Uptake of long-chain fatty acids from the bone marrow suppresses CD8+ T-cell metabolism and function in multiple myeloma.

T cells demonstrate impaired function in Multiple Myeloma (MM), but suppressive mechanisms in the bone marrow microenvironment remain poorly defined. We observe that bone marrow CD8+ T-cell function is decreased in MM patients compared to controls, and also is consistently lower within bone marrow samples than matched peripheral blood. These changes are accompanied by decreased mitochondrial mass and markedly elevated long-chain fatty acid uptake. In vitro modelling confirmed that uptake of bone marrow lipids suppresses CD8+ T function, which is impaired in autologous bone marrow plasma, but rescued by lipid removal. Analysis of single-cell RNA-sequencing data identified expression of fatty acid transport protein 1 (FATP1) in bone marrow CD8+ T cells in MM, and FATP1 blockade also rescued CD8+ T-cell function, thereby identifying this as a novel target to augment T cell activity in MM. Finally, analysis of samples from treated patient cohorts identified that CD8+ T cell metabolic dysfunction resolves in treatment-responsive but not relapsed MM patients and is associated with substantial T cell functional restoration.