Tumor antigen-specific FOXP3+ CD4 T cells identified in human metastatic melanoma: peptide vaccination results in selective expansion of Th1-like counterparts

Impact of Immunotherapy on CD4 T Cell Phenotypes and Function in Cancer

Immunotherapy has become a standard treatment in many cancers and it is based on three main therapeutic axes: immune checkpoint blockade (ICB), vaccination and adoptive cell transfer (ACT). If originally these therapies mainly focused on exploiting CD8 T cells given their role in the direct elimination of tumor cells, increasing evidence highlights the crucial role CD4 T cells play in the antitumor immune response. Indeed, these cells can profoundly modulate the tumor microenvironment (TME) by secreting different types of cytokine or by directly eliminating cancer cells. In this review, we describe how different CD4 T cell subsets can contribute to tumor immune responses during immunotherapy and the novel high-throughput immune monitoring tools that are expected to facilitate the study of CD4 T cells, at antigen-specific and single cell level, thus accelerating bench-to-bed translational research in cancer.

The Future of Cancer Diagnosis, Treatment and Surveillance: A Systemic Review on Immunotherapy and Immuno-PET Radiotracers

Immunotherapy is an effective therapeutic option for several cancers. In the last years, the introduction of checkpoint inhibitors (ICIs) has shifted the therapeutic landscape in oncology and improved patient prognosis in a variety of neoplastic diseases. However, to date, the selection of the best patients eligible for these therapies, as well as the response assessment is still challenging. Patients are mainly stratified using an immunohistochemical analysis of the expression of antigens on biopsy specimens, such as PD-L1 and PD-1, on tumor cells, on peritumoral immune cells and/or in the tumor microenvironment (TME). Recently, the use and development of imaging biomarkers able to assess in-vivo cancer-related processes are becoming more important. Today, positron emission tomography (PET) with 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) is used routinely to evaluate tumor metabolism, and also to predict and monitor response to immunotherapy. Although highly sensitive, FDG-PET in general is rather unspecific. Novel radiopharmaceuticals (immuno-PET radiotracers), able to identify specific immune system targets, are under investigation in pre-clinical and clinical settings to better highlight all the mechanisms involved in immunotherapy. In this review, we will provide an overview of the main new immuno-PET radiotracers in development. We will also review the main players (immune cells, tumor cells and molecular targets) involved in immunotherapy. Furthermore, we report current applications and the evidence of using [18F]FDG PET in immunotherapy, including the use of artificial intelligence (AI).

High-throughput Screening of Human Tumor Antigen-specific CD4 T Cells, Including Neoantigen-reactive T Cells

PURPOSE

Characterization of tumor antigen-specific CD4 T-cell responses in healthy donors and malignant melanoma patients using an in vitro amplified T-cell library screening procedure.

PATIENTS AND METHODS

A high-throughput, human leukocyte antigen (HLA)-independent approach was used to estimate at unprecedented high sensitivity level precursor frequencies of tumor antigen- and neoantigen-specific CD4 T cells in healthy donors and patients with cancer. Frequency estimation was combined with isolation and functional characterization of identified tumor-reactive CD4 T-cell clones.

RESULTS

In healthy donors, we report frequencies of naïve tumor-associated antigen (TAA)-specific CD4 T cells comparable with those of CD4 T cells specific for infectious agents (Tetanus toxoid). Interestingly, we also identified low, but consistent numbers of memory CD4 T cells specific for several TAAs. In patients with melanoma, low frequencies of circulating TAA-specific CD4 T cells were detected that increased after peptide-based immunotherapy. Such antitumor TAA-specific CD4 T-cell responses were also detectable within the tumor-infiltrated tissues. TAA-specific CD4 T cells in patients displayed a highly polyfunctional state, with partial skewing to Type-2 polarization. Finally, we report the applicability of this approach to the detection and amplification of neoantigen-specific CD4 T cells.

CONCLUSIONS

This simple, noninvasive, high-throughput screening of tumor- and neoantigen-specific CD4 T cells requires little biologic material, is HLA class II independent and allows the concomitant screening for a large number of tumor antigens of interest, including neoantigens. This approach will facilitate the immunomonitoring of preexisting and therapy-induced CD4 T-cell responses, and accelerate the development of CD4 T-cell-based therapies.

