Immune tolerance against infused FVIII in hemophilia A is mediated by PD-L1+ Tregs

Binding Promiscuity of Therapeutic Factor VIII

The binding promiscuity of proteins defines their ability to indiscriminately bind multiple unrelated molecules. Binding promiscuity is implicated, at least in part, in the off-target reactivity, nonspecific biodistribution, immunogenicity, and/or short half-life of potentially efficacious protein drugs, thus affecting their clinical use. In this review, we discuss the current evidence for the binding promiscuity of factor VIII (FVIII), a protein used for the treatment of hemophilia A, which displays poor pharmacokinetics, and elevated immunogenicity. We summarize the different canonical and noncanonical interactions that FVIII may establish in the circulation and that could be responsible for its therapeutic liabilities. We also provide information suggesting that the FVIII light chain, and especially its C1 and C2 domains, could play an important role in the binding promiscuity. We believe that the knowledge accumulated over years of FVIII usage could be exploited for the development of strategies to predict protein binding promiscuity and therefore anticipate drug efficacy and toxicity. This would open a mutational space to reduce the binding promiscuity of emerging protein drugs while conserving their therapeutic potency.

Abnormal frequency of the memory B cell subsets and plasmablasts in patients with congenital severe hemophilia A: correlation with "Inhibitor" formation

BACKGROUND

Development of antibodies against infused Factor VIII (FVIII) or "inhibitors" represents a major challenge following FVIII replacement therapy in patients with hemophilia A (HA). Recent studies have shown that certain cellular compartments of the immune system contribute to the production of such antibodies. Herein, we determined the frequency of class-switched CD19+IgD-CD27+/non-class-switched CD19+IgD+CD27+ memory B cell subsets and CD19+CD27hiCD38hi plasmablasts in patients with severe HA and their association with the development of inhibitors in these patients.

METHODS

This cross-sectional case-control study enrolled 32 patients with severe HA, including 8 with and 24 without inhibitors, and 24 healthy individuals. The frequencies of the memory B cell subsets and plasmablasts were determined using flow cytometry.

RESULTS

The frequency of CD19+IgD+CD27+ non-class-switched memory B cells was significantly lower in patients with HA (including both patients with and without inhibitors) than in healthy controls. The percentages of both CD19+IgD-CD27+ class-switched and CD19+IgD+CD27+ non-class-switched memory B cells did not differ significantly between patients with and without inhibitors. HA patients with inhibitors had significantly higher proportions of CD19+CD27hiCD38hi plasmablasts than the control group as well as the inhibitor (-) ones. No significant correlation was observed between the inhibitor levels with the percentages of memory B cell subsets and plasmablasts.

CONCLUSION

This study is the first to demonstrate a dysregulated proportion of CD19+IgD+CD27+ non-class-switched memory B cells and CD19+CD27hiCD38hi plasmablasts in patients with severe HA. Therefore, strategies targeting memory B-cell/plasmablast differentiation may have promising outcomes in the management of inhibitor formation in patients with severe HA.

Targeted delivery of Fc-fused PD-L1 for effective management of acute and chronic colitis

The PD-1/PD-L1 pathway in mucosal immunity is currently actively explored and considered as a target for inflammatory bowel disease (IBD) treatment. However, systemic PD-L1 administration may cause unpredictable adverse effects due to immunosuppression. Here we show that reactive oxygen species (ROS)-responsive nanoparticles enhance the efficacy and safety of PD-L1 in a mouse colitis model. The nanoparticles control the accumulation and release of PD-L1 fused to Fc (PD-L1-Fc) at inflammatory sites in the colon. The nanotherapeutics shows superiority in alleviating inflammatory symptoms over systemic PD-L1-Fc administration and mitigates the adverse effects of PD-L1-Fc administration. The nanoparticles-formulated PD-L1-Fc affects production of proinflammatory and anti-inflammatory cytokines, attenuates the infiltration of macrophages, neutrophils, and dendritic cells, increases the frequencies of Treg, Th1 and Tfh cells, reshapes the gut microbiota composition; and increases short-chain fatty acid production. In summary, PD-L1-Fc-decorated nanoparticles may provide an effective and safe strategy for the targeted treatment of IBD.

