FSGS biomarker updates—suPAR, B7-1, CD40 and more…

FSGS is the most common glomerular disorder causing end-stage kidney disease in the USA with a high post-transplant recurrence rate of 20-50%. Furthermore, the treatment of post-transplant recurrent FSGS is extremely challenging. While reading a recent article on biomarkers predicting post-transplant recurrent FSGS by Delville et al. (discussed below), it seemed a good idea to cover recent advancement in FSGS research. 

 suPAR (soluble plasminogen activator receptor) 
Since the first report by Wei et al. of suPAR as a circulating permeability factor causing FSGS, there has been extensive research to elucidate its role in FSGS. Although administration of suPAR molecule to mice was initially thought to be sufficient to cause proteinuria mimicking FSGS, via activation of integrin beta 3 and derangement of actin cytoskeleton, the situation does not seem that straightforward. As Reiser et al. discussed, there are challenges to overcome: existence of different suPAR isoforms with different disease modifying effects; heterogeneity of FSGS itself, which make it complicated to interpret correlation between levels of suPAR and disease activity; involvement of suPAR in other disease process, including cardiovascular disease (KI 2014). However, suPAR remains an intriguing molecule and potential biomarker in FSGS disease process.

 B7-1 (CD80)
A case series in the NEJM from Peter Mundel’s group in the end of 2013 brought us to an excitement for personalized treatment of a subgroup of B7-1 positive FSGS patients. They found strong B7-1 stain in primary FSGS as well as post-transplant recurrent FSGS. These patients were successfully treated with abatacept (CTLA4-Ig), resulting in complete remission of proteinuria. The hypothetical pathophysiological mechanism was via direct interaction of B7-1 and integrin beta 1 causing podocyte actin cytoskeleton changes. However, it was followed by comments and larger case series (AJKD 2014) questioning specificity of the immunostaining and treatment effect of abatacept. Exploration of this costimulatory molecule in FSGS was just started and further research is needed. 

Micro RNA(s) as biomarkers for FSGS disease activity 
A group from China suggested that certain micro RNAs are associated with disease activity (level of proteinuria) and progression (Zhang et al. CJASN and AJKD 2014). Potential candidates are miR-186 (involved in cell cycle control, AKT and insulin signaling etc.) and miR-125b (involved in NFkB signaling etc.). However, their contribution to pathogenesis is not clear so far.

 Pre-transplant antibody panel (including anti-CD40) to predict post transplant recurrent FSGS
Expanding potential FSGS biomarkers is the publication by Delville et al. The authors did a beautiful translational work using human serum in protein arrays, validation of specific auto-antibodies and further experimentation using cell cultures and animals models. The authors elegantly showed that pre-transplant antibody panel, especially anti-CD40 antibody, can predict risk of post-transplant recurrent FSGS.
In more detail, they started by comparing pre-transplant sera of non-recurrent FSGS (nrFSGS) vs recurrent FSGS (rFSGS), identifying 789 autoantibodies upregulated only in rFSGS but not in nrFSGS. Then those antibodies were enriched for those Ab with antigen targets expressed in kidney (151 autoAbs) and more specifically in glomeruli (10 autoAbs). They validated the 7-antibody panel (CD40, CGB5 (chorionic gonadotropin b), PTPRO (protein tyrosine phosphatase receptor O), FAS (TNF receptor superfamily member 6), P2RY11 (P2Y purinoceptor 11), SNRPB2 (small nuclear retinoid X receptor a), and APOL2 (Apolipoprotein 2)) in rFSGS vs nrFSGS cohort, and obtained ROC AUC of 0.92. Surprisingly, anti-CD40 itself had a high ROC AUC (0.77). Then, the involvement of rFSGS-anti-CD40 IgG to enhance FSGS recurrence was confirmed in vitro—rFSGS-anti-CD40 IgG caused actin cytoskeleton derangement in podocyte cell culture—, as well as in vivo—co-injection of rFSGS-anti-CD40 IgG and suPAR molecule markedly enhanced proteinuria (in a suPAR-dependent manner), which was inhibited by CD40-blocking antibody or in CD40 knockout mice. This suggests that by checking pre-transplant anti-CD40 antibody, we may be able to identify a high risk FSGS recurrence group. To manage these patients, current options are: peritransplant plasmaphresis or rituximab. Interesting to see if CD40 antagonist or blocking antibody can play a role in preventing/treating rFSGS in the clinic...

