[Treatment strategies for ANCA-associated vasculitides]

Active but not inactive granulomatosis with polyangiitis is associated with decreased and phenotypically and functionally altered CD56(dim) natural killer cells

Background

The role of natural killer (NK) cells in granulomatosis with polyangiitis (GPA) is poorly understood. We recently reported that peripheral blood NK cell percentages correlate with the suppression of GPA activity (cohort I). The purpose of the current study was to further characterize NK cell subsets, phenotype and function in a second GPA cohort (cohort II).

Methods

Peripheral blood lymphocyte subsets were analyzed at a clinical diagnostic laboratory. Clinical data were extracted from medical records and patients were grouped according to their activity state (remission vs. active/non-remission). Separate analysis (cohort II, n = 22) and combined analysis (cohorts I and II, n = 34/57) of NK cell counts/percentages was performed. NK cell subsets and phenotypes were analyzed by multicolor flow cytometry. Cytotoxicity assays were performed using ⁵¹Cr-labeled K562 target cells.

Results

In cohort II, NK cell counts were lower than the lower limit of normal in active GPA, despite normal percentages due to lymphopenia. NK cell counts, but not other lymphocyte counts, were significantly higher in remission. Combined analysis of cohorts I and II confirmed decreased NK cell counts in active GPA and increased percentages in long-term remission. Follow-up measurements of six patients revealed increasing NK cell percentages during successful induction therapy. Multicolor analysis from cohort II revealed that in active GPA, the CD56^dim subset was responsible for decreased NK cell counts, expressed more frequently CD69, downregulated the Fc-receptor CD16 and upregulated the adhesion molecule CD54, the chemokine receptor CCR5 and the activating receptor NKG2C. In remission, these markers were unaltered or marginally altered. All other receptors investigated (NKp30, NKp44, NKp46, NKG2D, DNAM1, 2B4, CRACC, 41BB) remained unchanged. Natural cytotoxicity was not detectable in most patients with active GPA, but was restored in remission.

Conclusions

NK cell numbers correlate inversely with GPA activity. Reduced CD56^dim NK cells in active GPA have an activated phenotype, which intriguingly is associated with profound deficiency in cytotoxicity. These data suggest a function for NK cells in the pathogenesis and/or modulation of inflammation in GPA. NK cell numbers, phenotype (CD16, CD69, NKG2C) or overall natural cytotoxicity are promising candidates to serve as clinical biomarkers to determine GPA activity.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1098-7) contains supplementary material, which is available to authorized users.

[Therapy of ANCA-associated vasculitis with severe renal manifestation under routine conditions]

INTRODUCTION

In the MEPEX trial the poor prognosis of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis with severe renal manifestation (AAVr) could be significantly improved in the first year by plasmapheresis. How and to what extent is this knowledge of AAVr therapy implemented into routine practice and what effectiveness and adverse events resulted?

METHODS

This was a retrospective cohort study in which all patients who received remission induction therapy for AAVr under routine clinical conditions (RCC) in this hospital from 2009 to 2014 after publication of the MEPEX trial (n = 22) were compared with those in the plasmapheresis arm of the MEPEX trial (n = 70). Endpoints were dialysis-dependent chronic kidney disease and mortality after 3 and 12 months and severe life-threatening adverse events during the first 12 months.

RESULTS

All patients with AAVr were treated by plasmapheresis under RCC. The two groups showed no differences with respect to the rate of dialysis dependency (after 3 months RCC 14 % versus MEPEX 16 %, P = 1.00 and after 12 months RCC 23 % versus MEPEX 14 %, P = 0.55) or mortality (after 3 months RCC 18 % versus MEPEX 16 %, P = 0.75 and after 12 months RCC 18 % versus MEPEX 27 %, P = 0.57). The rate of severe life-threatening adverse events was similar under RCC and under controlled study conditions (64 % versus 69 %, P = 0.87).

CONCLUSION

Under RCC there is a high quality of medical treatment for AAVr. All patients received plasmapheresis for remission induction with comparable effectiveness and safety compared to controlled study conditions.