Age is no barrier for adults undergoing HCT for AML in CR1: contemporary CIBMTR analysis.

Acute Myeloid Leukemia (AML) has a median age at diagnosis of 67 years. The most common curative therapy remains an allogeneic hematopoietic stem cell transplantation (HCT), yet it is complicated by treatment-related mortality (TRM) and ongoing morbidity including graft versus host disease (GVHD) that may impact survival, particularly in older patients. We examined the outcomes and predictors of success in 1321 patients aged 60 years and older receiving a HCT for AML in first complete remission (CR1) from 2007-2017 and reported to the CIBMTR. Outcomes were compared in three age cohorts (60-64; 65-69; 70+). With median follow-up of nearly 3 years, patients aged 60-64 had modestly, though significantly better OS, DFS and lower TRM than those either 65-69 or 70+; cohorts with similar outcomes. Three-year OS for the 3 cohorts was 49.4%, 42.3%, and 44.7% respectively (p = 0.026). TRM was higher with increasing age, cord blood as graft source and HCT-CI score of ≥3. Conditioning intensity was not a significant predictor of OS in the 60-69 cohort with 3-year OS of 46% for RIC and 49% for MAC (p = 0.38); MAC was rarely used over age 70. There was no difference in the relapse rate, incidence of Grade III/IV acute GVHD, or moderate-severe chronic GVHD across the age cohorts. After adjusting for other predictors, age had a small effect on OS and TRM. High-risk features including poor cytogenetics and measurable residual disease (MRD) prior to HCT were each significantly associated with relapse and accounted for most of the adverse impact on OS and DFS. Age did not influence the incidence of either acute or chronic GVHD; while graft type and associated GVHD prophylaxis were most important. These data suggest that age alone is not a barrier to successful HCT for AML in CR1 and should not exclude patients from HCT. Efforts should focus on minimizing residual disease and better donor selection.

Acquired decrease of the C3b/C4b receptor (CR1, CD35) and increased C4d deposits on erythrocytes from ICU COVID-19 patients.

In order to study the mechanisms of COVID-19 damage following the complement activation phase occurring during the innate immune response to SARS-CoV-2, CR1 (the regulating complement activation factor, CD35, the C3b/C4b receptor), C4d deposits on Erythrocytes (E), and the products of complement activation C3b/C3bi, were assessed in 52 COVID-19 patients undergoing O2 therapy or assisted ventilation in ICU units in Rheims France. An acquired decrease of CR1 density on E from COVID-19 patients was observed (Mean = 418, SD = 162, N = 52) versus healthy individuals (Mean = 592, SD = 287, N = 400), Student's t-test p < 10-6, particularly among fatal cases, and in parallel with several parameters of clinical severity. Large deposits of C4d on E in patients were well above values observed in normal individuals, mostly without concomitant C3 deposits, in more than 80% of the patients. This finding is reminiscent of the increased C4d deposits on E previously observed to correlate with sub endothelial pericapillary deposits in organ transplant rejection, and with clinical SLE flares. Conversely, significant C3 deposits on E were only observed among » of the patients. The decrease of CR1/E density, deposits of C4 fragments on E and previously reported detection of virus spikes or C3 on E among COVID-19 patients, suggest that the handling and clearance of immune complex or complement fragment coated cell debris may play an important role in the pathophysiology of SARS-CoV-2. Measurement of C4d deposits on E might represent a surrogate marker for assessing inflammation and complement activation occurring in organ capillaries and CR1/E decrease might represent a cumulative index of complement activation in COVID-19 patients. Taken together, these original findings highlight the participation of complement regulatory proteins and indicate that E are important in immune pathophysiology of COVID-19 patients. Besides a potential role for monitoring the course of disease, these observations suggest that novel therapies such as the use of CR1, or CR1-like molecules, in order to down regulate complement activation and inflammation, should be considered.

A novel soluble complement receptor 1 fragment with enhanced therapeutic potential.

