Recent advances in monoclonal antibody therapy in IBD: practical issues

Advancements in Targeted Therapies for the Management of Crohn's Disease: A Comprehensive Review

Crohn's disease (CD) is a complex clinical condition characterized by persistent gastrointestinal inflammation that leads to episodes of flare-ups and subsequent healing. The treatment options for this disease are heterogeneous as its impact on different patients is also different. This study aims to evaluate the effectiveness of recently approved drugs that specifically target certain pathways within cells that are involved in CD pathogenesis. These medicines include biologics like anti-TNF agents, interleukin inhibitors, and small molecule inhibitors; they work by altering the modulation of immune responses and reducing inflammation. These drugs seem promising in terms of inducing remission in moderate to severe CD among various patient populations. Conversely, it is possible to examine how well these drugs perform using gene expression and molecular markers. By understanding these results along with other ongoing trials, personalized medicine can be used more frequently by doctors who will adopt a strategy for an individual patient, maximizing benefits while minimizing adverse effects. There are still some issues that need to be worked out like the high cost associated with these drugs or immunogenicity risk and infectious complications too. In conclusion, there has been a remarkable improvement in CD management over the past decade with customized drugs leading toward a precision medical era. Further understanding of molecular mechanisms implicated in CD pathogenesis and new therapeutic approaches could potentially improve treatment outcomes among affected individuals. This research is crucial in understanding how CD therapeutics are changing, thus facilitating selection by doctors on the most appropriate methods for individualized patient care.

Clinical Validation of a Capillary Blood Home-Based Self-Sampling Technique for Monitoring of Infliximab, Vedolizumab, and C-Reactive Protein Concentrations in Patients With Inflammatory Bowel Disease

BACKGROUND

Therapeutic drug monitoring provides important guidance for treatment of patients with inflammatory bowel disease (IBD) and could help to early identify treatment failure. This study aimed to validate a finger prick-based capillary blood sampling technique to measure biological trough levels and C-reactive protein (CRP) and evaluate patient performance and -support.

METHODS

In this prospective cohort study, patients with IBD receiving infliximab (IFX) or vedolizumab (VEDO) therapy performed finger prick-based capillary blood sampling at home. Additionally, blood was collected through routinely performed in-hospital venepuncture prior to biological infusion. IFX, VEDO, and CRP concentrations were measured by enzyme-linked immunosorbent assay. The concordance between methods was statistically evaluated and a survey was conducted to assess practicality and patient support.

RESULTS

In total, 81 patients (46 IFX, 35 VEDO) were enrolled. Mean differences between both methods were 0.42 (95% confidence interval, -1.74 to 2.58) μg/mL for IFX and 0.72 (95% confidence interval, -5.50 to 6.94) μg/mL for VEDO. Passing-Bablok regressions demonstrated no evidence for systematic or proportional biases. Venous and capillary IFX (ρ = 0.96, P < .001) and VEDO (ρ = 0.97, P < .001) levels strongly correlated and showed high intermethod agreement (Cohen's kappa: IFX = 0.82; VEDO = 0.94). Similarly, venous and capillary CRP levels were strongly correlated (ρ = 0.99, P < .001). Most patients (>95%) were able to successfully perform the self-sampling at home without prior instructions.

CONCLUSIONS

This study clinically validated a finger prick-based capillary blood self-sampling technique allowing concomitant home monitoring of biological levels and CRP for patients with IBD, who reported substantial support, tolerability, and practicality.

