The extent of HLA-DR expression on HLA-DR(+) Tregs allows the identification of patients with clinically relevant borderline rejection.

Regulatory T cells (Tregs) were shown to be involved into the pathogenesis of acute rejection after transplantation. The suppressive activity of the total regulatory T cell pool depends on its percentage of highly suppressive HLA-DR(+) -Treg cells. Therefore, both the suppressive activity of the total Treg pool and the extent of HLA-DR expression of HLA-DR(+) -Tregs (MFI HLA-DR) were estimated in non transplanted volunteers, patients with end-stage renal failure (ESRF), healthy renal transplant patients with suspicion on rejection, due to sole histological Bord-R or sole acute renal failure (ARF), and patients with clinically relevant borderline rejection (Bord-R and ARF). Compared to patients with only Bord-R or only ARF, the suppressive activity of the total Treg cell pool was exclusively reduced in patients with clinically relevant Bord-R. In parallel, the HLA-DR MFI of the DR(+) -Treg subset was significantly decreased in these patients, due to a significantly lower proportion of DR(high+) -Tregs, which were shown to have the highest suppressive capacity within the total Treg pool. Our findings clearly demonstrate that the determination of the HLA-DR MFI of the HLA-DR(+) -Treg subset allows a highly sensitive, specific and non-invasive discrimination between patients with clinically relevant Bord-R (Bord and ARF) and patients with subclinical rejection or other causes of transplant failure.

Methylprednisolone treatment increases the proportion of the highly suppressive HLA-DR(+)-Treg-cells in transplanted patients.

Methylprednisolone is widely used to improve immune suppression in transplanted patients threatened by acute rejection. Recently, we showed that the suppressive activity of a Treg cell population depends decisively on their percentage of highly suppressive HLA-DR(high+)-Treg cells, which are strongly reduced in rejecting transplant patients. In order to examine whether the composition of the total CD4(+)CD127(low+/-)FoxP3(+)-Treg cell pool with different Treg-subsets (DR(high+)CD45RA(-)-Tregs, DR(low+)CD45RA(-)-Tregs, DR(-)CD45RA(-)-Tregs, DR(-)CD45RA(+)-Tregs) is affected by methylprednisolone bolus therapy we compared the percentages of these four different Treg cell subsets in transplant patients with biopsy proven rejection before and after steroid bolus therapy (n=23). In patients treated with steroid bolus therapy, the percentage of the naïve DR(-)CD45RA(+)-Tregs was significantly decreased, whereas the percentage of the DR(+)CD45RA(-)-Tregs was significantly increased. By that, the strongest increase was detected for the most suppressive DR(high+)CD45RA(-)-Tregs. However, these effects were only temporarily and closely associated to the duration of the bolus therapy. Our results suggest that besides various anti-inflammatory effects on cells of the adaptive and innate immune system, methylprednisolone also has the capacity to enhance the suppressive activity of the total Treg cell pool by increasing its percentage of highly differentiated and highly suppressive DR(high+)CD45RA(-)-Tregs.

DR(high+)CD45RA(-)-Tregs potentially affect the suppressive activity of the total Treg pool in renal transplant patients.

Recent studies show that regulatory T cells (Tregs) play an essential role in tolerance induction after organ transplantation. In order to examine whether there are differences in the composition of the total CD4(+)CD127(low+/-)FoxP3(+)- Treg cell pool between stable transplant patients and patients with biopsy proven rejection (BPR), we compared the percentages and the functional activity of the different Treg cell subsets (DR(high+)CD45RA(-)-Tregs, DR(low+)CD45RA(-)-Tregs, DR(-)CD45RA(-)-Tregs, DR(-)CD45RA(+)-Tregs). All parameters were determined during the three different periods of time after transplantation (0-30 days, 31-1,000 days, >1,000 days). Among 156 transplant patients, 37 patients suffered from BPR. The most prominent differences between rejecting and non-rejecting patients were observed regarding the DR(high+)CD45RA(-)-Treg cell subset. Our data demonstrate that the suppressive activity of the total Treg pool strongly depends on the presence of these Treg cells. Their percentage within the total Treg pool strongly decreased after transplantation and remained relatively low during the first year after transplantation in all patients. Subsequently, the proportion of this Treg subset increased again in patients who accepted the transplant and reached a value of healthy non-transplanted subjects. By contrast, in patients with acute kidney rejection, the DR(high+)CD45RA(-)-Treg subset disappeared excessively, causing a reduction in the suppressive activity of the total Treg pool. Therefore, both the monitoring of its percentage within the total Treg pool and the monitoring of the HLA-DR MFI of the DR(+)CD45RA(-)-Treg subset may be useful tools for the prediction of graft rejection.