Immunostimulants versus placebo for preventing exacerbations in adults with chronic bronchitis or chronic obstructive pulmonary disease

Abstract

This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:

To determine the efficacy of immunostimulants in preventing respiratory exacerbations in adult patients with chronic obstructive pulmonary disease, chronic bronchitis, or both.

Background

Description of the condition

Chronic obstructive pulmonary disease (COPD) is defined by the Global Initiative for Chronic Obstructive Lung Disease (GOLD) as "a common, preventable and treatable disease which is characterised by persistent respiratory symptoms and airflow limitation that is due to airway and/or alveolar abnormalities, usually caused by significant exposure to noxious particles or gases" (GOLD 2019). Globally, COPD is a major cause of morbidity and mortality. In 2015, there was an estimated prevalence of 174 million cases, with three million deaths attributable to COPD (GBD 2015). Currently, COPD is considered the third leading cause of death worldwide (WHO GHE 2016). These numbers are projected to increase even further over the next 30 years, with COPD‐related deaths predicted to rise due to a combination of population aging and ongoing exposure to COPD risk factors (Lopez 2006; WHO 2018). The economic burden associated with COPD is also substantial, with direct and indirect costs placing significant financial strain on individuals, their families, wider society and healthcare systems worldwide (ATS Foundation 2014; Jinjuvadia 2017).

The symptoms of COPD include dyspnoea (breathlessness), chronic cough and sputum production. COPD encompasses a range of clinical phenotypes, including emphysema and chronic bronchitis, with the latter condition classically being defined as chronic cough and sputum production for at least three months per year for two consecutive years (Ferris 1978). Alternative definitions of chronic bronchitis exist, including cough and phlegm almost every day or several times a week (Kim 2015). Whilst chronic bronchitis is not technically defined by airflow limitation, it may precede the development of this, and is still thought to be associated with airway disease and inflammation, an increased risk in the total number and severity of respiratory exacerbations, and functional limitation (Kim 2011; Woodruff 2016).

A COPD exacerbation is defined as an acute worsening of respiratory symptoms that results in additional treatment (Wedzicha 2007). Exacerbations are often associated with increased airway inflammation, gas trapping, and mucus production (GOLD 2019); these changes typically lead to symptoms of increased dyspnoea, alteration in sputum colour or volume, increased cough and wheeze, or a combination of these. Most COPD exacerbations are triggered by viral or bacterial respiratory infections (or both); however, environmental changes and air pollution may also play a role in either causing or worsening exacerbations (GOLD 2019; Woodhead 2011). Studies have suggested that viruses are the causative pathogen in 34% to 56% of COPD exacerbations (Mohan 2010; Papi 2006; Rohde 2003), with bacterial infections reportedly associated with up to 50% of exacerbations (Papi 2006). Additionally, viral and bacterial coinfection is common, and has been shown to correlate with an increased severity of exacerbations and longer duration of hospitalisation (Papi 2006; Singanayagam 2012).

It is widely known that respiratory exacerbations in COPD are associated with increased mortality, accelerated decline in lung function, increased hospitalisation and readmission rates, and decreased quality of life (Kanner 2001; Soler‐Cataluña 2005). In addition, a history of previous exacerbations is said to be the single biggest risk factor for future exacerbations (Hurst 2010). Some patients with COPD are more prone to having frequent exacerbations (defined as two or more exacerbations per year) and this group has been shown to have worse outcomes and morbidity than those who experience less frequent exacerbations (Seemungal 1998). Aside from impacting the health status and prognosis of individual patients, exacerbations also impose a significant socioeconomic burden on society, particularly those that necessitate hospital admission.

A number of evidence‐based therapies exist to reduce symptoms and exacerbations, and improve lung function, exercise tolerance and quality of life, in patients with COPD. Key aspects of COPD management include smoking cessation, exercise, pulmonary rehabilitation, and regular vaccinations for both influenza and pneumococcal infections (GOLD 2019). Other non‐pharmacological options for select patients include treatment of hypoxaemia with long‐term oxygen therapy (Cranston 2005), treatment of hypercapnia with long‐term non‐invasive ventilation (Kohnlein 2014), and surgical or bronchoscopic lung volume reduction procedures (Marruchella 2018). Pharmacologically, the mainstay of treatment in stable COPD involves inhaled bronchodilators, including beta‐agonists and anti‐muscarinic agents (GOLD 2019; Kew 2010; Tashkin 2008). If patients still have a high symptom or exacerbation burden, the addition of inhaled corticosteroids (ICS) to a long‐acting beta‐agonist (LABA) is recommended (Nannini 2012). A number of oral anti‐inflammatory agents have also been found to reduce exacerbations in COPD, and are currently recommended for use in select patients, including phosphodiesterase‐4 inhibitors, mucolytic agents and macrolide antibiotics (Chong 2013; Ni 2015; Poole 2015).

Description of the intervention

A glossary of the main immunological terms used is provided in Appendix 1.

