- Email: [email protected]
A window into immunosuppressant immunoregulation: recipient conversion to rapamycin increases potentially tolerogenic immune cells
commentary
This is in concordance with the better patient survival in recent years, underlining the continuing improvement of overall practices in PD. The main conclusion we can draw based on the current evidence is that surgically placed double-cuffed straight catheters display better survival rates than surgically placed double-cuffed coiled catheters, for reasons that remain unknown. This new evidence may have a significant impact on our everyday practice. It may offer PD patients a longer stay on the method and may help increase the utilization of PD as a renal replacement therapy. DISCLOSURE
The authors declared no competing interests. REFERENCES 1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Perl J, Wald R, Bargman JM et al. Changes in patient and technique survival over time among incident peritoneal dialysis patients in Canada. Clin J Am Soc Nephrol 2012; 7: 1145–1154. Chaudhary K, Sangha H, Khanna R. Peritoneal dialysis first: rationale. Clin J Am Soc Nephrol 2011; 6: 447–456. Kolesnyk I, Dekker FW, Boeschoten EW et al. Time-dependent reasons for peritoneal dialysis technique failure and mortality. Perit Dial Int 2010; 30: 170–177. Ash SR. Chronic peritoneal dialysis catheters: overview of design, placement, and removal procedures. Semin Dial 2003; 16: 323–334. Perakis KE, Stylianou KG, Kyriazis JP et al. Long-term complication rates and survival of peritoneal dialysis catheters: the role of percutaneous versus surgical placement. Semin Dial 2009; 22: 569–575. Dombros N, Dratwa M, Feriani M et al. European best practice guidelines for peritoneal dialysis. 3. Peritoneal access. Nephrol Dial Transplant 2005; 20(Suppl 9): ix8–ix12. Flanigan M, Gokal R. Peritoneal catheters and exit-site practices toward optimum peritoneal access: a review of current developments. Perit Dial Int 2005; 25: 132–139. The CARI guidelines. Evidence for peritonitis treatment and prophylaxis: type of peritoneal dialysis catheter. Caring for Australians with Renal Impairment (CARI). Nephrology (Carlton) 2004; 9(Suppl 3): S59–S64. Hagen SM, Lafranca JA, IJzermans JNM et al. A systematic review and meta-analysis of the influence of peritoneal dialysis catheter type on complication rate and catheter survival. Kidney Int 2014; 85: 920–932. Nielsen PK, Hemmingsen C, Friis SU et al. Comparison of straight and curled Tenckhoff peritoneal dialysis catheters implanted by percutaneous technique: a prospective randomized study. Perit Dial Int 1995; 15: 18–21. Johnson DW, Wong J, Wiggins KJ et al. A randomized controlled trial of coiled versus straight swan-neck Tenckhoff catheters in peritoneal dialysis patients. Am J Kidney Dis 2006; 48: 812–821.
