Acute rejection of a transplanted organ is a cellular-level rejection mediated by T cells recognizing foreign tissue.

“what was actually happening was not this circulating what we came to call antibody mediated or humeral rejection but actually was happening on a cellular level so-called cellular rejection and as we learned eventually over time that had to do with kind of what we now learn in basic immunology antigen presenting cell with carrying an antigen from the the foreign tissue in this case the donor tissue immune immune mediator cells and we've discovered and learned eventually they were t cells”