Efficacy and Safety of Adalimumab Biosimilar GP2017 in Patients with Inflammatory Bowel Disease

(1) Background: GP2017 is one of the biosimilar drugs of adalimumab, one of the anti-TNF agents used for inflammatory bowel disease (IBD). To date, there is little real-world data about the use of GP2017 in IBD patients. The aim of our study was to evaluate the effectiveness and safety of this biosimilar in an IBD population. (2) Methods: This is an observational retrospective study including patients that were all treated with GP2017 as a first step or as a switch from the originator or other biosimilars. The clinical activity was evaluated at baseline and after 6 and 12 months of therapy. The therapy discontinuation and side effects were also evaluated. (3) Results: a total of 72 patients were included (65 with Crohn's disease and 7 with ulcerative colitis). Of the 29 patients starting GP2017 as a first adalimumab therapy, clinical remission was achieved in 58.6%. Of the patients starting GP2017 as a switch from the originator (33 patients) or other biosimilars (10 patients), clinical remission was maintained in 78.8% and in 70%, respectively. Regarding the safety, only 11 patients experienced non-serious side effects. During the follow-up, nine patients suspended treatment mainly due to side effects or secondary failure. (4) Conclusions: GP2017 is an effective and safe therapy for IBD patients.

Unmet Challenges in Patients with Crohn's Disease

Patients with Crohn's disease can present with a variety of clinical manifestations; treatment strategies should focus on long-term remission and improvement of quality of life. There is no standardized process of diagnosing, predicting prognosis, and treating the disease. This narrative review was based on a literature search using PubMed, Embase, and Science Direct. Data on unmet challenges in patients with Crohn's disease were extracted from identified manuscripts. The aim was to discuss present research on standardized processes in the management of patients with Crohn's disease and to identify the unmet needs in clinical evaluation and treatment approaches. There is no consensus on standardized diagnostic, treatment, and surveillance algorithms, particularly in assessing complications of Crohn's, such as stricturing disease, intestinal cancer risk, and cutaneous manifestations. Complications and treatment failure rates of conventional, interventional, and surgical therapy place emphasis on the need for standardized treatment algorithms, particularly in the case of acute complications of the disease. Research on standardized clinical approaches, reliable biomarkers for disease diagnosis and therapy monitoring, and new treatment agents is necessary to improve therapy and reduce complications in patients with Crohn's disease.

Revealing the SARS-CoV-2 Spike Protein and Specific Antibody Immune Complex Formation Mechanism for Precise Evaluation of Antibody Affinity

The profound understanding and detailed evaluation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (SCoV2-S) protein and specific antibody interaction mechanism is of high importance in the development of immunosensors for COVID-19. In the present work, we studied a model system of immobilized SCoV2-S protein and specific monoclonal antibodies by molecular dynamics of immune complex formation in real time. We simultaneously applied spectroscopic ellipsometry and quartz crystal microbalance with dissipation to reveal the features and steps of the immune complex formation. We showed direct experimental evidence based on acoustic and optical measurements that the immune complex between covalently immobilized SCoV2-S and specific monoclonal antibodies is formed in two stages. Based on these findings it was demonstrated that applying a two-step binding mathematical model for kinetics analysis leads to a more precise determination of interaction rate constants than that determined by the 1:1 Langmuir binding model. Our investigation showed that the equilibrium dissociation constants (KD) determined by a two-step binding model and the 1:1 Langmuir model could differ significantly. The reported findings can facilitate a deeper understanding of antigen-antibody immune complex formation steps and can open a new way for the evaluation of antibody affinity towards corresponding antigens.

Drug delivery improvements to enable a flexible care setting for monoclonal antibody medications in oncology - Analogue-based decision framework

INTRODUCTION

The substantial acceleration in healthcare spending together with the expenditures to manage the COVID19 pandemic demand drug delivery solutions that enable a flexible care setting for high-dose monoclonal antibodies (mAbs) in oncology.

AREAS COVERED

This expert opinion introduces an analogue-based framework applied to guide decision-making for associated product improvements for mAb medications that are either already authorized or in late-stage clinical development. The four pillars of this framework comprise (1) the drug delivery profile of current and emerging treatments in the market, (2) the needs and preferences of people treated with mAbs, (3) existing healthcare infrastructures, and (4) country-dependent reimbursement and procurement models. The following product optimization examples for mAb-based treatments are evaluated based on original research and review articles in the field: subcutaneous formulations, an established drug delivery modality to reduce parenteral dosing complexity, fixed-dose combinations, an emerging concept to complement combination therapy, and (connected) on-body delivery systems, an identified future opportunity to support dosing outside of a controlled healthcare institutional environment.