Kidney International (2014) 85
see clinical investigation on page 888
A window into immunosuppressant immunoregulation: recipient conversion to rapamycin increases potentially tolerogenic immune cells Brian R. Rosborough1,2,3, Holger Hackstein4,5 and He¯th R. Turnquist1,2,3 Mechanistic target of rapamycin inhibitors (mTORi) have a complex immunoregulatory profile in both animal models and transplant patients. Studies suggest that mTORi act as tolerance-supporting and regulatory T cell (Treg)-promoting immunosuppressants. Yet proinflammatory influences on myeloid dendritic cells have been established. Insight is needed into the impact of mTORi on immune cells. Stallone et al. describe a clinical study identifying a potential immunoregulatory pathway involving plasmacytoid dendritic cells and Tregs in renal transplant patients on mTORi. Kidney International (2014) 85, 743–745. doi:10.1038/ki.2013.420
From a clinical perspective, a major challenge in transplant medicine remains the identification of nontoxic pharmacological substances that target the pathways preventing rejection and promoting transplant tolerance. Despite the development of potent immunosuppressive agents, long-term transplant outcome has improved only moderately in recent years. Five-year kidney transplant survival in optimally matched patients (0 HLAA,B,DR mismatch, deceased organ donor) has increased from 69.9% for 1 Starzl Transplantation Institute, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA; 2Department of Surgery, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA; 3Department of Immunology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA; 4 Institute for Clinical Immunology and Transfusion Medicine, Justus Liebig University, Giessen, Germany and 5University Hospital Giessen and Marburg, Giessen, Germany Correspondence: He¯th R. Turnquist, Starzl Transplantation Institute, University of Pittsburgh School of Medicine, 200 Lothrop Street, E1554 BST, Pittsburgh, Pennsylvania, 15261, USA. E-mail: [email protected]
transplantations performed between 1985 and 1994 to 76.5% for transplantations performed between 1995 and 2004.1 Whereas calcineurin inhibitors (CNIs) are understood to act as a barrier to tolerance development in experimental animal models and transplant patients, studies have suggested that mechanistic target of rapamycin pathway inhibitors (mTORi), such as rapamycin or everolimus, may act as tolerance-supporting and regulatory T cell (Treg)-promoting immunosuppressants.2,3 Yet, even with these significant clinical implications, it is important to emphasize that our understanding of the molecular and immunological events that support these proposed capacities of mTORi is very limited. Interestingly, data from the study of transplant-patient samples strongly support earlier rodent studies that identified the mTOR pathways as a critical regulator of antigen-presenting cell (APC) homeostasis and function.2 Notably, myeloid dendritic cells (mDCs) isolated from the peripheral blood of kidney transplant recipients receiving mTORi demonstrated an increased stimulatory 743
commentary
a
Proinflammatory CD86 PD-L1
IL-12p40
LPS BDCA1+ mDC
IL-10
b
Regulatory CD8+ CD28– T cells Treg Foxp3 ?
Tbet CTLA-4
? ?
Th1
?
Foxp3
Th2
?
ILT3/ILT4
HLA-G
GATA3
?
CD40 BDCA2+ pDC Th1 Tbet
ion ft at ra ul og ri c all C ey dn
Th2 GATA3
Ki
?
ILT3/ILT4
Endothelial cells
Figure 1 | Potential proinflammatory and regulatory effects of rapamycin in kidney transplant recipients. (a) Rapamycin increases the immunostimulatory potential of myeloid dendritic cells (mDCs) by increasing their expression of CD86 and IL-12p40 but reducing expression of PD-L1 (B7-H1) and IL-10.4 (b) Stallone et al.6 identify that mTORi increases the frequency of BDCA2 þ plasmacytoid dendritic cells (pDCs) that express ILT3 and ILT4. These changes in pDCs correlate with increases in circulating CD8 þ CD28 T cells and regulatory T cells (Tregs) and Th2 cells, as well as reductions in Th1 cells. Within the allograft, endothelial cells express ILT3 and ILT4, and there is reduced Th1 but increased Th2 T cell infiltration. LPS, lipopolysaccharide.
