16th International Congress on Antiphospholipid Antibodies Task Force Report on Antiphospholipid Syndrome Treatment Trends

Randomized controlled trial (RCT) evidence

Other evidence

A phase 4 pilot study of rivaroxaban 20 mg daily was completed in 82 APS patients with prior VTE. The authors reported recurrent thrombosis in 4.9% (n = 4) ²² and concluded that the rate of recurrent thrombosis after at least a year of follow-up was comparable to previous RCTs (annualised recurrent thrombosis rate 1.3-4%)^23,24 among thrombotic APS patients treated with warfarin. A prospective cohort study of 176 patients with 51 months follow-up (82 on DOACs [42 on apixaban, 36 on rivaroxaban and 4 on dabigatran] and 94 on VKA) reported annualized recurrent thrombosis rates of 3.3% (3/10 arterial) and 2.5% (2/12 arterial) for DOACs and warfarin, respectively. ²⁵ A retrospective case control study including 18 patients on DOACs (12 on edoxaban, 5 on rivaroxaban and 1 on apixaban) and 36 matched controls on VKA followed for 5 years reported annualized recurrent thrombosis rates of 6.6% for DOACs and 4.4% for VKA. ²⁶

A systematic review of 728 APS patients on DOACs (48% triple aPL-positive) reported an annualised recurrent thrombosis rate of 11%. Factors associated with a higher risk for recurrent thrombosis included a higher mean number of prior thrombotic events, a history of combined arterial and venous thrombosis, previous treatment with low-molecular-weight heparin (LMWH), use of immunosuppressant treatment, and patient preference to switch to a DOAC. ²⁷ An earlier individual patient data meta-analysis of 447 patients, in which the annualised recurrent thrombosis rate was 11.7%, suggested that additional risk factors for recurrent thrombosis include triple aPL-positivity, a higher number of clinical criteria for APS classification, prior thrombosis while on a VKA and, in patients treated with anti-Xa inhibitors, a history of arterial or small vessel thrombosis. Among the 73/447 patients with recurrent thrombosis, 31 had arterial events; 18 (58%) of these had a prior single VTE, with 10/18 (56%) triple aPL-positive. ²⁸

DOACs and VTE among patients with APS

DOACs are established as standard treatment for ‘general population’ patients with a first unprovoked VTE following large phase 3 multicentre international RCTs of DOACs versus standard-intensity warfarin. ²⁹ These trials did not focus on APS patients, although post hoc analysis of the RE-COVER®, RE-COVER II™, and RE-MEDY™ RCTs indicated that the efficacy and safety of dabigatran etexilate were not significantly different among patients with at least one positive criteria aPL test and VTE. ³⁰ A prospective cohort study in 290 patients with a first unprovoked VTE found that 9% met criteria for APS, showing persistent aPL. Two patients, i.e., 1% of the 191 patients tested for all three aPL, were triple aPL-positive, with persistent triple aPL-positivity proven in one. ³¹ A cross-sectional study of 491 patients with a first unprovoked VTE also found that 9% (44/491) of patients met criteria for APS, with 1.4% (7/491) being persistently triple aPL-positive. ³² These observations raise the issue of the optimal timing for aPL testing after a first VTE.

Testing for LA in the acute post-thrombotic state may be confounded by acute phase reactants such as factor VIII ³³ and C-reactive protein, ³⁴ as well as the effects of anticoagulation treatment, ³⁵ as false positive and negative results can occur. In contrast, triple aPL-positivity persists in the majority of patients,^36,37 although it occurs in only a minority of patients with a first VTE.^31,32 Guidance regarding the timing of thrombophilia testing including testing for APS exists. ³⁸ It may be preferable to defer screening for aPL for most patients with a new VTE in the acute setting. For those patients in whom there is clinical concern for APS, however (e.g., patients with a new VTE and obstetric or non-criteria manifestations of APS), testing can be performed with appropriate interpretation of the laboratory results.