Regulatory T Cells in Ovarian Cancer Are Characterized by a Highly Activated Phenotype Distinct from that in Melanoma

Purpose: Regulatory T (Treg) cells expressing the transcription factor FOXP3 are essential for the maintenance of immunologic self-tolerance but play a detrimental role in most cancers due to their ability to suppress antitumor immunity. The phenotype of human circulating Treg cells has been extensively studied, but less is known about tumor-infiltrating Treg cells. We studied the phenotype and function of tumor-infiltrating Treg cells in ovarian cancer and melanoma to identify potential Treg cell-associated molecules that can be targeted by tumor immunotherapies.Experimental Design: The phenotype of intratumoral and circulating Treg cells was analyzed by multicolor flow cytometry, mass cytometry, RNA-seq, and functional assays.Results: Treg cells isolated from ovarian tumors displayed a distinct cell surface phenotype with increased expression of a number of receptors associated with TCR engagement, including PD-1, 4-1BB, and ICOS. Higher PD-1 and 4-1BB expression was associated with increased responsiveness to further TCR stimulation and increased suppressive capacity, respectively. Transcriptomic and mass cytometry analyses revealed the presence of Treg cell subpopulations and further supported a highly activated state specifically in ovarian tumors. In comparison, Treg cells infiltrating melanomas displayed lower FOXP3, PD-1, 4-1BB, and ICOS expression and were less potent suppressors of CD8 T-cell proliferation.Conclusions: The highly activated phenotype of ovarian tumor-infiltrating Treg cells may be a key component of an immunosuppressive tumor microenvironment. Receptors that are expressed by tumor-infiltrating Treg cells could be exploited for the design of novel combination tumor immunotherapies. Clin Cancer Res; 24(22); 5685-96. ©2018 AACR.

A phase 1 trial extension to assess immunologic efficacy and safety of prime-boost vaccination with VXM01, an oral T cell vaccine against VEGFR2, in patients with advanced pancreatic cancer

VXM01 is a first-in-kind orally applied tumor vaccine based on live attenuated Salmonella typhi carrying an expression plasmid encoding VEGFR2, an antigen expressed on tumor vasculature and a stable and accessible target for anti-angiogenic intervention. A recent randomized, placebo-controlled, phase I dose-escalation trial in advanced pancreatic cancer patients demonstrated safety, immunogenicity and transient, T-cell response-related anti-angiogenic activity of four priming vaccinations applied within one week. We here evaluated whether monthly boost vaccinations are safe and can sustain increased frequencies of vaccine-specific T cells. Patients with advanced pancreatic cancer were randomly assigned at a ratio of 2:1 to priming with VXM01 followed by up to six monthly boost vaccinations, or placebo treatment. Vaccinations were applied orally at two alternative doses of either 10⁶ colony-forming units (CFU) or 10⁷ CFU, and concomitant treatment with standard-of-care gemcitabine during the priming phase, and any treatment thereafter, was allowed in the study. Immunomonitoring involved interferon-gamma (IFNγ) ELIspot analysis with long overlapping peptides spanning the entire VEGFR2 sequence. A total of 26 patients were treated. Treatment-related adverse events preferentially associated with VXM01 were decreases in lymphocyte numbers in the blood, increased frequencies of neutrophils and diarrhea. Eight out of 16 patients who received at least one boosting vaccination responded with pronounced, i.e. at least 3-fold, increase in VEGFR2-specific T cell response over baseline levels. In the VXM01 vaccination group, VEGFR2-specific T cells peaked preferentially during the boosting phase with an average 4-fold increase over baseline levels. In conclusion, prime/boost vaccination with VXM01 was safe and immunogenic and increased vaccine specific T cell responses compared with placebo treatment.

Ontogeny of Tumor-associated CD4+CD25+Foxp3+ T-regulatory Cells

The critical contribution of CD4+CD25+Foxp3+ T-regulatory cells (Treg) to immune suppression in the tumor microenvironment is well-established. Whereas the mechanisms that drive the generation and accumulation of Treg in tumors have been an active area of study, the information on their origin and population dynamics remains limited. In this review, we discuss the ontogeny of tumor-associated Treg in light of the recently identified lineage markers.

