CTLA-4: new insights into its biological function and use in tumor immunotherapy

Pivotal advance: CTLA-4+ T cells exhibit normal antiviral functions during acute viral infection

Previous studies have shown that T cells, which are genetically deficient in CTLA-4/CD152 expression, will proliferate uncontrollably, resulting in lethal autoimmune disease. This and other evidence indicate that CTLA-4 plays a critical role in the negative regulation of effector T cell function. In contrast to expectations, BrdU incorporation experiments demonstrated that CTLA-4 expression was associated with normal or even enhanced in vivo proliferation of virus-specific CD4+ and CD8+ T cells following acute lymphocytic choriomeningitis virus or vaccinia virus infection. When compared with CTLA-4- T cells directly ex vivo, CTLA-4+ T cells also exhibited normal antiviral effector functions following stimulation with peptide-coated cells, virus-infected cells, plate-bound anti-CD3/anti-CTLA-4, or the cytokines IL-12 and IL-18. Together, this indicates that CTLA-4 does not directly inhibit antiviral T cell expansion or T cell effector functions, at least not under the normal physiological conditions associated with either of these two acute viral infections.

Immunotherapy for prostate cancer

Whereas androgen deprivation and chemotherapy have become the cornerstone of therapy for advanced prostate cancer, novel therapies are being developed that may expand upon currently available treatments. The identification of antigens expressed by prostate tissue and/or prostate cancer that are recognized by T cells or antibodies creates opportunities to develop novel immunotherapeutic approaches including tumor vaccines. Proteins expressed in prostate cancer including prostate-specific antigen, prostatic acid phosphatase, and prostate membrane antigen have been used as immunologic targets for immunotherapy. Moreover, innovations in cancer genomics and proteomics also will aid in the identification of immunologic targets. Emerging trials have demonstrated that immunotherapy may not only generate immune responses in patients, but also clinical responses. Future studies will be directed at capitalizing on these findings.

Emerging drugs for chronic lymphocytic leukaemia

Although the philosophy of management of patients with chronic lymphocytic leukaemia (CLL) has been altered with the advent of fludarabine-based therapies, impact on long-term survival is unclear and a significant proportion of patients will develop resistance to fludarabine. Similar to other haematological malignancies, a potential for 'cure' is likely to be achieved only if 'high-quality' complete remissions (CRs) are achieved. Treatment options for patients who develop resistance to fludarabine continue to be limited, with only a proportion obtaining a response (usually not CRs) with salvage therapies. This review summarises novel therapies that are being evaluated in patients with CLL, specifically those targeting the antiapoptotic Bcl-2 family of proteins and receptors (e.g., CD40, CD80, HLA-DR) involved in mediating survival signals from the microenvironment.

Building a better model of cancer

The 2006 Cold Spring Harbor Laboratory meeting on the Mechanisms and Models of Cancer was held August 16–20. The meeting featured several hundred presentations of many short talks (mostly selected from the abstracts) and posters, with the airing of a number of exciting new discoveries. We will focus this meeting review on models of cancer (primarily mouse models), highlighting recent advances in new mouse models that better recapitulate sporadic tumorigenesis, demonstrations of tumor addiction to tumor suppressor inactivation, new insight into senescence as a tumor barrier, improved understanding of the evolutionary paths of cancer development, and environmental/immunological influences on cancer.

Blockade of CTLA-4 on CD4+CD25+ regulatory T cells abrogates their function in vivo

Naturally occurring CD4+ regulatory T cells (T(R)) that express CD25 and the transcription factor FoxP3 play a key role in immune homeostasis, preventing immune pathological responses to self and foreign Ags. CTLA-4 is expressed by a high percentage of these cells, and is often considered as a marker for T(R) in experimental and clinical analysis. However, it has not yet been proven that CTLA-4 has a direct role in T(R) function. In this study, using a T cell-mediated colitis model, we demonstrate that anti-CTLA-4 mAb treatment inhibits T(R) function in vivo via direct effects on CTLA-4-expressing T(R), and not via hyperactivation of colitogenic effector T cells. Although anti-CTLA-4 mAb treatment completely inhibits T(R) function, it does not reduce T(R) numbers or their homing to the GALT, suggesting the Ab mediates its function by blockade of a signal required for T(R) activity. In contrast to the striking effect of the Ab, CTLA-4-deficient mice can produce functional T(R), suggesting that under some circumstances other immune regulatory mechanisms, including the production of IL-10, are able to compensate for the loss of the CTLA-4-mediated pathway. This study provides direct evidence that CTLA-4 has a specific, nonredundant role in the function of normal T(R). This role has to be taken into account when targeting CTLA-4 for therapeutic purposes, as such a strategy will not only boost effector T cell responses, but might also break T(R)-mediated self-tolerance.

The clinical utility of cytotoxic T lymphocyte antigen 4 abrogation by human antibodies

The recent cloning and identification of a variety of regulatory and counter-regulatory molecules on T cells and antigen presenting cells has led to the development of antibodies and other molecules that either stimulate or abrogate these immune functions. Patients with autoimmune disease, graft rejection and cancer might benefit from the ability to manipulate immune regulatory pathways. The first demonstration of clinical benefit by modulation of immune regulation in cancer involves the use of human antibodies against cytotoxic T lymphocyte antigen 4. Murine preclinical studies suggested that cytotoxic T lymphocyte antigen-4 abrogation would provide clinical benefit after an antitumor vaccination. Early trials of this antibody in patients with melanoma have shown antitumor activity with and without vaccines that is associated with a state of autoimmunity. Surprisingly, the reversal of the state of autoimmunity induced by cytotoxic T lymphocyte antigen 4 antibodies by the use of corticosteroids does not eliminate clinical benefit.

