How much longer will tumour cells fool the immune system?

Recruitment of Oligoclonal Viral-Specific T cells to Kill Human Tumor Cells Using Single-Chain Antibody-Peptide-HLA Fusion Molecules

Tumor progression is often associated with the development of diverse immune escape mechanisms. One of the main tumor escape mechanism is HLA loss, in which human solid tumors exhibit alterations in HLA expression. Moreover, tumors that present immunogenic peptides via class I MHC molecules are not susceptible to CTL-mediated lysis, because of the relatively low potency of the tumor-specific CLTs. Here, we present a novel cancer immunotherapy approach that overcomes these problems by using the high affinity and specificity of antitumor antibodies to recruit potent antiviral memory CTLs to attack tumor cells. We constructed a recombinant molecule by genetic fusion of a cytomegalovirus (CMV)-derived peptide pp65 (NLVPMVATV) to scHLA-A2 molecules that were genetically fused to a single-chain Fv Ab fragment specific for the tumor cell surface antigen mesothelin. This fully covalent fusion molecule was expressed in E. coli as inclusion bodies and refolded in vitro. The fusion molecules could specifically bind mesothelin-expressing cells and mediate their lysis by NLVPMVATV-specific HLA-A2-restricted human CTLs. More importantly, these molecules exhibited very potent antitumor activity in vivo in a nude mouse model bearing preestablished human tumor xenografts that were adoptively transferred along with human memory CTLs. These results represent a novel and powerful approach to immunotherapy for solid tumors, as demonstrated by the ability of the CMV-scHLA-A2-SS1(scFv) fusion molecule to mediate specific and efficient recruitment of CMV-specific CTLs to kill tumor cells.

Cytosolic phospholipase A₂ε drives recycling through the clathrin-independent endocytic route

Previous studies have demonstrated that membrane tubule-mediated transport events in biosynthetic and endocytic routes require phospholipase A2 (PLA2) activity. Here, we show that cytosolic phospholipase A2ε (cPLA2ε, also known as PLA2G4E) is targeted to the membrane compartments of the clathrin-independent endocytic route through a C-terminal stretch of positively charged amino acids, which allows the enzyme to interact with phosphoinositide lipids [especially PI(4,5)P2] that are enriched in clathrin-independent endosomes. Ablation of cPLA2ε suppressed the formation of tubular elements that carry internalized clathrin-independent cargoes, such as MHC-I, CD147 and CD55, back to the cell surface and, therefore, caused their intracellular retention. The ability of cPLA2ε to support recycling through tubule formation relies on the catalytic activity of the enzyme, because the inactive cPLA2ε(S420A) mutant was not able to recover either tubule growth or transport from clathrin-independent endosomes. Taken together, our findings indicate that cPLA2ε is a new important regulator of trafficking processes within the clathrin-independent endocytic and recycling route. The affinity of cPLA2ε for this pathway supports a new hypothesis that different PLA2 enzymes use selective targeting mechanisms to regulate tubule formation locally during specific trafficking steps in the secretory and/or endocytic systems.

Modulation of Immune Response by B7 Family Molecules in Tumor Microenvironments

The importance of co-stimulatory and co-inhibitory molecules has been confirmed on a grand scale; with the identification of new B7 family molecules, possessing both immune activating and inhibiting functions, this family has exploded onto the scene of immune regulation. Nowhere, however, has the role of B7 family members been more apparent than in the fight against cancer. In this review, we will discuss recent data regarding the essential and complex role of B7 family members in regulating the immune response within tumor microenvironment.

Cancer vaccines: on the threshold of success

BACKGROUND

Cancer vaccines are a unique approach to cancer therapy. They exert an antitumor effect by engaging the host immune response, and have great potential for circumventing the intrinsic drug resistance that limits standard cancer management. Additional advantages of cancer vaccines are exquisite specificity, low toxicity, and the potential for a durable treatment effect due to immunologic memory.

