Conversion of tumor-specific CD4+ T-cell tolerance to T-cell priming through in vivo ligation of CD40

Tumor-specific CD4+ T cells render the tumor environment permissive for infiltration by low-avidity CD8+ T cells

CD4+ T cells enhance tumor destruction by CD8+ T cells. One benefit that underlies CD4+ T cell help is enhanced clonal expansion of newly activated CD8+ cells. In addition, tumor-specific CD4+ help is also associated with the accumulation of greater numbers of CD8+ T cells within the tumor. Whether this too is attributable to the effects of help delivered to the CD8+ cells during priming within secondary lymphoid tissues, or alternatively is due to the action of CD4+ cells within the tumor environment has not been examined. In this study, we have evaluated separately the benefits of CD4+ T cell help accrued during priming of tumor-specific CD8+ T cells with a vaccine, as opposed to the benefits delivered by the presence of cognate CD4+ cells within the tumor. The presence of CD4+ T cell help during priming increased clonal expansion of tumor-specific CD8+ T cells in secondary lymphoid tissue; however, CD8+ T cells that have low avidity for tumor Ag were inefficient in tumor invasion. CD4+ T cells that recognized tumor Ag were required to facilitate accumulation of CD8+ T cells within the tumor and enhance tumor lysis during the acute phase of the response. These experiments highlight the ability of tumor-specific CD4+ T cells to render the tumor microenvironment receptive for CD8+ T cell immunotherapy, by facilitating the accumulation of all activated CD8+ T cells, including low-avidity tumor-specific and noncognate cells.

Myeloid-derived suppressor cells promote cross-tolerance in B-cell lymphoma by expanding regulatory T cells

Tumor-induced T-cell tolerance is a major mechanism that facilitates tumor progression and limits the efficacy of immune therapeutic interventions. Regulatory T cells (Treg) play a central role in the induction of tolerance to tumor antigens, yet the precise mechanisms regulating its induction in vivo remain to be elucidated. Using the A20 B-cell lymphoma model, here we identify myeloid-derived suppressor cells (MDSC) as the tolerogenic antigen presenting cells capable of antigen uptake and presentation to tumor-specific Tregs. MDSC-mediated Treg induction requires arginase but is transforming growth factor-beta independent. In vitro and in vivo inhibition of MDSC function, respectively, with NOHA or sildenafil abrogates Treg proliferation and tumor-induced tolerance in antigen-specific T cells. These findings establish a role for MDSCs in antigen-specific tolerance induction through preferential antigen uptake mediating the recruitment and expansion of Tregs. Furthermore, therapeutic interventions, such as in vivo phosphodiesterase 5-inhibition, which effectively abrogate the immunosuppressive role of MDSCs and reduce Treg numbers, may play a critical role in delaying and/or reversing tolerance induction.

CD40 ligation in vivo can induce T cell independent antitumor effects even against immunogenic tumors

Antitumor effects of CD40 ligation appear to involve distinct antitumor effector cells in different experimental models. In this study, we tested whether T cells were required for antitumor effects of agonistic anti-CD40 mAb (alphaCD40) against immunogenic versus poorly immunogenic tumors. Treatment of mice bearing poorly immunogenic B16 melanoma and its more immunogenic variant, B16-hsp72.1, with alphaCD40 resulted in a similar level of tumor growth suppression. Depletion of T cells did not reduce the antitumor effects in these 2 tumor models. To generate antitumor T cell responses, C57BL/6 mice were immunized with irradiated B16-hsp72.1. Treatment of these vaccinated mice challenged with a high dose of B16-hsp72.1 tumor cells with alphaCD40 induced tumor growth suppression, which was reduced by T-cell depletion, demonstrating that T cells were involved in the antitumor effect of alphaCD40. However, immunized mice depleted of T cells and treated with alphaCD40 were still able to suppress tumor growth as compared to tumor growth in immunized, T cell-depleted mice not treated with alphaCD40, suggesting that T cells were not required for the antitumor effect of alphaCD40. To confirm a lack of correlation between tumor immunogenicity and T-cell requirement in antitumor effects of CD40 ligation, we found that alphaCD40 induced tumor growth suppression in nude and SCID/beige mice bearing highly immunogenic tumors such as Meth A sarcoma, suggesting that macrophages may play a role. Indeed, both poorly immunogenic and highly immunogenic tumors were sensitive to in vitro growth inhibition by macrophages from alphaCD40-treated mice. Taken together, our results indicate that antitumor effects induced by alphaCD40, even against immunogenic tumors, can be observed in the absence of T cells and may involve macrophages.

Therapeutics targeting tumor immune escape: towards the development of new generation anticancer vaccines

Despite the evidence that immune effectors can play a significant role in controlling tumor growth under natural conditions or in response to therapeutic manipulation, it is clear that malignant cells evade immune surveillance in most cases. Considering that anticancer vaccination has reached a plateau of results and currently no vaccination regimen is indicated as a standard anticancer therapy, the dissection of the molecular events underlying tumor immune escape is the necessary condition to make anticancer vaccines a therapeutic weapon effective enough to be implemented in the routine clinical setting. Recent years have witnessed significant advances in our understanding of the molecular mechanisms underlying tumor immune escape. These mechanistic insights are fostering the development of rationally designed therapeutics aimed at reverting the immunosuppressive circuits that undermine an effective antitumor immune response. In this review, the best characterized mechanisms that allow cancer cells to evade immune surveillance are overviewed and the most debated controversies constellating this complex field are highlighted. In addition, the latest therapeutic strategies devised to overcome tumor immune escape are described, with special regard to those entering clinical phase investigation.

Phase I/II study of treatment with matured dendritic cells with or without low dose IL-2 in patients with disseminated melanoma

BACKGROUND

In the present study, we have examined whether treatment of patients with metastatic melanoma with matured dendritic cell (DC) vaccines with or without low dose IL-2 may improve treatment outcomes.

METHODS

Sixteen patients received DC vaccines (DCs) sensitized with autologous melanoma lysates and 18 patients received DCs sensitized with peptides from gp100, MART-1, tyrosinase, MAGE-3.A2, MAGE-A10 and NA17. IL-2 was given subcutaneously (sc) at 1 MU/m2 on the second day after each injection for 5-14 days in half of each group. DCs were given by intranodal injection.

RESULTS

There were 2 partial responses (PR) and 3 with stable disease (SD) in the nine patients receiving DCs + peptides + IL-2, and 1 PR and 1 SD in nine patients treated with DCs + peptides without IL-2. There were only two patients with SD in the group receiving DCs + autologous lysates and no IL-2. Median overall survival for all patients was very good at 18.5 months but this was most probably due to selection of a favourable group of patients for the study. There was no significant difference in survival between the groups by log rank analysis. Treatment was not associated with significant side effects. The quality and yield of the DCs in the preparations were generally good.

CONCLUSIONS

We conclude that mature DC preparations may be superior to immature DC preparations for presentation of melanoma peptides and that IL-2 may increase clinical responses to the DCs plus peptides. However, in our view the low response rates do not justify the cost and complexity of this treatment approach.

