T cell landscape and dynamics in immunoglobulin light chain amyloidosis before and after daratumumab‐based therapy

Amyloid light‐chain (AL) is characterized by the presence of small, poorly proliferating plasma cell clones with the production and deposition of light chains into tissues. T cell changes within the tumour microenvironment in AL are poorly understood. By sequencing at a single‐cell level of CD3(+) T cells purified from bone marrow (BM) and blood of newly diagnosed AL patients before and after a combination of daratumumab with cyclophosphamide, bortezomib, and dexamethasone (Dara‐BCD), we analysed the transcriptomic features of T cells and found an expansion, activation and type I cytokine upregulation in BM and circulating T cells after the treatment. More prominent changes were shown in CD8(+) T cells. In particular, we found the presence of CD8(+) BM resident memory T cells (T(RM)) with high expression of inhibitory molecules in AL patients at diagnosis. After Dara‐BCD, these T(RM) cells were quickly activated with downregulation of suppressive molecules and upregulation of IFNG expression. These data collectively demonstrate that Dara‐based therapy in patients with AL amyloidosis promotes anti‐tumour T cell responses. The similar transcriptomic features of BM and circulating T cells before and after therapy further provide a less invasive approach for molecular monitoring of T cell response in AL amyloidosis.