OBJECTIVES

This review aims to consider the promise of cancer vaccines, review the current state of cancer vaccine development, and suggest directions for future research.

METHODS

The scope of this review was defined peer-reviewed information found on Medline, and information found on the Internet about Phase III clinical trials that are ongoing and not yet published.

RESULTS/CONCLUSIONS

Multiple Phase III clinical trials have demonstrated the promise and challenges posed by therapeutic vaccines, and defined the next steps in their clinical development. Determining the optimal integration of cancer vaccines with chemotherapy, radiation, surgery, and biologically targeted therapies, defining predictive biomarkers of immunologic and clinical response, and combining tumor vaccines with new drugs that effectively modulate the antitumor immune response, will ensure that cancer vaccines become part of standard cancer therapy and prevention.

Enhanced expression of interferon-gamma-induced antigen-processing machinery components in a spontaneously occurring cancer

In human tumors, changes in the surface expression and/or function of major histocompatibility complex (MHC) class I antigens are frequently found and may provide malignant cells with a mechanism to escape control of the immune system. This altered human lymphocyte antigen (HLA) class I phenotype can be caused by either structural alterations or dysregulation of genes encoding subunits of HLA class I antigens and/or components of the MHC class I antigen-processing machinery (APM). Herein we analyze the expression of several proteins involved in the generation of MHC class I epitopes in feline injection site sarcoma, a spontaneously occurring tumor in cats that is an informative model for the study of tumor biology in other species, including humans. Eighteen surgically removed primary fibrosarcoma lesions were analyzed, and an enhanced expression of two catalytic subunits of immunoproteasomes, PA28 and leucine aminopeptidase, was found in tumors compared to matched normal tissues. As a functional counterpart of these changes in protein levels, proteasomal activities were increased in tissue extracts from fibrosarcomas. Taken together, these results suggest that alterations in the APM system may account for reduced processing of selected tumor antigens and may potentially provide neoplastic fibroblasts with a mechanism for escape from T-cell recognition and destruction.

Synergistic antitumor effect of chemotactic-prostate tumor-associated antigen gene-modified tumor cell vaccine and anti-CTLA-4 mAb in murine tumor model

In this study, we demonstrate that an effective immune response against prostate tumors in mouse tumor model can be elicited using a strategy that combines CTLA-4 blockade and pSLC-3P-Fc-modified tumor cell vaccine (named B16F10-SLC-3P-Fc). Treatment of B16F10-3P-bearing mice resulted in a significant reduction in tumor incidence as assessed 2 months after treatment. In vivo Ab depletion confirmed that the antitumor effect was primarily CD8+ T cells and CD4+ T lymphocytes were required for the induction of CD8+ CTL response in B16F10-SLC-3P-Fc+anti-CTLA-4 mAb-immunized mice. Moreover, mice that were cured of an established tumor were protected against a rechallenge with the same tumor for at least 4 months, suggesting the generation of memory responses. Adoptive transfer experiments further indicate that antitumor reactivity can be transferred to naïve mice by splenocytes. These findings demonstrate that this combinatorial treatment can elicit a potent anti-tumor immune response and suggest potential of this approach for treatment of prostate cancer.

Lymphocyte activation in response to melanoma: interaction of NK-associated receptors and their ligands

In recent years, studies on the molecular and cellular mechanisms of immune responses against melanoma have contributed to a better understanding of how these tumours can be recognised by cytotoxic cells and the mechanisms they have developed to escape from innate and adaptive immunity. Lysis of melanoma cells by natural killer (NK) cells and cytolytic T cells is the result of a fine balance between signals transmitted by activating and inhibitory receptors. In addition to the T cell receptor, these were initially described as NK cell-associated receptors (NKRs) and were later also found on subsets of T lymphocytes, particularly effector-memory and terminally differentiated CD8 T cells. An increase of NKR(+)CD8(+) T cells has been found in melanoma patients, correlating with the expansion of differentiated effector CD8(+)CD28(null) CD27(null) T cells. NKRs can regulate the lysis of target cells expressing appropriate ligands. Activating receptors recognise ligands on tumours whereas inhibitory receptors are specific for MHC class I antigens and sense missing self. Altered expression of MHC class I antigens is frequently found on melanoma cells, preventing recognition by specific cytolytic T cells but favouring NK cell recognition. Changes in the expression of NKR-ligands in melanoma contribute in explaining the differences in the capacity of cytotoxic immune cells to control melanoma growth and dissemination.