Vascular targeting of anti-CD40 antibodies and IL-2 into autochthonous tumors enhances immunotherapy in mice

Current anticancer therapy is a delicate balance between elimination of malignant cells and harmful side effects for the host. In this study, we used a tumor-homing peptide to engineer anti-CD40 agonist antibodies and recombinant IL-2 such that they were selectively delivered into spontaneously arising tumors in a transgenic mouse model of islet cell carcinogenesis. Intravenous injection of these agents, either separately or together, led to accumulation in the vicinity of tumor neovessels without toxic side effects. Although both molecules are critical for adaptive immunity, the most profound effects were seen in endothelial cells. Combined, local anti-CD40 and IL-2 therapy reduced tumor vascularity and significantly delayed tumor growth in mice. Remarkably, tumor-bearing mice remained disease-free long-term when targeted anti-CD40 and IL-2 were combined with transfers of preactivated antitumor immune cells. In this therapeutic setting, triggering of CD40 on endothelial cells induced an inflammatory response of the vessel wall and facilitated effector cell accumulation in the tumor parenchyma while IL-2 promoted antigen-specific immune cell persistence. We believe this is a novel and highly effective anticancer approach, whereby tumor stroma is "conditioned" for enhanced immune cell entry and survival, facilitating immune-mediated tumor destruction and leading to a sustained antitumor response.

Synthetic CD4+ T cell-targeted antigen-presenting cells elicit protective antitumor responses

CD4(+) helper T cells are critical for protective immune responses and yet suboptimally primed in response to tumors. Cell-based vaccination strategies are under evaluation in clinical trials but limited by the need to derive antigen-presenting cells (APC) from patients or compatible healthy donors. To overcome these limitations, we developed CD4(+) T cell-targeted synthetic microbead-based artificial APC (aAPC) and used them to activate CD4(+) T lymphocytes specific for a tumor-associated model antigen (Ag) directly from the naive repertoire. In vitro, aAPC specifically primed Ag-specific CD4(+) T cells that were activated to express high levels of CD44, produced mainly interleukin 2, and could differentiate into Th1-like or Th2-like cells in combination with polarizing cytokines. I.v. administration of aAPC led to Ag-specific CD4(+) T-cell activation and proliferation in secondary lymphoid organs, conferred partial protection against subcutaneous tumors, and prevented the establishment of lung metastasis. Taken together, our data support the use of cell-free, synthetic aAPC as a specific and versatile alternative to expand peptide-specific CD4(+) T cells in adoptive and active immunotherapy.

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.

T cell-antigen-presenting cell interactions visualized in vivo in a model of antigen-specific inflammation

Videomicroscopy is being used increasingly to characterize the interaction of T cells and antigen-presenting cells (APCs) within lymphatic tissues but has not been reported, to our knowledge, at sites of inflammation. We employed intravital videomicroscopy to study an anterior uveitis model using DO11.10 T cells and ovalbumin (OVA). T cell movement in iris was consistent with a random walk independent of the presence of recognized antigen and had a lateral speed slower than T cells in lymph node. Lingering of T cells adjacent to APCs suggested that they were physically interacting. This apparent contact demonstrated antigen specificity when comparing results from DO11.10 cells with OVA versus bovine serum albumin (BSA) loaded APCs but not when comparing results from OVA-loaded APCs with DO11.10 versus HA clonotype 6.5 T cells. Further studies with this model system should clarify the contribution of T cell-APC communication at a site of inflammation, infection, or immunization.

Enhanced efficacy and reduced toxicity of multifactorial adjuvants compared with unitary adjuvants as cancer vaccines

Identification of Toll-like receptors (TLRs) and their ligands, and tumor necrosis factor-tumor necrosis factor receptor (TNF-TNFR) pairs have provided the first logical, hypothesis-based strategies to molecularly concoct adjuvants to elicit potent cell-mediated immunity via activation of innate and adaptive immunity. However, isolated activation of one immune pathway in the absence of others can be toxic, ineffective, and detrimental to long-term, protective immunity. Effective engineered vaccines must include agents that trigger multiple immunologic pathways. Here, we report that combinatorial use of CD40 and TLR agonists as a cancer vaccine, compared with monotherapy, elicits high frequencies of self-reactive CD8(+) T cells, potent tumor-specific CD8(+) memory, CD8(+) T cells that efficiently infiltrate the tumor-burdened target organ; therapeutic efficacy; heightened ratios of CD8(+) T cells to FoxP3(+) cells at the tumor site; and reduced hepatotoxicity. These findings provide intelligent strategies for the formulation of multifactorial vaccines to achieve maximal efficacy in cancer vaccine trials in humans.

Anti-CD40 conditioning enhances the T(CD8) response to a highly tolerogenic epitope and subsequent immunotherapy of simian virus 40 T antigen-induced pancreatic tumors

Rapid loss of adoptively transferred tumor-specific CD8(+) T cells (T(CD8)) following Ag recognition in the periphery and their limited accumulation within the tumor stroma reduces the effectiveness of T cell-based immunotherapy. To better understand the role of T(CD8) in the control of autochthonous tumors, we have used mice of the RIP1-Tag4 lineage that develop pancreatic beta cell tumors due to expression of the SV40 large T Ag from the rat insulin promoter. We previously showed that the kinetics of functional T(CD8) tolerance varies toward two distinct epitopes derived from T Ag. Epitope I ((206)SAINNYAQKL(215))-specific T(CD8) are rapidly deleted whereas T(CD8) targeting epitope IV ((404)VVYDFLKC(411)) persist over the lifetime of tumor-bearing animals. In this report, we show that the conditioning of tumor-bearing RIP1-Tag4 mice with agonistic anti-CD40 Ab induces extensive expansion of naive epitope I-specific TCR transgenic (TCR-I) T cells in this tolerogenic environment and delays their loss from the host. In addition, functional TCR-I T cells intensively infiltrate pancreatic tumors, resulting in increased survival of RIP1-Tag4 mice. These results suggest that a similar approach could effectively enhance T cell-based immunotherapies to cancer when targeting other highly tolerogenic epitopes.

Treatment of pulmonary metastatic tumors in mice using lentiviral vector-engineered stem cells

Active cancer immunotherapy relies on functional tumor-specific effector T lymphocytes for tumor elimination. Dendritic cells (DCs), as most potent antigen-presenting cells, have been popularly employed in clinical and experimental tumor treatments. We have previously demonstrated that lentiviral vector-mediated transgene delivery to DC progenitors, including bone marrow cells and hematopoietic stem cells, followed by transplantation supports systemic generation of great numbers of tumor antigen-presenting DCs. These DCs subsequently stimulate marked and systemic immune activation. Here, we examined whether this level of immune activation is sufficient to overcome tumor-induced tolerogenic environment for treating an established aggressive epithelial tumor. We showed that a combination treatment of granulocyte macrophage-colony stimulating factor and cytosine-phosphate-guanine-containing oligonucleotide stimulated large numbers of tumor antigen-presenting DCs in situ from transgene-modified stem cells. Moreover, these in situ generated and activated DCs markedly stimulated activation of antigen-specific CD4 and CD8 T cells by augmenting their numbers, as well as function, even in a tumor-bearing tolerogenic environment. This leads to significant improvement in the therapeutic efficacy of established pulmonary metastases. This study suggests that lentiviral vector-modified stem cells as DC progenitors may be used as an effective therapeutic regimen for treating metastatic epithelial tumors.

