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Summary: A subset of individuals with 'primary' or 'idiopathic' immune thrombocytopenia (ITP) who fail to respond to conventional first‐ and second‐line agents or who lose responsiveness are considered to have 'refractory' disease (rITP), placing them at increased risk of bleeding and complications of intensive treatment. However, the criteria used to define the refractory state vary among studies, which complicates research and clinical investigation. Moreover, it is unclear whether rITP is simply 'more severe' ITP, or if there are specific pathogenic pathways that are more likely to result in refractory disease, and whether the presence or development of rITP can be established or anticipated based on these differences. This paper reviews potential biological features that may be associated with rITP, including genetic and epigenetic risk factors, dysregulation of T cells and cytokine networks, antibody affinity and specificity, activation of complement, impaired platelet production and alterations in platelet viability and clearance. These findings indicate the need for longitudinal studies using novel clinically available methodologies to identify and monitor pathogenic T cells, platelet antibodies and other clues to the development of refractory disease. [ABSTRACT FROM AUTHOR]

Summary: Patients with sickle cell disease (SCD) are considered to be immunocompromised, yet data on the antibody response to SARS‐CoV‐2 vaccination in SCD is limited. We investigated anti‐SARS‐CoV‐2 IgG titres and overall neutralizing activity in 201 adults with SCD and demographically matched non‐SCD controls. Unexpectedly, patients with SCD generate a more robust and durable COVID‐19 vaccine IgG response compared to matched controls, though the neutralizing activity remained similar across both cohorts. These findings suggest that patients with SCD achieve a similar antibody response following COVID‐19 vaccination compared to the general population, with implications for optimal vaccination strategies for patients with SCD. [ABSTRACT FROM AUTHOR]

Bispecific antibodies offer the possibility of improving effector-cell recruitment for antibody therapy. For this purpose, a recombinant bispecific single-chain Fv antibody (bsscFv), directed against Fc γRIII (CD16) and human leucocyte antigen (HLA) class II, was constructed and tested in functional assays. RNA from the hybridomas 3G8 and F3.3, reacting with CD16 and HLA class II, respectively, was used to generate phage display libraries. From these libraries, reactive phages were isolated and the bsscFv was constructed by connecting both single-chain Fv components through a 20 amino acid flexible linker. After expression in SF21 insect cells and chromatographic purification, the bsscFv bound specifically and simultaneously to both antigens. The affinities of the anti-CD16 and the anti-HLA class II scFv components of the bsscFv were 8·6 × 10−8 mol/l and 13·7 × 10−8 mol/l, respectively, which was approximately sevenfold lower than the F(ab) fragments of the parental antibodies. In antibody-dependent cellular cytotoxicity experiments with human mononuclear cells as effectors, the bsscFv-mediated specific lysis of both HLA class II-positive, malignant human B-lymphoid cell lines and primary cells from patients with chronic B-cell lymphocytic leukaemia. Optimal lysis was obtained at bsscFv concentrations of approximately 400 ng/ml, similar to the concentration required for maximum lysis by the corresponding chemically linked bispecific antibody. Thus, this recombinant bsscFv-antibody is an efficient molecule for effector-cell mediated lysis of malignant human B-lymphoid cells. [ABSTRACT FROM AUTHOR]

Anti-spike antibody levels significantly increased by exposure number (i.e., vaccination and/or infection, I R i SP 2 sp = 0.34, I p i < 0.001), but anti-nucleocapsid antibody levels did not (Figure 1E,F). Anti-spike and anti-nucleocapsid antibody levels were quantified in 36 patients with sickle cell disease (SCD) and 22 control patients without SCD seen in the same haematology adult and paediatric clinics. All SCD participants and 95% of controls had detectable anti-spike protein antibodies; 21 (58.3%) and 11 (50.0%) had anti-nucleocapsid antibodies, respectively. Keywords: antibodies; coronavirus 2019 (COVID-19); severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2); sickle cell disease; splenic function EN antibodies coronavirus 2019 (COVID-19) severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sickle cell disease splenic function 680 683 4 08/10/22 20220815 NES 220815 Antibody response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and/or vaccination reduces infection risk.1 In the United States, people with sickle cell disease (SCD) have experienced considerable complications from SARS-CoV-2 infection.2,3 Functional hyposplenia, asplenia, or splenectomy in SCD can increase pathogen susceptibility and reduce vaccine responsiveness.4 We evaluated serum antibody levels for anti-nucleocapsid antibodies from past infection and anti-spike antibodies from vaccination and/or past infection in people with SCD. [Extracted from the article]

