Dendritic cell vaccination as a treatment modality for melanoma

Adjuvant Therapy of Uveal Melanoma: Current Status

The survival of patients with uveal melanoma remains poor because of the development of metastatic disease. Adjuvant therapy after treatment of the primary tumor has been tested but has not been shown to prevent the development of metastasis. Several new approaches are being developed. Cytotoxic and immunotherapeutic regimens are being more rationally applied using tumor genetic criteria to better identify patients at risk. Trials in the adjuvant setting of novel immunotherapeutic and targeted agents active in the metastatic setting are being developed, as are approaches to promote cellular differentiation and dormancy. The rarity and biology of uveal melanoma present challenges. Participation in well-designed, scientifically sound clinical trials is critical.

Antigen cross-presentation of immune complexes

The ability of dendritic cells (DCs) to cross-present tumor antigens has long been a focus of interest to physicians, as well as basic scientists, that aim to establish efficient cell-based cancer immune therapy. A prerequisite for exploiting this pathway for therapeutic purposes is a better understanding of the mechanisms that underlie the induction of tumor-specific cytotoxic T-lymphocyte (CTL) responses when initiated by DCs via cross-presentation. The ability of humans DC to perform cross-presentation is of utmost interest, as this cell type is a main target for cell-based immunotherapy in humans. The outcome of a cross-presentation event is guided by the nature of the antigen, the form of antigen uptake, and the subpopulation of DCs that performs presentation. Generally, CD8α⁺ DCs are considered to be the most potent cross-presenting DCs. This paradigm, however, only applies to soluble antigens. During adaptive immune responses, immune complexes form when antibodies interact with their specific epitopes on soluble antigens. Immunoglobulin G (IgG) immune complexes target Fc-gamma receptors on DCs to shuttle exogenous antigens efficiently into the cross-presentation pathway. This receptor-mediated cross-presentation pathway is a well-described route for the induction of strong CD8⁺ T cell responses. IgG-mediated cross-presentation is intriguing because it permits the CD8⁻ DCs, which are commonly considered to be weak cross-presenters, to efficiently cross-present. Engaging multiple DC subtypes for cross-presentation might be a superior strategy to boost CTL responses in vivo. We here summarize our current understanding of how DCs use IgG-complexed antigens for the efficient induction of CTL responses. Because of its importance for human cell therapy, we also review the recent advances in the characterization of cross-presentation properties of human DC subsets.

Implementing combinatorial immunotherapeutic regimens against cancer: The concept of immunological conditioning

Harnessing the host immune system to eradicate cancer has a high therapeutic potential. One paradigm of anticancer immunotherapy is represented by allogeneic stem cell transplantation. In this setting, the host must be conditioned prior to transplantation, allowing for engraftment and subsequent graft-vs.-tumor reactivity. Conditioning may also be a prerequisite for the efficacy of other immunotherapeutic regimens. In particular, tumor debulking followed by conditioning (aimed at blocking endogenous inhibitory stimuli, for instance upon the depletion of regulatory T cells or the inhibition of immune checkpoints) and subsequent immunization (for instance by means of patient-tailored vaccines) based on innovative adjuvants (such as RIG-I ligands) may allow for the elicitation of superior antitumor immune responses. Repetitive boosting might then maintain immunosurveillance. An intense wave of investigation on the optimal timing of immunostimulatory interventions with respect to the administration of immunogenic chemotherapeutics and on the use of small drugs that promote efficient antitumor immune responses will end up in the generation of highly effective immunotherapeutic anticancer regimens.

Cancer stem cell antigen-based vaccines: the preferred strategy for active specific immunotherapy of metastatic melanoma?

INTRODUCTION

There are now two chemotherapy agents, one tyrosine kinase inhibitor and three immunotherapy products approved for the treatment of metastatic melanoma, but an unmet need persists because these options are toxic and of limited therapeutic benefit. Active specific immunotherapy with therapeutic vaccines could be a useful addition to the therapeutic armamentarium, especially in patients whose tumor burden has been reduced by other treatment modalities.

