Eculizumab's Unintentional Mayhem: A Systematic Review

Eculizumab, first-line therapy for paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS), has infectious side effects in addition to its therapeutic benefits. This study aims to discuss the mechanism of development of infections, prevention, and timely treatment to prevent complications such as septic shock and mortality. The study was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) checklist and reporting guidelines for systematic review. Inclusion and exclusion criteria were determined. A total of 10 research papers were extracted after exploring Pubmed and Google Scholar from 2001 to 2021. The New Castle Ottawa Questionnaire for non-randomized clinical trials and the National Institutes of Health (NIH) quality assessment tool for case reports and case series were used to assess the risk of bias. The studies included in this systematic review describe infections with Neisseria meningitidis, Neisseria gonorrhoeae, unusual Neisseria species, Moraxella lacunata, and Pseudomonas aeruginosa. The main goal of this review is to impress upon the seriousness of the infectious complications associated with eculizumab. Health care providers should maintain a high index of suspicion for early identification and treatment.


Introduction And Background
"But however secure and well-regulated civilized life may become, bacteria, protozoa, viruses, infected fleas, lice, ticks, mosquitoes, and bed bugs will always lurk in the shadows ready to pounce when neglect, poverty, famine, or war lets down the defenses" -Hans Zinsser [1].
Eculizumab, a monoclonal antibody, approved by the United States Food and Drug Administration (FDA) for three indications: paroxysmal nocturnal hemoglobinuria (PNH), atypical hemolytic uremic syndrome (aHUS), and anti-acetylcholine receptor-positive generalized myasthenia gravis (gMG), is a complement inhibitor that inhibits the complement C5 that normally mounts a defense response against the encapsulated bacteria, Neisseria meningitidis (N. meningitidis), causing the bacteria to take advantage of this vulnerable situation and lead to meningitis, septic shock, and severe end-organ damage [2].
PNH is a rare hematologic disorder with an incidence of 15.9 individuals per million worldwide with most of the patients falling in the range of 30-40 years. It is an X-linked disease with a mutation in the phosphatidylinositol glycan class A (PIGA) gene producing a deficiency in glycosylphosphatidylinositol (GPI) protein, which anchors protein moieties such as CD55 and CD59 that further block the activity of membrane attack complex (C5b-C9). Due to loss of complement inhibition, RBCs become vulnerable to destruction by membrane attack complex resulting in hemolytic anemia. Thus, PNH presents with hemolytic anemia, hemoglobinuria, thrombosis, renal insufficiency, and aplastic anemia [3].
aHUS is a disorder of dysregulation of the alternative complement pathway in which there is uncontrolled activation of the alternative complement pathway resulting in inflammation, which produces endothelial injury, platelet activation and aggregation, leukocyte recruitment, and pro-coagulative signaling leading to thrombosis. Hence, it is called thrombotic microangiopathy, which is characterized by thrombocytopenia, hemolytic anemia, acute kidney injury, and other end-organ damage. Without treatment, it may progress to renal failure with mortality occurring in up to 7% of patients after one year [4].
Eculizumab (Soliris®, Alexion Pharmaceuticals, Boston, Massachusetts, United States), a complement component 5 targeted agent is a recognized therapeutic modality for PNH [5] and is the only treatment agent approved by the FDA and European Medicines Agency as well as 49 countries worldwide for treating aHUS [4]. Though eculizumab is very beneficial for the aforementioned diseases, it is associated with some major adverse effects. The prescribing information for the FDA-approved eculizumab includes a black box warning of the elevated risk of N. meningitidis infection. Since membrane attack complex is required for the serum meningococcal bactericidal activity, its inhibition by eculizumab poses a risk of a full-fledged infection with meningococcus [6]. The risk for invasive meningococcal infection increases by 1000-2000 times [5]. The symptoms caused by N. meningitidis can range from fever, vomiting, headache, cold hands and feet, pallor or mottling of the skin to hemorrhagic rash, impaired consciousness, and death. The case fatality rate of meningococcemia is 40%. The incidence of N. meningitidis infection varies between 0.11 and 2.8 per 100,000 person-years in Europe, Australia, New Zealand, South America, and North America and 112 per 100,000 person-years in the African meningococcal belt zone [7]. Meningococcal vaccination should be provided two weeks before the initiation of eculizumab to prevent infection with meningococcus [8].
Based on the case reports of disseminated gonococcal infections (DGI) in patients treated with eculizumab, we need to study and find out the association between Neisseria gonorrhoeae (N. gonorrhoeae) infections and the use of eculizumab [5,9]. Not only N. gonorrhoeae, but there have also been cases where invasive infections have been caused by non-meningococcal, non-gonococcal Neisseria species like N. mucosa, N. subflava, and N. cinerea in association with eculizumab. These organisms are commensal and can lead to endocarditis, meningitis, pneumonia, peritonitis, septic arthritis, etc [2]. Another commensal organism that has been a culprit in causing infection with the use of eculizumab is Moraxella lacunata. It is a gramnegative coccobacillus found in the upper respiratory tract and conjunctiva and is known to cause bacteremia and systemic inflammatory response syndrome (SIRS) in one of the cases receiving eculizumab for aHUS [10]. There have been instances where infections by Pseudomonas aeruginosa, Aspergillus niger, polyomavirus John Cunningham (JC) virus, and herpes simplex virus have been documented while the patient was treated with eculizumab [11]. Although the mechanism is not clear, there is a dire need to consider the risk of infections other than N. meningitidis in association with the use of eculizumab.
This systematic review is an up-to-date synthesis of various infections that occurred in different countries during different years in patients with PNH/aHUS being treated with eculizumab. Our study builds on previous results by including the analysis of study quality. There is extensive literature related to the adverse effects associated with the use of eculizumab and this information must be summarized to get an overview of the literature. Given the above, the purpose of the current study was to review the qualitative literature and answer two primary research questions: (1) What are the adverse effects associated with the use of eculizumab in PNH/aHUS patients? and (2) Is there a way to prevent/treat these adverse effects?

