Vaccination with dendritic cells pulsed with apoptotic tumors in combination with anti-OX40 and anti-4-1BB monoclonal antibodies induces T cell-mediated protective immunity in Her-2/neu transgenic mice

Targeting the tumor microenvironment with anti-neu/anti-CD40 conjugated nanoparticles for the induction of antitumor immune responses

Clinical and preclinical data indicate that immunotherapeutic interventions could induce immune responses capable of controlling or retard the tumor growth. However, immunotherapies need to be further optimized. We hypothesized that a more effective strategy for tumor eradication is to directly target the tumor microenvironment in order to generate a proinflammatory response and induce a localized antitumor immune response capable of eliminating the tumor cells. Nanoparticles have been proven to be an effective delivery system. In these studies we evaluated conjugated anti-RNEU and anti-CD40 antibodies onto PLA-(poly dl-lactic acid)-biodegradable nanoparticles (PLA-NP) for the induction of antitumor immune responses. The anti-neu/anti-CD40-NP were functional in vitro recognizing RNEU(+) tumors and activating dendritic cells. The delivery of anti-neu/anti-CD40-NP but not anti-neu-NP or anti-CD40-NP induced an antitumor response resulting in complete tumor elimination and generation of protective memory responses. The anti-neu/anti-CD40-NP specifically activated an antitumor response against RNEU(+) tumors but not against RNEU(-) tumors. The antitumor immune responses correlate with the induction of a Th1-proinflammatory response, reduction in the number of Tregs within the tumor and activation of a specific cytotoxic response. These results indicate that anti-neu/anti-CD40-NP with immunomodulatory properties are safe and can be used effectively as cancer vaccines strategy for the specific induction of antitumor immune responses.

Cutting Edge: OX40 agonists can drive regulatory T cell expansion if the cytokine milieu is right

We report that OX40 stimulation drives all lineages of CD4 T cell development, including regulatory T cells (Tregs), and the plasticity of the response is dependant on local cytokines. In TGF-beta1-treated cultures, an OX40 agonist increased IFN-gamma and IL-4 production and diverted T cells from the Treg lineage. However, cytokine blockade in the context of OX40 stimulation promoted enhanced Treg accumulation. This observation was evident in naive mice, as OX40 engagement enhanced Treg proliferation and accumulation in vivo. Lastly, OX40 agonist administration influenced experimental autoimmune encephalomyelitis disease severity in opposing directions, depending on the timing of administration. Given during Ag priming, the OX40 agonist drove Treg expansion and inhibited disease, whereas given later it enhanced T cell effector cytokine production in the CNS and exacerbated disease. Hence, OX40 signaling can augment the accumulation of all CD4 T cell lineages; however, its accentuation of immune responses may have vastly different biologic outcomes depending upon the local cytokine milieu.

The significance of OX40 and OX40L to T-cell biology and immune disease

SUMMARY

OX40 (CD134) and its binding partner, OX40L (CD252), are members of the tumor necrosis factor receptor/tumor necrosis factor superfamily and are expressed on activated CD4(+) and CD8(+) T cells as well as on a number of other lymphoid and non-lymphoid cells. Costimulatory signals from OX40 to a conventional T cell promote division and survival, augmenting the clonal expansion of effector and memory populations as they are being generated to antigen. OX40 additionally suppresses the differentiation and activity of T-regulatory cells, further amplifying this process. OX40 and OX40L also regulate cytokine production from T cells, antigen-presenting cells, natural killer cells, and natural killer T cells, and modulate cytokine receptor signaling. In line with these important modulatory functions, OX40-OX40L interactions have been found to play a central role in the development of multiple inflammatory and autoimmune diseases, making them attractive candidates for intervention in the clinic. Conversely, stimulating OX40 has shown it to be a candidate for therapeutic immunization strategies for cancer and infectious disease. This review provides a broad overview of the biology of OX40 including the intracellular signals from OX40 that impact many aspects of immune function and have promoted OX40 as one of the most prominent costimulatory molecules known to control T cells.