Human complement receptor 1 (HuCR1) is a pivotal regulator of complement activity, acting on all three complement pathways as a membrane-bound receptor of C3b/C4b, C3/C5 convertase decay accelerator, and cofactor for factor I-mediated cleavage of C3b and C4b. In this study, we sought to identify a minimal soluble fragment of HuCR1, which retains the complement regulatory activity of the wildtype protein. To this end, we generated recombinant, soluble, and truncated versions of HuCR1 and compared their ability to inhibit complement activation in vitro using multiple assays. A soluble form of HuCR1, truncated at amino acid 1392 and designated CSL040, was found to be a more potent inhibitor than all other truncation variants tested. CSL040 retained its affinity to both C3b and C4b as well as its cleavage and decay acceleration activity and was found to be stable under a range of buffer conditions. Pharmacokinetic studies in mice demonstrated that the level of sialylation is a major determinant of CSL040 clearance in vivo. CSL040 also showed an improved pharmacokinetic profile compared with the full extracellular domain of HuCR1. The in vivo effects of CSL040 on acute complement-mediated kidney damage were tested in an attenuated passive antiglomerular basement membrane antibody-induced glomerulonephritis model. In this model, CSL040 at 20 and 60 mg/kg significantly attenuated kidney damage at 24 h, with significant reductions in cellular infiltrates and urine albumin, consistent with protection from kidney damage. CSL040 thus represents a potential therapeutic candidate for the treatment of complement-mediated disorders.

Anti-complement therapy for glomerular diseases.

A major shift in our understanding of glomerular diseases is the focus on which components of the complement pathway are involved in mediating kidney injury. For example, the membranoproliferative glomerulonephritis lesion is no longer classified solely by ultrastructural findings on biopsy and is now divided into immune-complex-mediated lesions vs complement-mediated lesions. In turn, this emphasis on complement leads to interest in therapies that target complement as potential disease-modifying agents. Eculizumab, the first available anti-complement therapy, blocks at the level of C5 and has revolutionized the treatment of atypical hemolytic uremic syndrome. Whether this agent will work equally well for the far more heterogeneous entities of C3 glomerulonephritis and dense deposit disease remains unclear. Instead, newer agents that target C3 may turn out to be the most effective and specific therapy for these C3 glomerulopathies.

Soluble CR1 therapy improves complement regulation in C3 glomerulopathy.

Dense deposit disease (DDD) and C3 glomerulonephritis (C3GN) are widely recognized subtypes of C3 glomerulopathy. These ultra-rare renal diseases are characterized by fluid-phase dysregulation of the alternative complement pathway that leads to deposition of complement proteins in the renal glomerulus. Disease triggers are unknown and because targeted treatments are lacking, progress to end stage renal failure is a common final outcome. We studied soluble CR1, a potent regulator of complement activity, to test whether it restores complement regulation in C3 glomerulopathy. In vitro studies using sera from patients with DDD showed that soluble CR1 prevents dysregulation of the alternative pathway C3 convertase, even in the presence of C3 nephritic factors. In mice deficient in complement factor H and transgenic for human CR1, soluble CR1 therapy stopped alternative pathway activation, resulting in normalization of serum C3 levels and clearance of iC3b from glomerular basement membranes. Short-term use of soluble CR1 in a pediatric patient with end stage renal failure demonstrated its safety and ability to normalize activity of the terminal complement pathway. Overall, these data indicate that soluble CR1 re-establishes regulation of the alternative complement pathway and provide support for a limited trial to evaluate soluble CR1 as a treatment for DDD and C3GN.

Elimination of autoreactive B cells in humanized SCID mouse model of SLE.

Although the exact etiology of systemic lupus erythematosus (SLE) remains elusive, B-cell hyperactivity and production of autoantibodies directed to components of the cell nucleus are a well-established pathogenetic mechanism of the disease. Therefore, the targeted inhibition of DNA-specific B cells is a logical therapeutic approach. The complement receptor type 1 (CR1, CD35) has been shown to suppress human B-cell activation and proliferation after co-cross-linking with the BCR, and may serve as a mediator for negative signal delivery. In order to evaluate this therapeutic approach in a human-like system, we used immune-restricted SCID mice transferred with PBMCs from SLE patients. The tolerance of these humanized SCID mice to native DNA was re-established after administration of a chimeric molecule consisting of a CR1-specific mAb coupled to the decapeptide DWEYSVWLSN that mimics dsDNA. The generated protein-engineered chimera was able to co-cross-link selectively native DNA-specific BCR with the B-cell inhibitory receptor CR1, thus delivering a strong inhibitory signal.