profile characterized by enhanced costimulatory molecule (CD86) and IL-12p40 expression, but reduced B7 homolog 1 (B7-H1; programmed cell death 1 ligand 1, PD-L1) and IL-10 expression, following ex vivo stimulation with lipopolysaccharide compared with patients receiving CNIs.4 Transcriptional profiling of kidney transplant recipients found that compared with CNIs, mTORi caused a nuclear factor-kB-related, proinflammatory gene signature in innate immune cells, including APCs.5 With the apparent contrasting pro-tolerogenic effect of mTORi on Tregs, but potentially proinflammatory impact on innate 744
APCs, further study dissecting immune modulation by mTORi in human transplant recipients is clearly warranted. The study by Stallone et al.6 (this issue) provides new insights into the complex, but potentially pro-tolerogenic, regulation of alloimmunity provided by mTORi in humans. The authors investigated the impact of mTORi in 40 renal transplant recipients with biopsy-proven chronic allograft nephropathy and undergoing CNI reduction or CNI withdrawal with mTORi introduction. Compared with the 20 patients undergoing CNI reduction, the 20 rapamycin-treated patients
had an increased number of immunoglobulin-like transcript 3 (ILT3)/ILT4 þ BDCA2 þ plasmacytoid dendritic cells (pDCs). ILTs are inhibitory receptors that are emerging as important regulators of the function of dendritic cells (DCs) and support their expansion and differentiation of Tregs.7 This is consistent with evidence provided by the authors that ILT3/ILT4 þ pDC incidence correlates with increased numbers of circulating Tregs. Interestingly, rapamycin treatment results in a reduction of BDCA1 þ mDCs. Thus, despite proinflammatory effects of rapamycin described for both mouse and human mDCs, the current findings provide support for the facilitation of a regulatory population of pDCs by rapamycin. Indeed, pDCs are required for experimental transplant tolerance induction, inducing Tregs in the lymph nodes.8 In the context of the findings of Stallone et al.6 and previous findings, it is rational to hypothesize that mTOR inhibition has unique immunomodulatory properties depending on the APC population. On the basis of the current6 and past studies of renal transplant recipients,4,5 it can be proposed that rapamycin has proinflammatory effects on reduced numbers of mDCs while promoting pDCs with an immunoregulatory phenotype, characterized by increased expression of ILT3 and ILT4. Further studies in kidney transplant recipients examining ILT expression by mDCs and assessing resistance to maturation and cytokine production by ILT3/ILT4 þ pDCs following ex vivo restimulation would further enhance the findings. In total, the clinical data suggest that the reported proinflammatory and regulatory effects of mTORi may be compartmentalized to distinct cell populations, including Tregs, mDCs, and pDCs. Although Stallone et al.6 phenotypically characterize a population of ILT þ pDCs, the data do not establish whether pDCs mediate the identified increase in Tregs, nor the suggested shift from Th1 to Th2 balance in graft biopsies. While it has been suggested that ILT expression by APCs results in the generation of Tregs, the authors do not present any ex vivo data to support the role of ILT3/ILT4 þ pDCs in modulation Kidney International (2014) 85
commentary
of T cell responses. This is a critical point since rapamycin can act on T cells to control activation, differentiation, and Treg expansion.2 Examination of these complex mechanisms will be difficult to complete in renal transplant recipients and is more suited for investigation in transgenic murine models. In such transgenic mice studies, ligation of DC ILT4 mitigated rejection of allografts.9 As the addition of rapamycin to human pDCs in vitro did not result in increased ILT expression, further studies will be required to dissect the mechanisms leading to increased ILT expression on pDCs under the conditions of mTORi. The article by Stallone et al.6 also suggests new avenues of study. In addition to DCs, endothelial cells express ILT3 and ILT4, and endothelial expression of these molecules regulates allogeneic T cells. When the authors examined ILT3 and ILT4 protein expression in allograft biopsies, it was detectable only in patients who were treated with rapamycin. In addition to localization within infiltrating mononuclear cells, peritubular capillary endothelial cells also expressed ILT3/ILT4. Rapamycin pretreatment of endothelial cells reduces their ability to stimulate CD4 þ memory T cell activity and promotes Foxp3 þ T cells.10 Furthermore, rapamycin pretreatment of endothelial cells reduced the rate of their rejection in a human-to-mouse xenograft model.10 Thus, it is clear that immunomodulation of endothelial cells may also be an important contributor to regulation of antigraft immune responses. Since ILT3 and ILT4 were increased in allograft peritubular capillary endothelial cells in the study by Stallone et al.,6 it will be imperative to determine the contribution of these cells to the reported regulatory properties of mTORi, particularly within the graft immune microenvironment. The immunoregulatory properties of mTORi in transplant patients could be multifold (Figure 1). Studies in human transplant recipients investigating the mechanisms of immunoregulation by immunosuppressive drugs, particularly in APCs, remain inadequate. Thus, this work by Stallone and colleagues6 represents an advance in our understanding of the immunoregulatory Kidney International (2014) 85
properties of rapamycin in human renal transplant recipients. This study provides preliminary evidence for a regulatory role for APCs in transplant recipients receiving mTORi and furthers our understanding of the complex mechanisms involved in the pro- and anti-inflammatory effects of mTORi. These findings should inspire future studies in animal models and the clinic to continue to finely dissect the effect of mTORi on Tregs, mDCs, pDCs, and endothelial cells. Such investigation of the immune cell-specific outcomes of mTORi will be imperative to fully understand the mechanisms by which rapamycin promotes a tolerancesparing immune environment. This knowledge, combined with the need to limit any proinflammatory effects of mTORi, will no doubt be applied rapidly in our collective quest for donor-specific tolerance in individuals with transplants.
