Kinetic analysis reveals potency of CD4+ CD25bright+ regulatory T-cells in kidney transplant patients.

Donor-specific hyporesponsiveness as occurs after allogeneic kidney transplantation may be mediated by repression of effector cells by a specific subset of T-cells: the CD4(+) CD25(bright+) FoxP3(+) regulatory T-cells (Tregs). Here, we examined the suppressive capacity of Tregs isolated from the leukafereses product of 6 kidney transplant recipients, by reconstituting Tregs to responder T-cells at several time-points after initiation of proliferation. We show that Tregs derived from kidney transplant patients potently restrain proliferation to donor-antigens and 3rd party-antigens in classic reconstitution assays (i.e. addition of Tregs at the start of the co-incubation). However, when Tregs were added 5 days after initiation of proliferation, they were still capable of suppressing proliferation to donor-antigens (by 38%) but no longer to 3rd party-antigens. Thus, we conclude that the potency of Tregs to suppress reactivity to specific antigens should be determined by reconstitution to ongoing reactions.

Clinical rejection and persistent immune regulation in kidney transplant patients.

We evaluated whether the regulatory function of CD4(+)CD25(high+)FoxP3(+) T-cells from patients on tacrolimus and mycophenolate mofetil (MMF) is affected by preceding steroid and anti-CD25 mAb induction therapy and whether this function is associated with rejection after kidney transplantation. Kidney recipients (N=15) were randomized to receive either anti-CD25 mAb induction (i.e., daclizumab) or steroids for 4 months. We analyzed the presence and suppressive activity of CD4(+)CD25(high+)FoxP3(+) peripheral T-cells in samples obtained at pre and 4-6 months after transplantation. Anti-CD25 mAb therapy and treatment with steroids did not significantly affect protein expression of FoxP3. However, at the functional level, significant differences were found in the regulatory activities of CD4(+)CD25(high+) T-cells from the anti-CD25 group vs those from the steroid group. At 4-6 months after transplantation, the regulatory activities of CD4(+)CD25(high+) T-cells were comparable to those before anti-CD25 mAb therapy; 49+/-13% (mean+/-SEM) vs 40+/-14% at a 1:20 ratio (CD25(high+):CD25(-/dim)), respectively. In contrast, the regulatory capacities of CD(+)D25(bright+) T-cells from the steroid patient group became significantly impaired. The percentage inhibition of the anti-donor response decreased from 57+/-12% before transplantation to 12+/-7% after transplantation (p<0.01). Five out of 15 patients experienced a rejection episode. At 4-6 months after transplantation, the CD25(high+) cells from these rejectors (who all received daclizumab induction therapy) had clear regulatory function, while suppression by CD25(high+) cells from non-rejectors (N=10) was significantly lower. The percentage inhibition of the anti-donor response was 48+/-14% (mean+/-SEM) vs 10+/-7%, respectively, p=0.02. Anti-CD25 mAb induction therapy does not negatively influence the regulatory function of CD4(+)CD25(high+)FoxP3(+) T-cells from kidney transplant recipients on tacrolimus and MMF. The majority of these patients experienced an acute rejection episode, which suggests that immune activation is required for persistent immunoregulatory function.