Concomitant Immunosuppressive Therapy and Eculizumab Use in Patients with Paroxysmal Nocturnal Hemoglobinuria: An International PNH Registry Analysis

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare hematologic disorder characterized by uncontrolled terminal complement activation. This may lead to intravascular hemolytic anemia, thrombosis, and other life-threatening consequences [1]. PNH has a global incidence of ∼1.3 cases/million inhabitants [2] with ∼500 US patients diagnosed per year [3]. Mutations in the phosphatidylinositol glycan class A (PIGA) gene within one or more hematopoietic stem cell (HSC) clones cause reduced or absent surface expression of the glycosylphosphatidylinositol (GPI)-anchored complement regulatory proteins CD55 and CD59, which leaves red blood cells (RBCs) susceptible to complement-mediated intravascular hemolysis, and PNH white cells and platelets susceptible to activation, which increases the risk of thrombosis [4].

PNH often arises in patients with aplastic anemia (AA) [5, 6]. AA is a rare disorder that is caused by lymphocyte-mediated destruction of HSCs [7‒9]. AA can be inherited or acquired and has a global incidence of 1.5–7 cases/million inhabitants [10] with 600–900 US patients diagnosed per year [11]. Acquired AA and PNH overlap in many patients [5, 6], as approximately 50% of patients with newly diagnosed AA have detectable PNH cells; however, the proportion of GPI-deficient erythrocytes or granulocytes is often small and may not immediately induce PNH symptoms [7, 12, 13]. As AA or PNH evolves, the clinical signs of either may reappear [5]. With increased screening for PNH cells in patients with AA, earlier diagnosis of AA-PNH (even if subclinical) allows for better monitoring and timely treatment of those patients who may become symptomatic or develop complications in the future [5, 14].

Inhibition of the terminal complement pathway is a pillar of PNH management. Eculizumab, a humanized monoclonal antibody that blocks terminal complement protein C5, was the first approved treatment for PNH [8] and has been the standard of care since 2007 [15, 16] with established effectiveness and safety over 21,000 patient-years [17]. Clinical trial data show that patients with PNH treated with eculizumab experienced a reduction in thrombosis risk, reduction in RBC transfusion requirements, improvements in anemia, a greater quality of life, and improved survival [18‒20]. These data are further supported by real-world evidence from the International PNH Registry (NCT01374360), an ongoing prospective, multinational, observational study initially established in 2004 to record the natural history of patients with PNH [9]. Registry data showed that treatment with eculizumab was effective and safe in patients with PNH symptoms of varying intensity [21‒25].

Treatments for AA include blood transfusions, immunosuppressive therapy (IST, inclusive of cyclosporine and anti-thymocyte globulin [ATG]), or bone marrow transplantation (BMT). Since most patients are not suitable candidates for BMT, first-line medical management generally involves IST [7, 26]. Monitoring the PNH cell population in patients with AA is important not only because these cells can multiply and eventually cause PNH-related symptoms, but evidence indicates that the presence of PNH cells in patients with AA may also be predictive of a patient’s responsiveness to IST [27, 28]. Despite what is known about treating patients with eculizumab and IST separately, limited data exist in patients with AA-PNH who may require treatment with both eculizumab and IST [14, 29, 30]. Furthermore, it is unknown whether the order of eculizumab and IST administration or concomitant administration affects the safety and effectiveness of one or both treatments. Here, we describe the results of an analysis that used patient data from the International PNH Registry to evaluate the real-world effectiveness and safety of eculizumab in the context of a treatment sequence with IST.

The International PNH Registry (NCT01374360) is an ongoing, prospective, multinational, observational study to record the natural history of PNH and to evaluate the long-term safety and effectiveness of eculizumab. Patients enrolled in the PNH Registry had a clinical diagnosis of PNH (by any applicable diagnostic method) and/or a detectable PNH clone (defined as a population of GPI-deficient granulocytes and/or erythrocytes) of ≥0.01% [9]. This study was performed in accordance with the principles of the Declaration of Helsinki. The Registry was approved by the institutional review boards (or equivalent) of participating centers and is being conducted in accordance with the International Council for Harmonisation Good Clinical Practice guidelines. All patients provided written informed consent before inclusion in the Registry. Alexion, AstraZeneca Rare Disease, sponsors the Registry, which is overseen by an independent executive committee of international PNH experts [9]. To be eligible for this analysis, patients must have been enrolled in the Registry on or before January 1, 2018, with a known date of birth, gender, Registry enrollment date, and eculizumab treatment status. Patients were required to have a history of AA, defined as a record in the case report form of “yes” for aplastic or hyperplastic anemia, as of their last follow-up visit in the Registry, have a history of receiving eculizumab treatment, have a history of being treated with IST (cyclosporine and/or ATG) after diagnosis with PNH as of their last follow-up visit in the Registry, and have a known IST initiation date. If a patient discontinued IST or eculizumab at any point, a known date of last dose was also required.

