Reconstitution of FOXP3+ regulatory T cells (Tregs) after CD25-depleted allotransplantion in elderly patients and association with acute graft-versus-host disease

Selective depletion (SID) of host-reactive donor T cells from allogeneic stem-cell transplants (SCTs) using an anti-CD25 immunotoxin (IT) is a strategy to prevent acute graft-versus-host disease (aGvHD). There is concern that concurrent removal of regulatory T cells (T-regs) with incomplete removal of alloactivated CD25(+) T cells could increase the risk of aGvHD. We therefore measured T,g, in the blood of 16 patients receiving a T-cell-depleted allograft together with anti-CD25-IT-treated SD lymphocytes, in 13 of their HLA-Identical donors, and in 10 SD products. T-regs were characterized by intracellular staining for forkhead box protein 3 (FOXP3) and by quantitative reversetranscription-polymerase chain reaction (qRT-PCR) for FOXP3 gene in CD4(+) cells. Patients received a median of 1.0 x 10(8)/kg SD T cells and a stem cell product containing a median of 0.25 x 10(4)/kg residual T cells. Tregs reconstituted promptly after SCT and underwent further expansion. Of the CD4(+) T cells in SD products, 1.5% to 4.8% were CD25(-) T-regs. Acute GvHD (>= grade II) was restricted to 5 patients whose donors had significantly (P = .019) fewer Tregs compared with those without clinically significant aGvHD. These results suggest that rapid T-reg reconstitution can occur following SD allografts, either from CD25(-) T-regs escaping depletion, or from residual CD25(-) and CD25(+) T-regs contained in the stem-cell product that expand after transplantation and may confer additional protection against GvHD.