Naoka Murakami

NephMadness 2014 Part 8 - Biologics Bracket

This is a really exciting bracket and is full of new agents that will hopefully lead to major advances in our field. Acthar is the outlier here as, even though it is a peptide, it is not an antibody. For all the other agents I find it helpful to visualize what the antibody is targeting and on which cell type. Hopefully these cartoons will help. I think Rituximab and bortezomib should always go hand in hand when treating and auto- or alloimmune process as rituximab eliminates immature and naïve B cells and bortezomib eliminates B cells that have matured into antibody producing Plasma cells. There are some small trials reporting the use of both agents including a phase 2 trial in Waldenstroms Macroglobulinaemia but a large clinical trials using both these agents would be great.

In 2005 the FDA approved abatacept for RA after clinical trials showed benefit. However, there was evidence that this biologic might not be so efficacious in transplantation. Co-stimulation blockade on individual CD4+ T helper-cell subsets suggested a resistance of IL-17 secreting CCR6+ memory type 17 T helper cells (TH17) cells to CD28 and CTLA-4 blockade by abatacept. Effectively, abatacept inhibits the responsiveness of the total population, but a subset of cells are resistant to this inhibition. Belatacept is a second-generation CTLA-4 Ig fusion protein that differs from abatacept by only 2 amino acid substitutions (L104E and A29Y), which gives rise to slower dissociation rates from both CD86 and CD80. Subsequent research revealed this agent to be 10-fold more potent in vitro, and a more effective inhibitor of renal transplant rejection than abatacept. The subsequent BENEFIT trials proved belatacepts efficacy in transplantation.

CR1 or complement receptor type 1 or C3b/C4b receptor or CD35 is protein encoded the CR1 gene. This gene is in the RCA (regulators of complement activation) cluster region of human chromosome 1. This region includes the CFHR 1-5 and CFH genes. All these genes when mutated can cause immune-complex glomerular diseases such as MPGN. This CR1 protein also accounts for all the Knops blood group antigens. Reductions in CR1 or down regulating mutations can also cause SLE. Soluble CR1 may be useful in transplantation also. One study showed that sCR1 treatment improved 24 hour creatinine and inflammatory profiles post transplant in rats transplanted after brain death.

As precursors to the plasma cells that secrete antibodies, B cells are central in the pathology of SLE. Increased B-cell activation is due in part to increased levels of growth factors, including B-lymphocyte stimulator (BLyS), also called B-cell activating factor (BAFF). Belimumab is a human IgG1 monoclonal antibody that binds to soluble BLyS and thus prevents it from binding the BAFF receptors on B cells. So you can see where the trial names BLISS-52 and BLISS-76 come from, the numbers refer to the number of weeks the trials lasted. BLyS is a growth factor required for B-cell survival, maturation, and activation; germinal-center formation; the development of B cells into plasma cells; and immunoglobulin production. Many maturing B cells are completely dependent on the binding of BAFF receptors by BLyS to survive and mature. Memory B cells cells lack BAFF receptors. At least 50% of people with SLE have elevated plasma levels of soluble BLyS and there is a weak but significant correlation between high levels and active disease. Unfortunately patients with severe active LN were excluded from the BLISS trials.

For me Rituximab was the favourit in this groups as it is probably used in the greatest variety of diseases.

Thanks for reading and i hope you all learned something as i learned alot from NephMadness 2014. Now go to the NephMadness site and submit your brackets if you have not done so already!

Top nephrology-related stories of 2013

The votes are in! Hard to believe that another year has come and gone. RFN has presented the top 10 stories as voted by the readers of RFN since 2010. 2013 proved to be another interesting year. This years list is almost completely dominated by clinical trials. Basic science was snubbed this year (unlike other years). New this year was the active participation of the nephrology blogosphere in promoting different stories. Eleven different people posting on six different blogs and discussed why some of the stories were worthy of the top 10 list this year. These bloggers included Joel, Christos and Ed El Sayed over at PBFluids. Myself and Edgar at eAJKD. Adrian at Red Beans. Kenar at Nephron Power. Pascale at WhizBANG. Andrew, Paul and Gearoid here on RFN. This was a lot of fun and a great learning opportunity. Going into greater detail and hearing about different perspectives about how each of these stories might impact the field of nephrology was nice. This year set a record in voting at 155. Thanks to all who took the time to vote. As always this is not by any means a comprehensive list. If you have additions, feel free to add your story below as a comment. Now lets get to it...