EXPERT OPINION

Leveraging existing synergies and learnings from other disease areas is a measure to reduce associated development and commercialization costs and thus to provide sustainable product offerings already at the initial launch of a medication.

Autoantibodies - enemies, and/or potential allies?

Autoantibodies are well known as potentially highly harmful antibodies which attack the host via binding to self-antigens, thus causing severe associated diseases and symptoms (e.g. autoimmune diseases). However, detection of autoantibodies to a range of disease-associated antigens has enabled their successful usage as important tools in disease diagnosis, prognosis and treatment. There are several advantages of using such autoantibodies. These include the capacity to measure their presence very early in disease development, their stability, which is often much better than their related antigen, and the capacity to use an array of such autoantibodies for enhanced diagnostics and to better predict prognosis. They may also possess capacity for utilization in therapy, in vivo. In this review both the positive and negative aspects of autoantibodies are critically assessed, including their role in autoimmune diseases, cancers and the global pandemic caused by COVID-19. Important issues related to their detection are also highlighted.

Curcumin-Loaded Microspheres Are Effective in Preventing Oxidative Stress and Intestinal Inflammatory Abnormalities in Experimental Ulcerative Colitis in Rats

Curcumin’s role in the treatment of ulcerative colitis (UC) has been proven by numerous studies, but its preventive administration, with the aim of reducing the remission episodes that are characteristic of this disease, must be further investigated. This study investigates the effects of a novel curcumin-loaded polymeric microparticulate oral-drug-delivery system for colon targeting (Col-CUR-MPs) in an experimental model of UC. Male Wistar rats (n = 40) were divided into five groups (n = 8), which were treated daily by oral gavage for seven days with a 2% aqueous solution of carboxymethylcellulose sodium salt (CMCNa) (healthy and disease control), free curcumin powder (reference), Col-CUR-MPs (test) and prednisolone (reference) prior to UC induction by the intrarectal administration of acetic acid (AA), followed by animal sacrification and blood and colonic samples’ collection on the eighth day. Col-CUR-MPs exhibited an important preventive effect in the severity degree of oxidative stress that resulted following AA intrarectal administration, which was proved by the highest catalase (CAT) and total antioxidant capacity (TAC) levels and the lowest nitrites/nitrates (NOx), total oxidative status (TOS) and oxidative stress index (OSI) levels. Biochemical parameter analysis was supported by histopathological assessment, confirming the significant anti-inflammatory and antioxidant effects of this novel colon-specific delivery system in AA-induced rat models of UC. Thus, this study offers encouraging perspectives regarding the preventive administration of curcumin in the form of a drug delivery system for colon targeting.

Application of recombinant antibodies for treatment of Clostridioides difficile infection: Current status and future perspective

Clostridioides difficile (C. difficile), known as the major cause of antibiotic-associated diarrhea, is regarded as one of the most common healthcare-associated bacterial infections worldwide. Due to the emergence of hypervirulent strains, development of new therapeutic methods for C. difficile infection (CDI) has become crucially important. In this context, antibodies have been introduced as valuable tools in the research and clinical environments, as far as the effectiveness of antibody therapy for CDI was reported in several clinical investigations. Hence, production of high-performance antibodies for treatment of CDI would be precious. Traditional approaches of antibody generation are based on hybridoma technology. Today, application of in vitro technologies for generating recombinant antibodies, like phage display, is considered as an appropriate alternative to hybridoma technology. These techniques can circumvent the limitations of the immune system and they can be exploited for production of antibodies against different types of biomolecules in particular active toxins. Additionally, DNA encoding antibodies is directly accessible in in vitro technologies, which enables the application of antibody engineering in order to increase their sensitivity and specificity. Here, we review the application of antibodies for CDI treatment with an emphasis on recombinant fragment antibodies. Also, this review highlights the current and future prospects of the aforementioned approaches for antibody-mediated therapy of CDI.