REFERENCES 1.
2.
3.
4.
5.
6.
7.
8.
DISCLOSURE
All the authors declared no competing interests. ACKNOWLEDGMENTS
We acknowledge Angus W. Thomson for insightful suggestions provided during the generation of this Commentary.
9.
10.
Opelz G, Do¨hler B. Effect of human leukocyte antigen compatibility on kidney graft survival: comparative analysis of two decades. Transplantation 2007; 84: 137–143. Thomson AW, Turnquist HR, Raimondi G. Immunoregulatory functions of mTOR inhibition. Nat Rev Immunol 2009; 9: 324–337. Akimova T, Kamath BM, Goebel JW et al. Differing effects of rapamycin or calcineurin inhibitor on T-regulatory cells in pediatric liver and kidney transplant recipients. Am J Transplant 2012; 12: 3449–3461. Haidinger M, Poglitsch M, Geyeregger R et al. A versatile role of mammalian target of rapamycin in human dendritic cell function and differentiation. J Immunol 2010; 185: 3919–3931. Brouard S, Puig-Pey I, Lozano J-J et al. Comparative transcriptional and phenotypic peripheral blood analysis of kidney recipients under cyclosporin A or sirolimus monotherapy. Am J Transplant 2010; 10: 2604–2614. Stallone G, Pontrelli P, Infante B et al. Rapamycin induces ILT3highILT4high dendritic cells promoting a new immunoregulatory pathway. Kidney Int 2014; 85: 888–897. Wu J, Horuzsko A. Expression and function of immunoglobulin-like transcripts on tolerogenic dendritic cells. Hum Immunol 2009; 70: 353–356. Ochando JC, Homma C, Yang Y et al. Alloantigen-presenting plasmacytoid dendritic cells mediate tolerance to vascularized grafts. Nat Immunol 2006; 7: 652–662. Ristich V, Liang S, Zhang W et al. Tolerization of dendritic cells by HLA-G. Eur J Immunol 2005; 35: 1133–1142. Wang C, Yi T, Qin L et al. Rapamycin-treated human endothelial cells preferentially activate allogeneic regulatory T cells. J Clin Invest 2013; 123: 1677–1693.
