Peripheral blood allogeneic microchimerism in lung and cardiac allograft recipients

We have been investigating two parameters, donor antigen-specific hyporeactivity and peripheral blood allogeneic microchimerism, to determine whether these parameters will predict a chronic rejection-free state and which recipients may be candidates for steroid withdrawal. We have identified donor antigen-specific hyporeactivity for 33% (16/48) of lung and 23% (11/47) of heart recipients. For both organ groups, the hyporeactive subgroup experienced 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 recipients tested at 12-18 months posttransplant. Donor antigen- specific hyporeactivity correlates with a critical level of donor cells in lung recipients; the probability of high peripheral blood allogeneic microchimerism levels predicting a chronic rejection-free state in lung recipients is 100%. The 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 usefulness of immune parameters to predict long-term graft outcome in an organ-specific manner.