Activation pathways that drive CD4+ T cells to break tolerance in autoimmune diseases. Immunol Rev 2022;307:161-190. [PMID: 35142369 PMCID: PMC9255211 DOI: 10.1111/imr.13071]

Autoimmune diseases are characterized by dysfunctional immune systems that misrecognize self as non-self and cause tissue destruction. Several cell types have been implicated in triggering and sustaining disease. Due to a strong association of major histocompatibility complex II (MHC-II) proteins with various autoimmune diseases, CD4+ T lymphocytes have been thoroughly investigated for their roles in dictating disease course. CD4+ T cell activation is a coordinated process that requires three distinct signals: Signal 1, which is mediated by antigen recognition on MHC-II molecules; Signal 2, which boosts signal 1 in a costimulatory manner; and Signal 3, which helps to differentiate the activated cells into functionally relevant subsets. These signals are disrupted during autoimmunity and prompt CD4+ T cells to break tolerance. Herein, we review our current understanding of how each of the three signals plays a role in three different autoimmune diseases and highlight the genetic polymorphisms that predispose individuals to autoimmunity. We also discuss the drawbacks of existing therapies and how they can be addressed to achieve lasting tolerance in patients.

Recent advancements in clearance monitoring of monoclonal antibodies in patients with inflammatory bowel diseases

INTRODUCTION

Less than 50% of patients with inflammatory bowel diseases (IBD) receiving monoclonal antibody (mAb) therapy achieve endoscopic remission. Poor outcomes may indicate a need for dose optimization. During therapeutic drug monitoring (TDM), drug concentrations are measured, and when found too low, dosage regimen escalations are performed. To date, benefits of TDM of mAbs in patients with IBD are uncertain.

AREAS COVERED

This review presents an overview of what clearance monitoring is, how it can be performed, and why and when it may be valuable in treating patients with IBD. Virtual patients were used for illustration. A literature search was performed to summarize current evidence for clearance monitoring in IBD and other disease settings.

EXPERT OPINION

During clearance monitoring, mAb clearance is calculated and monitored over time. Higher mAb clearance in patients with IBD has been associated with higher target load (target-mediated drug disposition), protein-losing enteropathy (fecal drug loss), and immunogenicity. Although not prospectively confirmed, clearance monitoring might facilitate identification of (yet) asymptomatic disease flares or presence of (yet) undetectable anti-drug antibodies. Furthermore, clearance monitoring may be used to predict treatment outcomes. Whether dosage regimen adjustments can modify the clearance time course and the treatment outcome is to be determined.

Determining Response to Treatment for Drug-Induced Bronchocentric Granulomatosis by the Forced Oscillation Technique

Anti-tumor necrosis factor alpha (TNFα) therapy is widely used to treat various inflammatory conditions. Paradoxically, there are several case reports describing the development of bronchocentric granulomatosis treated with TNFα inhibitors, and it is difficult to determine the effect of treatment using conventional spirometry because the lesions are located in small airways. However, it has been reported that the forced oscillation technique (FOT) is useful in the evaluation of small airway disease in bronchial asthma or chronic obstructive pulmonary disease. We performed the FOT to determine the effect of treatment on bronchocentric granulomatosis and found it to be useful. We report the case of a 55-year-old female with ulcerative colitis who was treated with golimumab and who developed bronchocentric granulomatosis as a sarcoid-like reaction to golimumab. She was successfully treated with prednisone, and the treatment efficacy was confirmed by the FOT. The FOT may be useful in the evaluation of small airway disease in bronchocentric granulomatosis. This case may help inform clinicians of the usefulness of the FOT to assess small airway disease in various diseases.