see clinical trial on page 962
The perils of clinical trials Richard E. Gilbert1 When the maximal reabsorptive capacity for glucose is lowered by blockade of the activity of sodium–glucose cotransporter-2 (SGLT2), glucosuria occurs in proportion to the plasma glucose and glomerular filtration rate. Accordingly, the modest, 0.44%, hemoglobin A1c reduction found by Kohan et al. in diabetic patients with relatively good glycemic control and chronic kidney disease stage 3 treated with an SGLT2 inhibitor might have been anticipated. The 0.32% fall in hemoglobin A1c in the placebo group, however, seems less expected. Kidney International (2014) 85, 745–747. doi:10.1038/ki.2013.406
1
Department of Medicine, University of Toronto, St Michael’s Hospital, Li Ka Shing Knowledge Institute, Toronto, Ontario, Canada Correspondence: Richard E. Gilbert, Division of Endocrinology, St Michael’s Hospital, 61 Queen Street East, Toronto, Ontario, Canada M5C 2T2. E-mail: [email protected]
The prevalence of diabetes is approaching 10% of the adult population in many industrialized nations, where for a long time diabetes has also been the major cause of end-stage kidney disease. Thus we are not surprised to learn 745
This is in concordance with the better patient survival in recent years, underlining the continuing improvement of overall practices in PD. The main conclusion we can draw based on the current evidence is that surgically placed double-cuffed straight catheters display better survival rates than surgically placed double-cuffed coiled catheters, for reasons that remain unknown. This new evidence may have a significant impact on our everyday practice. It may offer PD patients a longer stay on the method and may help increase the utilization of PD as a renal replacement therapy. DISCLOSURE
The authors declared no competing interests. REFERENCES 1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Perl J, Wald R, Bargman JM et al. Changes in patient and technique survival over time among incident peritoneal dialysis patients in Canada. Clin J Am Soc Nephrol 2012; 7: 1145–1154. Chaudhary K, Sangha H, Khanna R. Peritoneal dialysis first: rationale. Clin J Am Soc Nephrol 2011; 6: 447–456. Kolesnyk I, Dekker FW, Boeschoten EW et al. Time-dependent reasons for peritoneal dialysis technique failure and mortality. Perit Dial Int 2010; 30: 170–177. Ash SR. Chronic peritoneal dialysis catheters: overview of design, placement, and removal procedures. Semin Dial 2003; 16: 323–334. Perakis KE, Stylianou KG, Kyriazis JP et al. Long-term complication rates and survival of peritoneal dialysis catheters: the role of percutaneous versus surgical placement. Semin Dial 2009; 22: 569–575. Dombros N, Dratwa M, Feriani M et al. European best practice guidelines for peritoneal dialysis. 3. Peritoneal access. Nephrol Dial Transplant 2005; 20(Suppl 9): ix8–ix12. Flanigan M, Gokal R. Peritoneal catheters and exit-site practices toward optimum peritoneal access: a review of current developments. Perit Dial Int 2005; 25: 132–139. The CARI guidelines. Evidence for peritonitis treatment and prophylaxis: type of peritoneal dialysis catheter. Caring for Australians with Renal Impairment (CARI). Nephrology (Carlton) 2004; 9(Suppl 3): S59–S64. Hagen SM, Lafranca JA, IJzermans JNM et al. A systematic review and meta-analysis of the influence of peritoneal dialysis catheter type on complication rate and catheter survival. Kidney Int 2014; 85: 920–932. Nielsen PK, Hemmingsen C, Friis SU et al. Comparison of straight and curled Tenckhoff peritoneal dialysis catheters implanted by percutaneous technique: a prospective randomized study. Perit Dial Int 1995; 15: 18–21. Johnson DW, Wong J, Wiggins KJ et al. A randomized controlled trial of coiled versus straight swan-neck Tenckhoff catheters in peritoneal dialysis patients. Am J Kidney Dis 2006; 48: 812–821.
Kidney International (2014) 85
see clinical investigation on page 888
