Peripheral blood allogeneic microchimerism in lung and cardiac allograft recipients

We have been investigating two parameters, donor antigen-specific hyporeact ivity and peripheral blood allogeneic microchimerism, to determine whether these parameters will predict a chronic rejection-free state and which reci pients may be candidates for steroid withdrawal. We have identified donor a ntigen-specific hyporeactivity for 33% (16/48) of lung and 23% (11/47) of h eart recipients. For both organ groups, the hyporeactive subgroup experienc ed a lower incidence of chronic rejection. The probability of donor antigen -specific hyporeactivity predicting a chronic rejection-free state is 100% for lung and 91% for heart recipients. We have identified peripheral blood allogeneic microchimerism for 77% (20/26) of lung and 36% (9/25) of heart r ecipients tested at 12-18 months posttransplant. Donor antigen-specific hyp oreactivity correlates with a critical level of donor cells in lung recipie nts; the probability of high peripheral blood allogeneic microchimerism lev els predicting a chronic rejection-free state in lung recipients is 100%. T he results in heart recipients are not as clear with a short-, but not long -term, trend of higher chimerism levels correlating with the development of donor antigen-specific hyporeactivity. These results illustrate the useful ness of immune parameters to predict long-term graft outcome in an organ-sp ecific manner.