Apoptotic, necrotic, or fused tumor cells: an equivalent source of antigen for dendritic cell loading

Previous radiotherapy increases the efficacy of cemiplimab in the treatment of locally advanced and metastatic cutaneous squamous cell carcinoma: A retrospective analysis

BACKGROUND

Cemiplimab, a programmed cell death-1 inhibitor approved in 2018 for patients with locally advanced or metastatic cutaneous squamous cell carcinoma (cSCC) who are ineligible for curative therapies, lacks clarity regarding the optimal patient selection despite its known efficacy.

OBJECTIVE

This retrospective study aims to assess the real-world treatment patterns and outcomes in patients with cSCC at our institution.

METHODS

A retrospective analysis of consecutively treated patients with cemiplimab for cSCC was conducted. Progression-free survival (PFS) and overall survival were evaluated alongside clinical-pathologic characteristics.

RESULTS

Forty-five patients were included, of which 73.3% were male with a median age of 77 years. After 18 months of median follow-up median PFS and overall survival were not reached with a mean of 21.3 months ± 2.2 months and 25.3 ± 2.1 months, respectively. Univariate and multivariate analyses revealed significant correlations only between PFS and previous radiotherapy (P values: .043 and .046, respectively).

LIMITATIONS

Limitations include its retrospective nature, the low number of patients analyzed, and the potential for inherent biases.

CONCLUSIONS

The study reveals a significant association between prior radiotherapy and improved PFS in cemiplimab-treated cSCC, suggesting the potential for combining radiotherapy with cemiplimab. Further exploration of this combined approach is warranted.

Safety and potential increased risk of toxicity of radiotherapy combined immunotherapy strategy

Accumulating interest has emerged in exploring the toxicity profiles of the combination strategy of radiotherapy (RT) and immune checkpoint inhibitors (ICIs). Much remains unknown regarding safety and the potential increased risk of toxicity of a combined treatment. ICI prolongs survival but can induce immune-related adverse events as well. To increase awareness of adverse effect and support immediate and successful management, we go over the literature on the safety of RT combined immunotherapy strategy. Representative evidence relevant to RT combined with ICI in the brain, lung, head and neck, and pelvic malignance was reviewed respectively. Given radiation doses and fractionation, the irradiated volume, the timing of RT, and ICI would significantly affect the safety and efficiency of ICI+RT combination therapy, and no consensus had been reached about how to arrange RT delivery in the combined contexture, we went over the available literature and tried to address these challenges including the timing of RT, optimal dose and fractionations, RT target and target volume, and potential biomarkers to predict toxicity. We found even though RT+ICI combination therapy might augment toxicities, the majority of patients experienced grade 4 or 5 AE are relatively rare and no significant difference could be found between combination group and monotherapy group. Sometimes the acute toxicity with ICI is much less predictable and often life threatening and in some can give rise to permanent effects. Clinicians across disciplines should be aware of these uncommon lethal complications induced by ICI+RT. Early recognition is the key to successful treatment, reversibility of organ dysfunction, and in some cases even prevention of fatal outcome. If recognized early, managed properly, and no fatal AE occurs, the development of irAE indicates a good prognosis. It should be noted that nothing is known about potential late effects because very few studies have 5-year follow-up. The nature of irAE is the attack of activated immune cells on normal tissues. The nature of RT-induced AE is the DNA damage on normal tissue, which is related with the dose delivered and volume irradiated and the tolerance of surrounding normal tissues. The immune-modulating effect of SBRT may augment the damage on normal tissues. To maximize the antitumor immune response, 8-12 Gy/fraction is preferred when conducting RT. The available clinical evidence suggest RT of this dose/fractionated strategy combined with ICI have a tolerable AE profile, which need further validation by more clinical trials in the future. The combination strategy of RT with anti-PD1/PDL1 anti-body is supposed to be concurrent or RT followed by anti-PD1/PDL1 antibody. Although RT and ipilimumab combination sequence is controversial, ipilimumab prior to or concurrent with RT might be proper, which need more clinical validation. Under the concept of immunological dose painting, SBRT work as a trigger of immune response. It has been observed that SBRT of partially radiated tumors combined with ICI could induce similar tumor control compared with total tumor irradiation. The side effects of RT may be mitigated potentially due to the reduction of irradiated volume. The antitumor efficiency and safety profile of immunological RT dose painting+ICI deserve further investigation. Clinical predictive factors for irAE risk remain unclear, and more investigation deserves to be conducted about the irAE prediction.

The Evolving Interplay of SBRT and the Immune System, along with Future Directions in the Field

Simple Summary

We provide this commentary of stereotactic body radiotherapy (SBRT), and describe our evolving understanding of this treatment approach, its effects on the immune system, and the ability to stimulate immune cells to further recognize and attack cancer. The aim of this work is to describe our current knowledge of how SBRT effects the environment within the tumor and the immune cells present, whether timing the combination of this treatment with that of immunotherapy may have an impact on the body’s own immune response, and what the latest approaches in the field are in regards to this radiation treatment modality. Among these latest and exciting developments is Personalized Ultrafractionated Stereotactic Adaptive Radiation Therapy, known as PULSAR. This latest approach is described in detail herein, and may represent a leading novel method for adapting radiation treatments to treatment-induced tumor changes over time and stimulating the body’s immune response against tumor cells.