Selective antibody-mediated targeting of class I MHC to EGFR-expressing tumor cells induces potent antitumor CTL activityin vitro andin vivo

Epidermal growth factor receptor (EGFR) is highly overexpressed in many tumor types. We present a new fusion molecule that can target solid tumors that express EGFR. The fusion molecule combines the advantage(s) of the well-established tumor targeting capabilities of high affinity recombinant fragments of antibodies with the known efficient, specific and potent killing ability of CD8 T lymphocytes directed against highly antigenic MHC/peptide complexes. A recombinant chimeric molecule was created by the genetic fusion of the scFv antibody fragment derived from the anti-EGFR monoclonal antibody C225, to monomeric single-chain HLA-A2 complexes containing immunodominant tumor or viral-specific peptides. The fusion protein can induce very efficiently CTL-dependent lysis of EGFR-expressing tumor cells regardless of the expression of self peptide-MHC complexes. Moreover, the molecule exhibited very potent antitumor activity in vivo in nude mice bearing preestablished human tumor xenografts. These in vitro and in vivo results indicate that recombinant scFv-MHC-peptide fusion molecules might represent a novel and powerful approach to immunotherapy of solid tumors, bridging antibody and T lymphocyte attack on cancer cells.

Analysis of host versus tumor interaction in cancer patients: opposing role of transforming growth factor-β1 and interleukin-6 in the development of in situ tumor immunity

A different degree of immunodeficiency is often found at tumor sites in cancer patients. At the late stage many patients develop malignant effusion that contains large numbers of tumor cells and host immune cells that constantly interact with each other. These sites may provide an ideal model to examine in situ anti-tumor immunity. The T cells in effusion were found to be immunodeficient, which suggested a defective anti-tumor cytotoxic T lymphocytes response. To pursue the mechanism for the T cell deficiency, we determined the production of immunomodulating cytokines in the effusion and detected the presence of transforming growth factor-beta1 (TGFbeta), prostaglandin E2, IL-6, IL-10, and IFNgamma. There was no detectable IL-2, IL-4, IL-12, or TNFalpha. The most prominent feature was the presence of TGFbeta and IL-6 at a very high level. Thus, the possible role of these two cytokines on T cell competence was further determined. TGFbeta was found to induce T cell anergy and reduced the production of perforin in T killer cells and their lytic activity. These events lead to the induction of peripheral T cell tolerance with profound T cell deficiency. IL-6 did not affect perforin production or cytolytic activity of the T killer cells. But the CD4+ CD25+ regulatory T cells (TR) that were often employed by TGFbeta to suppress T cell response were reduced in the malignant effusion, consistent with the fact that IL-6 down-regulates TR and this may represent the host's vigorous response to the tumor's subversion. These results show that TGFbeta and IL-6 might play pivotal but opposing roles in the host tumor interaction that, together with other immunomodulating components, determines the outcome for the development of local tumor immunity.