HER-2/neu mediated down-regulation of MHC class I antigen processing prevents CTL-mediated tumor recognition upon DNA vaccination in HLA-A2 transgenic mice

To study DNA vaccination directed against human HER-2 in the HHD mouse Tg strain, we created a novel HER-2-expressing syngeneic tumor transplantation model. We found that a DNA vaccine encoding the full length HER-2 DNA protected HHD mice from HER-2(+) tumor challenge by a CTL independent mechanism. A more efficient approach to induce HLA-A2 restricted CTLs, through immunization with a multi-epitope DNA vaccine expressing the HLA-A2 restricted HER-2 369-377, 435-443 and 689-697 epitopes, resulted in high numbers of peptide specific T cells but failed to induce tumor protection. Subsequently we discovered that HER-2 transfected tumor cells down-regulated MHC class I antigen expression and exhibited a series of defects in the antigen processing pathway which impaired the capacity to produce and display MHC class I peptide-ligands to specific CTLs. Our data demonstrate that HER-2 transfection is associated with defects in the MHC class I presentation pathway, which may be the underlying mechanism behind the inability of CTLs to recognize tumors in this HLA-A2 transgenic model. As defective MHC class I presentation may be a common characteristic of HER-2 expressing tumors, vaccines targeting HER-2 should aim at inducing an integrated immune response where also CD4(+) T cells and antibodies are important components.

The role of TNF superfamily members in T-cell function and diseases

Interactions that occur between several tumour necrosis factor (TNF)-TNF receptors that are expressed by T cells and various other immune and non-immune cell types are central to T-cell function. In this Review, I discuss the biology of four different ligand-receptor interactions - OX40 ligand and OX40, 4-1BB ligand and 4-1BB, CD70 and CD27, and TL1A and death receptor 3 - and their potential to be exploited for therapeutic benefit. Manipulating these interactions can be effective for treating diseases in which T cells have an important role, including inflammatory conditions, autoimmunity and cancer. Here, I explore how blocking or inducing the signalling pathways that are triggered by these different interactions can be an effective way to modulate immune responses.

Self-antigen prevents CD8 T cell effector differentiation by CD134 and CD137 dual costimulation

We compared how CD4 vs CD8 cells attain the capacity to express the effector cytokine IFN-gamma under both immunogenic and tolerogenic conditions. Although the Ifng gene locus was epigenetically repressed in naive Ag-inexperienced CD4 cells, it had already undergone partial remodeling toward a transcriptionally competent configuration in naive CD8 cells. After TCR stimulation, CD8 cells fully remodeled the Ifng locus and gained the capacity to express high levels of IFN-gamma more rapidly than CD4 cells. Enforced dual costimulation through OX40 and 4-1BB redirected CD8 cells encountering soluble exogenous peptide to expand and differentiate into IFN-gamma and TNF-alpha double-producing effectors rather than becoming tolerant. Despite this and the stronger tendency of CD8 compared with CD4 cells to differentiate into IFN-gamma-expressing effectors, when parenchymal self-Ag was the source of tolerizing Ag, enforced dual costimulation selectively boosted expansion but did not push effector differentiation in CD8 cells while both expansion and effector differentiation were dramatically boosted in CD4 cells. Notably, enforced dual costimulation was able to push effector differentiation in CD8 cells encountering cognate parenchymal self-Ag when CD4 cells were simultaneously engaged. Thus, the ability of enforced OX40 plus 4-1BB dual costimulation to redirect CD8 cells to undergo effector differentiation was unexpectedly influenced by the source of tolerizing Ag and help was selectively required to facilitate CD8 cell effector differentiation when the tolerizing Ag derived from self.

Melanoma and lymphoma rejection associated with eosinophil infiltration upon intratumoral injection of dendritic and NK/LAK cells

Dendritic cells (DCs) are promising tools for tumor immunotherapy. Their efficacy in the tumor environment increases when tumor cells die as a consequence of chemo/radiotherapy or when local stimuli promoting DC maturation and function are available. Dying tumor cells could represent a source of tumor antigens, which DCs cross-present to tumor-specific T cells. The outcome of cross presentation is in turn determined by the maturation state of DCs. Natural killer (NK)/lymphokine-activated killer (LAK) cells injected into growing tumors could both provide a source of dying cells for cross-presentation and deliver stimuli for DC maturation. Here, we report that NK/LAK cells recognized and killed in vivo major histocompatibility complex class I(low) highly tumorigenic, nonimmunogenic B16F1 melanoma cells when injected into exponentially growing neoplastic lesions. The simultaneous injection of immature DCs was required to heal animals. Similar results were obtained injecting NK/LAK cells and DC into growing Raucher leukaemia virus induced cell line lymphomas. Cured mice failed to reject other implantable tumors, and developed a specific cytotoxic response against the original neoplasm; moreover, they developed a long-lasting memory, and were protected against further challenges with living tumor cells only when both cell populations were introduced. The response associated to the preferential recruitment within tumors of eosinophils. The simultaneous injection in solid tumors of DCs and NK/LAK cells represents an attractive approach for antineoplastic immunotherapeutic strategies.