DOACs and APS-related stroke

Standard dosages of DOACs have been established to be effective versus standard-intensity warfarin as the comparator following a first VTE episode in ‘general population’ patients. ²⁹ However, whether standard doses of DOACs offer sufficient protection against recurrent thrombosis when high intensity anticoagulation is recommended is an uncertainty.^16,39 There is a lack of consensus regarding appropriate VKA anticoagulation intensity for APS patients in certain circumstances which reflects the lack of conclusive data. The European League against Rheumatism (EULAR) guidelines, based on pooled data from two retrospective studies and two RCTs showing no significant difference in thrombosis recurrences between INR target 3.0–4.0 versus 2.0–3.0 (relative risk 0.46 [0.06–3.52]), recommend treatment with VKA with INR 2.0–3.0 or INR 3.0–4.0 in APS patients with a first arterial thrombosis, considering the individual’s risk of bleeding.^16,40 The RISAPS RCT aims to investigate the use of high-intensity rivaroxaban 15 mg twice daily versus warfarin in APS patients with stroke or other ischaemic brain manifestations: (ClinicalTrials.gov Identifier: NCT03684564).

Other considerations regarding DOAC use in APS

The role of DOACs in APS is not established, and APS, by definition a syndrome, includes a population that is heterogenous in clinical and laboratory manifestations of disease. The TRAPS trial ¹⁸ triggered the risk assessment that led to the European Medicines Agency (EMA) statement that DOACs are not recommended for thrombotic APS patients, especially those who are triple positive for aPL. The United States Food and Drug Administration (FDA) has endorsed the EMA recommendations, ⁴¹ as have other regulatory authorities worldwide. Of note, DOACs are not contraindicated for APS.^42–45 The TRAPS trial included only triple aPL positive patients, whereas the EMA recommendation extends to all APS patients. Definitive evidence regarding the role of DOAC therapy among patients with thrombotic APS is required. However, concern remains that guidance from regulatory bodies, such as that noted above, will diminish clinician drive and patient willingness to participate in clinical studies necessary to inform optimal care.

Task force recommendations

Low dose aspirin

Aspirin irreversibly inhibits the cyclooxygenase activity of prostaglandin H synthase-1 in platelets, thereby blocking the formation of thromboxane A2, which is a potent vasoconstrictor and facilitates platelet aggregation. Low dose aspirin (LDA), in combination with prophylactic dose LMWH, is standard treatment during pregnancy for obstetric APS.^15,16,46 A meta-analysis of five trials involving 334 patients with recurrent miscarriage, reported live birth rates of 74.3% and 55.9% in women who received a combination of unfractionated heparin/LMWH plus LDA or LDA alone, respectively. ⁴⁷ The role of LDA for primary prevention of thrombosis in non-pregnant women with a history of obstetric APS and individuals with persistent aPL is considered below.

Low dose aspirin for primary prevention of thrombosis in patients with persistent antiphospholipid antibodies

A meta-analysis of 10 observational studies, and one RCT (1208 patients and 139 thrombotic events), investigated the utility of LDA in aPL-positive individuals asymptomatic for thrombosis. The majority of the patients had double- or triple-aPL positivity, or persistently high aPL titres. Subgroup analysis showed that the risk of a first venous thromboembolic event (VTE) was significantly decreased by the use of LDA among asymptomatic aPL-positive individuals (7 observational studies; odds ratio (OR): 0.50 [0.25–0.99]); patients with SLE (7 observational studies, 1 RCT; OR: 0.55 [0.31–0.98]); or those with a history of obstetric APS (5 observational studies; OR: 0.25 [0.10–0.62]). ⁴⁸

An individual patient meta-analysis of five cohort studies by the same group included 497 subjects with 79 first thrombotic events. After adjustment of cardiovascular risk factors, aPL profiles, and treatment with hydroxychloroquine, a hazard ratio (HR) for the risk of a first thrombosis of any type in aPL carriers treated with LDA versus those not treated with aspirin was 0.43 (95%CI 0.25–0.75). Subgroup analysis showed a protective effect of LDA against arterial (HR: 0.48 [95%CI: 0.28–0.82]) but not venous thrombosis as well as in retrospective (OR: 0.23 [0.13–0.42]) but not prospective studies (OR: 0.91 [0.52–1.59]. After further adjustment on the gender, age, and presence of cardiovascular risk factors, subgroup analysis showed a protective effect of aspirin against arterial thrombosis was observed in patients with SLE (HR: 0.43 [95%CI: 0.20–0.93]) and asymptomatic aPL carriers (HR: 0.21 [95%CI 0.04–0.99). The number of women with obstetric APS was relatively small, limiting conclusions: 15/221 (7%) of patients on LDA and 65/276 (24%) of those not on LDA. ⁴⁹ The APLASA (Antiphospholipid Antibody Acetylsalicylic Acid) trial was the only RCT that directly addressed the question of the efficacy of LDA in primary thrombosis prevention in asymptomatic, persistently aPL-positive individuals, but could not confirm the benefit of low dose aspirin for primary prophylaxis in this setting, perhaps due to limited power and/or sample size. ⁵⁰ Of note, a prospective study reported a significantly increased rate of VTE and cerebrovascular events, in women with obstetric APS, despite low-dose aspirin primary prophylaxis, compared to women with heritable thrombophilia or with negative thrombophilia screens. ⁵¹