Vaccination of stage III/IV melanoma patients with long NY-ESO-1 peptide and CpG-B elicits robust CD8+ and CD4+ T-cell responses with multiple specificities including a novel DR7-restricted epitope

Long synthetic peptides and CpG-containing oligodeoxynucleotides are promising components for cancer vaccines. In this phase I trial, 19 patients received a mean of 8 (range 1-12) monthly vaccines s.c. composed of the long synthetic NY-ESO-1_79-108 peptide and CpG-B (PF-3512676), emulsified in Montanide ISA-51. In 18/18 evaluable patients, vaccination induced antigen-specific CD8⁺ and CD4⁺ T-cell and antibody responses, starting early after initiation of immunotherapy and lasting at least one year. The T-cells responded antigen-specifically, with strong secretion of IFNγ and TNFα, irrespective of patients' HLAs. The most immunogenic regions of the vaccine peptide were NY-ESO-1_89-102 for CD8⁺ and NY-ESO-1_83-99 for CD4⁺ T-cells. We discovered a novel and highly immunogenic epitope (HLA-DR7/NY-ESO-1_87-99); 7/7 HLA-DR7⁺ patients generated strong CD4⁺ T-cell responses, as detected directly ex vivo with fluorescent multimers. Thus, vaccination with the long synthetic NY-ESO-1_79-108 peptide combined with the strong immune adjuvant CpG-B induced integrated, robust and functional CD8⁺ and CD4⁺ T-cell responses in melanoma patients, supporting the further development of this immunotherapeutic approach.

Short Peptide Vaccine Induces CD4+ T Helper Cells in Patients with Different Solid Cancers

Previous cancer vaccination trials often aimed to activate CD8(+) cytotoxic T-cell (CTL) responses with short (8-10mer) peptides and targeted CD4(+) helper T cells (TH) with HLA class II-binding longer peptides (12-16 mer) that were derived from tumor antigens. Accordingly, a study of immunomonitoring focused on the detection of CTL responses to the short, and TH responses to the long, peptides. The possible induction of concurrent TH responses to short peptides was widely neglected. In a recent phase I vaccination trial, 53 patients with different solid cancers were vaccinated with EMD640744, a cocktail of five survivin-derived short (9- or 10-mer) peptides in Montanide ISA 51VG. We monitored 49 patients and found strong CD8(+) T-cell responses in 63% of the patients. In addition, we unexpectedly found CD4(+) TH cell responses against at least two of the five short peptides in 61% (23/38) of the patients analyzed. The two peptides were recognized by HLA-DP4- and HLA-DR-restricted TH1 cells. Some short peptide-reactive (sp)CD4 T cells showed high functional avidity. Here, we show that a short peptide vaccine is able to activate a specific CD4(+) T-cell repertoire in many patients, facilitating a strong combined CD4(+)/CD8(+) T-cell response.

High-throughput monitoring of human tumor-specific T-cell responses with large peptide pools

In immune intervention trials, the comprehensive investigation of immunogenicity or T-cell epitope-mapping is challenging especially when a large set of epitopes needs to be screened and limited sample material is available. To this end, T-cell responses are often monitored using peptide pools. Here, we assessed the magnitude and sensitivity of detection of antigen-specific CD8⁺ and CD4⁺ T cells using a single peptide alone or mixed into large pools. Interestingly the magnitude of ex vivo anti-viral and anti-tumor T-cell responses was identical irrespective of the presence and number of irrelevant peptides, in different functional assays with PBMCs from healthy donors and cancer patients. Moreover, the presence of up to 300 irrelevant peptides did not affect the threshold of responsiveness of antigen-specific CD8⁺ T cells to single cognate peptides. These data demonstrate the relevance of using very large peptide pools for the sensitive and specific immune-monitoring of epitope-specific T cells in natural or immune-modulated context.

High-throughput epitope discovery reveals frequent recognition of neo-antigens by CD4+ T cells in human melanoma

Tumor-specific neo-antigens that arise as a consequence of mutations are thought to be important for the therapeutic efficacy of cancer immunotherapies. Accumulating evidence suggests that neo-antigens may be commonly recognized by intratumoral CD8+ T cells, but it is unclear whether neo-antigen-specific CD4+ T cells also frequently reside within human tumors. In view of the accepted role of tumor-specific CD4+ T-cell responses in tumor control, we addressed whether neo-antigen-specific CD4+ T-cell reactivity is a common property in human melanoma.