The 2019 GOLD guidelines have specifically mentioned use of immunostimulant or immunoregulatory agents for preventing exacerbations in patients with COPD (GOLD 2019). Immunostimulants (IS) are defined as agents that create a state of non‐specific immunity and enhance the immune response towards infection or malignancy (Hadden 1993). They have existed for many years, and have long been suggested to have efficacy in preventing or reducing the severity of acute respiratory tract infections (ARTIs).

In some countries, IS are regularly used for the prevention of ARTIs in children and for reducing the frequency and severity of exacerbations in adult patients with COPD or chronic bronchitis (Del‐Rio‐Navarro 2007). However, their widespread and routine use has been limited due to a shortage of high‐quality data regarding their efficacy, and a lack of understanding of their mechanisms of action and long‐term safety profiles. The 2019 GOLD guidelines acknowledge that, whilst older studies have demonstrated the efficacy of immunostimulants in reducing the severity and frequency of COPD exacerbations (Collet 1997; Li 2004), further studies are needed to examine the effects of these agents in patients who are receiving current gold‐standard COPD maintenance therapy.

The IS agents that have been studied and used for the purpose of preventing acute respiratory tract infections fall into three main categories: bacteria‐derived agents, synthetic agents, and thymic extracts (Del‐Rio‐Navarro 2007). Most of the IS used in the prevention of acute respiratory tract infections are orally or sublingually‐administered bacteria‐derived agents. These can be further categorized into those that are inactivated whole‐cell formulations, those that contain a mixture of antigenic fragments derived from several different bacterial strains (bacterial lysates), and those that consist of a specific immunogenic component of a bacteria, such as ribosomal fractions or glycoproteins (Cazzola 2008; Del‐Rio‐Navarro 2007; Giovannini 2014).

Bacterial lysates (BLs) are composed of constituted fragments of bacterial antigens, obtained through the chemical or mechanical lysis (breakdown) of multiple inactivated bacterial strains that are commonly associated with respiratory infections, such as Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, Klebsiella pneumoniae, Moraxella catarrhalis, Streptococcus pyogenes and Streptococcus viridans (De Benedetto 2013).

How the intervention might work

Immunostimulants, used for the purpose of preventing respiratory tract infections in patients with COPD or chronic bronchitis, aim to heighten the host immune response against infective insults that may subsequently trigger an exacerbation. However, despite there being much research and knowledge gained about the effects of individual immunostimulatory agents on the immune system, the exact mechanisms of action of both synthetic and bacteria‐derived agents at a molecular level is still not completely understood (De Benedetto 2013; Del‐Rio‐Navarro 2007).

OM‐85, a bacterial lysate derived by the chemical lysis of a number of the aforementioned bacterial strains, is thought to exert its effects through both cell‐mediated and humoral immune system pathways (De Benedetto 2013; Rozy 2008). These include augmentation of the T helper cell lymphocyte (Th1) response (Huber 2005), induction of specific immunoglobulin A antibody secretion by B lymphocyte cells (Rial 2004; Rossi 2003) direct activation of lung macrophages and monocytes (Mauel 1989; Rozy 2008), up‐regulation of adhesion molecules (Duchow 1992), and stimulation of phagocytic cell activity (Rozy 2008). It is thought that the immunostimulant components of OM‐85 bind to toll‐like receptors (TLRs), triggering signalling pathways that lead to activation and potentiation of the innate immune response (Alyanakian 2006; Huber 2005; Navarro 2011; Nikolova 2009).

Mechanical bacterial lysates, specifically polyvalent mechanical bacterial lysates (PMBLs), have been demonstrated to stimulate dendritic cell maturation (Morandi 2011), increase the number of circulating natural killer (NK) cells (Lanzilli 2013), increase specific immunoglobulin A antibody secretion by B cells, (Rossi 2003) and activate both memory B lymphocytes and regulatory T lymphocytes (Lanzilli 2013). Studies have shown that the degree of the immune response created by the administration of mechanical bacterial lysates to patients directly correlates with positive clinical outcomes, such as reduced exacerbation frequency (Braido 2011; Lanzilli 2006; Ricci 2014).

Other bacterial extracts, made up of bacterial proteins or ribosomal fragments, also have specific immunomodulatory effects. For example, the immunostimulant RU41740 (made up of Klebsiella pneumoniae glycoproteins and membrane fragments) has been shown to activate macrophages, stimulate the B lymphocyte cell response (Boissier 1988), and enhance antigen presentation (Pedraza‐Sanchez 2006). Like bacterial lysates, RU41740 is thought to initiate an immune response through binding of its molecular components (such as lipopolysaccharide) to TLRs (Miller 2005).

The immunostimulants containing thymic extracts also appear to interact with other TLRs and precursor T lymphocytes to increase dendritic cell, NK cell and T cell activity, thus enhancing both innate and cell‐mediated immune responses (Del‐Rio‐Navarro 2007; Tuthill 2013). Synthetic IS compounds are reportedly better understood in terms of their molecular mechanism of action (Del‐Rio‐Navarro 2007). Examples of synthetic IS include: tucaresol, which acts by promoting the interaction between antigen‐presenting cells and T cells (Rhodes 1996); imiquimod, which acts through TLR7 and TLR8 (Spaner 2005); and pidotimod, which acts by enhancing cell‐mediated immunity (Benetti 1994).