Abstract

In this commentary, we describe the potential of highly ablative doses utilizing Stereotactic Body Radiation Therapy (SBRT) in single or few fractions to enhance immune-responsiveness, how timing of this approach in combination with immune-checkpoint inhibitors may augment treatment-effect, and whether Personalized Ultrafractionated Stereotactic Adaptive Radiation Therapy (PULSAR) is an avenue for future advancement in the continued endeavor to foster a systemic effect of therapy beyond the radiation treatment field. The ablative potential of SBRT may support an increase in tumor-antigen presentation, enhancement of immune-stimulatory components, and an improvement in tumor-microenvironment immune cell infiltration. Furthermore, the latest advancement of ablative radiation delivery is PULSAR-based therapy, whereby ablative doses are delivered in pulses of treatment that may be several weeks apart, combined with adaptive treatment to tumor changes across time. The benefits of this novel approach include the ability to optimize direct tumor control by assessment of tumor size and location via dedicated imaging acquired prior to each delivered pulse, and further potentiation of immune recognition through combination with concurrent immune-checkpoint blockade.

Predictors of immunotherapy benefit in Merkel cell carcinoma

Merkel cell carcinoma is a rare cancer for which immune checkpoint blockade is standard-of-care for recurrent/metastatic disease. However, not all patients benefit from immunotherapy. A greater understanding of molecular mechanisms and predictive biomarkers are unmet needs. We retrospectively analyzed electronic health records and next-generation sequencing data of 45 patients treated at our institution from 2013 to 2020 to understand clinical and genomic correlates of benefit from immunotherapy. Our cohort predominantly included individuals with stage III disease at primary disease diagnosis and individuals with stage IV disease at recurrent/metastatic disease diagnosis. Most received immunotherapy as first-line treatment. 43% experienced objective response (median duration of response 24.2 months, 95% confidence interval 8.8-not reached). Median overall survival was 15.5 months (95% confidence interval 9.0–28.7) (median follow-up 25.2 months). Less advanced stage at primary disease diagnosis and shorter disease-free interval between completion of initial treatment and recurrence were each associated with greater odds of response (odds ratio of 0.06, p = 0.04 for stage; odds ratio 0.75, p = 0.05 for disease-free interval). Single-nucleotide variants in ARID2 and NTRK1 were associated with response (p = 0.05, without Bonferroni correction), while none of Merkel cell polyomavirus status, total mutational burden, ultraviolet mutational signatures, and copy-number alterations predicted outcomes. Patients with shorter disease-free interval may be particularly suitable immunotherapy candidates. Our molecular findings point to ARID2 and NTRK1 as potential predictive markers and/or therapeutic targets (e.g., with Trk inhibitors), although this association needs to be confirmed in a larger sample.

Chitosan-Based Nanoparticles for Intracellular Delivery of ISAV Fusion Protein cDNA into Melanoma Cells: A Path to Develop Oncolytic Anticancer Therapies

Oncolytic virus therapy has been tested against cancer in preclinical models and clinical assays. Current evidence shows that viruses induce cytopathic effects associated with fusogenic protein-mediated syncytium formation and immunogenic cell death of eukaryotic cells. We have previously demonstrated that tumor cell bodies generated from cells expressing the fusogenic protein of the infectious salmon anemia virus (ISAV-F) enhance crosspriming and display prophylactic antitumor activity against melanoma tumors. In this work, we evaluated the effects of the expression of ISAV-F on the B16 melanoma model, both in vitro and in vivo, using chitosan nanoparticles as transfection vehicle. We confirmed that the transfection of B16 tumor cells with chitosan nanoparticles (NP-ISAV) allows the expression of a fusogenically active ISAV-F protein and decreases cell viability because of syncytium formation in vitro. However, the in vivo transfection induces a delay in tumor growth, without inducing changes on the lymphoid populations in the tumor and the spleen. Altogether, our observations show that expression of ISAV fusion protein using chitosan nanoparticles induces cell fusion in melanoma cells and slight antitumor response.

Evaluation of cell surface reactive immuno-adjuvant in combination with immunogenic cell death inducing drug for in situ chemo-immunotherapy

Apoptotic cells and cell fragments, especially those produced as a result of immunogenic cell death (ICD), are known to be a potential source of cancer vaccine immunogen. However, due to variation between tumours and between individuals, methods to generate such preparations may require extensive ex vivo personalisation. To address this, we have utilised the concept of in situ vaccination whereby an ICD inducing drug is injected locally to generate immunogenic apoptotic fragments/cells. These fragments are then adjuvanted by a co-administered cell reactive CpG adjuvant. We first evaluate means of labelling tumour cells with CpG adjuvant, we then go on to demonstrate in vitro that labelling is preserved following apoptosis and, furthermore, that the apoptotic body-adjuvant complexes are readily transferred to macrophages. In in vivo studies we observe synergistic tumour growth delays and elevated levels of CD4+ and CD8+ cells in tumours receiving adjuvant drug combination. CD4+/CD8+ cells are likewise elevated in the tumour draining lymph node and activated to a greater extent than individual treatments. This study represents the first steps toward the evaluation of rationally formulated drug-adjuvant combinations for in situ chemo-immunotherapy.

