PB0770 - Hyperinflammation and extensive cell death occurred in VITT and indicate severity and poor outcomes

Background: Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a rare, life-threatening condition following adenovirus vector vaccination (ChAdOx1) against COVID-19. However, the molecular mechanism is still not clear.

Aims: Systematically analyse the abnormal immune response and pathological features of VITT patients.

Methods: VITT patients (N=22) were recruited across multiple hospitals in UK, based on these diagnostic criteria: Onset of symptoms 5 to 30 days after COVID-19 vaccination, presence of anti-PF4 antibodies, thrombosis, thrombocytopenia ( < 150x109/L) and elevated D-dimer levels (>4000 FEU). Controls without VITT were also recruited including 9 pre- and 23 post-ChAdOx1 vaccination. Levels of circulating histones, cytokines, and blood cell counts as well as coagulation parameters were analysed and along with their association with mortality 28-days post VITT diagnosis.

Results: All patients had elevated D-dimer levels and thrombocytopenia. Pro-inflammatory cytokines were significantly elevated in VITT patients compared to pre- and post-ChAdOx1 vaccine controls, including IL-6 (Median=37.2pg/ml [Q1=12.9-Q3=432.8] vs 0.0pg/ml [0.0-0.0] vs 0.0pg/ml [0.0-0.0]; P< 0.001) and IL-8 (77.4pg/ml [0.0-416.9] vs 0.0pg/ml [0.0-0.0] vs 0.0pg/ml [0.0-10.9]; P=0.004). Sixteen patients (72.7%) had lymphopenia [Median=1.0x109/L [0.6-0.4] at diagnosis. Circulating histones were elevated at VITT diagnosis (29.6µg/ml [3.2-54.2]) compared to pre-(0.14µg/ml [0.1-1.7]) and post-(0.22µg/ml [0.1-1.9]) ChAdOx1 vaccine controls (Fig.1A), and higher in non-survivors (n=12; 50.0µg/ml [33.0, 75.1]) than survivors (n=10; 3.3µg/ml [0.5-4.7]) (Fig.1B). Univariate analysis demonstrated their association with mortality (OR=1.10 [95% CI=1.02-1.17], P< 0.001). Subsequent multivariate analysis demonstrated that histones were independently associated with mortality after adjustment for age and gender (aOR= 1.097; 95% CI=1.023-1.177 P=0.009)(Fig.1C). The area under the ROC curve (AUC) reached 0.93 ([95% CI=0.83-1.00], P=0.001). Kaplan-Meier survival curve demonstrated significantly higher 28-days mortality in patients with ≥30µg/ml than patients with < 30µg/ml circulating histones (P=0.002)(Fig.1D).

Conclusion(s): This study indicates that VITT is a hyperinflammatory-thrombotic disease with extensive cell death, including lymphocyte loss and NETosis, whereby circulating histones are of prognostic and pathogenic importance.