A number of trials and systematic reviews exist that analyse the use of IS in preventing ARTIs in children and adults, and in preventing exacerbations in adult patients with chronic bronchitis or COPD. One previous Cochrane Review evaluated IS for preventing respiratory tract infections in children. These reviewers looked at 34 placebo‐controlled trials, and reported that IS were associated with approximately 40% fewer acute respiratory infections compared with placebo. However, they also commented that "trial quality was generally poor and a high level of statistical heterogeneity was evident" (Del‐Rio‐Navarro 2012). A meta‐analysis looking at the efficacy of PMBLs in preventing respiratory tract infections in children and adults looked at data across 15 randomized controlled trials. Treatment with PMBLs was found to be associated with a significant reduction in respiratory infections compared with placebo (Cazzola 2012).

A previous systematic review found that the bacterial extracts OM‐85 BV, LW‐50020, and SL‐04 were associated with improved symptoms in people with COPD, chronic bronchitis or both, and the meta‐analysis suggested a lessened exacerbation duration. However, there was no significant difference found between the extracts and placebo in preventing exacerbations (Steurer‐Stey 2004). Another systematic review looked at the efficacy of OM‐85 BV in preventing exacerbations in patients with COPD or chronic bronchitis (or both). A non‐statistically significant trend was found in favour of OM‐85 BV; however, benefit was not clearly demonstrated across a range of important clinical outcomes (Sprenkle 2005). In 2015, a meta‐analysis and systematic review looked at the effects of OM‐85 BV in patients with COPD on exacerbation rate, in addition to a number of other minor clinical end points. OM‐85 BV was associated with a 20% reduction in exacerbation rate and 39% reduction in the incidence rate of patients using antibiotics compared with placebo (Pan 2015). However, the authors concluded that there was not enough evidence to support the routine use of OM‐85 BV in patients with COPD, suggesting that further larger‐scale trials needed to be undertaken.

Why it is important to do this review

Immunostimulant agents in COPD or chronic bronchitis could theoretically enhance non‐specific immunity against a number respiratory insults, which is an important concept given the number of pathogens, including myriad viruses, that can precipitate an exacerbation. However, the use of immunostimulants in this patient population thus far has been controversial. This is largely due to concerns about quantity and quality of evidence in the past, a lack of understanding of their long‐term effects, and existing uncertainty around their exact mechanisms of action. As aforementioned, the latest GOLD guidelines recognize that some older studies have reported a decrease in the severity and frequency of COPD exacerbations, but more trials are needed in patients receiving currently recommended maintenance therapy (GOLD 2019). Overall, there have been mixed results from previous trials and systematic reviews regarding clinical efficacy of IS in adult patients with COPD or chronic bronchitis; many have reported positive impacts on exacerbation rates (or a trend towards this) and other clinically relevant outcomes, but have been unable to suggest an overall benefit in these patients due to limited availability of data, poor trial quality, or both.

This systematic review aims to critically appraise all available data regarding the efficacy and use of IS as a preventative therapy in stable adult patients with COPD or chronic bronchitis (or both). This may help to further understand their clinical value and safety, and may highlight areas requiring further research and development.

Objectives

To determine the efficacy of immunostimulants in preventing respiratory exacerbations in adult patients with chronic obstructive pulmonary disease, chronic bronchitis, or both.

Methods

Criteria for considering studies for this review

Types of studies

We will include parallel randomized controlled trials (RCTs) comparing immunostimulant therapy, administered by any method, with placebo. We will include studies reported in full text, those published as an abstract only, and unpublished data. Cross‐over trials will be excluded due to the nature of chronic obstructive pulmonary disease (COPD) as a progressive disease and because of the possibility of a carry‐over effect from the first treatment period.

Types of participants

We will include adults (older than 18 years of age) who have a diagnosis of COPD (defined by a post‐bronchodilator FEV1/FVC ratio of less than 0.7) and/or chronic bronchitis (defined by either the classic definition of chronic cough and sputum production for at least three months per year for two consecutive years (Ferris 1978), or alternative definitions such as cough and phlegm almost every day or several times a week (Kim 2015)). An underlying principle is that study participants met well‐established criteria at the time, whether for chronic bronchitis or for COPD.

We will exclude participants with asthma, bronchiectasis, or genetic/other lung conditions that predispose or lead to chronic airflow obstruction, such as cystic fibrosis, or patients with known specific immunodeficiencies. However, if there are studies that include these types of participants and additionally include patients with COPD, data will be analyzed for this subset of COPD patients if the data are presented separately.

Types of interventions

We will include studies of immunostimulant therapy compared to placebo, to prevent respiratory exacerbations. Interventions may be administered by any method (oral, subcutaneous or intravenous) and must be given for at least one month.