Strong-arming immune regulation: suppressing regulatory T-cell function to treat cancers

In recent years there has been an accelerated understanding of immune regulatory mechanisms. Much of this immune regulation is linked to a collection of specialized regulatory cells of the T-cell lineage (Tregs). This collection consists of Tregs that are either thymically derived or peripherally induced. Tregs are important for controlling potentially autoreactive immune effectors and immune responses to foreign organisms and molecules. Their importance in maintaining immune homeostasis and the overall health of an organism cannot be overstated. However, there is a dark side, and Tregs may also be involved in the pathogenesis of malignancies. Evidence shows that tumors induce or recruit Tregs to block antitumor effectors. Thus, there are efforts underway to identify approaches that specifically inhibit the function of intratumoral Tregs, which could lead to increased immunity to tumors without off-target immune-related pathologies (i.e., autoimmune disease). In this review, the biology of Tregs is discussed along with their involvement in malignancies and emerging strategies to block their function.

Targeted therapies in melanoma

In the last decade the incidence of melanoma has been rising. Despite this, survival remains substantially constant because early diagnosis of thin lesions has increased. By contrast, metastatic melanoma continues to have a poor prognosis and it still represents a challenge for oncologists. Response rates with single agent dacarbazine range from 10% to 25% with median survival of 8 months. The advent of new drugs with specific mechanisms of action could help to improve the poor results of traditional therapies. In this review, we focused on the novel agents that entered clinical trials in melanoma patients. We show the results of some clinical trials with target-oriented drugs in melanoma patients. Moreover pre-clinical data and rationale for use in melanoma was explained. Trials with protein-kinase inhibitors, anti-CTLA-4 agents, pro-apoptotic oligonucleotides and anti-angiogenic agents were reviewed. Combinations with chemotherapeutic agents, immunotherapy and vaccine therapy were also analyzed.

DNA vaccines against cancer

Significant progress made in the field of tumor immunology by the characterization of a large number of tumor antigens, and the better understanding of the mechanisms preventing immune responses to malignancies has led to the extensive study of cancer immunization approaches such as DNA vaccines encoding tumor antigens. This article reviews major aspects of DNA immunization in cancer. It gives a brief history and then discusses the proposed mechanism of action, preclinical and clinical studies, and methods of enhancing the immune responses induced by DNA vaccines.

Malignant melanoma: genetics and therapeutics in the genomic era

Cell for cell, probably no human cancer is as aggressive as melanoma. It is among a handful of cancers whose dimensions are reported in millimeters. Tumor thickness approaching 4 mm presents a high risk of metastasis, and a diagnosis of metastatic melanoma carries with it an abysmal median survival of 6-9 mo. What features of this malignancy account for such aggressive behavior? Is it the migratory history of its cell of origin or the programmed adaptation of its differentiated progeny to environmental stress, particularly ultraviolet radiation? While the answers to these questions are far from complete, major strides have been made in our understanding of the cellular, molecular, and genetic underpinnings of melanoma. More importantly, these discoveries carry profound implications for the development of therapies focused directly at the molecular engines driving melanoma, suggesting that we may have reached the brink of an unprecedented opportunity to translate basic science into clinical advances. In this review, we attempt to summarize our current understanding of the genetics and biology of this disease, drawing from expanding genomic information and lessons from development and genetically engineered mouse models. In addition, we look forward toward how these new insights will impact on therapeutic options for metastatic melanoma in the near future.

Physiologic regulation of central and peripheral T cell tolerance: lessons for therapeutic applications

Immunologic tolerance is a state of unresponsiveness that is specific for a particular antigen. The immune system has an extraordinary potential for making T cell and B cell that recognize and neutralize any chemical entity and microbe entering the body. Certainly, some of these T cells and B cells recognize self-components; therefore, cellular mechanisms have evolved to control the activity of these self-reactive cells and achieve immunological self-tolerance. The most important in vivo biological significance of mechanisms regulating self-tolerance is to prevent the immune system from mounting an attack against the host's own tissues resulting in autoimmunity. This review summarizes recent developments in our understanding of T-helper cell tolerance and discusses how the new findings can be exploited to prevent and treat autoimmune diseases, allergy, cancer, and chronic infection, or establish donor-specific transplantation tolerance.

Inhibition of T cell activation and autoimmune diabetes using a B cell surface-linked CTLA-4 agonist

CTL-associated antigen 4 (CTLA-4) engagement negatively regulates T cell activation and function and promotes immune tolerance. However, it has been difficult to explore the biology of selective engagement of CTLA-4 in vivo because CTLA-4 shares its ligands, B7-1 and B7-2, with CD28. To address this issue, we developed a Tg mouse expressing a single-chain, membrane-bound anti-CTLA-4 Ab (scFv) on B cells. B and T cells developed normally and exhibited normal phenotype in the steady state and after activation in these mice. However, B cells from scFv Tg+ mice (scalphaCTLA4+) prevented T cell proliferation and cytokine production in mixed lymphocyte reactions. Additionally, mice treated with scalphaCTLA4+ B cells had decreased T cell-dependent B cell Ab production and class switching in vivo after antigen challenge. Furthermore, expression of this CTLA-4 agonist protected NOD mice from spontaneous autoimmune diabetes. Finally, this disease prevention occurred in Treg-deficient NOD.B7-1/B7-2 double-knockout mice, suggesting that the effect of the CTLA-4 agonist directly attenuates autoreactive T cell activation, not Treg activation. Together, results from this study demonstrate that selective ligation of CTLA-4 attenuates in vivo T cell responses, prevents development of autoimmunity, and represents a novel immunotherapeutic approach for the induction and maintenance of peripheral tolerance.