First, a review of the top stories for the last several years can be found below.
Top stories of 2010
Top stories of 2011
Top stories of 2012

Hold up, stop the press, we have a last minute addition..
Honorable Mention- The much awaited hypertension guidelines (JNC 8 aka JNC late) was finally published in JAMA. I guess it is fitting that JNC 8 was published AFTER the year-end poll. The recommendations were a vast simplification to the JNC 7 report. In a nutshell, the JNC 8 committee recommended to treat blood pressure to 150/90 (JNC 7- 140/90) in patients greater than 60 yrs old and 140/90 (JNC 7- 130/80) for everyone else including patients with CKD, diabetes and those less than 60 years old. The new guidelines also recommend black patients take either a thiazide diuretic or a calcium channel blocker (CCB) as initial Rx. They recommended non-black patients to take thiazides, ACEi, ARB or CCB. Patients with CKD should be on ACEi or ARB. JNC 8 will still be fair game for next years top nephrology-related story.

10. Controversial cholesterol guideline published by AHA/ACC (14%)- Coming in at number 10 is the new cholesterol guidelines published in JACC by the AHA/ACC. There was much debate about the calculator that accompanied these guidelines as many felt that it was flawed and over-estimated the risk of cardiovascular disease. This over-estimation (75-150%) would place many more people on statins that would not be warranted. Joel over at PBFluids has a nice discussion about this. For a review on treating cholesterol in patients with kidney disease check out Andrew's post at RFN.

9. A novel potassium binder ZS-9 presented at ASN (14%)- This was a big surprise for just about everyone at ASN this year. However, the study is not published yet. The medical community is sorely in need of a better potassium binder for treating hyperkalemia. This is a frequently encountered problem with life threatening implications. Sodium polystyrene sulphonate (kayexalate) has been put through the ringer as of late. Many have been calling into question its effectiveness and potential risks (bowel necrosis). For another view on SPS check out Joel at PBFluids. The company ZS Pharma presented results from a phase II clinical trial and demonstrated that ZS-9 was capable of lowering potassium with minimal side effects. This could be a huge breakthrough and a much needed drug to treat a common medical condition. This is a well-deserved top story of the year in my opinion.

8. APOL1 risk alleles linked to CKD progression in AASK and CRIC cohorts presented at ASN and published in NEJM (15%)- The story of APOL1 risk alleles continues to gain traction in the medical literature. This year at ASN the story deepened with a study by Parsa et al. I discussed this on eAJKD. The authors showed that having 2 APOL1 risk alleles was associated with faster decline of kidney function in both the AASK and CRIC cohorts. The original APOL1 study published in Science was the #4 RFN top story of 2010. This is an exciting avenue of investigation as a target for APOL1 could have huge ramifications in treating kidney disease. However, this could be a long way off.

7. JASN paper by DeSilva et al showing that Fistula First perhaps not best for Elderly CKD patients (16%)- Coming in at number 7 is a very interesting paper from DeSilva et al in JASN. The Fistula First campaign has largely been seen as effective in decreasing the number of patients initiating dialysis with either a catheter or a graft. However, the benefit of performing dialysis with a fistula over a graft might not be apparent until several years. Is is possible that the survival benefit of a fistula over a graft is lost in the elderly? This group showed that in patients over 80 years old mortality did not differ between patients with a fistula versus a graft. Furthermore, they show that patients receiving a fistula were much more likely to require a catheter at some point as compared to a graft. An accompanied editorial states that we should shift our focus from a "fistula first" to a "patient first" approach. A one size fits all approach to medicine can be dangerous. This is an important study and worthy of the top 10 list.

6. Tolvaptan fails to gain approval from FDA for ADPKD (18%)- Number 6 is #TeamTolvaptan. Joel pushed for this story to be the number one story of the year over at PBFluids. Patients with CKD and in particular ADPKD have few pharmacological weapons to combat the relentless decline of renal function. The results of the TEMPO3:4 trial was the number 1 story of last year and the nephrology community was hopeful tolvaptan would gain FDA approval for ADPKD this year.  However, this was not the case as the FDA focused on liver toxicity and lack of hard outcomes (no ESRD outcomes only change in cyst size and slope of creatinine). I hope we see the tolvaptan story making the number 1 story of 2014 with approval from the FDA. We will see.

