T h e n e w e ng l a n d j o u r na l o f m e dic i n e stages of the trial, including funding acquisition and publication. Finally, we clearly state in the article that mycophenolate increases the risk of miscarriage and birth defects, and stringent contraceptive measures were required during the trial. In addition, we have been very careful to avoid the conclusion of recommending myco- phenolate mofetil as a routine first-line option and have called for further research to clarify the role of this drug in treatment pathways. In response to van Dijk and Schutgens: we selected the generic quality-of-life tools for their validity, reliability, and responsiveness in adult patients with ITP.3 We chose to use the area under the curve (as is used in health economic analysis) to assess patients’ quality of life during the entire follow-up period rather than at an individual time point. We acknowledge that the differences in quality-of-life scores could be chance findings after adjustment for multiple testing, and we agree that the clinical impor- tance of this difference has not been proved and that combination therapy may be justified in some circumstances. Charlotte A. Bradbury, M.D., Ph.D. University of Bristol Bristol, United Kingdom c . bradbury@ bristol . ac . uk Quentin Hill, M.D. Leeds Teaching Hospital NHS Trust Leeds, United Kingdom Rosemary Greenwood, M.Sc. University Hospitals Bristol and Weston NHS Trust Bristol, United Kingdom Since publication of their article, the authors report no fur- ther potential conflict of interest. 1. Provan D, Arnold DM, Bussel JB, et al. Updated international consensus report on the investigation and management of pri- mary immune thrombocytopenia. Blood Adv 2019; 3: 3780-817. 2. Rothwell PM. Subgroup analysis in randomised controlled trials: importance, indications, and interpretation. Lancet 2005; 365: 176-86. 3. Signorovitch J, Brainsky A, Grotzinger KM. Validation of the FACIT-fatigue subscale, selected items from FACT-thrombocyto- penia, and the SF-36v2 in patients with chronic immune throm- bocytopenia. Qual Life Res 2011; 20: 1737-44. DOI: 10.1056/NEJMc2115772 VITT after ChAdOx1 nCoV-19 Vaccination To the Editor: The Journal recently published three studies involving a total of 39 persons in whom vaccine-induced immune thrombotic thrombocytopenia (VITT), a devastating syn- drome characterized by thromboses in unusual sites, developed after they received the ChAdOx1 nCoV-19 vaccine. The articles by Schultz et al. and Greinacher et al. (June 3 issue)1,2 and by Scully et al. (June 10 issue)3 all conclude that it was highly unlikely that the patients had been previ- ously infected with SARS-CoV-2, since they tested negative for antibodies to the SARS-CoV-2 nucleo- capsid protein. I believe that this statement is questionable and probably erroneous. Studies have shown that most SARS-CoV-2 infections are in asymptomatic persons and that up to 10% of mild-to-moderate confirmed cases of Covid-19 do not involve serologic conversion, so SARS-CoV-2 antibodies will not be detectable during or after infection.4,5 Given that data on T-cell responses, which are highly sensitive (and more specific than antibodies for previous expo- sure to SARS-CoV-2), are missing, previous SARS-CoV-2 infection cannot be ruled out.4,5 It is disappointing that none of the three studies re- ported in the Journal took advantage of the T-cell– receptor sequencing tests that have been ap- proved by the Food and Drug Administration (FDA) (https://www . fda . gov/ news - events/ press - announcements/ coronavirus - covid - 19 - update - fda - authorizes - adaptive - biotechnologies - t - detect - covid - test) to rule out the presence of Covid-19–spe- cific T lymphocytes. Confirmed exposure to SARS-CoV-2 might link the syndrome to persis- tent vascular inflammation in a small subgroup of persons,6 allow for the implementation of risk-mitigation strategies, and explain why VITT is more frequent than had been found in an early trial of the ChAdOx1 nCoV-19 vaccine.7 Alessandro D. Santin, M.D. Yale University School of Medicine New Haven, CT alessandro . santin@ yale . edu No potential conflict of interest relevant to this letter was reported. This letter was published on November 3, 2021, at NEJM.org. 1. Schultz NH, Sørvoll IH, Michelsen AE, et al. Thrombosis and thrombocytopenia after ChAdOx1 nCoV-19 vaccination. N Engl J Med 2021; 384: 2124-30. 2. Greinacher A, Thiele T, Warkentin TE, Weisser K, Kyrle PA, Eichinger S. Thrombotic thrombocytopenia after ChAdOx1 nCov-19 vaccination. N Engl J Med 2021; 384: 2092-101. 3. Scully M, Singh D, Lown R, et al. Pathologic antibodies to platelet factor 4 after ChAdOx1 nCoV-19 vaccination. N Engl J Med 2021; 384: 2202-11. 