Immunosuppressive role of semaphorin-3A on T cell proliferation is mediated by inhibition of actin cytoskeleton reorganization

Timely negative regulation of the immune system is critical to allow it to perform its duty while maintaining it under tight control to avoid overactivation. We previously reported that the neuronal receptor neuropilin-1 (NP-1) is expressed in human lymph nodes. However, the role of NP-1 interaction with its physiological ligand semaphorin-3A (Sema-3A) on immune cells remains elusive. Here we show that Sema-3A is expressed by activated DC and T cells, and that its secretion in DC/T cell cocultures is delayed. Sema-3A/NP-1 interaction down-modulated T cell activation since addition of Sema-3A in DC/T cell cocultures dramatically inhibited allogeneic T cell proliferation. More importantly, neutralization by blocking antibodies or by antagonist peptide of endogenous Sema-3A produced by DC/T cell cocultures resulted in a 130% increase in T cell proliferation. Sema-3A acted directly on T cells, since it could block anti-CD3/CD28-stimulated proliferation of T cells. Finally, immunomodulatory functions of Sema-3A relied on the blockage of actin cytoskeleton reorganization, affecting TCR polarization and interfering with early TCR signal transduction events such as ZAP-70 or focal adhesion kinase phosphorylation. Therefore, we propose that Sema-3A secretion and the resulting NP-1/Sema-3A interaction are involved in a late negative feedback loop controlling DC-induced T cell proliferation.

Efficient loading of dendritic cells following cryo and radiofrequency ablation in combination with immune modulation induces anti-tumour immunity

Dendritic cells (DC) are professional antigen-presenting cells that play a pivotal role in the induction of immunity. Ex vivo-generated, tumour antigen-loaded mature DC are currently exploited as cancer vaccines in clinical studies. However, antigen loading and maturation of DC directly in vivo would greatly facilitate the application of DC-based vaccines. We formerly showed in murine models that radiofrequency-mediated tumour destruction can provide an antigen source for the in vivo induction of anti-tumour immunity, and we explored the role of DC herein. In this paper we evaluate radiofrequency and cryo ablation for their ability to provide an antigen source for DC and compare this with an ex vivo-loaded DC vaccine. The data obtained with model antigens demonstrate that upon tumour destruction by radiofrequency ablation, up to 7% of the total draining lymph node (LN) DC contained antigen, whereas only few DC from the conventional vaccine reached the LN. Interestingly, following cryo ablation the amount of antigen-loaded DC is almost doubled. Analysis of surface markers revealed that both destruction methods were able to induce DC maturation. Finally, we show that in situ tumour ablation can be efficiently combined with immune modulation by anti-CTLA-4 antibodies or regulatory T-cell depletion. These combination treatments protected mice from the outgrowth of tumour challenges, and led to in vivo enhancement of tumour-specific T-cell numbers, which produced more IFN-γ upon activation. Therefore, in situ tumour destruction in combination with immune modulation creates a unique, ‘in situ DC-vaccine’ that is readily applicable in the clinic without prior knowledge of tumour antigens.

CD80 and CD86 control antiviral CD8+ T-cell function and immune surveillance of murine gammaherpesvirus 68

The interactions between CD80 and CD86 on antigen-presenting cells and CD28 on T cells serve as an important costimulatory signal in the activation of T cells. Although the simplistic two-signal hypothesis has been challenged in recent years by the identification of different costimulators, this classical pathway has been shown to significantly impact antiviral humoral and cellular immune responses. How the CD80/CD86-CD28 pathway affects the control of chronic or latent infections has been less well characterized. In this study, we investigated its role in antiviral immune responses against murine gammaherpesvirus 68 (MHV-68) and immune surveillance using CD80/CD86(-/-) mice. In the absence of CD80/CD86, primary antiviral CD8(+) T-cell responses and the induction of neutralizing antibodies were severely impaired. During long-term immune surveillance, the virus-specific CD8(+) T cells were impaired in IFN-gamma production and secondary expansion and exhibited an altered phenotype. Surprisingly, a low level of viral reactivation in the lung was observed, and this effect was independent of CD28 and CTLA-4. Thus, CD80 and CD86, signaling through CD28 and possibly another unidentified receptor, are required for optimal immune surveillance and antiviral immune responses to murine gammaherpesvirus.

Reversal of the TCR stop signal by CTLA-4

The coreceptor cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) is pivotal in regulating the threshold of signals during T cell activation, although the underlying mechanism is still not fully understood. Using in vitro migration assays and in vivo two-photon laser scanning microscopy, we showed that CTLA-4 increases T cell motility and overrides the T cell receptor (TCR)-induced stop signal required for stable conjugate formation between T cells and antigen-presenting cells. This event led to reduced contact periods between T cells and antigen-presenting cells that in turn decreased cytokine production and proliferation. These results suggest a fundamentally different model of reverse stop signaling, by which CTLA-4 modulates the threshold for T cell activation and protects against autoimmunity.

Distribution of CTLA-4 polymorphisms in allergic asthma

BACKGROUND

The CTLA-4 molecule is an important negative regulator of T cell activation. It is encoded on chromosome 2q33 and found to be associated with several allergic phenotypes including asthma. However, the association of CTLA-4 gene polymorphisms with allergic asthma is still controversial and therefore was the subject of this study.

METHODS

By PCR-RFLP, the distribution of three single nucleotide polymorphisms (SNPs), -1147 C/T, -318 C/T, and +49 A/G, was examined in 219 Polish Caucasoid patients diagnosed with allergic asthma and in 102 ethnically matched healthy control individuals. (AT)(n) microsatellite polymorphism was also tested in the same individuals.

RESULTS

No statistically significant differences in SNPs or microsatellite allele, genotype or haplotype frequencies between patients and controls were found.

CONCLUSION

CTLA-4 polymorphisms do not seem to be a risk factor for allergic asthma in Poles.