It is unclear whether the benefit of LDA outweighs the risk of major bleeding associated with LDA in a low-risk population. The estimated average annual incidence rate of overall VTE in the general population is 0.1–0.18 per 100 patient-years and similar to that of stroke. ⁵² The annual incidence of thrombosis in unselected aPL-positive patients is reported to be 0 to 2.8%. ⁵³ A more recent review estimated that the annual thrombosis rate among aPL-positive individuals with or without systemic autoimmune disease (SAID) is 0 to 5.3%, probably very low (<1%/year) in those with no other SAID or other thrombosis risk factors. The authors suggest risk stratification, based on aPL profile, age, additional SAIDs and traditional cardiovascular or VTE risk factors. ⁵⁴ Compared with the general (non-aspirin treated) population, the risk of major bleeding with LDA for primary cardiovascular disease prevention was reported in a systematic review to be 3.6 per 1000 person-years. ⁵⁵ This systematic review reported that LDA increased major gastrointestinal bleeding risk by 58% (OR, 1.58 [95% CI, 1.29 to 1.95]) and haemorrhagic stroke risk by 27% (OR, 1.27 [CI, 0.96 to 1.68]). ⁵⁵ SLE is associated with increased thrombotic risk, (both arterial and venous), increased by the presence of aPL. ⁵⁶ In the absence of RCTs evaluating prophylactic strategies, recommendations are based on analysis of lower quality studies and expert opinion.

The EULAR guidelines advise that the decision to treat with LDA for primary thromboprophylaxis should be based on stratification of thrombotic risk: ¹⁶ thus, in asymptomatic aPL carriers, with a ‘high-risk’ aPL profile (defined as the presence of persistent LA, double- or triple-aPL positivity, or persistently high aPL titres) with or without traditional risk factors and in patients with SLE and a ‘high-risk’ aPL profile, prophylactic treatment with LDA is recommended (2a/B). In individuals with a ‘low-risk’ aPL profile (defined as isolated aCL or aβ₂GPI at low-medium titres, particularly if transiently positive), the EULAR guidelines advise that LDA may be considered (2 b/C). They advise that non-pregnant women with a history of obstetric APS (with or without SLE) as the sole manifestation of APS should receive prophylactic treatment with LDA, after adequate risk/benefit evaluation (2a/B).^16,40

Low dose aspirin for secondary prevention of thrombosis

Optimal antithrombotic therapy among APS patients with prior stroke/transient ischaemic attack remains uncertain. Prospective evidence has suggested that no substantive benefit exists between high-intensity and standard-intensity warfarin, although patients with arterial thrombosis were under-represented.^23,24 Small prospective cohort evidence suggests VKA over LDA for APS-related stroke.⁵⁷ The APASS (Antiphospholipid Antibodies and Stroke Study) in older patients with stroke reported no difference in event recurrences between LDA and warfarin,⁵⁸ but aPL testing did not fulfil the international APS laboratory classification criteria.¹ While no definitive data exist, professional society guidance to elect either high-intensity VKA or standard-intensity VKA, with or without antiplatelet therapy has been recommended. ¹⁶ Based mainly on expert consensus, the EULAR guidelines recommend consideration of LDA plus standard-intensity VKA (4/C) as an option, in addition to consideration of standard- versus high-intensity VKA alone, following a first arterial thrombosis; and, in APS patients with recurrent arterial or venous thrombosis on standard-intensity VKA, addition of LDA, increase of INR target to 3.0–4.0 or change to LMWH.^16,40

There is a lack of data about the use of other antiplatelet agents in patients with aPL/thrombotic APS, including clopidogrel, prasugrel, ticagrelor and cangrelor. Dipyridamole, a phosphodiesterase inhibitor, that inhibits platelet function and induces vasodilation, ⁵⁹ also appears to inhibit aPL-mediated NETosis (discussed below).

