Polyfunctional anti-human epidermal growth factor receptor 3 (anti-HER3) antibodies induced by HER3 vaccines have multiple mechanisms of antitumor activity against therapy resistant and triple negative breast cancers.

BACKGROUND: Upregulation of human epidermal growth factor receptor 3 (HER3) is a major mechanism of acquired resistance to therapies targeting its heterodimerization partners epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2), but also exposes HER3 as a target for immune attack. We generated an adenovirus encoding full length human HER3 (Ad-HER3) to serve as a cancer vaccine. Previously we reported the anti-tumor efficacy and function of the T cell response to this vaccine. We now provide a detailed assessment of the antitumor efficacy and functional mechanisms of the HER3 vaccine-induced antibodies (HER3-VIAs) in serum from mice immunized with Ad-HER3. METHODS: Serum containing HER3-VIA was tested in complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC) assays and for its effect on HER3 internalization and degradation, downstream signaling of HER3 heterodimers and growth of metastatic HER2+ (BT474M1), HER2 therapy-resistant (rBT474), and triple negative (MDA-MB-468) breast cancers. RESULTS: HER3-VIAs mediated CDC and ADCC, HER3 internalization, interruption of HER3 heterodimer-driven tumor signaling pathways, and anti-proliferative effects against HER2+ tumor cells in vitro and significant antitumor effects against metastatic HER2+ BT474M1, treatment refractory HER2+ rBT474 and triple negative MDA-MB-468 in vivo. CONCLUSIONS: In addition to the T cell anti-tumor response induced by Ad-HER3, the HER3-VIAs provide additional functions to eliminate tumors in which HER3 signaling mediates aggressive behavior or acquired resistance to HER2-targeted therapy. These data support clinical studies of vaccination against HER3 prior to or concomitantly with other therapies to prevent outgrowth of therapy-resistant HER2+ and triple negative clones.

Vaccines targeting ESR1 activating mutations elicit anti-tumor immune responses and suppress estrogen signaling in therapy resistant ER+ breast cancer.

ER+ breast cancers (BC) are characterized by the elevated expression and signaling of estrogen receptor alpha (ESR1), which renders them sensitive to anti-endocrine therapy. While these therapies are clinically effective, prolonged treatment inevitably results in therapeutic resistance, which can occur through the emergence of gain-of-function mutations in ESR1. The central importance of ESR1 and development of mutated forms of ESR1 suggest that vaccines targeting these proteins could potentially be effective in preventing or treating endocrine resistance. To explore the potential of this approach, we developed several recombinant vaccines encoding different mutant forms of ESR1 (ESR1mut) and validated their ability to elicit ESR1-specific T cell responses. We then developed novel ESR1mut-expressing murine mammary cancer models to test the anti-tumor potential of ESR1mut vaccines. We found that these vaccines could suppress tumor growth, ESR1mut expression and estrogen signaling in vivo. To illustrate the applicability of these findings, we utilize HPLC to demonstrate the presentation of ESR1 and ESR1mut peptides on human ER+ BC cell MHC complexes. We then show the presence of human T cells reactive to ESR1mut epitopes in an ER+ BC patient. These findings support the development of ESR1mut vaccines, which we are testing in a Phase I clinical trial.

A randomized phase II study of immunization with dendritic cells modified with poxvectors encoding CEA and MUC1 compared with the same poxvectors plus GM-CSF for resected metastatic colorectal cancer.

OBJECTIVE: To determine whether 1 of 2 vaccines based on dendritic cells (DCs) and poxvectors encoding CEA (carcinoembryonic antigen) and MUC1 (PANVAC) would lengthen survival in patients with resected metastases of colorectal cancer (CRC). BACKGROUND: Recurrences after complete resections of metastatic CRC remain frequent. Immune responses to CRC are associated with fewer recurrences, suggesting a role for cancer vaccines as adjuvant therapy. Both DCs and poxvectors are potent stimulators of immune responses against cancer antigens. METHODS: Patients, disease-free after CRC metastasectomy and perioperative chemotherapy (n = 74), were randomized to injections of autologous DCs modified with PANVAC (DC/PANVAC) or PANVAC with per injection GM-CSF (granulocyte-macrophage colony-stimulating factor). Endpoints were recurrence-free survival overall survival, and rate of CEA-specific immune responses. Clinical outcome was compared with that of an unvaccinated, contemporary group of patients who had undergone CRC metastasectomy, received similar perioperative therapy, and would have otherwise been eligible for the study. RESULTS: Recurrence-free survival at 2 years was similar (47% and 55% for DC/PANVAC and PANVAC/GM-CSF, respectively) (χ P = 0.48). At a median follow-up of 35.7 months, there were 2 of 37 deaths in the DC/PANVAC arm and 5 of 37 deaths in the PANVAC/GM-CSF arm. The rate and magnitude of T-cell responses against CEA was statistically similar between study arms. As a group, vaccinated patients had superior survival compared with the contemporary unvaccinated group. CONCLUSIONS: Both DC and poxvector vaccines have similar activity. Survival was longer for vaccinated patients than for a contemporary unvaccinated group, suggesting that a randomized trial of poxvector vaccinations compared with standard follow-up after metastasectomy is warranted. (NCT00103142).