Targeting death-inducing receptors in cancer therapy

Deregulated cell death pathways may lead to the development of cancer, and induction of tumor cell apoptosis is the basis of many cancer therapies. Knowledge accumulated concerning the molecular mechanisms of apoptotic cell death has aided the development of new therapeutic strategies to treat cancer. Signals through death receptors of the tumor necrosis factor (TNF) superfamily have been well elucidated, and death receptors are now one of the most attractive therapeutic targets in cancer. In particular, DR5 and DR4, death receptors of TNF-related apoptosis-inducing ligand (TRAIL or Apo2L), are interesting targets of antibody-based therapy, since TRAIL may also bind decoy receptors that may prevent TRAIL-mediated apoptosis, whereas TRAIL ligand itself selectively induces apoptosis in cancer cells. Here, we review the potential therapeutic utility of agonistic antibodies against DR5 and DR4 and discuss the possible extension of this single-antibody-based strategy when combined with additional modalities that either synergizes to cause enhanced apoptosis or further engage the cellular immune response. Rational design of antibody-based therapies combining the induction of tumor cell apoptosis and activation of tumor-specific adaptive immunity enables promotion of distinct steps of the antitumor immune response, thereby enhancing tumor-specific lymphocytes that can eradicate TRAIL/DR5-resistant mutating, large established and heterogeneous tumors in a manner that does not require the definition of individual tumor-specific antigens.

Prospect of targeting the CD40 pathway for cancer therapy

The cell surface molecule CD40 is a member of the tumor necrosis factor receptor superfamily and is broadly expressed by immune, hematopoietic, vascular, epithelial, and other cells, including a wide range of tumor cells. CD40 itself lacks intrinsic kinase or other signal transduction activity but rather mediates its diverse effects via an intricate series of downstream adapter molecules that differentially alter gene expression depending on cell type and microenvironment. As a potential target for novel cancer therapy, CD40 may mediate tumor regression through both an indirect effect of immune activation and a direct cytotoxic effect on the tumor, resulting in a "two-for-one" mechanism of action of CD40 agonists. Several drug formulations that target the CD40 pathway have undergone phase 1 clinical evaluation in advanced-stage cancer patients, and initial findings show objective clinical responses and immune modulation in the absence of major toxicity.

Cooperation between CD4 and CD8 T cells for anti-tumor activity is enhanced by OX40 signals

The relative contribution of OX40 (CD134) to priming of CD8 T cells in complex systems where CD4 and CD8 cells respond and cooperate together is not clear. We previously found that OX40 expressed on tumor-reactive CD8 T cells controls their initial persistence when adoptively transferred in vivo and is required for delayed tumor growth. We now show that exogenous stimulation of OX40 with agonist antibody augments its ability to suppress the growth of new as well as established tumors, correlating with marked expansion of adoptively transferred CD8 T cells. Concomitantly, anti-OX40 strongly enhanced the number of tumor antigen-reactive CD4 T cells. Moreover, the augmented accumulation of CD8 T cells was prevented in animals lacking MHC class II or depleted of CD4 cells and did not occur in OX40-deficient animals receiving wild-type CD8 cells, demonstrating that non-CD8 cells are the major target of OX40 signals. These results suggest that while OX40 signaling to a CD8 T cell can control its expansion, OX40 expressed on non-CD8 cells strongly influences CD8 priming and in vivo activity. OX40 therefore represents an important signal for allowing effective cooperation between CD4 and CD8 cells and for promoting cell interplay and tumor rejection where CD8 activity is limiting.

Altered recognition of antigen is a mechanism of CD8+ T cell tolerance in cancer

Antigen-specific CD8+ T-cell tolerance, induced by myeloid-derived suppressor cells (MDSCs), is one of the main mechanisms of tumor escape. Using in vivo models, we show here that MDSCs directly disrupt the binding of specific peptide-major histocompatibility complex (pMHC) dimers to CD8-expressing T cells through nitration of tyrosines in a T-cell receptor (TCR)-CD8 complex. This process makes CD8-expressing T cells unable to bind pMHC and to respond to the specific peptide, although they retain their ability to respond to nonspecific stimulation. Nitration of TCR-CD8 is induced by MDSCs through hyperproduction of reactive oxygen species and peroxynitrite during direct cell-cell contact. Molecular modeling suggests specific sites of nitration that might affect the conformational flexibility of TCR-CD8 and its interaction with pMHC. These data identify a previously unknown mechanism of T-cell tolerance in cancer that is also pertinent to many pathological conditions associated with accumulation of MDSCs.

Immunosuppressive strategies that are mediated by tumor cells

Despite major advances in understanding the mechanisms leading to tumor immunity, a number of obstacles hinder the successful translation of mechanistic insights into effective tumor immunotherapy. Such obstacles include the ability of tumors to foster a tolerant microenvironment and the activation of a plethora of immunosuppressive mechanisms, which may act in concert to counteract effective immune responses. Here we discuss different strategies employed by tumors to thwart immune responses, including tumor-induced impairment of antigen presentation, the activation of negative costimulatory signals, and the elaboration of immunosuppressive factors. In addition, we underscore the influence of regulatory cell populations that may contribute to this immunosuppressive network; these include regulatory T cells, natural killer T cells, and distinct subsets of immature and mature dendritic cells. The current wealth of preclinical information promises a future scenario in which the synchronized blockade of immunosuppressive mechanisms may be effective in combination with other conventional strategies to overcome immunological tolerance and promote tumor regression.

Anti-CD40 agonist antibodies: preclinical and clinical experience

The cell-surface molecule CD40, a member of the tumor necrosis factor receptor superfamily, broadly regulates immune activation and mediates tumor apoptosis. CD40 is expressed by antigen-presenting cells (APC) and engagement of its natural ligand on T cells activates APC including dendritic cells and B cells. Agonistic CD40 antibodies have been shown to substitute for T cell help provided by CD4+ lymphocytes in murine models of T cell-mediated immunity. In tumor-bearing hosts, CD40 agonists trigger effective immune responses against tumor-associated antigens. In contrast, CD40 is also expressed on many tumor cells and its ligation in this setting mediates a direct cytotoxic effect. Engagement of CD40 on tumor cells results in apoptosis in vitro and impaired tumor growth in vivo. These observations have prompted efforts to use agonistic CD40 antibodies for the treatment of cancer patients and initial clinical results have been promising.

An Agonist Antibody Specific for CD40 Induces Dendritic Cell Maturation and Promotes Autologous Anti-tumour T-cell Responses in an In vitro Mixed Autologous Tumour Cell/Lymph Node Cell Model

CD40-mediated interactions play an important role in the response to a variety of diseases, including cancer. Engagement of CD40 on antigen-presenting cells, namely dendritic cells (DC), by CD40L leads to maturation and up-regulation of co-stimulatory molecules B7.1 and B7.2 (CD80 and CD86). These molecules are requisite to subsequent antigen-specific activation of T cells. T-cell activation is a critical aspect of specific anti-tumour immune responses that have become the focus of a variety of cancer immunotherapy approaches. Clinical trials involving immunologic interventions have shown clinical responses confirming that the immune system can be harnessed for the treatment of cancer. However, the clinical response rate has been low, signifying the need for new immunotherapeutic strategies. To this end, an agonist antibody specific for CD40, CP-870,893, has been developed. A fully autologous mixed tumour cell/lymph node cell model was utilized to demonstrate that CP-870,893 promotes the responsiveness of lymph node-derived T cells to autologous tumour. Specifically, T cells from the tumour-draining lymph nodes are not responsive to autologous tumour cells; however, in the presence of CP-870,893, this unresponsiveness is reversed, as indicated by lymph node cell proliferation and cytokine secretion. Monocyte-derived DC treated with CP-870,893 consistently display a mature phenotype: up-regulation of CD80, CD83, CD86 and HLA-DR expression, increased Mip1alpha and IL-12 secretion, and the loss of exogenous antigen-presenting capability subsequent to treatment with the antibody. These data indicate that CP-870,893 binds to and activates DC, ultimately driving a specific anti-tumour T-cell response.

