As a multi-cellular organism, a brain-dead human is not alive, even if most of its cells may remain alive as long as they are fed from outside.

OK, what I have said above is not generally true, as some brain-dead humans may be more alive than others, e.g. some integrative functions, like some feedback loops that function through the endocrine system or through the autonomous nervous system, may still be working, connecting some organs with each other.

My comparison was with a very dead brain-dead human, who was reduced to the equivalent of a tissue culture.

These artificial cells also have some components that continue to work like in a living cell, doing some nucleic acid replication and some protein and lipid synthesis from precursors provided from outside, but they lack the capability to perform many of the chemical reactions that would be needed to close the complex network of feedback loops that enable a true living cell to live autonomously.