Review Protocol
We conducted our systematic review using Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines [12].

Database
We started our research on December 20, 2021, using online libraries as our database. A systematic search of major electronic databases (PubMed and Google Scholar) was conducted by the primary author.

Search strategy
We included the studies describing various infections associated with the use of eculizumab in PNH/aHUS patients. To include pertinent papers, snowballing technique was used. Also, we followed the authors who cited the articles pertinent to our topic. It was conducted independently by two reviewers (R.D. and R.S.) and in the event of disagreement, a third opinion was sought (S.S). Our keywords, medical subject heading (MeSH) search strategies, and each search result have been described in Table 1.

Inclusion criteria
We selected free full articles in the English language. Only human studies that were done in the last 20 years from January 1, 2001, to December 31, 2021, were included. The population included has PNH or aHUS, with eculizumab being their only treatment modality.

Exclusion criteria
We excluded any population not having PNH/aHUS and any population having PNH/aHUS being treated with a complement inhibitor other than eculizumab. We excluded animal studies, articles published in languages other than English, and studies done before the last 20 years. Letters and Editorials were excluded.

Quality assessment tools
We used the New Castle Ottawa questionnaire for non-randomized clinical trials and the National Institutes of Health (NIH) quality assessment tool for case reports and case series. Studies of low quality were excluded. This was conducted independently by two reviewers (R.D. and R.S.) and in the event of disagreement, a third opinion was sought (S.S).

Data collection
Data were extracted from the final articles by two independent reviewers (R.D. and R.S). Any discrepancies between the reviewers were resolved through discussion with a third author (S.S).

Results
In total, 261 articles were identified; 197 from databases (157 from PubMed, 40 from Google Scholar), and 64 via citation searching. After duplicates were removed, 182 records were screened (abstract and title) and four records were assessed for eligibility. Of the 64 articles found via citation searching, 44 records were assessed for eligibility. After further assessment, it was determined that the review inclusion criteria were met by 10 studies [2,5,6,8,9,10,11,12,13,14]. The PRISMA flow diagram is shown in Figure 1. Publication

Discussion
This review article will discuss the types of bacterial infections that develop secondary to eculizumab therapy. This research report goes into detail about the clinical presentation of the infections, their prevention, and treatment.

Neisseria meningitidis
The terminal complement pathway inhibition caused by eculizumab increases the risk of invasive meningococcal disease (IMD) [13]. In a cohort study undertaken by Ladhani et al., IMD was found in six patients with PNH and three people with aHUS who were treated with eculizumab. The probability of IMD due to capsular group Y is 1/9, or 11%. Four of the nine IMD events in patients treated with eculizumab were NG or Group E. These strains aren't as virulent as others and are only linked to the carriage [13]. Also, Nolfi-Donegan describes a case report of a patient who developed fatal N. meningitidis disease while receiving eculizumab [6]. The characteristics of patients developing IMD are described in Table 3.

