Naive CD4+ T cells confer idiotype-specific tumor resistance in the absence of antibodies

Id-neoantigen vaccine induces therapeutic CD8+ T cells against multiple myeloma: H chain-loss escapees cause FLC MM

BACKGROUND

Multiple myeloma (MM) cancers originate from plasma cells that have passed through the germinal center reaction where somatic hypermutation of Ig V regions takes place. Myeloma protein V regions often express many mutations and are thus a rich source of neoantigens (traditionally called idiotopes (Id)). Therefore, these are highly tumor-specific and excellent targets for immunotherapy.

METHODS

We have developed a DNA Id vaccine which as translated protein targets conventional dendritic cells (cDC) for CCL3-mediated delivery of myeloma protein V regions in a single-chain fragment variable (scFv) format. Vaccine efficacy was studied in the mouse MM model, mineral oil-induced plasmacytoma 315.BM.

RESULTS

The Id vaccine protected mice against a challenge with MM cells. Moreover, the vaccine had a therapeutic effect. However, in some of the vaccinated mice, MM cells not producing H chains escaped rejection, resulting in free light chain (FLC) MM. Depletion of CD8+ T cells abrogated vaccine efficacy, and protection was observed to be dependent on cDC1s, using Batf3-/- mice. Modifications of scFv in the vaccine demonstrated that CD8+ T cells were specific for two mutated VH sequences.

CONCLUSIONS

VH neoantigen-specific CD8+ T cells elicited by CCL3-containing Id vaccines had a therapeutic effect against MM in a mouse model. MM cells could escape rejection by losing expression of the H chain, thus giving rise to FLC MM.

Neoantigen vaccine-induced CD4 T cells confer protective immunity in a mouse model of multiple myeloma through activation of CD8 T cells against non-vaccine, tumor-associated antigens

Background

Cancer-associated neoantigens (neoAg) derived from tumor genomic sequencing and predictive algorithms for mutated peptides are a promising basis for therapeutic vaccines under investigation. Although these are generally designed to bind major histocompatibility complex class I and induce CD8 cytolytic T lymphocyte (CTL) activity, results from preclinical and clinical studies demonstrate that the majority of neoAg vaccines efficiently induce CD4 T helper (Th) responses but not CTL. Despite this, these vaccines have demonstrated clinical efficacy. Therefore, understanding the mechanisms of CD4 + T cell-mediated tumor protection is critical to optimizing this immunotherapeutic strategy.

Methods

We investigated this phenomenon in the mineral oil-induced plasmacytoma (MOPC).315.BM (MOPC315) mouse model of multiple myeloma, a malignancy of plasma cells. MOPC315 cells express in their lambda chain a unique tumor-specific neoAg, an idiotypic (Id) peptide. We generated a vaccine formulated with this Id peptide fused to a heat shock protein HSC70 binding (HSB) motif co-delivered with poly (I:C). The immunogenicity of the Id-vaccine was measured in splenocytes by ELISpot. Mice were challenged with MOPC315 cells and antitumor immunity was assessed by co-incubating splenocytes and bone marrow mononuclear cells derived from vaccinated mice and controls, with the Id antigen and irradiated MOPC315 cells. The frequency of activated CD4 and CD8 T cells and their phenotype were characterized by flow cytometry.

Results

Id-vaccine efficiently induced antigen-specific CD4 Th activity and antitumor immunity, protecting mice from MOPC315 tumor growth. CD4 cytolytic activity was not detected under these conditions. Polyfunctional CD8 T cells homed to the bone marrow microenvironment of protected mice and preferentially expanded only when restimulated ex vivo with both Id peptide and MOPC315 cells. Protective activity was abrogated by depletion of either CD4 or CD8 lymphocytes.

Conclusion

These results demonstrate that Id-HSB +poly (I:C) vaccine protects against MOPC315 growth by priming Id-specific CD4 Th cells that confer protection against tumor but are not directly cytotoxic. These data indicate that activation of CD8 CTL against MOPC315-associated antigens not present in the vaccine is one of the major mechanisms of tumor immunity.

Tackling cancer cell dormancy: Insights from immune models, and transplantation

Disseminated non-dividing (dormant) cancer cells as well as those in equilibrium with the immune response remain the major challenge for successful treatment of cancer. The equilibrium between disseminated dormant cancer cells and the immune system is reminiscent of states that can occur during infection or allogeneic tissue and cell transplantation. We discuss here the major competing models of how the immune system achieves a self nonself discrimination (pathogen/danger patterns, quorum, and coinhibition/tuning models), and suggest that taking advantage of a combination of the proposed mechanisms in each model may lead to increased efficacy in tackling cancer cell dormancy.

A DNA Vaccine That Encodes an Antigen-Presenting Cell-Specific Heterodimeric Protein Protects against Cancer and Influenza

Immunogenicity of DNA vaccines can be increased by constructing the DNA in such a way that it encodes secreted homodimeric fusion proteins that target antigen-presenting cells (APCs). In this study, we have developed novel APC-targeting vaccine molecules with an increased flexibility due to introduction of a heterodimerization motif. The heterodimeric proteins permit four different fusions within a single molecule, thus allowing expression of two different APC-targeting moieties and two different antigens. Two types of heterodimeric fusion proteins were developed that employed either the ACID/BASE or the Barnase/Barstar motifs, respectively. The ACID/BASE heterodimeric vaccines conferred protection against challenges with either influenza virus or tumor cells in separate preclinical models. The ACID/BASE motif was flexible since a large number of different targeting moieties and antigens could be introduced with maintenance of specificity, antigenicity, and secretion. APC-targeting ACID/BASE vaccines expressing two different antigens induced antibody and T cell responses against either of the two antigens. Heterodimeric ACID/BASE DNA vaccines were of approximately the same potency as previously reported homodimeric DNA vaccines. The flexibility and potency of the ACID/BASE format suggest that it could be a useful platform for DNA vaccines that encode APC-targeting fusion proteins.

CD4+ T cells indirectly kill tumor cells via induction of cytotoxic macrophages in mouse models

It is well recognized that CD4⁺ T cells may play an important role in immunosurveillance and immunotherapy against cancer. However, the details of how these cells recognize and eliminate the tumor cells remain incompletely understood. For the past 25 years, we have focused on how CD4⁺ T cells reject multiple myeloma cells in a murine model (MOPC315). In our experimental system, the secreted tumor-specific antigen is taken up by tumor-infiltrating macrophages that process it and present a neoepitope [a V region-derived idiotypic (Id) peptide] on MHC class II molecules to Th1 cells. Stimulated Th1 cells produce IFNγ, which activates macrophages in a manner that elicits an M1-like, tumoricidal phenotype. Through an inducible nitric oxide synthetase (iNOS)-dependent mechanism, the M1 macrophages secrete nitric oxide (NO) that diffuses into neighboring tumor cells. Inside the tumor cells, NO-derived reactive nitrogen species, including peroxynitrite, causes nitrosylation of proteins and triggers apoptosis by the intrinsic apoptotic pathway. This mode of indirect tumor recognition by CD4⁺ T cells operates independently of MHC class II expression on cancer cells. However, secretion of the tumor-specific antigen, and uptake and MHCII presentation on macrophages, is required for rejection. Similar mechanisms can also be observed in a B-lymphoma model and in the unrelated B16 melanoma model. Our findings reveal a novel mechanism by which CD4⁺ T cells kill tumor cells indirectly via induction of intratumoral cytotoxic macrophages. The data suggest that induction of M1 polarization of tumor-infiltrating macrophages, by CD4⁺ T cells or through other means, could serve as an immunotherapeutic strategy.