Radiotherapy as a Backbone for Novel Concepts in Cancer Immunotherapy

Radiation-induced immunogenic cell death has been described to contribute to the efficacy of external beam radiotherapy in local treatment of solid tumors. It is well established that radiation therapy can induce immunogenic cell death in cancer cells under certain conditions. Initial clinical studies combining radiotherapy with immunotherapies suggest a synergistic potential of this approach. Improving our understanding of how radiation reconditions the tumor immune microenvironment should pave the way for designing rational and robust combinations with immunotherapeutic drugs that enhance both local and systemic anti-cancer immune effects. In this review, we summarize irradiation-induced types of immunogenic cell death and their effects on the tumor microenvironment. We discuss preclinical insights on mechanisms and benefits of combining radiotherapy with immunotherapy, focusing on immune checkpoint inhibitors. In addition, we elaborate how these observations were translated into clinical studies and which parameters may be optimized to achieve best results in future clinical trials.

Interaction of Immune Cells and Tumor Cells in Gold Nanorod-Gelatin Composite Porous Scaffolds

Composite porous scaffolds prepared by immobilization of photothermal nano-agents into porous scaffold have been used for both cancer therapy and tissue regeneration. However, it is not clear how the host immune cells and ablated tumor cells interact and stimulate each other in the composite scaffolds. In this research, a gold nanorod-incorporated gelatin composite scaffold with controlled spherical large pores and well interconnected small pores was fabricated by using ice particulates as a porogen. The composite porous scaffold was used for investigating the interaction between dendritic cells and photothermally ablated breast tumor cells. The composite scaffold demonstrated excellent photothermal property and the temperature change value could be adjusted by irradiation time and laser power density. The composite scaffold showed excellent photothermal ablation ability towards breast tumor cells. The photothermally ablated tumor cells induced activation of dendritic cells when immature dendritic cells were co-cultured in the composite scaffold. Consequently, the gold nanorod-incorporated gelatin composite porous scaffold should provide a useful platform for simultaneous photothermal-immune ablation of breast tumor.

Photothermal Ablation of Cancer Cells by Albumin-Modified Gold Nanorods and Activation of Dendritic Cells

Nanoparticle-mediated photothermal therapy has been widely studied for cancer treatment. It is important to disclose how photothermally ablated tumor cells trigger immune responses. In this study, bovine serum albumin (BSA)-coated gold nanorods (BSA-coated AuNRs) were prepared and used for photothermal ablation of breast tumor cells. The BSA-coated AuNRs showed high photothermal conversion efficiency and good photothermal ablation effect towards tumor cells. The ablated tumor cells were co-cultured with immature dendritic cells (DCs) through a direct cell contacting model and diffusion model to confirm the stimulatory effects of cell⁻cell interaction and soluble factors released from ablated tumor cells. The results indicated that photothermally ablated tumor cells induced immune-stimulatory responses of DCs through both cell⁻cell interaction and soluble factors. The results should be useful for synergistic photothermal-immunotherapy of primary and metastatic cancer.

Previous radiotherapy and the clinical activity and toxicity of pembrolizumab in the treatment of non-small-cell lung cancer: a secondary analysis of the KEYNOTE-001 phase 1 trial

BACKGROUND

Preclinical studies have found radiotherapy enhances antitumour immune responses. We aimed to assess disease control and pulmonary toxicity in patients who previously received radiotherapy for non-small-cell lung cancer (NSCLC) before receiving pembrolizumab.

METHODS

We assessed patients with advanced NSCLC treated on the phase 1 KEYNOTE-001 trial at a single institution (University of California, Los Angeles, CA, USA). Patients were aged 18 years or older, had an Eastern Cooperative Oncology Group performance status of 1 or less, had adequate organ function, and no history of pneumonitis. Patients received pembrolizumab at a dose of either 2 mg/kg of bodyweight or 10 mg/kg every 3 weeks, or 10 mg/kg every 2 weeks, until disease progression, unacceptable toxicity, or other protocol-defined reasons for discontinuation. Disease response and pulmonary toxicity were prospectively assessed by Immune-related Response Criteria and Common Terminology Criteria for Adverse Events version 4.0. The primary objective of the KEYNOTE-001 trial was to assess the safety, side-effect profile, and antitumour activity of pembrolizumab. For our secondary analysis, patients were divided into subgroups to compare patients who previously received radiotherapy with patients who had not. Our primary objective was to determine whether previous radiotherapy affected progression-free survival, overall survival, and pulmonary toxicity in the intention-to-treat population. The KEYNOTE-001 trial was registered with ClinicalTrials.gov, number NCT01295827.

FINDINGS

Between May 22, 2012, and July 11, 2014, 98 patients were enrolled and received their first cycle of pembrolizumab. One patient was lost to follow-up. 42 (43%) of 97 patients had previously received any radiotherapy for the treatment of NSCLC before the first cycle of pembrolizumab. 38 (39%) of 97 patients received extracranial radiotherapy and 24 (25%) of 97 patients received thoracic radiotherapy. Median follow-up for surviving patients was 32·5 months (IQR 29·8-34·1). Progression-free survival with pembrolizumab was significantly longer in patients who previously received any radiotherapy than in patients without previous radiotherapy (hazard ratio [HR] 0·56 [95% CI 0·34-0·91], p=0·019; median progression-free survival 4·4 months [95% CI 2·1-8·6] vs 2·1 months [1·6-2·3]) and for patients who previously received extracranial radiotherapy compared with those without previous extracranial radiotherapy (HR 0·50 [0·30-0·84], p=0·0084; median progression-free survival 6·3 months [95% CI 2·1-10·4] vs 2·0 months [1·8-2·1]). Overall survival with pembrolizumab was significantly longer in patients who previously received any radiotherapy than in patients without previous radiotherapy (HR 0·58 [95% CI 0·36-0·94], p=0·026; median overall survival 10·7 months [95% CI 6·5-18·9] vs 5·3 months [2·7-7·7]) and for patients who previously received extracranial radiotherapy compared with those without previous extracranial radiotherapy (0·59 [95% CI 0·36-0·96], p=0·034; median overall survival 11·6 months [95% CI 6·5-20·5] vs 5·3 months [3·0-8·5]). 15 (63%) of 24 patients who had previously received thoracic radiotherapy had any recorded pulmonary toxicity versus 29 (40%) of 73 patients with no previous thoracic radiotherapy. Three (13%) patients with previous thoracic radiotherapy had treatment-related pulmonary toxicity compared with one (1%) of those without; frequency of grade 3 or worse treatment-related pulmonary toxicities was similar (one patient in each group).