Eligible patients from the Registry were divided into two groups based on the sequence in which they received eculizumab and IST (Fig. 1): patients receiving IST first and then concomitant eculizumab (IST + c-Ecu) and patients receiving eculizumab first and then concomitant IST (Ecu + c-IST).

In order to evaluate the safety and effectiveness of eculizumab and IST separately, time points of interest, baseline and last follow-up, were defined as follows: for the eculizumab analyses, baseline was defined as the first recorded date of eculizumab treatment and the last follow-up visit was considered the last recorded date of eculizumab; for the IST analyses, baseline was defined as the first recorded date of IST treatment or the first recorded PNH diagnosis (whichever was later) and the last follow-up visit was considered the last recorded date of IST (Fig. 1). For both analyses, patients with a follow-up period of less than 6 months were excluded.

For eculizumab effectiveness analyses, lactate dehydrogenase (LDH) ratio (LDH/upper limit of normal [ULN], expressed as ×ULN), thrombotic event (TE) rates, select hematological laboratory values (platelets, absolute neutrophils, absolute reticulocytes, hemoglobin), and RBC transfusion rate were assessed. For IST effectiveness analyses, select hematological laboratory values (platelets, absolute neutrophils, absolute reticulocytes, hemoglobin) and RBC transfusion rate were assessed. Eculizumab and IST safety analyses included incidence rates of infections (i.e., Neisseria, encapsulated bacterial infection, or other serious infection), major adverse vascular events (MAVEs), and deaths.

Descriptive statistics were generated for baseline patient demographics and disease characteristics. Rates of RBC transfusions and MAVEs (including TEs) with 95% confidence intervals (CIs) during the time periods of interest were estimated using Poisson regression with over-dispersion or generalized estimating equations with a log link. Rate ratios and 95% CIs of RBC transfusions, TEs, and MAVEs between patient cohorts were estimated using Poisson regression with treatment duration as an offset term. Least squares mean change in hematological laboratory values from baseline to last follow-up visit were estimated using general linear mixed models with adjustment for baseline values and patient cohort. Analyses of hematology parameters and transfusion rates over time were conducted in patients who had data at enrollment and at their last follow-up visit.

As of the data cutoff of January 1, 2018, the International PNH Registry included 5,065 patients. For the analyses focusing on the safety and effectiveness of eculizumab (“eculizumab analyses”), 181 patients met all inclusion criteria: 138 patients receiving IST first followed by concomitant eculizumab (IST + c-Ecu) and 43 patients receiving eculizumab followed by concomitant IST (Ecu + c-IST) (Fig. 1). Patient demographics in both groups were generally similar and their disease characteristics met clinical expectations for the individual group (Table 1).

Patients in both groups had similar reductions in the least squares (LS) mean changes in LDH ratio from baseline (IST + c-Ecu, −3.4; Ecu + c-IST, −3.5; p = 0.88; Fig. 2a). The rate ratio of TEs (95% CI) was also similar in both groups with 0.3 (0.1–0.7) in the IST + c-Ecu group and 0.3 (0.0–2.7) in the Ecu + c-IST group (Fig. 2b).

Patients in the IST + c-Ecu group experienced a decrease in RBC transfusion rate from the year before baseline to last follow-up (6.3 to 4.2 per 100 patient-years) and patients in the Ecu + c-IST group experienced an increase (6.3–7.7 per 100 patient-years; Fig. 3a). The RBC transfusion rate ratio (95% CI) was 0.7 (0.6–0.7) in the IST + c-Ecu group and 1.2 (1.0–1.4) in the Ecu + c-IST group.

Some differences were noted in blood count parameters between groups. The LS mean change in platelets from baseline to last follow-up was 8.2 × 10⁹/L in the IST + c-Ecu group and −30.6 × 10⁹/L in the Ecu + c-IST group (p < 0.01; Table 2). Patients in the Ecu + c-IST group experienced a reduction in absolute neutrophils from baseline of −0.7 × 10⁹/L compared with −0.1 × 10⁹/L for the IST + c-Ecu group (p < 0.05). The LS mean change in absolute reticulocytes from baseline in the IST + c-Ecu group was 22.9 × 10⁹/L and 6.1 × 10⁹/L in the Ecu + c-IST group (p = 0.63). The LS mean change in hemoglobin levels was 8.2 g/L in the IST + c-Ecu group and −1.8 g/L in the Ecu + c-IST group (p = 0.02).

