Antigen-specific cytotoxicity and cell number of adoptively transferred T cells are efficiently maintained in vivo by re-stimulation with an antigen/interleukin-2 fusion protein

IL-2 suppression of IL-12p70 by a recombinant HSV-1 expressing IL-2 induces T-cell auto-reactivity and CNS demyelination

To evaluate the role of cellular infiltrates in CNS demyelination in immunocompetent mice, we have used a model of multiple sclerosis (MS) in which different strains of mice are infected with a recombinant HSV-1 expressing IL-2. Histologic examination of the mice infected with HSV-IL-2 demonstrates that natural killer cells, dendritic cells, B cells, and CD25 (IL-2rα) do not play any role in the HSV-IL-2-induced demyelination. T cell depletion, T cell knockout and T cell adoptive transfer experiments suggest that both CD8⁺ and CD4⁺ T cells contribute to HSV-IL-2-induced CNS demyelination with CD8⁺ T cells being the primary inducers. In the adoptive transfer studies, all of the transferred T cells irrespective of their CD25 status at the time of transfer were positive for expression of FoxP3 and depletion of FoxP3 blocked CNS demyelination by HSV-IL-2. The expression levels of IL-12p35 relative to IL-12p40 differed in BM-derived macrophages infected with HSV-IL-2 from those infected with wild-type HSV-1. HSV-IL-2-induced demyelination was blocked by injecting HSV-IL-2-infected mice with IL-12p70 DNA. This study demonstrates that suppression of the IL-12p70 function of macrophages by IL-2 causes T cells to become auto-aggressive. Interruption of this immunoregulatory axis results in demyelination of the optic nerve, the spinal cord and the brain by autoreactive T cells in the HSV-IL-2 mouse model of MS.

IL-2/neuroantigen fusion proteins as antigen-specific tolerogens in experimental autoimmune encephalomyelitis (EAE): correlation of T cell-mediated antigen presentation and tolerance induction

The purpose of this study was to assess whether the Ag-targeting activity of cytokine/neuroantigen (NAg) fusion proteins may be associated with mechanisms of tolerance induction. To assess this question, we expressed fusion proteins comprised of a N-terminal cytokine domain and a C-terminal NAg domain. The cytokine domain comprised either rat IL-2 or IL-4, and the NAg domain comprised the dominant encephalitogenic determinant of the guinea pig myelin basic protein. Subcutaneous administration of IL2NAg (IL-2/NAg fusion protein) into Lewis rats either before or after an encephalitogenic challenge resulted in an attenuated course of experimental autoimmune encephalomyelitis. In contrast, parallel treatment of rats with IL4NAg (IL-4/NAg fusion protein) or NAg lacked tolerogenic activity. In the presence of IL-2R(+) MHC class II(+) T cells, IL2NAg fusion proteins were at least 1,000 times more potent as an Ag than NAg alone. The tolerogenic activity of IL2NAg in vivo and the enhanced potency in vitro were both dependent upon covalent linkage of IL-2 and NAg. IL4NAg also exhibited enhanced antigenic potency. IL4NAg was approximately 100-fold more active than NAg alone in the presence of splenic APC. The enhanced potency of IL4NAg also required covalent linkage of cytokine and NAg and was blocked by soluble IL-4 or by a mAb specific for IL-4. Other control cytokine/NAg fusion proteins did not exhibit a similar enhancement of Ag potency compared with NAg alone. Thus, the IL2NAg and IL4NAg fusion proteins targeted NAg for enhanced presentation by particular subsets of APC. The activities of IL2NAg revealed a potential relationship between NAg targeting to activated T cells, T cell-mediated Ag presentation, and tolerance induction.

Prolongation of the survival of breast cancer-bearing mice immunized with GM-CSF-secreting syngeneic/allogeneic fibroblasts transfected with a cDNA expression library from breast cancer cells

Breast cancer cells, like other types of neoplastic cells, form weakly immunogenic tumor-associated antigens. The antigenic properties of the tumor-associated antigens can be enhanced if they are expressed by highly immunogenic cells. In this study, a cancer vaccine was prepared by transfer of a cDNA expression library from SB5b breast carcinoma into mouse fibroblast cells of C3H/He mouse origin (H-2(k)), that had been previously modified to secrete GM-CSF and to express allogeneic class I-determinants (H-2(b)). The transfected syngeneic/allogeneic fibroblasts secreting GM-CSF were used as a vaccine in C3H/He mice. Robust cell-mediated immunity toward the breast cancer cells was generated in mice immunized with the cDNA-based vaccine. The immunity, mediated predominantly by CD8(+) T lymphocytes, was directed toward the breast cancer cells, but not against either of two other non-cross-reactive neoplasms of C3H/He mice. The immunity was sufficient to prolong the survival of mice with established breast cancer. Among other advantages, preparation of the vaccine by cDNA-transfer into a fibroblast cell line enabled the recipient cells to be modified in advance of DNA-transfer to augment their immunogenic properties. As the transferred DNA is replicated as the transfected cells divide, the vaccine could be prepared from microgram quantities of tumor tissue.

