Subjects being low-level are essentially runtime-only entities and can not be serialized directly. A special kind of Subject should be used instead. These are called Subject Records.

Subject Records are essentially storable and editable entities which are not Iterated upon directly, but are used as templates (or prefabs) to create new Subjects and/or capture the state of existing ones. Think of them as of Subjects’ immediate replicas.

The great thing about Records is that they’re fully editable within the Unreal Editor, i.e. you can declare class properties with the corresponding type.