AREAS COVERED

This article reviews various sources of melanoma antigens, such as peptides, gangliosides, autologous tumor and cancer stem cells including allogeneic and autologous cell lines. The advantages and disadvantages of various antigen sources and allogeneic and autologous approaches are discussed with an emphasis on the theoretical benefits of immunizing against cancer stem cells. The results from published randomized trials testing the benefit of various vaccine approaches are summarized, as well as promising results from three Phase II trials (one randomized) of patient-specific stem cell antigen-based products.

EXPERT OPINION

Immune responses directed toward the unique neoantigens and stem cell antigens expressed on continuously proliferating, self-renewing, autologous tumor cells could potentially overcome the limitations inherent in these other antigen-based approaches, that to date, have yielded disappointing results in randomized trials.

Melanoma stem cells in experimental melanoma are killed by radioimmunotherapy

INTRODUCTION

In spite of recently approved B-RAF inhibitors and immunomodulating antibodies, metastatic melanoma has poor prognosis and novel treatments are needed. Melanoma stem cells (MSC) have been implicated in the resistance of this tumor to chemotherapy. Recently we demonstrated in a Phase I clinical trial in patients with metastatic melanoma that radioimmunotherapy (RIT) with 188-Rhenium((188)Re)-6D2 antibody to melanin was a safe and effective modality. Here we investigated the interaction of MSC with RIT as a possible mechanism for RIT efficacy.

METHODS

Mice bearing A2058 melanoma xenografts were treated with either 1.5 mCi (188)Re-6D2 antibody, saline, unlabeled 6D2 antibody or (188)Re-labeled non-specific IgM.

RESULTS

On Day 28 post-treatment the tumor size in the RIT group was 4-times less than in controls (P<0.001). The tumors were analyzed by immunohistochemistry and FACS for two MSC markers--chemoresistance mediator ABCB5 and H3K4 demethylase JARID1B. There were no significant differences between RIT and control groups in percentage of ABCB5 or JARID1B-positive cells in the tumor population. Our results demonstrate that unlike chemotherapy, which kills tumor cells but leaves behind MSC leading to recurrence, RIT kills MSC at the same rate as the rest of tumor cells.

CONCLUSIONS

These results have two main implications for melanoma treatment and possibly other cancers. First, the susceptibility of ABCB5+ and JARID1B+cells to RIT in melanoma might be indicative of their susceptibility to antibody-targeted radiation in other cancers where they are present as well. Second, specifically targeting cancer stem cells with radiolabeled antibodies to ABCB5 or JARID1B might help to completely eradicate cancer stem cells in various cancers.

Dendritic cells: indispensable?

Dendritic cells (DCs) control the initiation and differentiation of T cells. In the steady state, DCs mediate tolerance. To achieve immunization, the tolerogenic function of DCs must be switched off by inducing their maturation with appropriate "adjuvants." Dendritic cells form a system composed of distinct subsets that differ in their expression of endocytic and signaling receptors. These subsets have different capacities to differentiate and polarize T cells and to cross-present antigen to expand CD8+ T cells. Optimization of vaccines is possible by exploiting the unique biological properties of DCs.

Off-the-shelf adenoviral-mediated immunotherapy via bicistronic expression of tumor antigen and iMyD88/CD40 adjuvant

Recent modest successes in ex vivo dendritic cell (DC) immunotherapy have motivated continued innovation in the area of DC manipulation and activation. Although ex vivo vaccine approaches continue to be proving grounds for new DC manipulation techniques, the intrinsic limits of ex vivo therapy, including high cost, minimal standardization, cumbersome delivery, and poor accessibility, incentivizes the development of vaccines compatible with in vivo DC targeting. We describe here a method to co-deliver both tumor-specific antigen (TSA) and an iMyD88/CD40 adjuvant (iMC), to DCs that combines toll-like receptor (TLR) and CD40 signaling. In this study, we demonstrate that simple TSA delivery via adenoviral vectors results in strong antitumor immunity. Addition of iMC delivered in a separate vector is insufficient to enhance this effect. However, when delivered simultaneously with TSA in a single bicistronic vector (BV), iMC is able to significantly enhance antigen-specific cytotoxic T-cell (CTL) responses and inhibit established tumor growth. This study demonstrates the spatial-temporal importance of concurrent DC activation and TSA presentation. Further, it demonstrates the feasibility of in vivo molecular enhancement of DCs necessary for effective antitumor immune responses.