Novel adenoviral vector induces T-cell responses despite anti-adenoviral neutralizing antibodies in colorectal cancer patients.

First-generation, E1-deleted adenovirus subtype 5 (Ad5)-based vectors, although promising platforms for use as cancer vaccines, are impeded in activity by naturally occurring or induced Ad-specific neutralizing antibodies. Ad5-based vectors with deletions of the E1 and the E2b regions (Ad5 [E1-, E2b-]), the latter encoding the DNA polymerase and the pre-terminal protein, by virtue of diminished late phase viral protein expression, were hypothesized to avoid immunological clearance and induce more potent immune responses against the encoded tumor antigen transgene in Ad-immune hosts. Indeed, multiple homologous immunizations with Ad5 [E1-, E2b-]-CEA(6D), encoding the tumor antigen carcinoembryonic antigen (CEA), induced CEA-specific cell-mediated immune (CMI) responses with antitumor activity in mice despite the presence of preexisting or induced Ad5-neutralizing antibody. In the present phase I/II study, cohorts of patients with advanced colorectal cancer were immunized with escalating doses of Ad5 [E1-, E2b-]-CEA(6D). CEA-specific CMI responses were observed despite the presence of preexisting Ad5 immunity in a majority (61.3 %) of patients. Importantly, there was minimal toxicity, and overall patient survival (48 % at 12 months) was similar regardless of preexisting Ad5 neutralizing antibody titers. The results demonstrate that, in cancer patients, the novel Ad5 [E1-, E2b-] gene delivery platform generates significant CMI responses to the tumor antigen CEA in the setting of both naturally acquired and immunization-induced Ad5-specific immunity.

Clinical trials of self-replicating RNA-based cancer vaccines.

Therapeutic cancer vaccines, designed to activate immune effectors against tumor antigens, utilize a number of different platforms for antigen delivery. Among these are messenger RNAs (mRNA), successfully deployed in some prophylactic SARS-CoV2 vaccines. To enhance the immunogenicity of mRNA-delivered epitopes, self-replicating RNAs (srRNA) that markedly increase epitope expression have been developed. These vectors are derived from positive-strand RNA viruses in which the structural protein genes have been replaced with heterologous genes of interest, and the structural proteins are provided in trans to create single cycle viral replicon particles (VRPs). Clinical stage srRNA vectors have been derived from alphaviruses, including Venezuelan Equine Encephalitis (VEE), Sindbis, and Semliki Forest virus (SFV) and have encoded the tumor antigens carcinoembryonic antigen (CEA), human epidermal growth factor receptor 2 (HER2), prostate specific membrane antigen (PSMA), and human papilloma virus (HPV) antigens E6 and E7. Adverse events have mainly been grade 1 toxicities and minimal injection site reactions. We review here the clinical experience with these vaccines and our recent safety data from a study combining a VRP encoding HER2 plus an anti-PD1 monoclonal antibody (pembrolizumab). This experience with VRP-based srRNA supports recent development of fully synthetic srRNA technologies, where the viral structural proteins are replaced with protective lipid nanoparticles (LNP), cationic nanoemulsions or polymers.

Polyclonal HER2-specific antibodies induced by vaccination mediate receptor internalization and degradation in tumor cells.

