Interaction of nonclassical monocyes in the myeloma niche with CD4+ CAR T cells is linked to TGFb, blunting their killing capacity. (A) UMAP of CD14⁺ myeloid cells with annotated cell states. (B) Violin plots showing normalized expression of selected genes for each cell state. (C) Box plot showing the proportions of CD14⁺ myeloid cells (median % ± 1.5 interquartile range) of each cell state, by group. Statistical significance is marked by asterisk and determined by Wilcoxon rank-sum test (P < .001). (D) Enrichment score (see "Methods”) for TGF-β pathway of CD4⁺ CAR T cells from DR group vs TR group. (E) Dot plots showing normalized expression of genes related to TGF-β pathway in CD4⁺ CAR T cells, by group. Dot size is proportional to fraction of cells. (F) Scheme depicting experimental design of CD4⁺ CAR T cells in vitro killing assay performed by coculture with myeloma cell line MM1.S, with or without TGF-β. (G) Bar plot showing killing efficacy of CD4⁺ CAR T cells (number of cancer cells killed per CD4⁺ CAR T cell) after 3 weeks of coculture with myeloma cell line MM1.S, with or without TGF-β. (H) Frequency of CD4⁺ CAR T cells expressing 3 exhaustion markers (programmed cell death protein, TIM3, and CD39) after repetitive stimulation. (I) Flow cytometry histogram of programmed cell death protein mean fluorescence intensity (MFI) of CD4⁺ CAR T cells from 2 donors after 3 weeks of coculture with myeloma cell line MM1.S, with or without TGF-β. Mono, monocyte; pDC, plasmacytoid dendritic cell.