A table will be created to summarize the characteristics of the studies, and to provide an overview of the main variables of the trial interventions; for example, agent type, mode of delivery, dose and schedule, and duration of therapy.

We will exclude specific immunostimulants, such as influenza or pneumococcal vaccines, immunotherapy used to treat cancer (either directly, or the immune deficiency resulting from chemotherapy), allergic disease, and treatment to replace immunoglobulins in known specific immune deficiency disorders. Trials referring to vitamins, nutritional supplements, herbal extracts or homeopathic remedies will not be included. We will exclude studies that focus on treatment of acute exacerbations with immunostimulants (as opposed to prevention and prophylaxis). Studies that focus on improvement in immunologic parameters as the primary outcome will not be considered.

Types of outcome measures

This review is concerned primarily with prevention of exacerbations of COPD or chronic bronchitis, particularly those which are moderate or severe.

An exacerbation of COPD will be defined as an acute worsening of respiratory symptoms that results in additional therapy (GOLD 2019; Seemungal 1998; Wedzicha 2007). A mild exacerbation will be defined as needing treatment with short‐acting bronchodilators (SABDs) in the community setting only; a moderate exacerbation will be defined as needing treatment with SABDs plus antibiotics or oral corticosteroids (or both) in the community setting, or in the emergency department but without subsequently requiring admission; a severe exacerbation will be defined as requiring hospital admission, or as being associated with acute respiratory failure (GOLD 2019).

An exacerbation of chronic bronchitis will be defined as an acute change in the frequency and/or severity of cough and change in sputum volume and/or character, although we acknowledge that definitions for an exacerbation of chronic bronchitis may vary considerably between the studies. We will describe the criteria used in each chronic bronchitis trial for a mild, moderate or severe exacerbation. If they are substantially similar to those used for COPD, it may be possible to combine data on these outcomes.

Primary outcomes

1. Moderate exacerbations requiring treatment with antibiotics or oral corticosteroids (or both), or emergency department visit without subsequently needing hospital admission (number of people experiencing one or more events, and rate of events per person).

2. Severe exacerbations requiring hospital admission (number of people experiencing one or more events, and rate of events per person).

3. Mortality (all‐cause).

Primary outcomes will be measured over a period of at least 12 weeks.

Secondary outcomes

1. Total number of exacerbations (including total number of participants with any exacerbation in the study period, and frequency of exacerbations).

2. Mortality (respiratory‐related).

3. Duration of exacerbations.

4. Quality of life (patient reported, measured by a validated scale, such as St George's Respiratory Questionnaire (SGRQ) (Jones 2009) or Chronic Respiratory Diseases Questionnaire (CRQ) (Guyatt 1987).

5. Adverse events/side‐effects.

We chose exacerbations as the primary outcome as immunostimulant therapy is most commonly administered as a preventative therapy, and thus far exacerbations have represented the main clinically relevant end‐point used for efficacy of immunostimulant agents and many other anti‐inflammatory drugs used in COPD or chronic bronchitis (GOLD 2019). As aforementioned, exacerbations significantly affect patient morbidity and mortality and have a significant impact on overall disease burden, therefore it was felt that exacerbations and mortality were important to consider as primary outcomes in this review.

The secondary outcomes are other important measures of the efficacy and safety of immunostimulant agents. Analysing exacerbation duration may provide indirect information regarding the potential socioeconomic and quality‐of‐life impacts of the intervention. Quality‐of‐life assessments highlight information regarding the impact of the intervention on the objective and subjective wellbeing of the patient, and are an important outcome in any chronic disease. Given that little is understood about the long‐term safety of these agents and concerns around this have previously limited recommendation for widespread use, adverse events are an additional secondary outcome for this review.

Reporting of one or more of the outcomes listed here in the study is not an inclusion criterion for the review.

Search methods for identification of studies

Electronic searches

We will identify studies from the Cochrane Airways Trials Register, which is maintained by the Information Specialist for the Group. The Cochrane Airways Trials Register contains studies identified from several sources:

1. monthly searches of the Cochrane Central Register of Controlled Trials (CENTRAL), through the Cochrane Register of Studies (CRS) from inception to date;

2. weekly searches of MEDLINE Ovid SP from 1946 to date;

3. weekly searches of Embase Ovid SP from 1974 to date;

4. monthly searches of PsycINFO Ovid SP from 1967 to date;

5. monthly searches of CINAHL EBSCO (Cumulative Index to Nursing and Allied Health Literature) from 1937 to date;

6. monthly searches of AMED EBSCO (Allied and Complementary Medicine) from inception to date;

7. handsearches of the proceedings of major respiratory conferences.

Studies contained in the Trials Register are identified through search strategies based on the scope of Cochrane Airways. Details of these strategies, as well as a list of handsearched conference proceedings, can be found in Appendix 2. See Appendix 3 for search terms used to identify studies for this review.