INTRODUCTION: Sustained HER2 signaling at the cell surface is an oncogenic mechanism in a significant proportion of breast cancers. While clinically effective therapies targeting HER2 such as mAbs and tyrosine kinase inhibitors exist, tumors overexpressing HER2 eventually progress despite treatment. Thus, abrogation of persistent HER2 expression at the plasma membrane to synergize with current approaches may represent a novel therapeutic strategy. METHODS: We generated polyclonal anti-HER2 antibodies (HER2-VIA) by vaccinating mice with an adenovirus expressing human HER2, and assessed their signaling effects in vitro and anti-tumor effects in a xenograft model. In addition, we studied the signaling effects of human HER2-specific antibodies induced by vaccinating breast cancer patients with a HER2 protein vaccine. RESULTS: HER2-VIA bound HER2 at the plasma membrane, initially activating the downstream kinases extracellular signal-regulated protein kinase 1/2 and Akt, but subsequently inducing receptor internalization in clathrin-coated pits in a HER2 kinase-independent manner, followed by ubiquitination and degradation of HER2 into a 130 kDa fragment phosphorylated at tyrosine residues 1,221/1,222 and 1,248. Following vaccination of breast cancer patients with the HER2 protein vaccine, HER2-specific antibodies were detectable and these antibodies bound to cell surface-expressed HER2 and inhibited HER2 signaling through blocking tyrosine 877 phosphorylation of HER2. In contrast to the murine antibodies, human anti-HER2 antibodies induced by protein vaccination did not mediate receptor internalization and degradation. CONCLUSION: These data provide new insight into HER2 trafficking at the plasma membrane and the changes induced by polyclonal HER2-specific antibodies. The reduction of HER2 membrane expression and HER2 signaling by polyclonal antibodies induced by adenoviral HER2 vaccines supports human clinical trials with this strategy for those breast cancer patients with HER2 therapy-resistant disease.

Phase 1 clinical trial of HER2-specific immunotherapy with concomitant HER2 kinase inhibition [corrected].

BACKGROUND: Patients with HER2-overexpressing metastatic breast cancer, despite initially benefiting from the monoclonal antibody trastuzumab and the EGFR/HER2 tyrosine kinase inhibitor lapatinib, will eventually have progressive disease. HER2-based vaccines induce polyclonal antibody responses against HER2 that demonstrate enhanced anti-tumor activity when combined with lapatinib in murine models. We wished to test the clinical safety, immunogenicity, and activity of a HER2-based cancer vaccine, when combined with lapatinib. METHODS: We immunized women (n = 12) with metastatic, trastuzumab-refractory, HER2-overexpressing breast cancer with dHER2, a recombinant protein consisting of extracellular domain (ECD) and a portion of the intracellular domain (ICD) of HER2 combined with the adjuvant AS15, containing MPL, QS21, CpG and liposome. Lapatinib (1250 mg/day) was administered concurrently. Peripheral blood antibody and T cell responses were measured. RESULTS: This regimen was well tolerated, with no cardiotoxicity. Anti-HER2-specific antibody was induced in all patients whereas HER2-specific T cells were detected in one patient. Preliminary analyses of patient serum demonstrated downstream signaling inhibition in HER2 expressing tumor cells. The median time to progression was 55 days, with the majority of patients progressing prior to induction of peak anti-HER2 immune responses; however, 300-day overall survival was 92% (95% CI: 77-100%). CONCLUSIONS: dHER2 combined with lapatinib was safe and immunogenic with promising long term survival in those with HER2-overexpressing breast cancers refractory to trastuzumab. Further studies to define the anticancer activity of the antibodies induced by HER2 vaccines along with lapatinib are underway. TRIAL REGISTRY: ClinicalTrials.gov NCT00952692.

Immunomodulatory gene therapy prevents antibody formation and lethal hypersensitivity reactions in murine pompe disease.

Infantile Pompe disease progresses to a lethal cardiomyopathy in absence of effective treatment. Enzyme-replacement therapy (ERT) with recombinant human acid alpha-glucosidase (rhGAA) has been effective in most patients with Pompe disease, but efficacy was reduced by high-titer antibody responses. Immunomodulatory gene therapy with a low dose adeno-associated virus (AAV) vector (2 x 10(10) particles) containing a liver-specific regulatory cassette significantly lowered immunoglobin G (IgG), IgG1, and IgE antibodies to GAA in Pompe disease mice, when compared with mock-treated mice (P < 0.05). AAV-LSPhGAApA had the same effect on GAA-antibody production whether it was given prior to, following, or simultaneously with the initial GAA injection. Mice given AAV-LSPhGAApA had significantly less decrease in body temperature (P < 0.001) and lower anaphylactic scores (P < 0.01) following the GAA challenge. Mouse mast cell protease-1 (MMCP-1) followed the pattern associated with hypersensitivity reactions (P < 0.05). Regulatory T cells (Treg) were demonstrated to play a role in the tolerance induced by gene therapy as depletion of Treg led to an increase in GAA-specific IgG (P < 0.001). Treg depleted mice were challenged with GAA and had significantly stronger allergic reactions than mice given gene therapy without subsequent Treg depletion (temperature: P < 0.01; symptoms: P < 0.05). Ubiquitous GAA expression failed to prevent antibody formation. Thus, immunomodulatory gene therapy could provide adjunctive therapy in lysosomal storage disorders treated by enzyme replacement.