2202 n engl j med 385;23 nejm.org December 2, 2021 The New England Journal of Medicine Downloaded from nejm.org on October 4, 2022. For personal use only. No other uses without permission. Copyright © 2021 Massachusetts Medical Society. All rights reserved. Correspondence static functions.1,2 We found that low concen- trations of the BTK inhibitors ibrutinib and fenebrutinib prevented platelet aggregation in- A Donor Sample 1 200 Serum obtained from Patient 1 at admission AUC 3695 861 724 +Ibrutinib 1450 +Fenebrutinib SPA Serum obtained from Patient 2 at admission +Ibrutinib +Fenebrutinib SPA AUC 1586 54 301 228 5 10 Minutes 15 20 B Donor Sample 2 5 10 Minutes 15 20 C Donor Sample 3 200 Serum obtained from Patient 1 at 7 days after initiation of IVIG +Ibrutinib +Fenebrutinib SPA AUC 1896 84 136 282 4. Sekine T, Perez-Potti A, Rivera-Ballesteros O, et al. Robust T cell immunity in convalescent individuals with asymptomatic or mild COVID-19. Cell 2020; 183(1): 158.e14-168.e14. 5. Gittelman RM, Lavezzo E, Snyder TM, et al. Diagnosis and tracking of past SARS-CoV-2 infection in a large study of Vo’, Italy through T-cell receptor sequencing. November 12, 2020 (https://www . medrxiv . org/ content/ 10 . 1101/ 2020 . 11 . 09 . 20228023v1). preprint. 6. Varga Z, Flammer AJ, Steiger P, et al. Endothelial cell infec- tion and endotheliitis in COVID-19. Lancet 2020; 395: 1417-8. 7. Ramasamy MN, Minassian AM, Ewer KJ, et al. Safety and immunogenicity of ChAdOx1 nCoV-19 vaccine administered in a prime-boost regimen in young and old adults (COV002): a sin- gle-blind, randomised, controlled, phase 2/3 trial. Lancet 2021; 396: 1979-93. DOI: 10.1056/NEJMc2111026 To the Editor: The occurrence of thrombocyto- penia and thrombosis at unusual vascular sites after adenoviral vector–based vaccination against SARS-CoV-2 has alarmed the public. Laboratory findings from three independent case series in- dicate a pathomechanism similar to that of auto- immune heparin-induced thrombocytopenia (HIT) — namely, high titers of IgG antibodies to plate- let factor 4 (PF4)–polyanion complexes that acti- vated platelets by means of FcγIIA receptors. We note that the syndrome was termed VITT and that patients were treated with intravenous im- mune globulin. Nevertheless, the high mortality suggests the need for other, possibly more effec- tive, treatment options. Bruton’s tyrosine kinase (BTK) inhibitors that have been approved for the treatment of B-cell cancers block the FcγIIA receptor–mediated platelet aggregation induced by serum obtained from patients with HIT and inhibit various pro- thrombotic pathways while also preserving hemo- Figure 1. Platelet-Aggregating Activity in Donor Samples in Response to Serum Obtained from Patients with Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT). Shown are results in blood samples obtained from healthy donors whose platelet-aggregating activity in response to serum obtained from patients with VITT was inhibited by a Bruton’s tyrosine kinase inhibitor (ibrutinib or fenebrutinib). Serum samples from two patients with VITT were obtained at admission; an ad- ditional sample from Patient 1 was obtained 7 days after the initiation of intravenous immune globulin (IVIG) therapy. Also shown is the mean spontaneous platelet aggregation (SPA) without added serum (blue); the shaded area around the blue line in each panel indi- cates the standard deviation. Full experimental details are provided in the Supplementary Appendix, available with the full text of this letter at NEJM.org. AU denotes arbitrary units, and AUC the area under the curve. ) U A ( n o i t a g e r g g A 150 100 50 0 0 200 150 100 50 ) U A ( n o i t a g e r g g A 0 0 ) U A ( n o i t a g e r g g A 150 100 50 0 0 5 10 Minutes 15 20 n engl j med 385;23 nejm.org December 2, 2021 2203 The New England Journal of Medicine Downloaded from nejm.org on October 4, 2022. For personal use only. No other uses without permission. Copyright © 2021 Massachusetts Medical Society. All rights reserved. T h e n e w e ng l a n d j o u r na l o f m e dic i n e duced by serum obtained from patients with VITT and that the drugs added to partial inhibi- tion with intravenous immune globulin therapy or FcγIIA receptor blockade (Fig. 1). Therefore, we consider the oral application of low-dose BTK inhibitors for the early treatment of sus- pected VITT (on the basis of symptoms, elevated d-dimer level, and thrombocytopenia) to be a therapeutic option beyond intravenous immune globulin and direct oral anticoagulants that is worthy of testing. Christian Weber, M.D. Philipp von Hundelshausen, M.D. Wolfgang Siess, M.D. University Hospital at LMU Munich Munich, Germany chweber@ med . lmu . de No potential conflict of interest relevant to this letter was reported. This letter was published on November 3, 2021, at NEJM.org. 1. Goldmann L, Duan R, Kragh T, et al. Oral Bruton tyrosine kinase inhibitors block activation of the platelet Fc receptor CD32a (FcγRIIA): a new option in HIT? Blood Adv 2019; 3: 4021- 33. 