For the analyses focusing on safety and effectiveness of IST (“IST analyses”), 195 patients met all inclusion criteria: 162 patients for IST + c-Ecu and 33 patients for Ecu + c-IST. In addition, 87 patients received IST alone. Patient demographics among groups were generally similar and their disease characteristics met clinical expectations for the individual group (Table 3).

Patients in the IST + c-Ecu group had a lower RBC transfusion rate in the year prior to baseline (1.3 per 100 patient-years) compared with patients in the Ecu + c-IST cohort (9.3 per 100 patient-years) (Fig. 3b). The RBC transfusion rate in the year prior to baseline was 0.2 per 100 patient-years for those who received IST alone. During the follow-up period, the RBC transfusion rate was 2.8 per 100 patient-years in the IST + c-Ecu group and 7.2 per 100 patient-years in the Ecu + c-IST group. The RBC transfusion rate ratio (95% CI) was 2.2 (1.9–2.6) in the IST + c-Ecu group and 0.8 (0.7–0.9) in the Ecu + c-IST group. There were no RBC transfusions in the cohort who received IST alone.

The LS mean change in platelets from baseline to last follow-up was 75.3 × 10⁹/L in the IST + c-Ecu group, 47.1 × 10⁹/L in the Ecu + c-IST group, and 58.3 × 10⁹/L in the IST alone group (Table 4). Patients in the IST + c-Ecu, Ecu + c-IST, and IST alone groups experienced increases in absolute neutrophils from baseline of 1.0 × 10⁹/L, 0.1 × 10⁹/L, and 1.2 × 10⁹/L, respectively. The LS mean change in absolute reticulocytes from baseline was 24.8 × 10⁹/L in the IST + c-Ecu group, −16.6 × 10⁹/L in the Ecu + c-IST group, and −640.2 × 10⁹/L in the IST alone group. The LS mean change in hemoglobin levels was 17.4 g/L in the IST + c-Ecu group, −2.5 g/L in the Ecu + c-IST group, and 19.4 g/L in the IST alone group.

In the eculizumab analyses, the rate (95% CI) of infections in patients in the IST + c-Ecu group was 5.3 per 100 patient-years (3.1–9.2) and 10.9 per 100 patient-years (2.7–43.6) in the Ecu + c-IST group (Table 5). The incidence rate of MAVEs and TEs (95% CI) in the IST + c-Ecu group was 1.7 (0.9–3.2) and 1.3 (0.6–2.8) per 100 patient-years, respectively, and 1.4 (0.4–5.6) and 0.7 (0.1–0.5) per 100 patient-years, respectively, in the Ecu + c-IST group. The incidence rate of deaths (95% CI) was 1.1 per 100 patient-years (0.5–2.6) in the IST + c-Ecu group and 0.7 per 100 patient-years (0.1–5.0) in the Ecu + c-IST group.

In the IST analyses, the rate (95% CI) of infections was 4.3 per 100 patient-years (2.8–6.6) in patients in the IST + c-Ecu group, 23.4 per 100 patient-years (5.8–93.4) in the Ecu + c-IST group, and 1.9 per 100 patient-years (0.5–7.4) in the IST alone group (Table 6). The incidence rate (95% CI) of MAVEs and TEs in the IST + c-Ecu group was 4.1 (2.9–5.8) and 2.7 (1.8–4.2) per 100 patient-years, respectively. In the Ecu + c-IST group, incidence rates (95% CI) of MAVEs and TEs were 1.1 (0.2–7.9) and 1.1 (0.2–7.9) per 100 patient-years, respectively. In the IST alone group, incidence rates (95% CI) of MAVEs and TEs were 2.3 (1.0–5.5) and 1.4 (0.4–4.3) per 100 patient-years, respectively. The incidence rate (95% CI) of deaths was 0.9 per 100 patient-years (0.4–1.9) in the IST + c-Ecu group and 1.1 per 100 patient-years (0.2–7.9) in the Ecu + c-IST group. There were no deaths in the IST alone group.