5. Abatacept in B7-1 Postivie Proteinuric Kidney Disease presented at ASN and published in NEJM (22%)- This was a small case series published in NEJM of abatacept (fusion protein composed of the Fc region of IgG1 fused to CTLA-4 inhibiting B7-1 binding) in patients with FSGS. Five patients with FSGS underwent immunostaining for B7-1 and showed positivity. These patients were subsequently treated with abatacept. All had either a partial or a complete remission. The thought is that B7-1 activation leads to podocyte dysfunction and abnormal motility through its interaction with beta-1-integrin. Paul discussed the utility of abatacept in FSGS, Lupus Nephritis and Diabetic Nephropathy on RFN. I hope a large trial will be underway soon as these are encouraging results.

4. RAVE Trial showing Rituximab as effective as conventional immunosuppression as induction agent in ANCA vasculitis reported in NEJM (25%)- The use of rituximab has continued to gain popularity treating a variety of autoimmune-related diseases. The difficulty in treating ANCA vasculitis is that the toxicity of the meds can sometimes be worse than the disease itself. Enter the RAVE trial. This was a randomized trial originally published in 2010 and demonstrated non-inferiority of rituximab as compared to oral cyclophosphamide for remission of severe ANCA associated vasculitis at 6 months. The follow-up to RAVE was reported in NEJM and discussed by Paul at RFN in December. In the RAVE trial the experimental group received rituximab and those who had remission only recieve placebo therafter. Whereas the comparison group received continued immunosuppression with cyclophosphamide followed by azathioprine (conventional group). Overall results showed that the rituximab group was non-inferior to the conventional group at 18 months. Rituximab was also superior to conventional immunosuppression in relapsing patients over the first 12 months. Interestingly and surprisingly, adverse events were similar between the two groups. These are encouraging results and adds to the armamentarium of drugs for ANCA vasculitis.

3. JASN paper by Maduell et al showing Online Hemodiafiltration reduces mortality compared to standard HD (27%)- Online hemodiafiltration continues to gain traction in Europe but its use the US has been slow to catch up. Online hemodiafiltration is a technique that involves the addition of convective clearance (hemofiltration) to the diffusive clearance of hemodialysis. This gives better middle molecule clearance of uremic toxins. Maduell et al reported in JASN this year a multicenter, open-label, randomized controlled trial with 906 patients on HD with either hemodialysis versus online-hemodiafiltration. After 2-years the online hemodiafiltration group had a 30% reduction in mortality (P=0.01). Paul at RFN reviews the evidence for why online hemodiafltration has gained momentum in Europe. Lets hope the big dialysis groups catch on and start offering this therapy to patients on hemodialysis. 

2. NEPHRON-D trial presented at ASN and published in NEJM (27%)- Number 2 is the NEPHRON-D trial. Edgar covered this at eAJKD and Ed Al Sayed at PBFluids. This trial effectively put the nail in the coffin of combined ACEi/ARB therapy for diabetic nephropathy. In short the trial was stopped early due to adverse events such as  hyperkalemia and acute renal failure, but still didn't show a difference in CKD progression or death. Even though this was a negative trial it answered an important question about the use of combination therapy and appears that readers agree as it is the number 2 story of the year.

1. CORAL trial for Renal Artery Stenosis presented at AHA and published in NEJM (33%)- Coming in at number 1 is the CORAL trial. This was presented at AHA Scientific Sessions and published in NEJM. As with combo ACEi/ARB therapy this is another nail in the coffin for this time stenting renal arteries in hypertension associated with renal artery stenosis. The CORAL trial was a large trial of 947 patients with renal artery stenosis. There was no difference in any of the outcomes most notably death, MI, stroke, progression of CKD or need for RRT. Jonathan has a nice discussion about this trial at RFN. There still could be a small subset of patients who might benefit from stenting (e.g. flash pulm edema). However, this could be the end of routine stenting in renal artery stenosis.

Again, quite a busy and exciting year in the world of nephrology in 2013. Thanks to all of the contributors and readers for keeping the site fun, interesting and educational.