INTERPRETATION

Our data suggest that previous treatment with radiotherapy in patients with advanced NSCLC results in longer progression-free survival and overall survival with pembrolizumab treatment than that seen in patients who did not have previous radiotherapy, with an acceptable safety profile. Further clinical trials investigating this combination are needed to determine the optimal treatment strategy for patients with advanced NSCLC.

FUNDING

US National Institutes of Health.

Enhanced protective immunity derived from dendritic cells with phagocytosis of CD40 ligand transgene-engineered apoptotic tumor cells via increased dendritic cell maturation

AIMS AND BACKGROUND

Dendritic cells (DCs) play a pivotal role in regulating CD8+ cytotoxic T-lymphocyte (CTL) responses. Currently, DC vaccines have been used in experimental animal models and clinical trials for evaluation of antitumor immunity. However, their efficacy is limited, warranting the improvement of DC-based cancer vaccines. CD40 ligand (CD40L) stimulates DC activation and maturation via CD40-CD40L interaction. We demonstrated that DCs that had phagocytized apoptotic tumor cells induced antitumor immunity.

METHODS

We generated CD40L-expressing (EG7-CD40L) and the control (EG7-Null) EG7 tumor cells by transfection of EG7 tumor cells with CD40L-expressing adenoviral vector AdVCD40L and the control vector AdV(pLpA), respectively. We also generated DC vaccines (DC-EG7/CD40L and the control DC-EG7/Null) using DCs with phagocytosis of irradiated EG7-CD40L and EG7-Null tumor cells, and assessed their phenotype and immunogenicity by flow cytometry and animal studies in C57BL/6 mice.

RESULTS

We demonstrate that an irradiation of 9000-rad induced Annexin V-expressing cell apoptosis in most (~75%) tumor cells, and provide evidence for phagocytosis of apoptotic tumor cells by flow cytometry and confocal microscopy. The DC-EG7/CD40L cells showed higher expression of DC maturation markers (Ia(b), CD40, CD80, and CD86) and peptide/major histocompatibility complex I than the control DC-EG7/Null cells. In addition, DC-EG7/CD40L vaccine stimulates more efficient (0.97%) tumor-specific CTL responses than DC-EG7/Null cells (0.31%). Furthermore, 80% (4/5) of mice immunized with DC-EG7/CD40L vaccine become tumor-free after EG7 tumor cell challenge, whereas DC-EG7/Null vaccine only delays immunized mouse death.

CONCLUSIONS

Dendritic cells that have phagocytized CD40L-expressing apoptotic tumor cells appear to offer new strategies in DC cancer vaccines.

PIAS1 and STAT-3 impair the tumoricidal potential of IFN-γ-stimulated mouse dendritic cells generated with IL-15

Primarily defined by their antigen-presenting property, dendritic cells (DCs) are being implemented as cancer vaccines in immunotherapeutic interventions. DCs can also function as direct tumor cell killers. How DC cytotoxic activity can be efficiently harnessed and the mechanisms controlling this nonconventional property are not fully understood. We report here that the tumoricidal potential of mouse DCs generated from myeloid precursors with GM-CSF and IL-15 (IL-15 DCs) can be triggered with the Toll-like receptor (TLR) 4 ligand lipopolysaccharide to a similar extent compared with that of their counterparts, conventionally generated with IL-4 (IL-4 DCs). The mechanism of tumor cell killing depends on the induction of iNOS expression by DCs. In contrast, interferon (IFN)-γ induces the cytotoxic activity of IL-4 but not IL-15 DCs. Although the IFN-γ-STAT-1 signaling pathway is overall functional in IL-15 DCs, IFN-γ fails to induce iNOS expression in these cells. iNOS expression is negatively controlled in IFN-γ-stimulated IL-15 DCs by the cooperation between the E3 SUMO ligase PIAS1 and STAT-3, and can be partially restored with PIAS1 siRNA and STAT-3 inhibitors.

Dendritic cell-tumor cell hybrids and immunotherapy: what's next?

Dendritic cells (DC) are professional antigen-presenting cells currently being used as a cellular adjuvant in cancer immunotherapy strategies. Unfortunately, DC-based vaccines have not demonstrated spectacular clinical results. DC loading with tumor antigens and DC differentiation and activation still require optimization. An alternative technique for providing antigens to DC consists of the direct fusion of dendritic cells with tumor cells. These resulting hybrid cells may express both major histocompatibility complex (MHC) class I and II molecules associated with tumor antigens and the appropriate co-stimulatory molecules required for T-cell activation. Initially tested in animal models, this approach has now been evaluated in clinical trials, although with limited success. We summarize and discuss the results from the animal studies and first clinical trials. We also present a new approach to inducing hybrid formation by expression of viral fusogenic membrane glycoproteins.