Tumor Killing by CD4+ T Cells Is Mediated via Induction of Inducible Nitric Oxide Synthase-Dependent Macrophage Cytotoxicity

CD4⁺ T cells can induce potent anti-tumor immune responses. Due to the lack of MHC class II expression in most cancer cells, antigen recognition occurs indirectly via uptake and presentation on tumor-infiltrating antigen-presenting cells (APCs). Activation of the APCs can induce tumor rejection, but the mechanisms underlying tumor killing by such cells have not been established. To elucidate the molecular basis of CD4⁺ T-cell-mediated tumor rejection, we utilized a murine model of multiple myeloma, in which the T cells recognize a secreted tumor neoantigen. Our findings demonstrate that T cell recognition triggers inducible nitric oxide synthase activity within tumor-infiltrating macrophages. Diffusion of nitric oxide into surrounding tumor cells results in intracellular accumulation of toxic secondary oxidants, notably peroxynitrite. This results in tumor cell apoptosis through activation of the mitochondrial pathway. We find that this mode of cytotoxicity has strict spatial limitations, and is restricted to the immediate surroundings of the activated macrophage, thus limiting bystander killing. These findings provide a molecular basis for macrophage-mediated anti-tumor immune responses orchestrated by CD4⁺ T cells. Since macrophages are abundant in most solid tumors, evoking the secretion of nitric oxide by such cells may represent a potent therapeutic strategy.

Tumor-specific CD4+ T cells eradicate myeloma cells genetically deficient in MHC class II display

CD4⁺ T cells have been shown to reject tumor cells with no detectable expression of major histocompatibility complex class II (MHC II). However, under certain circumstances, induction of ectopic MHC II expression on tumor cells has been reported.

To confirm that CD4⁺ T cell-mediated anti-tumor immunity can be successful in the complete absence of antigen display on the tumor cells themselves, we eliminated MHC II on tumor cells using CRISPR/Cas9. Our results demonstrate that ablation of the relevant MHC II (I-E^d) in multiple myeloma cells (MOPC315) does not hinder rejection by tumor-specific CD4⁺ T cells. These findings provide conclusive evidence that CD4⁺ T cells specific for tumor antigens can eliminate malignant cells in the absence of endogenous MHC class II expression on the tumor cells. This occurs through antigen uptake and indirect presentation on tumor-infiltrating macrophages.

Adoptive Transfer of Tumor-Specific Th2 Cells Eradicates Tumors by Triggering an In Situ Inflammatory Immune Response

Adoptive cell therapy (ACT) trials to date have focused on transfer of autologous tumor-specific cytotoxic CD8⁺ T cells; however, the potential of CD4⁺ T helper (Th) cells for ACT is gaining interest. While encouraging results have been reported with IFNγ-producing Th1 cells, tumor-specific Th2 cells have been largely neglected for ACT due to their reported tumor-promoting properties. In this study, we tested the efficacy of idiotype-specific Th2 cells for the treatment of mice with MHC class II-negative myeloma. Th2 ACT efficiently eradicated subcutaneous myeloma in an antigen-specific fashion. Transferred Th2 cells persisted in vivo and conferred long-lasting immunity. Cancer eradication mediated by tumor-specific Th2 cells did not require B cells, natural killer T cells, CD8⁺ T cells, or IFNγ. Th2 ACT was also curative against B-cell lymphoma. Upon transfer, Th2 cells induced a type II inflammation at the tumor site with massive infiltration of M2-type macrophages producing arginase. In vivo blockade of arginase strongly inhibited Th2 ACT, consistent with a key role of arginase and M2 macrophages in myeloma elimination by Th2 cells. These results illustrate that cancer eradication may be achieved by induction of a tumor-specific Th2 inflammatory immune response at the tumor site. Thus, ACT with tumor-specific Th2 cells may represent a highly efficient immunotherapy protocol against cancer. Cancer Res; 76(23); 6864-76. ©2016 AACR.

Interleukin-1 is required for cancer eradication mediated by tumor-specific Th1 cells

The role of inflammation in cancer is controversial as both tumor-promoting and tumor-suppressive aspects of inflammation have been reported. In particular, it has been shown that pro-inflammatory cytokines, like interleukin-1α (IL-1α), IL-1β, IL-6, and tumor necrosis factor α (TNFα), may either promote or suppress cancer. However, the cellular and molecular basis underlying these opposing outcomes remains enigmatic. Using mouse models for myeloma and lymphoma, we have recently reported that inflammation driven by tumor-specific T helper 1 (Th1) cells conferred protection against B-cell cancer and that interferon-γ (IFN-γ) was essential for this process. Here, we have investigated the contribution of several inflammatory mediators. Myeloma eradication by Th1 cells was not affected by inhibition of TNF-α, TNF-related weak inducer of apoptosis (TWEAK), or TNF-related apoptosis-inducing ligand (TRAIL). In contrast, cancer elimination by tumor-specific Th1 cells was severely impaired by the in vivo neutralization of both IL-1α and IL-1β (collectively named IL-1) with IL-1 receptor antagonist (IL-1Ra). The antitumor functions of tumor-specific Th1 cells and tumor-infiltrating macrophages were both affected by IL-1 neutralization. Secretion of the Th1-derived cytokines IL-2 and IFN-γ at the incipient tumor site was severely reduced by IL-1 blockade. Moreover, IL-1 was shown to synergize with IFN-γ for induction of tumoricidal activity in tumor-infiltrating macrophages. This synergy between IL-1 and IFN-γ may explain how inflammation, when driven by tumor-specific Th1 cells, represses rather than promotes cancer. Collectively, the data reveal a central role of inflammation, and more specifically of the canonical pro-inflammatory cytokine IL-1, in enhancing Th1-mediated immunity against cancer.

Limitations of bystander killing in Th1/M1 immune responses against a secreted tumor antigen

T-cell recognition of tumor antigens presented on tumor-infiltrating macrophages (TAMs) induces a tumoricidal M1-like phenotype. Resultant indirect immune responses could eliminate not only antigen secreting (Ag^POS), but also antigen negative (Ag^NEG) tumor cells via bystander killing. Such broad-spectrum response could eliminate antigenically heterogeneous tumors. Using an in vivo model of CD4⁺ T-cell mediated immunity against MHC II negative myeloma cells, bystander killing of Ag^NEG cells was ineffective due to strict spatial constraints of Th1-induced TAM cytotoxicity.

Molecular profiling of tumor-specific TH1 cells activated in vivo

The central role of tumor-specific T_H1 cells in anticancer immune responses is becoming increasingly appreciated. However, little is known about how these cells are generated in vivo. Here, we used flow cytometry and gene expression microarrays to characterize the primary activation and T_H1 differentiation of naïve tumor-specific CD4⁺ T cells in a mouse model of cancer immunosurveillance. We took advantage of T-cell receptor-transgenic mice in which CD4⁺ T cells recognize a tumor-specific antigen secreted by MHC class II-negative MOPC315 myeloma cells. Cancer cells were injected subcutaneously and T-cell activation was analyzed in draining lymph nodes and at the incipient tumor site 8 d later. Upon activation and migration to incipient tumor sites, tumor-specific CD4⁺ T cells exhibited the upregulation of 29 cell-surface molecules (CD2, CD5, CD11a, CD18, CD25, CD28, CD44, CD45, CD49d, CD51, CD54, CD69, CD71, CD83, CD86, CD90, CD95, CD102, CD122, CD153, CD166, CD200, CD249, CD254, CD274, CD279, Ly6C, MHC class I and CCR7) and the downregulation of five (CD27, CD31, CD45RB, CD62L and CD126). Activated CD4⁺ T cells produced interferon γ, a cytokine consistent with a T_H1-polarized response, tumor necrosis factor α as well as interleukin (IL)-2, IL-3 and IL-10. The activation of naïve tumor-specific CD4⁺ T cells in draining lymph nodes resulted in the upregulation of 609 genes and the downregulation of 284 genes. The bioinformatic analysis of differentially expressed genes identified functional pathways related to tumor-specific T_H1 cell activation. This study may represent a useful resource to guide the development of T_H1-based immunotherapies against cancer.