Switching from Biosimilar to Biosimilar Adalimumab, Including Multiple Switching, in Crohn's Disease: A Prospective Study

No data are available regarding the safety and effectiveness of the biosimilar-to-biosimilar switch of adalimumab in any disease, and in particular in Crohn’s disease (CD). The aim of our study was to provide real world data on switching from biosimilar adalimumab to another biosimilar, including multiple switching. We conducted a prospective, single-centre observational study in which we consecutively recruited all CD patients who switched from adalimumab biosimilar ABP 501 to biosimilar SB5 from January to July 2021. Sixty-one patients were included in the final analysis, of whom 43/61 (70.5%) were multiple switches (Humira^® → ABP 501 → SB5). After 6 months of follow up, 88.5% (54/61) of patients maintained SB5 on therapy. The success of the switch (defined as no systemic corticosteroids within 6 months, non-discontinuation of SB5, no dose escalation) was achieved by 82.0% (50/61) of patients. At multivariate analysis, C-reactive protein > 5 mg/L predicted switch failure (p = 0.03). Seven patients (11.5%) experienced side effects, compared to one patient (1.6%) in the 6 pre-switch months (p = 0.03). In conclusion, switching from biosimilar to biosimilar of adalimumab did not lead to signs of safety or loss of efficacy other than those already known in the literature for the class of drugs.

Second Mexican consensus on biologic therapy and small-molecule inhibitors in inflammatory bowel disease

INTRODUCTION

Inflammatory bowel disease (IBD) is a chronic and incurable entity. Therapy with anti-TNF-α agents was the first biologic therapy approved in Mexico for IBD. New biologic agents, such as vedolizumab and ustekinumab, have recently been added, as have small-molecule inhibitors.

AIM

To update the biologic therapeutic approach to IBD in Mexico with new anti-TNF-α agents and novel biologics whose mechanisms of action induce and maintain remission of Crohn's disease and ulcerative colitis (UC).

MATERIALS AND METHODS

Mexican specialists in the areas of gastroenterology and inflammatory bowel disease were summoned to participate. The consensus was divided into 3 modules, with 49 statements. The Delphi method was applied, sending the statements to all participants to be analyzed and edited, before the face-to-face meeting. During said meeting, the clinical studies were shown, emphasizing the level of clinical evidence, and the final discussion and voting round on the level of agreement of all the statements was conducted.

RESULTS

In this second Mexican consensus, recommendations are made for new anti-TNF-α agents, such as golimumab, new biologics with other mechanisms of action, such as vedolizumab and ustekinumab, as well as for the small-molecule inhibitor, tofacitinib.

CONCLUSIONS

The updated recommendations focus on patient-reported outcomes, biologic therapy, small-molecule inhibitors, and the safety aspects of each of the drugs.

Combination of Biological Agents in Moderate to Severe Pediatric Inflammatory Bowel Disease: A Case Series and Review of the Literature

BACKGROUND

Treatment with biological agents such as anti-tumor necrosis factors (TNFs) has become standard of care in moderate to severe pediatric inflammatory bowel disease (IBD). However, a significant proportion of patients experience loss of response to anti-TNFs, need treatment escalation, or develop side effects. There is no data in the literature regarding combination of biological agents in pediatric IBD.

METHODS

At our hospital, which is a tertiary referral center, we have combined the anti-TNF infliximab with either vedolizumab or ustekinumab in patients with severe pediatric IBD. The indications for dual biological therapy were insufficient efficacy of infliximab or vedolizumab monotherapy, or side effects such as psoriasis due to anti-TNFs.

RESULTS

Eight patients (four boys) aged 14-17.5 years received a combination of infliximab and vedolizumab due to only a partial response to infliximab, four with Crohn's disease (CD) and four with ulcerative colitis (UC). Clinical remission was achieved in four patients (3 UC) and four had a colectomy (3 CD, 1 UC). Five CD patients (3 girls) aged 11-17 years, on maintenance therapy with infliximab, developed psoriasis resistant to topical treatment. A combination of infliximab and ustekinumab resulted in clinical remission of CD without skin symptoms. No serious adverse events occurred in any of the patients on combination therapy. Thirteen publications report on combining biologicals, all in adult IBD.

CONCLUSION

In pediatric IBD, combining biological agents seems to be safe and beneficial in selected patients. The safety should be addressed in long-term follow-up studies.

Vaccination in patients under monoclonal antibody treatment: an updated comprehensive review

INTRODUCTION

Monoclonal antibodies (mAbs) have become an increasing source of biological treatments. Clinicians should make an effort to update their knowledge on mechanisms of action, indications, and adverse events of these novel therapies. Most of them have immunosuppressive effects and, therefore, vaccination is indicated.

