Immune landscape of sarcoma patients treated with an autologous dendritic cell vaccine.

Abstract

e23530 Background: The role of the sarcoma immune tumor microenvironment (TME) is a critical area of ongoing research, particularly to understand responses to immunotherapy. We previously conducted a phase I trial (2014-2019) of autologous dendritic cell (DC) vaccination in 19 patients with advanced or metastatic sarcomas (NCT01803152). Median PFS was 9.5 months (95% CI 5.6-28.7), with 4 of 19 patients (20%) exhibiting durable PFS with a median follow-up of two years, including two patients with pleomorphic myxofibrosarcoma, one with leiomyosarcoma and one pediatric patient with Ewing sarcoma, far exceeding outcomes expected with recurrent metastatic sarcoma. We hypothesized that increased pro-inflammatory immune cells at baseline in the TME would associate with prolonged PFS after treatment with DC vaccine. Methods: Components of the immune TME were assessed in archival tumor tissue from study patients using imaging mass cytometry with the Standard Biotools Hyperion platform. A panel was designed to quantify and phenotype the following immune cells: CD8+ cytotoxic T cells, CD4+ helper T cells, FOXP3+ T reg cells, B cells, natural killer (NK) and NK-T cells, and multiple myeloid populations including M1 pro-inflammatory tumor-associated macrophages (TAMs), M2 suppressive TAMs, and DC and MDSC subsets. We also analyzed expression of checkpoint proteins PD-1, PD-L1, CTLA-4, TIM3. Imaging data was analyzed using the Visiopharm Phenoplex Guided Workflow module (v2023.09.4.15595 x64). An Unpaired t-test with Welch correction for each population was performed to compare proportion of cells across the responders and non-responder samples. The pixel intensity for Granzyme B and PDL-1, was compared using Mann-Whitney test and the Kolmogorov-Smirnov test. Results: The TME of the responders (n = 4) was different compared to the non-responders (n = 7), as evidenced by the t-SNE plot. Although not statistically significant, tissue from the responders exhibited a 2.5 fold higher density of M2 Macrophages (mean 10.46% SD 15.97 vs 4.15% SD 3.12), a 7.5 fold higher % of CD4 T cells (mean 3.88%, SD 6.41 vs 0.52%, SD 0.63), 11.7 fold higher % of CD8 T cells (mean 4.11%, SD 6.97 vs 0.35%, SD 0.36 ) and 2-fold higher M1 macrophages (mean 19.90%, SD 38.27 vs 11.45%, SD 19.80) when compared with non-responders, respectively. While there was no statistical difference in the percentage of Granzyme B+ and PD-L1+ cells between responders and non-responders, we did note a statistically significant difference in the expression as evidenced by difference in the pixel intensities, p < 0.0001. Conclusions: Responding patients to autologous DC vaccines demonstrate more robust baseline immune infiltration, in line with previous studies showing higher immune related gene expression correlates with pre-existing immune responses and better outcomes with immunotherapy.