T-Cell Distribution and Adhesion Receptor Expression in Metastatic Melanoma

PURPOSE

Metastatic malignant melanoma is a devastating disease with a poor prognosis. Recent therapeutic trials have focused on immunotherapy to induce development of endogenous antitumor immune responses. To date, such protocols have shown success in activation of tumor-specific CTL but no overall improvement in survival. To kill tumor, antigen-specific CTL must efficiently target and enter tumor tissue. The purpose of this study was to examine the pathway of leukocyte migration to metastatic melanoma.

EXPERIMENTAL DESIGN

Peripheral blood and metastatic melanoma tissues (n = 65) were evaluated for expression of adhesion molecules using immunohistochemistry of tumor sections and flow cytometry of tumor-associated and peripheral blood CTL and compared with healthy controls. CTL expressing T-cell receptors for the melanoma antigen MART-1 were identified in a subset of samples by reactivity with HLA-A2 tetramers loaded with MART-1 peptide.

RESULTS

Results show that the majority of metastatic melanoma samples examined do not express the vascular adhesion receptors E-selectin (CD62E), P-selectin (CD62P), and intercellular adhesion molecule-1 (CD54) on vessels within the tumor boundaries. Strong adhesion receptor expression was noted on vessels within adjacent tissue. Tumor-associated T lymphocytes accumulate preferentially in these adjacent areas and are not enriched for skin- or lymph node-homing receptor phenotype.

CONCLUSION

Expression of leukocyte homing receptors is dysregulated on the vasculature of metastatic melanoma. This results in a block to recruitment of activated tumor-specific CTL to melanoma metastases and is a likely factor limiting the effectiveness of current immunotherapy protocols.

Clinical activity and immune modulation in cancer patients treated with CP-870,893, a novel CD40 agonist monoclonal antibody

PURPOSE

The cell-surface molecule CD40 activates antigen-presenting cells and enhances immune responses. CD40 is also expressed by solid tumors, but its engagement results in apoptosis. CP-870,893, a fully human and selective CD40 agonist monoclonal antibody (mAb), was tested for safety in a phase I dose-escalation study.

PATIENTS AND METHODS

Patients with advanced solid tumors received single doses of CP-870,893 intravenously. The primary objective was to determine safety and the maximum-tolerated dose (MTD). Secondary objectives included assessment of immune modulation and tumor response.

RESULTS

Twenty-nine patients received CP-870,893 in doses from 0.01 to 0.3 mg/kg. Dose-limiting toxicity was observed in two of seven patients at the 0.3 mg/kg dose level (venous thromboembolism and grade 3 headache). MTD was estimated as 0.2 mg/kg. The most common adverse event was cytokine release syndrome (grade 1 to 2) which included chills, rigors, and fever. Transient laboratory abnormalities affecting lymphocytes, monocytes, platelets, D-dimer and liver function tests were observed 24 to 48 hours after infusion. Four patients with melanoma (14% of all patients and 27% of melanoma patients) had objective partial responses at restaging (day 43). CP-870,893 infusion resulted in transient depletion of CD19+ B cells in blood (93% depletion at the MTD for < 1 week). Among B cells remaining in blood, we found a dose-related upregulation of costimulatory molecules after treatment.

CONCLUSION

The CD40 agonist mAb CP-870,893 was well tolerated and biologically active, and was associated with antitumor activity. Further studies of repeated doses of CP-870,893 alone and in combination with other antineoplastic agents are warranted.

A phase-I trial using a universal GM-CSF-producing and CD40L-expressing bystander cell line (GM.CD40L) in the formulation of autologous tumor cell-based vaccines for cancer patients with stage IV disease

BACKGROUND

Significant antitumor T-cell responses are generated in vitro when human lymphocytes are stimulated with autologous tumor cells in the presence of bystander cells transfected with CD40L and GM-CSF. Our goal was to test this bystander-based vaccine strategy in vivo in cancer patients with stage IV disease.

METHODS

Patients received three intradermal vaccine injections (irradiated autologous tumor cells plus GM.CD40L bystander cells) at 28-day intervals. Patients with no disease progression received three additional vaccines at 4, 12, and 24 months. Patients were monitored for toxicity, tumor response, and tumor-specific immune responses.

RESULTS

Twenty-one patients received at least three vaccine injections, with no toxicity attributable to the vaccine. Immunohistochemistry of vaccine injection site biopsies with CD1a and CD86 antibodies confirmed recruitment and activation of dendritic cells. There was no tumor regression after vaccination, but many patients had stable disease, including six of ten melanoma patients. Four patients developed tumor-specific T-cell responses on ELISPOT testing. One patient, who had stable disease for 24 months, demonstrated an increase in MART-1-specific T-cells by tetramer analysis after re-immunization; biopsy of the tumor that progressed 2 years after the onset of vaccination revealed a massive peritumoral and intratumoral T-cell infiltrate.

CONCLUSIONS

Vaccination of cancer patients with autologous tumor cells and GM.CD40L bystander cells (engineered to express GM-CSF and CD40L) is safe, can recruit and activate dendritic cells, and can elicit tumor-specific T-cell responses. Phase-II trials are underway to evaluate the impact of bystander-based vaccines on melanoma and mantle cell lymphoma.

Killing of normal melanocytes, combined with heat shock protein 70 and CD40L expression, cures large established melanomas

Previously, we showed that nine intradermal injections of a plasmid in which the HSVtk suicide gene is expressed from a melanocyte-specific promoter (Tyr-HSVtk), combined with a plasmid expressing heat shock protein 70 (CMV-hsp70), along with systemic ganciclovir, kills normal melanocytes and raises a CD8+ T cell response that is potent enough to eradicate small, 3-day established B16 tumors. We show in this study that, in that regimen, hsp70 acts as a potent immune adjuvant through TLR-4 signaling and local induction of TNF-alpha. hsp70 is required for migration of APC resident in the skin to the draining lymph nodes to present Ags, derived from the killing of normal melanocytes, to naive T cells. The addition of a plasmid expressing CD40L increased therapeutic efficacy, such that only six plasmid injections were now required to cure large, 9-day established tumors. Generation of potent immunological memory against rechallenge in cured mice accompanied these therapeutic gains, as did induction of aggressive autoimmune symptoms. Expression of CD40L, along with hsp70, increased both the frequency and activity of T cells activated against melanocyte-derived Ags. In this way, addition of CD40L to the hsp70-induced inflammatory killing of melanocytes can be used to cure large established tumors and to confer immunological memory against tumor cells, although a concomitant increase in autoimmune sequelae also is produced.