Recommendations for clinicians

In asymptomatic aPL carriers, with or without SLE, or in individuals with prior obstetric APS, with persistent LA, double- or triple-aPL positivity, or persistently high aPL titre, LDA should be considered for primary prevention of thrombosis on a case-by-case basis.

Clinical research agenda

RCTs should be undertaken to define the potential role of LDA or other antiplatelet agents for primary prevention of thrombosis in aPL-positive patients asymptomatic for thrombosis.

Hydroxychloroquine

In vitro and in vivo studies show that antithrombotic effects of hydroxychloroquine (HCQ), standard treatment in SLE, include reversal of aPL-induced platelet activation,⁶⁰ reduction of LDL and VDRL cholesterol, and increased HDL cholesterol levels. ⁶¹ HCQ also protects the annexin A5 anticoagulant shield from syncytiotrophoblast disruption by aPL. ⁶² HCQ reduced clot formation and thrombin generation in a mouse model and in human endothelial cells. It may improve endothelial function and correct the proinflammatory phenotype observed both in vivo and in vitro. ⁶¹ A retrospective study suggested that HCQ may also reduce aPL titres in primary APS patients. ⁶³ A prospective study showed that long-term HCQ use (average 2.6 years) was associated with a decrease in aPL titers. ⁶⁴

Primary prevention of thrombosis

HCQ has been related to a reduction in thrombosis risk in aPL-positive patients with SLE, ⁶⁵ although the aforementioned individual patient meta-analysis found no independent protective effect of hydroxychloroquine. ⁴⁹ The Antiphospholipid Syndrome Alliance for Clinical Trials and International Networking (APS ACTION) initiated a multicentre, international RCT of HCQ versus standard care in persistently aPL-positive, thrombosis-free patients without systemic autoimmune diseases. The trial was terminated early due to the low recruitment rate (n = 20), exacerbated by the prolonged manufacturing shortage and significant price increase of HCQ in the United States. Thus, no conclusions on the effectiveness of HCQ could be made. The authors concluded that conducting an international RCT without pharmaceutical industry support is extremely challenging. ⁶⁶

Hydroxychloroquine: Secondary prevention of thrombosis

Data on the role of HCQ in secondary prevention of thrombosis in primary APS patients are also scarce. A prospective non-randomised study in 40 patients suggested that adding HCQ to oral anticoagulation with VKA reduced VTE in patients with primary APS. ⁶⁷ The HIBISCUS project was proposed to study the use of HCQ in secondary prevention of thrombotic and obstetric events in primary APS. ⁶⁸ A prospective RCT of HCQ versus placebo aims to assess the role of HCQ in the secondary prevention of thrombotic events (ClinicalTrials.gov Identifier: NCT03540810). A pilot open-label RCT of 50 primary APS patients and 15 asymptomatic aPL carriers showed a significantly lower thrombosis rate (average follow-up 2.6 years) in patients randomised to HCQ plus standard care vs. standard care alone. ⁶⁴

Hydroxychloroquine: Obstetric APS

Standard treatment with LDA plus LMWH to improve obstetric outcome fails in 20-30% of APS patients. ⁴⁷ A systematic review analysed the limited evidence and found that one study showed that HCQ improved pregnancy outcome, but its effect was not adjusted for the use of other medications (LDA, LMWH, steroids). An expert panel concluded that HCQ use could be considered after failure of standard treatment and in women with previous thrombosis (either arterial and/or venous), and/or with previous ischaemic placenta-mediated complications. ⁶⁹ EULAR recommendations for the use of HCQ in pregnancy state that in women with ‘criteria’ obstetric APS with recurrent pregnancy complications despite combination treatment with LDA and heparin at prophylactic dosage, increase of heparin to therapeutic dose, addition of hydroxychloroquine or addition of low-dose prednisolone in the first trimester may be considered.¹⁶ In a retrospective cohort study of 170 pregnancies in 96 women, HCQ treatment was associated with a higher rate of live births (67% in HCQ-treated vs 57% in those who did not receive hydroxychloroquine; P = 0.05) and a lower prevalence of aPL-related pregnancy morbidity (47% vs 63% respectively; P = 0.004). ⁷⁰ A multicentre RCT of HCQ versus placebo during pregnancy in women with aPL (HYPATIA; HYdroxychloroquine to Improve Pregnancy Outcome in Women with AnTIphospholipid Antibodies) is assessing the effect of HCQ on adverse pregnancy outcomes. ⁷¹ A prospective RCT of HCQ versus placebo aims to assess the role of HCQ in achieving an uncomplicated term pregnancy in primary obstetric APS (ClinicalTrials.gov Identifier: NCT04275778).