Synergism from combined immunologic and pharmacologic inhibition of HER2 in vivo.

The monoclonal antibody trastuzumab and the EGFR/HER2 tyrosine kinase inhibitor lapatinib improve the clinical outcome of patients with HER2-overexpressing breast cancer. However, the majority of metastatic cancers will eventually progress, suggesting the need for other therapies. Because HER2 overexpression persists, we hypothesized that the anti-HER2 immune response induced by cancer vaccines would be an effective strategy for treating trastuzumab- and lapatinib-refractory tumors. Furthermore, we hypothesized that the antibody response could synergize with lapatinib to enhance tumor inhibition. We developed a recombinant adenoviral vector expressing a kinase-inactive HER2 (Ad-HER2-ki) to use as a cancer vaccine. Vaccine-induced polyclonal HER2-specific antiserum was analyzed for receptor internalization and signaling effects alone and in combination with lapatinib. Ad-HER2-ki vaccine-induced potent T cell and antibody responses in mice and the vaccine-induced polyclonal HER2-specific antiserum mediated receptor internalization and degradation much more effectively than trastuzumab. Our in vitro studies demonstrated that HER2 vaccine-induced antibodies effectively caused a decrease in HER2 expression, but when combined with lapatinib caused significant inhibition of HER2 signaling, decreased pERK and pAKT levels and reduced breast tumor cell proliferation. In addition, a known mechanism of resistance to lapatinib, induction of survivin, was inhibited. The combination of Ad-HER2-ki plus lapatinib also showed superior antitumor efficacy in vivo. Based on these results, we feel clinical studies using this approach to target HER2-overexpressing breast cancer, including trastuzumab- and lapatinib-resistant tumors is warranted.

Depletion of human regulatory T cells specifically enhances antigen-specific immune responses to cancer vaccines.

CD4(+)CD25(high)FoxP3(+) regulatory T (Treg) cells limit antigen-specific immune responses and are a cause of suppressed anticancer immunity. In preclinical and clinical studies, we assessed the immune consequences of FoxP3(+) Treg-cell depletion in patients with advanced malignancies. We demonstrated that a CD25(high) targeting immunotoxin (denileukin diftitox) depleted FoxP3(+) Treg cells, decreased Treg-cell function, and enhanced antigen-specific T-cell responses in vitro. We then attempted to enhance antitumor immune responses in patients with carcinoembryonic antigen (CEA)-expressing malignancies by Treg-cell depletion. In a pilot study (n = 15), denileukin diftitox, given as a single dose or repeated dosing, was followed by immunizations with dendritic cells modified with the fowlpox vector rF-CEA(6D)-TRICOM. By flow cytometric analysis, we report the first direct evidence that circulating CD4(+)CD25(high)FoxP3(+) Treg cells are depleted after multiple doses of denileukin diftitox. Earlier induction of, and overall greater exposure to, the T-cell response to CEA was observed in the multiple-dose group, but not the single-dose group. These results indicate the potential for combining Treg-cell depletion with anticancer vaccines to enhance tumor antigen-specific immune responses and the need to explore dose and schedule of Treg depletion strategies in optimizing vaccine efforts.

Long-term survival of patients with stage III colon cancer treated with VRP-CEA(6D), an alphavirus vector that increases the CD8+ effector memory T cell to Treg ratio.