Immune resistance orchestrated by the tumor microenvironment

It is now little disputed that most if not all cancer cells express antigens that can be recognized by specific CD8(+) T lymphocytes. However, a central question in the field of anti-tumor immunity is why such antigen-expressing tumors are not spontaneously eliminated by the immune system. While in some cases, this lack of rejection may be due to immunologic ignorance, induction of anti-tumor T-cell responses in many patients has been detected in the peripheral blood, either spontaneously or in response to vaccination, without accompanying tumor rejection. These observations argue for the importance of barriers downstream from initial T-cell priming that need to be addressed to translate immune responses into clinical tumor regression. Recent data suggest that the proper trafficking of effector T cells into the tumor microenvironment may not always occur. T cells that do effectively home to tumor metastases are often found to be dysfunctional, pointing toward immunosuppressive mechanisms in the tumor microenvironment. T-cell anergy due to insufficient B7 costimulation, extrinsic suppression by regulatory cell populations, inhibition by ligands such as programmed death ligand-1, metabolic dysregulation by enzymes such as indoleamine-2,3-dioxygenase, and the action of soluble inhibitory factors such as transforming growth factor-beta have all been clearly implicated in generating this suppressive microenvironment. Identification of these downstream processes points to new therapeutic targets that should be manipulated to facilitate the effector phase of anti-tumor immune responses in concert with vaccination or T-cell adoptive transfer.

Why can't the immune system control HIV-1? Defining HIV-1-specific CD4+ T cell immunity in order to develop strategies to enhance viral immunity

Globally, at least 60 million people have been infected with the human immunodeficiency virus type 1 (HIV-1), the majority of whom will develop the acquired immunodeficiency syndrome (AIDS) leading to tremendous morbidity and the mortality. Understanding the immunopathogenesis of AIDS and the immune correlates of viral protection are necessary to develop effective vaccines and immunotherapies. A major focus of our laboratory has been to understand the CD4+ T cell immune response directed against HIV- 1, and to determine mechanisms of T cell dysfunction that lead to viral escape. In addition, we are interested in evaluating the TNF-TNFR family members as potential molecular adjuvants that could be incorporated into vaccines which could be used to further boost T cell immunogenicity in healthy or HIV-1-infected individuals, as many of these molecules have been shown to replace the functions of CD4+ T cell help.

A modified tyrosinase-related protein 2 epitope generates high-affinity tumor-specific T cells but does not mediate therapeutic efficacy in an intradermal tumor model

The generation of tumor-specific T cells is hampered by the presentation of poorly immunogenic tumor-specific epitopes by the tumor. Here, we demonstrate that, although CD8+ T cells specific for the self/tumor Ag tyrosinase-related protein 2 (TRP2) are readily detected in tumor-bearing hosts, vaccination of either tumor-bearing or naive mice with an epitope derived from TRP2 fails to generate significant numbers of tetramer-staining TRP2-specific T cells or antitumor immunity. We identified an altered peptide epitope, called deltaV, which elicits T cell responses that are cross-reactive to the wild-type TRP2 epitope. Immunization with deltaV generates T cells with increased affinity for TRP2 compared with immunization with the wild-type TRP2 epitope, although TRP2 immunization often generates a greater number of TRP2-specific T cells based on intracellular IFN-gamma analysis. Despite generating higher affinity responses, deltaV immunization alone fails to provide any greater therapeutic efficacy against tumor growth than TRP2 immunization. This lack of tumor protection is most likely a result of both the deletion of high affinity and functional tolerance induction of lower affinity TRP2-specific T cells. Our data contribute to a growing literature demonstrating the ability of variant peptide epitopes to generate higher affinity T cell responses against tumor-specific Ags. However, consistent with most clinical data, simple generation of higher affinity T cells is insufficient to mediate tumor immunity.

Immune suppression in the tumor microenvironment

The identification of tumor-expressed antigens that can be recognized by specific T lymphocytes has made it possible both to study the properties of T cells participating in anti-tumor immune responses in patients and also to develop antigen-specific immunotherapies as a treatment modality. Interestingly, moves toward intervention have proceeded at a faster pace than have investigations toward understanding. In melanoma in particular, many clinical trials of active immunization have been performed, and many of these have shown increases in tumor antigen-specific T cells circulating in the blood. However, clinical responses have been infrequent, arguing that mechanisms of resistance downstream from initial T cell priming may be dominant in many cases. In fact, may patients show spontaneous generation of immune effector cells and/or antibodies, implying that the priming phase has occurred already in such individuals even without vaccination. Recent attention has turned toward mechanisms of immune evasion at the effector phase of the anti-tumor immune response, predominantly within the tumor microenvironment. Evidence is accumulating that T cell-intrinsic hyporesponsiveness or anergy, extrinsic suppression by regulatory cell populations, inhibitory ligands such as PD-L1, soluble factors such as TGF-beta, and the activity of nutrient-catabolizing enzymes such as indoleamine 2,3-dioxygenase (IDO), may contribute to immune escape in different settings. Murine preclinical models have shown that interfering with each of these processes can translate into T cell-mediated tumor control. Clinical studies to estimate the frequency of specific immune evasion mechanisms in individual patients, to correlate specific events with clinical outcome, and to develop strategies to counter resistance mechanisms should receive a high priority.

Conversion of alloantigen-specific CD8+ T cell anergy to CD8+ T cell priming through in vivo ligation of glucocorticoid-induced TNF receptor

In this study, we investigated the effect of an agonistic mAb (DTA-1) against glucocorticoid-induced TNF receptor (GITR) in a murine model of systemic lupus erythematosus-like chronic graft-vs-host disease (cGVHD). A single dose of DTA-1 inhibited the production of anti-DNA IgG1 autoantibody and the development of glomerulonephritis, typical symptoms of cGVHD. DTA-1-treated mice showed clinical and pathological signs of acute GVHD (aGVHD), such as lymphopenia, loss of body weight, increase of donor cell engraftment, and intestinal damage, indicating that DTA-1 shifted cGVHD toward aGVHD. The conversion of cGVHD to aGVHD occurred because DTA-1 prevented donor CD8+ T cell anergy. Functionally active donor CD8+ T cells produced high levels of IFN-gamma and had an elevated CTL activity against host Ags. In in vitro MLR, anergic responder CD8+ T cells were generated, and DTA-1 stimulated the activation of these anergic CD8+ T cells. We further confirmed in vivo that donor CD8+ T cells, but not donor CD4+ T cells, were responsible for the DTA-1-mediated conversion of cGVHD to aGVHD. These results indicate that donor CD8+ T cell anergy is a restriction factor in the development of aGVHD and that in vivo ligation of GITR prevents CD8+ T cell anergy by activating donor CD8+ T cells that otherwise become anergic. In sum, our data suggest GITR as an important costimulatory molecule regulating cGVHD vs aGVHD and as a target for therapeutic intervention in a variety of related diseases.