Opportunistic Autoimmune Disorders Potentiated by Immune-Checkpoint Inhibitors Anti-CTLA-4 and Anti-PD-1

To improve the efficacy of immunotherapy for cancer and autoimmune diseases, recent ongoing and completed clinical trials have focused on specific targets to redirect the immune network toward eradicating a variety of tumors and ameliorating the self-destructive process. In a previous review, both systemic immunomodulators and monoclonal antibodies (mAbs), anti-CTLA-4, and anti-CD52, were discussed regarding therapeutics and autoimmune sequelae, as well as predisposing factors known to exacerbate immune-related adverse events (irAEs). This review will focus on immune-checkpoint inhibitors, and the data from most clinical trials involve blockade with anti-CTLA-4 such as ipilimumab. However, despite the mild to severe irAEs observed with ipilimumab in ~60% of patients, overall survival (OS) averaged ~22-25% at 3-5 years. To boost OS, other mAbs targeting programed death-1 and its ligand are undergoing clinical trials as monotherapy or dual therapy with anti-CTLA-4. Therapeutic combinations may generate different spectrum of opportunistic autoimmune disorders. To simulate clinical scenarios, we have applied regulatory T cell perturbation to murine models combined to examine the balance between thyroid autoimmunity and tumor-specific immunity.

Identification of CDCA1-derived long peptides bearing both CD4+ and CD8+ T-cell epitopes: CDCA1-specific CD4+ T-cell immunity in cancer patients

We recently identified a novel cancer-testis antigen, cell division cycle associated 1 (CDCA1) using genome-wide cDNA microarray analysis, and CDCA1-derived cytotoxic T lymphocyte (CTL)-epitopes. In this study, we attempted to identify CDCA1-derived long peptides (LPs) that induce both CD4+ helper T (Th) cells and CTLs. We combined information from a recently developed computer algorithm predicting HLA class II-binding peptides with CDCA1-derived CTL-epitope sequences presented by HLA-A2 (A*02:01) or HLA-A24 (A*24:02) to select candidate CDCA1-LPs encompassing both Th cell epitopes and CTL-epitopes. We studied the immunogenicity of CDCA1-LPs and the cross-priming potential of LPs bearing CTL-epitopes in both human in vitro and HLA-class I transgenic mice in vivo. Then we analyzed the Th cell response to CDCA1 in head-and-neck cancer (HNC) patients before and after vaccination with a CDCA1-derived CTL-epitope peptide using IFN-γ enzyme-linked immunospot assays. We identified two CDCA1-LPs, CDCA1(39–64)-LP and CDCA1(55–78)-LP, which encompass naturally processed epitopes recognized by Th cells and CTLs. CDCA1-specific CTLs were induced through cross-presentation of CDCA1-LPs in vitro and in vivo. In addition, CDCA1-specific Th cells enhanced induction of CDCA1-specific CTLs. Furthermore, significant frequencies of CDCA1-specific Th cell responses were detected after short-term in vitro stimulation of peripheral blood mononuclear cells (PBMCs) with CDCA1-LPs in HNC patients (CDCA1(39–64)-LP, 74%; CDCA1(55–78)-LP, 68%), but not in healthy donors. These are the first results demonstrating the presence of CDCA1-specific Th cell responses in HNC patients and underline the possible utility of CDCA1-LPs for propagation of both CDCA1-specific Th cells and CTLs.

AE37 peptide vaccination in prostate cancer: a 4-year immunological assessment updates on a phase I trial

In our recent phase I trial, we demonstrated that the AE37 vaccine is safe and induces HER-2/neu-specific immunity in a heterogeneous population of HER-2/neu (+) prostate cancer patients. Herein, we tested whether one AE37 boost can induce long-lasting immunological memory in these patients. Twenty-three patients from the phase I study received one AE37 boost 6-month post-primary vaccinations. Local/systemic toxicities were evaluated following the booster injection. Immunological responses were monitored 1-month (long-term booster; LTB) and 3-year (long-term immunity; LTI) post-booster by delayed-type hypersensitivity, IFN-γ ELISPOT and proliferation assays. Regulatory T cell (Treg) frequencies, plasma transforming growth factor-β (TGF-β) and indoleamine 2,3-deoxygenase (IDO) activity levels were also determined at the same time points. The AE37 booster was safe and well tolerated. Immunological monitoring revealed vaccine-specific long-term immunity in most of the evaluated patients during both LTB and LTI, although individual levels of immunity during LTI were decreased compared with those measured 3 years earlier during LTB. This was paralleled with increased Tregs, TGF-β levels and IDO activity. One AE37 booster generated long-term immunological memory in HER-2/neu (+) prostate cancer patients, which was detectable 3 years later, albeit with a tendency to decline. Boosted patients had favorable clinical outcome in terms of overall and/or metastasis-free survival compared with historical groups with similar clinical characteristics at diagnosis. We suggest that more boosters and/or concomitant disarming of suppressor circuits may be necessary to sustain immunological memory, and therefore, further studies to optimize the AE37 booster schedule are warranted.

