Mark R. Nicolls

Characterization of Connective Tissue Disease-Associated Pulmonary Arterial Hypertension From REVEAL: Identifying Systemic Sclerosis as a Unique Phenotype

BACKGROUND REVEAL (the Registry to Evaluate Early and Long-term Pulmonary Arterial Hypertension Disease Management) is the largest US cohort of patients with pulmonary arterial hypertension (PAH) confirmed by right-sided heart catheterization (RHC), providing a more comprehensive subgroup characterization than previously possible. We used REVEAL to analyze the clinical features of patients with connective tissue disease-associated PAH (CTD-APAH). METHODS All newly and previously diagnosed patients with World Health Organization (WHO) group 1 PAH meeting RHC criteria at 54 US centers were consecutively enrolled. Cross-sectional and 1-year mortality and hospitalization analyses from time of enrollment compared CTD-APAH to idiopathic disease and systemic sclerosis (SSc) to systemic lupus erythematosus (SLE), mixed connective tissue disease (MCTD), and rheumatoid arthritis (RA). RESULTS Compared with patients with idiopathic disease (n = 1,251), patients with CTD-APAH (n = 641) had better hemodynamics and favorable right ventricular echocardiographic findings but a higher prevalence of pericardial effusions, lower 6-min walk distance (300.5 ± 118.0 vs 329.4 ± 134.7 m, P = .01), higher B-type natriuretic peptide (BNP) levels (432.8 ± 789.1 vs 245.6 ± 427.2 pg/mL, P < .0001), and lower diffusing capacity of carbon monoxide (Dlco) (44.9% ± 18.0% vs 63.6% ± 22.1% predicted, P < .0001). One-year survival and freedom from hospitalization were lower in the CTD-APAH group (86% vs 93%, P < .0001; 67% vs 73%, P = .03). Compared with patients with SSc-APAH (n = 399), those with other CTDs (SLE, n = 110; MCTD, n = 52; RA, n = 28) had similar hemodynamics; however, patients with SSc-APAH had the highest BNP levels (552.2 ± 977.8 pg/mL), lowest Dlco (41.2% ± 16.3% predicted), and poorest 1-year survival (82% vs 94% in SLE-APAH, 88% in MCTD-APAH, and 96% in RA-APAH). CONCLUSIONS Patients with SSc-APAH demonstrate a unique phenotype with the highest BNP levels, lowest Dlco, and poorest survival of all CTD-APAH subgroups. TRIAL REGISTRY ClinicalTrials.gov; No.: NCT00370214; URL: clinicaltrials.gov.

Autoimmunity and pulmonary hypertension: a perspective

The association between autoimmunity and pulmonary arterial hypertension (PAH) has been appreciated for >40 yrs, but how autoimmune injury might contribute to the pathogenesis of this disease has only been examined in a case-specific manner. It is becoming increasingly clear that a variety of diverse clinical diseases, ranging from viral infections to connective tissue disorders, can culminate in pulmonary vascular pathology that is indistinguishable. Is there a hitherto unappreciated biology that unites these seemingly unrelated conditions? The answer to this question may come from the increasing body of evidence concerned with the central importance of regulatory T-cells in preventing inappropriate B-cell activity. Two striking similarities between conditions associated with severe angioproliferative pulmonary hypertension are a defect in the CD4 T-cell compartment and auto-antibody production. Pathogenic auto-antibodies targeting endothelial cells are capable of inducing vascular endothelial apoptosis and may initiate the development of PAH. The present review will focus on what is known about autoimmune phenomena in pulmonary arterial hypertension patients, in order to better consider whether an early loss of self-tolerance followed by autoimmune injury could influence the early development of severe angioproliferative pulmonary hypertension.

Inflammation and Immunity in the Pathogenesis of Pulmonary Arterial Hypertension

This review summarizes an expanding body of knowledge indicating that failure to resolve inflammation and altered immune processes underlie the development of pulmonary arterial hypertension. The chemokines and cytokines implicated in pulmonary arterial hypertension that could form a biomarker platform are discussed. Pre-clinical studies that provide the basis for dysregulated immunity in animal models of the disease are reviewed. In addition, we present therapies that target inflammatory/immune mechanisms that are currently enrolling patients, and discuss others in development. We show how genetic and metabolic abnormalities are inextricably linked to dysregulated immunity and adverse remodeling in the pulmonary arteries.