A model for cancer-suppressive inflammation

In oncology, inflammation is generally regarded as a cancer-promoting process only. Here, we argue that this view may represent a misleading oversimplification. We present evidence from our own work and from the literature documenting cancer-suppressive aspects of inflammation. We propose that specific types of inflammation, in particular inflammation driven by tumor-specific Th1 cells, may repress rather than promote cancer. Th1 cells collaborate with tumor-infiltrating M1 macrophages to efficiently recognize and eliminate malignant cells. In a Th1 environment, pro-inflammatory cytokines such as interleukin (IL)-1α, IL-1β, IL-6 and tumor-necrosis factor α (TNFα) enhance anti-cancer immunity. Inducing Th1-type inflammation may significantly improve immunotherapeutic strategies against cancer.

Indirect CD4+ T-cell-mediated elimination of MHC II(NEG) tumor cells is spatially restricted and fails to prevent escape of antigen-negative cells

Tumor-specific Th1 cells can activate tumor-infiltrating macrophages that eliminate MHC class II negative (MHC II(NEG)) tumor cells. Activated M1-like macrophages lack antigen (Ag) receptors, and are presumably unable to discriminate and thus kill both Ag-positive (Ag(POS)) and Ag-negative (Ag(NEG)) tumor cells (bystander killing). The lack of specificity of macrophage-mediated cytotoxicity might be of clinical importance as it could provide a means of avoiding tumor escape. Here, we have tested this idea using mixed populations of Ag(POS) and Ag(NEG) tumor cells in a TCR-transgenic model in which CD4(+) T cells recognize a secreted tumor-specific antigen. Surprisingly, while Ag(POS) tumor cells were recognized and rejected, Ag(NEG) cells grew unimpeded and formed tumors. We further demonstrated that macrophage-mediated cytotoxicity was spatially restricted to areas dominated by Ag(POS) tumor cells, sparing Ag(NEG) tumor cells in the vicinity. As a consequence, macrophage tumoricidal activity did not confer bystander killing in vivo. The present results offer novel insight into the mechanisms of indirect Th1-mediated elimination of MHC II(NEG) tumor cells.

How Do CD4(+) T Cells Detect and Eliminate Tumor Cells That Either Lack or Express MHC Class II Molecules?

CD4⁺ T cells contribute to tumor eradication, even in the absence of CD8⁺ T cells. Cytotoxic CD4⁺ T cells can directly kill MHC class II positive tumor cells. More surprisingly, CD4⁺ T cells can indirectly eliminate tumor cells that lack MHC class II expression. Here, we review the mechanisms of direct and indirect CD4⁺ T cell-mediated elimination of tumor cells. An emphasis is put on T cell receptor (TCR) transgenic models, where anti-tumor responses of naïve CD4⁺ T cells of defined specificity can be tracked. Some generalizations can tentatively be made. For both MHCII^POS and MHCII^NEG tumors, presentation of tumor-specific antigen by host antigen-presenting cells (APCs) appears to be required for CD4⁺ T cell priming. This has been extensively studied in a myeloma model (MOPC315), where host APCs in tumor-draining lymph nodes are primed with secreted tumor antigen. Upon antigen recognition, naïve CD4⁺ T cells differentiate into Th1 cells and migrate to the tumor. At the tumor site, the mechanisms for elimination of MHCII^POS and MHCII^NEG tumor cells differ. In a TCR-transgenic B16 melanoma model, MHCII^POS melanoma cells are directly killed by cytotoxic CD4⁺ T cells in a perforin/granzyme B-dependent manner. By contrast, MHCII^NEG myeloma cells are killed by IFN-γ stimulated M1-like macrophages. In summary, while the priming phase of CD4⁺ T cells appears similar for MHCII^POS and MHCII^NEG tumors, the killing mechanisms are different. Unresolved issues and directions for future research are addressed.

The translation elongation factor eEF2 is a novel tumor‑associated antigen overexpressed in various types of cancers

Recent studies have shown that cancer immunotherapy could be a promising therapeutic approach for the treatment of cancer. In the present study, to identify novel tumor-associated antigens (TAAs), the proteins expressed in a panel of cancer cells were serologically screened by immunoblot analysis and the eukaryotic elongation factor 2 (eEF2) was identified as an antigen that was recognized by IgG autoantibody in sera from a group of patients with head and neck squamous cell carcinoma (HNSCC) or colon cancer. Enzyme-linked immunosorbent assay showed that serum eEF2 IgG Ab levels were significantly higher in colorectal and gastric cancer patients compared to healthy individuals. Immunohistochemistry experiments showed that the eEF2 protein was overexpressed in the majority of lung, esophageal, pancreatic, breast and prostate cancers, HNSCC, glioblastoma multiforme and non-Hodgkin's lymphoma (NHL). Knockdown of eEF2 by short hairpin RNA (shRNA) significantly inhibited the growth in four eEF2-expressing cell lines, PC14 lung cancer, PCI6 pancreatic cancer, HT1080 fibrosarcoma and A172 glioblastoma cells, but not in eEF2-undetectable MCF7 cells. Furthermore, eEF2-derived 9-mer peptides, EF786 (eEF2 786-794 aa) and EF292 (eEF2 292-300 aa), elicited cytotoxic T lymphocyte (CTL) responses in peripheral blood mononuclear cells (PBMCs) from an HLA-A*24:02- and an HLA-A*02:01-positive healthy donor, respectively, in an HLA-A-restricted manner. These results indicated that the eEF2 gene is overexpressed in the majority of several types of cancers and plays an oncogenic role in cancer cell growth. Moreover, the eEF2 gene product is immunogenic and a promising target molecule of cancer immunotherapy for several types of cancers.

A novel mouse model for multiple myeloma (MOPC315.BM) that allows noninvasive spatiotemporal detection of osteolytic disease

Multiple myeloma (MM) is a lethal human cancer characterized by a clonal expansion of malignant plasma cells in bone marrow. Mouse models of human MM are technically challenging and do not always recapitulate human disease. Therefore, new mouse models for MM are needed. Mineral-oil induced plasmacytomas (MOPC) develop in the peritoneal cavity of oil-injected BALB/c mice. However, MOPC typically grow extramedullary and are considered poor models of human MM. Here we describe an in vivo-selected MOPC315 variant, called MOPC315.BM, which can be maintained in vitro. When injected i.v. into BALB/c mice, MOPC315.BM cells exhibit tropism for bone marrow. As few as 10(4) MOPC315.BM cells injected i.v. induced paraplegia, a sign of spinal cord compression, in all mice within 3-4 weeks. MOPC315.BM cells were stably transfected with either firefly luciferase (MOPC315.BM.Luc) or DsRed (MOPC315.BM.DsRed) for studies using noninvasive imaging. MOPC315.BM.Luc cells were detected in the tibiofemoral region already 1 hour after i.v. injection. Bone foci developed progressively, and as of day 5, MM cells were detected in multiple sites in the axial skeleton. Additionally, the spleen (a hematopoietic organ in the mouse) was invariably affected. Luminescent signals correlated with serum myeloma protein concentration, allowing for easy tracking of tumor load with noninvasive imaging. Affected mice developed osteolytic lesions. The MOPC315.BM model employs a common strain of immunocompetent mice (BALB/c) and replicates many characteristics of human MM. The model should be suitable for studies of bone marrow tropism, development of osteolytic lesions, drug testing, and immunotherapy in MM.