Systemic targeting of CpG-ODN to the tumor microenvironment with anti-neu-CpG hybrid molecule and T regulatory cell depletion induces memory responses in BALB-neuT tolerant mice

We have shown that neu transgenic mice are immunotolerant and that immunizations with dendritic cells (DC) pulsed with neu-derived antigens were not able to control tumor growth in these animals. We tested whether, by modulating the tumor microenvironment with Toll-like receptor ligands, it could be possible to induce the activation of antitumor responses in neu mice. Our results indicate that only intratumoral (i.t.) injections of CpG-ODN induce an antitumor response in neu mice. To target the CpG-ODN to the tumor site anywhere within the body, we chemically conjugated an anti-Her-2/neu monoclonal antibody (mAb) with CpG-ODN. The anti-neu-CpG hybrid molecule retained its ability to bind to Her-2/neu(+) tumors, activate DCs, and induce antitumor responses. Our results indicated that injections of anti-neu-CpG induced the rejection of primary tumors in 100% of BALB/c mice and only in approximately 30% of BALB-neuT mice. After challenging the BALB/c and BALB-neuT mice, we observed that BALB/c mice developed a protective memory response; in contrast, BALB-neuT mice succumbed to the challenge. After injections of anti-neu-CpG, T regulatory cells (T-reg) were drastically reduced at the tumor site, but a large number were still present in the lymphoid organs. When BALB-neuT mice were treated with anti-neu-CpG plus anti-GITR mAb, but not with anti-CD25 mAb, 100% of the BALB-neuT mice rejected the primary tumor and developed a protective memory response indicating the critical role of T-regs in regulating the repertoire against self antigens. Taken together, these results indicate that CpG-ODN-targeted therapy and depletion of T-regs optimally activate a primary response and generate a protective memory response against self-tumor antigens.

Implications of aging and self-tolerance on the generation of immune and antitumor immune responses

Cancer statistics show a disproportionately higher burden of tumors in the old. Most of the studies evaluating vaccination strategies have not taken into consideration the effect that aging has on the immune system. For the first time, we describe an animal tumor model in which self-tolerance and aging are present at the same time. FVB-Her-2/neu mice which are tolerant to neu antigens crossed with HLA-A2/Kb mice (A2xneu) develop spontaneous tumors when they are more than 22 months old. Analysis of CD8(+) T-cell-specific responses in A2xneu mice indicated that the priming activity of old A2xneu mice to induce an immune response was diminished compared with young animals. Following intratumoral injections of CpG-ODN, approximately 30% of young A2xneu mice rejected the tumor; however, no antitumor effect was observed in old A2xneu mice. Analysis of T regulatory cells (Treg) indicated that there are significantly more Tregs in old animals. After CpG-ODN vaccination plus Treg depletion, 70% of young A2xneu mice rejected the tumor. The same treatment prolonged survival in old A2xneu mice, but none of the animals rejected the tumor. Even though CpG-ODN injections plus Treg depletion could rescue the antitumor responses against self-tumor antigens in young tolerant mice, the same therapy is not as effective in old tolerant hosts. Relevant tumor models such as the A2xneu mice in which self-tolerance and aging are present at the same time are critical to allow the optimization of vaccination strategies to effectively stimulate immune responses against self-tumor antigens in the young and the old.

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.

Immunotherapy for gastrointestinal cancer: current status and strategies for improving efficacy

BACKGROUND

Despite improvement in conventional strategies for treating gastrointestinal (GI) carcinoma, large numbers of patients still suffer from incurable or progressive disease.

OBJECTIVE

Here we consider the prospects for circumventing limitations and maximising the efficacy of different immunotherapies.

METHODS

We summarise different cancer vaccines and targeted drugs and highlight the scientific rationale of using immunotherapy for targeting GI cancers, in addition to the potential strategies for improving immunotherapeutic efficacy.

