A 3D engineered multiple myeloma niche for evaluating CAR T cell therapy.

Chimeric antigen receptor (CAR) T cell therapies targeting B cell maturation antigen (BCMA) have shown unprecedented success in treating multiple myeloma (MM), yet long-term relapse remains a critical challenge, possible due to the protective influence of the bone marrow (BM) microenvironment. Current in vitro models often rely on simplistic 2D cocultures of CAR T and MM cells, and fail to recapitulate the 3D structural and cellular complexity of the osteogenic niche, which is known to facilitate immune evasion. In this study, we aimed to develop a physiologically relevant 3D in vitro MM model using a perfusion bioreactor system, hydroxyapatite scaffolds, and osteogenically-differentiated human BM mesenchymal stromal cells. Our results demonstrate that this system effectively supports the engraftment and 3D clustering of MM cells while successfully mimicking the suppressive effect of the tumor on osteogenic matrix deposition. Use of the platform to assess BCMA-targeted CAR T cell activity indicated that, while CAR T cells efficiently cleared circulating tumor cells in the fluidic phase, the 3D osteogenic niche provided a protective environment that blunted cytotoxic efficacy. This resistance was not associated with T cell recruitment, suggesting that the 3D niche provides complex protection. Our study provides a proof-of-concept for a humanized, dynamic cell culture platform capturing the influence of the BM niche-MM cell crosstalk on the efficacy of immunotherapy. The model represents a promising tool for evaluating next-generation CAR T cell potencies and for investigating associated resistance mechanisms.