Immunization
Meningococcal ACWY (Men ACWY), a polysaccharide conjugate vaccine against groups A, C, W, and Y, Meningococcal B vaccine (4CMenB) against IMD in infants and toddlers, and two novel broad-spectrum protein-based meningococcal vaccines that have been approved in Europe are available [13].
Vaccine failure has been documented after 4CMenB and MenACWY. Patients with complement insufficiency still acquire IMD despite having high post-immunization antibody titers [13,15]. Langereis et al. conducted a clinical experiment employing whole blood killing assay to investigate opsonophagocytic Neisseria meningitidis serogroup B (MenB) killing in PNH patients receiving eculizumab who were vaccinated with 4CMenB. Despite IgG and C3 opsonization of the bacterial surface, the whole blood lysis of MenB was not detected after vaccination with the 4CMenB vaccine indicating the need to use antibiotics prophylactically to prevent MenB infections [15].

Prophylactic Antibiotics
Prophylactic antibiotics are recommended until two weeks after vaccination, according to the US FDA. The European Society of Clinical Microbiology and Infectious Diseases recommends the use of antibiotics for four weeks after immunization [15]. Penicillin or erythromycin are used in the majority of chemoprophylactic regimens for eculizumab-treated patients. Meningococcal disease caused by strains with penicillin resistance or intermediate sensitivity has been reported despite penicillin chemoprophylaxis [6].  [5,8,9]. The features of patients who developed the gonococcal infection are shown in Table 4.  Gonococci has 70% DNA similarity to N. meningitidis. Complement insufficiency has long been reported to be a risk factor for gonococcal infections as it is for N. meningitidis. Since eculizumab is a complement inhibitor, it has the potential to cause gonococcal infection [5].

Treatment
Uncomplicated gonococcal infections of the cervix, urethra, throat, and rectum should be treated with the CDC-recommended regimen of 250mg ceftriaxone intramuscularly and 1g azithromycin orally in a single dosage. For patients with disseminated gonococcal infection (DGI) presenting as arthritis or arthritisdermatitis syndrome, 1g intramuscular or intravenous ceftriaxone daily and a single oral dose of 1g azithromycin is recommended. DGI presenting as gonococcal meningitis or endocarditis should be treated with 1-2g intravenous ceftriaxone every 12-24 hours and a one-time dosage of 1g oral azithromycin. For meningitis, parenteral treatment should be continued for 10-14 days; for endocarditis, parenteral medication should be given for four weeks [9].

Prevention
Patients should be informed about the significant risk of DGI. Sexual histories should be obtained, including the number and gender of sex partners as well as the type of sexual contact, as this information will aid in the development of suitable screening recommendations. Safe sex habits such as the regular use of condoms should be encouraged [9].

Unusual Neisseria species
Meningococcus expresses factor H binding protein (fHbp), which attracts the inhibitory complementregulatory protein factor H (CFH) to the microbial surface, preventing opsonophagocytosis and bacteriolysis.
Recently, it was discovered that N. cinerea can also express fHBP, which binds CFH with the same affinity as meningococcal fHBP. This organism's immune escape strategy, together with eculizumab-induced suppression of opsonophagocytosis and cell lysis, gives scientific plausibility to how a nonpathogenic organism such as unusual Neisseria species can become invasive [14]. Crew et al. searched through the FAERS database and medical literature for reports of non-meningococcal and non-gonococcal Neisseria species infection in eculizumab patients. They were able to create a case series consisting of six cases of unusual Neisseria species infection [2]. Walsh et al. have also described a case report of a patient with N. cinerea infection [14]. The features of patients who became infected with uncommon Neisseria species are listed in Table 5.   [11]. The P. aeruginosa infection is described in Figure 2.

Limitations
Our study did not include articles that were freely unavailable, in languages other than English, and written before the last 20 years. As a result, other probable infections are not mentioned.

Conclusions
Our systematic review identifies a number of infections that have been linked to the use of eculizumab in individuals with PNH/aHUS. The bacteria that cause the infection are N. meningitides, N. gonorrhea, N. flavescens (subflava), N. cinerea, N. sicca, P. aeruginosa, and M. lacunata. The therapeutic regimens for prophylaxis and treatment of infections are outlined in our article. These groundbreaking cases highlight the importance of a high susceptibility index among health care providers and patients for the various infections described above, resulting in early detection and consideration of empiric antibiotics, regardless of the patient's immunization status or prophylactic regimen. We propose more research in the form of a prospective cohort study in a large population of eculizumab-treated patients to seek for infections not included in our analysis.

Conflicts of interest:
In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.