Page 208 - 2021_12-Haematologica-web

Letters to the Editor
Platelet activation and modulation in thrombosis with thrombocytopenia syndrome associated with ChAdOx1 nCov-19 vaccine
A severe clinical syndrome has been observed in some recipients of the ChAdOx1 nCov-19 or Ad26.COV2.S vaccine, characterized by the presence of antibodies against platelet factor 4 (PF4)/polyanions complexes, thrombocytopenia and thrombosis,1-6 thus resembling heparin-induced thrombocytopenia (HIT).1 The syn- drome has been termed “thrombosis with thrombocy- topenia syndrome (TTS)”, or “vaccine-induced immune thrombotic thrombocytopenia (VITT)”.7,8 Intravenous immunoglobulin (IVIg) has been successfully used to increase the platelet count in patients with TTS.3,4 Here we report on the management of two patients with TTS, the effect of their serum or plasma on normal platelets and its modulation by IVIg and anti-platelet agents. IVIg
increased the platelet count and blunted the pro-throm- botic effect of sera and plasma from two patients with TTS, whereas IVIg and anti-platelets prevented in vitro TTS sera/plasma-supported thrombogenicity, platelet reactivity and markers of platelet activation.
Patient 1 is a 47 years old man who had an episode of syncope on March 15th 2021, 7 days after the first ChAdOx1 nCov-19 injection. He had thalassemia trait and had never been previously exposed to heparin. His platelet count was 92x109/L at presentation and decreased to a nadir of 27x109/L on day 4. A computed tomography angiography (CTA) detected pulmonary embolism, which was hemodynamically stable. Patient 2 is a 36 years old woman who experienced severe abdom- inal pain on March 17th 2021, 18 days after the first ChAdOx1 nCov-19 injection. She had never been previ- ously exposed to heparin and never used oral contracep- tives. Platelet count at presentation was 133x109/L and decreased to a nadir of 106x109/L on day 4. An abdomi-
ABC
DE
Figure 1. Immunologic tests and platelet parameters in patients before and after intravenous immunoglobulin administration and healthy subjects.
Immunologic tests and platelet parameters in patients before and after intravenous immunoglobulin administration and healthy subjects. Blood withdrawal for all after intravenous immunoglobulin (IVIg) experiments was performed on day 15 for patient 1 and on day 13 for patient 2. Open squares: healthy subjects; open circles: patient 1; closed triangles: patient 2; open diamonds: patient 3 (post-vaccine thrombocytopenia without thrombosis). (A) Detection of anti-platelet factor 4 (PF4)/polyanions immunoglobulins by enzyme-linked immunosorbent assay (ELISA) in patients’ sera in absence or presence of high concentrations of heparin (100 U/mL). The horizontal dotted line indicates the cut-off value of 0.4 optical density (O.D.) for normal values. (B) Platelet activation test (PAT), meas- ured by light transmission aggregometry (LTA) in normal washed platelet suspensions (WPS). Serum samples (60 mL) from 7 healthy subjects and from patients 1 and 2 were added to 222 mL of normal WPS in a LTA aggregometer and platelet aggregation was measured as increase in light transmission for 30 minutes (min), in the absence and presence of low (0.2 U/mL) and high concentrations (100 U/mL) of heparin in 2 different experimental sessions, and in the presence of PF4 10 mg/mL in 2 (patient 1) and 3 (patient 2) experimental sessions. Individual results obtained in patients’ sera and mean values obtained in sera from 7 healthy subjects are displayed. The horizontal dotted line indicates the cut-off value of 3.2% for normal values, which was calculated as mean + 2 standard deviations of results obtained in healthy subjects. (C) PAT, measured by impedance aggregometry (HIMEA) in normal whole blood (WB) samples. Serum samples (200 mL) from 1 healthy subject and from patients 1 and 2 were added to 300 mL of normal WB in a multiplate aggregometer and platelet aggregation was measured as area under the curve (AUC) for 15 min in the absence and presence of low (1.0 U/mL) and high concentrations (200 U/mL) of heparin. Sera from patients 1 and 2 were tested only before IVIg infusions. (D) Effects of IVIg infusion (2 gr/Kg body weight over 5 days) on platelet count in patient 1 and patient 2. (E) Percent of platelet/monocyte hetero-aggregates before and after IVIg infusion in patients 1 and 2. The horizontal dotted line indicates the cut-off value of 13.44% for normal values, which was calculated as mean + 2 standard deviations of results obtained with normal sera from 5 healthy subjects. Hep 0.2: heparin 0.2 U/mL; Hep 1: heparin 1 U/mL; Hep 100: heparin 100 U/mL; Hep 200: heparin 200 U/mL; PF4: platelet factor 4.
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haematologica | 2021; 106(12)