Thanks for supporting RFN and happy holidays. Can't wait to see what 2014 has in store!

Top 10 Nephrology 2013 - Summaries

Four days left to vote for the top nephrology story of 2013. So far, the top 3 are:

1. The CORAL Trial
2. The Nephron-D Trial
3. JASN paper showing improved mortality for online HDF compared with standard HD.

The first two are not so surprising - high profile papers presented at the ASN and published in the NEJM. Even if they were negative trials, they have a significant impact and will change clinical practice. The third is more surprising to me personally although it is an important paper.

For a round up of pieces promoting various stories in this and other blogs:

• My own take on KIM1 and a piece on the uselessness of urinary eosinophils
• Andrew on UMOD, new targets for PKD and the new cholesterol guidelines
• Paul on Rituximab for ANCA-associated vasculitis
• Edgar on Nephron D at eAJKD
• Matt on APOL1 also at eAJKD
• Kenar at Nephron Power on Abatacept for FSGS
• Ed El Sayed at PBF also on Nephron D
• Joel on Tolvaptan in PKD at PBF
• Christos on HDPAL also at PBF
• Adrian on 23andMe at Red Beans
• Pascale on 23andMe at WhizBANG

Even if you don't feel like voting, this is a great set of summaries about some of the most important stories in nephrology for the year. Vote early and vote often

Rituximab for ANCA Associated Vasculitis (AAV): Contender for top 10 of 2013

In a year which gave us the bardoxolone failure, NEPHRON-D and the CORAL trial to name a few, a study with a positive result should be celebrated and the RAVE follow-up must be a contender for top 10 nephrology stories of 2013. The original RAVE trial was a multicenter, blinded, RCT which was published in 2010 (n=197). It demonstrated non-inferiority of rituximab (375 mg/m²/week for 4 weeks) as compared to oral cyclophosphamide for remission of severe AAV at 6 months. Moreover, among patients who had relapsing disease at baseline, rituximab was superior to conventional immunosuppression, at least at 6 months.  Of note, in the same issue of the NEJM in 2010, the smaller RITUXIVAS study (n=44) compared IV cyclophosphamide for 3-6 months to a rituximab based regime (same dosing as RAVE but including 2 IV cyclophosphamide pulses) with equivalent remission rates at 1 year. In both studies, conventional steroid treatment was employed.

The follow-up to RAVE was reported in the NEJM in August. Patients achieving a remission with rituximab received only placebo from month 6 through 18 while the comparison group received continued immunosuppressive therapy comprising cyclophosphamide followed by azathioprine. Overall results demonstrated that the rituximab group non-inferior to cyclophosphamide followed by maintenance therapy with azathioprine for 18 months. Echoing the original RAVE report, rituximab was superior to conventional immunosuppression in relapsing patients (>50% of patients at enrollment) at 12 months (P=0.009). However, at 18 months when most patients in the rituximab group had reconstituted B cells, the significance was lost (P=0.06). There was no significant difference between the groups in the numbers of total adverse events, serious adverse events or the number of discontinuations.

A few points to consider:

·         Regarding the relevancy of the results for nephrologists, it must be noted that only 66% had renal involvement and creatinine clearance was 54-69mls/min in the 2 groups. The mean increase in creatinine clearance was similar at approximately 11mls/min in both groups and response rate was similar between the 2 groups in patients with ‘severe’ renal disease.

·         Rituximab is often considered a ‘clean’ drug. What strikes me after reading many studies using rituximab is that the adverse event rate is usually similar to the comparison group, in this case cyclophosphamide.

·         A persistent concern with rituximab is whether or not to re-treat, and if so when, after B cell re-population occurs. In this 18 month follow-up, non-inferiority was maintained at up to 18 months, when most patients in the rituximab group had reconstituted B cells. However, B cells were detectable in 88% of rituximab patients who relapsed between 6-18 months. 

Verdict: A knowledge gap may still exist for patients presenting with a rapidly progressive GN requiring dialysis although the RITUXIVAS trial contained patients with worse renal function, some needing dialysis, and suggested equivalent early outcomes (but compared to IV cyclophosphamide). Also, we lack clarity on whether to re-treat and if steroids are necessary with rituximab. Overall, however, there is robust evidence that a 4 week course of rituximab is non-inferior to cyclophosphamide in the treatment of (most?) AAV patients.