Dendritic cells pulsed with gp96-peptide complexes derived from human hepatocellular carcinoma (HCC) induce specific cytotoxic T lymphocytes

Dendritic cells (DCs) are one of the most potent antigen-presenting cells (APCs) capable of activating immune responses. Different forms of tumor antigens have been used to load DCs to initiate tumor-specific immune responses. Heat shock proteins (HSPs) are considered natural adjuvants which have the ability to chaperone peptides associated with them presented efficiently by interaction with professional APCs through specific receptors. In the present study, we used HSP, gp96-peptide complexes, derived from human hepatocellular carcinoma (HCC) cells as antigens for pulsing DCs. We found that gp96-peptide complexes derived from HCC cells induced the maturation of DCs by enhancing expression of human leukocyte antigen class II, CD80, CD86, CD40, and CD83. The matured DCs stimulated a high level of autologous T cell proliferation and induced HCC specific cytotoxic T lymphocytes, which specifically killed HCC cells by a major histocompatability complex (MHC) class I restricted mechanism. These findings demonstrate that DCs pulsed with gp96-peptide complexes derived from HCC cells are effective in activating specific T cell responses against HCC cells.

Antibody-mediated targeting of human single-chain class I MHC with covalently linked peptides induces efficient killing of tumor cells by tumor or viral-specific cytotoxic T lymphocytes

Soluble forms of human MHC class I HLA-A2 were produced in which the peptide binding groove was uniformly occupied by a single tumor or viral-derived peptides attached via a covalent flexible peptide linker to the N terminus of a single-chain beta-2-microglobulin-HLA-A2 heavy chain fusion protein. A tetravalent version of this molecule with various peptides was found to be functional. It could stimulate T cells specifically as well as bind them with high avidity. The covalently linked single chain peptide-HLA-A2 construct was next fused at its C-terminal end to a scFv antibody fragment derived from the variable domains of an anti-IL-2R alpha subunit-specific humanized antibody, anti-Tac. The scFv-MHC fusion was thus encoded by a single gene and produced in E. coli as a single polypeptide chain. Binding studies revealed its ability to decorate Ag-positive human tumor cells with covalent peptide single-chain HLA-A2 (scHLA-A2) molecules in a manner that was entirely dependent upon the specificity of the targeting Antibody fragment. Most importantly, the covalent scHLA-A2 molecule, when bound to the target tumor cells, could induce efficient and specific HLA-A2-restricted, peptide-specific CTL-mediated lysis. These results demonstrate the ability to generate soluble, stable, and functional single-chain HLA-A2 molecules with covalently linked peptides, which when fused to targeting antibodies, potentiate CTL killing. This new approach may open the way for the development of new immunotherapeutic strategies based on antibody targeting of natural cognate MHC ligands and CTL-based cytotoxic mechanisms.

Production and characterization of amplified tumor-derived cRNA libraries to be used as vaccines against metastatic melanomas

Background

Anti-tumor vaccines targeting the entire tumor antigen repertoire represent an attractive immunotherapeutic approach. In the context of a phase I/II clinical trial, we vaccinated metastatic melanoma patients with autologous amplified tumor mRNA. In order to provide the large quantities of mRNA needed for each patient, the Stratagene Creator™ SMART™ cDNA library construction method was modified and applied to produce libraries derived from the tumors of 15 patients. The quality of those mRNA library vaccines was evaluated through sequencing and microarray analysis.

Results

Random analysis of bacterial clones of the library showed a rate of 95% of recombinant plasmids among which a minimum of 51% of the clones contained a full-Open Reading Frame. In addition, despite a biased amplification toward small abundant transcripts compared to large rare fragments, we could document a relatively conserved gene expression profile between the total RNA of the tumor of origin and the corresponding in vitro transcribed complementary RNA (cRNA). Finally, listing the 30 most abundant transcripts of patient MEL02's library, a large number of tumor associated antigens (TAAs) either patient specific or shared by several melanomas were found.

Conclusion

Our results show that unlimited amounts of cRNA representing tumor's transcriptome could be obtained and that this cRNA was a reliable source of a large variety of tumor antigens.