We will search the following trials registries:

1. US National Institutes of Health Ongoing Trials Register ClinicalTrials.gov (www.clinicaltrials.gov)

2. World Health Organization International Clinical Trials Registry Platform (apps.who.int/trialsearch)

We will search the Cochrane Airways Trials Register and additional sources from inception to present, with no restriction on language of publication.

Searching other resources

We will check the reference lists of all primary studies and review articles for additional references. Study authors will be contacted for identification of other published and unpublished data. We will search relevant manufacturers' websites for study information.

We will search for errata or retractions from included studies published in full text on PubMed, and report the date this was done within the review.

Data collection and analysis

Selection of studies

Two review authors (AF and PP) will screen the titles and abstracts of the search results independently and code them as 'retrieve' (eligible or potentially eligible/unclear) or 'do not retrieve'. We will retrieve the full‐text study reports of all potentially eligible studies and two review authors (AF and PP) will independently screen them for inclusion, recording the reasons for exclusion of ineligible studies. We will resolve any disagreement through discussion or, if required, we will consult a third person. We will identify and exclude duplicates and collate multiple reports of the same study so that each study, rather than each report, is the unit of interest in the review. We will record the selection process in sufficient detail to complete a PRISMA flow diagram and 'Characteristics of excluded studies' table (Moher 2009).

Data extraction and management

We will use a data collection form for study characteristics and outcome data, which has been piloted on at least one study in the review. Two review authors (AF and PP) will extract the following study characteristics from included studies.

1. Methods: study design, total duration of study, details of any 'run‐in' period, number of study centres and location, study setting, withdrawals and date of study.

2. Participants: number (N), mean age, age range, gender, severity of condition, diagnostic criteria, baseline lung function, smoking history, baseline exacerbation frequency, inclusion criteria and exclusion criteria.

3. Interventions: intervention, comparison, concomitant medications and excluded medications.

4. Outcomes: primary and secondary outcomes specified and collected, and time points reported.

5. Notes: funding for studies and notable conflicts of interest of trial authors.

These data will be cross‐checked between the two review authors. The two review authors (AF and PP) will independently extract outcome data from included studies. We will note in the 'Characteristics of included studies' table if outcome data were not reported in a usable way. We will resolve disagreements by consensus or by involving a third person. One review author (AF) will transfer data into the Review Manager file (RevMan 2014). We will double‐check that data are entered correctly by comparing the data presented in the systematic review with the study reports. A second review author (PP) will spot‐check study characteristics for accuracy against the study report.

Assessment of risk of bias in included studies

Two review authors (AF and PP) will assess risk of bias independently for each study using the criteria outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). We will resolve any disagreements by discussion or by involving another person (ZK). We will assess the risk of bias according to the following domains.

1. Random sequence generation.

2. Allocation concealment.

3. Blinding of participants and personnel.

4. Blinding of outcome assessment.

5. Incomplete outcome data.

6. Selective outcome reporting.

7. Other bias.

We will judge each potential source of bias as high, low, or unclear, and provide a quote from the study report together with a justification for our judgement in the 'Risk of bias' table. We will summarize the 'Risk of bias' judgements across different studies for each of the domains listed. We will consider blinding separately for different key outcomes where necessary (e.g. for unblinded outcome assessment, risk of bias for all‐cause mortality may be very different than for a patient‐reported pain scale). Where information on risk of bias relates to unpublished data or correspondence with a trialist, we will note this in the 'Risk of bias' table.

When considering treatment effects, we will take into account the risk of bias for the studies that contribute to that outcome.

Assessment of bias in conducting the systematic review

We will conduct the review according to this published protocol and justify any deviations from it in the 'Differences between protocol and review' section of the systematic review.

Measures of treatment effect

We will analyse dichotomous data as odds ratios (ORs) with a 95% confidence interval (CI), and continuous data as the mean difference (MD) or standardized mean difference (SMD) with a 95% CI. For patient‐reported outcomes, such as quality of life/symptoms, the analysis will be formulated depending on how these are reported in the individual trials. For dichotomous outcomes, we will calculate the number needed to treat for an additional beneficial outcome (NNTB) and number needed to treat for an additional harmful outcome (NNTH). If data from rating scales are combined in a meta‐analysis, we will ensure they are entered with a consistent direction of effect (e.g. lower scores always indicate improvement).

We will undertake meta‐analyses only where this is meaningful; that is, if the treatments, participants and the underlying clinical question are similar enough for pooling to make sense.

We will describe skewed data narratively (for example, as medians and interquartile ranges for each group).

Where multiple trial arms are reported in a single study, we will include only the relevant arms. If two comparisons (e.g. drug A versus placebo and drug B versus placebo) are combined in the same meta‐analysis, we will either combine the active arms or halve the control group to avoid double‐counting.

If adjusted analyses are available (ANOVA or ANCOVA) we will use these as a preference in our meta‐analyses. If both change‐from‐baseline and endpoint scores are available for continuous data, we will preferentially use change‐from‐baseline scores.