Adjuvants that improve the ratio of antigen-specific effector to regulatory T cells enhance tumor immunity

Antitumor immunity is strongly influenced by the balance of tumor antigen-specific effector T cells (Teff) and regulatory T cells (Treg). However, the impact that vaccine adjuvants have in regulating the balance of antigen-specific T-cell populations is not well understood. We found that antigen-specific Tregs were induced following subcutaneous vaccination with either OVA or melanoma-derived peptides, with a restricted expansion of Teffs. Addition of the adjuvants CpG-ODN or Poly(I:C) preferentially amplified Teffs over Tregs, dramatically increasing the antigen-specific Teff:Treg ratios and inducing polyfunctional effector cells. In contrast, two other adjuvants, imiquimod and Quil A saponin, favored an expansion of antigen-specific Tregs and failed to increase Teff:Treg ratios. Following therapeutic vaccination of tumor-bearing mice, high ratios of tumor-specific Teffs:Tregs in draining lymph nodes were associated with enhanced CD8(+) T-cell infiltration at the tumor site and a durable rejection of tumors. Vaccine formulations of peptide+CpG-ODN or Poly(I:C) induced selective production of proinflammatory type I cytokines early after vaccination. This environment promoted CD8(+) and CD4(+) Teff expansion over that of antigen-specific Tregs, tipping the Teff to Treg balance to favor effector cells. Our findings advance understanding of the influence of different adjuvants on T-cell populations, facilitating the rational design of more effective cancer vaccines.

Convergences and divergences of thymus- and peripherally derived regulatory T cells in cancer

The expansion of regulatory T cells (T_reg) is a common event characterizing the vast majority of human and experimental tumors and it is now well established that T_reg represent a crucial hurdle for a successful immunotherapy. T_reg are currently classified, according to their origin, into thymus-derived T_reg (tT_reg) or peripherally induced T_reg (pT_reg) cells. Controversy exists over the prevalent mechanism accounting for T_reg expansion in tumors, since both tT_reg proliferation and de novo pT_reg differentiation may occur. Since tT_reg and pT_reg are believed as preferentially self-specific or broadly directed to non-self and tumor-specific antigens, respectively, the balance between tT_reg and pT_reg accumulation may impact on the repertoire of antigen specificities recognized by T_reg in tumors. The prevalence of tT_reg or pT_reg may also affect the outcome of immunotherapies based on tumor-antigen vaccination or T_reg depletion. The mechanisms dictating pT_reg induction or tT_reg expansion/stability are a matter of intense investigation and the most recent results depict a complex landscape. Indeed, selected T_reg subsets may display peculiar characteristics in terms of stability, suppressive function, and cytokine production, depending on microenvironmental signals. These features may be differentially distributed between pT_reg and tT_reg and may significantly affect the possibility of manipulating T_reg in cancer therapy. We propose here that innovative immunotherapeutic strategies may be directed at diverting unstable/uncommitted T_reg, mostly enriched in the pT_reg pool, into tumor-specific effectors, while preserving systemic immune tolerance ensured by self-specific tT_reg.

Modulation of regulatory T cell function by monocyte-derived dendritic cells matured through electroporation with mRNA encoding CD40 ligand, constitutively active TLR4, and CD70

Regulatory T cells (Tregs) counteract anticancer immune responses through a number of mechanisms, limiting dendritic cell (DC)-based anticancer immunotherapy. In this study, we investigated the influence of various DC activation stimuli on the Treg functionality. We compared DCs activated by electroporation with mRNA encoding constitutively active TLR4 (caTLR4) and CD40 ligand (DiMix-DCs), or these factors together with mRNA encoding the costimulatory molecule CD70 (TriMix-DCs) with DCs maturated in the presence of a mixture of inflammatory cytokines (DCs maturated with a combination of the cytokines IL-1β, IL-6, TNF-α, and PGE2) for their ability to counteract Tregs on different levels. We first demonstrated that there was no difference in the extent of Treg induction starting from CD4(+)CD25(-) T cells under the influence of the different DC maturation stimuli. Second, we showed that both DiMix- and TriMix-DCs could partly alleviate Treg inhibition of CD8(+) T cells. Third, we observed that CD8(+) T cells that had been precultured with DiMix-DCs or TriMix-DCs were partially protected against subsequent Treg suppression. Finally, we showed that Tregs cocultured in the presence of TriMix-DCs, but not DiMix-DCs, partially lost their suppressive capacity. This was accompanied by a decrease in CD27 and CD25 expression on Tregs, as well as an increase in the expression of T-bet and secretion of IFN-γ, TNF-α, and IL-10, suggesting a shift of the Treg phenotype toward a Th1 phenotype. In conclusion, these data suggest that TriMix-DCs are not only able to suppress Treg functions, but moreover could be able to reprogram Tregs to Th1 cells under certain circumstances.

