Lene Vimeux

The chemokine CXCL12 plays central roles in hematopoiesis, immune cell trafficking and adaptive responses, yet how its multiple isoforms contribute to these processes remains poorly understood. Here we delineate distinct expression patterns and physiological functions of the CXCL12 α and γ isoforms within bone marrow niches and immune organs. By combining genetic deletion, expression studies and functional assays, we show that the strongly matrix-anchored CXCL12γ predominates in endothelial cells and controls both the size of the hematopoietic stem cell pool and mature lymphocyte entry into the bone marrow parenchyma. In contrast, we found that the more diffusible CXCL12α is the major isoform produced by non-endothelial stromal cells, and particularly by the CXCL12-expressing reticular cells of germinal centers where it is uniquely concentrated in the dark zone and supports antibody affinity maturation. These results uncover an isoform-specific division of labor in the CXCL12 system and point to cell type-specific differential splicing as an important determinant for the control of the diverse biological roles of CXCL12, highlighting the importance of ECM attachment as a regulator of chemokine function.

Adoptive transfer of T cells expressing chimeric antigen receptors (CAR) has shown remarkable clinical efficacy against advanced B-cell malignancies but not yet against solid tumors. Here, we used fluorescent imaging microscopy and ex vivo assays to compare the early functional responses (migration, Ca2+, and cytotoxicity) of CD20 and EGFR CAR T cells upon contact with malignant B cells and carcinoma cells. Our results indicated that CD20 CAR T cells rapidly form productive ICAM-1–dependent conjugates with their targets. By comparison, EGFR CAR T cells only initially interacted with a subset of carcinoma cells located at the periphery of tumor islets. After this initial peripheral activation, EGFR CAR T cells progressively relocated to the center of tumor cell regions. The analysis of this two-step entry process showed that activated CAR T cells triggered the upregulation of ICAM-1 on tumor cells in an IFNγ-dependent pathway. The ICAM-1/LFA-1 interaction interference, through antibody or shRNA blockade, prevented CAR T-cell enrichment in tumor islets. The requirement for IFNγ and ICAM-1 to enable CAR T-cell entry into tumor islets is of significance for improving CAR T-cell therapy in solid tumors.

Distribution and migration and EGFR CAR T cells in a vibratome section of a human lung tumor

Ca2+ responses of EGFR CAR T cells in human renal tumor slices positive for ICAM-1

Ca2+ responses of Fura-2-loaded CD20 CAR T cells during their interaction with CD20-expressing BxPC3 tumor cells

Ca2+ responses of Fluo-4-loaded EGFR CAR T cells in a vibratome section of a BxPC3 tumor

CAR T cell-induced ICAM-1 expression by tumor cells facilitates lymphocyte activation and entry into tumor islets