We will use intention‐to‐treat (ITT) or 'full analysis set' analyses where they are reported (i.e. those where data have been imputed for participants who were randomly assigned but did not complete the study) instead of completer or per‐protocol analyses.

Unit of analysis issues

For dichotomous outcomes, we will use participants, rather than events, as the unit of analysis (i.e. number of adults admitted to hospital, rather than number of admissions per adult). However, if rate ratios are reported in a study, we will analyse them on this basis. Care will be taken to avoid treating count data as dichotomous data, to avoid unit‐of‐analysis error in recurring events. We will only meta‐analyse data from cluster‐RCTs if the available data have been adjusted (or can be adjusted), to account for the clustering. Any other variations on the simple parallel‐group design for a clinical trial (e.g. multiple observations for the same outcome) will be taken into account and analyzed for their effects on the data. If we encounter studies with a non‐standard design we plan to analyse the data with the aid of a statistician.

Dealing with missing data

We will contact investigators or study sponsors in order to verify key study characteristics and obtain missing numerical outcome data where possible (e.g. when a study is identified as an abstract only). Where this is not possible, and the missing data are thought to introduce serious bias, we will take this into consideration in the GRADE rating for affected outcomes.

The exact nature of missing data suitable for sensitivity analyses will be identified during the review process. Any assumptions made around the reason or nature of missing data will be made clear within the systematic review. Sensitivity analyses may be performed to assess how variable the results may be to any assumptions made about missing data, such as repeating the meta‐analysis after exclusion of those studies with unclear or missing data.

Assessment of heterogeneity

We will use the I² statistic to measure heterogeneity among the studies in each analysis. If we identify substantial heterogeneity we will report it and explore the possible causes by prespecified subgroup analysis. 

Assessment of reporting biases

If we are able to pool more than 10 studies, we will create and examine a funnel plot to explore possible small‐study and publication biases.

Data synthesis

We will use a random‐effects model and perform a sensitivity analysis with a fixed‐effect model.

'Summary of findings' table

We will create a 'Summary of findings' table using some or all of the following outcomes.

1. Moderate exacerbations requiring treatment with antibiotics or oral corticosteroids (or both), or emergency department visit without subsequently needing hospital admission (number of people experiencing one or more events, and rate of events per person).

2. Severe exacerbations requiring hospital admission (number of people experiencing one or more events, and rate of events per person).

3. Mortality (all‐cause).

4. Quality of life.

5. Adverse events/side‐effects.

We will use the five GRADE considerations (risk of bias, consistency of effect, imprecision, indirectness, and publication bias) to assess the quality of a body of evidence as it relates to the studies that contribute data for the prespecified outcomes. We will use the methods and recommendations described in Section 8.5 and Chapter 12 of the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011), using GRADEpro GDT software (GRADEpro GDT). We will justify all decisions to downgrade the quality of studies using footnotes and we will make comments to aid the reader's understanding of the review where necessary.

Subgroup analysis and investigation of heterogeneity

We plan to carry out the following subgroup analyses.

1. Severity of COPD based on lung function testing: mild (defined by FEV1 ≥ 80% predicted) versus moderate (FEV1 ≥ 50% and < 80% predicted) versus severe (FEV1 ≥ 30 and < 50% predicted) versus very severe (FEV1 < 30% predicted) (GOLD 2019).

2. Baseline exacerbation frequency prior to intervention (zero to one exacerbations versus two or more exacerbations per year).

3. Type of immunostimulant agent used.

4. Mode of delivery (oral versus subcutaneous versus intravenous).

We will use the following outcomes in subgroup analyses.

1. Moderate exacerbations (people experiencing one or more).

2. Severe exacerbations (people experiencing one or more).

3. Mortality (all‐cause).

We will use the formal test for subgroup interactions in Review Manager 5 (RevMan 2014).

Sensitivity analysis

We plan to carry out the following sensitivity analyses, removing the following from the primary outcome analyses:

1. Trials judged in the 'Risk of bias' table to be at high risk of bias for any of the six domains;

2. Trials where decisions or assumptions have been made around missing data.

We will compare the results from a fixed‐effect model with the random‐effects model.

