High dose-rate brachytherapy of localized prostate cancer converts tumors from cold to hot.

BACKGROUND: Prostate cancer (PCa) has a profoundly immunosuppressive microenvironment and is commonly immune excluded with few infiltrative lymphocytes and low levels of immune activation. High-dose radiation has been demonstrated to stimulate the immune system in various human solid tumors. We hypothesized that localized radiation therapy, in the form of high dose-rate brachytherapy (HDRBT), would overcome immune suppression in PCa. METHODS: To investigate whether HDRBT altered prostate immune context, we analyzed preradiation versus postradiation human tissue from a cohort of 24 patients with localized PCa that received HDRBT as primary treatment (RadBank cohort). We performed Nanostring immune gene expression profiling, digital spatial profiling, and high-throughput immune cell multiplex immunohistochemistry analysis. We also resolved tumor and nontumor zones in spatial and bioinformatic analyses to explore the immunological response. RESULTS: Nanostring immune profiling revealed numerous immune checkpoint molecules (eg, B7-H3, CTLA4, PDL1, and PDL2) and TGFß levels were increased in response to HDRBT. We used a published 16-gene tumor inflammation signature (TIS) to divide tumors into distinct immune activation states (high:hot, intermediate and low:cold) and showed that most localized PCa are cold tumors pre-HDRBT. Crucially, HDRBT converted 80% of these 'cold'-phenotype tumors into an 'intermediate' or 'hot' class. We used digital spatial profiling to show these HDRBT-induced changes in prostate TIS scores were derived from the nontumor regions. Furthermore, these changes in TIS were also associated with pervasive changes in immune cell density and spatial relationships-in particular, between T cell subsets and antigen presenting cells. We identified an increased density of CD4+ FOXP3+ T cells, CD68+ macrophages and CD68+ CD11c+ dendritic cells in response to HDRBT. The only subset change specific to tumor zones was PDL1- macrophages. While these immune responses were heterogeneous, HDRBT induced significant changes in immune cell associations, including a gained T cell and HMWCK+ PDL1+ interaction in tumor zones. CONCLUSION: In conclusion, we showed HDRBT converted "cold" prostate tumors into more immunologically activated "hot" tissues, with accompanying spatially organized immune infiltrates and signaling changes. Understanding and potentially harnessing these changes will have widespread implications for the future treatment of localized PCa, including rational use of combination radio-immunotherapy.

CMRF-56(+) blood dendritic cells loaded with mRNA induce effective antigen-specific cytotoxic T-lymphocyte responses.

There are numerous transcriptional, proteomic and functional differences between monocyte-derived dendritic cells (Mo-DC) and primary blood dendritic cells (BDC). The CMRF-56 monoclonal antibody (mAb) recognizes a cell surface marker, which is upregulated on BDC following overnight culture. Given its unique ability to select a heterogeneous population of BDC, we engineered a human chimeric (h)CMRF-56 IgG4 mAb to isolate primary BDC for potential therapeutic vaccination. The ability to select multiple primary BDC subsets from patients and load them with in vitro transcribed (IVT) mRNA encoding tumor antigen might circumvent the issues limiting the efficacy of Mo-DC. After optimizing and validating the purification of hCMRF-56(+) BDC, we showed that transfection of hCMRF-56(+) BDC with mRNA resulted in efficient mRNA translation and antigen presentation by myeloid BDC subsets, while preserving superior DC functions compared to Mo-DC. Immune selected and transfected hCMRF-56(+) BDC migrated very efficiently in vitro and as effectively as cytokine matured Mo-DC in vivo. Compared to Mo-DC, hCMRF-56(+) BDC transfected with influenza matrix protein M1 displayed superior MHC peptide presentation and generated potent antigen specific CD8(+) T-cell recall responses, while Wilms tumor 1 (WT1) transfected CMRF-56(+) BDC generated effective primary autologous cytotoxic T-cell responses. The ability of the combined DC subsets within hCMRF-56(+) BDC to present mRNA delivered tumor antigens merits phase I evaluation as a reproducible generic platform for the next generation of active DC immune therapies.