Allogeneic effector/memory Th-1 cells impair FoxP3+ regulatory T lymphocytes and synergize with chaperone-rich cell lysate vaccine to treat leukemia

Therapeutic strategies combining the induction of effective antitumor immunity with the inhibition of the mechanisms of tumor-induced immunosuppression represent a key objective in cancer immunotherapy. Herein we demonstrate that effector/memory CD4(+) T helper-1 (Th-1) lymphocytes, in addition to polarizing type-1 antitumor immune responses, impair tumor-induced CD4(+)CD25(+)FoxP3(+) regulatory T lymphocyte (Treg) immunosuppressive function in vitro and in vivo. Th-1 cells also inhibit the generation of FoxP3(+) Tregs from naive CD4(+)CD25(-)FoxP3(-) T cells by an interferon-γ-dependent mechanism. In addition, in an aggressive mouse leukemia model (12B1), Th-1 lymphocytes act synergistically with a chaperone-rich cell lysate (CRCL) vaccine, leading to improved survival and long-lasting protection against leukemia. The combination of CRCL as a source of tumor-specific antigens and Th-1 lymphocytes as an adjuvant has the potential to stimulate efficient specific antitumor immunity while restraining Treg-induced suppression.

Recent advances in antigen-loaded dendritic cell-based strategies for treatment of minimal residual disease in acute myeloid leukemia

Therapeutic vaccination with dendritic cells (DCs) is recognized as an important experimental therapy for the treatment of minimal residual disease in acute myeloid leukemia. Many sources of leukemia-associated antigens and different methods for antigen loading of DCs have been used in an attempt to optimize anti-tumor responses. For instance, monocyte-derived DCs have been loaded with apoptotic whole-cell suspensions, necrotic cell lysates, tumor-associated peptides, eluted peptides and cellular DNA or RNA. Furthermore, monocyte-derived DCs can be chemically or electrically fused with leukemic blasts, and DCs have been cultured out of leukemic blasts. However, it remains a challenge in cancer immunotherapy to identify which of these methods is the most optimal for antigen loading and activation of DCs. This review discusses recent advances in DC research and the application of this knowledge towards new strategies for antigen loading of DCs in the treatment of minimal residual disease in acute myeloid leukemia.

Efficacy of dendritic cells matured early with OK-432 (Picibanil), prostaglandin E2, and interferon-alpha as a vaccine for a hormone refractory prostate cancer cell line

Dendritic cells (DCs) are potent antigen-presenting cells. OK432 (Picibanil) was introduced as a potent stimulator of DC maturation in combination with prostaglandin-E(2) and interferon-alpha. We compared the efficacy of a DC-prostate cancer vaccine using early-mature DCs stimulated with OK432, PGE2 and INF-alpha (OPA) with that of vaccines using other methods. On days 3 or 7 of DC culture, TNF-alpha (T), TNF-alpha and LPS (TL) or OPA were employed as maturation stimulators. DU145 cells subjected to heat stress were hybridized with mature DCs using polyethyleneglycol. T cells were sensitized by the hybrids, and their proliferative and cytokine secretion activities and cytotoxicity were measured. The yields of early-mature DCs were higher, compared to yields at the conventional maturation time (P<0.05). In the early maturation setting, the mean fusion ratios, calculated from the fraction of dual-positive cells, were 13.3%, 18.6%, and 39.9%, respectively (P=0.051) in the T only, TL, and OPA-treated groups. The function of cytotoxic T cells, which were sensitized with the hybrids containing DCs matured early with OPA, was superior to that using other methods. The antitumor effects of DC-DU145 hybrids generated with DCs subjected to early maturation with the OPA may be superior to that of the hybrids using conventional maturation methods.

Peroxynitrite-dependent killing of cancer cells and presentation of released tumor antigens by activated dendritic cells

Dendritic cells (DCs), essential for the initiation and regulation of adaptive immune responses, have been used as anticancer vaccines. DCs may also directly trigger tumor cell death. In the current study, we have investigated the tumoricidal and immunostimulatory activities of mouse bone marrow-derived DCs. Our results indicate that these cells acquire killing capabilities toward tumor cells only when activated with LPS or Pam3Cys-SK4. Using different transgenic mouse models including inducible NO synthase or GP91 knockout mice, we have further established that LPS- or Pam3Cys-SK4-activated DC killing activity involves peroxynitrites. Importantly, after killing of cancer cells, DCs are capable of engulfing dead tumor cell fragments and of presenting tumor Ags to specific T lymphocytes. Thus, upon specific stimulation, mouse bone marrow-derived DCs can directly kill tumor cells through a novel peroxynitrite-dependent mechanism and participate at virtually all levels of antitumor immune responses, which reinforces their interest in immunotherapy.

Personalized dendritic cell-based tumor immunotherapy

Advances in the understanding of the immunoregulatory functions of dendritic cells (DCs) in animal models and humans have led to their exploitation as anticancer vaccines. Although DC-based immunotherapy has proven clinically safe and efficient to induce tumor-specific immune responses, only a limited number of objective clinical responses have been reported in cancer patients. These relatively disappointing results have prompted the evaluation of multiple approaches to improve the efficacy of DC vaccines. The topic of this review focuses on personalized DC-based anticancer vaccines, which in theory have the potential to present to the host immune system the entire repertoire of antigens harbored by autologous tumor cells. We also discuss the implementation of these vaccines in cancer therapeutic strategies, their limitations and the future challenges for effective immunotherapy against cancer.