RESULTS/CONCLUSION

Many cancer vaccines and antibody-directed therapies have been tested in early phase clinical trials and demonstrated proof of concept and safety. As yet few have been properly evaluated for clinical efficacy; although adoptive transfer of tumour-associated-antigen-specific T cells has shown dramatic clinical responses in some patients. The recognition of a role for T regulatory cells in limiting anti-tumour immunity has provided momentum for developing strategies to over-ride such immunoinhibitory effects. There is some evidence that conventional therapies may work by influencing these negative factors and allowing expression of immune control mechanisms. An important developing area for clinical evaluation is the testing of combined conventional and immunotherapeutic modalities which may provide for synergy; thereby circumventing the limitations of individualised treatments and generating additional clinical benefits.

CD134 Costimulation Couples the CD137 Pathway to Induce Production of Supereffector CD8 T Cells That Become IL-7 Dependent

The TNFR superfamily members 4-1BB (CD137) and OX40 (CD134) are costimulatory molecules that potently boost CD8 and CD4 T cell responses. Concomitant therapeutic administration of agonist anti-CD137 and -CD134 mAbs mediates rejection of established tumors and fosters powerful CD8 T cell responses. To reveal the mechanism, the role of CD137 expression by specific CD8 T cells was determined to be essential for optimal clonal expansion and accumulation of effector cells. Nonetheless, dual costimulation induced production of supereffector CD8 T cells when either the specific T cells or the host alone bore CD137. Perhaps surprisingly, the total absence of CD137 prevented anti-CD134 augmentation of supereffector differentiation demonstrating an unappreciated link between these related pathways. Ultimately, it was reasoned that these powerful dual costimulatory responses involved common gamma family members, and we show substantial increases of CD25 and IL-7Ralpha-chain expression by the specific CD8 T cells. To investigate this further, it was shown that IL-7 mediated T cell accumulation, but importantly, a gradual and preferential effect of survival was directed toward supereffector CD8 T cells. In fact, a clear enhancement of effector differentiation was demonstrated to be proportional to the increasing amount of IL-7Ralpha expression by the specific CD8 T cells. Therefore, dual costimulation through CD137 and CD134 drives production and survival of supereffector CD8 T cells through a distinct IL-7-dependent pathway.

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.

T-regulatory cells are relatively deficient in squamous carcinomas undergoing regression in mice immunized with a squamous carcinoma vaccine enriched for immunotherapeutic cells

In a prior report (Int J Cancer 2006; 119: 339-348), we described a new vaccination strategy for squamous cell carcinoma (SCC). The vaccine was prepared by transfer of unfractionated DNA-fragments (25 kb) from KLN205 cells, a squamous carcinoma cell line (DBA/2 origin; H-2(d)) into LM cells, a highly immunogenic mouse fibroblast cell line (C3H/He origin; (H-2(k))). As only a small proportion of the transfected cell population was expected to have incorporated DNA segments that included genes specifying antigens associated with the squamous carcinoma cells, we devised a novel strategy to enrich the vaccine for immunotherapeutic cells. Enhanced immunity to squamous carcinoma was induced in tumor-bearing mice treated solely by immunization with the enriched vaccine, which translated into prolonged survival without toxicity. Here, we describe the characteristics of the cell populations infiltrating established squamous carcinomas undergoing regression in mice immunized with vaccines enriched for immunotherapeutic cells. The results indicated that CD8+ T cells were predominant and that T-regulatory cells (FoxP3+, CD4/CD25+, CD4/CD62L(high), CD4/CTLA-4e) were relatively deficient in the regressing tumors. Inflammatory infiltrates were not detected in various organs and tissues of mice immunized with the DNA-based vaccine.

New strategy for the identification of squamous carcinoma antigens that induce therapeutic immune responses in tumor-bearing mice

This study describes a new strategy for the identification of squamous carcinoma antigens tumor-associated antigens (TAA). The antigens were discovered by comparing microarrays of squamous carcinoma vaccines highly enriched for immunotherapeutic cells with non-enriched vaccines. The vaccines were prepared by transferring sheared genomic DNA fragments (25 kb) from KLN205 cells, a squamous carcinoma cell line (DBA/2 mouse origin (H-2(d)) into LM fibroblasts (C3H/He origin, H-2(k)). The transferred tumor DNA segments integrate spontaneously into the genome of the recipient cells, replicate as the cells divide and are expressed. As only a small proportion of the transfected cell population was expected to have incorporated DNA segments that included genes specifying TAA (the vast majority specify normal cellular constituents), a novel strategy was employed to enrich the vaccine for TAA-positive cells. Microarrays were used to compare genes expressed by enriched and non-enriched vaccines. Seventy-five genes were overexpressed in cells from the enriched vaccine. One, the gene for Cytochrome P450 (family 2, subfamily e, polypeptide 1) (Cyp2e1), was overexpressed in the enriched but not the non-enriched vaccine. A vaccine for squamous carcinoma was prepared by transfer of a 357 bp fragment of the gene for Cyp2e1 into the fibroblast cell line. Robust immunity, sufficient to result in indefinite survival, was induced in tumor-bearing mice immunized with cells transfected with this gene fragment.

