P-076: Evaluating the changes treatment elicit on the immune repertoire of the myeloma niche using patient-derived multiple myeloma organoid models.

Background Multiple myeloma (MM) cells have an intricate interaction with immune components of the bone marrow (BM) niche that are key for survival and drug resistance. Evaluating the immune system in ex-vivo models has been a challenge that is being partially overcome by xenografts or 3D cultures that replicate the tumor niche. The purpose of this study is to use an established 3D myeloma organoid platform to evaluate changes in cellular immunity within a tumor niche caused by different therapeutic agents using patient-derived BM aspirate samples. Methods MM patients scheduled for BM biopsy were consented and 3-5 ml of aspirate was collected. Mononuclear cells from BM aspirates were co-cultured and suspended in Matrigel. Individual 40-50μm 3D organoids were placed in each well of a 48-well plate. Partial exchange of media containing RPMI, GM-CSF, IL6, IL7, and EGF (cocktail #3) was performed every 2-3 days. Organoids from the same patient were exposed to different drugs on day 5 for 48 hours and the following tests performed at different time points: viability with ATP, immunohistochemistry, flow-cytometry, chemosensitivity assays, AlamarBlue, RayBio, and cell sequencing (Proteona). The primary objective was to maintain viability of the 3D organoid components long enough to study the immune components in the MM tumor niche over an extended period of time. Secondary objective was to evaluate the impact therapies may have on the immune cell function within the tumor niche to identify targetable mechanisms of resistance/sensitization. Results Patient-derived BM aspirate samples were collected and used for this study. Number of organoids made and conditions tested varied based on sample quality and quantity. Organoid lifespan using Matrigel and partial exchange of cocktail #3 allowed for heterogeneous and adequate viability for up to 21 days as seen by flow and histology. Expansion of immune cells was seen during the course of the experiments with variability based on the conditions exposed to (see graph attached). When analyzing for chemosensitivity, there was not a significant difference seen between some agents likely due to the low drug concentrations used. Despite of that, cytokines on supernatant and gene expression profiling at different time points showed distinct changes in immune cell activity from the same patient when exposed to different conditions (see image). These findings suggest off-tumor targets drugs may have on the tumor niche. Conclusion This platform maintained viability of MM cells and its stroma for up to 21 days with good representation of its immune compartment. Immune cells such as dendritic cells, NK cells, and T-cell showed changes in activity and gene expression after exposure to different therapeutic agents using this organoid model. Further studies to evaluate how to optimize the activity of the immune cells within the MM tumor niche and better understand the impact current therapies have are needed.