Hemostatic Markers, Adamts-13 Profile and Anti-Sars-Cov-2 Antibody Levels in Patients with Immune Thrombotic Thrombocytopenic Purpura Receiving BNT162b2 Vaccination

Introduction: Patients (pts) with immune thrombotic thrombocytopenic purpura (iTTP) are at high risk of severe COVID-19, therefore protection from SARS-CoV-2 by vaccination is particularly relevant in this setting, although concerns may exist on possible adverse reactions or disease relapse after vaccination. In this study, in a group of iTTP pts who received in-hospital COVID-19 vaccination in a special program for 'fragile patients', we prospectively evaluated over time the antibody response, the clinical and laboratory disease parameters and hemostatic biomarker levels.

Methods: Twelve iTTP pts in clinical remission and regularly followed-up in our Center were enrolled in April 2021, all of them received 2 doses of BNT162b2 vaccine (Pfizer-BioNTech) over 21 days, and were followed-up for clinical and laboratory testing for 60 days. Blood samples were collected at enrollment (day 0, D0) before the 1 ^st vaccine dose; on day 21 (D21) before the 2 ^nd dose; and on day 60 (D60) after the 1 ^st dose. Blood cell counts, anti-Spike receptor-binding-domain protein (anti-S/RBD) IgG, ADAMTS-13 activity, and anti-ADAMTS-13 IgG (chromogenic assay and ELISA), were measured at each time point. Additionally, an extensive study of hemostatic markers (i.e. FVIII, von Willebrand Factor (vWF) antigen and activity, fibrinogen, D-dimer, tPA, PAI, and F1+2) was performed. Follow up is currently continuing.

Results: Median age of our cohort was 65 years with M/F ratio of 4/8. Median time since last acute iTTP episode was 40 months, median follow up of the cohort was 71 months (95% CI 30-126). All pts were in clinical remission, except one patient (P1) who had an iTTP relapse after contracting SARS-CoV-2 infection, in Dec 2020, and was on low-dose steroids on D0. One patient (P2) had an ADAMTS-13 relapse in Jan 2021, and received pre-emptive rituximab. No other pts were on immunosuppressive therapy. Concerning the status of ADAMTS-13 activity on D0, 6 pts showed normal levels (>50%), while 5 had a moderate (50-20%) and 1 a complete (<10%) ADAMTS-13 deficiency. This latter patient (P3) had normal ADAMTS-13 activity before the pandemic. All patients were negative for anti-ADAMTS-13 inhibitor. Further, on D0, the anti-S/RBD IgG testing was positive in 3/12 pts (median 704,1 AU/mL), due to symptomatic infection in 1 case (P1), and asymptomatic in 2 (P3 and 1 pt with ADAMTS-13 activity of 54%, P4).

The study of hemostatic markers on D0 showed an increase in median levels of FVIII and vWF antigen and activity. These parameters were altered in 7/12, 11/12 and 8/12 pts, respectively. Fibrinogen and D-dimer were increased in 3/12 and 2/12, respectively. Notably, P1, P3 and P4 presented the highest levels of FVIII and vWF antigen, associated with high levels of vWF activity in P1 and P3 (mean 233%); moreover, P3 showed higher levels of D-dimer (708 ng/mL) and tPA (13 ng/ml).

After the 2 doses of BNT162b2, no significant clinical side effects were reported, and no changes in platelet counts. ADAMTS-13 activity and inhibitors did not significantly change on D21 and D60. A complete ADAMTS-13 activity deficiency persisted in P3 on D21 and D60, associated with anti-ADAMTS-13 IgG titer >15 U/ml, despite clinical remission. Overall, a significant increase in anti-S/RBD IgG level was observed on D21 (p = 0.0005) and D60 (p = 0.0005). Remarkably, only P2 did not show an increase in anti-S/RBD IgG titer after both doses of BNT162b2. Median levels of FVIII and vWF antigen did not significantly change during follow up, while increased vWF activity was seen on D60 (p = 0.05). Fibrinogen levels were stable, and an increase in D-dimer (>1000 ng/mL both on D21 and D60) was seen in P3. There were no changes in the other hemostatic parameters, and no thromboses were observed.

Conclusions: In our cohort of iTTP pts, COVID-19 was associated with 1 clinical and 1 ADAMTS-13 relapse. Our data show that SARS-CoV-2 vaccination was effective in inducing an antibody response in all but one patient who received rituximab within 3 months before vaccination, confirming recent findings. Overall, vaccination had no relevant impact on the hemostatic profile of our pts, and did not appear to be a driver of iTTP relapses. However, anti-SARS-CoV-2 antibodies monitoring in iTTP pts may be useful after vaccination, as currently it is unknown how long the antibody titer may persist. Although small, this study is in favor of efficacy and safety of mRNA vaccines in pts with iTTP.