Figure 1.

Formulation that a kidney allograft functions as an in vivo flow cytometer. Acute T cell–mediated rejection is characterized by the infiltration of the kidney allograft by T cells, macrophages, and other cell types. The concurrent presence of graft-infiltrating cells in the interstitial space and the presence of cells within the tubules (tubulitis) are the histologic hallmarks of T cell–mediated rejection. In our conceptualization, a kidney allograft undergoing acute T cell–mediated rejection functions as an in vivo flow cytometer and sorts graft-infiltrating cells and targeted graft parenchymal cells into the urinary space; therefore, profiling of urinary cells for their gene expression pattern offers a noninvasive means of diagnosing acute T cell–mediated rejection. Adapted from ref. 11, with permission.