Task force recommendations

Statins

Statins inhibit the enzyme HMG-CoA reductase which has a central role in hepatic cholesterol production, but also have pleiotropic effects including anti-inflammatory and antithrombotic actions on endothelial cells and monocytes. ⁷²

Task force recommendations

Task force recommendations

Rituximab

Rituximab is a chimeric monoclonal antibody that blocks the CD20 molecule on many B-cell precursors and is currently approved in several countries for the treatment of rheumatoid arthritis and anti-neutrophil cytoplasmic antibodies (ANCA) vasculitis. Clinical trials in lupus failed to reach their primary endpoints,^106,107 though rituximab is widely used in clinical practice and has been recommended in the guidelines of the American College of Rheumatology (ACR) ¹⁰⁸ and EULAR ¹⁰⁹ for the treatment of lupus nephritis and by NHS England for more general use in lupus. ¹¹⁰

The evidence for the use of rituximab in APS derives from multiple case reports, case series and an open label clinical trial. However, reports of its use for recurrent thrombosis are scarce. The largest reported case series includes five patients with SLE/APS patients who had recurrent thrombosis despite appropriate anticoagulation with warfarin. Four of these patients had no further thrombotic events after its use. ¹¹¹ In primary APS, only sporadic reports of successful treatment for thrombotic events are available.^112,113 The data seem to be more promising for some non-criteria manifestations. An open-label phase II study of rituximab for non-criteria manifestations of APS demonstrated that the safety profile of rituximab in the disease was very similar to that reported in other autoimmune diseases. More than half (13/19) of the patients enrolled had partial or complete response in treating aPL-related thrombocytopenia, cognitive dysfunction, aPL-related nephropathy or skin ulcers, despite no substantial change in aPL profiles. ¹¹⁴ In contrast, a small observational study showed significant reductions of aCL levels in seven SLE patients (mean baseline IgG aCL level: 20.6 standardized IgG antiphospholipid units (GPLU) (range (SD) 10–32, (10.1), normal level <5) at 6-9 months post B-cell depletion with rituximab. ¹¹⁵ Numerous cases have been reported describing the successful use of rituximab, in particular, for thrombocytopenia ¹¹⁶ and skin ulcers. ¹¹⁷ A growing number of case reports and series report on the use of rituximab for diffuse alveolar hemorrhage. Approximately 13 cases have been reported, with 50% of patients achieving remission using rituximab monotherapy or in combination with cyclophosphamide or mycophenolate mofetil.^118–121

Rituximab has been reported in the treatment of CAPS. Based on the CAPS international registry, its use has been proposed for those patients who have had CAPS refractory to triple therapy (steroids, anticoagulation and plasma exchange).^122–124 Finally, for obstetric manifestations of the disease, there is one case report of unsuccessful treatment in SLE/APS. ¹²⁵ The main caveat about the evidence available is that is predominantly based on case reports or series. This type of evidence is often biased as unsuccessfully treated patients are less frequently reported.