Interleukin-2-dependent mechanisms of tolerance and immunity in vivo

IL-2 is a critical T cell growth factor in vitro, but predominantly mediates tolerance in vivo. IL-2 is mainly produced by CD4(+) Th cells, but the role of Th cell-derived IL-2 in vivo is controversial. We demonstrate that during immunity to a tumor/self-Ag, the predominant role of Th cell-derived IL-2 was to maintain IL-2Ralpha (CD25) on CD4(+) T regulatory cells (T(reg)), which resulted in their maintenance of the T(reg) cell lineage factor, Forkhead/winged helix transcription factor (Foxp3), and tolerance. However, in the absence of T(reg) cells, Th cell-derived IL-2 maintained effector T cells and caused autoimmunity. IL-2R signaling was indispensable for T(reg) cell homeostasis and efficient suppressor function in vivo, but, surprisingly, was not required for their generation, because IL-2(-/-) and CD25(-/-) mice both contained Foxp3(+) T cells in the periphery. IL-2R signaling was also important for CD8(+) T cell immunity, because CD25(-/-) tumor-reactive CD8(+) T cells failed to affect established tumors. Conversely, IL-2R signaling was not required for Th cell function. Lastly, administration of anti-IL-2 plus exogenous IL-15 to tumor-bearing mice enhanced the adoptive immunotherapy of cancer. Therefore, Th cell-derived IL-2 paradoxically controls both tolerance and immunity to a tumor/self-Ag in vivo.

Adenovirus-mediated CD40 ligand therapy induces tumor cell apoptosis and systemic immunity in the TRAMP-C2 mouse prostate cancer model

BACKGROUND

The interaction between CD40 ligand (CD40L) and CD40 on antigen presenting cells is essential for the initiation of antigen-specific T-cell responses, whereas CD40L stimulation of CD40+ tumor cells can induce cellular apoptosis. We investigated the anti-tumor effects induced by CD40L gene transfer into the mouse prostate adenocarcinoma cell line TRAMP-C2, both in vitro and in vivo.

METHODS

TRAMP-C2 cells were transduced with an adenoviral vector encoding CD40L (AdCD40L). The induced expression of co-stimulatory molecules and cell viability was analyzed. AdCD40L-transduced TRAMP-C2 cells were used in prophylactic vaccination studies, while therapeutic studies were performed using peritumoral injections of AdCD40L.

RESULTS

AdCD40L yielded reduced TRAMP-C2 cell viability and induced apoptosis in vitro. Vaccination with CD40L-expressing TRAMP-C2 cells induced anti-tumor immunity and peritumoral AdCD40L injections induced tumor growth suppression.

CONCLUSIONS

Our observations highlight the therapeutic potential of using AdCD40L as a monotherapy or in combination with conventional chemotherapy or novel therapies (e.g., oncolytic viruses). The use of AdCD40L offers an attractive option for future clinical trials.

Renewed interest in cancer immunotherapy with the tumor necrosis factor superfamily molecules

Molecules belonging to the Tumor Necrosis Factor (TNF) and TNF receptor superfamilies have explosively expanded through the era of genomics and bioinformatics. Biological investigations of these molecules have explored their potency as attractive targets for cancer therapy. Anti-tumor mechanisms mediated by TNF superfamily molecules (TNFSF) could be classified into direct actions onto tumor cells and indirect effects through immune or non-immune components of tumor-bearing host. In this review, we focus on TRAIL, CD40, 4-1BB (CD137), and LIGHT as promising molecules to mediate powerful and selective anti-tumor responses, and summarize their unique effector mechanisms. In addition, optimal approaches to manipulate these molecules for cancer therapy are also discussed. We try to provide an insight into a role of TNFSF in cancer therapeutics and highlight each of their potency to be an important player in anti-cancer strategies.

Identifying and overcoming immune resistance mechanisms in the melanoma tumor microenvironment

The continually growing list of defined tumor antigens is broadening the potential applicability of tumor antigen-targeted cancer therapies. Although cancer vaccines and adoptive T-cell transfer have been shown to increase the frequency of circulating tumor antigen-specific T cells, these approaches cause clinical responses in a few patients. In melanoma, approximately one third of metastatic lesions contain activated T cells, including those specific for tumor antigens, arguing that the priming phase has occurred already in such individuals even without vaccination. These observations indicate that tumor resistance to immune destruction may dominate in many instances, arguing for a thorough analysis of the melanoma tumor microenvironment in individual patients. Recent work has suggested that T-cell anergy, the influence of CD4+ CD25+ regulatory T cells, the expression of inhibitory ligands, such as PD-L1, and the activity of nutrient-catabolizing enzymes, such as indoleamine 2,3-dioxygenase, may be involved. Preclinical murine models have shown that interfering with each of these processes can translate into T-cell-mediated tumor control. Importantly, each of these targets is amenable to clinical manipulation. Clinical translation of these approaches to counter negative regulation of antitumor immunity should receive high priority.

OX40 costimulation synergizes with GM-CSF whole-cell vaccination to overcome established CD8+ T cell tolerance to an endogenous tumor antigen

T cell costimulation via OX40 is known to increase CD4+ T cell expansion and effector function and enhances the development of T cell memory. OX40 costimulation can also prevent, and even reverse, CD4+ T cell anergy. However, the role of OX40 in CD8+ T cell function is less well defined, particularly in the setting of immune tolerance. To determine the effects of OX40 costimulation on the induction of the host CD8+ T cell repertoire to an endogenous tumor Ag, we examined the fate of CD8+ T cells specific for the immunodominant rat HER-2/neu epitope, RNEU420-429, in FVB MMTV-neu (neu-N) mice, which express rat HER-2/neu protein in a predominantly mammary-restricted fashion. We show that the RNEU420-429-specific T cell repertoire in neu-N mice expands transiently after vaccination with a neu-targeted GM-CSF-secreting whole-cell vaccine, but quickly declines to an undetectable level. However, OX40 costimulation, when combined with GM-CSF-secreting tumor-targeted vaccination, can break established CD8+ T cell tolerance in vivo by enhancing the expansion, and prolonging the survival and effector function of CD8+ T cells specific for RNEU420-429. Moreover, we demonstrate that OX40 expression is up-regulated on both CD4+ and CD8+ T cells shortly after administration of a GM-CSF expressing vaccine. These studies highlight the increased efficacy of OX40 costimulation when combined with a GM-CSF-secreting vaccine, and define a new role for OX40 costimulation of CD8+ T cells in overcoming tolerance and boosting antitumor immunity.

Multimeric soluble CD40 ligand and GITR ligand as adjuvants for human immunodeficiency virus DNA vaccines

For use in humans, human immunodeficiency virus (HIV) DNA vaccines may need to include immunostimulatory adjuvant molecules. CD40 ligand (CD40L), a member of the tumor necrosis factor (TNF) superfamily (TNFSF), is one candidate adjuvant, but it has been difficult to use because it is normally expressed as a trimeric membrane molecule. Soluble trimeric forms of CD40L have been produced, but in vitro data indicate that multimeric, many-trimer forms of soluble CD40L are more active. This multimerization requirement was evaluated in mice using plasmids that encoded either 1-trimer, 2-trimer, or 4-trimer soluble forms of CD40L. Fusion with the body of Acrp30 was used to produce the 2-trimer form, and fusion with the body of surfactant protein D was used to produce the 4-trimer form. Using plasmids for secreted HIV-1 antigens Gag and Env, soluble CD40L was active as an adjuvant in direct proportion to the valence of the trimers (1 < 2 < 4). These CD40L-augmented DNA vaccines elicited strong CD8(+) T-cell responses but did not elicit significant CD4(+) T-cell or antibody responses. To test the applicability of the multimeric fusion protein approach to other TNFSFs, a 4-trimer construct for the ligand of glucocorticoid-induced TNF family-related receptor (GITR) was also prepared. Multimeric soluble GITR ligand (GITRL) augmented the CD8(+) T-cell, CD4(+) T-cell, and antibody responses to DNA vaccination. In summary, multimeric CD40L and GITRL are new adjuvants for DNA vaccines. Plasmids for expressing multimeric TNFSF fusion proteins permit the rapid testing of TNFSF molecules in vivo.