In this analysis of real-world data from patients with AA-PNH enrolled in the International PNH Registry, there were no clinically meaningful differences in measures of eculizumab effectiveness (e.g., LDH ratio, TE rate) regardless of concomitant IST and sequence of use (whether eculizumab is administered before or after commencement of IST). Furthermore, hematological parameters (i.e., platelet count, reticulocyte count, and hemoglobin) generally improved in most patients treated with eculizumab, except for those who commenced IST after initiation of eculizumab. There were fewer patients in the Ecu + c-IST group, though a plausible explanation for the decrease in hematological parameters in patients who commenced IST after eculizumab is the subsequent development of AA in these patients. The safety analyses of both eculizumab and IST were consistent with what has been observed in patients with AA-PNH with each treatment regimen administered separately [30].

In the eculizumab analyses, RBC transfusion rates decreased in the IST + c-Ecu group and increased in the Ecu + c-IST group. On the other hand, in the IST analyses, RBC transfusion rates increased in the IST + c-Ecu group and decreased in the Ecu + c-IST group. Both PNH and bone marrow failure can contribute to anemia requiring an RBC transfusion. A complicating factor was that the baseline periods in each group were defined differently. In the eculizumab analyses, the baseline in the IST + c-Ecu group occurred after patients had initiated IST, which was a period when bone marrow failure was assumed to be the underlying condition. In the Ecu + c-IST group, baseline occurred after patients had initiated eculizumab, which was a period when hemolysis was assumed to be the underlying condition. Due to this design, the observed increase in RBC transfusion rate occurred in groups of patients who likely had PNH and bone marrow failure that required treatment with IST and eculizumab but was not the effect of the treatments.

The data described here have important relevance for clinicians and build upon recent publications that describe similar findings in smaller patient populations. For example, a recent UK case series showed that patients with AA-PNH treated concurrently with eculizumab and IST for treatment of AA (n = 25) did not have significantly different outcomes compared with age-matched control patients diagnosed with only AA. The authors concluded that treatment for AA should not be influenced by the presence of PNH [14]. Additionally, a retrospective US study of 8 patients with severe AA-PNH treated with eculizumab prior to BMT conditioning (which contains treatment with ATG in addition to other chemotherapy agents) showed that all patients were successfully transplanted without adverse events related to inhibition of the complement C5 pathway; this result is notable given that “ATG has also been shown to cause hypercoagulability via complement-mediated mechanisms” [29]. The findings from the current registry analyses provide further evidence to suggest that concomitant treatment with eculizumab and IST does not impact the effectiveness of either therapy and does not raise any new safety concerns in patients with AA-PNH.

Differences among the 3 patient populations in this analysis (the IST + c-Ecu group, the Ecu + c-IST group, and the IST alone group) warrant consideration. Patients treated with IST and then eculizumab (with or without an overlap in treatment) may be more likely to have had a PNH clone and AA at diagnosis, which may eventually have caused hemolysis or thrombosis, prompting the initiation of eculizumab. In contrast, patients treated with eculizumab at diagnosis likely had “primary” PNH. The majority of patients with AA express PNH mutant cells at diagnosis, and a considerable proportion of these patients will evolve to frank hemolytic PNH [28, 31]. In patients with AA and PNH, a larger population of PNH cells correlates with the presence of clinical hemolysis [28, 32]. The development of PNH in the setting of AA is typically characterized by a smaller population of PNH cells and by lower absolute neutrophil and platelet counts at diagnosis than “primary” PNH [28, 31, 33, 34]. As observed in the IST alone and IST + c-Ecu groups, both groups had a smaller mean population of PNH cells and lower platelet counts at baseline compared to the Ecu + c-IST group. Irrespective of the size of the population of PNH cells, the presence of PNH cells in patients with AA is associated with a greater response to IST as well as higher reticulocyte counts and LDH values [26, 33].

The major limitation of this study is the observational nature of the Registry. Although data from a randomized trial specifically designed to rigorously address the clinical questions explored in this analysis are preferred, the rarity of AA-PNH makes the reality of conducting such a trial challenging to implement. Patients enrolled in the Registry are more heterogeneous, which can be advantageous for addressing the generalizability of a drug’s effect in a broad patient population but can also lead to difficulties in identifying and/or controlling for confounding variables, especially for AA-specific parameters. For unclear reasons, the majority of patients in both analyses received cyclosporine alone rather than the standard of care for IST (i.e., ATG plus cyclosporine [7, 35]), limiting the generalizability of the results. Also, owing to the small sample of patients receiving ATG only or ATG plus cyclosporine, conclusions cannot be made as to the influence of complement inhibition on the effectiveness of treatment with ATG. Another limitation is that data were only available for a limited number of patients at the time points of interest because the Registry was not designed to assess IST effectiveness and thus did not specifically aim to collect data at the start of IST use. However, the relative paucity of information on AA should not be considered a weakness of the Registry itself, as the Registry was originally designed to capture information related to PNH.