Interleukin 27 negatively regulates the development of interleukin 17-producing T helper cells during chronic inflammation of the central nervous system

Studies have focused on the events that influence the development of interleukin 17 (IL-17)-producing T helper cells (T(H)-17 cells) associated with autoimmunity, such as experimental autoimmune encephalitis, but relatively little is known about the cytokines that antagonize T(H)-17 cell effector responses. Here we show that IL-27 receptor-deficient mice chronically infected with Toxoplasma gondii developed severe neuroinflammation that was CD4+ T cell dependent and was associated with a prominent IL-17 response. In vitro, treatment of naive primary T cells with IL-27 suppressed the development T(H)-17 cells induced by IL-6 and transforming growth factor-beta, which was dependent on the intracellular signaling molecule STAT1 but was independent of inhibition of IL-6 signaling mediated by the suppressor protein SOCS3. Thus IL-27, a potent inhibitor of T(H)-17 cell development, may be a useful target for treating inflammatory diseases mediated by these cells.

Blockade of PD-L1 (B7-H1) augments human tumor-specific T cell responses in vitro

Human tumors frequently escape immune destruction, despite the presence of cytotoxic T cells (CTL) recognizing tumor-associated antigens (TAA). We have previously shown that programmed death ligand-1 (PD-L1), a recently identified ligand of the B7 superfamily, is expressed on murine tumors and can inhibit antitumor immune responses. To evaluate the clinical relevance of our animal model findings, we examined human tumors and tumor-specific T cells. We found PD-L1 to be constitutively expressed on human renal cell carcinoma (RCC) cell lines and upregulated on human melanoma cell lines upon exposure to interferon-gamma. Similarly, we found binding of anti-PD-L1 monoclonal antibody (mAb) on frozen sections from RCC and melanomas, but not on normal tissues. The corresponding inhibitory receptor of PD-L1, PD-1, revealed a higher expression on tumor-infiltrating lymphocytes than on peripheral blood lymphocytes (PBL) from melanoma patients upon specific antigen stimulation. Stimulation of PBL from healthy donors with peptide-loaded dendritic cells in the presence of anti-PD-L1 mAb altered neither the total T cell numbers after expansion, nor the percentage of peptide-specific CTL, when providing a T cell help by addition of cytokines. However, when stimulating TAA-specific CTL and T helper cells with Ag-pulsed dendritic cells in the absence of exogenous cytokines, PD-L1 blockade increased the cytokine production. Similar to the data achieved in the murine system, the blockade of PD-L1 on human tumors resulted in enhanced cytolytic activity of TAA-specific CTLs and cytokine production of TAA-specific T helper cells when interacting directly with the tumor. In summary, our data suggest that PD-L1/PD-1 interactions negatively regulate T cell effector functions predominantly in the absence of exogenous cytokine support, indicating an important role for this pathway in tumor evasion.

Intrapatient dose escalation of anti-CTLA-4 antibody in patients with metastatic melanoma

We previously reported our experience in treating 56 patients with metastatic melanoma using a human anti-cytotoxic T-lymphocyte antigen 4 (CTLA-4) antibody. Durable tumor regressions were seen that correlated with the induction of autoimmune toxicities. In this study, we treated 46 additional patients using an intrapatient dose escalation schema to test whether higher doses of anti-CTLA-4 antibody would induce increased autoimmunity and concomitant tumor regression. Twenty-three patients started anti-CTLA-4 antibody administration at 3 mg/kg and 23 patients started treatment at 5 mg/kg, receiving doses every 3 weeks. Patients were dose-escalated every other dose to a maximum of 9 mg/kg or until objective clinical responses or grade III/IV autoimmune toxicity were seen. Escalating doses of antibody resulted in proportionally higher plasma concentrations. Sixteen patients (35%) experienced a grade III/IV autoimmune toxicity. Five patients (11%) achieved an objective clinical response. Two of the responses are ongoing at 13 and 16 months, respectively. Flow cytometric analysis of peripheral blood revealed significant increases in both T-cell surface markers of activation and memory phenotype. Thus, higher serum levels and prolonged administration of anti-CTLA-4 antibody resulted in a trend toward a greater incidence of grade III/IV autoimmune toxicity than previously reported, but did not seem to increase objective response rates.

Development of the PANVAC-VF vaccine for pancreatic cancer

PANVAC-VF is a vaccine regimen composed of a priming dose of recombinant vaccinia virus and booster doses of recombinant fowlpox virus expressing carcinoembryonic antigen, mucin-1 and a triad of costimulatory molecules (TRICOM), which include B7.1, intercellular adhesion molecule-1 and leukocyte function-associated antigen-3. Vaccination is administered by subcutaneous injection followed by 4 days of local recombinant adjuvant granulocyte-macrophage colony-stimulating factor at the vaccination site. The vaccine has been developed for patients with advanced pancreatic cancer and has now entered a randomized Phase III clinical trial. This review will describe the background of recombinant poxvirus technology for tumor vaccine development, detail the key preclinical studies supporting the regimen, review the clinical trials supporting the current Phase III study, and highlight the key challenges and future obstacles to successful implementation of PANVAC-VF for pancreatic cancer.

CTLA4 blockade and GM-CSF combination immunotherapy alters the intratumor balance of effector and regulatory T cells

CTL-associated antigen 4 (CTLA4) blockade releases inhibitory controls on T cell activation and proliferation, inducing antitumor immunity in both preclinical and early clinical trials. We examined the mechanisms of action of anti-CTLA4 and a GM-CSF-transduced tumor cell vaccine (Gvax) and their impact on the balance of effector T cells (Teffs) and Tregs in an in vivo model of B16/BL6 melanoma. Tumor challenge increased the frequency of Tregs in lymph nodes, and untreated tumors became infiltrated by CD4+Foxp3- and CD4+Foxp3+ T cells but few CD8+ T cells. Anti-CTLA4 did not deplete Tregs or permanently impair their function but acted in a cell-intrinsic manner on both Tregs and Teffs, allowing them to expand, most likely in response to self antigen. While Gvax primed the tumor-reactive Teff compartment, inducing activation, tumor infiltration, and a delay in tumor growth, the combination with CTLA4 blockade induced greater infiltration and a striking change in the intratumor balance of Tregs and Teffs that directly correlated with tumor rejection. The data suggest that Tregs control both CD4+ and CD8+ T cell activity within the tumor, highlight the importance of the intratumor ratio of effectors to regulators, and demonstrate inversion of the ratio and correlation with tumor rejection during Gvax/anti-CTLA4 immunotherapy.