Summary: Patients with multiple myeloma (MM) have a suboptimal antibody response following vaccination against severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) and lower seroconversion rates following coronavirus disease 2019 (COVID‐19) compared with healthy individuals. In this context, we evaluated the development of neutralising antibodies (NAbs) against SARS‐CoV‐2 in non‐vaccinated patients with MM and COVID‐19 compared with patients after vaccination with two doses of the BNT162b2 vaccine. Serum was collected either four weeks post confirmed diagnosis or four weeks post a second dose of BNT162b2. NAbs were measured with a Food and Drug Administration‐approved enzyme‐linked immunosorbent assay methodology. Thirty‐five patients with COVID‐19 and MM along with 35 matched patients were included. The two groups did not differ in age, sex, body mass index, prior lines of therapy, disease status, lymphocyte count, immunoglobulin levels and comorbidities. Patients with MM and COVID‐19 showed a superior humoral response compared with vaccinated patients with MM. The median (interquartile range) NAb titre was 87·6% (71·6–94%) and 58·7% (21·4–91·8%) for COVID‐19‐positive and vaccinated patients, respectively (P = 0·01).Importantly, there was no difference in NAb production between COVID‐19‐positive and vaccinated patients who did not receive any treatment (median NAb 85·1% vs 91·7%, P = 0·14). In conclusion, our data indicate that vaccinated patients with MM on treatment without prior COVID‐19 should be considered for booster vaccine doses. [ABSTRACT FROM AUTHOR]

Summary: Inhibitor development is a major complication of treatment with factor VIII concentrates in nonsevere haemophilia A. It has been suggested that plasma‐derived factor VIII (FVIII) concentrates elicit fewer inhibitors than recombinant FVIII concentrates, but studies in severe haemophilia A patients have shown conflicting results. We designed a case‒control study to investigate the clinical and genetic risk factors for inhibitor development in nonsevere haemophilia A patients. We investigated whether the type of FVIII concentrate was associated with inhibitor development in nonsevere haemophilia A patients. This nested case‒control study includes 75 inhibitor patients and 223 controls, from a source population of the INSIGHT study, including all nonsevere haemophilia A patients (FVIII:C 2–40%) that were treated with FVIII concentrates in 33 European and one Australian centre. Cases and controls were matched for date of birth and cumulative number of exposure days (CED) to FVIII concentrate. A conditional logistic regression model was used to calculate unadjusted and adjusted odds ratios. No increased risk for inhibitor development was found for any type of FVIII concentrate; either when comparing recombinant FVIII concentrates to plasma‐derived FVIII concentrates (adjusted odds ratio 0·96, 95% confidence interval (CI) 0·36–2·52) or for specific types of FVIII concentrates. [ABSTRACT FROM AUTHOR]

