Human renal tubular epithelial cells suppress alloreactive T cell proliferation.

Renal tubular epithelial cells (TECs) are one of the main targets of alloreactive T cells during acute rejection. We hypothesize that TECs modulate the outcome of alloimmunity by executing immunosuppressive effects in order to dampen the local inflammation. We studied whether TECs possess immunosuppressive capacities and if indoleamine 2,3-dioxygenase (IDO) might play a role in suppressing T cell alloreactivity. Next, we studied the role of programmed death ligand 1 (PD-L1) and intercellular adhesion molecule-1 (ICAM-1 with regard to TEC-related immunomodulatory effects. CD3/CD28 and alloactivated peripheral blood mononuclear cells were co-cultured with activated TECs. We analysed CD4(+) and CD8(+) T cell proliferation and apoptosis in the absence or presence of IDO inhibitor 1-methyl-L-tryptophan (1-L-MT), anti-PD-L1 and anti-ICAM-1. Further, we examined whether inhibition of T cell proliferation was cell-cell contact-dependent. We found that TECs dose-dependently inhibited CD4(+) and CD8(+) T cell proliferation (P<0.05). Activated TECs showed significantly increased IDO activity and up-regulated PD-L1 and ICAM-1 expression. Suppressed CD4(+) and CD8(+) T cell proliferation was only partially restored or failed to restore using 1-L-MT. Activated TECs increased early and late apoptosis of proliferating CD4(+) and CD8(+) T cells; only CD4(+) T cell apoptosis was statistically affected by 1-L-MT. Transwell experiments revealed that TEC-mediated immunosuppression is cell-cell contact-dependent. We found that anti-ICAM-1 affected only CD4(+) T cell apoptosis and not T cell proliferation. Our data show that TECs suppress both CD4(+) and CD8(+) T cell proliferation contact dependently. Interestingly, inhibition of proliferation and enhancement of apoptosis of T cell subsets is differentially regulated by indoleamine 2,3-dioxygenase and ICAM-1, with no evidence for the involvement of PD-L1 in our system.

Immunological aspects of allogeneic and autologous mesenchymal stem cell therapies.

Mesenchymal stem cells (MSCs) have potential for therapeutic application as an immunomodulatory and regenerative agent. The immunogenicity and survival of MSCs after infusion are, however, not clear and evidence suggests that allogeneic but also autologous MSCs disappear rapidly after infusion. This may be associated with the susceptibility of MSCs to lysis by natural killer (NK) cells, possibly a result of culture-induced stress. In the present study we examined whether NK cell-mediated lysis of MSCs could be inhibited by immunosuppressive drugs. Human MSCs were isolated from adipose tissue and expanded in culture. Peripheral blood mononuclear cells were activated with interleukin (IL)-2 (200 U/ml) and IL-15 (10 ng/ml) for 7 days. CD3(-)CD16(+)CD56(+) NK cells were then isolated by fluorescence-activated cell sorting and added to europium-labeled MSCs for 4 hr in the presence or absence of immunosuppressive drugs. Lysis of MSCs was determined by spectrophotometric measurement of europium release. Nonactivated NK cells were not capable of lysing MSCs. Cytokine-activated NK cells showed upregulated levels of granzyme B and perforin and efficiently lysed allogeneic and autologous MSCs. Addition of tacrolimus, rapamycin or sotrastaurin to the lysis assay did not inhibit MSC killing. Furthermore, preincubation of activated NK cells with the immunosuppressive drugs for 24 hr before exposure to MSCs had no effect on MSC lysis. Last, addition of the immunosuppressants before and during the activation of NK cells, reduced NK cell numbers but did not affect their capacity to lyse MSCs. We conclude that the immunosuppressive drugs tacrolimus, rapamycin, and sotrastaurin are not capable of inhibiting the lysis of allogeneic and autologous MSCs by activated NK cells. Other approaches to controlling lysis of MSCs should be investigated, as controlling lysis may determine the efficacy of MSC therapy.