Killer dendritic cells and their potential for cancer immunotherapy

Known for years as the principal messengers of the immune system, dendritic cells (DC) represent a heterogeneous population of antigen presenting cells critically located at the nexus between innate and adaptive immunity. DC play a central role in the initiation of tumor-specific immune responses as they are endowed with the unique ability to take up, process and present tumor antigens to naïve CD4(+) or CD8(+) effector T lymphocytes. By virtue of the cytokines they produce, DC also regulate the type, strength and duration of T cell immune responses. In addition, they can participate in anti-tumoral NK and NKT cell activation and in the orchestration of humoral immunity. More recent studies have documented that besides their primary role in the induction and regulation of adaptive anti-tumoral immune responses, DC are also endowed with the capacity to directly kill cancer cells. This dual role of DC as killers and messengers may have important implications for tumor immunotherapy. First, the direct killing of malignant cells by DC may foster the release and thereby the immediate availability of specific tumor antigens for presentation to cytotoxic or helper T lymphocytes. Second, DC may participate in the effector phase of the immune response, potentially augmenting the diversity of the killing mechanisms leading to tumor elimination. This review focuses on this non-conventional cytotoxic function of DC as it relates to the promotion of cancer immunity and discusses the potential application of killer DC (KDC) in tumor immunotherapy.

Signaling pathways induced by a tumor-derived vaccine in antigen presenting cells

We have previously reported on the anti-tumoral potential of a chaperone-rich cell lysate (CRCL) vaccine. Immunization with CRCL generated from tumors elicits specific T and NK cell-dependent immune responses leading to protective immunity in numerous mouse tumor models. CRCL provides both a source of tumor antigens and danger signals leading to dendritic cell activation. In humans, tumor-derived CRCL induces dendritic cell activation and CRCL-loaded dendritic cells promote the generation of cytotoxic T lymphocytes in vitro. The current study was designed to identify the signaling events and modifications triggered by CRCL in antigen presenting cells. Our results indicate that tumor-derived CRCL not only promotes the activation of dendritic cells, but also significantly fosters the function of macrophages that thus appear as major targets of this vaccine. Activation of both cell types is associated with the induction of the MAP kinase pathway, the phosphorylation of STAT1, STAT5 and AKT and with transcription factor NF-kappaB activation in vitro and in vivo. These results thus provide important insights into the mechanisms by which CRCL-based vaccines exert their adjuvant effects on antigen presenting cells.

Dendritic cell-based cancer immunotherapies

Because of their unique role in linking the innate and adaptive immune systems, dendritic cells (DCs) have been a logical focus for novel immunotherapies. However, strategies employing active immunization with ex vivo generated and antigen-pulsed DCs have shown limited efficacy in clinical trials. These past approaches did not take into account the complex interactions between cells of the innate immune system and DCs during DC maturation, antigen processing, and presentation to naïve T cells. By better understanding the natural sequence of events occurring in vivo during an effective immune response, we can tailor antitumor immunotherapeutic strategies to augment aspects of this response from the activation of innate immune cells to antigen uptake and DC maturation to priming of naïve T cells and, ultimately, to the establishment of antitumor immunity. Current DC vaccination strategies utilize a number of methods to recapitulate the cascade of events that culminate in a protective antitumor immune response.

Optimization of dendritic cell loading with tumor cell lysates for cancer immunotherapy

The immune response to cancer is critically determined by the way in which tumor cells die. As necrotic, stress-associated death can be associated with activation of antitumor immunity, whole tumor cell antigen loading strategies for dendritic cell (DC)-based vaccination have commonly used freeze-thaw "necrotic" lysates as an immunogenic source of tumor-associated antigens. In this study, the effect of such lysates on the ability of DCs to mature in response to well-established maturation stimuli was examined, and methods to enhance lysate-induced DC activation explored. Freeze-thaw lysates were prepared from murine tumor cell lines and their effects on bone marrow-derived DC maturation and function examined. Unmodified freeze-thaw tumor cell lysates inhibited the toll-like receptor-induced maturation and function of bone marrow-derived DCs, preventing up-regulation of CD40, CD86, and major histocompatibility complex class II, and reducing secretion of inflammatory cytokines [interleukin (IL)-12 p70, tumor necrosis factor-alpha, and IL-6]. Although IL-10 secretion was increased by lysate-pulsed DCs, this was not responsible for the observed suppression of IL-12. Although activation of the nuclear factor-kappaB pathway remained intact, the kinase activity of phosphorylated p38 mitogen-activated protein kinase was inhibited in lysate-pulsed DCs. Lysate-induced DC suppression was partially reversed in vitro by induction of tumor cell stress before lysis, and only DCs loaded with stressed lysates afforded protection against tumor challenge in vivo. These data suggest that ex vivo freeze-thaw of tumor cells does not effectively mimic in vivo immunogenic necrosis, and advocates careful characterization and optimization of tumor cell-derived vaccine sources for cancer immunotherapy.