2. von Hundelshausen P, Lorenz R, Siess W, Weber C. Vaccine- induced immune thrombotic thrombocytopenia (VITT): target- ing pathomechanisms with Bruton tyrosine kinase inhibitors. Thromb Haemost 2021 April 13 (Epub ahead of print). DOI: 10.1056/NEJMc2111026 Drs. Greinacher and Thiele and a colleague reply: Santin suggests an interesting approach for ruling out previous asymptomatic SARS- CoV-2 infection by means of a T-cell–receptor se- quencing test. Unfortunately, this assay may not be able to confirm or rule out prevaccination SARS-CoV-2 infection. The FDA emergency use authorization for this assay indicates that pedi- greed specimens with direct evidence of previous non–SARS-CoV-2 coronavirus (common cold) strains such as HCoV-HKU1, HCoV-NL63, HCoV- OC43, or HCoV-229E have not been evaluated.1 Persons who had a common cold before testing might have a false positive result. Furthermore, vaccination induces a T-cell response mainly against the SARS-CoV-2 spike protein.2 To our knowledge, it remains unclear whether the assay can differentiate between T-cell receptors that are specific for the spike protein and T-cell recep- tors that recognize epitopes on other proteins of SARS-CoV-2. The performance of this test has not been established in persons who have re- ceived a Covid-19 vaccine. We had the opportu- nity to interview 30 patients with VITT. Most patients were young and had been healthy before vaccination without any evidence of clinical symptoms associated with ongoing inflamma- tion or persistent vascular inflammation. Weber and colleagues build on their recent article,3 the hypothesis of which is consistent with in vitro experiments that have been con- ducted by others.4 Pharmacologic interference with the activation pathway of the FcγIIA recep- tor may be an attractive option in the treatment of patients with VITT. Such approaches include BTK inhibitors, Src and Syk inhibitors, and de- glycosylation of IgG by a specific enzyme that abrogates the binding of IgG to the FcγIIA re- ceptor.5 However, no clinical data are available on the application of these strategies in patients with VITT or other FcγIIA receptor–mediated platelet-activating disorders, including HIT. Cur- rently, most clinical experience involves the use of intravenous immune globulins for blocking FcγIIA receptor–mediated platelet activation in patients with VITT or autoimmune HIT. How- ever, the proposed options might be of high in- terest in persons in whom VITT antibodies per- sist as autoantibodies causing platelet activation and recurrent thrombosis or in medical systems that have limited access to or an insufficient supply of pharmacologic intravenous immune globulins. Andreas Greinacher, M.D. Linda Schönborn, M.D. Thomas Thiele, M.D. Universitätsmedizin Greifswald Greifswald, Germany andreas . greinacher@ med . uni-greifswald . de Dr. Schönborn reports no potential conflict of interest rel- evant to this letter. Since publication of their article, Drs. Grein- acher and Thiele report no further potential conflict of interest. This letter was published on November 3, 2021, at NEJM.org. 1. Food and Drug Administration. Emergency Use Authoriza- tion (EUA) summary: T-Detect COVID Test. September 2, 2021 (https://www . fda . gov/ media/ 146481/ download). 2. Ewer KJ, Barrett JR, Belij-Rammerstorfer S, et al. T cell and antibody responses induced by a single dose of ChAdOx1 nCoV-19 (AZD1222) vaccine in a phase 1/2 clinical trial. Nat Med 2021; 27: 270-8. 3. von Hundelshausen P, Lorenz R, Siess W, Weber C. Vaccine- induced immune thrombotic thrombocytopenia (VITT): target- ing pathomechanisms with Bruton tyrosine kinase inhibitors. Thromb Haemost 2021 April 13 (Epub ahead of print). 4. Smith CW, Montague SJ, Kardeby C, et al. Anti-platelet drugs block platelet activation by vaccine-induced immune thrombocy- topenia and thrombosis patient serum. Blood 2021 August 10 (Epub ahead of print). 