CD8+-dependent CNS demyelination following ocular infection of mice with a recombinant HSV-1 expressing murine IL-2

Demyelinating diseases comprise a spectrum of immunopathologic syndromes in which myelin, the fatty covering of nerve cell fibers in the brain and spinal cord, is destroyed. In this study, we have shown for the first time that ocular infection of BALB/c mice with a recombinant herpes simplex virus type 1 (HSV-1) expressing IL-2 (HSV-IL-2) results in CNS demyelination as determined by light microscopy and EM. The demyelinated lesions involve periventricular white matter, brain stem, and spinal cord white matter. Demyelination was detected in the CNS of infected mice up to 75 days (the longest time point tested) post HSV-IL-2 infection. In contrast, mice infected with HSV-IFN-gamma or HSV-IL-4, which are identical to HSV-IL-2 but express IFN-gamma or IL-4 instead of IL-2, did not exhibit demyelination. Control mice infected with wild-type HSV-1 or parental virus also remained free of these symptoms. During early times (days 3-7), post-infection with HSV-IL-2 virus, a T(H)1 + T(H)2 pattern of cytokines was produced by lymphocytes of infected mice while mice infected with HSV-IFN-gamma or control viruses produced a T(H)1 pattern of cytokine. By day 21 post-infection, all infected groups exhibited a T(H)1 pattern of response. Immunohistochemistry and FACS analyses of infiltrates in the brains and spinal cords of HSV-IL-2-infected mice showed elevations in CD4+ and CD8+ T cells and macrophages. However, T cell depletion studies suggest that only central memory CD8+ T cells are directly involved in the demyelination process, with macrophages being involved through a bystander effect.

Immunity to breast cancer in mice immunized with fibroblasts transfected with a cDNA expression library derived from small numbers of breast cancer cells

Immunotherapy of breast cancer at an early stage of the disease increases the likelihood of success. Here, in a mouse model, we report a new strategy that enables vaccines to be prepared from microgram amounts of tumor tissue. The vaccine is prepared by transfer of a cDNA expression library from relatively small numbers of breast cancer cells into a highly immunogenic cell line, where genes specifying TAA are expressed. As the transferred DNA is integrated and replicated as the recipient cells divide, the number of vaccine cells can be conveniently expanded for repeated immunizations. A cDNA expression library prepared from a breast cancer that arose spontaneously in a C3H/He mouse (H-2(k)) was transferred into a mouse fibroblast cell line derived from C3H/He mice. To augment their nonspecific immunogenic properties, the fibroblasts were genetically modified before DNA transfer to secrete IL-2 and to express allogeneic MHC class I H-2K(b)-determinants. C3H/He mice, highly susceptible to growth of the breast cancer cells, were immunized with the cDNA-transfected cells. Robust breast cancer-specific CD8(+) T-cell-mediated immunity was generated in the mice, raising the possibility that an analogous treatment strategy could be used to treat breast cancer patients at an early stage of the disease.

Generation of tumor-specific cytotoxic T lymphocyte and prolongation of the survival of tumor-bearing mice using interleukin-18-secreting fibroblasts loaded with an epitope peptide

There is currently much interest in generating cytotoxic T lymphocyte (CTL) responses against tumor antigens as a therapy for cancer. In this study mouse fibroblasts (H-2(b)) were genetically modified to express a costimulatory B7.1 and a mature interleukin (IL)-18, and then loaded with an ovalbumin (OVA) epitope (SIINFEKL, H-2K(b) restricted) as a model antigen, and tested for the induction of OVA-specific CTLs in C57BL/6 mice (H-2(b)). The genetically modified fibroblasts lacking either IL-18 or B7.1 were also constructed. Immunization with the IL-18/B7.1-transfected fibroblasts induced strong cytotoxic activities against OVA-expressing EL4 (EG7) tumor cells, but not against other H-2(b) tumor cells such as EL4, C1498, and B16F1 cells. The magnitude of the cytotoxic response in mice with the IL-18/B7.1-transfected fibroblasts was significantly higher than the response in mice immunized with any other cell constructs. CD8(+) T cells with OVA-specific cytotoxic activities were predominant in mice immunized with the IL-18/B7.1-transfected fibroblasts. Furthermore, treatment with the IL-18/B7.1-transfected fibroblasts significantly prolonged the survival period of EG7 tumor-bearing mice. Anti-tumor CTL immunity by the IL-18/B7.1-transfected fibroblasts could be induced without the help of host antigen-presenting cells (APCs) and NK1.1(+) cells, whereas partially decreased by the depletion of CD4(+) T cells at the inductive stage. These results support the ability of IL-18/B7.1 gene transfer to enhance the antigen-presenting capacity of fibroblasts for inducing antigen-specific CTL response.