[The role of CR1 complement receptor in pathology]. / Rola receptora CR1 ukladu dopelniacza w patologii.

CR1 (Complement Receptor 1, CD35) is a membrane receptor for C3b and C4b expressed on erythrocytes, leukocytes and podocytes. It plays an important role in removal of immune complexes and pathogens coated with C3b and C4b. It also regulates the complement cascade activation by preventing formation of classical and alternative pathway convertases and by acting as a cofactor for factor 1 mediated cleavage of C3b to iC3b, C3c and C3dg. CR1 is a polymorphic molecule differing in molecular weight and the level of the CR1 expression on erythrocytes. It takes part in pathogenesis and development of various autoimmune and infectious diseases. The difference in expression of CR1 seems to correlate directly with the development of systemic lupus erythematosus (SLE) and severe form of malaria. The therapeutical potential of soluble CR1 (sCR1) is at present the subject of many investigations.

Improving therapeutic efficacy of a complement receptor by structure-based affinity maturation.

CRIg is a recently discovered complement C3 receptor expressed on a subpopulation of tissue-resident macrophages. The extracellular IgV domain of CRIg (CRIg-ECD) holds considerable promise as a potential therapeutic because it selectively inhibits the alternative pathway of complement by binding to C3b and inhibiting proteolytic activation of C3 and C5. However, CRIg binds weakly to the convertase subunit C3b (K(D) = 1.1 microm), and thus a relatively high concentration of protein is required to reach nearly complete complement inhibition. To improve therapeutic efficacy while minimizing risk of immunogenicity, we devised a phage display strategy to evolve a high affinity CRIg-ECD variant with a minimal number of mutations. Using the crystal structure of CRIg in complex with C3b as a guide for library design, we isolated a CRIg-ECD double mutant (Q64R/M86Y, CRIg-v27) that showed increased binding affinity and improved complement inhibitory activity relative to CRIg-ECD. In a mouse model of arthritis, treatment with a Fc fusion of CRIg-v27 resulted in a significant reduction in clinical scores compared with treatment with an Fc fusion of CRIg-ECD. This study clearly illustrates how phage display technology and structural information can be combined to generate proteins with nearly natural sequences that act as potent complement inhibitors with greatly improved therapeutic efficacy.

Review: complement receptor 1 therapeutics for prevention of immune hemolysis.

The complement system plays a crucial role in fighting infections and is an important link between the innate and adaptive immune responses. However, inappropriate complement activation can cause tissue damage, and it underlies the pathology of many diseases. In the transfusion medicine setting, complement sensitization of RBCs can lead to both intravascular and extravascular destruction. Moreover, complement deficiencies are associated with autoimmune disorders, including autoimmune hemolytic anemia (AIHA). Complement receptor 1 (CR1) is a large single-pass glycoprotein that is expressed on a variety of cell types in blood, including RBCs and immune cells. Among its multiple functions is its ability to inhibit complement activation. Furthermore, gene knockout studies in mice implicate a role for CR1 (along with the alternatively spliced gene product CR2) in prevention of autoimmunity. This review discusses the possibility that the CR1 protein may be manipulated to prevent and treat AIHA. In addition, it will be shown in an in vivo mouse model of transfusion reaction that recombinant soluble forms of CR1 can reduce complement-mediated RBC destruction, thereby prolonging survival of transfused RBCs. It is proposed that CR1-based therapeutics have potential for effective and safe prophylactic short-term use and for treatment of hemolytic transfusion reactions.

Development of complement therapeutics for inhibition of immune-mediated red cell destruction.

A major objective of my National Blood Foundation (NBF)-funded proposal was to produce recombinant soluble forms of a complement regulatory protein called complement receptor 1 (CR1) that carries the Knops blood group system antigens to perform antibody neutralization studies. By generating these recombinant proteins, we were able to inhibit several Knops antibodies in patient serum samples, thereby demonstrating their usefulness for clinical use. Interestingly, the recombinant CR1 proteins generated through NBF funding were also found to strongly reduce complement-mediated red cell destruction in a mouse hemolytic transfusion model. In this review, I will outline our NBF-funded studies, give an overview of recent advances from our group and others in the development of complement therapeutics, and highlight their potential use in the transfusion medicine setting.