A window into immunosuppressant immunoregulation: recipient conversion to rapamycin increases potentially tolerogenic immune cells Brian R. Rosborough1,2,3, Holger Hackstein4,5 and He¯th R. Turnquist1,2,3 Mechanistic target of rapamycin inhibitors (mTORi) have a complex immunoregulatory profile in both animal models and transplant patients. Studies suggest that mTORi act as tolerance-supporting and regulatory T cell (Treg)-promoting immunosuppressants. Yet proinflammatory influences on myeloid dendritic cells have been established. Insight is needed into the impact of mTORi on immune cells. Stallone et al. describe a clinical study identifying a potential immunoregulatory pathway involving plasmacytoid dendritic cells and Tregs in renal transplant patients on mTORi. Kidney International (2014) 85, 743–745. doi:10.1038/ki.2013.420
From a clinical perspective, a major challenge in transplant medicine remains the identification of nontoxic pharmacological substances that target the pathways preventing rejection and promoting transplant tolerance. Despite the development of potent immunosuppressive agents, long-term transplant outcome has improved only moderately in recent years. Five-year kidney transplant survival in optimally matched patients (0 HLAA,B,DR mismatch, deceased organ donor) has increased from 69.9% for 1 Starzl Transplantation Institute, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA; 2Department of Surgery, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA; 3Department of Immunology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA; 4 Institute for Clinical Immunology and Transfusion Medicine, Justus Liebig University, Giessen, Germany and 5University Hospital Giessen and Marburg, Giessen, Germany Correspondence: He¯th R. Turnquist, Starzl Transplantation Institute, University of Pittsburgh School of Medicine, 200 Lothrop Street, E1554 BST, Pittsburgh, Pennsylvania, 15261, USA. E-mail: [email protected]
transplantations performed between 1985 and 1994 to 76.5% for transplantations performed between 1995 and 2004.1 Whereas calcineurin inhibitors (CNIs) are understood to act as a barrier to tolerance development in experimental animal models and transplant patients, studies have suggested that mechanistic target of rapamycin pathway inhibitors (mTORi), such as rapamycin or everolimus, may act as tolerance-supporting and regulatory T cell (Treg)-promoting immunosuppressants.2,3 Yet, even with these significant clinical implications, it is important to emphasize that our understanding of the molecular and immunological events that support these proposed capacities of mTORi is very limited. Interestingly, data from the study of transplant-patient samples strongly support earlier rodent studies that identified the mTOR pathways as a critical regulator of antigen-presenting cell (APC) homeostasis and function.2 Notably, myeloid dendritic cells (mDCs) isolated from the peripheral blood of kidney transplant recipients receiving mTORi demonstrated an increased stimulatory 743
commentary
a
Proinflammatory CD86 PD-L1
IL-12p40
LPS BDCA1+ mDC
IL-10
b
Regulatory CD8+ CD28– T cells Treg Foxp3 ?
Tbet CTLA-4
? ?
Th1
?
Foxp3
Th2
?
ILT3/ILT4
HLA-G
GATA3
?
CD40 BDCA2+ pDC Th1 Tbet
ion ft at ra ul og ri c all C ey dn
Th2 GATA3
Ki
?
ILT3/ILT4
Endothelial cells
Figure 1 | Potential proinflammatory and regulatory effects of rapamycin in kidney transplant recipients. (a) Rapamycin increases the immunostimulatory potential of myeloid dendritic cells (mDCs) by increasing their expression of CD86 and IL-12p40 but reducing expression of PD-L1 (B7-H1) and IL-10.4 (b) Stallone et al.6 identify that mTORi increases the frequency of BDCA2 þ plasmacytoid dendritic cells (pDCs) that express ILT3 and ILT4. These changes in pDCs correlate with increases in circulating CD8 þ CD28 T cells and regulatory T cells (Tregs) and Th2 cells, as well as reductions in Th1 cells. Within the allograft, endothelial cells express ILT3 and ILT4, and there is reduced Th1 but increased Th2 T cell infiltration. LPS, lipopolysaccharide.