SH2D2A modulates T cell mediated protection to a B cell derived tumor in transgenic mice

Background

T cell specific adapter protein (TSAd), encoded by the SH2D2A gene, modulates signaling downstream of the T cell receptor (TCR). Young, unchallenged SH2D2A-deficient C57BL/6 mice exhibit a relatively normal immune phenotype. To address whether SH2D2A regulates physiologic immune responses, SH2D2A-deficient TCR-transgenic BALB/c mice were generated. The transgenic TCR recognizes a myeloma-derived idiotypic (Id) peptide in the context of the major histocompatibility complex (MHC) class II molecule I-E^d, and confers T cell mediated resistance to transplanted multiple myeloma development in vivo.

Principal Findings

The immune phenotype of SH2D2A-deficient C57BL/6 and BALB/c mice did not reveal major differences compared to the corresponding wild type mice. When challenged with myeloma cells, Id-specific TCR-transgenic BALB/c mice lacking SH2D2A displayed increased resistance towards tumor development. Tumor free TCR-transgenic SH2D2A-deficient mice had higher numbers of Id-specific single positive CD4+ thymocytes compared to TCR-transgenic wild-type mice.

Conclusion

Our results suggest a modulatory role for SH2D2A in T cell mediated immune surveillance of cancer. However, it remains to be established whether its effect is T-cell intrinsic. Further studies are required to determine whether targeting SH2D2A function in T cells may be a potential adjuvant in cancer immunotherapy.

Novel strategies for immunotherapy in multiple myeloma: previous experience and future directions

Multiple myeloma (MM) is a life-threatening haematological malignancy for which standard therapy is inadequate. Autologous stem cell transplantation is a relatively effective treatment, but residual malignant sites may cause relapse. Allogeneic transplantation may result in durable responses due to antitumour immunity mediated by donor lymphocytes. However, morbidity and mortality related to graft-versus-host disease remain a challenge. Recent advances in understanding the interaction between the immune system of the patient and the malignant cells are influencing the design of clinically more efficient study protocols for MM. Cellular immunotherapy using specific antigen-presenting cells (APCs), to overcome aspects of immune incompetence in MM patients, has received great attention, and numerous clinical trials have evaluated the potential for dendritic cell (DC) vaccines as a novel immunotherapeutic approach. This paper will summarize the data investigating aspects of immunity concerning MM, immunotherapy for patients with MM, and strategies, on the way, to target the plasma cell more selectively. We also include the MM antigens and their specific antibodies that are of potential use for MM humoral immunotherapy, because they have demonstrated the most promising preclinical results.

The aging immune system and its relationship with cancer

The incidence of most common cancers increases with age. This occurs in association with, and is possibly caused by a decline in immune function, termed immune senescence. Although the size of the T-cell compartment is quantitatively maintained into older age, several deleterious changes (including significant changes to T-cell subsets) occur over time that significantly impair immunity. This article highlights some of the recent findings regarding the aging immune system, with an emphasis on the T-cell compartment and its role in cancer.

Inflammation driven by tumour-specific Th1 cells protects against B-cell cancer

The immune system can both promote and suppress cancer. Chronic inflammation and proinflammatory cytokines such as interleukin (IL)-1 and IL-6 are considered to be tumour promoting. In contrast, the exact nature of protective antitumour immunity remains obscure. Here, we quantify locally secreted cytokines during primary immune responses against myeloma and B-cell lymphoma in mice. Strikingly, successful cancer immunosurveillance mediated by tumour-specific CD4⁺ T cells is consistently associated with elevated local levels of both proinflammatory (IL-1α, IL-1β and IL-6) and T helper 1 (Th1)-associated cytokines (interferon-γ (IFN-γ), IL-2 and IL-12). Cancer eradication is achieved by a collaboration between tumour-specific Th1 cells and tumour-infiltrating, antigen-presenting macrophages. Th1 cells induce secretion of IL-1β and IL-6 by macrophages. Th1-derived IFN-γ is shown to render macrophages directly cytotoxic to cancer cells, and to induce macrophages to secrete the angiostatic chemokines CXCL9/MIG and CXCL10/IP-10. Thus, inflammation, when driven by tumour-specific Th1 cells, may prevent rather than promote cancer.

Inflammation can result in the formation of tumours, but the immune system is also involved in the elimination of cancer cells. Here, the authors show that inflammation driven by tumour-specific CD4⁺ T cells results in tumour regression and identify a list of cytokines associated with cancer prevention.

Is secretion of tumour-specific antigen important for cancer eradication by CD4(+) T cells?--Implications for cancer immunotherapy by adoptive T cell transfer

The potential for cancer immunotherapy by adoptive transfer of CD4(+) T cells is gaining increased attention. Most cancer cells lack major histocompatibility complex (MHC) class II molecules and cannot present tumour-specific antigens (TSA) directly to CD4(+) T cells. We have reported that tumour-specific CD4(+) T cells collaborate with macrophages and dendritic cells. These professional antigen-presenting cells endocytose and process TSA to display antigenic peptides on their MHC class II molecules for indirect cancer cell recognition by CD4(+) T cells. We hypothesized that this critical step may depend on secretion of TSA by cancer cells. This was investigated in a mouse model for myeloma immunosurveillance mediated by CD4(+) T cells. From this study, several conclusions could be drawn. First, TSA secretion facilitates cancer immunosurveillance. Second, TSA secretion results in stronger activation of naïve tumour-specific CD4(+) T cells in lymph nodes. Third, TSA concentration within the tumour extracellular matrix must reach a certain threshold to allow successful cancer immunosurveillance. Fourth, treatment by local injection of purified TSA enhances immunity against cancer cells that do not secrete TSA. Fifth, secretion of TSA by at least some cancer cells within a tumour favours antitumour immunity. Therefore, we propose that CD4(+) T cells that recognize secreted TSA may be superior for immunotherapy by T cell transfer, because the local extracellular antigen concentration will be higher for secreted TSA. Thus, it is anticipated that secreted TSA will be more readily detected in vivo by transferred CD4(+) T cells, resulting in more efficient tumour eradication.

Histone deacetylase inhibitor LAQ824 augments inflammatory responses in macrophages through transcriptional regulation of IL-10

APCs are important in the initiation of productive Ag-specific T cell responses and the induction of T cell anergy. The inflammatory status of the APC at the time of encounter with Ag-specific T cells plays a central role in determining such divergent T cell outcomes. A better understanding of the regulation of proinflammatory and anti-inflammatory genes in its natural setting, the chromatin substrate, might provide novel insights to overcome anergic mechanisms mediated by APCs. In this study, we show for the first time, to our knowledge, that treatment of BALB/c murine macrophages with the histone deacetylase inhibitor LAQ824 induces chromatin changes at the level of the IL-10 gene promoter that lead to enhanced recruitment of the transcriptional repressors HDAC11 and PU.1. Such an effect is associated with diminished IL-10 production and induction of inflammatory cells able of priming naive Ag-specific T cells, but more importantly, capable of restoring the responsiveness of anergized Ag-specific CD4(+) T cells.

