.