Immunostimulatory monoclonal antibodies for cancer therapy

Increasing immune responses with immunostimulatory monoclonal antibodies (mAbs) directed to immune-receptor molecules is a new and exciting strategy in cancer therapy. This expanding class of agents functions on crucial receptors, either antagonizing those that suppress immune responses or activating others that amplify immune responses. Complications such as autoimmunity and systemic inflammation are problematic side effects associated with these agents. However, promising synergy has been observed in preclinical models using combinations of immunostimulatory antibodies and other immunotherapy strategies or conventional cancer therapies. Importantly, mAbs of this type have now entered clinical trials with encouraging initial results.

Enhanced antitumor effect against human telomerase reverse transcriptase (hTERT) by vaccination with chemotactic-hTERT gene-modified tumor cell and the combination with anti-4-1BB monoclonal antibodies

Human telomerase reverse transcriptase (hTERT) represents an attractive target for cancer immunotherapy because hTERT is reactivated in most human tumors. In an attempt to develop an effective vaccine against most human cancers, we constructed chemotactic-hTERT vaccine. Two hTERT fragments encoding multiple cytotoxic T lymphocyte and T helper cell epitopes were fused as a tumor antigen (named Te). The plasmid based DNA vaccine (pCCL21-Te-Fc) was constructed by linking human CCL21 and IgG Fc gene sequences to each end of Te. In poorly immunogenic B16F10 mouse melanoma model, DNA (pCCL21-Te-Fc) vaccination significantly inhibited tumor growth and all of the mice were dead by day 52. The immunization with pCCL21-Te-Fc-modified tumor cells (B16/CCL21-Te-Fc) resulted in a higher antitumor effect than DNA vaccination and 25% of tumor-bearing mice achieved long-term survival (> 120 days). The combined therapy of B16/CCL21-Te-Fc plus anti-4-1BB MAbs further enhanced the immune response, resulting in 75% of tumor-bearing mice achieved long-term survival (> 120 days) in subcutaneous model and few lung nodules in pulmonary metastasis model. Rechallenge experiment showed that a persistent memory response was successfully induced by the combined therapy. In vivo depletion of lymphocytes indicated that CD8+ T cells were essential in the antitumor activity induced by B16/CCL21-Te-Fc plus anti-4-1BB MAbs, whereas NK cells and CD4+ T cells played substantial roles. The CTL activity induced by pCCL21-Te-Fc-transfected PBMCs specifically lysed a variety of human leukocyte antigen-matched and hTERT-positive human tumor cells, suggesting pCCL21-Te-Fc could serve as a vaccine against most human cancers.

Activity of DNA vaccines encoding self or heterologous Her-2/neu in Her-2 or neu transgenic mice

To assess the efficacy of self versus heterologous ErbB-2 vaccines, the reactivity to human and rat ErbB-2 (Her-2 and neu, respectively) DNA vaccines were tested in normal, Her-2 or neu transgenic mice. When immunized with either Her-2 or neu DNA, normal BALB/c and C57BL/6 mice produced cross-reactive T cells, but only antigen specific antibodies. In Her-2 Tg mice, weak to no anti-Her-2 response was induced by either self Her-2 or heterologous neu DNA, demonstrating profound tolerance to Her-2 and the inability to induce anti-Her-2 immunity with either vaccine. In NeuT mice, vaccination with self neu but not heterologous Her-2 DNA induced anti-neu antibodies and delayed spontaneous tumorigenesis. Both neu and Her-2 DNA induced anti-neu T cell response, but depletion of CD8 T cells did not change the delay in tumorigenesis. Therefore, in NeuT mice, both self and heterologous DNA activated anti-neu T cells, although T cell response did not reach sufficient level to suppress spontaneous tumorigenesis. Rather, induction of anti-neu antibodies by self neu DNA is associated with the delay in spontaneous tumor growth. Overall, NeuT mice were more responsive to DNA vaccination than Her-2 Tg mice and this may be associated with the continuous production of neu by the 10 mammary glands undergoing tumor progression.