The new era in cancer research

For many years, discoveries about the genetic determinants of cancer appeared to be having only minor effects on efforts to control the disease in the clinic. Following advances made over the past decade, however, a description of cancer in molecular terms seems increasingly likely to improve the ways in which human cancers are detected, classified, monitored, and (especially) treated. Achieving the medical promise of this new era in cancer research will require a deeper understanding of the biology of cancer and imaginative application of new knowledge in the clinic, as well as political, social, and cultural changes.

A nonclassical non-Valpha14Jalpha18 CD1d-restricted (type II) NKT cell is sufficient for down-regulation of tumor immunosurveillance

The importance of immunoregulatory T cells has become increasingly apparent. Both CD4⁺CD25⁺ T cells and CD1d-restricted NKT cells have been reported to down-regulate tumor immunity in mouse tumor models. However, the relative roles of both T cell populations have rarely been clearly distinguished in the same tumor models. In addition, CD1d-restricted NKT cells have been reported to play a critical role not only in the down-regulation of tumor immunity but also in the promotion of the immunity. However, the explanation for these apparently opposite roles in different tumor models remains unclear. We show that in four mouse tumor models in which CD1d-restricted NKT cells play a role in suppression of tumor immunity, depletion of CD4⁺CD25⁺ T cells did not induce enhancement of immunosurveillance. Surprisingly, among the two subpopulations of CD1d-restricted NKT cells, Vα14Jα18⁺ (type I) and Vα14Jα18⁻ (type II) NKT cells, type I NKT cells were not necessary for the immune suppression. These unexpected results may now resolve the paradox in the role of CD1d-restricted NKT cells in the regulation of tumor immunity, in that type II NKT cells may be sufficient for negative regulation, whereas protection has been found to be mediated by α-galactosylceramide–responsive type I NKT cells.

Immunization with a circumsporozoite epitope fused to Bordetella pertussis adenylate cyclase in conjunction with cytotoxic T-lymphocyte-associated antigen 4 blockade confers protection against Plasmodium berghei liver-stage malaria

The adenylate cyclase toxoid (ACT) of Bordetella pertussis is capable of delivering its N-terminal catalytic domain into the cytosol of CD11b-expressing professional antigen-presenting cells such as myeloid dendritic cells. This allows delivery of CD8+ T-cell epitopes to the major histocompatibility complex (MHC) class I presentation pathway. Recombinant detoxified ACT containing an epitope of the Plasmodium berghei circumsporozoite protein (CSP), indeed, induced a specific CD8+ T-cell response in immunized mice after a single application, as detected by MHC multimer staining and gamma interferon (IFN-gamma) ELISPOT assay. This CSP-specific response could be significantly enhanced by prime-boost immunization with recombinant ACT in combination with anti-CTLA-4 during the boost immunization. This increased response was accompanied by complete protection in a number of mice after a challenge with P. berghei sporozoites. Transient blockade of CTLA-4 may overcome negative regulation and hence provide a strategy to enhance the efficacy of a vaccine by amplifying the number of responding T cells.

CTLA-4 Engagement and Regulatory CD4+CD25+T Cells Independently Control CD8+-Mediated Responses under Costimulation Blockade

Blockade of costimulatory signals is a promising therapeutic target to prevent allograft rejection. In this study, we sought to characterize to what extent CTLA-4 engagement contributes to the development of transplantation tolerance under the cover of CD40/CD40L and CD28/CD86 blockade. In vitro, we found that inhibition of the primary alloresponse and induction of alloantigen hyporesponsiveness by costimulation blockade was abrogated by anti-CTLA-4 mAb. In addition, regulatory CD4(+)CD25(+) T cells (T(REG)) were confirmed to play a critical role in the induction of hyporesponsiveness by anti-CD40L and anti-CD86 mAb. Our data indicated that CTLA-4 engagement is not required for activation or suppressor function of T(REG). Instead, in the absence of either CTLA-4 signaling or T(REG), CD8(+) T cell division was enhanced, whereas the inhibition of CD4(+) T cell division by costimulation blockade remained largely unaffected. In vivo, the administration of additional anti-CTLA-4 mAb abrogated anti-CD40L- and anti-CD86 mAb-induced cardiac allograft survival. Correspondingly, rejection was accompanied by enhanced allograft infiltration of CD8(+) cells. We conclude that CTLA-4 signaling and T(REG) independently cooperate in the inhibition of CD8(+) T cell expansion under costimulation blockade.

Low surface expression of B7-1 (CD80) is an immunoescape mechanism of colon carcinoma

Artificially enforced expression of CD80 (B7-1) and CD86 (B7-2) on tumor cells renders them more immunogenic by triggering the CD28 receptor on T cells. The enigma is that such B7s interact with much higher affinity with CTLA-4 (CD152), an inhibitory receptor expressed by activated T cells. We show that unmutated CD80 is spontaneously expressed at low levels by mouse colon carcinoma cell lines and other transplantable tumor cell lines of various tissue origins. Silencing of CD80 by interfering RNA led to loss of tumorigenicity of CT26 colon carcinoma in immunocompetent mice, but not in immunodeficient Rag-/- mice. CT26 tumor cells bind CTLA-4Ig, but much more faintly with a similar CD28Ig chimeric protein, thus providing an explanation for the dominant inhibitory effects on tumor immunity displayed by CD80 at that expression level. Interestingly, CD80-negative tumor cell lines such as MC38 colon carcinoma and B16 melanoma express CD80 at dim levels during in vivo growth in syngeneic mice. Therefore, low CD80 surface expression seems to give an advantage to cancer cells against the immune system. Our findings are similar with the inhibitory role described for the dim CD80 expression on immature dendritic cells, providing an explanation for the low levels of CD80 expression described in various human malignancies.

