Functional characterization of alloreactive T cells identifies CD25 and CD71 as optimal targets for a clinically applicable allodepletion strategy.

Immunotherapy with allodepleted donor T cells (ADTs) improves immunity after T cell-depleted stem cell transplantation, but infection/relapse remain problematic. To refine this approach, we characterized the expression of surface markers/cytokines on proliferating alloreactive T cells (ATs). CD25 was expressed on 83% of carboxyfluorescein diacetate succinimidyl ester(dim) ATs, confirming this as an excellent target for allodepletion. Seventy percent of CD25(-) ATs expressed CD71 (transferrin receptor), identifying this as a novel marker to target ATs persisting after CD25 depletion. Comparison of residual alloreactivity after combined CD25/71 versus CD25 immunomagnetic depletion showed enhanced depletion of alloreactivity to host with CD25/71 depletion in both secondary (2 degrees) mixed lymphocyte reactions (P < .01) and interferon-gamma enzyme-linked immunospot assays (P < .05) with no effect on third-party responses. In pentamer/interferon-gamma enzyme-linked immunospot assays, antiviral responses to cytomegalovirus, Epstein-Barr virus, and adenovirus were preserved after CD25/71 allodepletion. CD25/71 ADTs can be redirected to recognize leukemic targets through lentiviral transfer of a chimeric anti-CD19zeta T-cell receptor. Finally, we have established conditions for clinically applicable CD25/71 allodepletion under European Union Good Manufacturing Practice conditions, resulting in highly effective, reproducible, and selective depletion of ATs (median residual alloreactivity to host in 2 degrees mixed lymphocyte reaction of 0.39% vs third-party response of 62%, n = 5). This strategy enables further clinical studies of adoptive immunotherapy with larger doses of ADTs to enhance immune reconstitution after T cell-depleted stem cell transplantation.