Belimumab

Belimumab is a monoclonal antibody directed against BAFF, a B cell activating molecule. ¹²⁶ This drug has been approved for use in SLE in several parts of the world. Several reports have shown that aPL titers in SLE patients treated with belimumab decrease. This effect was observed for both aCL and aβ₂GPI, but no change in LA status was noted.^127,128 A post-hoc analysis of two randomised placebo-controlled trials in SLE did not show any significant effect of belimumab on IgG or IgM aCL titres, but only on IgA, notably in patients on concomitant antimalarials: median titre (interquartile range [IQR]) IgA aCL at baseline; placebo 22 (18; 30); belimumab 10 mg/kg 24 (19; 37); median change [IQR] at 12 months: placebo −7 (−12; 2); belimumab 10 mg/kg: −10 (−15; −7), p < 0.0007. ¹²⁹ Only two APS cases with clinical outcomes have been published; one with refractory lower extremity skin ulcers and one with thrombocytopenia. Both had a partial response and were able to taper glucocorticoids after the introduction of belimumab to the therapeutic regimen. ¹³⁰

Anti-TNF therapy

The PROMISSE (Predictors of Pregnancy Outcome: Biomarkers in Antiphospholipid Antibody Syndrome and Systemic Lupus Erythematosus), a longitudinal, prospective, multicenter observational study that enrolled pregnant women with aPL/APS and SLE (ClinicalTrials.gov Identifier: NCT00198068), has led to new insights about the role of TNF-α in pregnancy morbidity. In the PROMISSE study, 39% of pregnancies in women with APS and LA resulted in adverse pregnancy outcomes (APO) despite treatment with LMWH/unfractionated heparin and LDA. ¹³¹ Angiogenic dysregulation early in pregnancy predicted APO, most of which were due to failure of adequate vascularization of the developing placenta and underperfusion of the fetus. ¹³² Mouse models show that aPL causes elevation of TNF-α levels in the placental tissues, that TNF-α levels are associated with pregnancy loss, and its blockade rescues pregnancies. ¹³³ In a recent case series, 18 aPL-positive women with obstetric APS refractory to LMWH, aspirin and hydroxychloroquine were treated with adalimumab or certolizumab. Seventy percent of the patients had a live birth. ¹³⁴ Currently the IMProve Pregnancy in APS with Certolizumab Therapy (IMPACT: ClinicalTrials.gov Identifier: NCT03152058) clinical trial is ongoing in patients with obstetric APS. This trial should clarify the role of anti-TNF therapy for this APS manifestation. It is important to note that there are reported cases of the development^135,136 or exacerbation ¹³⁷ of APS while using anti TNF therapy. These drugs currently have no role in other disease manifestations and may have deleterious effects. ¹³⁸

Task force recommendations

Ongoing interventional clinical studies in antiphospholipid antibody-positive patients

Prospective validation for complement blockade findings from case reports is necessary. New treatment targets from the complement cascade are an alternative that should be further explored. Clinical trials of varying status are detailed below:

Terminated due to slow patient enrollment: A Phase IIa for the Treatment of Non-Criteria Manifestations of Antiphospholipid Syndrome: Nephropathy, Thrombocytopenia and Skin ulcers was designed to evaluate safety of an intravenous C5a inhibitor (ClinicalTrials.gov Identifier: #NCT02128269).

Task force recommendations

Peptides that target domain V

The aim of these agents is to block Domain V from binding to cell surfaces. Early work utilised the peptide TIFILFCCSKEKRKKKQAAT, which is derived from cytomegalovirus and has homology to Domain V. In comparison to a control peptide, TIFI reduced binding of β₂GPI to endothelial cells ¹⁶⁵ and of IgG from patients with APS (APS-IgG) to human trophoblast in-vitro. ¹⁶⁶ Furthermore, TIFI reduced the ability of human aPL to stimulate thrombosis ¹⁶⁵ or fetal loss ¹⁶⁶ in mouse models. However, no new work on TIFI has been presented for some time.

Kolyada and colleagues have developed a dimer of the A1 domain of the apolipoprotein E receptor (ApoER2). This domain binds Domain V of β₂GPI, so that the dimer acts as an inhibitor preventing β₂GPI from binding to cells. In a series of papers this group showed that A1-A1 blocks binding of β₂GPI-anti-β₂GPI complexes to cardiolipin, ¹⁶⁷ and inhibits the induction of thrombosis by laser both in autoimmune (NZW x BXSB) F1 mice and non-autoimmune BALB/c mice infused with human APS-IgG. ¹⁶⁸ In the latter experiment 84% of A1-A1 was lost from the blood of the mice within an hour. More recently, the group achieved longer-term delivery of A1-A1 in (NZW x BXSB) F1 mice by implanting a subcutaneous osmotic pump. ¹⁶⁹ This led to a reduction in blood pressure in the mice – though this method may not be acceptable to patients. Unlike TIFI, there is currently no evidence that A1-A1 inhibits aPL-induced fetal loss in mice.