Exposure of human primary colon carcinoma cells to anti-Fas interactions influences the emergence of pre-existing Fas-resistant metastatic subpopulations

Fas, an important death receptor-mediated signaling pathway, has been shown to be down-regulated during human colon tumorigenesis; however, how alterations in Fas expression influence the metastatic process remains unresolved. In mouse models, loss of Fas function was found to be both necessary and sufficient for tumor progression. In this study, we investigated the link between functional Fas status and malignant phenotype using a matched pair of naturally occurring primary (Fas-sensitive) and metastatic (Fas-resistant) human colon carcinoma cell lines in both in vitro and in vivo (xenograft) settings. Metastatic sublines were produced in vitro from the primary tumor cell line by functional elimination of Fas-responsive cells. Conversely, sublines derived from the primary tumor in vivo at distal metastatic sites were Fas-resistant. In contrast, simply disrupting the Fas pathway by molecular-based strategies in the Fas-sensitive primary tumor failed to achieve the same metastatic outcome. Interestingly, both in vitro- and in vivo-produced sublines resembled the naturally occurring metastatic population, based on functional and morphologic studies and genome-scale gene expression profiling. Overall, using this human colon carcinoma model, we: 1) showed that loss of Fas function was linked to, but alone was insufficient for, acquisition of a detectable metastatic phenotype; 2) demonstrated that metastatic subpopulations pre-existed within the heterogeneous primary tumor, and that anti-Fas interactions served as a selective pressure for their outgrowth; and 3) identified a large set of differentially expressed genes distinguishing the primary from metastatic malignant phenotypes. Thus, Fas-based interactions may represent a novel mechanism for the biologic or immunologic selection of certain types of Fas-resistant neoplastic clones with enhanced metastatic ability.

B7-H1 pathway and its role in the evasion of tumor immunity

B7-H1 is a recently identified member of the B7 family molecules. Upon ligation to its receptors on T cells it regulates activation and differentiation of T cells. B7-H1 preferentially costimulates IL-10 production in resting T cells and further induces the apoptosis of activated T cells. PD-1 is a receptor of B7-H1 and is shown to mediate the inhibition of activated T cell response, presumably by inhibiting cell cycle progression. The expression of B7-H1 protein is limited to macrophage lineage of cells in normal tissues, although its mRNA transcription is found in a broad range of tissues. In contrast, B7-H1 is abundant in various human cancers. The tumor-associated B7-H1 increases apoptosis of antigen specific T cells, leading to growth of immunogenic tumor growth in vivo. Current data suggest that B7-H1 regulates the organ-specific tolerance in normal tissue and may contribute to immune evasion by cancers. Selective manipulation of B7-H1 pathway thus aids in the design of new regimens in the treatment of human autoimmune disease and the control of malignant cancers.

Impaired expression of proteasome subunits and human leukocyte antigens class I in human colon cancer cells

BACKGROUND AND AIM

The presentation of human leukocyte antigens (HLA) class I requires the coordinated expression of numerous components involved in antigen processing and antigen presentation. Tumor cells may alter the expression of these components to decrease HLA class I expression, allowing them to escape immune surveillance. The aim of this study is to investigate the expressions of these components, including proteasome subunits, and their involvement in the expression of HLA class I in human colon cancer cells.

METHODS

Four human colon cancer cell lines, HCT116, SW403, LoVo and DLD-1, were used to examine the expression of HLA class I by flow cytometry. Reverse transcription-polymerase chain reaction was performed to assess the expression of beta2-microglobulin, heavy chains, transporter subunits, immunoproteasomes subunits and proteasome activator 28 (PA28) subunits.

RESULTS

Human leukocyte antigen class I was expressed highly in HCT116 and SW403 cells and weakly in LoVo cells, but was not expressed in DLD-1 cells. The DLD-1 cells were deficient in the expression of proteasome subunits including low molecular weight polypeptide proteasome subunit 2 (LMP2), multicatalytic endopeptidase complex-like-1 (MECL-1), PA28alpha and PA28beta, whereas other HLA class I-expressing cell lines expressed all components tested. gamma-Interferon (IFN-gamma) treatment of DLD-1 cells restored the expression of LMP2, MECL-1 and PA28beta, but not the expression of HLA class I. Enforced expression of PA28alpha induced the expression of HLA class I in IFN-gamma-treated DLD-1 cells, but not in untreated DLD-1 cells.