profile characterized by enhanced costimulatory molecule (CD86) and IL-12p40 expression, but reduced B7 homolog 1 (B7-H1; programmed cell death 1 ligand 1, PD-L1) and IL-10 expression, following ex vivo stimulation with lipopolysaccharide compared with patients receiving CNIs.4 Transcriptional profiling of kidney transplant recipients found that compared with CNIs, mTORi caused a nuclear factor-kB-related, proinflammatory gene signature in innate immune cells, including APCs.5 With the apparent contrasting pro-tolerogenic effect of mTORi on Tregs, but potentially proinflammatory impact on innate 744
APCs, further study dissecting immune modulation by mTORi in human transplant recipients is clearly warranted. The study by Stallone et al.6 (this issue) provides new insights into the complex, but potentially pro-tolerogenic, regulation of alloimmunity provided by mTORi in humans. The authors investigated the impact of mTORi in 40 renal transplant recipients with biopsy-proven chronic allograft nephropathy and undergoing CNI reduction or CNI withdrawal with mTORi introduction. Compared with the 20 patients undergoing CNI reduction, the 20 rapamycin-treated patients
had an increased number of immunoglobulin-like transcript 3 (ILT3)/ILT4 þ BDCA2 þ plasmacytoid dendritic cells (pDCs). ILTs are inhibitory receptors that are emerging as important regulators of the function of dendritic cells (DCs) and support their expansion and differentiation of Tregs.7 This is consistent with evidence provided by the authors that ILT3/ILT4 þ pDC incidence correlates with increased numbers of circulating Tregs. Interestingly, rapamycin treatment results in a reduction of BDCA1 þ mDCs. Thus, despite proinflammatory effects of rapamycin described for both mouse and human mDCs, the current findings provide support for the facilitation of a regulatory population of pDCs by rapamycin. Indeed, pDCs are required for experimental transplant tolerance induction, inducing Tregs in the lymph nodes.8 In the context of the findings of Stallone et al.6 and previous findings, it is rational to hypothesize that mTOR inhibition has unique immunomodulatory properties depending on the APC population. On the basis of the current6 and past studies of renal transplant recipients,4,5 it can be proposed that rapamycin has proinflammatory effects on reduced numbers of mDCs while promoting pDCs with an immunoregulatory phenotype, characterized by increased expression of ILT3 and ILT4. Further studies in kidney transplant recipients examining ILT expression by mDCs and assessing resistance to maturation and cytokine production by ILT3/ILT4 þ pDCs following ex vivo restimulation would further enhance the findings. In total, the clinical data suggest that the reported proinflammatory and regulatory effects of mTORi may be compartmentalized to distinct cell populations, including Tregs, mDCs, and pDCs. Although Stallone et al.6 phenotypically characterize a population of ILT þ pDCs, the data do not establish whether pDCs mediate the identified increase in Tregs, nor the suggested shift from Th1 to Th2 balance in graft biopsies. While it has been suggested that ILT expression by APCs results in the generation of Tregs, the authors do not present any ex vivo data to support the role of ILT3/ILT4 þ pDCs in modulation Kidney International (2014) 85
commentary
of T cell responses. This is a critical point since rapamycin can act on T cells to control activation, differentiation, and Treg expansion.2 Examination of these complex mechanisms will be difficult to complete in renal transplant recipients and is more suited for investigation in transgenic murine models. In such transgenic mice studies, ligation of DC ILT4 mitigated rejection of allografts.9 As the addition of rapamycin to human pDCs in vitro did not result in increased ILT expression, further studies will be required to dissect the mechanisms leading to increased ILT expression on pDCs under the conditions of mTORi. The article by Stallone et al.6 also suggests new avenues of study. In addition to DCs, endothelial cells express ILT3 and ILT4, and endothelial expression of these molecules regulates allogeneic T cells. When the authors examined ILT3 and ILT4 protein expression in allograft biopsies, it was detectable only in patients who were treated with rapamycin. In addition to localization within infiltrating mononuclear cells, peritubular capillary endothelial cells also expressed ILT3/ILT4. Rapamycin pretreatment of endothelial cells reduces their ability to stimulate CD4 þ memory T cell activity and promotes Foxp3 þ T cells.10 Furthermore, rapamycin pretreatment of endothelial cells reduced the rate of their rejection in a human-to-mouse xenograft model.10 Thus, it is clear that immunomodulation of endothelial cells may also be an important contributor to regulation of antigraft immune responses. Since ILT3 and ILT4 were increased in allograft peritubular capillary endothelial cells in the study by Stallone et al.,6 it will be imperative to determine the contribution of these cells to the reported regulatory properties of mTORi, particularly within the graft immune microenvironment. The immunoregulatory properties of mTORi in transplant patients could be multifold (Figure 1). Studies in human transplant recipients investigating the mechanisms of immunoregulation by immunosuppressive drugs, particularly in APCs, remain inadequate. Thus, this work by Stallone and colleagues6 represents an advance in our understanding of the immunoregulatory Kidney International (2014) 85
properties of rapamycin in human renal transplant recipients. This study provides preliminary evidence for a regulatory role for APCs in transplant recipients receiving mTORi and furthers our understanding of the complex mechanisms involved in the pro- and anti-inflammatory effects of mTORi. These findings should inspire future studies in animal models and the clinic to continue to finely dissect the effect of mTORi on Tregs, mDCs, pDCs, and endothelial cells. Such investigation of the immune cell-specific outcomes of mTORi will be imperative to fully understand the mechanisms by which rapamycin promotes a tolerancesparing immune environment. This knowledge, combined with the need to limit any proinflammatory effects of mTORi, will no doubt be applied rapidly in our collective quest for donor-specific tolerance in individuals with transplants.
