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Abstract
The recent therapeutic success of immune checkpoint inhibitors in the treatment of advanced melanoma highlights the potential of cancer immunotherapy. Oncolytic virus-based therapies may further improve the outcome of these cancer patients. A human ex vivo melanoma model was used to investigate the oncolytic parvovirus H-1 (H-1PV) in combination with ipilimumab and/or nivolumab. The effect of this combination on activation of human T lymphocytes was demonstrated. Expression of CTLA-4, PD-1, and PD-L1 immune checkpoint proteins was upregulated in H-1PV-infected melanoma cells. Nevertheless, maturation of antigen presenting cells such as dendritic cells was triggered by H-1PV infected melanoma cells. Combining H-1PV with checkpoint inhibitors, ipilimumab enhanced TNFα release during maturation of dendritic cells; nivolumab increased the amount of IFNγ release. H-1PV mediated reduction of regulatory T cell activity was demonstrated by lower TGF-ß levels. The combination of ipilimumab and nivolumab resulted in a further decline of TGF-ß levels. Similar results were obtained regarding the activation of cytotoxic T cells. H-1PV infection alone and in combination with both checkpoint inhibitors caused strong activation of CTLs, which was reflected by an increased number of CD8+GranB+ cells and increased release of granzyme B, IFNγ, and TNFα. Our data support the concept of a treatment benefit from combining oncolytic H-1PV with the checkpoint inhibitors ipilimumab and nivolumab, with nivolumab inducing stronger effects on cytotoxic T cells, and ipilimumab strengthening T lymphocyte activity.
Highlights
In recent years, major advances have been achieved in the treatment of advanced melanoma based on a better understanding of the interaction between melanoma cells and the cells of the human immune system [1]
H-1PV inoculation generates immunogenic tumor cell lysates which have been shown to induce the maturation of dendritic cells (DCs), the release of pro-inflammatory cytokines, tumor associated antigen cross presentation, and T cell stimulation in human melanoma and glioma cells [6, 9, 10]
In order to assess the potential in combining oncolytic virotherapy with immune checkpoint inhibition, melanoma cell lines Sk29Mel-1 and Mz7Mel were first analyzed for expression of the immune checkpoint proteins cytotoxic T lymphocyte associated protein-4 (CTLA-4), PD-1, and PDL1
Summary
Major advances have been achieved in the treatment of advanced melanoma based on a better understanding of the interaction between melanoma cells and the cells of the human immune system [1]. Immune-based therapies including ipilimumab and nivolumab or oncolytic virus therapies such as Talimogene laherparepvec (T-VEC) have been developed and approved for the treatment of melanoma patients leading to an improvement in response rates and progression-free survival [2,3,4]. Autonomous rat parvovirus H-1 (H-1PV), a small nuclear-replicating DNA virus, has been shown to induce cell lysis in human malignant cells including colon carcinoma, melanoma and pancreatic adenocarcinoma leaving healthy cells unaffected (oncotropism) [5,6,7,8]. Clinical trials in patients with glioblastoma have demonstrated that H-1PV suppresses the activity of regulatory T cells (Treg) and promotes immune cell activation (CD8+- and CD4+- T lymphocytes as well as tumor associated macrophages) as indicated by increasing serum levels of perforin, granzyme B, IFNγ, and IL-2 [11,12,13,14]. Synergistic cytotoxic effects of H-1PV combined with gemcitabine in pancreatic cancer have been demonstrated, little is known about combinations of H-1PV with other cytotoxic drugs or checkpoint inhibitors [8, 15]
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