Haemolytic disease of the fetus and newborn (HDFN) is a severe disease in which fetal red blood cells (RBC) are destroyed by maternal anti-RBC IgG alloantibodies. HDFN is most often caused by anti-D but may also occur due to anti-K, -c- or -E. We recently found N-linked glycosylation of anti-D to be skewed towards low fucosylation, thereby increasing the affinity to IgG-Fc receptor IIIa and IIIb, which correlated with HDFN disease severity. Here, we analysed 230 pregnant women with anti-c, -E or -K alloantibodies from a prospective screening cohort and investigated the type of Fc-tail glycosylation of these antibodies in relation to the trigger of immunisation and pregnancy outcome. Anti-c, -E and -K show - independent of the event that had led to immunisation - a different kind of Fc-glycosylation compared to that of the total IgG fraction, but with less pronounced differences compared to anti-D. High Fc-galactosylation and sialylation of anti-c correlated with HDFN disease severity, while low anti-K Fc-fucosylation correlated with severe fetal anaemia. IgG-Fc glycosylation of anti-RBC antibodies is shaped depending on the antigen. These features influence their clinical potency and may therefore be used to predict severity and identify those needing treatment. [ABSTRACT FROM AUTHOR]

This systematic review was designed to summarize the reported valid quantitative evidence on the association between use of von Willebrand factor ( VWF)-containing Factor VIII ( FVIII) concentrates and successful immune tolerance induction ( ITI) in patients with severe haemophilia A. The primary outcome was successful ITI; secondary outcomes were time to success, complications of the inhibitor or ITI and relapse of the inhibitor. A systematic literature search identified 26 randomized controlled trials, registries and cohort studies, evaluating a total of 1284 patients. For a pooled meta-analysis, 13 studies evaluating 382 patients were included. Due to incomplete data we were not able to assign pre- ITI risk categories to all patients for risk factor analysis. The meta-analysis did not demonstrate a difference in the proportion of patients with successful inhibitor eradication between those treated with VWF-containing products and those treated with FVIII concentrates devoid of VWF (relative risk [ RR] 0·70 (95% confidence interval [ CI] 0·52-0·89) and 0·84 (95% CI 0·75-0·93) respectively). Bleeding rate during ITI ranged from 0·00 to 0·85 bleeding episodes per year. The proportion of patients with a relapse of the inhibitor (range 0-20%) was mentioned in four studies that were included in the meta-analysis. The results of this systematic review do not support the idea of a positive effect of VWF-containing products in ITI. [ABSTRACT FROM AUTHOR]

Haemolytic disease of the newborn (HDN) can be prevented by the passive administration of anti-D to the mother. The most accepted theory to describe this activity of anti-D is based upon its ability to clear opsonized erythrocytes before their recognition by the maternal immune system. We examined this hypothesis using a murine model of immunity to foreign erythrocytes. Whereas transfusion of foreign erythrocytes into mice induced immunoglobulin (Ig)M and IgG antibodies specific for the erythrocytes, these humoral immune responses were inhibited when the erythrocytes were opsonized with IgG. To specifically determine if immunological evasion occurs with these opsonized erythrocytes, we examined T-cell responses from these mice. An erythrocyte-specific T-cell response was clearly detected. We then tested whether phagocytosis of opsonized erythrocytes is sufficient to prevent the antibody response. We exposed mononuclear phagocytic cells to sheep red blood cells (SRBC) in vitro and then adoptively transferred the phagocytic cells to recipient mice; opsonized SRBC unexpectedly increased, rather than decreased, the antibody response. These data indicate that removal of opsonized erythrocytes by phagocytic cells does not prevent their immunological recognition and suggest that antigen clearance may not be the predominant mechanism of anti-erythrocyte action in downregulating the humoral immune response. [ABSTRACT FROM AUTHOR]

Idiopathic CD4+ T lymphocytopenia (ICL) is defined as a CD4+ T-cell count <0·3 × 109/l or <20% of the total T-cell count on two occasions in the absence of any immunodeficiency disorder or therapy associated with reduced CD4+ T-cell count. Although several mechanisms of ICL have been reported, the pathophysiology is still largely unknown. This case report describes a patient who presented with cryptococcal meningitis and was subsequently discovered to meet the criteria for ICL. Flow cytometric analysis of the patient's peripheral blood mononuclear cells revealed antibodies coating a much larger proportion of his CD4+ T cells (33·61%) than the CD4+ T cells of normal donors (3·94 ± 1·77%). The reasons behind the development of these autoantibodies are explored. [ABSTRACT FROM AUTHOR]