BACKGROUND: There remains a significant need to eliminate the risk of recurrence of resected cancers. Cancer vaccines are well tolerated and activate tumor-specific immune effectors and lead to long-term survival in some patients. We hypothesized that vaccination with alphaviral replicon particles encoding tumor associated antigens would generate clinically significant antitumor immunity to enable prolonged overall survival (OS) in patients with both metastatic and resected cancer. METHODS: OS was monitored for patients with stage IV cancer treated in a phase I study of virus-like replicon particle (VRP)-carcinoembryonic antigen (CEA), an alphaviral replicon particle encoding a modified CEA. An expansion cohort of patients (n=12) with resected stage III colorectal cancer who had completed their standard postoperative adjuvant chemotherapy was administered VRP-CEA every 3 weeks for a total of 4 immunizations. OS and relapse-free survival (RFS) were determined, as well as preimmunization and postimmunization cellular and humoral immunity. RESULTS: Among the patients with stage IV cancer, median follow-up was 10.9 years and 5-year survival was 17%, (95% CI 6% to 33%). Among the patients with stage III cancer, the 5-year RFS was 75%, (95%CI 40% to 91%); no deaths were observed. At a median follow-up of 5.8 years (range: 3.9-7.0 years) all patients were still alive. All patients demonstrated CEA-specific humoral immunity. Patients with stage III cancer had an increase in CD8 +TEM (in 10/12) and decrease in FOXP3 +Tregs (in 10/12) following vaccination. Further, CEA-specific, IFNγ-producing CD8+granzyme B+TCM cells were increased. CONCLUSIONS: VRP-CEA induces antigen-specific effector T cells while decreasing Tregs, suggesting favorable immune modulation. Long-term survivors were identified in both cohorts, suggesting the OS may be prolonged.

Vaccine-Induced Memory CD8+ T Cells Provide Clinical Benefit in HER2 Expressing Breast Cancer: A Mouse to Human Translational Study.

PURPOSE: Immune-based therapy for metastatic breast cancer has had limited success, particularly in molecular subtypes with low somatic mutations rates. Strategies to augment T-cell infiltration of tumors include vaccines targeting established oncogenic drivers such as the genomic amplification of HER2. We constructed a vaccine based on a novel alphaviral vector encoding a portion of HER2 (VRP-HER2). PATIENTS AND METHODS: In preclinical studies, mice were immunized with VRP-HER2 before or after implantation of hHER2+ tumor cells and HER2-specific immune responses and antitumor function were evaluated. We tested VRP-HER2 in a phase I clinical trial where subjects with advanced HER2-overexpressing malignancies in cohort 1 received VRP-HER2 every 2 weeks for a total of 3 doses. In cohort 2, subjects received the same schedule concurrently with a HER2-targeted therapy. RESULTS: Vaccination in preclinical models with VRP-HER2 induced HER2-specific T cells and antibodies while inhibiting tumor growth. VRP-HER2 was well tolerated in patients and vaccination induced HER2-specific T cells and antibodies. Although a phase I study, there was 1 partial response and 2 patients with continued stable disease. Median OS was 50.2 months in cohort 1 (n = 4) and 32.7 months in cohort 2 (n = 18). Perforin expression by memory CD8 T cells post-vaccination significantly correlated with improved PFS. CONCLUSIONS: VRP-HER2 increased HER2-specific memory CD8 T cells and had antitumor effects in preclinical and clinical studies. The expansion of HER2-specific memory CD8 T cells in vaccinated patients was significantly correlated with increased PFS. Subsequent studies will seek to enhance T-cell activity by combining with anti-PD-1.

Phase I study of immunization with dendritic cells modified with fowlpox encoding carcinoembryonic antigen and costimulatory molecules.

PURPOSE: To determine the safety and immunologic and clinical efficacy of a dendritic cell vaccine modified to hyperexpress costimulatory molecules and tumor antigen. EXPERIMENTAL DESIGN: In this phase I study, we administered one or two cycles of four triweekly s.c./intradermal injections of ex vivo generated dendritic cells modified with a recombinant fowlpox vector encoding carcinoembryonic antigen (CEA) and a triad of costimulatory molecules [rF-CEA(6D)-TRICOM]. Controls consisted of immature dendritic cells loaded with tetanus toxoid and a HLA A2-restricted peptide derived from cytomegalovirus pp65 protein. RESULTS: Fourteen patients (11 with colorectal cancer and 3 with non-small cell lung cancer) were enrolled and 12 completed at least one cycle of immunization. There were no grade 3/4 toxicities directly referable to the immunizations. One patient had a decrease in the CEA level from 46 to 6.8 and a minor regression in adenopathy that occurred several months after completion of the immunizations. Five other patients were stable through at least one cycle of immunization (3 months). Direct analysis of peripheral blood mononuclear cells using the ELISpot assay showed an increase in the frequency of CEA-specific T cells in 10 patients (range, 10-541 CEA-specific cells/10(5) peripheral blood mononuclear cells). There was a trend for a greater peak frequency of CEA-specific T cells among those with either a minor response or a stable disease following at least one cycle of therapy. A second cycle was not associated with higher T-cell frequencies. Cytokine flow cytometry showed CEA-specific immune response among both CD4(+) and CD8(+) T cells in all immune responders. CONCLUSION: This immunization strategy is safe and activates potent CEA-specific immune responses.