Optimization of dendritic cell loading with tumor cell lysates for cancer immunotherapy

The immune response to cancer is critically determined by the way in which tumor cells die. As necrotic, stress-associated death can be associated with activation of antitumor immunity, whole tumor cell antigen loading strategies for dendritic cell (DC)-based vaccination have commonly used freeze-thaw "necrotic" lysates as an immunogenic source of tumor-associated antigens. In this study, the effect of such lysates on the ability of DCs to mature in response to well-established maturation stimuli was examined, and methods to enhance lysate-induced DC activation explored. Freeze-thaw lysates were prepared from murine tumor cell lines and their effects on bone marrow-derived DC maturation and function examined. Unmodified freeze-thaw tumor cell lysates inhibited the toll-like receptor-induced maturation and function of bone marrow-derived DCs, preventing up-regulation of CD40, CD86, and major histocompatibility complex class II, and reducing secretion of inflammatory cytokines [interleukin (IL)-12 p70, tumor necrosis factor-alpha, and IL-6]. Although IL-10 secretion was increased by lysate-pulsed DCs, this was not responsible for the observed suppression of IL-12. Although activation of the nuclear factor-kappaB pathway remained intact, the kinase activity of phosphorylated p38 mitogen-activated protein kinase was inhibited in lysate-pulsed DCs. Lysate-induced DC suppression was partially reversed in vitro by induction of tumor cell stress before lysis, and only DCs loaded with stressed lysates afforded protection against tumor challenge in vivo. These data suggest that ex vivo freeze-thaw of tumor cells does not effectively mimic in vivo immunogenic necrosis, and advocates careful characterization and optimization of tumor cell-derived vaccine sources for cancer immunotherapy.

Recognition of live phosphatidylserine-labeled tumor cells by dendritic cells: a novel approach to immunotherapy of skin cancer

Dendritic cells (DC) loaded with tumor antigens from apoptotic/necrotic tumor cells are commonly used as vaccines for cancer therapy. However, the use of dead tumor cells may cause both tolerance and immunity, making the effect of vaccination unpredictable. To deliver live tumor "cargoes" into DC, we developed a new approach based on the "labeling" of tumors with a phospholipid "eat-me" signal, phosphatidylserine. Expression of phosphatidylserine on live tumor cells mediated their recognition and endocytosis by DC resulting in the presentation of tumor antigens to antigen-specific T cells. In mice, topical application of phosphatidylserine-containing ointment over melanoma induced tumor-specific CTL, local and systemic antitumor immunity, and inhibited tumor growth. Thus, labeling of tumors with phosphatidylserine is a promising strategy for cancer immunotherapy.

Dendritic cell vaccines in acute leukaemia

There is a need for novel treatment for acute leukaemia as relapse rates remain unacceptably high. Immunotherapy aims to stimulate the patient's immune responses to recognize and destroy leukaemia cells whilst activating immune memory. The qualities of the most potent professional antigen-presenting cell, the dendritic cell (DC), can be used to stimulate leukaemia-specific cytotoxic T cells. DCs can be loaded with leukaemia antigens, or leukaemia blasts can be modified to express DC-like properties for use in vaccine therapy. This chapter will review the rationale for DC vaccine therapy, the preclinical and clinical trials to date, the barriers to successful DC vaccine therapies and the role of immune adjuncts to improve outcomes.

Low-dose chemotherapeutic agents regulate small Rho GTPase activity in dendritic cells

Conventional chemotherapy targets dividing tumor cells and might support antitumor immunity by providing tumor antigens from dying tumor cells to antigen-presenting dendritic cells (DCs). Despite emerging evidence to suggest that phagocytosis of dying tumor cells by DCs requires membrane targeting of specific small Rho guanosine triphosphatases (GTPases), nothing is known with regard to the direct effect of chemotherapeutic agents on low molecular weight Rho GTPases in DCs. Prompted by a recent observation that low-dose chemotherapeutic drug paclitaxel could up-regulate DC maturation and function, here we studied putative regulatory roles for various chemotherapeutic agents in modulating small Rho GTPases in DC. Our results demonstrate that different classes of chemotherapeutic drugs at low nontoxic concentrations regulate activity of Rac, RhoA, and RhoE in murine DC, suggesting that small Rho GTPases might serve as new targets for modulating functional activity of DC vaccines or endogenous DCs in various immunotherapeutic or chemoimmunotherapeutic strategies.

T-cell responses to survivin in cancer patients undergoing radiation therapy

PURPOSE

The goal of this study was to determine if radiation therapy (RT) of human cancer enhances or diminishes tumor-specific T-cell reactivity. This is important if immunotherapy is to be harnessed to improve the outcome of cancer radiotherapy.

EXPERIMENTAL DESIGN

Lymphocytes were isolated from colorectal cancer (CRC) patients before, during, and after presurgical chemoradiotherapy. Similar samples were taken from prostate cancer patients receiving standard RT. The level of CD8(+) T cells capable of binding tetramers for the tumor-associated antigen survivin, which is overexpressed in both cancer types, was enumerated in HLA-A*0201 patient samples. CD4(+), CD25(high), Foxp3(+) cells were also enumerated to evaluate therapy-induced changes in T(regulatory) cells. For CRC patients, most of whom were enrolled in a clinical trial, pathologic response data were available, as well as biopsy and resection specimens, which were stained for cytoplasmic and intranuclear survivin.

RESULTS

Survivin-specific CD8(+) T lymphocytes were detected in the peripheral blood of CRC and prostate cancer patients and increased after therapy in some, but not all, patients. Increases were more common in CRC patients whose tumor was downstaged after chemoradiotherapy. Biopsy specimens from this cohort generally had higher nuclear to cytoplasmic survivin expression. T(regulatory) cells generally increased in the circulation following therapy but only in CRC patients.

CONCLUSION

This study indicates that RT may increase the likelihood of some cancer patients responding to immunotherapy and lays a basis for future investigations aimed at combining radiation and immunotherapy.