CR1-based inhibitors for prevention of complement-mediated immune hemolysis.

Complement receptor 1 (CR1) is a single pass transmembrane glycoprotein that, through its ability to bind key components of the complement cascade, can inhibit both the classical and alternative pathways. Using several animal models, a recombinant form of CR1 has been documented to be effective in reducing tissue damage that occurs as a result of complement activation in various inflammatory conditions. This strategy is currently being explored in human clinical trials. Activation of complement cascade via the antibody-mediated classical pathway can initiate red blood cell destruction, causing transfusion reactions and hemolytic anemia. We discuss here our approach of using CR1 derivatives as therapeutic targets for prevention of complement-dependent immune hemolysis. Using a mouse model of hemolytic transfusion reaction, we have found that sCR1 treatment reduces complement activation and prolongs the survival of transfused red blood cells. Through structure-function analysis, we have identified a complement inhibitory domain located at the amino-terminal region of CR1 that mediates its antihemolytic activity in vivo. Collectively, our data highlight a potential use for CR1 to control complement-dependent immune hemolysis and identify its functional domains for the future design of CR1-based inhibitors.

Contribution of anaphylatoxin C5a to late airway responses after repeated exposure of antigen to allergic rats.

We attempted to elucidate the contribution of complement to allergic asthma. Rat sensitized to OVA received repeated intratracheal exposures to OVA for up to 3 consecutive days, and pulmonary resistance was then estimated for up to 6 h after the last exposure. Whereas the immediate airway response (IAR) in terms of R(L) tended to decrease in proportion to the number of OVA exposures, late airway response (LAR) became prominent only after three. Although premedication with two kinds of complement inhibitors, soluble complement receptor type 1 (sCR1) or nafamostat mesylate, resulted in inhibition of the IAR after either a single or a double exposure, the LAR was inhibited after the triple. Premedication with a C5a receptor antagonist (C5aRA) before every exposure to OVA also inhibited the LAR after three. Repeated OVA exposure resulted in eosinophil and neutrophil infiltration into the bronchial submucosa which was suppressed by premedication with sCR1 or C5aRA. Up-regulation of C5aR mRNA was shown in lungs after triple OVA exposure, but almost no up-regulation of C3aR. Pretreatment with sCR1 or C5aRA suppressed the up-regulation of C5aR expression as well as cytokine messages in the lungs. The suppression of LAR by pretreatment with sCR1 was reversed by intratracheal instillation of rat C5a desArg the action of which was inhibited by C5aRA. In contrast, rat C3a desArg or cytokine-induced neutrophil chemoattractant-1 induced cellular infiltration into the bronchial submucosa by costimulation with OVA, but these had no influence on the LAR. These differences might be explained by the fact that costimulation with OVA and C5a synergistically potentiated IAR, whereas that with OVA and either C3a or cytokine-induced neutrophil chemoattractant-1 did not. C5a generated by Ag-Ab complexes helps in the production of cytokines and contributes to the LAR after repeated exposure to Ag.

Targeting complement in therapy.

With increasing evidence that complement activation significantly contributes to the pathogenesis of a large number of inflammatory diseases, strategies that interfere with its deleterious action have become a major focus in pharmacological research. Endogenous soluble complement inhibitors (C1 inhibitor, recombinant soluble complement receptor 1, antibodies) blocking key proteins of the cascade reaction, neutralizing the action of the complement-derived anaphylatoxin C5a, or interfering with complement receptor 3 (CR3, CD18/11b)-mediated adhesion of inflammatory cells to the vascular endothelium have successfully been tested in various animal models over the past years. Promising results consequently led to clinical trials. Furthermore, incorporation of membrane-bound complement regulators (decay-accelerating factor (CD55), membrane co-factor protein (CD46), CD59) in transgenic animals has provided a major step forward in protecting xenografts from hyperacute rejection. At the same time, the poor contribution of complement to the antitumor response, which is caused by multiple resistance mechanisms that hamper the efficacy of antibody-based tumor therapy, is increasingly recognized and requires pharmacologic intervention. First attempts have now been made to interfere with the resistance mechanisms, thereby improving complement-mediated tumor cell destruction.