In summary, the results of this retrospective study from the International PNH Registry showed that there was no clinically meaningful impact on the effectiveness of concomitant eculizumab and IST, regardless of treatment sequence. The combination also indicated no safety concerns regarding either therapy. Furthermore, differences observed in RBC transfusions and laboratory parameters likely reflect the evolution of the disease course or the underlying severity of AA. This analysis of Registry data provides clinicians with evidence from a real-world setting and contributes to the clinical understanding of AA-PNH.

Statistical consultation was provided by Ami Patel, PhD, MPH, of Alexion Pharmaceuticals, Inc., and Ke Zu, PhD, who was an employee of Alexion at the time of the study. Medical writing support was provided by Apurva Davé, PhD, and Amanda Martin, PhD, of Medical Expressions (Chicago, IL, USA), and was funded by Alexion Pharmaceuticals, Inc.

The Registry was approved by the institutional review boards (or equivalent) of participating centers and has been conducted in accordance with the International Council for Harmonisation Good Clinical Practice guidelines. The Registry is sponsored by Alexion, AstraZeneca Rare Disease, which is overseen by an independent executive committee of international PNH experts. This study was performed in accordance with the principles of the Declaration of Helsinki. All patients had provided written informed consent to have their data entered into the International PNH Registry.

Anita Hill, at the time of study, has received honoraria and/or consulting fees from Akari Therapeutics; Alexion, AstraZeneca Rare Disease; Apellis; Bioverativ; Novartis; Ra Pharma; Regeneron; and Roche and is a current employee and stockholder of Alexion, AstraZeneca Rare Disease.

Morag Griffin has served on advisory boards for Alexion, AstraZeneca Rare Disease, and Biocryst Pharmaceuticals and has received honoraria from Alexion, AstraZeneca Rare Disease.

Régis Peffault de Latour has received consultancies, honoraria, and research funding from Alexion, AstraZeneca Rare Disease; Novartis; and Pfizer and research funding from Amgen.

Austin G. Kulasekararaj has received honoraria from Alexion, AstraZeneca Rare Disease; Amgen; Celgene; Novartis; and Ra Pharma; has served on the Board of Directors or as an advisory board member for Alexion, AstraZeneca Rare Disease; Amgen; Celgene; Novartis; and Ra Pharma; and has received consulting fees from Achillion; Akari Therapeutics; Alexion, AstraZeneca Rare Disease; Celgene; and Novartis.

Robert Brodsky has received research funding from Achillion and has served on the Board of Directors or as an advisory board member for, and received grant funding from, Alexion, AstraZeneca Rare Disease.

Jaroslaw Maciejewski has received consulting fees from Alexion, AstraZeneca Rare Disease; Apellis Pharmaceuticals; and Ra Pharma; and speaker fees from, and is a member of the Executive Committee of the International PNH Registry for, Alexion, AstraZeneca Rare Disease.

Jing Marantz was an employee of Alexion, AstraZeneca Rare Disease, at the time when the study was conducted.

Philippe Gustovic has served as an employee and stockholder of Alexion, AstraZeneca Rare Disease.

Hubert Schrezenmeier has received honoraria and grants (to the University Hospital of Ulm) from Alexion, AstraZeneca Rare Disease, and Roche and grants (to the University Hospital of Ulm) from Apellis, Ra Pharmaceuticals, and Sanofi.

Alexion, AstraZeneca Rare Disease, funded the study and was involved in the study design; collection, analysis, and interpretation of data; and writing of the manuscript.

Anita Hill, Régis Peffault de Latour, Austin G. Kulasekararaj, Morag Griffin, Robert A. Brodsky, Jaroslaw P. Maciejewski, Jing L. Marantz, Philippe Gustovic, and Hubert Schrezenmeier were involved in the study design, reviewed and revised drafts of the manuscript, and approved the final draft for submission.

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Anita Hill: affiliation at the time of study; current affiliation: Alexion, AstraZeneca Rare Disease, Uxbridge, UK.Jing L. Marantz: affiliation at the time of study; current affiliation: Krystal Biotech, Inc., Pittsburgh, PA, USA