Treg and transplant rejection

Yesterday evening I heard an interesting talk here about lung transplant rejection where one of the best prognostic marker
was the (pre transplantation) Treg count.

I wonder if there are some preexisting patient conditions, like allergy, that are responsible for this phenomenon?
At least it is already known since 2008 that Treg function is important. Current Treg therapies are exploiting this. Another allergy hallmark the IL33/ST2 axis is actively tested at the moment in transplant rejection.

In contrast transplant acquired allergy is something different – a side effect of tacrolimus? Or any other ingredient of the cocktail of steroids, mycophenolate, and IL-2 receptor inhibitors such as basiliximab?