Effector and memory T-cell differentiation: implications for vaccine development

Recent work shows that after stimulation with antigen, CD4+ and CD8+ T cells embark on a programme of proliferation that is closely linked with the acquisition of effector functions and leads ultimately to memory-cell formation. Here, we discuss the signals required for commitment to this programme of development and the factors that might influence its progression. Models of the pathways of effector and memory T-cell differentiation are discussed, and we highlight the implications of this new understanding for the optimization of vaccine strategies.

Interleukin-2 fusion protein with anti-CD3 single-chain Fv (sFv) selectively protects T cells from dexamethasone-induced apoptosis

Apoptosis of mature T cells may be an important pathophysiologic mechanism in diseases such as AIDS, cancer, and autoimmunity. In this study, in order to selectively protect T cells from dexamethasone (DEX)-induced apoptosis we constructed a fusion protein (anti-CD3sFv-IL-2) in which anti-CD3 single-chain Fv (sFv), the smallest unit of antibody recognizing the CD3 epsilon moiety of the T-cell receptor (TCR), was covalently linked to murine interleukin-2 (IL-2). Recombinant anti-CD3sFv protein was also expressed and used as a control. The purified anti-CD3sFv-IL-2 protein displayed IL-2 bioactivity in an IL-2 proliferation assay, which was inhibited by a neutralizing mIL-2 mAb. The anti-CD3sFv-IL-2 protein protected T lymphoma cells (S49.1) from DEX-induced apoptosis as demonstrated by oligonucleosomal genomic DNA fragmentation assay, and also recovered proliferation capacity of DEX-treated S49.1 cells and increased T cell composition both in DEX-treated spleen cell-populations and in DEX-treated mice, while the anti-CD3sFv protein did not. In addition, the anti-CD3sFv-IL-2 fusion protein was more efficient than a simple mixture of anti-CD3sFv and free rIL-2 in selectively protecting T cells from DEX-induced apoptosis. The levels of bcl-2 gene expression were significantly increased in DEX-treated T cells in the presence of the anti-CD3sFv-IL-2 protein. These studies indicate that the anti-CD3sFv-IL-2 fusion protein can selectively protect T cells from DEX-induced apoptosis and that the covalent linkage of anti-CD3sFv and IL-2 confines the anti-apoptotic effect of IL-2 to T cells.

Leukocytes expressing green fluorescent protein as novel reagents for adoptive cell transfer and bone marrow transplantation studies

Transgenic mice expressing green fluorescent protein (GFP) were generated to provide a source of labeled leukocytes for cell transfer studies. The transgene comprises the GFP coding region under the transcriptional control of the chicken ss-actin promoter and human cytomegalovirus enhancer. Mice expressing this GFP transgene were generated in the B6D2 and in the 129SvEv backgrounds. Flow cytometric analysis of cells from the blood, spleen, and bone marrow of these transgenic mice revealed that most leukocytes, including dendritic cells and memory T cells, express GFP. In allogeneic cell transfers, donor GFP+ splenocytes were detected in the spleen and mesenteric lymph nodes of recipient mice within 2 hours after transfer and for at least 9 days thereafter. In syngeneic experiments using 129-derived GFP+ donor splenocytes, donor cells were detected in multiple tissues of 129 recipients from 2 hours to 3 weeks after transfer. In bone-marrow transplantation experiments using irradiated allogeneic recipients, the percent of GFP+ donor cells in recipients at 3 weeks was comparable to that seen in similar tissues of GFP+ donor mice. These data demonstrate that GFP+ transgenic mice provide a ready source of GFP-expressing primary cells that can be easily monitored after their transfer to recipient animals.

