A recent study showed in mice that Chimeric Antigen Receptor Synthetic T cells can be engineered with a synthetic receptor that targets the T cells to the brain and leads to a reduction in glioblastoma tumor volume.

How did the receptor enable targeting and activation of $T$ cells in the brain?

The T cell receptor is only expressed when the T cells enter the brain, but not other organs.

The T cell receptor had an intracellular domain that binds transcription factors only expressed in neural cells.

The T cell receptor had an extracellular domain that binds an extracellular matrix molecule only present in brain tissue.