Localized hyperthermia combined with intratumoral dendritic cells induces systemic antitumor immunity

Prostate adenocarcinoma, treated with localized tumor hyperthermia (LTH), can potentially serve as a source of tumor antigen, where dying apoptotic/necrotic cells release tumor peptides slowly over time. In addition, LTH-treated cells can release heat shock proteins that can chaperone antigenic peptides to antigen-presenting cells, such as dendritic cells. We attempted to discern whether sequential LTH and intratumoral dendritic cell and/or systemic granulocyte macrophage colony-stimulating factor (GM-CSF) would activate antitumor immune response in a syngeneic murine model of prostate cancer (RM-1). Palpable RM-1 tumors, grown in the distal appendage of C57BL/6 male mice, were subjected to LTH (43.7 degrees C for 1 h) x 2, separated by 5 days. Following the second LTH treatment, animals received either PBS or dendritic cells (2 x 10(6)) intratumorally (every 3 days for three injections). Separate cohorts also received i.v. injection of recombinant adenovirus-expressing murine GM-CSF (AdGMCSF), 1 day after LTH. Control animals received AdenoLacZ or AdenoGFP. Intratumoral dendritic cell injection induced tumor-specific T-helper cell activity (IFNgamma ELISPOTS) and CTL activity, which was further augmented by AdGMCSF, indicating amplification of tumor-specific TH1 immunity. The combination of LTH, AdGMCSF, and intratumoral dendritic cell injection resulted in significant tumor growth delays when compared with animal cohorts that received LTH alone. These results support an in situ autovaccination strategy where systemic administration of GM-CSF and/or intratumoral injection of autologous dendritic cells, when combined with LTH, could be an effective treatment for local and systemic recurrence of prostate cancer.

Dendritic cells trigger tumor cell death by a nitric oxide-dependent mechanism

Dendritic cells (DCs) are well known for their capacity to induce adaptive antitumor immune response through Ag presentation and tumor-specific T cell activation. Recent findings reveal that besides this role, DCs may display additional antitumor effects. In this study, we provide evidence that LPS- or IFN-gamma-activated rat bone marrow-derived dendritic cells (BMDCs) display killing properties against tumor cells. These cytotoxic BMDCs exhibit a mature DC phenotype, produce high amounts of IL-12, IL-6, and TNF-alpha, and retain their phagocytic properties. BMDC-mediated tumor cell killing requires cell-cell contact and depends on NO production, but not on perforin/granzyme or on death receptors. Furthermore, dead tumor cells do not exhibit characteristics of apoptosis. Thus, intratumoral LPS injections induce an increase of inducible NO synthase expression in tumor-infiltrating DCs associated with a significant arrest of tumor growth. Altogether, these results suggest that LPS-activated BMDCs represent powerful tumoricidal cells which enforce their potential as anticancer cellular vaccines.

Mechanisms of dendritic cell-based vaccination against infection

Due to their unique capacity to initiate and regulate adaptive immune responses, dendritic cells (DC) represent the most potent antigen-presenting cells of the immune system. Immature DC reside in peripheral tissues, where they sample and process antigens and efficiently sense a large variety of signals from the surrounding environment. Toll-like receptors (TLR) expressed by DC play a critical role in the detection of invading pathogens as well as in triggering the subsequent immune responses. The differential expression of TLR by different DC subsets may correlate with the induction of different patterns of adaptive immune responses. The rapidly expanding and fundamental knowledge of DC biology furthers promising perspectives for the development of vaccination strategies in different fields. For example, the immunotherapeutic potential of antigen-pulsed DC for the treatment of cancer has been confirmed in a number of experimental tumour models. Furthermore, DC have been shown to serve as natural adjuvants in different models of infectious diseases, mediating protection against various types of pathogens. Using murine leishmaniasis as an example, we have demonstrated that DC, once properly conditioned ex vivo, mediate complete and durable protection against infection. Critical parameters determining the efficiency of DC-based vaccination against microbial pathogens include the origin of DC, the choice of antigen to be used for DC loading, the route of immunization and the state of DC maturation and activation. In the present review, we discuss the necessity to define the mechanisms responsible for the immunostimulatory capacity of DC in vivo, in order to exploit their full potential as vaccination tools.

The inhibition of TNF-alpha anti-tumoral properties by blocking antibodies promotes tumor growth in a rat model

Tumor necrosis factor (TNF) antagonists represent a milestone in the therapy of autoimmune conditions. Anti-TNF antibodies have been approved for clinical use and during the last eight years thousands of patients have been treated. However, the long-term sequelae of anti-TNF agents in promoting carcinogenesis remain unclear. This study sought to define the role of intra-tumor TNF-alpha production on cancer cell progression and to determine whether TNF-alpha antibodies can suppress anti-tumoral immunity. Using an experimental animal tumor model we demonstrate that anti-TNF-alpha antibodies hinder anti-tumor immune responses and promote growth of immunogenic rat colon tumors (REG) that are always rejected by immunocompetent untreated rats. The major role of TNF-alpha in the anti-tumoral immune response was confirmed by transfecting progressive and tolerogenic rat colon tumor cells (PRO) with the TNF-alpha gene. PRO tumor cells secreting TNF-alpha induce tumor-infiltrating dendritic cell (DC) activation. This triggers a potent immune response leading to tumor rejection and long-lasting immunity. Therefore, the prominent role of TNF-alpha in anti-tumoral immune responses underscores the need for caution and close surveillance following the administration of TNF inhibitors.