CONCLUSION

These results suggest that the impaired expression of proteasome subunits is involved in the loss of HLA class I expression in human colon cancer cells.

Recruitment of CTL activity by tumor-specific antibody-mediated targeting of single-chain class I MHC-peptide complexes

The MHC class I-restricted CD8 CTL effector arm of the adaptive immune response is uniquely equipped to recognize tumor cells as foreign and consequently initiates the cascade of events resulting in their destruction. However, tumors have developed sophisticated strategies to escape immune effector mechanisms; their most well-known strategy is down-regulation of MHC class I molecules. To overcome this and develop new approaches for immunotherapy, we have constructed a recombinant molecule in which a single-chain MHC is specifically targeted to tumor cells through its fusion to cancer-specific recombinant Ab fragments. As a model we used a single-chain HLA-A2 molecule genetically fused to the variable domains of an anti-IL-2Ralpha subunit-specific humanized Ab, anti-Tac. The construct, termed B2M-aTac(dsFv), was expressed in Escherichia coli, and functional molecules were produced by in vitro refolding in the presence of HLA-A2-restricted antigenic peptides. Flow cytometry studies revealed the ability to decorate Ag-positive, HLA-A2-negative human tumor cells with HLA-A2-peptide complexes in a manner that was entirely dependent upon the specificity of the targeting Ab fragment. Most importantly, the B2M-aTac(dsFv)-mediated coating of the target tumor cells made them susceptible for efficient and specific HLA-A2-restricted, melanoma gp100 peptide-specific CTL-mediated lysis. These results demonstrate the concept that Ab-guided, Ag-specific targeting of MHC-peptide complexes on tumor cells can render them susceptible and more receptive and thus potentiate CTL killing. This type of approach may open the way for the development of new immunotherapeutic strategies based on Ab targeting of natural cognate MHC ligands and CTL-based cytotoxic mechanisms.

Implications of the network structure of cellular control circuits for the design of anti-cancer vaccine therapies

I describe the use of a statistical mechanical model of a heirarchical network of failure-prone elements as a model for the failure of a network of interconnected biological elements that are or could be involved in the causation of cancer. From its topology, such a model predicts some of the properties of observed oncogene/tumour suppressor gene networks. I show that the same model suggests that a cancer vaccine strategy that targets 'key' network elements, such as p53 or RAS gene products, is not the only effective strategy for a broadly effective anti-cancer therapy. A mixed antigen or whole cell strategy could be as effective as single antigen vaccines, even if the latter are targeted at the most commonly mutated gene products.

Tumor-targeted immune complex formation: effects on myeloid cell activation and tumor-directed immune cell migration

The effectiveness of cellular immunotherapy of solid tumors is often hampered by the lack of specific infiltration of immune effector cells into the tumor mass. Therefore, we studied the potential of tumor antigen-specific antibodies to elicit tumor-specific myeloid cell activation, to induce or enhance tumor infiltration by immune cells. To this end, we developed an in vitro model system using the human myeloid cell line MonoMac-6. Incubation of IFN-gamma-primed MonoMac-6 cells with serum-opsonized zymosan or EGP-2-directed, mouse IgG2a-opsonized, EGP-2-positive tumor cells resulted in the production of ROS and TNF-alpha and induced E-selectin and ICAM-1 expression on HUVECs. FcR-mediated MonoMac-6 cell activation was strictly dependent on the activation of MonoMac-6 cells with IFN-gamma. In addition, no myeloid cell activation was observed in the presence of human serum or using tumor antigen-specific mouse antibody subclasses other than IgG2a, suggesting the crucial involvement of CD64 (FcgammaR1) in the effects observed. However, serum-inhibited myeloid cell activation was completely restored employing a 2-step targeting approach in which tumor cell opsonization with mouse anti-EGP-2 antibodies was followed by incubation with human antimouse Ig antibodies. Moreover, using this 2-step approach, not only anti-EGP-2-directed mouse IgG2a but also mouse IgG1 antibodies effectively induced tumor-specific myeloid cell activation. In conclusion, we describe a method to induce efficient and tumor-specific activation of myeloid cells based on the sequential use of mouse tumor antigen-specific and human antimouse Ig antibodies. Targeted myeloid cell activation may provide a means to aid in the induction of a tumor-directed immune response and as such, the method described here could be of clinical significance.

