Neoantigen-targeted DC vaccine generates durable T cell responses exhibiting the full spectrum of differentiation states in NSCLC patients

Background. Dendritic cell (DC)-based neoantigen vaccination holds potential as a safe and effective adjuvant therapy for patients with early-stage, resectable NSCLC. DCs have the unique ability to elicit robust antitumoral T-cell responses, while neoantigens are ideal targets to elicit high-affinity T cell responses with excellent tumor specificity. Here, we present the results of a phase I clinical trial in which a novel DC vaccine targeting neoantigens was evaluated in six patients with early stage, resected NSCLC. Methods. Autologous monocyte-derived DCs loaded with neoantigens (Neo-mDCs) were manufactured according to a 4-day protocol. Neo-mDCs were injected intravenously following an intrapatient dose escalation scheme. Primary endpoint of the trial was safety. Secondary endpoints were feasibility, immunogenicity, and relapse-free survival. Results. Vaccine manufacturing was feasible in 6 of 10 patients. Toxicity was limited to grade 1-2 adverse events. Systemic T cell responses were observed in 5 out of 6 vaccinated patients and were dominated by CD8+ T cells, which could be detected ex vivo at high frequencies >1.5 years after the last dose. Furthermore, single cell analysis indicated that the CD8+ T cell responsive population was polyclonal and exhibited the near entire spectrum of T cell differentiation states, including a naïve-like state associated with long lasting memory, but excluding exhausted cell states. Three of six vaccinated patients experienced disease relapse.Conclusion. Neo-mDC vaccination is safe, feasible and induces polyclonal populations of neoantigen-specific T-cell responses containing long lasting memory and effector cells in early-stage NSCLC patients, suggesting clinical potential. Overall design: We aimed to study the differentiation states and clonal expansion of neoantigen-vaccine responding T cells over the course of vaccination and during oncological follow-up. Therefore, we performed a single cell RNA sequencing experiment on the BD Rhapsody system. First, we isolated all CD8+ T cells from a baseline blood sample from two patients, 08 and 11. This to get an overview of all possible differentiation states of CD8+ T cells. Subsequently, we isolated neoantigen-vaccine responding CD8+ T cells from both patients at serial time points during treatment and 3 weeks and 6 months post-treatment through a pHLA tetramer staining. On these cells we performed single cell RNA and TCR sequencing. In this second sequencing experiment we also included two neoantigen responsive T cell lines, one from each patient, to use as a control for the single cell TCR sequencing.