Original ResearchPulmonary Arterial HypertensionCharacterization of Connective Tissue Disease-Associated Pulmonary Arterial Hypertension From REVEAL: Identifying Systemic Sclerosis as a Unique Phenotype

BACKGROUND REVEAL (the Registry to Evaluate Early and Long-term Pulmonary Arterial Hypertension Disease Management) is the largest US cohort of patients with pulmonary arterial hypertension (PAH) confirmed by right-sided heart catheterization (RHC), providing a more comprehensive subgroup characterization than previously possible. We used REVEAL to analyze the clinical features of patients with connective tissue disease-associated PAH (CTD-APAH). METHODS All newly and previously diagnosed patients with World Health Organization (WHO) group 1 PAH meeting RHC criteria at 54 US centers were consecutively enrolled. Cross-sectional and 1-year mortality and hospitalization analyses from time of enrollment compared CTD-APAH to idiopathic disease and systemic sclerosis (SSc) to systemic lupus erythematosus (SLE), mixed connective tissue disease (MCTD), and rheumatoid arthritis (RA). RESULTS Compared with patients with idiopathic disease (n = 1,251), patients with CTD-APAH (n = 641) had better hemodynamics and favorable right ventricular echocardiographic findings but a higher prevalence of pericardial effusions, lower 6-min walk distance (300.5 ± 118.0 vs 329.4 ± 134.7 m, P = .01), higher B-type natriuretic peptide (BNP) levels (432.8 ± 789.1 vs 245.6 ± 427.2 pg/mL, P < .0001), and lower diffusing capacity of carbon monoxide (Dlco) (44.9% ± 18.0% vs 63.6% ± 22.1% predicted, P < .0001). One-year survival and freedom from hospitalization were lower in the CTD-APAH group (86% vs 93%, P < .0001; 67% vs 73%, P = .03). Compared with patients with SSc-APAH (n = 399), those with other CTDs (SLE, n = 110; MCTD, n = 52; RA, n = 28) had similar hemodynamics; however, patients with SSc-APAH had the highest BNP levels (552.2 ± 977.8 pg/mL), lowest Dlco (41.2% ± 16.3% predicted), and poorest 1-year survival (82% vs 94% in SLE-APAH, 88% in MCTD-APAH, and 96% in RA-APAH). CONCLUSIONS Patients with SSc-APAH demonstrate a unique phenotype with the highest BNP levels, lowest Dlco, and poorest survival of all CTD-APAH subgroups. TRIAL REGISTRY ClinicalTrials.gov; No.: NCT00370214; URL: clinicaltrials.gov.

Pathobiology of pulmonary arterial hypertension and right ventricular failure

Pulmonary arterial hypertension (PAH) is no longer an orphan disease. There are three different classes of drugs for the treatment of PAH that are currently being used and an increasing number of patients are being treated with a single drug or combination therapy. During the last 25 yrs, new insights into the pathobiology of PAH have been gained. The classical mechanical concepts of pressure, flow, shear stress, right ventricle wall stress and impedance have been complemented with the new concepts of cell injury and repair and interactions of complex multicellular systems. Integrating these concepts will become critical as we design new medical therapies in order to change the prognosis of patients with these fatal diseases. This review intends to summarise recent pathobiological concepts of PAH and right ventricle failure mainly derived from human studies, which reflect the progress made in the understanding of this complex group of pulmonary vascular diseases.

Induction of long-term specific tolerance to allografts in rats by therapy with an anti-CD3-like monoclonal antibody