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.

Assumptions of the tumor 'escape' hypothesis

The reasons why cancer cells are not destroyed by the immune system are likely to be similar, in most cases, to the reasons why normal cells are not destroyed by the immune system. Unfortunately for tumor immunologists, these reasons have not yet been fully elucidated. What is known, however, is that the lack of autoimmune destruction of normal tissue after immune activation is a finely regulated, highly orchestrated sequence of events. Viewed in this light, it is interesting to conceptualize the derangement of the tumor genome not merely as an engine that enables cancer cells to dodge immune recognition. The dysregulation characteristic of the transformed genome is also what makes tumor immunity, a specialized form of autoimmunity, possible.

Human T-lymphocyte cytotoxicity and proliferation directed by a single chimeric TCRzeta /CD28 receptor

Artificial receptors provide a promising approach to target T lymphocytes to tumor antigens. However, the receptors described thus far produce either an activation or a co-stimulatory signal alone, thus limiting the spectrum of functions accomplished by the genetically modified cells. Here we show that human primary T lymphocytes expressing fusion receptors directed to prostate-specific membrane antigen (PSMA) and containing combined T-cell receptor-zeta (TCRzeta), and CD28 signaling elements, effectively lyse tumor cells expressing PSMA. When stimulated by cell-surface PSMA, retrovirally transduced lymphocytes undergo robust proliferation, expanding by more than 2 logs in three weeks, and produce large amounts of interleukin-2 (IL-2). Importantly, the amplified cell populations retain their antigen-specific cytolytic activity. These data demonstrate that fusion receptors containing both TCR and CD28 signaling moieties are potent molecules able to redirect and amplify human T-cell responses. These findings have important implications for adoptive immunotherapy of cancer, especially in the context of tumor cells that fail to express major histocompatibility complex antigens and co-stimulatory molecules.

Therapeutic potential of mycobacterial cell wall-DNA complexes

Cell wall skeletons isolated from many bacteria have been shown to possess anticancer activity. The anticancer activities of such preparations have been attributed to the activation of immune effector cells and not to a direct effect on cancer cell division. A cell wall extract from Mycobacterium phlei, wherein mycobacterial DNA in the form of short oligonulceotides is preserved to the cell wall, has anticancer activity against a wide range of cancer cells. Mycobacterial cell wall-DNA complexes (MCC) exert their anticancer activity by a dual mechanism of action: an indirect effect via the induction of anticancer cytokines and a direct effect on cancer cell division mediated by the induction of apoptosis. In this review, the immunomodulatory and the pro-apoptotic mechanisms of action of MCC will be explored. The identification of the active component in MCC will be discussed, as well as the composition differences with cell wall skeletons and live mycobacteria. Finally, the use of MCC against bladder and prostate cancers will be discussed and compared to standard therapies, particularly therapy using mycobacteria and mycobacteria-derived products.

