Developing a zebrafish launchpad for CART technology

Cytotoxic T lymphocytes (CTLs) are our bodies’ most potent defence against the development of cancer. With correct priming, CTLs can also be prompted to attack established cancers. For CTLs to destroy their targets, they must express an antigen receptor (so-called T-cell receptor or TCR) recognising an antigen expressed on MHC by cancer cells. Tumours may not always express antigens or may otherwise interfere with the priming of CTLs. T cells engineered ex vivo to express chimeric antigen receptors (CARTs) represent an exciting application of synthetic biology that can circumvent the limitations of natural CTLs. The CAR comprises an extracellular antigen recognition domain capable of binding a surface antigen on the cancer cell (independently of MHC), fused to intracellular domains of signalling molecules which stimulate CTLs to proliferate and kill target cells (independently of cytokine stimulation by helper cells). If depletion of a cell lineage, such as melanocytes, can be tolerated then the antigen targeted needn’t even be specific to cancer cells although it should be lineage restricted to avoid catastrophic organ damage. Alternatively, combinations of stimulatory and inhibitory receptors or partitioning stimulatory signals over multiple CARs (examples of logical gating) can still permit a relatively selective cytotoxic response.

To date, clinical success with CARTs has been limited to a few cancer types, notably haematological malignancies, but it is a highly innovative approach, progressing rapidly. We have recently determined that melanoma in zebrafish is also under surveillance by T cells. This implies that zebrafish T cells also provide protection against cancer. Furthermore, there is significant sequence conservation for putative components of T-cell signalling pathways. We envisage zebrafish becoming a versatile in vivo test-tube for evaluating CART technology. Using highly efficient transgenic tools and established melanoma models, the successful candidate will work toward developing CART which recognise and selectively attack melanoma cells.