Several methods to detect anti-A/B antibodies based on haemagglutination and haemolysis have been described. These methods measure predominantly anti-A/B immunoglobulin (Ig)M, whereas anti-A/B IgG and IgG subclasses are less well examined. We established a flow cytometry method (ABO-fluorescence-activated cell sorting; ABO-FACS) to quantify binding of anti-A/B IgM, IgG and IgG subclasses to human A or B red blood cells. Anti-A/B IgM were present in the majority of 120 blood donors, as expected from blood group typing. The sensitivity and specificity of anti-A/B IgM to predict the blood group was 93% and 96% respectively. Anti-A/B IgG was found in 34/38 blood group O samples (89%). Anti-B IgG in blood group A or anti-A IgG in blood group B was present in 4/28 (14%) and 1/28 (4%) samples, respectively, and absent in 26 AB sera. IgG2 was the predominant IgG subclass. The correlation of anti-A/B IgM and IgG in the ABO-FACS with haemagglutination titres was 0·870 and 0·783, respectively ( n = 240; P < 0·001) whereas the comparison of ABO-FACS with ABO-enzyme-linked immunosorbent assay was less significant. In conclusion, ABO-FACS is a valid method to quantify anti-A/B IgM, IgG and IgG subclasses. It opens the possibility of isotype-specific monitoring of anti-A/B antibodies levels after ABO-incompatible solid organ and stem cell transplantation. [ABSTRACT FROM AUTHOR]

ABO blood group antigens are immunodominant cell surface oligosaccharides. The function of the ABO system is clinically important in blood transfusion and solid organ transplantation but there is no small animal model of ABO discordance. The present study demonstrated A glycoconjugate-reactive IgM in the serum of CBA/Ca mice by enzyme-linked immunosorbent assay but showed with sugar blocking that the specificity of this IgM was different from that of human anti-A IgM. Furthermore, immunisation of CBA/Ca mice with the A antigen did not increase reactive IgM titre. In contrast, knock-out mice for the related carbohydrate antigen galactose( α1,3)galactose mounted a serum IgM response when immunised with the non-self galactose( α1,3)galactose antigen, which was shown to be T cell-dependent using a nude/knock-out animal. Reverse transcription-polymerase chain reaction identified transcripts for the enzyme likely to be responsible for the synthesis of the A antigen in organs from CBA/Ca mice although the A antigen was not detected in the same organs by immunohistochemistry. We conclude that CBA/Ca mice possess natural serum IgM with different characteristics to human anti-A IgM and that CBA/Ca mice may also express the A antigen. As a result, these mice are not suitable for use as a small animal model of ABO discordance. [ABSTRACT FROM AUTHOR]

A fully human IgG1 kappa antibody (MDE-8) was generated, which recognised Fc-gamma receptor IIa (Fc γRIIa) molecules on CD32 transfectants, peripheral blood monocytes, polymorphonuclear cells and platelets. This antibody blocked Fc γRIIa ligand-binding via its F(ab′)2 fragment. Overnight incubation of monocytes with F(ab′)2 fragments of MDE-8 leads to a c. 60% decrease in cell surface expression of Fc γRIIa. MDE-8 whole antibody induced a concomitant c. 30% decrease of Fc γRI on THP-1 cells and monocytes. In humans Fc γRIIa plays an important role in the clearance of antibody-coated red blood cells in vivo. As an equivalent of Fc γRIIa does not exist in mice, the in vivo effect of MDE-8 was studied in an Fc γRIIa transgenic mouse model. In these mice, antibody-induced anaemia could readily be blocked by MDE-8. These data document a new human antibody that effectively blocks Fc γRIIa, induces modulation of both Fc γRIIa and Fc γRI from phagocytic cells, and ameliorates antibody-induced anaemia in vivo. [ABSTRACT FROM AUTHOR]