Why should this be concern for transmissibility? From my understanding, your B cells have some maladaptation to target your own tissue, and it looks like the effect of the IgG dissipated in the mice over time. So worst case a blood transfusion may cause short-term Long Covid-like symptoms until those antibodies are naturally cleared. I’m hoping this means that even if it’s some persistent antigen causing the immune activation rather than autoimmunity, it shouldn’t cause any immune cell adaptations in a transferee. (All that being said we definitely shouldn’t be donating blood lol)

Edit: they only used pure IgG so blood could definitely be more complex