The cellular mechanism by which complementary Id+ and anti-Id antibodies communicate: T cells integrated into idiotypic regulation

The V region antigenic determinants (idiotopes (Ids)) of antibodies (Abs) have been suggested to be involved in regulating the immune system. Certain diseases such as diabetes mellitus have recently been associated with a disequilibrium between Id(+) and anti-Id Abs. However, it is unknown how Abs carrying complementary idiotypes (that is, Id(+) and anti-Id Abs) regulate each other at the level of B and T cells. In this study, we show that B lymphoma cells genetically equipped with anti-Id BCR V regions receive a signal when exposed to Id(+)Ig. Moreover, they become x 10(4) more efficient at presenting exogenous Id(+) Ab to CD4(+) T cells in vitro. Activated Id-specific T cells in turn regulated the Id-specific B lymphoma cells. Similar results were obtained in vivo in a surrogate model in which an Id-peptide was incorporated genetically into the C-region of a recombinant Ab that targeted IgD on B cells. The findings suggest that conventional T-B collaboration can explain communication between complementary Id(+) and anti-Id Ab at the cellular level. A model is suggested that integrates present and previous data on B-cell regulation by Id-specific T cells.

Secretion of tumor-specific antigen by myeloma cells is required for cancer immunosurveillance by CD4+ T cells

Tumor-specific CD4(+) T cells orchestrate the adaptive immune responses against cancer. We have previously shown that CD4(+) T cells recognize MHC class II-negative myeloma cells indirectly by collaborating with tumor-infiltrating macrophages. We, here, hypothesize that this critical step may be dependent on secretion of tumor-specific antigens by cancer cells. This was investigated using T-cell receptor-transgenic mice, in which CD4(+) T cells mediate rejection of syngeneic MOPC315 myeloma cells. We analyzed the immune response against myeloma cell variants, which either secrete or retain intracellularly a tumor-specific idiotypic (Id) antigen. Our results reveal that CD4(+) T cells helped by macrophages are capable of detecting nonsecreted tumor antigens from MHC class II-negative cancer cells. However, Id secretion was required for successful myeloma immunosurveillance. Antigen secretion resulted in stronger priming of naive myeloma-specific CD4(+) T cells in tumor-draining lymph nodes. Secretion of antigen by at least some cancer cells within a tumor was shown to facilitate immunosurveillance. Treatment by local injection of purified tumor-specific antigen successfully enhanced immunity against nonsecreting myeloma cells. Collectively, the data indicate that antigen concentration within the tumor extracellular matrix must reach a certain threshold to allow successful cancer immunosurveillance by CD4(+) T cells.

Tumor-specific Th17-polarized cells eradicate large established melanoma

CD4+ T cells can differentiate into multiple effector subsets, but the potential roles of these subsets in anti-tumor immunity have not been fully explored. Seeking to study the impact of CD4+ T cell polarization on tumor rejection in a model mimicking human disease, we generated a new MHC class II-restricted, T-cell receptor (TCR) transgenic mouse model in which CD4+ T cells recognize a novel epitope in tyrosinase-related protein 1 (TRP-1), an antigen expressed by normal melanocytes and B16 murine melanoma. Cells could be robustly polarized into Th0, Th1, and Th17 subtypes in vitro, as evidenced by cytokine, chemokine, and adhesion molecule profiles and by surface markers, suggesting the potential for differential effector function in vivo. Contrary to the current view that Th1 cells are most important in tumor rejection, we found that Th17-polarized cells better mediated destruction of advanced B16 melanoma. Their therapeutic effect was critically dependent on interferon-gamma (IFN-gamma) production, whereas depletion of interleukin (IL)-17A and IL-23 had little impact. Taken together, these data indicate that the appropriate in vitro polarization of effector CD4+ T cells is decisive for successful tumor eradication. This principle should be considered in designing clinical trials involving adoptive transfer-based immunotherapy of human malignancies.

Chemokine-idiotype fusion DNA vaccines are potentiated by bivalency and xenogeneic sequences

V regions of monoclonal Ig express an exquisite B-cell tumor–specific antigen called idiotype (Id). Id is a weak antigen and it is important to improve immunogenicity of Id vaccines. Chemokine receptors are expressed on antigen-presenting cells (APCs) and are promising targets for Id vaccines. Here we compare monomeric and dimeric forms of MIP-1α and RANTES that target Id to APCs in a mouse B lymphoma (A20) and a multiple myeloma model (MOPC315). MIP-1α was more potent than RANTES. The dimeric proteins were more potent than monomeric equivalents in short-term assays. When delivered in vivo by intramuscular injection of plasmids followed by electroporation, dimeric proteins efficiently primed APCs in draining lymph nodes for activation and proliferation of Id-specific CD4+ T cells. Good anti-Id antibody responses were obtained, and mice immunized only once were 60% to 80% protected in both tumor models. CD8+ T cells contributed to the protection. Antibody responses and tumor protection were reduced when the human Ig hinge = CH3 dimerization motif was replaced with syngeneic mouse counterparts, indicating that tumor-protective responses were dependent on xenogeneic sequences. The results suggest that bivalency and foreign sequences combine to increase the efficiency of chemokine-Id DNA vaccines.

Delivery of antigen to CD40 induces protective immune responses against tumors

Ligation of CD40 induces maturation of dendritic cells (DC) and could be a useful target for vaccines. In this study, we have constructed two types of Ab-based vaccine constructs that target mouse CD40. One type is a recombinant Ab with V regions specific for CD40 and has defined T cell epitopes inserted into its C region. The other type is a homodimer, each chain of which is composed of a targeting unit (single-chain fragment variable targeting CD40), a dimerization motif, and an antigenic unit. Such proteins bound CD40, stimulated maturation of DC, and enhanced primary and memory T cell responses. When delivered i.m. as naked DNA followed by electroporation, the vaccines induced T cell responses against MHC class II-restricted epitopes, Ab responses, and protection in two tumor models (myeloma and lymphoma). Two factors apparently contributed to these results: 1) agonistic ligation of CD40 and induction of DC maturation, and 2) delivery of Ag to APC and presentation on MHC class II molecules. These results highlight the importance of agonistic targeting of Ag to CD40 for induction of long-lasting and protective immune responses.

Human receptors of innate immunity (CD14, TLR2) are promising targets for novel recombinant immunoglobulin-based vaccine candidates

Experiments in mice have suggested that engagement of receptors of innate immunity has an adjuvant effect on adaptive immune responses. Such studies need to be extended to humans. We have here constructed recombinant scFv-based vaccine candidate proteins (vaccibodies) that target human TLR2 and CD14 for delivery of large antigens. Vaccibodies are homodimers, each chain consisting of scFv specific for surface molecules on antigen-presenting cells (APC), a homodimerization motif, and an antigenic unit. The TLR2- and CD14-specific vaccibodies bound their respective target receptors expressed on transfected CHO cells and PBMC. Large proteins such as paired mouse Ckappa-domains (229 aa) and fragment C of tetanus toxin (TetC, 451 aa) could be expressed as antigenic units with intact serological determinants detected by mAb or polyclonal antisera. In the presence of monocytes, TLR2- and CD14-specific vaccibodies having either Ckappa or TetC as antigenic unit were 100-10,000 more efficient at stimulating T cell clones in vitro compared to non-targeted vaccibodies expressing the same antigens. The results show that TLR2 and CD14 are efficient targets for delivery of antigen to APC for stimulation of HLA class II-restricted CD4(+) T cells. Thus, receptors of innate immunity should be further explored as targets for vaccines.

