Targeting Therapeutic T Cells to Tumour Niches.

Interactions between tumour cells and host cells within the microenvironment are important in promoting the development of cancer. Tumor niches provide crucial anti-apoptotic and anti-proliferative signals that drive tumor chemoresistance. The CXCR4-CXCL12 chemokine axis forms a critical component of this niche. CXCL12 produced by stromal cells has direct pro-survival effects upon tumor cells, promotes metastasis and recruits CXCR4-expressing regulatory T cell populations that block anti-tumour immunity. In this study, we have tested the hypothesis that targeting therapeutic T cells to CXCR4-dependent niches will improve eradication of tumours in mice.

The murine CXCR4 gene was inserted into retroviral vector, pMP71. Murine T cells were transduced with CXCR4 or control vector and tested for homing in vitro to CXCL12 through chemotaxis assays. In vivo imaging of the putative endosteal bone marrow (BM) niche was performed by multiphoton imaging through cranial frontal bones in osteoblast (collagen 1-α-GFP) reporter mice. In vivo trafficking, competitive transfer and memory recall experiments were performed following transfer of transduced T cells to syngeneic, sub-lethally irradiated mice. Anti-tumour reactivity of CXCR4-transduced T cells was tested in models of allogeneic BM transplantation (BMT).

CXCR4-transduced T cells demonstrated enhanced migration towards CXCL12 in vitro. No differences in viability, phenotype or function were observed in CXCR4-transduced versus control T cells in the presence or absence of CXCL12. In competitive assays, CXCR4-transduced CD8 T cells demonstrated a 2-fold greater capacity than controls to home to the BM by 24h after transfer to sub-lethally-irradiated recipients. Multiphoton imaging through cranial frontal bones indicated that fluorescently labelled CXCR4-transduced T cells were closer than control cells to the endosteum (13 μm versus 17 μm, p<0.01). By 14 days, the numbers of CXCR4-transduced CD8 T cells in the BM were 15-fold greater than controls. To test immunity to model antigen, CXCR4 or control vector-transduced OT-1 TCR-transgenic CD8 cells were transferred to sub-lethally irradiated mice before challenge with OVA peptide-loaded dendritic cells. Pre-vaccination, CXCR4-transduced OT-1 cells demonstrated greater engraftment than controls in the BM and spleen. Seven days following vaccination, CXCR4 OT-1 cells demonstrated a greater capacity than control cells to generate IFN-γ to OVA-peptide. Four weeks following vaccination, CXCR4-transduced CD8 T cells showed increased frequencies of cells with a CD44^highIL-7Rα^high memory phenotype than controls, with a greater proportion of cells undergoing proliferation as evaluated by BrdU incorporation. To test T cell immunity against a tumor that exploits the CXCR4-CXCL12 axis to recruit regulatory T cells, B6 BM and CXCR4- or control transduced B6 T cells were transferred to irradiated BALB/c recipients given A20 tumor. Tumor growth was delayed to a greater extent following transfer of CXCR4-compared to control-transduced donor T cells.

Over-expression of CXCR4 in CD8 T cells potentiates engraftment, initial effector function and generation of memory cells.

Stauss:Cell Medica: Scientific Advisor Other.