Multiple signals are required for maturation of human dendritic cells mobilized in vivo with Flt3 ligand.

The ligand for the receptor tyrosine kinase fms-like tyrosine kinase 3 (Flt3L) is a growth factor for hematopoietic progenitors and induces expansion of the two distinct lineages of dendritic cells (DC) that have been described in humans. These two lineages, DC1 and DC2, have been described according to their ability to induce naive T cell differentiation to T helper cell type 1 (Th1) and Th2 effector cells, respectively. The immunoregulatory potential of DC1 and DC2 depends on their state of maturation and activation, which can be mediated by several molecules. Because monocyte-derived DC1 produce interleukin-12 (IL-12) when stimulated with CD40 ligand (CD40L), we hypothesized that similar results would be obtained with DC1 mobilized by Flt3L. Unexpectedly, we found that immature DC expanded in vivo by Flt3L treatment could not be stimulated to produce IL-12 in vitro using CD40L and/or interferon-gamma (IFN-gamma) alone. Instead, we found that Flt3L-mobilized DC from cancer patients require a sequence of specific signals for maturation, which included initial treatment with granulocyte macrophage-colony stimulating factor followed by a combination of maturation signals such as CD40L and IFN-gamma. Flt3L-mobilized DC matured in this manner possessed greater T cell-stimulatory function than nonmatured DC. The ability to generate phenotypically mature, IL-12-producing DC1 from peripheral blood mononuclear cells mobilized by Flt3L will have important implications for the development of effective cancer immunotherapy strategies.

Proteomics for monitoring immune responses to cancer vaccines.

Standardized biomarkers for the detection of clinically significant immunological responses would be extremely valuable in immunotherapy trials. Most available assays measure either the frequency or function of antigen-specific T-cells, or the titers of antibodies or immune complexes. These assays have generally exhibited either inadequate sensitivity or too high a signal-to-noise ratio to reliably detect the low-frequency T-cell responses induced by cancer vaccines. In addition, such assays reflect only one aspect of the immune response rather than the complete picture. Proteomics, the study of proteins within a cell or biological sample, may offer a novel approach to immunological monitoring that complements existing immunological assays. By studying the protein content of T-cells responding to a vaccine or in the serum of vaccinated individuals, it may be possible to develop a metric for quantitating the magnitude of immunological responses. Proteomics could also provide a tool for establishing the quality of the immune response and for obtaining valuable information regarding the underlying regulatory mechanisms and pathways. Advances in miniaturization and automation may also permit characterization of the immune response more rapidly and from smaller amounts of biological material than is possible with existing assay systems.

Depletion of human regulatory T cells.

Regulatory T cells (Treg) have become increasingly relevant in the study of human disease including cancer. Treg cells have been shown to inhibit anti-tumor immune responses, and elevated Treg levels have been associated with certain types of cancer. Similarly, depletion of Tregs by various methods can also enhance anti-tumor immune responses. We have found a prevalence of Treg in cancer patients when compared to normal volunteers. In addition, we have shown that the depletion of Treg using the IL-2 fusion protein denileukin diftitox decreased Treg function and increased antigen-specific T cell response to a cancer vaccine. These results indicate the potential for combining Treg depletion with anti-cancer vaccines to enhance tumor antigen-specific immune responses and the need to explore the dose and schedule of Treg depletion strategies in optimizing vaccine efforts.

MHC class I-presented tumor antigens identified in ovarian cancer by immunoproteomic analysis are targets for T-cell responses against breast and ovarian cancer.