Therapeutic anti-tumor response induced with epitope-pulsed fibroblasts genetically engineered for B7.1 expression and IFN-gamma secretion

Mouse fibroblasts (H-2(b)) were genetically engineered to express a co-stimulatory B7.1 and an IFN-gamma (Fb/IFN-gamma/B7.1). The Fb/IFN-gamma/B7.1 cells were then pulsed with an ovalbumin epitope (amino acids 257-264, SIINFEKL, H-2K(b)-restricted) as a model antigen (Fb/IFN-gamma/B7.1/OVA) and tested for the induction of OVA-specific cytotoxic T lymphocytes (CTLs) in C57BL/6 mice (H-2(b)). Genetically engineered fibroblasts lacking either IFN-gamma or B7.1 were constructed and used as controls. Immunization with the Fb/IFN-gamma/B7.1/OVA cells induced strong cytotoxic activity against OVA-expressing EL4 (EG7) tumor cells but not against other H-2(b) tumor cells, such as EL4, C1498, and B16F1. The magnitude of the cytotoxic response in mice with the Fb/IFN-gamma/B7.1/OVA cells was significantly higher than that in mice immunized with any other cell construct. CD8(+) T cells with OVA-specific cytotoxic activity were predominant in mice immunized with Fb/IFN-gamma/B7.1/OVA cells. Furthermore, treatment with Fb/IFN-gamma/B7.1/OVA cells significantly prolonged the survival period of EG7 tumor-bearing mice. Anti-tumor CTL immunity by the Fb/IFN-gamma/B7.1/OVA cells could be induced without the help of host antigen-presenting cells, CD4(+) T cells, or NK1.1(+) cells. Our results suggest that fibroblasts can be genetically modified into efficient antigen-presenting cells for the induction of antigen-specific CTL response in cancer immunotherapy.

Augmentation of antitumor immunity by genetically engineered fibroblast cells to express both B7.1 and interleukin-7

Mouse fibroblasts (H-2(b)) were genetically engineered to express a costimulatory B7.1 and an interleukin-7 (IL-7; Fb/B7.1/IL7). The Fb/B7.1/IL7 cells were then pulsed with an ovalbumin (OVA) epitope (amino acids 257-264, SIINFEKL, H-2 K(b) restricted; Fb/B7. 1/IL7/OVA) and tested for the induction of OVA-specific cytotoxic T lymphocytes (CTLs) in C57BL/6 mice (H-2(b)). The genetically engineered fibroblasts lacking either B7.1 or IL-7 were constructed and used as controls. Immunization with the Fb/B7.1/IL7/OVA cells induced strong cytotoxic activities against OVA-expressing EL4 (EG7) tumor cells. The magnitude of the cytotoxic response in mice with the Fb/B7.1/IL7/OVA cells was significantly higher than the response in mice immunized with any other cell constructs. CD8(+) T cells were a major effector cell-type of antitumor response in the immunized mice with the Fb/B7.1/IL7/OVA cells. Furthermore, immunization with the Fb/B7.1/IL7/OVA cells significantly prolonged the survival period of mice when the mice were injected with EG7 tumor cells one week after the immunization. These results suggest that fibroblasts can be genetically modified to an efficient cell vaccine for the induction of antitumor response.

Targeting early events in T cell activation to construct improved vaccines

Live, attenuated vaccines currently offer the best protection against virulent pathogens. Recent advances in Immunology and Molecular Biology provide an opportunity to design vaccines that will be more effective and safer than existing ones. Immunologists are rapidly developing the capacity to identify and construct the minimal immunogenic units from pathogens. The molecular signals required to fully activate antigen presenting cells (APCs) and responder T cells are becoming apparent. Improved vaccine delivery systems are being designed which will mimic the actions of pathogens in vivo. These vaccines will incorporate protective epitopes fused to immunoregulatory cytokines in chimeric proteins. They will be encapsulated in formulations which allow for the slow release of these chimeric proteins thereby inducing the memory T cells required for long-lived immunity. These vaccine formulations will target receptors present on the most active APCs. Here we discuss how these advances will allow us to rationally construct "virtual pathogens" which will provide improved protection against new and old microbial foes.

In vivo cytotoxic T lymphocyte elicitation by mycobacterial heat shock protein 70 fusion proteins maps to a discrete domain and is CD4(+) T cell independent

To gain insights into the mechanisms by which soluble heat shock protein (hsp) fusions can elicit CD8(+) cytotoxic T lymphocytes (CTLs) against the fusion partner, mycobacterial (Mycobacterium tuberculosis) hsp70 was dissected to ascertain whether a particular hsp domain is necessary, and knockout mice were used to determine whether the fusion protein's immunogenicity is dependent on CD4(+) T lymphocytes. We found that the ability to elicit CD8(+) CTLs depends on a discrete 200-amino acid protein domain, indicating that the fusion protein's immunogenicity for CD8(+) T cells does not require coupled chaperone function or peptide binding. Further, we found that ovalbumin (OVA).hsp70 fusion protein elicited anti-OVA CD8(+) CTLs about equally well in CD4 knockout and wild-type C57BL/6 mice, and also when the hsp70 was of murine (self) origin. The ability of hsp70 fusion proteins to elicit CD4-independent CTL responses suggests that hsp70 fusion proteins may be useful for immunological prophylaxis and therapy against disease in CD4(+) T cell-deficient individuals.