HLA Class II tetramers reveal tissue-specific regulatory T cells that suppress T-cell responses in breast carcinoma patients

Regulatory T cells (Tregs) play an important role in controlling antitumor T-cell responses and hence represent a considerable obstacle for cancer immunotherapy. The abundance of specific Treg populations in cancer patients has been poorly analyzed so far. Here, we demonstrate that in breast cancer patients, Tregs often control spontaneous effector memory T-cell responses against mammaglobin, a common breast tissue-associated antigen that is overexpressed by breast carcinoma. Using functional assays, we identified a HLA-DRB1*04:01- and HLA-DRB1*07:01-restricted epitope of mammaglobin (mam_34–48) that was frequently recognized by Tregs isolated from breast cancer patients. Using mam_34–48-labeled HLA Class II tetramers, we quantified mammaglobin-specific Tregs and CD4⁺ conventional T (Tcon) cells in breast carcinoma patients as well as in healthy individuals. Both mammaglobin-specific Tregs and Tcon cells were expanded in breast cancer patients, each constituting approximately 0.2% of their respective cell subpopulations. Conversely, mammaglobin-specific Tregs and CD4⁺ Tcon cells were rare in healthy individuals (0.07%). Thus, we provide here for the first time evidence supporting the expansion of breast tissue-specific Tregs and CD4⁺ Tcon cells in breast cancer patients. In addition, we substantiate the potential implications of breast tissue-specific Tregs in the suppression of antitumor immune responses in breast cancer patients. The HLA Class II tetramers used in this study may constitute a valuable tool to elucidate the role of antigen-specific Tregs in breast cancer immunity and to monitor breast cancer-specific CD4⁺ T cells.

Effects of cyclophosphamide and IL-2 on regulatory CD4+ T cell frequency and function in melanoma patients vaccinated with HLA-class I peptides: impact on the antigen-specific T cell response

The frequency and function of regulatory T cells (Tregs) were studied in stage II–III melanoma patients who were enrolled in a phase II randomized trial of vaccination with HLA-A*0201-modified tumor peptides versus observation. The vaccinated patients received low-dose cyclophosphamide (CTX) and low-dose interleukin-2 (IL-2). Tregs were analyzed in the lymph nodes (LNs) of stage III patients who were undergoing complete lymph node dissection and in peripheral blood mononuclear cells (PBMCs) collected before vaccination and at different time points during the vaccination period. The LNs of the vaccinated patients, which were surgically removed after two rounds of vaccination and one dose of CTX, displayed a low frequency of Tregs and a less immunosuppressive environment compared with those of the untreated patients. The accurate time-course analysis of the PBMCs of patients enrolled in the vaccination arm indicated a limited and transient modulation in the frequencies of Tregs in PBMCs collected after low-dose CTX administration and a strong Treg boost in those PBMCs collected after low-dose IL-2 administration. However, a fraction of the IL-2-boosted Tregs was functionally modulated to a Th-1-like phenotype in the vaccinated patients. Moreover, low-dose IL-2 promoted the concomitant expansion of conventional activated CD4⁺ T cells. Despite the amplification of Tregs, IL-2 administration maintained or further increased the number of antigen-specific CD8⁺ T cells that were induced by vaccination as demonstrated by the ex vivo human leukocyte antigen-multimer staining and IFN-γ ELISpot assays. Our study suggests that the use of CTX as a Treg modulator should be revised in terms of the administration schedule and of patients who may benefit from this drug treatment. Despite the Treg expansion that was observed in this study, low-dose IL-2 is not detrimental to the functional activities of vaccine-primed CD8⁺ T cell effectors when used in the inflammatory environment of vaccination.

Basic principles of tumor-associated regulatory T cell biology

Due to the critical role of forkhead box (Fox)p3(+) regulatory T cells (Tregs) in the regulation of immunity and the enrichment of Tregs within many human tumors, several emerging therapeutic strategies for cancer involve the depletion or modulation of Tregs, with the aim of eliciting enhanced antitumor immune responses. Here, we review recent advances in understanding of the fundamental biology of Tregs, and discuss the implications of these findings for current models of tumor-associated Treg biology. In particular, we discuss the context-dependent functional diversity of Tregs, the developmental origins of these cells, and the nature of the antigens that they recognize within the tumor environment. In addition, we highlight critical areas of focus for future research.