DNA vaccines increase immunogenicity of idiotypic tumor antigen by targeting novel fusion proteins to antigen-presenting cells

Naked DNA vaccines have a number of advantages over conventional vaccines, but induce only weak immune responses. We have here investigated if this inadequacy may be overcome by inducing muscle to secrete fusion proteins with the ability to target antigen-presenting cells (APC). The novel targeted vaccines are homodimers with (i) two identical single-chain fragment variable (scFv) targeting units specific for MHC class II molecules on mouse APC, (ii) a human Ig hinge and C(H)3 dimerization unit, and (iii) two identical scFv tumor antigenic units (idiotypes) from B cell cancers. After plasmid injection and electroporation of mouse muscle, secreted vaccine proteins (vaccibodies) delivered idiotypic tumor antigen to APC in draining lymph nodes for induction of T and B cell responses that protected mice against tumor challenges with a multiple myeloma (MOPC315) and a B cell lymphoma (A20). Targeting to APC was essential for these effects. The results show that immunogenicity of plasmid DNA vaccines can be increased by inducing muscle to secrete proteins that target antigen to APC.

Mechanisms of immune evasion by tumors

In the past decade, basic studies in animal models have begun to elucidate the physiological barriers which impede a successful antitumor immune response. These barriers operate at a number of levels, and involve the tumor, the tumor microenvironment and various components of the innate and adaptive immune systems. In this review, we discuss the multiple mechanisms by which tumors evade an immune response, with an emphasis on clinically relevant strategies to overcome these inhibitory checkpoints.

Induction of central T cell tolerance: Recombinant antibodies deliver peptides for deletion of antigen-specific CD4+8+ thymocytes

In order to prevent or ameliorate autoimmune disease, it would be desirable to induce central tolerance to peripheral self-antigens. We have investigated whether recombinant antibodies (Ab) that deliver T cell epitopes to antigen-presenting cells (APC) in the thymus can be used to induce thymocyte deletion. Troybodies are recombinant Ab with V regions specific for APC surface molecules that have T cell epitopes genetically introduced in their C domains. When MHC class II-specific Troybodies with the lambda2(315)T cell epitope were injected into lambda2(315)-specific TCR transgenic mice, a profound deletion of (CD4+)8+ thymocytes was observed. MHC class II-specific Troybodies were 10-100-fold more efficient than non-targeting peptide Ab, and 500-fold more efficient than synthetic peptide at inducing deletion. Similar findings were observed when MHC class II-specific Troybodies with the OVA(323-339) T cell epitope were injected into OVA-specific TCR transgenic mice. Although deletion was transient after a single injection, newborn mice repeatedly injected with MHC class II-specific Troybodies for 4 weeks, had reduced antigen-specific T cells in peripheral lymphoid tissues and reduced T cell responses. These experiments suggest that Troybodies constructed to target specifically thymic APC could be useful tools for induction and maintenance of central T cell tolerance in autoimmune diseases.

Primary Antitumor Immune Response Mediated by CD4+ T Cells

Gene-targeted mice have recently revealed a role for lymphocytes and interferon-gamma (IFNgamma) in conferring protection against cancer, but the mechanisms remain unclear. Here, we have characterized a successful primary antitumor immune response initiated by naive CD4+ T cells. Major histocompatibility complex class II (MHC-II)-negative myeloma cells injected subcutaneously into syngeneic mice were surrounded within 3 days by macrophages that captured tumor antigens. Within 6 days, naive myeloma-specific CD4+ T cells became activated in draining lymph nodes and subsequently migrated to the incipient tumor site. Upon recognition of tumor-derived antigenic peptides presented on MHC-II by macrophages, the myeloma-specific CD4+ T cells were reactivated and started to secrete cytokines. T cell-derived IFNgamma activated macrophages in close proximity to the tumor cells. Tumor cell growth was completely inhibited by such locally activated macrophages. These data indicate a mechanism for immunosurveillance of MHC-II-negative cancer cells by tumor-specific CD4+ T cells through collaboration with macrophages.

Anti-Class II Antibodies, but not Cytotoxic T-Lymphocyte Antigen 4-Immunoglobulin Hybrid Molecules, Prevent Rejection of Major Histocompatibility Complex Class II-Negative Myeloma in T-Cell Receptor-Transgenic Mice

We have previously shown that tumour-specific CD4+ T cells protect against subcutaneous injections of major histocompatibility complex (MHC) class II-negative MOPC315 myeloma cells. Here, we have interfered with the immunologic events that lead to successful rejection of MOPC315 challenges in T-cell receptor (TCR)-transgenic mice. The CD4+ T cells have a transgene-encoded TCR specific for a MOPC315 V-region idiotypic (Id) peptide presented on the MHC class II molecule E(d). A side-by-side comparison indicated that DNA-recombination-deficient TCR-transgenic mice were better protected against MOPC315 tumour development than recombination-sufficient counterparts, suggesting that B cells or endogenous TCR chains might facilitate tumour progression in this model. Intraperitoneal injections of E(d)-specific antibodies over a period of initial 24 days, abrogated protection against tumours in both strains of mice. By contrast, injections of anticostimulatory molecules (cytotoxic T-lymphocyte antigen 4-immunoglobulin hybrid molecules) had no effect. The findings demonstrate that tumour rejection depends on the presence of MHC class II molecules, despite the fact that MOPC315 tumour cells themselves do not express them. The results are consistent with the idea that secreted myeloma protein is processed and presented by class II+ antigen-presenting cells to Id-specific naïve CD4+ T cells that become activated and kill the myeloma cells by a bystander mechanism. While Id presentation on class II molecules is absolutely required for tumour rejection, costimulatory CD80/CD86 molecules might be dispensible in this process.

Does the immune system see tumors as foreign or self?

Given the vast number of genetic and epigenetic changes associated with carcinogenesis, it is clear that tumors express many neoantigens. A central question in cancer immunology is whether recognition of tumor antigens by the immune system leads to activation (i.e., surveillance) or tolerance. Paradoxically, while strong evidence exists that specific immune surveillance systems operate at early stages of tumorigenesis, established tumors primarily induce immune tolerance. A unifying hypothesis posits that the fundamental processes of cancer progression, namely tissue invasion and metastasis, are inherently proinflammatory and thus activating for innate and adaptive antitumor immunity. To elude immune surveillance, tumors must develop mechanisms that block the elaboration and sensing of proinflammatory danger signals, thereby shifting the balance from activation to tolerance induction. Elucidation of these mechanisms provides new strategies for cancer immunotherapy.

Therapeutic effect of idiotype-specific CD4+ T cells against B-cell lymphoma in the absence of anti-idiotypic antibodies

Immunoglobulin (Ig) variable (V) region idiotypes (Id's) are highly tumor-specific antigens produced by B-lymphoma cells and are promising targets for immunotherapy. Id vaccination has proven effective in experimental mouse models and may possibly prevent recurrence of B lymphomas in humans. It has previously been shown that anti-Id antibodies protect against B-cell lymphoma in the absence of T cells. We here demonstrate in a T-cell-receptor transgenic mouse model that the contrary is also true: Id-specific CD4+ T cells can protect against Id+ B-lymphoma cells in the absence of B cells, antibodies, and CD8+ T cells. Moreover, Id-specific CD4+ T cells have a curative potential since they could be transferred as late as 17 days after subcutaneous tumor cell injection of severe combined immunodeficiency (SCID) mice and still abrogate tumor development in about 50% of mice. Such mice undergo an acute inflammatory swelling with infiltration of neutrophils at the site of tumor injection, which subsides over weeks, with some mice cured and delayed emergence of lymphomas in other mice. Adoptively transferred CD4+ T cells accumulated in the tumor and were activated (CD69+). In vitro experiments demonstrated that memory, but not naive, Id-specific CD4+ T cells kill Id+ B-lymphoma cells. The results show that Id-specific CD4+ T cells, in the absence of antibodies home to subcutaneous Id+ B lymphoma, become activated, induce inflammation, and prevent tumor development.

