LRP1/CD91 is up-regulated in monocytes from patients with haemophilia A: a single-centre analysis

Multi-faceted role of LRP1 in the immune system

Graft versus host disease (GVHD) represents the major complication after allogeneic hematopoietic stem cell transplantation (Allo-SCT). GVHD-prone patients rely on GVHD prophylaxis (e.g. methotrexate) and generalized anti-GVHD medical regimen (glucocorticoids). New anti-GVHD therapy strategies are being constantly explored, however there is an urgent need to improve current treatment, since GVHD-related mortality reaches 22% within 5 years in patients with chronic GVHD. This review is an attempt to describe a very well-known receptor in lipoprotein studies - the low-density lipoprotein receptor related protein 1 (LRP1) - in a new light, as a potential therapeutic target for GVHD prevention and treatment. Our preliminary studies demonstrated that LRP1 deletion in donor murine T cells results in significantly lower GVHD-related mortality in recipient mice with MHC (major histocompatibility complex) -mismatched HSCT. Given the importance of T cells in the development of GVHD, there is a significant gap in scientific literature regarding LRP1's role in T cell biology. Furthermore, there is limited research interest and publications on this classical receptor molecule in other immune cell types. Herein, we endeavor to summarize existing knowledge about LRP1's role in various immune cells to demonstrate the possibility of this receptor to serve as a novel target for anti-GVHD treatment.

LRP1/CD91 is highly expressed in monocytes from patients with vitiligo - even after repigmentation

Vitiligo pathophysiology is mediated by antigen-specific cytotoxic T cells. Environmental stressors cause susceptible melanocytes to secrete damage-associated molecular patterns (DAMPs). DAMPs are recognized by receptors such as the endocytic low-density lipoprotein receptor-related protein (LRP1/CD91), expressed in antigen-presenting cells, which activate self-reactive CD8+ T cells, leading to melanocyte destruction. Within this response, interferon gamma triggers production of cytokine CXCL10, recruiting more activated T cells causing further melanocytic damage. We hypothesized that expression of LRP1/CD91 was higher in vitiligo patients compared to non-vitiligo individuals. And further that levels/expression of CXCL10 in plasma were linked to disease severity. We enrolled forty individuals in this study: 18 patients with vitiligo and 22 healthy volunteers. We assessed LRP1/CD91 expression and plasma CXCL10 in patients with vitiligo and healthy volunteers. Additionally, vitiligo patients received combined treatment for 16 weeks following which the said parameters were reassessed. Vitiligo Area Scoring Index was calculated before and after treatment for these patients. Analysis of LRP1/CD91 MFI values in monocytes from vitiligo patients showed high surface levels of LRP1/CD91 than from healthy volunteers (10.50 ± 0.77 vs. 6.55 ± 0.77 MFI units, p < 0.001). This expression did not change after treatment. Plasma levels of CXCL10 were higher in vitiligo patients than healthy volunteers (93.78 ± 7.73 vs. 40.17 ± 6.25 pg/ml). The patients with a good clinical response to treatment had a parallel reduction in plasma CXCL10 levels (105.8 ± 18.44 vs. 66.13 ± 4.87 pg/ml) before and after treatment. LRP1/CD91 expression may reflect susceptibility to vitiligo. Plasma levels of CXCL10 can represent a biomarker for monitoring treatment response. LRP1 and CXCL10 may represent therapeutic targets.

Recombinant factor VIII Fc fusion protein drives regulatory macrophage polarization

The main complication of replacement therapy with factor in hemophilia A (HemA) is the formation of inhibitors (neutralizing anti-factor VIII [FVIII] antibodies) in ∼30% of severe HemA patients. Because these inhibitors render replacement FVIII treatment essentially ineffective, preventing or eliminating them is of top priority in disease management. The extended half-life recombinant FVIII Fc fusion protein (rFVIIIFc) is an approved therapy for HemA patients. In addition, it has been reported that rFVIIIFc may induce tolerance to FVIII more readily than FVIII alone in HemA patients that have developed inhibitors. Given that the immunoglobulin G1 Fc region has the potential to interact with immune cells expressing Fc receptors (FcRs) and thereby affect the immune response to rFVIII, we investigated how human macrophages, expressing both FcRs and receptors reported to bind FVIII, respond to rFVIIIFc. We show herein that rFVIIIFc, but not rFVIII, uniquely skews macrophages toward an alternatively activated regulatory phenotype. rFVIIIFc initiates signaling events that result in morphological changes, as well as a specific gene expression and metabolic profile that is characteristic of the regulatory type Mox/M2-like macrophages. Further, these changes are dependent on rFVIIIFc-FcR interactions. Our findings elucidate mechanisms of potential immunomodulatory properties of rFVIIIFc.

Regulatory B Cells Are Functionally Impaired in Patients Having Hemophilia A With Inhibitors

Development of inhibitors remains a major clinical complication in patients with hemophilia A receiving replacement therapy with factor VIII (FVIII). Understanding the immune mechanisms involved in the development of inhibitors can provide valuable information about pathways to human tolerance. Recent evidence indicates that B regulatory (Breg) cells play a pivotal role in controlling the production of antibodies (Abs) while promoting follicular T helper (Tfh) cells and monocytes, expressing the low-density lipoprotein receptor-related protein (LRP/CD91), which is involved in FVIII intake from the circulation. We studied circulating levels of Breg cells along with Tfh cells and the expression of LRP/CD91 on monocytes in patients with hemophilia A using 8-color flow cytometry and cell culture. Compared to healthy controls, patients with hemophilia A with inhibitors showed a severe reduction in levels of Breg cells and produced less interleukin-10 when activated via the CD40 signaling pathway. In addition, patients with hemophilia A with inhibitors exhibited an overexpression of LPR/CD91 on monocytes and normal levels of Tfh cells. Levels of Breg cells were not significantly related to LPR/CD91 although negative associations were evidenced. Collectively, these results provide new insights into the role of Breg cells and LPR/CD91 in the development of inhibitors in patients with hemophilia A.