Immunosuppression in melanoma immunotherapy: potential opportunities for intervention

Although melanomas are substantially more immunogenic than other tumors, current immunotherapeutic approaches for melanoma patients have met with only limited success. Although melanoma-specific CD8+ T-cell responses can often be generated in patients naturally or through vaccination regimens, tumors frequently continue to grow unabated, suggesting that tumor-specific immune responses may be actively dampened in vivo. Research over the past decade has brought to light several mechanisms used by melanomas and other tumors to suppress tumor-specific immune responses. These include the presence of regulatory immune cells within the tumor microenvironment and draining lymph nodes that serve to shut down effector T-cell function. In addition, melanoma tumors themselves express a number of soluble and membrane-bound molecules that are responsible for inhibiting activated immune cells. The identification of these suppressive mechanisms has provided significant opportunities for designing novel therapeutic interventions that could augment current vaccination and adoptive transfer approaches for treatment of melanoma.

OX40 ligation of CD4+ T cells enhances virus-specific CD8+ T cell memory responses independently of IL-2 and CD4+ T regulatory cell inhibition

We have previously shown that CD4(+) T cells are required to optimally expand viral-specific memory CD8(+) CTL responses using a human dendritic cell-T cell-based coculture system. OX40 (CD134), a 50-kDa transmembrane protein of the TNFR family, is expressed primarily on activated CD4(+) T cells. In murine models, the OX40/OX40L pathway has been shown to play a critical costimulatory role in dendritic cell/T cell interactions that may be important in promoting long-lived CD4(+) T cells, which subsequently can help CD8(+) T cell responses. The current study examined whether OX40 ligation on ex vivo CD4(+) T cells can enhance their ability to "help" virus-specific CTL responses in HIV-1-infected and -uninfected individuals. OX40 ligation of CD4(+) T cells by human OX40L-IgG1 enhanced the ex vivo expansion of HIV-1-specific and EBV-specific CTL from HIV-1-infected and -uninfected individuals, respectively. The mechanism whereby OX40 ligation enhanced help of CTL was independent of the induction of cytokines such as IL-2 or any inhibitory effect on CD4(+) T regulatory cells, but was associated with a direct effect on proliferation of CD4(+) T cells. Thus, OX40 ligation on CD4(+) T cells represents a potentially novel immunotherapeutic strategy that should be investigated to treat and prevent persistent virus infections, such as HIV-1 infection.

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.

Identification of Cross-Reactive Peptides Using Combinatorial Libraries Circumvents Tolerance against Her-2/neu-Immunodominant Epitope

The majority of the currently defined tumor-associated Ags are often overexpressed products of normal cellular genes. Therefore, tolerance deletes high-affinity T cells directed against the TAAs, leaving only a low-affinity repertoire. We have demonstrated previously that the T cell repertoire against the immunodominant p773-782 A2.1-Her-2/neu-restricted peptide has low affinity in A2xneu mice (Her-2/neu mice crossed with A2.1/Kb mice), compared with A2xFVB mice (A2.1/Kb crossed with FVB-wild-type mice). Immunizations with this peptide have a minor impact in preventing tumor growth in A2xneu mice. Therefore, attempts to expand these responses may be of little clinical value. We hypothesized that if not all possible cross-reactive peptides (CPs) are naturally processed and presented, the possibility exists that T cells against these CPs persist in the repertoire and can be used to induce antitumor responses with higher avidity against native epitopes present on the tumor cells. We have used the positional scanning synthetic peptide combinatorial library methodology to screen the p773-782 T cell clone. The screening data identified potential amino acids that can be substituted in the primary sequences of the p773-782 peptide. The designed CPs induce CTL responses of higher affinity in A2xneu mice compared with the native p773-783 peptide. These CTLs recognize A2+-Her-2/neu(+) tumors with high efficiency. Moreover, multiple immunizations with CPs significantly prolonged the survival of tumor-bearing A2xneu mice. These results have demonstrated that it was possible to circumvent tolerance with the identification of CPs and that these peptides could be of significant clinical value.