SITC 2015: Intralesional Rose Bengal in Melanoma Elicits Tumor Immunity via HMGB1

Updated again below.

Abstract: Intralesional (IL) therapy is under investigation to treat dermal and subcutaneous metastatic cancer. Rose Bengal (RB) is a staining agent that was originally used by ophthalmologists and in liver function studies. Previously, IL injection of RB induced regression of injected and uninjected tumors in murine models. However, the relevant mechanism is yet unknown. In this study, we used an OVA-expressing B16 melanoma murine model and found that IL RB treatment led to increased tumor-specific T cells with memory characteristics. CD8+ T cell are crucial for tumor-specific response elicited by IL RB. IL RB therapy also increased antigen-specific T cell proliferation and enhanced tumor regression. In addition, IL RB facilitated dendritic cells (DCs) infiltrating lymph nodes draining from tumor. Incubation of melanoma cells with RB led to necrosis and the release of High Mobility Group Box 1 (HMGB1), which activated DCs via up-regulation of CD40 expression. The blockade of HMGB1 significantly reduced the antigen-presenting ability of DCs. To determine whether this mechanism was relevant in patients treated with IL RB, we performed a pilot clinical study in melanoma patients (NCT01760499). IL RB led to tumor regression in both RB-injected and uninjected lesions, associated with an increase in circulating T cells. Increased tumor-specific response was found from those circulating T cells of 5 out of 7 tested patients after IL RB treatment. HMGB1 levels in patient sera were also elevated. Together, these results reveal a clinically relevant immunoadjuvant pathway triggered by tumor cell death secondary to ablation with RB.

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Updated (11/3/15): Items in the abstract of note [to me]:

• "However, the relevant mechanism is yet unknown."

• Clinical (human) data: "Increased tumor-specific response was found from those circulating T cells of 5 out of 7 tested patients after IL RB treatment." {Underlined emphasisis is mine}

• "Together, these results reveal a clinically relevant immunoadjuvant pathway triggered by tumor cell death secondary to ablation with RB."

• "clinically relevant"
• "immunoadjuvant pathway"

Updated (11/3/15): "Clinically relevant" {Underlined emphasis is mine}

"In clinical research is not only important to assess the significance of the differences between the evaluated groups but also it is recommended, if possible, to measure how meaningful the outcome is (for instance, to evaluate the effectiveness and efficacy of an intervention). Statistical significance does not provide information about the effect size or the clinical relevance. Because of that, researchers often misinterpret statistically significance as clinical one. On one hand, a large sample size study may have a statistically significant result but a small effect size. Outcomes with small p-values are often misunderstood as having strong effect sizes. On the other hand, another misinterpretation is present when non statistical significant difference could lead to a large effect size but a small sample may not have enough power to reveal that effect." (Source)

"Ideally, a clinical trial should be able to demonstrate not only a statistically significant improvement in the primary efficacy endpoint, but also that the magnitude of the effect is clinically relevant...However, it is not only important to assess statistical significance, but also to assess the clinical relevance of the effect, and the assessment of clinical relevance has received much less attention in the statistical literature." (Source)

"Immunoadjuvant pathway triggered by tumor cell death:" {Underlined emphasis is mine}

"Conventional cancer treatments rely on radiotherapy and chemotherapy. Such treatments supposedly mediate their effects via the direct elimination of tumor cells. Here we show that the success of some protocols for anticancer therapy depends on innate and adaptive antitumor immune responses. We describe in both mice and humans a previously unrecognized pathway for the activation of tumor antigen-specific T-cell immunity that involves secretion of the high-mobility-group box 1 (HMGB1) alarmin protein by dying tumor cells and the action of HMGB1 on Toll-like receptor 4 (TLR4) expressed by dendritic cells (DCs). During chemotherapy or radiotherapy, DCs require signaling through TLR4 and its adaptor MyD88 for efficient processing and cross-presentation of antigen from dying tumor cells. Patients with breast cancer who carry a TLR4 loss-of-function allele relapse more quickly after radiotherapy and chemotherapy than those carrying the normal TLR4 allele. These results delineate a clinically relevant immunoadjuvant pathway triggered by tumor cell death." (Source: Apetoh et al. Toll-like receptor 4-dependent contribution of the immune system to anticancer chemotherapy and radiotherapy. Nat. Med. 13, 1050–1059)

"Incubation of melanoma cells with RB led to necrosis and the release of High Mobility Group Box 1 (HMGB1), which activated DCs via up-regulation of CD40 expression."

"CD40 was initially characterized as a co-stimulatory molecule expressed on APCs that played a central role in B and T cell activation. However, this molecular pair functions in the regulation of both APCs and effector lymphocytes (Fig. 1). As we understand more about the number of different DC and T cell subsets, we are likely to find that CD40-CD40L interactions play important and distinct roles in regulating these novel subsets. In addition, as we continue to understand how innate immunity cells directly regulate B cells and antibody responses, the influence of CD40 and CD40L in these interactions should be further clarified. Further insights into the functions of CD40-CD40L interactions will advance our understanding of immune cell crosstalk and interdependent regulation of the immune system." (Source: Ma DY, Clark EA. The role of CD40 and CD40L in Dendritic Cells. Seminars in immunology. 2009;21(5):265-272.)