Targeting therapeutic T cells to the bone-marrow niche

Abstract

BackgroundImmunotherapy has demonstrated exciting curative potential in the treatment of lymphoid malignancies, but cancer cells have developed a variety of immune evasion mechanisms requiring targeted strategies. CXCR4 is a G-protein coupled receptor with crucial roles in homing, maintenance, and proliferation of a wide range of haematological cancers. We hypothesised that overexpression of CXCR4 in CD8 T cells (T-CXCR4) would improve homing to CXCL12-rich niches such as bone marrow, enhancing tumour killing. MethodsWe transduced murine CD8 T cells with a retroviral vector encoding either the Cxcr4 gene coupled to a GFP marker or a separate inducible vector encoding Cxcr4 and GFP under control of the Tet-On system. For allogeneic bone-marrow transplants, irradiated BALB/c recipient mice received intravenous B6 donor bone marrow and subcutaneous A20 lymphoma cells on day 0, and B6 T-CXCR4 or control T cells on day 2. For in-vivo imaging of T-cell accumulation, anaesthetised mice received luciferase-positive transduced T cells and luciferin. Transgenic OT-1 CD8 T cells expressing T-cell receptors specific for the SIINFEKL peptide were used in vaccination experiments. FindingsIn an allogeneic B-cell lymphoma model, T-CXCR4 were significantly better than control T cells at tumour control (p<0·0001, n=5 per group). In-vivo imaging did not demonstrate greater T-CXCR4 accumulation at the tumour site, suggesting superior per-cell function. In a vaccination model, OT-1 T-CXCR4 demonstrated substantially enhanced long-term persistence in bone marrow and spleen compared with control T cells (bone-marrow ratio 34 to 1, spleen 11 to 1; p<0·0001). T-CXCR4 express a distinctive CD62LHI CD122HI BCL2HI early memory phenotype post recall vaccination with increased effector cytokine production. This enhanced T-stem memory marker expression was not observed after in-vitro CXCL12 exposure and was specifically lost upon transfer to mice lacking interleukin 15 receptor α. InterpretationCoupled with gene expression data, these results suggest that heightened antitumour efficacy is mediated by successful homing and competition for cell-extrinsic niche-related factors, in particular interleukin 15 presentation by CXCL12-abundant reticular cells. Preferential generation of enhanced early memory T cells with therapeutic superiority to effector-type cells currently used in investigational protocols has great relevance for the design of next-generation immunotherapies. FundingBloodwise.