Blockade of Myd88 signaling induces antitumor effects by skewing the immunosuppressive function of myeloid-derived suppressor cells

Myd88 is an important adaptor molecule for the activation of NADPH oxidase and arginase-1, which are responsible for the suppressive function of myeloid-derived suppressor cells (MDSCs). When wild-type and Myd88(-/-) mice were subcutaneously injected with CT26 colon cancer cells expressing human Her-2/neu, tumor growth was retarded in Myd88(-/-) mice than in wild-type mice. Although the generation of CD11b(+) Gr-1(+) MDSCs was less in Myd88(-/-) mice than in wild-type mice, Myd88(-/-) mice having tumor masses still had significant quantities of MDSCs, suggesting that MDSC generation might be independent of Myd88 signaling. However, MDSCs obtained from tumor-bearing Myd88(-/-) mice failed to suppress antigen-specific proliferation of CD8(+) T cells and CD4(+) T cells, whereas MDSCs from wild-type mice significantly suppressed both types of T cells. Consistent with this, we found that the levels of costimulatory molecules and MHC class II were significantly increased in MDSCs obtained from Myd88(-/-) mice compared with wild-type mice after tumor challenge. Furthermore, CD4(+) T cells residing in tumor-draining lymph nodes of Myd88(-/-) mice secreted more TNF-α than those of wild-type mice. Finally, the blockade of Myd88 signaling by treatment with Myd88 inhibitory peptide, during later tumor stages, significantly inhibited the growth of immunogenic tumors. Overall, these data suggest that signaling through the Myd88 adaptor molecule is critical for the direct suppressive function of MDSCs and approaches to block Myd88-mediated signaling in MDSCs might be effective to inhibit the immunosuppressive function of MDSCs.

A cancer vaccine induces expansion of NY-ESO-1-specific regulatory T cells in patients with advanced melanoma

Cancer vaccines are designed to expand tumor antigen-specific T cells with effector function. However, they may also inadvertently expand regulatory T cells (Treg), which could seriously hamper clinical efficacy. To address this possibility, we developed a novel assay to detect antigen-specific Treg based on down-regulation of surface CD3 following TCR engagement, and used this approach to screen for Treg specific to the NY-ESO-1 tumor antigen in melanoma patients treated with the NY-ESO-1/ISCOMATRIX^TM cancer vaccine. All patients tested had Treg (CD25^bright FoxP3⁺ CD127^neg) specific for at least one NY-ESO-1 epitope in the blood. Strikingly, comparison with pre-treatment samples revealed that many of these responses were induced or boosted by vaccination. The most frequently detected response was toward the HLA-DP4-restricted NY-ESO-1_157–170 epitope, which is also recognized by effector T cells. Notably, functional Treg specific for an HLA-DR-restricted epitope within the NY-ESO-1_115–132 peptide were also identified at high frequency in tumor tissue, suggesting that NY-ESO-1-specific Treg may suppress local anti-tumor immune responses. Together, our data provide compelling evidence for the ability of a cancer vaccine to expand tumor antigen-specific Treg in the setting of advanced cancer, a finding which should be given serious consideration in the design of future cancer vaccine clinical trials.

Adoptive transfer with high-affinity TCR to treat human solid tumors: how to improve the feasibility?

The adoptive transfer of tumor antigen-specific T cells recently achieved clinical efficacy for a fraction of melanoma patients refractory to other therapies. Unfortunately, the application of this strategy to the remaining melanoma and most other cancer patients is hampered by the difficulty to generate high-affinity tumor-reactive T cells. Two strategies are currently developed to extend the feasibility of this therapeutic approach: clinical grade tool production for MHC-peptide multimer-driven sorting of antigen-specific T cells from the endogenous peripheral T cell repertoire and de novo engineering of the missing repertoire by genetic transfer of cloned specific T cell receptor (TCR) into T cells. The expected multiplication of adoptive transfer treatments, by these strategies, and their careful evaluation should enable the cure of a number of otherwise compromised cancer patients and to gain insight into the characteristics of transferred T cells best fitted to eradicate tumor cells, in terms of antigen specificities, phenotype, and functions. In particular, identification of tumor-rejection antigens by this approach would improve the design and efficacy of all immunotherapeutic approaches.