Therapeutic effects of idiotype vaccination can be enhanced by the combination of granulocyte-macrophage colony-stimulating factor and interleukin 2 in a myeloma model

Idiotype (Id) vaccination provides an interesting immunotherapeutic strategy against B-cell lymphomas. In multiple myeloma (MM), however, the therapeutic efficacy of Id vaccination has been disappointing. In an attempt to improve the antitumoral potential, we added granulocyte-macrophage colony stimulating factor (GM-CSF) and interleukin 2 (IL-2) to the protocol. Balb/c mice were inoculated i.p. (d 2) with different doses (1-5 x 10(5)) of HOPC myeloma cells secreting the Ig(HOPC) Id protein. Two days later, animals were injected with 10,000 U GM-CSF i.p. for 6 d consecutively (d 0-5). On d 5 and 11, myeloma-specific immunoglobulin (Ig(HOPC)) was administered i.p. together with incomplete Freund adjuvans followed by IL-2 (2 x 10,000 U/d; i.p) for 10 d (d 5-14). In animals inoculated with 10(5) myeloma cells, treatment with IL-2 given as a single agent prolonged the median survival time (MST, 67 d) when compared with the tumour control group (MST 48 d), whereas GM-CSF did not elicit any survival benefit (MST 49 d). Complete tumour rejection could be achieved in 27% (4/15) by the combination of Id vaccination and GM-CSF. Additional treatment with IL-2 further increased antimyeloma activity. In this case, 59% of the animals showed no signs of tumour recurrence. In mice with high tumour burden (5 x 10(5)), no treatment modality achieved long-term survivors. Both natural killer (NK) cells and CD8+ T cells may be involved in the anti-tumoural immune response. These data provide evidence for the combined use of GM-CSF and IL-2 to enhance the therapeutic effectiveness of clinical cancer vaccination protocols.

Altered mRNA expression of Pax5 and Blimp-1 in B cells in multiple myeloma

Multiple myeloma (MM) is a plasma cell disorder that potentially initiates during an early stage of B-cell development. We encountered an unidentified isoform of B cell-specific activator protein (BSAP, or Pax5) in MM cells while performing differential analyses to compare mRNA expression in malignant and normal plasma cells. Pax5 is a transcription factor that plays a central role throughout B-cell development until the point of terminal differentiation. Our finding of this unique isoform prompted us to investigate Pax5 isoform usage in plasma cells and B-cell populations in other MM and healthy subjects. In contrast to normal Pax5 expression, we observed multiple isoforms of Pax5 in conjunction with low levels of expression of the full-length Pax5 in B cells from MM patients. The expressed isoforms in MM varied considerably from patient to patient, with no clear pattern. We also performed semiquantitative analyses of the mRNA expression levels of B lymphocyte-induced maturation protein (Blimp-1), because expression levels of Pax5 and Blimp-1 have been shown to be inversely correlated. We observed the expression of Blimp-1 in the B-cell populations in all 11 MM patients but in none of 11 healthy subjects. We hypothesize that premature Blimp-1 expression coupled to altered and deficient Pax5 expression causes some proliferating B cells to prematurely differentiate to plasma cells in MM.

Generalization of single immunological experiences by idiotypically mediated clonal connections

Clonal interactions of B cells by idiotope-specific mutual recognition of their antigen receptors with the participation of T cells were assumed to form a web of unknown density, referred to as the idiotypic network. Although these clonal connections were proposed to fulfill important internal regulatory functions, their biological significance, especially in relation to antigen-induced immune responses, remained a mystery. In view of this, we postulate that the basic function of the idiotypic internal connection between B and T cell antigen receptors is to transform antigen-induced cellular activations, by idiotypic crossreactivity, into the regulation of cell clones with different antigen specificities. This process leads not only to the suppression of major clones but also to the activation of minor ones. The latter activating property may allow the generalization of single antigenic experiences, so that the immune system in its entirety benefits in its battle against environmental microbes. Such idiotypic clonal interactions are particularly effective in early ontogeny. During a short neonatal imprinting period, maternal immunological knowledge in the form of somatically mutated, high-affinity IgG antibodies, acquired through a continuous encounter with external antigens, guides the initial ontogenetic development of the immune system and so exerts long-lasting transgenerational advantageous effects in the offspring.

Negligible class II MHC presentation of B cell receptor-derived peptides by high density resting B cells

Resting B lymphocytes have been credited with inducing T cell tolerance to Ig-derived and monovalent self-Ags that are internalized via the B cell receptor (BCR). These conclusions are predicated upon the assumptions that resting B cells display BCR-associated peptides in class II MHC and that the cells remain quiescent during the course of experimental manipulation. To determine whether resting B cells display BCR-associated epitopes in class II MHC, we devised a sensitive assay that averted potential activation of B cells by Ag and minimized activation by prolonged culture. Ex vivo, Percoll-fractionated B cells expressing a kappa transgene encoding a T cell epitope were cultured with a reactive T cell hybridoma for 12 h. Whereas low density, LPS-activated, and BCR-activated B cells elicited significant IL-2 from the T cell hybridoma, resting high density B cells did not. Parallel results were obtained with normal B cells expressing a second epitope encoded by an endogenous V(H) gene. Anergic B cells, which are uniformly low density, also significantly stimulated the T cell hybridoma. Finally, longer culture periods with normal B cells resulted in a higher degree of B cell activation and significant stimulation of reactive T cell hybridomas. Our results provide evidence that activation of B cells profoundly enhances the processing and presentation of BCR-associated Ags.

Enhanced antitumoral effectiveness of idiotype vaccination induced by the administration of Flt3 ligand combined with interleukin 2 against a murine myeloma

Idiotype (Id) vaccination provides an innovative treatment modality against B-cell malignancies. In multiple myeloma patients, however, the antitumoral potential of this immunotherapeutic concept is limited. In an attempt to improve the therapeutic effectiveness of Id vaccination, we added Flt3 ligand (Flt3-L) and interleukin 2 (IL-2) to the protocol. Balb/c mice were inoculated i.p. (d -2) with different doses (1-5 x 10(5)) of HOPC myeloma cells, secreting the IgHOPC Id-protein. Two days later, animals were treated with Flt3-L (10 microg per mouse/d, given i.p) for 10 consecutive days (d 0-9). On d 5 and d 11, myeloma-specific immunoglobulin (Ig(HOPC)) was administered s.c., together with incomplete Freund adjuvans (IFA) followed by the administration of IL-2 (2 x 10.000/d given i.p) for 10 d (d 5-14). Whereas Ig(HOPC), Flt3-L or IL-2, given alone, did not elicit long-term survival, the combination of IL-2 or Flt3-L with Id vaccination achieved a complete tumour rejection in 27% and 41% of mice respectively. However, the most powerful antimyeloma effects were induced by Flt3-L + Id vaccination + IL-2: 81% of the treated animals experienced long-term survival (> 180 d). Both natural killer (NK) cells and CD8+ T cells may be involved in the antitumoral immune response. These data suggest that the combination of Flt3-L and IL-2 can be used to enhance the therapeutic effectiveness of clinical cancer vaccination protocols.

