A major barrier to successful antitumor vaccination is tolerance of high-avidity T cells specific to tumor antigens. In keeping with this notion, HER-2/neu (neu)-targeted vaccines, which raise strong CD8+ T cell responses to a dominant peptide (RNEU420-429) in WT FVB/N mice and protect them from a neu-expressing tumor challenge, fail to do so in MMTV-neu (neu-N) transgenic mice. However, treatment of neu-N mice with vaccine and cyclophosphamide-containing chemotherapy resulted in tumor protection in a proportion of mice. This effect was specifically abrogated by the transfer of neu-N–derived CD4+CD25+ T cells. RNEU420-429-specific CD8+ T cells were identified only in neu-N mice given vaccine and cyclophosphamide chemotherapy which rejected tumor challenge. Tetramer-binding studies demonstrated that cyclophosphamide pretreatment allowed the activation of high-avidity RNEU420-429-specific CD8+ T cells comparable to those generated from vaccinated FVB/N mice. Cyclophosphamide seemed to inhibit regulatory T (T reg) cells by selectively depleting the cycling population of CD4+CD25+ T cells in neu-N mice. These findings demonstrate that neu-N mice possess latent pools of high-avidity neu-specific CD8+ T cells that can be recruited to produce an effective antitumor response if T reg cells are blocked or removed by using approaches such as administration of cyclophosphamide before vaccination.

SummaryAutoimmunity occurs when the immune system recognizes and attacks host tissue. In addition to genetic factors, environmental triggers (in particular viruses, bacteria and other infectious pathogens) are thought to play a major role in the development of autoimmune diseases. In this review, we (i) describe the ways in which an infectious agent can initiate or exacerbate autoimmunity; (ii) discuss the evidence linking certain infectious agents to autoimmune diseases in humans; and (iii) describe the animal models used to study the link between infection and autoimmunity.

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The HER-2/neu (neu-N)-transgenic mice are a clinically relevant model of breast cancer. They are derived from the parental FVB/N mouse strain and are transgenic for the rat form of the proto-oncogene HER-2/neu (neu). In this study, we report the identification of a MHC class I peptide in the neu protein that is recognized by CD8+ T cells derived from vaccinated FVB/N mice. This 10-mer was recognized by all tumor-specific FVB/N T cells generated regardless of the TCR Vβ region expressed by the T cell or the method of vaccination used, establishing it as the immunodominant MHC class I epitope in neu. T cells specific for this epitope were able to cure FVB/N mice of transplanted neu-expressing tumor cells, demonstrating that this is a naturally processed peptide. Altered peptide analogs of the epitope were analyzed for immunogenicity. Vaccination with dendritic cells pulsed with a heteroclitic peptide provided FVB/N and neu-N mice with increased protection against tumor challenge as compared with mice immunized with dendritic cells loaded with either wild-type or irrelevant peptide. Discovery of this epitope allows for better characterization of the CD8+ T cell responses in the neu-N mouse model in which neu-specific tolerance must be overcome to produce effective antitumor immunity.

HER-2/neu is overexpressed in several cancers including 30% of breast carcinomas, and correlates with a poor outcome. HER-2/neu-transgenic (neu-N) mice that overexpress the non-transforming rat neu develop spontaneous mammary carcinomas and demonstrate immunotolerance to the neu protein similar to that observed in patients with neu-expressing cancers. In neu-N mice, neu-targeted vaccination induces weak T cell and negligible Ab responses sufficient to delay but not eradicate transplanted neu-expressing tumor. Here we demonstrate that passive infusion of neu-specific mAbs in sequence with whole cell vaccination significantly improves tumor-free survival over either modality alone. Importantly, treatment of neu-N mice with vaccine in combination with two distinct neu-specific Abs is particularly efficacious, preventing tumor in 70% and eradicating established tumor in 30% of neu-N mice. In vivo lymphocyte subpopulation depletion experiments demonstrate that the efficacy of Ab, alone or combined with vaccine, is dependent on both CD4+ and CD8+ T cells. Furthermore, the in vivo antitumor effects of vaccine and Ab are associated with a significant increase in the number and function of neu-specific CD8+ T cells. Collectively, these observations suggest that similarly increased efficacy could be obtained by combining neu-targeted vaccination and neu-specific Abs such as trastuzumab (Herceptin) in patients with neu-expressing cancers.

Many disorders of the CNS, such as multiple sclerosis (MS), are characterized by the loss of the myelin sheath surrounding nerve axons. MS is associated with infiltration of inflammatory cells into the brain and spinal cord, which may be the primary cause of demyelination or which may be induced secondary to axonal damage. Both the innate and adaptive arms of the immune system have been reported to play important roles in myelin destruction. Numerous murine demyelinating models, both virus-induced and/or autoimmune, are available, which reflect the clinical and pathological variability seen in human disease. This review will discuss the immunopathologic mechanisms involved in these demyelinating disease models.

Multiple sclerosis (MS) is a chronic autoimmune neurological disease characterized by infiltration of peripheral inflammatory cells to the central nervous system (CNS) and demyelination of CNS white matter. Epidemiological evidence suggests a possible infectious trigger. One potential mechanism by which an infectious agent may trigger MS is via molecular mimicry wherein T cells generated against foreign epitopes cross-react with self myelin epitopes, such as myelin basic protein (MBP), with sufficient sequence similarity. It has been previously reported that an MBP 85-99 -reactive T cell clone derived from an MS patient cross-reacted with multiple bacterial-derived mimic peptides in vitro. We show that the same mimic peptides can induce clinical disease in two different strains of mice transgenic for both a human MBP 85-99 -specific TCR and HLA-DR2 (MHC II), albeit with different disease patterns -relapsing-remitting vs. monophasic. Interestingly, clinical disease correlates with CNS infiltration of CD4 + T cells and F4/80 + macrophages, but not with in vitro proliferative or cytokine responses of splenocytes in response to either MBP 85-99 or its mimics.

MS is an autoimmune CNS demyelinating disease in which infection appears to be an important pathogenic factor. Molecular mimicry, the cross-activation of autoreactive T cells by mimic peptides from infectious agents, is a possible explanation for infectioninduced autoimmunity. Infection of mice with a non-pathogenic strain of Theiler's murine encephalomyelitis virus (TMEV) engineered to express an epitope from Haemophilus influenzae (HI) sharing 6/13 amino acids with the dominant proteolipid protein (PLP) epitope, PLP 139-151 , can induce CNS autoimmune disease. Here we demonstrate that another PLP 139-151 mimic sequence derived from murine hepatitis virus (MHV) which shares only 3/13 amino acids with PLP 139-151 can also induce CNS autoimmune disease, but only when delivered by genetically engineered TMEV, not by immunization with the MHV peptide. Further, we demonstrate the importance of proline at the secondary MHC class II contact residue for effective cross-reactivity, as addition of this amino acid to the native MHV sequence increases its ability to crossactivate PLP 139-151 -specific autoreactive T cells, while substitution of proline in the HI mimic peptide has the opposite effect. This study describes a structural requirement for potential PLP 139-151 mimic peptides, and provides further evidence for infectioninduced molecular mimicry in the pathogenesis of autoimmune disease.