For my other highlights of the year, see previous blogs regarding Abatacept  as targeted therapy for FSGS and the merits of high-volume online hemodiafiltration versus conventional high-flux dialysis. Don’t forget to vote for your top stories.

Abatacept for Glomerular Diseases: A New Era of Intelligent immunosuppression?

At ASN Kidney Week there was some interest in abatacept as a targeted therapy for glomerular diseases. T-cell activation requires 2 signals; (i) binding of the T-cell receptor to the antigen-MHC complex on the antigen-presenting cell and (ii) a co-stimulatory signal involving CTLA-4 on the T-cell and B7-1 on the antigen presenting cell. Abatacept is a fusion protein composed of the Fc region of IgG1 fused to the extracellular domain of CTLA-4 which inhibits the T-cell co-stimulatory pathway via B7-1 binding. 

          FSGS

The headlines must go to the small case series of abatacept in FSGS published in NEJM. The rationale for its use was the observation that B7-1 expression is not apparent in normal human podocytes but is found in certain diseased podocytes including a subset of FSGS patients. The series included 4 patients with recurrent FSGS post-transplantation (rituximab-resistant) and one with glucocorticoid-resistant primary FSGS. All patients achieved either partial or complete remission.

In vitro studies demonstrated that α3-Integrin knockout mice constitutively expressed B7-1 in podocytes and abatacept blocked B7-1 mediated podocyte migration in these cells. The molecular mechanism of B7-1-induced podocyte dysfunction was shown to be disruption of activation of the glomerular protein β1-integrin. The authors conclude that B7-1 immunostaining of biopsies may identify a subgroup of patients who would benefit from treatment with abatacept.

2       Lupus Nephritis

The late-breaking session included a randomized controlled trial of Euro-lupus regime cyclophosphamide (i.e. low dose IV) with or without abatacept for proliferative lupus nephritis [Access Trial]. Azathioprine was introduced at 3 months and stopped at 6 months in the abatacept group if they had achieved a remission. Overall, there was no difference in remission rate between the groups. Despite the neutral outcome, 2 points should be taken from the study: (i) The Euro-lupus regime appeared to work in a US cohort of patients where almost 80% were either Hispanic or African American. (ii) Abatacept patients who achieved remission maintained this at 1 year despite coming off immunosuppression at 6 months. However, with the growing confidence in Mycophenolate-based therapy for lupus nephritis and the lack of improved remission with Abatacept in this study, its place in the treatment of proliferative lupus nephritis remains uncertain.

3       Diabetic Nephropathy

An oral presentation on abatacept in Diabetic Nephropathy [FR-OR010] reported increased B7-1 expression in both murine podocytes cultured in high-glucose and on human glomerular podocytes from biopsy specimens. The use of Abatacept in diabetic mice prevented an increase in albuminuria.

Bottom Line: The FSGS case series beautifully illustrates how targeted therapies may be applied to immune-mediated renal diseases. While this case series is very small, it demonstrates the potential for reclassifying disease based on pathogenesis (i.e. B7-1-mediated) rather than crude pathological patterns (focal segmental sclerosis). This is similar to the recent re-classification of MPGN into complement or immune complex-mediated forms. With new targeted therapies like abatacept (and eculizumab for complement mediated glomerulopathies), we may be entering an era of intelligent immunosuppression based on molecular pathogenic signals rather than crude histological patterns.

Abatacept

A relatively new immunosuppressant agent--originally approved for treatment of refractory rheumatoid arthritis but now gaining steam as an anti-rejection medication for kidney transplant recipients--is abatacept (marketed under the trade name Orencia by Bristol-Myers-Squibb. Its mechanism of action is based on the idea of T-cell costimulation, a pathway which will likely be the target of further immunosuppressive drugs of the future.

Under normal conditions, full T-cell activation requires (a) binding of the T-cell receptor to the antigen-MHC complex on the antigen-presenting cell, and (b) a costimulatory signal--with two of the important molecules responsible for this signal being CD28 (expressed on T-cells) and B7 protein (expressed on antigen-presenting cells). Abatacept is a fusion protein comprised of an IgG fused to the extracellular domain of CTLA-4 (essentially a subtype of CD28, which binds to B7). The addition of this soluble B7 binder outcompetes the endogenous costimulatory interaction, and as a result, T-cell activation is prevented.