Soluble complement receptor one (sCR1) inhibits the development and progression of rat collagen-induced arthritis.

We set out to determine whether inhibition of complement using sCR1 could influence the development and progression of collagen arthritis in the Lewis rat. Collagen arthritis was successfully established in the Lewis rat, using a novel immunization schedule. In separate experiments, cobra venom factor (CVF) and sCR1 were used to achieve systemic complement inhibition. Their respective effects on disease onset and on the progression of established disease compared with saline-treated control animals was explored. Arthritis was assessed by measurement of clinical score, paw diameter and paw volume. Complement inhibition using either CVF or sCR1, prior to the onset of clinical signs of inflammation, delayed the development of disease. CVF was ineffective in the treatment of established disease, whereas sCR1 delayed the progression of disease in affected joints and prevented the recruitment of further joints while the animals were complement-depleted. In the control saline-treated groups the disease continued to progress relentlessly. We conclude that complement activation is important in the initiation and maintenance of inflammation in collagen arthritis. The potent disease-modulating effect of sCR1 provides persuasive evidence that specific complement inhibiting agents may be an effective approach to the treatment of inflammatory joint diseases

Endothelial targeting and enhanced antiinflammatory effects of complement inhibitors possessing sialyl Lewisx moieties.

The complement inhibitor soluble complement receptor type 1 (sCR1) and a truncated form of sCR1, sCR1[desLHR-A], have been generated with expression of the selectin-reactive oligosaccharide moiety, sialyl Lewisx (sLex), as N-linked oligosaccharide adducts. These modified proteins, sCR1sLex and sCR1[desLHR-A]sLex, were assessed in the L-selectin- and P-selectin-dependent rat model of lung injury following systemic activation of complement by cobra venom factor and in the L-selectin-, P-selectin-, and E-selectin-dependent model of lung injury following intrapulmonary deposition of IgG immune complexes. In the cobra venom factor model, sCR1sLex and sCR1[desLHR-A]sLex caused substantially greater reductions in neutrophil accumulation and in albumin extravasation in lung when compared with the non-sLex-decorated forms. In this model, increased lung vascular binding of sCR1sLex and sCR1[desLHR-A]sLex occurred in a P-selectin-dependent manner, in contrast to the absence of any increased binding of sCR1 or sCR1[desLHR-A]. In the IgG immune complex model, sCR1[desLHR-A]sLex possessed greater protective effects relative to sCR1[desLHR-A], based on albumin extravasation and neutrophil accumulation. Enhanced protective effects correlated with greater lung vascular binding of sCR1[desLHR-A]sLex as compared with the non-sLex-decorated form. In TNF-alpha-activated HUVEC, substantial in vitro binding occurred with sCR1[desLHR-A]sLex (but not with sCR1[desLHR-A]). This endothelial cell binding was blocked by anti-E-selectin but not by anti-P-selectin. These data suggest that sLex-decorated complement inhibitors have enhanced antiinflammatory effects and appear to have enhanced ability to localize to the activated vascular endothelium.

Antiinflammatory effects of soluble complement receptor type 1 promote rapid recovery of ischemia/reperfusion injury in rat small intestine.

We examined the effect of soluble complement receptor type 1 (sCR1) on mucosal injury and inflammation in a rat model of ischemia/reperfusion. Groups of vehicle- and sCR1-treated rats underwent 30 min of mesenteric ischemia followed by 60 or 120 min of reperfusion. When compared to vehicle-treated rats, treatment with sCR1 (12 mg/kg) prior to 120 min of reperfusion significantly reduced mucosal injury, neutrophil infiltration, leukotriene B4 production, and restored villus height to control levels. The protective effect of sCR1 evident at 120 min of reperfusion was not observed at 60 min of reperfusion despite rapid inactivation of complement. These data suggest that complement inhibition minimized mucosal disruption by facilitating mucosal restitution or interrupting the inflammatory process. Delayed administration of sCR1 for 30 or 60 min into the reperfusion period progressively reduced the protection. sCR1-mediated rapid recovery of rat intestine after ischemia/reperfusion underscores the fundamental role of complement activation in neutrophil-mediated tissue injury.