Targeting Dendritic Cells in vivo for Cancer Therapy

Monoclonal antibodies that recognize cell surface molecules have been used deliver antigenic cargo to dendritic cells (DC) for induction of immune responses. The encouraging anti-tumor immunity elicited using this immunization strategy suggests its suitability for clinical trials. This review discusses the complex network of DC, the functional specialization of DC subsets, the immunological outcomes of targeting different DC subsets and their cell surface receptors, and the requirements for the induction of effective anti-tumor CD4 and CD8 T cell responses that can recognize tumor-specific antigens. Finally, we review preclinical experiments and the progress toward targeting human DC in vivo.

Immunotherapy of malignant melanoma with tumor lysate-pulsed autologous monocyte-derived dendritic cells

PURPOSE

Dendritic cell (DC) vaccination for melanoma was introduced because melanoma carries distinct tumor-associated antigens. The purpose of this study was to investigate the efficacy and safety of DC vaccination for melanoma in Korea.

MATERIALS AND METHODS

Five patients with stage IV and one with stage II were enrolled. Autologous monocyte-derived DCs (MoDCs) were cultured and pulsed with tumor-lysate, keyhole limpet hemocyanin, and cytokine cocktail for mature antigen-loaded DC. DC vaccination was repeated four times at 2-week intervals and 2-4×10⁷ DC were injected each time.

RESULTS

Reduced tumor volume was observed by PET-CT in three patients after DC vaccination. Delayed type hypersensitivity responses against tumor antigen were induced in five patients. Tumor antigen-specific IFN-γ-producing peripheral blood mononuclear cells were detected with enzyme-linked immunosorbent spot in two patients. However, the overall clinical outcome showed disease progression in all patients.

CONCLUSION

In this study, DC vaccination using tumor antigen-loaded, mature MoDCs led to tumor regression in individual melanoma patients. Further standardization of DC vaccination protocol is required to determine which parameters lead to better anti-tumor responses and clinical outcomes.

Dendritic cells in cancer immunotherapy

DC initiate and regulate T-cell immunity and are thus the key to optimization of all types of vaccines. Insights into DC biology offer many opportunities to enhance immunogenicity. In this Viewpoint, I discuss some recent developments and findings that are of immediate relevance for the clinical development of cancer vaccines. In addition, I emphasize my personal view that we should explore the potential of adoptively transferred DC (i.e. DC vaccination) as cancer vaccines by performing two-armed trials that address critical variables and by delivering antigens via mRNA-transfected DC.

Optimizing dendritic cell-based immunotherapy in multiple myeloma: intranodal injections of idiotype-pulsed CD40 ligand-matured vaccines led to induction of type-1 and cytotoxic T-cell immune responses in patients

Vaccination with idiotype (Id) protein-pulsed dendritic cells (DCs) has been explored in multiple myeloma and the results have been disappointing. To improve the efficacy of DC vaccination in myeloma, we investigated the use of Id- and keyhole limpet haemocyanin (KLH)-pulsed, CD40 ligand-matured DCs administered intranodally. Nine patients with smouldering or stable myeloma without treatment were enrolled and DC vaccines were administered at weekly intervals for a total of four doses. Following vaccination, all patients mounted Id-specific gamma-interferon T-cell response. Interleukin-4 response was elicited in two, and skin delayed-type hypersensitivity reaction occurred in seven patients. More importantly, Id-specific cytotoxic T-cell responses were also detected in five patients. Most if not all patients mounted a positive T-cell response to KLH following vaccination. At 1-year follow-up, six of the nine patients had stable disease, while three patients had slowly progressive disease even during the vaccination period. At 5-year follow-up, four of the six patients continued with stable disease. No major side effects were noted. In summary, intranodal administration of Id-pulsed CD40 ligand-matured DCs was able to induce Id-specific T and B-cell responses in patients. Current efforts are geared towards breaking tumour-mediated immune suppression and improving clinical efficacy of this immunotherapy.