PURPOSE: The purpose of this study is to test whether peptide epitopes chosen from among those naturally processed and overpresented within MHC molecules by malignant, but not normal cells, when formulated into cancer vaccines, could activate antitumor T-cell responses in humans. EXPERIMENTAL DESIGN: Mixtures of human leukocyte antigen A2 (HLA-A2)-binding ovarian cancer-associated peptides were used to activate naive T cells to generate antigen-specific T cells that could recognize ovarian and breast cancers in vitro. Combinations of these peptides (0.3 mg of each peptide or 1 mg of each peptide) were formulated into vaccines in conjunction with Montanide ISA-51 and granulocyte monocyte colony stimulating factor which were used to vaccinate patients with ovarian and breast cancer without evidence of clinical disease in parallel pilot clinical trials. RESULTS: T cells specific for individual peptides could be generated in vitro by using mixtures of peptides, and these T cells recognized ovarian and breast cancers but not nonmalignant cells. Patient vaccinations were well tolerated with the exception of local erythema and induration at the injection site. Nine of the 14 vaccinated patients responded immunologically to their vaccine by inducing peptide-specific T-cell responses that were capable of recognizing HLA-matched breast and ovarian cancer cells. CONCLUSION: Mixtures of specific peptides identified as naturally presented on cancer cells and capable of activating tumor-specific T cells in vitro also initiate or augment immune responses toward solid tumors in cancer patients.

An alphavirus vector overcomes the presence of neutralizing antibodies and elevated numbers of Tregs to induce immune responses in humans with advanced cancer.

Therapeutic anticancer vaccines are designed to boost patients' immune responses to tumors. One approach is to use a viral vector to deliver antigen to in situ DCs, which then activate tumor-specific T cell and antibody responses. However, vector-specific neutralizing antibodies and suppressive cell populations such as Tregs remain great challenges to the efficacy of this approach. We report here that an alphavirus vector, packaged in virus-like replicon particles (VRP) and capable of efficiently infecting DCs, could be repeatedly administered to patients with metastatic cancer expressing the tumor antigen carcinoembryonic antigen (CEA) and that it overcame high titers of neutralizing antibodies and elevated Treg levels to induce clinically relevant CEA-specific T cell and antibody responses. The CEA-specific antibodies mediated antibody-dependent cellular cytotoxicity against tumor cells from human colorectal cancer metastases. In addition, patients with CEA-specific T cell responses exhibited longer overall survival. These data suggest that VRP-based vectors can overcome the presence of neutralizing antibodies to break tolerance to self antigen and may be clinically useful for immunotherapy in the setting of tumor-induced immunosuppression.

Vascular endothelial growth factor and immunosuppression in cancer: current knowledge and potential for new therapy.

Two decades of research into the role of immunosuppression and angiogenesis in tumor biology have revealed multiple links between the two. Vascular endothelial growth factor, originally thought to be solely involved in vascular growth and permeability, has emerged as a significant agent of immune tolerance in the tumor microenvironment. This review examines two major elements of this field: the research behind the role of vascular endothelial growth factor in immunosuppression, especially as pertains to dendritic cell function; and the subsequent research into the potential for using antiangiogenic therapy to both starve tumors by hypoxia and enhance the response of tumors to immunotherapy. Several strategies tested so far have yielded incomplete, yet promising, results.

Enumerating antigen-specific T-cell responses in peripheral blood: a comparison of peptide MHC Tetramer, ELISpot, and intracellular cytokine analysis.

Detection of the circulating antigen-specific T-cell response to immunization is an important biologic end point in clinical trials of cancer vaccines. Typically employed assays are peptide MHC tetramer, ELISpot, and intracellular cytokine analysis. Although there is no agreement on the definition of a positive response in these assays, many groups have chosen a number of T cells greater than 2 standard deviations above the mean of the negative controls. The authors wished to determine how well this cutoff performed for each of these assays in detecting positive and negative T-cell responses to a model antigen, the immunodominant HLA-A*0201-restricted epitope of cytomegalovirus (CMV) pp65. For each assay, the mean + 2 standard deviations of the response for CMV seronegatives was the point that best separated the two groups. Using this value, each assay had a sensitivity of 87.5% and specificity of 95% to 100% and exhibited a high degree of concordance (kappa 0.76-0.9) with the other two. The authors conclude that currently available immunologic assays perform well in detecting biologically relevant levels of antigen-specific T cells. These assays will better define the quantity and quality of protective immune responses to viral disease and offer insight into the requirements for protective anti-cancer immunity.