Altered frequency of FOXP3+ regulatory T cells is associated with development of inhibitors in patients with severe hemophilia A

INTRODUCTION

The development of anti-factor VIII (FVIII) antibodies or "inhibitors" is a major complication following FVIII replacement therapy in patients with severe hemophilia A (HA), rendering the treatment inefficient. Data on the role of regulatory T cells (Tregs) in inhibitor formation in these patients are rare. Herein, we aimed to investigate whether a difference in the FOXP3+ Tregs is linked to the formation of the inhibitors in severe HA patients.

METHODS

In this cross-sectional study, 32 patients with severe HA (8 patients with inhibitors and 24 without inhibitors) and 24 healthy controls were enrolled. The frequency of FOXP3+ Tregs was determined using multicolor flow cytometry method.

RESULTS

Our results showed that the median level of CD4+ CD25+ FOXP3+ Tregs did not significantly differ between HA patients and healthy controls and between HA patients with and without inhibitors (P > 0.05). However, patients with inhibitors had significantly lower amounts of CD4+ CD25- FOXP3+ Tregs compared to those without inhibitors as well as healthy controls (*P = 0.012 and *P = 0.004, respectively). The frequency of CD4+ CD25+ T cells was significantly higher in HA patients who developed inhibitors compared to the inhibitor-negative ones whereas they were lower in inhibitor-negative patients compared to the healthy controls (*P = 0.013 and *P = *0.029, respectively). The percentages of CD4+ CD25+ T cells were positively correlated with the levels of inhibitors in HA patients (r = 0.45, *P = 0.021).

CONCLUSION

Our data demonstrated for the first time that the CD4+ CD25- FOXP3+ Tregs might be implicated in the prevention of inhibitor formation in severe HA patients.

The spleen is the major site for the development and expansion of inhibitor producing-cells in hemophilia A mice upon FVIII infusion developing high-titer inhibitor

BACKGROUND

Hemophilia A (HA) is a hereditary bleeding disorder caused by defects in endogenous factor (F)VIII. Approximately 30 % of patients with severe HA treated with FVIII develop neutralizing antibodies (inhibitors) against FVIII, which render the therapy ineffective. The managements of HA patients with high-titter inhibitors are especially challenging. Therefore, it is important to understand the mechanism(s) of high-titer inhibitor development and dynamics of FVIII-specific plasma cells (FVIII-PCs).

AIMS

To identify the dynamics of FVIII-PCs and the lymphoid organs in which FVIII-PCs are localized during high-titer inhibitor formation.

METHODS AND RESULTS

When FVIII-KO mice were intravenously injected with recombinant (r)FVIII in combination with lipopolysaccharide (LPS), a marked enhancement of anti-FVIII antibody induction was observed with increasing FVIII-PCs, especially in the spleen. When splenectomized or congenitally asplenic FVIII-KO mice were treated with LPS + rFVIII, the serum inhibitor levels decreased by approximately 80 %. Furthermore, when splenocytes or bone marrow (BM) cells from inhibitor+ FVIII-KO mice treated with LPS + rFVIII were grafted into immune-deficient mice, anti-FVIII IgG was detected only in the serum of splenocyte-administered mice and FVIII-PCs were detected in the spleen but not in the BM. In addition, when splenocytes from inhibitor+ FVIII-KO mice were grafted into splenectomized immuno-deficient mice, inhibitor levels were significantly reduced in the serum.

CONCLUSION

The spleen is the major site responsible for the expansion and retention of FVIII-PCs in the presence of high-titer inhibitors.

Hemophilia a patients with inhibitors: Mechanistic insights and novel therapeutic implications

The development of coagulation factor VIII (FVIII) inhibitory antibodies is a serious complication in hemophilia A (HA) patients after FVIII replacement therapy. Inhibitors render regular prophylaxis ineffective and increase the risk of morbidity and mortality. Immune tolerance induction (ITI) regimens have become the only clinically proven therapy for eradicating these inhibitors. However, this is a lengthy and costly strategy. For HA patients with high titer inhibitors, bypassing or new hemostatic agents must be used in clinical prophylaxis due to the ineffective ITI regimens. Since multiple genetic and environmental factors are involved in the pathogenesis of inhibitor generation, understanding the mechanisms by which inhibitors develop could help identify critical targets that can be exploited to prevent or eradicate inhibitors. In this review, we provide a comprehensive overview of the recent advances related to mechanistic insights into anti-FVIII antibody development and discuss novel therapeutic approaches for HA patients with inhibitors.