High Proportion of PNH Type II Neutrophils, I.e. Relative Percentage ≥3%, Is Associated with Thrombosis in Patients Displaying a PNH Clone >1%: Evidence from Analysis of the 5-Year French Nation-Wide Multicenter Observational Study

Introduction

The distinction between type II and type III cells among the white blood cells (WBC) need to be further investigated since a recent British study reported that the highest proportion of type II red blood cells (RBC) were found in patients with thrombotic PNH (Richards, BJH 2020).

Objective

We assessed the relative percentage of type II cells among neutrophils in patients displaying a major PNH clone (defined as GPI-deficient cells above 50%) and subsequently in patients with a clone between 1% and 50%. In addition, we aimed to investigate correlation to biological and clinical presentations, notably thrombosis, using data from the 5-year French nation-wide multicenter observational study.

Methods

All patients, regardless of their age, with a newly or previously diagnosed PNH clone or GPI-deficient cells ≥0.01% on neutrophils, detected in France by flow cytometry (FCM) from 2016 to 2021, were eligible for inclusion in this observatory. For each patient, the baseline assessment was considered as the initial PNH clone detection. Follow-up assessments were conducted in accordance with routine clinical practice. The two principal investigators reviewed all the clinical and biological information, especially FCM raw data files provided by the centers. This study was approved by the national research ethics board.

Results

Forty-one participating FCM laboratories across France enrolled 352 patients with a PNH clone above 1%. We first focused on the 125 out of 131 patients with a major PNH clone (i-e, ≥ 50%) with evaluable type II neutrophil percentages. Using the 104 patients with available data on hemolysis status, we performed an AUROC test based on the presence of hemolysis, a main feature of patients with major PNH clone. We determined a threshold of 3% of type II neutrophils (the same value was obtained considering raw percentages and relative percentages (r%) among the total deficient cells, that may be useable for patients with a PNH clone between 1 and 50%). This enabled the distinction of two groups: 103 patients with low r% of type II neutrophils (0.00%; IQR [0.00–0.71]) and 22 patients with high r% of type II neutrophils (5.98% [4.75–12.26]; p<0.0001). In addition, type II monocyte r% were higher in the “high type II” group (7.75% [5.13–11.07]) compared to the “low type II” group (0.00% [0.00–0.83]; p<0.0001). However, the total clone size was similar for both groups on WBC (neutrophils: 90.69% [75.44–96.90] vs 92.15% [80.28–98.28]; p=0.66, monocytes: 87.53% [76.10–93.01] vs 91.48% [77.71–96.75]; p=0.69), in the “high type II” and the in the “low type II” group, respectively. Hemolysis was more frequent in “low type II” group: 94.3%(83/88) compared to “high type II” group: 61.1%(11/18) (p=0.0006) for the 106 patients with available data on hemolysis status and a trend to a reduced r% of RBC (0.82% [0.00-31.41] vs 22.19% [0.00-53.14]; p=0.19). Interestingly, thrombosis appears to be more frequent at diagnosis in “high type II” group: 28.6%(6/21) vs 6.3%(6/95) in the “low type II” group (p=0.008) and when analyzing the cumulative events during long-term follow-up (33%(7/21) vs 8.4%(8/95); p<0.005).

We then focused on the 205 out of the 221 patients with a lower PNH clone size between 1% and 50% with evaluable type II neutrophil percentages. The relative percentage threshold of 3% allowed the distinction of 118 patients with “low type II neutrophils” and 87 with “high type II”. Hemolysis was more frequent in “low type II’ group compared to “high type II” group (30% vs 15%; p=0.01). Remarkably, while no thrombosis was present at diagnosis, 2 thrombosis occurred during the follow-up of the “high type II” group (respective clone size on neutrophils: 21.77% (r% type II: 5.65%) and 4.74% (r% type II: 60.34%)) and none in the “low type II” group.

Long-term follow-up up to 14.2 years of 124 patients, of whom 69 were receiving anti-C5, showed that 55 patients (56% treated) displayed an increase of the total clone size (mean: +18.1%), 36 (78% treated) remained stable (+0.0%) and 33 (30% treated) exhibited a decrease (-6.9%). However, we did not observe any major modification of type II neutrophil percentage between the high and low type II groups (-0.3 % vs +0.0%).

Conclusion

Patients with higher r% of type II neutrophils displayed more thrombosis irrespective of the total PNH clone size. Accurate quantification of type II neutrophils may impact clinical management since a treatment initiation could be considered.