5. Vayne C, Rollin J, Gruel Y, et al. PF4 immunoassays in vac- 2204 n engl j med 385;23 nejm.org December 2, 2021 The New England Journal of Medicine Downloaded from nejm.org on October 4, 2022. For personal use only. No other uses without permission. Copyright © 2021 Massachusetts Medical Society. All rights reserved. Correspondence cine-induced thrombotic thrombocytopenia. N Engl J Med 2021; 385: 376-8. DOI: 10.1056/NEJMc2111026 Dr. Scully replies: Patients in the three cohorts presented with this new clinical syndrome of VITT after receiving their first dose of the ChAdOx1 nCoV-19 vaccine, and they met the di- agnostic criteria for VITT, including the presence of anti-PF4 antibodies. Important considerations included the role of SARS-CoV-2 infection and the presence of antibodies, both to SARS-CoV-2 and to the vaccine. In our cohort, we conducted extensive SARS-CoV-2 antibody testing with a flow cytometer (CytoFLEX, Beckman Coulter). SARS- CoV-2 spike, receptor-binding domain, and nucleo- capsid IgG serum angiotensin-converting–enzyme 2–receptor binding inhibition and spike antibod- ies to seasonal coronaviruses HCoV-OC43, HCoV- HKU1, HCoV-NL63, and HCoV-229E were mea- sured by a multiplexed electrochemiluminescent assay (Meso Scale Discovery), as previously de- scribed.1 These confirmed antibody levels were compatible with the receipt of one dose of vac- cine only and were not suggestive of antibodies to SARS-CoV-2. Persons may have asymptomatic SARS-CoV-2 infection, and the antibodies may not be detect- able by current assays. A plausible hypothesis is SARS-CoV-2 antibodies could be stimulated in relation to an acute event, such as VITT. SARS- CoV-2 was not detected in any patient on poly- merase-chain-reaction (PCR) testing. Santin asks why T-cell–receptor sequencing tests were not also used. The assay was approved by the FDA only under emergency use authoriza- tion, and we rely on evaluated PCR-based tests. As documented by the FDA,2 it is unknown how long the T-cell immune response remains after infection and how long protection is provided by the T-cell immune response. Finally, the impor- tance of the three Journal articles describing VITT cases was to highlight this life-threatening con- dition that may occur after ChAdOx1 nCoV-19 vaccination. Further work is necessary to under- stand the pathogenesis, and T-cell–receptor se- quencing tests may be a focal assay to help elu- cidate the cause. Weber and colleagues present their hypothesis and laboratory data on the use of BTK inhibitors in patients with VITT. Their data make perfect biologic sense. Companies that produce these compounds have been contacted but were unable to participate in a clinical study involving pa- tients with VITT. The initial treatment was based on the extrapolation of HIT treatment for this new syndrome. The treatment and outcomes have been presented for a large cohort of cases,3 but this study did not include BTK inhibitors. Marie Scully, M.D. University College London Hospitals NHS Foundation Trust London, United Kingdom m . scully@ ucl . ac . uk Since publication of her article, the author reports no further potential conflict of interest. This letter was published on November 3, 2021, at NEJM.org. 1. Johnson M, Wagstaffe HR, Gilmour KC, et al. Evaluation of a novel multiplexed assay for determining IgG levels and func- tional activity to SARS-CoV-2. J Clin Virol 2020; 130: 104572. 2. Food and Drug Administration. Coronavirus (COVID-19) up- date: FDA authorizes Adaptive Biotechnologies T-Detect COVID test. March 5, 2021 (https://www . fda . gov/ news - events/ press - announcements/ coronavirus - covid - 19 - update - fda - authorizes - adaptive - biotechnologies - t - detect - covid - test). 3. Pavord S, Scully M, Hunt BJ, et al. Clinical features of vac- cine-induced immune thrombocytopenia and thrombosis. N Engl J Med 2021; 385: 1680-9. DOI: 10.1056/NEJMc2111026 Convalescent Plasma for Outpatients with Covid-19 To the Editor: In the Covid-19 Convalescent Plasma in Outpatients (C3PO) trial,1 Korley et al., members of the Strategies to Innovate Emergency Care Clinical Trials Network (SIREN), adminis- tered convalescent plasma to high-risk outpa- tients within 1 week after the onset of symptoms of Covid-19. It is unclear why the authors selected 1 week instead of a shorter time frame, since it has been shown that the 30-day and 60-day mor- tality benefits of convalescent plasma have been observed when it is administered within 3 days after diagnosis and that the benefit dissipates af- ter this point.2,3 The aim of their trial was to determine wheth- er convalescent plasma prevents progression to severe Covid-19. However, severe Covid-19 was not defined, and the authors instead assessed disease progression, which relies on surrogate n engl j med 385;23 nejm.org December 2, 2021 2205 The New England Journal of Medicine Downloaded from nejm.org on October 4, 2022. For personal use only. No other uses without permission. Copyright © 2021 Massachusetts Medical Society. All rights reserved.