Circulating levels and clinical significance of soluble CD86 in myeloma patients

Circulating soluble CD86 (sCD86) levels are elevated in a number of leukaemias and are an independent prognostic factor in acute myeloid leukaemia. We investigated the clinical significance of circulating sCD86 in 299 patients from the UK Medical Research Council myeloma VIth trial, where patients received ABCM [adriamycin, carmustine (BCNU), cyclophosphamide, melphalan] either alone or with prednisolone (ABCM + P). Serum levels of sCD86 were significantly elevated (P = 0.0001) in myeloma patients and using the median normal donor level (0.621 ng/ml) as a cut-off point, 70% of patients had elevated levels (range = 0.015-15.87 ng/ml, median = 1.1 ng/ml). In univariate analysis elevated sCD86 levels were associated with significantly shorter (P < 0.001) survival (median = 22 vs. 51 months) and event-free survival (median = 14 vs. 31 months) in ABCM + P but not ABCM patients. Multivariate analysis demonstrated that sCD86 was a significant, independent prognostic marker of both overall [risk ratio (RR) = 2.04, P = 0.0006] and event-free (RR = 1.95, P = 0.0004) survival in ABCM + P patients. In conclusion, this study demonstrated that sCD86 levels are a significant independent prognostic marker in at least some myeloma treatment groups and its biological role and prognostic value should be further investigated.

Principles and use of anti-CTLA4 antibody in human cancer immunotherapy

Cytotoxic T lymphocyte antigen-4 has become recognized as one of the key negative regulators of adaptive immune responses, having a central role in the maintenance of peripheral tolerance and in shaping the repertoire of emergent T cell responses. Concurrent recognition of the potential importance of inhibitory immune regulators in limiting antitumor responses, either as a result of chronic antigenic stimulation or the self-nature of many tumor-selective target antigens, has led to the development of cytotoxic T lymphocyte antigen-4-blocking antibodies as therapeutic anticancer agents. Following extensive preclinical modeling, these agents have entered clinical trials, where they are showing encouraging activity in heavily pretreated patients with advanced-stage disease, particularly with melanoma or renal carcinoma. Finding ways to dissociate antitumor activity from adverse immune events should enable actualization of their therapeutic potential in the coming years.

Proteomics in cancer vaccine development

Proteomics is a new scientific field aimed at the large-scale characterization of the protein constituents of biologic systems. It facilitates comparisons between different protein preparations by searching for minute differences in their protein expression repertoires and the patterns of their post-translational modifications. These attributes make proteomics perfectly suited for searching for proteins and peptides expressed exclusively or preferentially in cancer cells as candidates for cancer vaccines. The main proteomics technologies include 2D polyacrylamide gel electrophoresis, multidimensional high-performance liquid chromatography, mass spectrometry and protein arrays. Proteomics technologies used to analyze cancer culture cells, fresh tumor specimens, human leukocyte antigen peptides, serum and serum antibodies (serologic proteomics) have successfully identified tumor markers. Turning the potential vaccine candidates identified by proteomics technologies into clinical treatments awaits demonstration.

See no evil, hear no evil, do no evil: the lessons of immune privilege

Immune-mediated inflammation and allograft rejection are greatly reduced in certain organs, a phenomenon called 'immune privilege'. Immune privilege is well developed in three regions of the body: the eye, the brain and the pregnant uterus. Immune-mediated inflammation has devastating consequences in the eye and brain, which have limited capacity for regeneration. Likewise, loss of immune privilege at the maternal-fetal interface culminates in abortion in rodents. However, all three regions share many adaptations that restrict the induction and expression of immune-mediated inflammation. A growing body of evidence from rodent studies suggests that a breakdown in immune privilege contributes to multiple sclerosis, uveitis, corneal allograft rejection and possibly even immune abortion.

The rationale for prophylactic cancer vaccines and need for a paradigm shift

This review summarizes clinical experience with infectious disease vaccines and data from animal tumor models that support a paradigm shift for cancer vaccines from therapeutic to prevention applications.

CD25 regulatory T cells determine secondary but not primary remission in EAE: Impact on long-term disease progression

Multiple sclerosis (MS) is often characterized by several relapses and remissions during long-term disease, but neither the responsible cells nor the mechanisms are known to date. Using an animal model of multiple sclerosis, relapsing experimental autoimmune encephalomyelitis (R-EAE) CD4+CD25+ Treg cells expressing Foxp3 and CTLA-4 intracellularly and T lymphocytes expressing surface CTLA-4 were identified in the CNS. The first remission occurred even after depletion of Treg cells, but secondary remissions from EAE were ablated. Despite the unaltered first remission autoantigen rechallenge revealed already an amplified cytokine response during acute phase. These results indicate that the cellular composition during first attack of MS predicts long-term disease progression.

Cycloxygenase-2 inhibition augments the efficacy of a cancer vaccine

Tumor-derived cyclooxygenase-2 (COX-2) and its product, prostaglandin E2, exert strong immunoinhibitory effects that block dendritic cell function and CD4+ and CD8+ T-cell proliferation and function. We have shown previously that the addition of an oral COX-2 inhibitor to immunogene therapy using IFN-beta markedly augmented therapeutic efficacy in murine tumor models. In this study, we hypothesized that COX-2 inhibition might also augment an antitumor vaccination strategy. Mice bearing tumors derived from TC1 cells, a tumor line that expresses the human papillomavirus (HPV) E7 protein, were thus vaccinated with an adenoviral vector expressing HPV E7 protein (Ad.E7). This vaccine approach effectively generated E7-specific CD8+ cells and slowed the growth of small tumors but had little effect on large tumors. However, feeding mice with the COX-2 inhibitor, rofecoxib, restored the effectiveness of the vaccine against large tumors and prolonged survival. This effect was accompanied by a larger percentage of E7-specific CD8+ cells in the regional draining lymph nodes and a markedly increased number of tumor-infiltrating E7-specific CD8+ cells (as determined by flow cytometry) and total CD8+ T cells (as determined by immunohistochemical staining). Increased immunocyte trafficking was likely mediated by the generation of a Th1-type tumor microenvironment because COX-2 inhibition increased expression levels of mRNA for IFN-gamma, interleukin-12, IP-10, and MIG while lowering the expression of vascular endothelial growth factor within tumors. This study shows that the effectiveness of a cancer vaccine can be significantly improved by adding COX-2 inhibition.

