B Cells Identified as Potential Drivers of Immune Dysregulation in Acquired Hemophilia A

Single-cell RNA sequencing revealed extensive disruption of CD4-positive (CD4+) T- and B-cell populations in patients with newly diagnosed acquired hemophilia A (AHA), with findings suggesting that B cells may be key drivers of the abnormal immune communication underlying the disease. The data were presented during an oral session at the European Hematology Association 2026 Congress.¹

AHA is a rare autoimmune bleeding disorder caused by neutralizing autoantibodies, also known as inhibitors, directed against coagulation factor VIII (FVIII). The resulting reduction in FVIII activity can cause spontaneous bleeding in patients without a personal or family history of a bleeding disorder.²

Current treatment generally includes hemostatic therapy to control clinically relevant bleeding and immunosuppressive therapy to eliminate the FVIII inhibitor. However, responses to immunosuppression vary substantially, and the biological mechanisms that cause patients to lose immune tolerance to their own FVIII are not fully understood.^2,3

In the GTH-AH 01/2010 study, approximately 83% of patients achieved partial remission following immunosuppressive therapy after a median of 5 weeks, although the time to remission ranged significantly (1–52 weeks).²

Single-Cell Profiling Maps Immune Changes at Diagnosis

To better characterize the immune environment at the onset of AHA, researchers performed single-cell RNA sequencing on peripheral blood mononuclear cells collected from 9 patients with newly diagnosed, treatment-naïve AHA and 5 healthy controls.¹

After quality control, the analysis included 124,715 cells and initially identified 15 cellular clusters. A more detailed analysis of 72,385 T- and natural killer cells subsequently identified 19 subsets, allowing the researchers to examine disease-associated changes within CD4+ T-cell and B-cell populations.¹

The use of samples obtained before treatment was important because corticosteroids, rituximab (Rituxan; Genentech), cyclophosphamide (Cytoxan; Baxter Healthcare), and other immunosuppressive therapies can substantially alter circulating immune-cell populations. Therefore, the findings provide a view of the immune abnormalities present near the time of diagnosis rather than changes that may have been caused by treatment.¹

CD4+ T Cells Demonstrate Broad Immune Activation

Patients with AHA had a reduced proportion of naïve CD4+ T cells and expanded populations of activated, effector, and memory CD4+ T cells. According to the researchers, this pattern suggested systemic immune hyperactivation accompanied by the loss of a reserve of naive T cells.¹

Across multiple CD4+ T-cell subsets, researchers observed increased expression of activation-associated genes, including CD69, FOS, JUN, NFKBIA, and NFKBIZ. The quantitative changes in cell populations and the altered transcriptional profiles indicated that CD4+ T cells were broadly activated in patients with AHA.¹

CD4+ T cells play an important role in antibody-mediated immunity by supporting the activation and maturation of B cells. Previous research has indicated that FVIII contains epitopes recognized by CD4+ T cells and that failures in peripheral immune tolerance may permit the development of FVIII-reactive T- and B-cell responses.⁴

B-Cell Repertoire Shifts Toward Activated and Memory Phenotypes

The B-cell compartment was also substantially altered. Patients with AHA demonstrated expansion of hyperactivated, homeostatic/IgE memory, and preplasma cell clusters, along with contraction of naïve B-cell and plasmablast populations.¹ These changes indicated a shift toward activated and memory B-cell phenotypes, as well as possible disruption of the normal process through which B cells terminally differentiate into antibody-producing cells.

Several B-cell subsets also showed increased expression of activation markers, including CD69, CD83, and genes involved in nuclear factor κB signaling. In contrast, HLA-DQA2 and CD81, which are involved in the physiological activation of B cells, were broadly downregulated.¹

The combination of heightened B-cell activation and reduced expression of these molecules suggested that B cells were not simply more active. Instead, their normal activation and differentiation pathways appeared to be fundamentally altered in AHA.

B Cells May Drive Abnormal Immune Crosstalk

Cell-to-cell communication analysis was used to measure the predicted interaction strength between individual CD4+ T- and B-cell subsets. In patients with AHA, B-cell subsets appeared to exert a stronger influence on CD4+ T-cell populations than CD4+ T cells exerted on B cells.¹

This directional imbalance positioned B cells as potential drivers of the pathological immune crosstalk associated with anti-FVIII autoimmunity. The findings may also help explain why B-cell–directed treatment with rituximab can contribute to inhibitor eradication in some patients with AHA; however, the study did not evaluate treatment response and cannot establish whether any identified cellular population predicts sensitivity to a particular immunosuppressive regimen.²

REFERENCES

1. Li E, Wu H, Wang J, et al. Dysregulated cellular crosstalk between CD4+ T and B cells in acquired hemophilia A revealed by single-cell analysis. Presented at: European Hematology Association 2026 Congress; June 11-14, 2026; Stockholm, Sweden. Abstract S321. https://library.ehaweb.org/eha/2026/eha-2026/4206875/enhao.li.dysregulated.cellular.crosstalk.between.cd42B.t.and.b.cells.in.html

2. Tiede A, Collins P, Knoebl P, et al. International recommendations on the diagnosis and treatment of acquired hemophilia A. Haematologica. 2020;105(7):1791-1801. doi:10.3324/haematol.2019.230771

3. Tiede A, Klamroth R, Scharf RE, et al. Prognostic factors for remission of and survival in acquired hemophilia A (AHA): results from the GTH-AH 01/2010 study. Blood. 2015;125(7):1091-1097. doi:10.1182/blood-2014-07-587089

4. Mingot-Castellano ME, Rodríguez-Martorell FJ, Nuñez-Vázquez RJ, Marco P. Acquired haemophilia A: A review of what we know. J Blood Med. 2022;13:691-710. doi:10.2147/JBM.S342077