Combination of oncolytic Maraba virus with immune checkpoint blockade overcomes therapy resistance in an immunologically cold model of advanced melanoma with dysfunctional T-cell receptor signalling.

BACKGROUND: Over the past decade, cancer immunotherapies have revolutionized the treatment of melanoma; however, responses vary across patient populations. Recently, baseline tumor size has been identified as an independent prognostic factor for overall survival in patients with melanoma receiving immune checkpoint inhibitors. MG1 is a novel oncolytic agent with broad tumor tropism that has recently entered early-phase clinical trials. The aim of this study was to characterize T-cell responses in human and mouse melanoma models following MG1 treatment and to establish if features of the tumor immune microenvironment (TIME) at two distinct tumor burdens would impact the efficacy of oncolytic virotherapy. METHODS: Human three-dimensional in vitro priming assays were performed to measure antitumor and antiviral T-cell responses following MG1 infection. T-cell receptor (TCR) sequencing, T2 killing assay, and peptide recall assays were used to assess the evolution of the TCR repertoire, and measure specific T-cell responses, respectively. In vivo, subcutaneous 4434 melanomas were characterized using RNA sequencing, immunohistochemistry, and flow cytometry. The effectiveness of intratumoral MG1 was assessed in advancing 4434 tumors and the generation of antitumor and antiviral T cells measured by splenocyte recall assays. Finally, combination MG1 and programmed cell death protein-1 antibody (αPD-1) therapy was investigated in advanced 4434 tumors. RESULTS: MG1 effectively supported priming of functional cytotoxic T cells (CTLs) against tumor-associated antigens as well as virus-derived peptides, as assessed using peptide recall and T2 killing assays, respectively. TCR sequencing revealed that MG1-primed CTL comprised larger clusters of similar CDR3 amino acid sequences compared with controls. In vivo testing of MG1 demonstrated that MG1 monotherapy was highly effective at treating early disease, resulting in 90% cures; however, the efficacy of MG1 reduced as the disease burden (local tumor size) increased, and the addition of αPD-1 was required to overcome resistance in more advanced disease. Differential gene expression profiles revealed that increased tumor burden was associated with an immunologically colder TIME. Furthermore, analysis of TCR signaling in advancing tumors demonstrated a different dynamic of TCR engagement compared with smaller tumors, in particular a shift in antigen recognition by CD4+ cells, from conventional to regulatory subsets. CONCLUSION: Addition of αPD-1 to MG1 is required to overcome viral therapy resistance in immunologically 'colder' more advanced melanoma, highlighting the importance of tumor burden to different types of immunotherapy.

Triggering anti-GBM immune response with EGFR-mediated photoimmunotherapy.

BACKGROUND: Surgical resection followed by chemo-radiation postpones glioblastoma (GBM) progression and extends patient survival, but these tumours eventually recur. Multimodal treatment plans combining intraoperative techniques that maximise tumour excision with therapies aiming to remodel the immunologically cold GBM microenvironment could improve patients' outcomes. Herein, we report that targeted photoimmunotherapy (PIT) not only helps to define tumour location and margins but additionally promotes activation of anti-GBM T cell response. METHODS: EGFR-specific affibody molecule (ZEGFR:03115) was conjugated to IR700. The response to ZEGFR:03115-IR700-PIT was investigated in vitro and in vivo in GBM cell lines and xenograft model. To determine the tumour-specific immune response post-PIT, a syngeneic GBM model was used. RESULTS: In vitro findings confirmed the ability of ZEGFR:03115-IR700 to produce reactive oxygen species upon light irradiation. ZEGFR:03115-IR700-PIT promoted immunogenic cell death that triggered the release of damage-associated molecular patterns (DAMPs) (calreticulin, ATP, HSP70/90, and HMGB1) into the medium, leading to dendritic cell maturation. In vivo, therapeutic response to light-activated conjugate was observed in brain tumours as early as 1 h post-irradiation. Staining of the brain sections showed reduced cell proliferation, tumour necrosis, and microhaemorrhage within PIT-treated tumours that corroborated MRI T2*w acquisitions. Additionally, enhanced immunological response post-PIT resulted in the attraction and activation of T cells in mice bearing murine GBM brain tumours. CONCLUSIONS: Our data underline the potential of ZEGFR:03115-IR700 to accurately visualise EGFR-positive brain tumours and to destroy tumour cells post-conjugate irradiation turning an immunosuppressive tumour environment into an immune-vulnerable one.

Bacterial ghosts as adjuvant to oxaliplatin chemotherapy in colorectal carcinomatosis.

Colorectal cancer (CRC) is one of the most commonly diagnosed cancers and a major cause of cancer mortality worldwide. At late stage of the disease CRC often shows (multiple) metastatic lesions in the peritoneal cavity which cannot be efficiently targeted by systemic chemotherapy. This is one major factor contributing to poor prognosis. Oxaliplatin is one of the most commonly used systemic treatment options for advanced CRC. However, drug resistance - often due to insufficient drug delivery - is still hampering successful treatment. The anticancer activity of oxaliplatin includes besides DNA damage also a strong immunogenic component. Consequently, the aim of this study was to investigate the effect of bacterial ghosts (BGs) as adjuvant immunostimulant on oxaliplatin efficacy. BGs are empty envelopes of gram-negative bacteria with a distinct immune-stimulatory potential. Indeed, we were able to show that the combination of BGs with oxaliplatin treatment had strong synergistic anticancer activity against the CT26 allograft, resulting in prolonged survival and even a complete remission in this murine model of CRC carcinomatosis. This synergistic effect was based on an enhanced induction of immunogenic cell death and activation of an efficient T-cell response leading to long-term anti-tumor memory effects. Taken together, co-application of BGs strengthens the immunogenic component of the oxaliplatin anticancer response and thus represents a promising natural immune-adjuvant to chemotherapy in advanced CRC.