Apoptosis: the quiet death silences the immune system

Apoptosis plays an essential role in maintaining cellular homeostasis during development, differentiation, and pathophysiological processes. In the immune system, recent investigations reveal that during the course of T-cell development in the thymus, negative selection of autoreactive immature T-cells is a typical apoptotic process. In addition, apoptosis is also involved in cytotoxic killing of target cells and the regulation of lymphocyte homeostasis during immune responses. Interestingly, recent evidence has suggested that cells dying by apoptosis are actively involved in immunosuppression in various circumstances. We have shown that apoptotic cells could inhibit the expression of CD69 during T-cell activation. Furthermore, apoptotic cells phagocytosed by macrophages and/or dendritic cells are immunosuppressive, a process likely mediated by the production of transforming growth factor-beta1. Since apoptosis is a common mechanism by which excessive cells in many tissues and organs are eliminated in various pathophysiological processes, we believe that further investigation into the mechanisms by which apoptotic cells affect the immune system will not only lead to a better understanding of the significance of apoptosis during immune responses, but will also provide novel strategies for the management of autoimmune diseases and transplantation.

Expression of HLA class I, beta(2)-microglobulin, TAP1 and IL-10 in Epstein-Barr virus-associated nasal NK/T-cell lymphoma: Implications for tumor immune escape mechanism

Several mechanisms of immune escape might be in operation in Epstein-Barr virus (EBV)-associated nasal NK/T-cell lymphoma. We have previously shown the downregulation of the immunogenic EBV nuclear antigens by alternative promoter usage and the preferential selection of the deletion genotype of latent membrane protein 1 in nasal lymphoma. To understand further the strategies used for immune escape by this tumor, we examined by immunohistochemistry HLA class I expression in 15 cases using frozen sections, along with beta(2)-microglobulin and transporter associated with antigen processing 1 (TAP1) expression in 39 cases using paraffin sections. All nasal NK/T-cell lymphomas showed positive staining for HLA class I, beta(2)-microglobulin and TAP1 on most tumor cells, except for two cases (5%) in which most of the tumor cells lacked beta(2)-microglobulin staining. We next immunostained for interleukin-10 on frozen sections in 13 cases, all of which showed strong expression by most tumor cells. Transcription of human interleukin-10 but not EBV BCRF1 (viral interleukin-10) was identified by reverse transcriptase-polymerase chain reaction in these nasal NK/T-cell lymphomas. Overall, our data suggest that global downregulation of HLA class I or TAP1 rarely accounts for the ability of nasal NK/T-cell lymphoma to evade immunosurveillance and that other immune escape mechanisms may be operating in nasal NK/T-cell lymphoma, such as production of interleukin-10 to suppress the local immune response.

Induction of polyclonal prostate cancer-specific CTL using dendritic cells transfected with amplified tumor RNA

Polyvalent cancer vaccines targeting the entire antigenic spectrum on tumor cells may represent a superior therapeutic strategy for cancer patients than vaccines solely directed against single Ags. In this study, we show that autologous dendritic cells (DC) transfected with RNA amplified from microdissected tumor cells are capable of stimulating CTL against a broad set of unidentified and critical prostate-specific Ags. Although the polyclonal CTL responses generated with amplified tumor RNA-transfected DC encompassed as a subcomponent a response against prostate-specific Ag (PSA) as well as against telomerase reverse transcriptase, the tumor-specific CTL were consistently more effective than PSA or telomerase reverse transcriptase CTL to lyse tumor targets, suggesting the superiority of the polyclonal response. Although tumor RNA-transfected DC stimulated CTL, which recognized not only tumor but also self-Ags expressed by benign prostate tissue, these cross-reactive CTL were exclusively specific for the PSA, indicating an immunodominant role of PSA in the prostate cancer-specific immune response. Our data suggest that tumor RNA-transfected DC may represent a broadly applicable, potentially clinically effective vaccine strategy for prostate cancer patients, which is not limited by tumor tissue availability for Ag preparation and may minimize the risk of clonal tumor escape.

Antigen-processing machinery breakdown and tumor growth

Defects in the major histocompatibility complex (MHC) class I antigen-processing machinery (APM) have been described in tumors of different histology. Murine data suggest that defects in the MHC class II APM might also be associated with malignant transformation of human cells. This article describes the pathophysiology of the MHC class I and II APM, reviews APM abnormalities in tumor cells and discusses their role in the escape of tumor cells from in vitro recognition by T cells.