Monoclonal antibody therapy of ovarian cancer

Despite advances in understanding and treatment, ovarian cancer remains a major cause of cancer mortality worldwide. Debulking surgery and paclitaxel/carboplatin chemotherapy induce good initial responses in most patients, although most cases of advanced disease are not controlled. Monoclonal antibodies hold promise as a potential incremental advance for the treatment of the disease. Antibodies can be used to stimulate the immune response, target tumor-specific receptors to induce antibody-dependent cellular cytotoxicity or interfere with biologic pathways. They can also be used to deliver therapeutic radioisotopes to malignant cells. Oregovomab is in Phase III clinical trials as a consolidation treatment post front-line therapy to trigger tumor-specific cellular immunity. Bevacizumab, which blocks vascular endothelial growth factor, will be entering Phase III as an adjuvant to front-line chemotherapy with a direct effect on angiogenesis. Additional immunostimulating, immune counter-regulatory and receptor-targeting approaches are also reviewed. The family of epidermal growth factor receptors including epidermal growth factor receptor 1 (HER-1) and 2 (HER-2) are both expressed in ovarian cancer and are the subject of ongoing research and development. The recent disappointing results with 90-yttrium-labeled anti-HMFG by single intraperitoneal administration have left the radiopharmaceutical field without a Phase III candidate. Identification of novel targets may advance this therapeutic area in the future. The rapid advances in the fields of immunoregulation and tumor biology should permit an accelerated introduction of antibodies for the treatment of ovarian cancer. These antibodies could complement novel small molecules that are also in development.

Analysis of the cellular mechanism of antitumor responses and autoimmunity in patients treated with CTLA-4 blockade

We have demonstrated previously that the administration of CTLA-4 blockade has mediated objective cancer regression and autoimmunity in patients with metastatic melanoma. To explore the mechanism of these in vivo effects, we have studied the changes in lymphocyte phenotype and function in patients receiving anti-CTLA-4 Ab (MDX-010). Patients with stage IV melanoma or renal cell cancer were treated every 3 wk with an anti-CTLA-4 Ab with or without peptide immunization. Pheresis samples were analyzed using flow cytometry to determine lymphocyte cell surface markers. Gene expression analyses and proliferation assays were conducted on purified T cell subsets. Anti-CTLA-4 Ab did not inhibit the suppressive activity of CD4+CD25+ cells in vitro or in vivo. In addition, there was no decrease in the expression of CD4+CD25+ cells in whole PBMC, nor a decrease in Foxp3 gene expression in the CD4+ or CD4+CD25+ purified cell populations posttreatment. The percentage of CD4+, CD8+, CD4+CD25+, and CD4+CD25- T cells in PBMC expressing the activation marker HLA-DR increased following anti-CTLA-4 Ab administration. Therefore, our results suggest that the antitumor effects of CTLA-4 blockade are due to increased T cell activation rather than inhibition or depletion of T regulatory cells.

Breaking down the barriers to cancer immunotherapy

Emerging insights into the mechanisms of activation and negative regulation of innate and adaptive immune cells are providing new opportunities for the development of safe and effective cancer vaccines.

Association of CTLA-4 gene polymorphism with oral squamous cell carcinoma

BACKGROUND

Oral squamous cell carcinoma (OSCC) is a worldwide problem. The main mechanism of tumor immunity is the destruction of tumor cells by cytolytic T lymphocytes. Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4; CD152), a negative regulator of T-lymphocyte activation, plays an extremely important role in the immune tolerance and anergy. This study was designed to investigate the role of CTLA-4 polymorphism in OSCC.

METHODS

The CTLA-4 +49 A/G polymorphism was studied in 118 patients with OSCC and 147 healthy controls by using restriction fragment length polymorphism (RFLP). The genotype and phenotype frequencies were evaluated in Fisher's exact test.

RESULTS

There was no significant difference in the frequency of CTLA-4 polymorphism between the OSCC study group and healthy controls. The CTLA-4 A/A genotype was significantly associated with a younger age of onset of OSCC (P = 0.04). The AA genotype was associated with significantly poorer survival (P = 0.003).

CONCLUSION

The present study is the first to shows that the A/A polymorphism is associated with poor survival in OSCC in Taiwan.

The effect of a therapeutic dendritic cell-based cancer vaccination depends on the blockage of CTLA-4 signaling

Dendritic cells (DCs) were pulsed with the H-2K(b) binding OVA(257-264)-peptide (SIINFEKL), and used as one single-injection vaccine in combination with anti-CTLA-4 monoclonal antibody (mAb) to treat mice inoculated 3 days previously with 3x10(5) E.G7-OVA lymphoma cells. Neither DC vaccination nor CTLA-4 blockage alone prevented tumor growth in tumor challenged mice. In contrast, the combination of one vaccination and injection of anti-CTLA-4 mAb lead to rejection or retarded tumor growth in more than 60% of the mice. The OVA-transgene or the SIINFEKL-epitope was not lost in the progressing tumors of vaccinated mice, however, the highest degree of anti-SIINFEKL reactivity of host CTLs in an IFN-gamma ELISPOT assay was found only in mice showing complete tumor rejection. Vaccinated mice having rejected E.G7-OVA tumors were capable of rejecting subsequent challenges with 1x10(6) E.G7-OVA tumor cells, and later on these mice even rejected wild-type EL-4 tumor cells indicating that tumor epitope spreading takes place during the process of vaccination-induced E.G7-OVA rejection. In agreement with these observations, mice having rejected E.G7-OVA tumors showed long lasting CTL memory in spleen and bone marrow towards both the SIINFEKL-peptide and other EL-4-derived tumor rejecting epitopes.