REFERENCES 1.
2.
3.
4.
5.
6.
7.
8.
DISCLOSURE
All the authors declared no competing interests. ACKNOWLEDGMENTS
We acknowledge Angus W. Thomson for insightful suggestions provided during the generation of this Commentary.
9.
10.
Opelz G, Do¨hler B. Effect of human leukocyte antigen compatibility on kidney graft survival: comparative analysis of two decades. Transplantation 2007; 84: 137–143. Thomson AW, Turnquist HR, Raimondi G. Immunoregulatory functions of mTOR inhibition. Nat Rev Immunol 2009; 9: 324–337. Akimova T, Kamath BM, Goebel JW et al. Differing effects of rapamycin or calcineurin inhibitor on T-regulatory cells in pediatric liver and kidney transplant recipients. Am J Transplant 2012; 12: 3449–3461. Haidinger M, Poglitsch M, Geyeregger R et al. A versatile role of mammalian target of rapamycin in human dendritic cell function and differentiation. J Immunol 2010; 185: 3919–3931. Brouard S, Puig-Pey I, Lozano J-J et al. Comparative transcriptional and phenotypic peripheral blood analysis of kidney recipients under cyclosporin A or sirolimus monotherapy. Am J Transplant 2010; 10: 2604–2614. Stallone G, Pontrelli P, Infante B et al. Rapamycin induces ILT3highILT4high dendritic cells promoting a new immunoregulatory pathway. Kidney Int 2014; 85: 888–897. Wu J, Horuzsko A. Expression and function of immunoglobulin-like transcripts on tolerogenic dendritic cells. Hum Immunol 2009; 70: 353–356. Ochando JC, Homma C, Yang Y et al. Alloantigen-presenting plasmacytoid dendritic cells mediate tolerance to vascularized grafts. Nat Immunol 2006; 7: 652–662. Ristich V, Liang S, Zhang W et al. Tolerization of dendritic cells by HLA-G. Eur J Immunol 2005; 35: 1133–1142. Wang C, Yi T, Qin L et al. Rapamycin-treated human endothelial cells preferentially activate allogeneic regulatory T cells. J Clin Invest 2013; 123: 1677–1693.
see clinical trial on page 962
The perils of clinical trials Richard E. Gilbert1 When the maximal reabsorptive capacity for glucose is lowered by blockade of the activity of sodium–glucose cotransporter-2 (SGLT2), glucosuria occurs in proportion to the plasma glucose and glomerular filtration rate. Accordingly, the modest, 0.44%, hemoglobin A1c reduction found by Kohan et al. in diabetic patients with relatively good glycemic control and chronic kidney disease stage 3 treated with an SGLT2 inhibitor might have been anticipated. The 0.32% fall in hemoglobin A1c in the placebo group, however, seems less expected. Kidney International (2014) 85, 745–747. doi:10.1038/ki.2013.406
1
Department of Medicine, University of Toronto, St Michael’s Hospital, Li Ka Shing Knowledge Institute, Toronto, Ontario, Canada Correspondence: Richard E. Gilbert, Division of Endocrinology, St Michael’s Hospital, 61 Queen Street East, Toronto, Ontario, Canada M5C 2T2. E-mail: [email protected]
The prevalence of diabetes is approaching 10% of the adult population in many industrialized nations, where for a long time diabetes has also been the major cause of end-stage kidney disease. Thus we are not surprised to learn 745