Efficient delivery of T cell epitopes to APC by use of MHC class II-specific Troybodies

A major objective in vaccine development is the design of reagents that give strong, specific T cell responses. We have constructed a series of rAb with specificity for MHC class II (I-E). Each has one of four different class II-restricted T cell epitopes genetically introduced into the first C domain of the H chain. These four epitopes are: 91-101 lambda2(315), which is presented by I-E(d); 110-120 hemagglutinin (I-E(d)); 323-339 OVA (I-A(d)); and 46-61 hen egg lysozyme (I-A(k)). We denote such APC-specific, epitope-containing Ab "Troybodies." When mixed with APC, all four class II-specific Troybodies were approximately 1,000 times more efficient at inducing specific T cell activation in vitro compared with nontargeting peptide Ab. Furthermore, they were 1,000-10,000 times more efficient than synthetic peptide or native protein. Conventional intracellular processing of the Troybodies was required to load the epitopes onto MHC class II. Different types of professional APC, such as purified B cells, dendritic cells, and macrophages, were equally efficient at processing and presenting the Troybodies. In vivo, class II-specific Troybodies were at least 100 times more efficient at targeting APC and activating TCR-transgenic T cells than were the nontargeting peptide Ab. Furthermore, they were 100-100,000 times more efficient than synthetic peptide or native protein. The study shows that class II-specific Troybodies can deliver a variety of T cell epitopes to professional APC for efficient presentation, in vitro as well as in vivo. Thus, Troybodies may be useful as tools in vaccine development.

Tumor immunology--towards a paradigm of reciprocal research

Recent advances in the field of tumor immunology highlight the difficulties involved in generating and maintaining a tumor-specific immune response. The tendency of T cells to be tolerized in vivo, and the tendency of tumors to escape immune recognition represent significant barriers to successful immunotherapy. The results of early clinical trials illustrate these points and underscore the critical importance of an interactive dialog between laboratory and clinical research efforts.

Idiotype protein-pulsed dendritic cells produce strong anti-myeloma effects after syngeneic stem cell transplantation in mice

Dendritic cell (DC) vaccination represents an interesting immunotherapeutic option in the treatment of several malignancies. In multiple myeloma (MM) patients, vaccination with autologous idiotype (Id) protein-pulsed DC is feasible, but their antitumoral effectiveness was rather limited. To improve the therapeutic potential of DC therapy, we studied the immunological effects of syngeneic peripheral blood stem cell transplantation (PBSCT) given in conjunction with Id-loaded DC. Balb/c mice were inoculated i.p. with 5 x 10(5) of HOPC myeloma cells (Balb/c origin). Animals were immunized with three injections of 5 x 10(5) DC pulsed with the IgG2a(HOPC) or with a control immunoglobulin (Ig(control)). Some experimental groups of myeloma-bearing animals received total body irradiation (7.5 Gy) and a subsequent transplant of 2 x 10(7)syngeneic peripheral blood progenitor cells (PBPC) followed by DC therapy beginning at day 10 post transplant. Animals receiving DC therapy or syngeneic PBPCT alone neither induce long-term survival nor tumor-specific CTL reactivity in vitro. In marked contrast, combination of syngeneic PBPC transplantation and subsequent DC therapy resulted in 78% survival after a follow-up of 180 days. In addition, this treatment modality conferred a generation of Id peptide-specific CD8-mediated T cell reactivity. These data provide a rationale for DC-based vaccination in multiple myeloma patients administered post syngeneic transplantation.

Clonal cytotoxic T cells are expanded in myeloma and reside in the CD8(+)CD57(+)CD28(-) compartment

The occurrence of clonal T cells in multiple myeloma (MM), as defined by the presence of rearrangements in the T-cell receptor (TCR)-beta chains detected on Southern blotting, is associated with an improved prognosis. Recently, with the use of specific anti-TCR-variable-beta (anti-TCRV(beta)) antibodies, the presence in MM patients of expanded populations of T cells expressing particular V(beta) regions was reported. The majority of these T-cell expansions have the phenotype of cytotoxic T cells (CD8(+)CD57(+) and perforin positive). Since V(beta) expansions can result from either a true clonal population or a polyclonal response, the clonality of CD8(+)TCRV(beta)(+) T cells was tested by TCRV(beta) complementarity-determining region 3 length analysis and DNA sequencing of the variable region of the TCR. In this report, the CD57(+) and CD57(-) subpopulations within expanded TCRV(beta)(+)CD8(+) cell populations are compared, and it is demonstrated that the CD57(+) subpopulations are generally monoclonal or biclonal, whereas the corresponding CD57(-) cells are frequently polyclonal. The oligoclonality of CD57(+) expanded CD8(+) T cells but not their CD57(-) counterparts was also observed in age-matched controls, in which the T-cell expansions were mainly CD8(-). The CD8(+)CD57(+) clonal T cells had a low rate of turnover and expressed relatively lower levels of the apoptotic marker CD95 than their CD57(-) counterparts. Taken together, these findings demonstrate that MM is associated with CD57(+)CD8(+) T-cell clones, raising the possibility that the expansion and accumulation of activated clonal CD8(+) T cells in MM may be the result of persistent stimulation by tumor-associated antigens, combined with a reduced cellular death rate secondary to reduced expression of the apoptosis-related molecule CD95.

Cancer immunotherapy: insights from transgenic animal models

A wide range of strategies in cancer immunotherapy has been developed in the last decade, some of which are currently being used in clinical settings. The development of these immunotherapeutical strategies has been facilitated by the generation of relevant transgenic animal models. Since the different strategies in experimental immunotherapy of cancer each aim to activate different immune system components, a variety of transgenic animals have been generated either expressing tumor associated, HLA, oncogenic or immune effector cell molecule proteins. This review aims to discuss the existing transgenic mouse models generated to study and develop cancer immunotherapy strategies and the variable results obtained. The potential of the various transgenic animal models regarding the development of anti-cancer immunotherapeutical strategies is evaluated.

Phagocytic dendritic cells from myelomas activate tumor-specific T cells at a single cell level

Antigen-presenting cells (APCs) from subcutaneous mouse MOPC315 plasmacytoma phagocytosed immunoglobulin G-coated magnetic beads, enabling efficient isolation within 2 hours by magnetic separation (APC-MB). Cell morphology was heterogeneous, with some of the cells having dendrites. The surface phenotype of purified tumor APCs-MB was CD11b(+), CD11c(+), CD40(+), CD80(+), CD86(+), and MHC class II(+). Tumor APCs-MB expressed messenger RNA for fractalkine and ABCD-1 chemokines, and for CC-type chemokine receptors CCR5 and CCR7, indicating the presence of mature dendritic cells (DCs). Visualized at a single cell level within 4 hours after disruption of the tumor, APCs-MB induced rapid Ca(++) mobilization in MHC class II-restricted tumor idiotype (Id)-specific cloned CD4(+) T cells. In long-term assays, tumor APCs-MB induced proliferation of naive T cells from Id-specific T-cell receptor transgenic mice. The results suggest that tumor APCs-MB represent a heterogeneous cell population that includes myeloid-derived DCs of various stages of maturation. A considerable fraction (> or = 15%) of DCs is spontaneously primed with tumor-specific antigen.