Over the past few years it has become evident that cancer cells can be recognized by the patient's own immune system. The immunological mechanisms at play are often referred to as the "cancer immune cycle" (Chen and Mellman 2013; Mellman 2013; Chen and Mellman 2017). Remarkable anti-tumor activity has been achieved by blocking the inhibitory T-cell receptor CTLA-4 and/or the PD-1/-L1 axis. Immune checkpoint inhibition by monoclonal antibody (mAb) therapy has become a standard of care in patients with advanced melanoma, renal cell carcinoma, non-small cell lung carcinoma, Hodgkin's lymphoma and bladder cancer. Indications are still expanding. Activity of PD-1 and CTLA-4 inhibition has been correlated with hallmarks of pre-existing anti-tumor T-cell response (e.g. presence of cytotoxic T lymphocytes (CTL) in the tumor microenvironment (TME), PD-L1 expression in response to T-cell secreted IFN-gamma and transcriptional evidence for CTL-activity), mutational load of the cancer cells and presence of highly immunogenic neo-epitopes in the cancer cell genome (Tumeh, Harview et al. 2014). In immune-evasive tumors a pivotal role has been attributed to myeloid dendritic cells (myDC) in regulating the activity of anti-tumor CTL activity within the TME (Broz, Binnewies et al. 2014). In animal models, myDC have been demonstrated to play an essential role in "licensing" anti-tumor CTLs to eradicate tumor cells. Activation of oncogenic signaling pathways such as the WNT/beta-Catenin pathway can lead to the exclusion of myeloid DC's from the TMZ (Spranger, Bao et al. 2015; Spranger and Gajewski 2016). Absence of myDCs at the invasive margin and within metastases has been correlated with defective CTL activation allowing the metastasis to escape the anti-tumor immune response (Salmon, Idoyaga et al. 2016). These myDC also migrate to tumor-draining lymph nodes and present tumor antigens to T-cells in these secondary lymphoid organs (Roberts, Broz et al. 2016). Presence of myeloid DC's was more strongly correlated with T-cell infiltration into tumors as compared to neo-antigen load in 266 melanomas from The Cancer Genome Atlas(Spranger, Luke et al. 2016). Human myDCs exist in two subsets that are differentiated by expression of either the BDCA-1 or BDCA-3 surface marker. The CD1c (BDCA-1)+ antigen is specifically expressed on human dendritic cells, which are CD11chighCD123low and represent the major subset of myDCs in human blood (about 0.6 % of all peripheral blood mononuclear cells (PBMC)). CD1c (BDCA-1)+ myDC have a monocytoid morphology and express myeloid markers such as CD13 and CD33 as well as Fc receptors such as CD32, CD64, and FceRI. Furthermore, myDC are determined to be CD4+, Lin (CD3, CD16, CD19, CD20, CD56)-, CD2+, CD45RO+, CD141 (BDCA-3)-low, CD303 (BDCA-2)-, and CD304 (BDCA-4/Neuropilin-1)-. A proportion of CD1c (BDCA-1)+ myDC co-expresses CD14 and CD11b. These dual positive cells for CD14+ and CD1c (BDCA-1) have immunosuppressive capacity and inhibit T-cell proliferation in vitro. Depletion of this cell type is preferred prior to using CD1c (BDCA-1)+ cells for immunostimulatory purposes (Bakdash, Buschow et al. 2016; Schroder, Melum et al. 2016). CD1c (BDCA-1)+ myDC play an important role in the cross-presentation of tumor antigens following immunogenic cell death (Di Blasio, Wortel et al. 2016). Under conditions of tumor growth, myDC will be poorly recruited to the tumor microenvironment, do not get activated and thereby fail to efficiently coordinate anti-tumor immunity within the tumor micro-environment and present tumor associated antigens within tumor-draining lymph nodes. When activated appropriately, human CD1c (BDCA-1)+ dendritic cells secrete high levels of IL-12 and potently prime CTL responses (Nizzoli, Krietsch et al. 2013). In vitro, IL-12 production by CD1c (BDCA-1)+ myDC can be boosted by exogenous IFN-gamma. (Nizzoli, Krietsch et al. 2013) CD1c (BDCA-1)+ myDC spontaneously "partially mature" within 12 hours following their isolation. Optimal maturation with secretion of IFN-gamma as well as the orientation of stimulated T-lymphocytes towards a Th1 phenotype is only achieved following Toll-like receptor stimulation.(Skold, van Beek et al. 2015) Talimogene laherparepvec (T-VEC; Imlygic) is a first-in-class oncolytic virus based on a modified herpes simplex virus (HSV) type 1 designed to selectively replicate in and lyse tumor cells while promoting regional and systemic antitumor immunity. T-VEC is modified through the deletion of two nonessential viral genes. Functional deletion of the herpes virus neurovirulence factor gene (ICP34.5) attenuates viral pathogenicity and enhances tumor-selective replication. T-VEC is further modified by deletion of the ICP47 gene to reduce virally mediated suppression of antigen presentation and increase the expression of the HSV US11 gene. Insertion and expression of the gene encoding human granulocyte macrophage colony-stimulating factor (GM-CSF) results in local GM-CSF production to recruit and activate antigen presenting cells with subsequent induction of tumor-specific T cell responses. T-VEC has been evaluated in early-phase studies, which demonstrated intratumoral replication and expression of GM-CSF and an acceptable safety profile (low-grade fever, chills, myalgias, and injection site reactions) after intralesional administration. In a single arm phase II study, an overall response rate (ORR) of 26% was reported in patients with stage IIIc to IV melanoma, with responses observed in both injected and non-injected lesions, including visceral lesions. Biopsy of regressing lesions suggested an association between response and presence of IFN- producing MART-1-specific CD8+ T cells and reduction in CD4+ FoxP3+ regulatory T cells, consistent with induction of host antitumor immunity. The efficacy and toxicity of T-VEC in advanced melanoma was evaluated in a randomized phase III trial comparing intratumoral T-VEC injections with subcutaneous GM-CSF injections. With T-VEC, the primary end point of durable response rate (DRR; continuous response lasting \> 6 months) was significantly higher (16% vs 2%; odds ratio, 8.9; P,.001), ORR improved (26% vs 6%), and the overall survival (OS) improved numerically but not statistically by 4.4 months (hazard ratio, 0.79; 95% CI, 0.62 to 1.00; P = .051). Tumor regression was seen in tumors both injected and not injected with T-VEC. The incidence of grade 3/4 T-VEC-related adverse events (AEs) was 11%. (Andtbacka, Kaufman et al. 2015) In an open-label, multicenter, phase Ib trial, the combination of T-VEC with ipilimumab had a tolerable safety profile, and the combination appeared to have greater efficacy than either T-VEC or ipilimumab monotherapy.(Puzanov, Milhem et al. 2016) The combination of T-VEC plus pembrolizumab (an anti-PD1 monoclonal antibody) was associated with clinical benefit in advanced melanoma, as assessed by ORR and CR rate (Ribas, Dummer et al. 2017). A randomized, double-blind phase 3 trial of T-VEC plus pembrolizumab vs T-VEC placebo plus pembrolizumab is ongoing. In this phase I clinical trial we propose to investigate the safety of intratumoral injection of autologous CD1c (BDCA-1)+ myDC in non-visceral metastases of melanoma plus intratumoral injection of T-VEC (at its approved dose and regimen for the treatment of melanoma).
We hypothesize that CD1c (BDCA-1)+ myDC in the T-VEC inflamed tumor microenvironment of the metastasis will capture tumor antigens in vivo and through cross-presentation of these antigens coordinate an effective anti-tumor T-cell response.
