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BackgroundIntratumoral (IT) myeloid dendritic cells (myDCs) play a pivotal role in initiating antitumor immune responses and relicensing of anti-tumor cytotoxic T lymphocytes within the tumor microenvironment. Talimogene laherparepvec (T-VEC) induces immunogenic cell death, thereby providing maturation signals and enhancing the release of tumor antigens that can be captured and processed by CD1c (BDCA-1)+ / CD141 (BDCA-3)+ myDCs, in order to reinvigorate the cancer-immunity cycle.MethodsIn this phase I trial, patients with advanced melanoma who failed standard therapy were eligible for IT injections of ≥1 non-visceral metastases with T-VEC on day 1 followed by IT injection of CD1c (BDCA-1)+ myDCs +/- CD141 (BDCA-3)+ myDCs on day 2. T-VEC injections were repeated on day 21 and every 14 days thereafter. The number of IT administered CD1c (BDCA-1)+ myDCs was escalated from 0.5×106, to 1×106, to a maximum of 10×106 cells in three sequential cohorts. In cohort 4, all isolated CD1c (BDCA-1)+ / CD141 (BDCA-3)+ myDCs were used for IT injection. Primary objectives were safety and feasibility. Repetitive biopsies of treated lesions were performed.ResultsIn total, 13 patients were enrolled (cohort 1 n=2; cohort 2 n=2; cohort 3 n=3; cohort 4 n=6). Patients received a median of 6 (range 3–8) T-VEC injections. The treatment was safe with most frequent adverse events being fatigue (n=11 (85%)), fever (n=8 (62%)), and chills/influenza-like symptoms (n=6 (46%)). Nine (69%) and four patients (31%), respectively, experienced pain or redness at the injection-site. Clinical responses were documented in injected and non-injected lesions. Two patients (cohort 3) who previously progressed on anti-PD-1 therapy (and one patient also on anti-CTLA-4 therapy) developed a durable, pathologically confirmed complete response that is ongoing at 33 and 35 months following initiation of study treatment. One additional patient treated (cohort 4) had an unconfirmed partial response as best response; two additional patients had a mixed response (with durable complete responses of some injected and non-injected lesions). On-treatment biopsies revealed a strong infiltration by inflammatory cells in regressing lesions.ConclusionsIT coinjection of autologous CD1c (BDCA-1)+ +/- CD141 (BDCA-3)+ myDCs with T-VEC is feasible, tolerable and resulted in encouraging early signs of antitumor activity in immune checkpoint inhibitor-refractory melanoma patients.Trial registration numberNCT03747744.

Ionizing radiation (IR) is a non-specific but highly effective way to kill malignant cells. However, tumor recurrence sustained by a minor fraction of surviving tumor cells is a commonplace phenomenon caused by the activation of both cancer cell intrinsic resistance mechanisms, and also extrinsic intermediaries of therapy resistance, represented by non-malignant cells and structural components of the tumor stroma. The improved accuracy offered by advanced radiotherapy (RT)-technology permits reduced volume of healthy tissue in the irradiated field, and has been triggering an increase in the prescription of high-dose oligo-fractionated regimens in the clinics. Given the remarkable clinical success of high-dose RT and the current therapeutic shift occurring in the field, in this review we revise the existing knowledge on the effects that different radiation regimens exert on the different compartments of the tumor microenvironment, and highlight the importance of anti-tumor immunity and other tumor cell extrinsic mechanisms influencing therapeutic responses to high-dose radiation.