I'm not entirely sure. It seems, from the paper, that mouse models do not share the same phenotype with humans, so animal tests may not be all that helpful, except for some safety data. I'm not sure they will be able to culture actual human neurons from tissue, as that was only recently accomplished back in 2017.

From the paper itself, this is what the researchers say: "These findings warrant further development of ApoE4 structure correctors and, ultimately, testing in clinical trials." So it looks like they want to move forward clinically.