Monoclonal antibodies to CDS have been shown to activate T cells in vivo and in vitro but have also been shown to render T cells anergic in vitro. In this study G4.18, a mouse IgG3 mAb, was produced that appeared to recognize CDS by its binding to all peripheral T cells, including a population not recognized by mAb to TCR-α/β that was presumed to be TCR-γ/δ cells. It precipitated molecules in the 24–26 kd region consistent with the CD3 complex as well as molecules ∼45 and ∼49 kd that corresponded to TCR α and β chains and a 92-kd complex. Incubating T cells for 24 hr with saturating concentrations of G4.18 caused modulation of the TCR complex. In vitro, it activated T cells but only if prebound to plastic. In solution it inhibited MLC and CML, but not PHA or Con A activation. In vivo, G4.18 was not toxic even in high doses, and this was thought to be due to the inability of this mAb to activate T cells in vitro because the rat lacks Fc receptors for mouse IgGS. Therapy with G4.18 resulted in transient modulation of TCR/CD3 on T cells and depletion of these cells from blood. G4.18 had no depleting effects by lymph node or spleen cells but caused marked, transient thymic involution. Therapy with G4.18 also induced indefinite survival (&100 days) of PVG (RTF) heart grafts but not skin grafts in DA (RTFα) hosts. These hosts with long-surviving cardiac transplants, when grafted from PVG skin, accepted these grafts but rejected third-party skin in first-set. Thus G4.18 was shown to induce long-term specific tolerance to an organ allograft.

Regulatory T Cells Limit Vascular Endothelial Injury and Prevent Pulmonary Hypertension

Rationale: Pulmonary arterial hypertension (PAH) is an incurable disease associated with viral infections and connective tissue diseases. The relationship between inflammation and disease pathogenesis in these disorders remains poorly understood. Objective: To determine whether immune dysregulation due to absent T-cell populations directly contributes to the development of PAH. Methods and Results: Vascular endothelial growth factor receptor 2 (VEGFR2) blockade induced significant pulmonary endothelial apoptosis in T-cell-deficient rats but not in immune-reconstituted (IR) rats. T cell–lymphopenia in association with VEGFR2 blockade resulted in periarteriolar inflammation with macrophages, and B cells even prior to vascular remodeling and elevated pulmonary pressures. IR prevented early inflammation and attenuated PAH development. IR with either CD8 T cells alone or with CD4-depleted spleen cells was ineffective in preventing PAH, whereas CD4-depleting immunocompetent euthymic animals increased PAH susceptibility. IR with either CD4+CD25hi or CD4+CD25− T cell subsets prior to vascular injury attenuated the development of PAH. IR limited perivascular inflammation and endothelial apoptosis in rat lungs in association with increased FoxP3+, IL-10- and TGF-&bgr;-expressing CD4 cells, and upregulation of pulmonary bone morphogenetic protein receptor type 2 (BMPR2)–expressing cells, a receptor that activates endothelial cell survival pathways. Conclusions: PAH may arise when regulatory T-cell (Treg) activity fails to control endothelial injury. These studies suggest that regulatory T cells normally function to limit vascular injury and may protect against the development of PAH.

Following Universal Prophylaxis with Intravenous Ganciclovir and Cytomegalovirus Immune Globulin, Valganciclovir is Safe and Effective for Prevention of CMV Infection Following Lung Transplantation

We prospectively determined the safety and efficacy of valganciclovir for prevention of cytomegalovirus (CMV) in at‐risk (donor positive/recipient negative [D+/R−] or R+) lung transplant recipients. We also determined the length of prophylaxis required to significantly decrease both CMV infection and disease. Consecutive lung transplant recipients surviving >30 days (n = 90) received combination prophylaxis with intravenous (i.v.) ganciclovir (GCV) 5 mg/kg/day and cytomegalovirus immune globulin (CMV‐IVIG) followed by valganciclovir (450 mg twice‐daily) to complete 180, 270 or 365 days of prophylaxis. This group was compared to a historical group (n = 140) who received high‐dose oral acyclovir following i.v. GCV and CMV‐IVIG. CMV disease was significantly lower in patients receiving valganciclovir compared to acyclovir (2.2% vs. 20%; p < 0.0001). Freedom from CMV infection and disease was significantly greater (p < 0.02) in patients receiving 180, 270 or 365 days of prophylaxis (90%, 95% and 90%, respectively) compared to those receiving 100–179 days (64%) or <100 days (59%). No patient receiving valganciclovir died during the study. Following prophylaxis with i.v. GCV and CMV‐IVIG, valganciclovir is safe and effective for prevention of CMV infection and disease in at‐risk lung transplant recipients. The required length of prophylaxis was at least 180 days.