Melanoma vaccines: developments over the past 10 years

Decades of preclinical evaluation and clinical trials into melanoma vaccines have yielded spectacular progress in our understanding of melanoma antigens and the immune mechanisms of tumor rejection. Key insights and the results of their clinical evaluation are reviewed in this article. Unfortunately, durable clinical benefit following vaccination remains uncommon. Two recent clinical advances that will impact on melanoma vaccine development are trials with inhibitors of CTLA-4 and oncogenic BRAF. Long-term therapeutic control of melanoma will require integration of specific active immunotherapy with these emerging successful therapies from the disparate fields of immune regulation and signal transduction.

Tumor vaccines and beyond

For the last two decades the immunotherapy of patients with solid and hematopoietic tumors has met with variable success. We have reviewed the field of tumor vaccines to examine what has worked and what has not, why this has been the case, how the anti-tumor responses were examined, and how we can make tumor immunity successful for the majority of individuals rather than for the exceptional patients who currently show successful immune responses against their tumors.

Repeated PR1 and WT1 peptide vaccination in Montanide-adjuvant fails to induce sustained high-avidity, epitope-specific CD8+ T cells in myeloid malignancies

BACKGROUND

We previously showed that vaccination with one dose of PR1 and WT1 peptides induces transient anti-leukemia immunity. We hypothesized that maintenance of a sustained anti-leukemia response may require frequent boost injections.

DESIGN AND METHODS

Eight patients with myeloid malignancies were enrolled in this phase II study, and 6 completed 6 injections of PR1 and WT1 peptides in Montanide-adjuvant with GM-CSF, every two weeks.

RESULTS

Both high- and low-avidity PR1 or WT1-specific CD8(+) T cells were detected in all evaluable patients after the first vaccine dose. Repeated vaccination led to selective deletion of high avidity PR1- and WT1-specific CD8(+) T cells and was not associated with significant reduction in WT1-expression. Additional boosting failed to increase vaccine-induced CD8(+) T-cell frequencies further and in all patients the response was lost before the 6(th) dose. PR1- or WT1-specific CD8(+) T cells were not detected in bone marrow samples, excluding their preferential localization to this site. Following a booster injection three months after the 6(th) vaccine dose, no high-avidity PR1 or WT1-specific CD8(+) T cells could be detected, whereas low-avidity T cells were readily expanded.

CONCLUSIONS

These data support the immunogenicity of PR1 and WT1 peptide vaccines. However, repeated delivery of peptides with Montanide-adjuvant and GM-CSF leads to rapid loss of high-avidity peptide-specific CD8(+) T cells. These results may offer an explanation for the lack of correlation between immune and clinical responses observed in a number of clinical trials of peptide vaccination. New approaches are needed to induce long-term high-avidity memory responses against leukemia antigens.

Evaluation of cellular immune responses in cancer vaccine recipients: lessons from NY-ESO-1

The rigorous evaluation of cancer vaccination requires evidence of benefit to patients with cancer or those at risk of relapse from the disease. Clinical trials are expensive and require considerable human and clinical resources in order to demonstrate this benefit. In the era of defined cancer antigens, it is possible to evaluate immunogenic targets, and assess the quality and magnitude of immune responses against these antigens following vaccination. Analyzing these surrogate end points complements clinical assessment and provides a depth of understanding to better inform trial evaluation and design. We have used the immunogenic cancer testis antigen NY-ESO-1 as a model antigen. This article summarizes our experience in monitoring immunity against NY-ESO-1.

Molecularly defined vaccines for cancer immunotherapy, and protective T cell immunity

Malignant cells are frequently recognized and destroyed by T cells, hence the development of T cell vaccines against established tumors. The challenge is to induce protective type 1 immune responses, with efficient Th1 and CTL activation, and long-term immunological memory. These goals are similar as in many infectious diseases, where successful immune protection is ideally induced with live vaccines. However, large-scale development of live vaccines is prevented by their very limited availability and vector immunogenicity. Synthetic vaccines have multiple advantages. Each of their components (antigens, adjuvants, delivery systems) contributes specifically to induction and maintenance of T cell responses. Here we summarize current experience with vaccines based on proteins and peptide antigens, and discuss approaches for the molecular characterization of clonotypic T cell responses. With carefully designed step-by-step modifications of innovative vaccine formulations, T cell vaccination can be optimized towards the goal of inducing therapeutic immune responses in humans.