Peptides that target domain I

A group at University College London, UK have used recombinant Domain I produced by bacterial expression, rather than a peptide. Initially wild-type Domain I and a series of point mutants were expressed. ¹⁷⁰ These different products varied in ability to block binding of APS-IgG to β₂GPI. In the same mouse model previously used in the TIFI experiments, wild-type Domain I and a high-binding mutant inhibited the ability of APS-IgG to promote thrombosis whereas a mutant with no binding had no such inhibitory effect. ¹⁷¹ Recombinant Domain I has now been PEGylated in an effort to increase its in-vivo half-life and reduce potential immunogenicity. ¹⁷² A potential disadvantage of PEGylation is reduction of the biological activity of the PEGylated molecule. McDonnell et al, however, have shown that PEGylated Domain I retains the ability of non-PEGylated Domain I to block binding of APS-IgG to β₂GPI in-vitro and the ability to block thrombosis induced by APS-IgG in-vivo. ¹⁷² The PEGylated product can be produced at 95% purity, but its half-life in-vivo has not yet been demonstrated and there have been no experiments to investigate whether either PEGylated or non-PEGylated Domain I blocks APS-IgG-induced fetal loss. Table 1 summarises and compares evidence for peptide therapies based on Domain I and Domain V.

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Table 1.

Summary and comparison of evidence for peptide therapies based on Domain I and Domain V.

	Domain I-based treatment	Domain V-based treatments
Agents tested	Only recombinant Domain I	Both TIFI and A1-A1 dimer
Blocks binding in vitro	Yes – blocks binding of APS-IgG to β2GPI	Yes – blocks binding of β2GPI to cells or cardiolipin.
Blocks thrombosis induced by APS-IgG in vivo	Yes	Yes
Blocks fetal loss induced by APS-IgG in vivo	No	Yes (TIFI only)
Measures to increase half-life in vivo	Yes – by PEGylation	Not for TIFI. A1-A1 has not been modified chemically, but has been administered by a subcutaneous osmotic pump

Task force recommendations

Coenzyme Q10

An example of such an approach is a recent APS clinical trial utilizing coenzyme Q10 (CoQ10). ¹⁷³ CoQ10 participates as an electron carrier in mitochondrial and other membranes, with adequate CoQ10 levels seemingly protecting cells from protein oxidation and lipid peroxidation. In the general population, CoQ10 supplementation decreases the production of proinflammatory cytokines in the context of heart failure and coronary disease. ¹⁷⁴ The APS CoQ10 trial arose from an earlier preclinical study in which the same team demonstrated anti-inflammatory effects (less oxidative stress, less mitochondrial dysfunction) when CoQ10 was added ex vivo to peripheral blood cells of patients with APS. ¹⁷⁵ For the clinical trial, 36 patients with APS were randomized to receive ubiquinol (reduced CoQ10, 200 mg/day) or placebo for one month; approximately 90% of subjects completed the study. ¹⁷³ Among other positive effects, ubiquinol improved endothelial function and decreased monocyte expression of prothrombotic mediators. ¹⁷³ Furthermore, ubiquinol ameliorated NET release by neutrophils, while also downregulating neutrophil peroxides. ¹⁷³ The authors pointed out that in the absence of clinically significant side effects, and given potential therapeutic benefits, ubiquinol might act as a safe adjunct to standard therapies in APS. ¹⁷³

Adenosine receptor agonists

It has recently been reported that the neutrophils of APS patients have a reduced threshold for the release of NETs (prothrombotic tangles of DNA, histones, and granule-derived proteins expelled from dying neutrophils). ¹⁷⁶ NETs are required for APS-potentiated thrombosis in at least one human/mouse chimeric model of APS. ¹³ Furthermore, profiling of APS neutrophils has identified novel therapeutic targets in APS, ¹⁷⁷ including surface adhesion molecules. ¹⁷⁸ Given recent evidence suggesting that the second messenger cyclic AMP (cAMP) may suppress NET release in some contexts,^179,180 a preclinical study hypothesized that activation of surface adenosine receptors (which trigger cAMP formation in neutrophils) might mitigate the thrombotic manifestations of APS. ¹⁸¹ Indeed, selective agonism of the adenosine A_2A receptor (with CGS21680) appeared to be highly effective in suppressing antiphospholipid antibody-mediated NET release from control neutrophils, as well as spontaneous NET release from APS neutrophils. ¹⁸¹ In vivo, CGS21680 reduced thrombosis in the inferior vena cavae of both control mice and mice administered aPL. ¹⁸¹