Appendices

Appendix 1. Glossary of Terms

Term	Definition	Term	Definition
Adaptive immunity	The components of the immune system involved in the specific and long‐term response to a particular antigen. Includes B and T lymphocyte activity.	Immunogenic	Describes a substance able to provoke an immune response.
Adhesion molecule	Cell‐surface proteins that interact with T lymphocytes and enable their migration through the endothelium at sites of inflammation.	Inactivated whole‐cell formulation	A substance that contains whole microorganisms (e.g. bacteria, viruses) that have been killed through physical or chemical processes.
Antibody	A specialised protein produced by B lymphocytes in response to an antigen, in order to help eliminate it. Also known as an immunoglobulin.	Innate immunity	The rapid and non‐specific components of the immune system that are involved in the first response to an antigen.
Antigen	A substance that is recognised by the immune system as being foreign, and that triggers an immune response e.g. bacteria, viruses.	Macrophage	A type of white blood cell involved in the innate immune response.
Antigen Presentation	The process by which antigen is "presented" to lymphocyte cells in order to activate the adaptive (i.e. specific) immune response against that antigen.	Monocyte	A type of white blood cell involved in the innate immune response.
B lymphocyte	A type of white blood cell involved in the adaptive immune response. B cells are responsible for antibody production and secretion.	Natural killer cell	A type of white blood cell involved in the innate immune response.
Cell‐mediated immunity	The component of the immune response that involves the direct action of immune cells (such as T lymphocytes) against a pathogen.	Phagocytic	Describes immune system cells which are capable of ingesting foreign particles, bacteria, and/or debris created by the immune response. E.g. macrophages, monocytes, dendritic cells.
Dendritic cell	An antigen‐presenting cell that is involved in the innate immune response.	Ribosome	A complex molecule, found in the cytoplasm of all living cells, which is responsible for the production of biologic proteins.
Glycoprotein	A protein that has a carbohydrate group attached. Often located at the cell surface, and play an important role in the mechanisms of infection by bacteria and viruses.	T lymphocyte	A type of white blood cell that plays an important role in the cell‐mediated, adaptive immune response.
Humoral immunity	The component of the immune response that involves action against the antigen by the molecules found in extracellular fluids (e.g. secreted antibodies). Also called antibody‐mediated immunity.	Toll‐like receptors	A class of cell surface‐membrane proteins that recognise molecules shared by a variety of pathogens. Binding of these pathogens leads to signalling pathways that activate the innate, and subsequently the adaptive, immune responses.

Appendix 2. Sources and search methods for the Cochrane Airways Trials Register

Electronic searches: core databases

Database	Dates searched	Frequency of search
CENTRAL (via the Cochrane Register of Studies (CRS))	From inception	Monthly
MEDLINE (Ovid)	1946 onwards	Weekly
Embase (Ovid)	1974 onwards	Weekly
PsycINFO (Ovid)	1967 onwards	Monthly
CINAHL (EBSCO)	1937 onwards	Monthly
AMED (EBSCO)	From inception	Monthly

Handsearches: core respiratory conference abstracts

Conference	Years searched
American Academy of Allergy, Asthma and Immunology (AAAAI)	2001 onwards
American Thoracic Society (ATS)	2001 onwards
Asia Pacific Society of Respirology (APSR)	2004 onwards
British Thoracic Society Winter Meeting (BTS)	2000 onwards
Chest Meeting	2003 onwards
European Respiratory Society (ERS)	1992, 1994, 2000 onwards
International Primary Care Respiratory Group Congress (IPCRG)	2002 onwards
Thoracic Society of Australia and New Zealand (TSANZ)	1999 onwards

Condition search

1. exp Asthma/

2. asthma$.mp.

3. (antiasthma$ or anti‐asthma$).mp.

4. Respiratory Sounds/

5. wheez$.mp.

6. Bronchial Spasm/

7. bronchospas$.mp.

8. (bronch$ adj3 spasm$).mp.

9. bronchoconstrict$.mp.

10. exp Bronchoconstriction/

11. (bronch$ adj3 constrict$).mp.

12. Bronchial Hyperreactivity/

13. Respiratory Hypersensitivity/

14. ((bronchial$ or respiratory or airway$ or lung$) adj3 (hypersensitiv$ or hyperreactiv$ or allerg$ or insufficiency)).mp.

15. ((dust or mite$) adj3 (allerg$ or hypersensitiv$)).mp.

16. or/1‐15

17. exp Aspergillosis, Allergic Bronchopulmonary/

18. lung diseases, fungal/

19. aspergillosis/

20. 18 and 19

21. (bronchopulmonar$ adj3 aspergillosis).mp.

22. 17 or 20 or 21

23. 16 or 22

24. Lung Diseases, Obstructive/

25. exp Pulmonary Disease, Chronic Obstructive/

26. emphysema$.mp.

27. (chronic$ adj3 bronchiti$).mp.

28. (obstruct$ adj3 (pulmonary or lung$ or airway$ or airflow$ or bronch$ or respirat$)).mp.

29. COPD.mp.

30. COAD.mp.

31. COBD.mp.

32. AECB.mp.

33. or/24‐32

34. exp Bronchiectasis/

35. bronchiect$.mp.

36. bronchoect$.mp.

37. kartagener$.mp.

38. (ciliary adj3 dyskinesia).mp.

39. (bronchial$ adj3 dilat$).mp.

40. or/34‐39

41. exp Sleep Apnea Syndromes/

42. (sleep$ adj3 (apnoea$ or apnoea$)).mp.

43. (hypopnoea$ or hypopnoea$).mp.

44. OSA.mp.

45. SHS.mp.

46. OSAHS.mp.

47. or/41‐46

48. Lung Diseases, Interstitial/

49. Pulmonary Fibrosis/

50. Sarcoidosis, Pulmonary/

51. (interstitial$ adj3 (lung$ or disease$ or pneumon$)).mp.