Impact of the immunological synapse on T cell signaling

T cell activation requires interactions of T cell antigen receptors and peptides presented by major histocompatibility complex molecules in an adhesive junction between the T cell and antigen-presenting cell (APC). Stable junctions with bull's-eye supramolecular activation clusters have been defined as immunological synapses (IS). These structures maintain T cell-APC interaction and allow directed secretion. T cells can also be activated by asymmetric hemisynapses (HS) that allow migration during signal integration. IS and HS dominate in different stages of T cell priming. Optimal effector functions may also depend upon cyclical use of IS and HS.

Vaccination for Treatment and Prevention of Cancer in Animal Models

Two approaches to immunological intervention in tumor-host interactions in mouse models are discussed in this review. The first is described with reference to experiments in which CD8(+) T lymphocytes are used to kill established transplantable tumors. Peptides and their optimal presentation by dendritic cells and intervention in immune regulatory mechanisms are the key issues for efficient induction of T-killer cell-mediated tumor eradication. The time frame of tumor therapy and the threat imposed by tumor growth in transplantable models and cancer patients require the induction of a robust T-cell reaction. Prevention of the progression of small preneoplastic lesions, on the other hand, requires the significant and prolonged immune protection sought in the second approach. This is based on antibody production and the coordinated activation of multiple low-avidity cell-mediated mechanisms elicited by DNA vaccination in genetically modified cancer-prone mice, transgenic for a mutant Her-2/neu growth factor receptor expressed at the plasma membrane surface of preneoplastic mammary gland epithelial cells. Vaccination with appropriate DNA formulations results in prolonged immune inhibition of the progression of preneoplastic mammary lesions but is ineffective against established tumors. The use of molecularly defined adjuvants and intervention in immune regulatory mechanisms are critical in both the elicitation of an effective T-cell mediated reaction required for tumor debulking in the first set of models and the induction by vaccination of a sustained immune memory able to prevent the expansion of preneoplastic lesions in genetically cancer-prone mice.

Restoring function in exhausted CD8 T cells during chronic viral infection

Functional impairment of antigen-specific T cells is a defining characteristic of many chronic infections, but the underlying mechanisms of T-cell dysfunction are not well understood. To address this question, we analysed genes expressed in functionally impaired virus-specific CD8 T cells present in mice chronically infected with lymphocytic choriomeningitis virus (LCMV), and compared these with the gene profile of functional memory CD8 T cells. Here we report that PD-1 (programmed death 1; also known as Pdcd1) was selectively upregulated by the exhausted T cells, and that in vivo administration of antibodies that blocked the interaction of this inhibitory receptor with its ligand, PD-L1 (also known as B7-H1), enhanced T-cell responses. Notably, we found that even in persistently infected mice that were lacking CD4 T-cell help, blockade of the PD-1/PD-L1 inhibitory pathway had a beneficial effect on the 'helpless' CD8 T cells, restoring their ability to undergo proliferation, secrete cytokines, kill infected cells and decrease viral load. Blockade of the CTLA-4 (cytotoxic T-lymphocyte-associated protein 4) inhibitory pathway had no effect on either T-cell function or viral control. These studies identify a specific mechanism of T-cell exhaustion and define a potentially effective immunological strategy for the treatment of chronic viral infections.

Monoclonal antibody therapy of cancer

The most significant recent advances in the application of monoclonal antibodies (mAbs) to oncology have been the introduction and approval of bevacizumab (Avastin), an anti-vascular endothelial growth factor antibody, and of cetuximab (Erbitux), an anti-epidermal growth factor antibody. In combination with standard chemotherapy regimens, bevacizumab significantly prolongs the survival of patients with metastatic cancers of the colorectum, breast and lung. Cetuximab, used alone or with salvage chemotherapy, produces clinically meaningful anti-tumor responses in patients with chemotherapy-refractory cancers of the colon and rectum. In addition, the anti-HER2/neu antibody trastuzumab (Herceptin), in combination with standard adjuvant chemotherapy, has been shown to reduce relapses and prolong disease-free and overall survival in high-risk patients after definitive local therapy for breast cancer. These exciting recent results provide optimism for the development of mAbs that bind novel targets, exploit novel mechanisms of action or possess improved tumor targeting. Progress in the clinical use of radioimmunoconjugates remains hindered by complexity of administration, toxicity concerns and insufficiently selective tumor targeting.

SOCS1 restricts dendritic cells' ability to break self tolerance and induce antitumor immunity by regulating IL-12 production and signaling

DC-based tumor vaccine research has largely focused on enhancing DC maturation/costimulation and antigen presentation in order to break tolerance against self tumor-associated antigens. DC immunization can activate autoreactive T cells but rarely causes autoimmune pathologies, indicating that self tolerance at the host level is still maintained in the vaccinated hosts. This study in mice reveals a novel regulatory mechanism for the control of self tolerance at the host level by DCs through the restriction of positive cytokine feedback loops by cytokine signaling inhibitor SOCS1. The study further finds the requirement of persistent antigen presentation by DCs for inducing pathological autoimmune responses against normal tissues and tumor, which can be achieved by silencing SOCS1 to unleash the unbridled signaling of IL-12 and the downstream cytokine cascade. However, the use of higher-affinity self peptides, enhancement of DC maturation, and persistent stimulation with cytokines or TLR agonists fail to break tolerance and induce pathological antitumor immunity. Thus, this study indicates the necessity of inhibiting SOCS1, an antigen presentation attenuator, to break self tolerance and induce effective antitumor responses.