Blocking Macrophage Leukotriene B4 Prevents Endothelial Injury and Reverses Pulmonary Hypertension

In a rat model of pulmonary hypertension, inhibition of LTB4 synthesis in macrophages that accumulate in lung tissue reverses the disease. How to Open a Blocked Vessel Like the pressure that builds up in a kinked garden hose, pulmonary hypertension occurs when the blood vessels in the lung become occluded. This hard-to-treat disease can arise in various settings, sometimes along with collagen vascular disease or HIV infection. It ultimately leads to heart failure as the heart tries to pump against higher resistance. Now, Tian and her colleagues show that certain types of pulmonary hypertension may be caused by a leukotriene B4 (LTB4) released from the macrophages that accumulate in lung tissue and that interruption of this process can reverse the disease. Although much of their evidence comes from a rat model of hypertension, the same may be true of some patients as well. Treatment of athymic rats with the tyrosine kinase inhibitor SU5416 causes them to acquire pulmonary hypertension. At the same time, macrophages gather around the small arterioles of the lung and synthesize an excess amount of LTB4. This leukotriene injures the endothelial cells of the nearby vessels, causing apoptosis while simultaneously provoking abnormal proliferation of the smooth muscle cells. This excess cell division results in arterial occlusion and hypertension. The authors found that damping down excess LTB4 by inhibiting its biosynthesis could reverse disease: In treated animals, cardiac function improved and obstructed arterioles opened. These results may apply to certain patients with pulmonary hypertension: Among a group of 19 patients, those that had pulmonary hypertension secondary to a connective tissue disease generally show higher LTB4 in serum. The next step will be to see whether therapies directed toward the LTB4 signaling system can help to clear the arterioles in patients with pulmonary hypertension, at least in those with associated inflammation. Pulmonary hypertension (PH) is a serious condition that affects mainly young and middle-aged women, and its etiology is poorly understood. A prominent pathological feature of PH is accumulation of macrophages near the arterioles of the lung. In both clinical tissue and the SU5416 (SU)/athymic rat model of severe PH, we found that the accumulated macrophages expressed high levels of leukotriene A4 hydrolase (LTA4H), the biosynthetic enzyme for leukotriene B4 (LTB4). Moreover, macrophage-derived LTB4 directly induced apoptosis in pulmonary artery endothelial cells (PAECs). Further, LTB4 induced proliferation and hypertrophy of human pulmonary artery smooth muscle cells. We found that LTB4 acted through its receptor, BLT1, to induce PAEC apoptosis by inhibiting the protective endothelial sphingosine kinase 1 (Sphk1)–endothelial nitric oxide synthase (eNOS) pathway. Blocking LTA4H decreased in vivo LTB4 levels, prevented PAEC apoptosis, restored Sphk1-eNOS signaling, and reversed fulminant PH in the SU/athymic rat model of PH. Antagonizing BLT1 similarly reversed established PH. Inhibition of LTB4 biosynthesis or signal transduction in SU-treated athymic rats with established disease also improved cardiac function and reopened obstructed arterioles; this approach was also effective in the monocrotaline model of severe PH. Human plexiform lesions, one hallmark of PH, showed increased numbers of macrophages, which expressed LTA4H, and patients with connective tissue disease–associated pulmonary arterial hypertension exhibited significantly higher LTB4 concentrations in the systemic circulation than did healthy subjects. These results uncover a possible role for macrophage-derived LTB4 in PH pathogenesis and identify a pathway that may be amenable to therapeutic targeting.

LFA-1 (CD11a) as a Therapeutic Target

Leukocyte function associated antigen‐1 (LFA‐1) was one of the earliest of cell‐surface molecules identified by monoclonal antibodies generated against leukocyte immunogens. This integrin heterodimer is perhaps best known as a classic adhesion molecule facilitating the interaction between T cells and antigen‐presenting cells. However, varied studies indicate that LFA‐1 has multi‐faceted roles in the immune response including adhesion, activation and trafficking of leukocyte populations. While there has been long‐standing interest in LFA‐1 as a therapeutic target for regulating immunity, anti‐LFA‐1 therapy is still not a first‐line indication for any clinical condition. Antagonism of LFA‐1 with monoclonal antibodies, either alone or in combination with other agents, can result in regulatory tolerance in vivo. Furthermore, new generation humanized anti‐LFA‐1 monoclonal antibodies (Efalizumab) show at least modest promise for continued application in clinical trials. Thus, anti‐LFA‐1 forms a potential, but still largely unexploited, immunotherapy which may find its greatest application as an agent which augments other therapies.