52. ((pulmonary$ or lung$ or alveoli$) adj3 (fibros$ or fibrot$)).mp.

53. ((pulmonary$ or lung$) adj3 (sarcoid$ or granulom$)).mp.

54. or/48‐53

55. 23 or 33 or 40 or 47 or 54

Filter to identify RCTs

1. exp "clinical trial [publication type]"/

2. (randomised or randomised).ab,ti.

3. placebo.ab,ti.

4. dt.fs.

5. randomly.ab,ti.

6. trial.ab,ti.

7. groups.ab,ti.

8. or/1‐7

9. Animals/

10. Humans/

11. 9 not (9 and 10)

12. 8 not 11

The MEDLINE strategy and RCT filter are adapted to identify studies in other electronic databases.

Appendix 3. Search strategy to identify relevant studies from the Cochrane Airways Trials Register

Database: Cochrane Airways Trials Register (Cochrane Register of Studies)

#1 MeSH DESCRIPTOR Pulmonary Disease, Chronic Obstructive Explode All

#2 MeSH DESCRIPTOR Bronchitis, Chronic

#3 (obstruct*) near3 (pulmonary or lung* or airway* or airflow* or bronch* or respirat*)

#4 COPD:MISC1

#5 (COPD OR COAD OR COBD OR AECOPD):TI,AB,KW

#6 #1 OR #2 OR #3 OR #4 OR #5

#7 MESH DESCRIPTOR Adjuvants, Immunologic EXPLODE ALL

#8 immunostimulant*

#9 immunomodulat*

#10 immunoadjuvant*

#11 immunologic adjuvant*

#12 immunobalt or lw50020 or luivac or paspat or munostin

#13 OM‐85 or OM85 or "OM 85"

#14 bronchovaxom or broncho‐vaxom or "broncho vaxom"

#15 pulmonar‐om or "pulmonar om" or pulmonarom

#16 D53

#17 ribomunyl or ribovac or immucytal

#18 MESH DESCRIPTOR Lipopolysaccharides EXPLODE ALL

#19 lipopolysaccharide*

#20 ru41740 or ru‐41740 or "ru 41740" or biostim

#21 MESH DESCRIPTOR Cell Extracts EXPLODE ALL

#22 MESH DESCRIPTOR Thymus Extracts EXPLODE ALL

#23 thymus extract*

#24 thymic extract* or thymomodulin*

#25 thymosin*

#26 MESH DESCRIPTOR Pelargonium

#27 pelargonium* or umckaloabo

#28 am3 or imunoferon or immunoferon or inmunoferon

#29 glycophosphopep*

#30 pidotimod or adimod

#31 MESH DESCRIPTOR Levamisole

#32 levamisole

#33 tucaresol

#34 imiquimod

#35 bacterial NEXT (lysate* OR extract* OR antigen*)

#36 (PMBL or BL):ti,ab

#37 Ismigen

#38 Lantigen B

#39 IRS19 OR "IRS 19"

#40 #7 OR #8 OR #9 OR #10 OR #11 OR #12 OR #13 OR #14 OR #15 OR #16 OR #17 OR #18 OR #19 OR #20 OR #21 OR #22 OR #23 OR #24 OR #25 OR #26 OR #27 OR #28 OR #29 OR #30 OR #31 OR #32 OR #33 OR #34 OR #35 OR #36 OR #37 OR #39

#41 #40 AND #6

Contributions of authors

A Fraser: draft the protocol (lead), develop and run the search strategy (along with Liz Stovold, Information Specialist), obtain copies of studies, select which studies to include, extract data from studies, enter data into Review Manager, carry out the analysis, interpret the analysis, draft the final review, update the review.

P Poole: draft the protocol, develop the search strategy, select which studies to include, extract data from studies, carry out the analysis, interpret the analysis, draft the final review, update the review.

Sources of support

Internal sources

• The authors declare that no such funding was received for this systematic review, Other.

External sources

• The authors declare that no such funding was received for this systematic review, Other.

Declarations of interest

A Fraser: no conflicts of interest to report. Employed initially by Bay of Plenty District Health Board and subsequently by Auckland, Waitemata and Counties Manukau District Health Boards, for the purpose of clinical work as a medical registrar. This financial relationship has no bearing or influence on the submission of this systematic review.

P. Poole: no conflicts of interest to report. Employed by the University of Auckland. This financial relationship has no bearing or influence on the submission of this systematic review.

Contributions of editorial team

Rebecca Fortescue (Co‐ordinating Editor): edited the protocol; advised on methodology; approved the protocol prior to publication. Chris Cates (Co‐ordinating Editor): checked the planned methods. Milo Puhan: edited the review; advised on content. Emma Dennett (Managing Editor): co‐ordinated the editorial process; advised on content; edited the protocol. Emma Jackson (Assistant Managing Editor): conducted peer review; edited the references. Elizabeth Stovold (Information Specialist): designed the search strategy.

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