Interleukin-12 production by leukemia-derived dendritic cells counteracts the inhibitory effect of leukemic microenvironment on T cells

OBJECTIVE

Acute myeloid leukemia (AML) cells are poorly immunogenic and inhibit T-cell function. AML-derived dendritic cells (AML-DCs) have better antigen-presentation capacity than undifferentiated leukemic blasts, but may not be fully competent to stimulate T cells previously inhibited by leukemic cells.

MATERIALS AND METHODS

AML-DCs were generated from AML cells and used to stimulate proliferation and cytokine production by T cells previously inhibited by AML cells. AML-DCs were also transfected with interleukin (IL)-12 gene by the nonviral method, nucleofection.

RESULTS

Mature AML-DCs stimulated naive and, to a lesser extent, leukemic cell (LC)-cultured T cells more efficiently than their immature counterparts and their activity was mediated by IL-12. AML-DCs generated from CD14(-) AML samples (which represent 80% of total AML patients) were defective in IL-12 production and T-cell activation. Addition of exogenous IL-12 to LC-cultured T cells stimulated by CD14(-)-derived AML-DCs restored optimal interferon-gamma (IFN-gamma) production and Th1 skewing. IL-12 gene-nucleofected AML-DCs derived from CD14(-) cells produced significant amounts of IL-12, maintained leukemia-specific karyotype, DC-like phenotype, and function. When stimulated by IL-12-gene transduced CD14(-)-derived AML-DCs, LC-cultured T cells produced higher concentrations of IFN-gamma, thus maintaining a Th1 cytokine profile.

CONCLUSION

IL-12 produced by AML-DCs plays a critical role in counteracting the inhibitory activity of LCs on T-cell function. IL-12 gene can be successfully expressed into AML-DCs defective in endogenous IL-12 production by using a novel nonviral method that does not modify their phenotypical, cytogenetic, and functional features. Genetically modified AML-DCs restore a near normal T-cell function.

Circumventing tolerance at the T cell or the antigen-presenting cell surface: Antibodies that ligate CD40 and OX40 have different effects

An adjuvant can be defined as an agent that non-specifically promotes the immune response to an accompanying antigen. Ligation of CD40 on the surface of the antigen-presenting cell leads to upregulation of OX40 ligand which, in turn, ligates OX40 on the activated T cell resulting in prolonged T cell proliferation/survival, boosting the immune response. Thus agonistic anti-CD40 and anti-OX40 might be viewed as "adjuvant antibodies" and have been shown in diverse experimental systems to either boost immune responses or prevent the establishment of immunological tolerance. Here we describe that both these antibodies are able to prevent the induction of tolerance induced using soluble peptide antigen. However, unlike lipopolysaccharide, they are not sufficient to convert tolerance to immunity (i.e. they are not true adjuvants in this system). Using mice that are prone to either Th1 or Th2 immunity under identical immunization conditions, we show that the effects of anti-OX40 are quantitative -- boosting whichever response is dominant. In contrast, anti-CD40 boosts Th1 immunity and converts a Th2 response to Th1. We conclude that, although these two antibodies seem to impact on the same molecular pathway of costimulation to prevent tolerance, their effects are qualitatively distinct and their use cannot be viewed as interchangeable.

Tumor-associated CD8+ T cell tolerance induced by bone marrow-derived immature myeloid cells

T cell tolerance is a critical element of tumor escape. However, the mechanism of tumor-associated T cell tolerance remains unresolved. Using an experimental system utilizing the adoptive transfer of transgenic T cells into naive recipients, we found that the population of Gr-1+ immature myeloid cells (ImC) from tumor-bearing mice was able to induce CD8+ T cell tolerance. These ImC accumulate in large numbers in spleens, lymph nodes, and tumor tissues of tumor-bearing mice and are comprised of precursors of myeloid cells. Neither ImC from control mice nor progeny of tumor-derived ImC, including tumor-derived CD11c+ dendritic cells, were able to render T cells nonresponsive. ImC are able to take up soluble protein in vivo, process it, and present antigenic epitopes on their surface and induce Ag-specific T cell anergy. Thus, this is a first demonstration that in tumor-bearing mice CD8+ T cell tolerance is induced primarily by ImC that may have direct implications for cancer immunotherapy.

C3-symmetric peptide scaffolds are functional mimetics of trimeric CD40L

Interaction between CD40, a member of the tumor necrosis factor receptor (TNFR) superfamily, and its ligand CD40L, a 39-kDa glycoprotein, is essential for the development of humoral and cellular immune responses. Selective blockade or activation of this pathway provides the ground for the development of new treatments against immunologically based diseases and malignancies. Like other members of the TNF superfamily, CD40L monomers self-assemble around a threefold symmetry axis to form noncovalent homotrimers that can each bind three receptor molecules. Here, we report on the structure-based design of small synthetic molecules with C3 symmetry that can mimic CD40L homotrimers. These molecules interact with CD40, compete with the binding of CD40L to CD40, and reproduce, to a certain extent, the functional properties of the much larger homotrimeric soluble CD40L. Architectures based on rigid C3-symmetric cores may thus represent a general approach to mimicking homotrimers of the TNF superfamily.

Immunotherapy of high-risk acute leukemia with a recipient (autologous) vaccine expressing transgenic human CD40L and IL-2 after chemotherapy and allogeneic stem cell transplantation

CD40L generates immune responses in leukemia-bearing mice, an effect that is potentiated by IL-2. We studied the feasibility, safety, and immunologic efficacy of an IL-2- and CD40L-expressing recipient-derived tumor vaccine consisting of leukemic blasts admixed with skin fibroblasts transduced with adenoviral vectors encoding human IL-2 (hIL-2) and hCD40L. Ten patients (including 7 children) with high-risk acute myeloid (n = 4) or lymphoblastic (n = 6) leukemia in cytologic remission (after allogeneic stem cell transplantation [n = 9] or chemotherapy alone [n = 1]) received up to 6 subcutaneous injections of the IL-2/CD40L vaccine. None of the patients were receiving immunosuppressive drugs. No severe adverse reactions were noted. Immunization produced a 10- to 890-fold increase in the frequencies of major histocompatibility complex (MHC)-restricted T cells reactive against recipient-derived blasts. These leukemia-reactive T cells included both T-cytotoxic/T-helper 1 (Th1) and Th2 subclasses, as determined from their production of granzyme B, interferon-gamma, and interleukin-5. Two patients produced systemic IgG antibodies that bound to their blasts. Eight patients remained disease free for 27 to 62 months after treatment (5-year overall survival, 90%). Thus, even in heavily treated patients, including recipients of allogeneic stem cell transplants, recipient-derived antileukemia vaccines can induce immune responses reactive against leukemic blasts. This approach may be worthy of further study, particularly in patients with a high risk of relapse.