Adenosine potentiation

The antithrombotic medication dipyridamole is known to potentiate adenosine signaling by increasing extracellular concentrations of adenosine and also by interfering with the breakdown of cAMP. Similar to CGS21680, dipyridamole appeared to suppress aPL-mediated NETosis (in adenosine A_2A receptor-dependent fashion) and to mitigate venous thrombosis in mice. ¹⁸¹ While dipyridamole has never been systematically studied in patients with APS, drugs with similar adenosine-amplifying properties such as defibrotide ¹⁸² and dilazep ¹⁸³ have been reported as effective in case reports and preclinical models.

Another recent study involved preclinical work in the area of aPL-induced pregnancy morbidity. ¹⁸⁴ Catabolism of extracellular ATP to adenosine by the cell-surface enzymes CD39 and CD73 has anti-inflammatory and antithrombotic effects in a number of contexts.^185,186 In a model involving passive transfer of human antiphospholipid antibodies into pregnant mice, pregnancy morbidity was exacerbated in mice with reduced ability to generate extracellular adenosine due to deficiency of either CD39 or CD73. ¹⁸⁴ In the absence of efficient adenosine generation, the placental decidua demonstrated increased tissue factor expression and complement deposition, as well as elevated oxidative stress and inflammatory cytokines. ¹⁸⁴ The potential for adenosine-mediated signaling to mitigate both thrombosis and pregnancy morbidity in APS-relevant models is intriguing and seems worthy of further investigation.

Other novel approaches

What other approaches may be on the horizon? One potential area of interest is targeting antibody-producing cells such as plasmablasts and longer-lived plasma cells. While agents that impact B cells via CD20 or the BAFF/BLyS receptor have not consistently demonstrated reduction in circulating aPL,^{113,114,128,129} it must be noted that these strategies do not directly impact antibody-producing cells. The potential utility of direct plasma cell agents in APS (for example, anti-CD38, as is currently employed for multiple myeloma) was recently emphasized by a preclinical study characterizing lymphocyte subsets of patients with primary APS. ¹⁸⁷ Elegant ex vivo experiments revealed that aPL were still robustly produced by peripheral-blood cells depleted of CD20+ B cells, but not when CD20- CD19+ B cells (i.e., CD38-positive plasmablasts) were depleted. ¹⁸⁷

Another target area is the development of anti-interferon therapies, as are being pursued for treatment of SLE. While the so-called interferon signature is classically associated with certain rheumatic diseases such as lupus and dermatomyositis, a number of groups have recently detected elevated levels of type I interferons in primary APS,^188,189 including potential associations with triple positivity and pregnancy morbidity. ¹⁹⁰ Whether neutralization of interferons might mitigate any of the thrombotic -- or perhaps more likely non-thrombotic -- manifestations of APS awaits further study.

A further area of potential interest is anti-FcRn targeted therapies that are being used in various autoimmune IgG driven diseases. Efgartigimod is a human IgG1 antibody Fc-fragment, a natural ligand of the neonatal Fc receptor (FcRn) that blocks FcRn, preventing IgG recycling, and causing targeted IgG degradation. In a Phase 2 study in 38 patients with primary immune thrombocytopenia predominantly refractory to previous lines of therapy, efgartigimod was well tolerated and had a favorable safety profile. It induced a rapid reduction of total IgG levels (mean change from baseline up to 63.7%), associated with clinically relevant increases in platelet counts: 46% patients on efgartigimod vs 25% on placebo achieved a platelet count of ≥50 × 10⁹/L on at least two occasions, and 38% vs 0% achieved ≥50 × 10⁹/L for at least 10 cumulative days. There was also a reduced proportion of patients with bleeding. The authors concluded that FcRn antagonism warrants further evaluation as a novel therapeutic approach in ITP. ¹⁹¹ This approach might be potentially useful in APS.

Task force recommendations