Phenotype and homing of CD4 tumor-specific T cells is modulated by tumor bulk

Technical difficulties in tracking endogenous CD4 T lymphocytes have limited the characterization of tumor-specific CD4 T cell responses. Using fluorescent MHC class II/peptide multimers, we defined the fate of endogenous Leishmania receptor for activated C kinase (LACK)-specific CD4 T cells in mice bearing LACK-expressing TS/A tumors. LACK-specific CD44(high)CD62L(low) CD4 T cells accumulated in the draining lymph nodes and had characteristics of effector cells, secreting IL-2 and IFN-gamma upon Ag restimulation. Increased frequencies of CD44(high)CD62L(low) LACK-experienced cells were also detected in the spleen, lung, liver, and tumor itself, but not in nondraining lymph nodes, where the cells maintained a naive phenotype. The absence of systemic redistribution of LACK-specific memory T cells correlated with the presence of tumor. Indeed, LACK-specific CD4 T cells with central memory features (IL-2(+)IFN-gamma(-)CD44(high)CD62L(high) cells) accumulated in all peripheral lymph nodes of mice immunized with LACK-pulsed dendritic cells and after tumor resection. Together, our data demonstrate that although tumor-specific CD4 effector T cells producing IFN-gamma are continuously generated in the presence of tumor, central memory CD4 T cells accumulate only after tumor resection. Thus, the continuous stimulation of tumor-specific CD4 T cells in tumor-bearing mice appears to hinder the systemic accumulation of central memory CD4 T lymphocytes.

Amplification of tumor-specific regulatory T cells following therapeutic cancer vaccines

The fate of tumor-specific CD4(+) T cells is central to the outcome of the host immune response to cancer. We show that tumor antigen recognition by a subset of CD4(+) T cells led to their differentiation into cells capable of suppressing naive and Th1 effector cells. Such tumor-induced regulatory T cells (TMTregs) arose both from precommitted "natural" regulatory T cells and CD4(+)CD25(-)GITR(low) precursors. Once induced, TMTregs were capable of maintaining suppressor activity long after transfer into antigen-free recipients. Suppression was mediated by GITR(high) cells residing within both CD25(+) and CD25(-) subsets. Vaccination of the tumor-bearing host concomitantly expanded TMTregs and effector cells, but suppression was dominant, blunting the expansion of naive tumor-specific T cells and blocking the execution of effector function in vitro and in vivo. These studies illustrate the possibility that therapeutic vaccination could actually worsen host tolerance to tumor antigens and support treatment paradigms that seek to not only increase the frequency of tumor-specific T cells, but to do so in conjunction with strategies that inactivate or remove regulatory T-cell populations.

CD40 ligation activates murine macrophages via an IFN-gamma-dependent mechanism resulting in tumor cell destruction in vitro

We have shown previously that agonistic anti-CD40 mAb induced T cell-independent antitumor effects in vivo. In this study, we investigated mechanisms of macrophage activation with anti-CD40 mAb treatment, assessed by the antitumor action of macrophages in vitro. Intraperitoneal injection of anti-CD40 mAb into C57BL/6 mice resulted in activation of peritoneal macrophages capable of suppressing B16 melanoma cell proliferation in vitro, an effect that was greatly enhanced by LPS and observed against several murine and human tumor cell lines. Anti-CD40 mAb also primed macrophages in vitro to mediate cytostatic effects in the presence of LPS. The tumoristatic effect of CD40 ligation-activated macrophages was associated with apoptosis and killing of tumor cells. Activation of macrophages by anti-CD40 mAb required endogenous IFN-gamma because priming of macrophages by anti-CD40 mAb was abrogated in the presence of anti-IFN-gamma mAb, as well as in IFN-gamma-knockout mice. Macrophages obtained either from C57BL/6 mice depleted of T and NK cells by Ab treatment, or from scid/beige mice, were still activated by anti-CD40 mAb to mediate cytostatic activity. These results argued against the role of NK and T cells as the sole source of exogenous IFN-gamma for macrophage activation and suggested that anti-CD40 mAb-activated macrophages could produce IFN-gamma. We confirmed this hypothesis by detecting intracytoplasmic IFN-gamma in macrophages activated with anti-CD40 mAb in vivo or in vitro. IFN-gamma production by macrophages was dependent on IL-12. Taken together, the results show that murine macrophages are activated directly by anti-CD40 mAb to secrete IFN-gamma and mediate tumor cell destruction.

Kinetics of costimulatory molecule expression by T cells and dendritic cells during the induction of tolerance versus immunity in vivo

Steady-state dendritic cells (DC) present peptide-MHC complexes to T cells in a tolerogenic manner, presumably because of deficient costimulation. However, it is clear that the path to tolerance involves initial T cell activation, suggesting that the deficit may lie in late-acting costimulatory molecules. With this in mind we have investigated the kinetics of expression of several costimulatory pairs on DC and OVA-reactive T cells after i.v. injection of mice with peptide and LPS (immunity), or peptide alone (tolerance). We find that T cells up-regulate CD154, OX40, RANKL and PD-1 whether they are destined for tolerance or immunity, although there are some differences in the levels and length of expression. In contrast, when analyzing DC, we found that up-regulation of CD80, CD86, CD40, RANK and PDL-1 occurred only when peptide was co-administered with LPS. These data give a picture of the T cell looking for costimulatory cues that are not forthcoming when pMHC is presented by steady-state DC, leading to tolerance. However, we did see a strong and rapid up-regulation of RANKL on T cells that occurred specifically when peptide was given in the absence of LPS, suggesting a possible positive signal influencing the decision between tolerance and immunity.

Intratumoral administration of immature dendritic cells following the adenovirus vector encoding CD40 ligand elicits significant regression of established myeloma

Our previous study showed that J558 myeloma cells engineered CD40L lost their tumorigenicity in syngeneic mice, and the inoculation of J558/CD40L tumor cells further led to the protective immunity against wild tumors. In the present study, we investigated whether the vaccine can exert more efficient antitumor immunity by combination with adenovirus mediated CD40L gene therapy and immature dendritic cells (iDCs). The results demonstrated that intratumoral administration of iDCs 2 days after AdVCD40L injection, not only significantly suppressed the tumor growth, but also eradiated the established tumors in 40% of the mice. The potent antitumor effect produced by the combination therapy correlated with high expression of MHC, costimulatory and Fas molecules on J558 cells, which was derived from CD40L transgene expression. In addition, transgene CD40L expression could dramatically induce J558 cell apoptosis. Effectively capturing apoptotic bodies by iDCs in vivo could induce DC maturation, prime tumor-specific CTLs and tend to Th1-type immune response. Finally, in vivo depletion experimentation suggested both CD4+ and CD8+ T cells were involved in mediating the antitumor immune responses of combined treatment of AdVCD40L and iDCs, with CD8+ T cells being the major effector. These findings could be beneficial for designing strategies of DCs vaccine and CD40L for anticancer immunotherapy.