AREAS COVERED

vaccination of patients under mAbs therapies.

EXPERT OPINION

Recommendations on vaccination are still based on expert recommendations and have not been updated in recent years. Specific recommendations for each mAb have not been addressed in the current literature. The aim of this comprehensive review was to collect all the therapeutic mAbs approved up to 1 January 2020 and, based on previous recommendations and the pharmaceutical characteristics of each drug, to propose an updated guide with recommendations on vaccination. Influenza, sequential pneumococcal and Hepatitis B vaccination in patients with negative serology were the only consistent recommendations. Hepatitis A vaccination was proposed for mAbs with special hepatotoxic characteristics. Other vaccines are reviewed and discussed. Several non-immunosuppressive mAbs were detected and, therefore, vaccinations not recommended. We hope that this review can serve as a starting point for compiling updated vaccination recommendations and collecting all the therapeutic mAbs approved up to 2020.

Safety and Immunological Evaluation of Interleukin-21 Plus Anti-α4β7 mAb Combination Therapy in Rhesus Macaques

Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) infections compromise gut immunological barriers, inducing high levels of inflammation and a severe depletion of intestinal CD4+ T cells. Expression of α4β7 integrin promotes homing of activated T cells to intestinal sites where they become preferentially infected; blockade of α4β7 with an anti-α4β7 monoclonal antibody (mAb) prior to infection has been reported to reduce gut SIV viremia in rhesus macaques (RMs). Interleukin-21 (IL-21) administration in antiretroviral therapy-treated, SIV-infected RMs reduces gut inflammation and improves gut integrity. We therefore hypothesized that the combination of IL-21 and anti-α4β7 mAb therapies could synergize to reduce inflammation and HIV persistence. We co-administered two intravenous doses of rhesus anti-α4β7 mAb (50 mg/kg) combined with seven weekly subcutaneous infusions of IL-21-IgFc (100 μg/kg) in four healthy, SIV-uninfected RMs to evaluate the safety and immunological profiles of this intervention in blood and gut. Co-administration of IL-21 and anti-α4β7 mAb showed no toxicity at the given dosages as assessed by multiple hematological and chemical parameters and did not alter the bioavailability of the therapeutics or result in the generation of antibodies against the anti-α4β7 mAb or IL-21-IgFc. Upon treatment, the frequency of CD4 memory T cells expressing β7 increased in blood and decreased in gut, consistent with an inhibition of activated CD4 T-cell homing to the gut. Furthermore, the frequency of T cells expressing proliferation and immune activation markers decreased in blood and, more profoundly, in gut. The combined IL-21 plus anti-α4β7 mAb therapy is well-tolerated in SIV-uninfected RMs and reduces the gut homing of α4β7+ CD4 T cells as well as the levels of gut immune activation.

Cannabidiol and Other Non-Psychoactive Cannabinoids for Prevention and Treatment of Gastrointestinal Disorders: Useful Nutraceuticals?

Cannabis sativa is an aromatic annual flowering plant with several botanical varieties, used for different purposes, like the production of fibers, the production of oil from the seeds, and especially for recreational or medical purposes. Phytocannabinoids (terpenophenolic compounds derived from the plant), include the well-known psychoactive cannabinoid Δ9-tetrahydrocannabinol, and many non-psychoactive cannabinoids, like cannabidiol. The endocannabinoid system (ECS) comprises of endocannabinoid ligands, enzymes for synthesis and degradation of such ligands, and receptors. This system is widely distributed in the gastrointestinal tract, where phytocannabinoids exert potent effects, particularly under pathological (i.e., inflammatory) conditions. Herein, we will first look at the hemp plant as a possible source of new functional food ingredients and nutraceuticals that might be eventually useful to treat or even prevent gastrointestinal conditions. Subsequently, we will briefly describe the ECS and the general pharmacology of phytocannabinoids. Finally, we will revise the available data showing that non-psychoactive phytocannabinoids, particularly cannabidiol, may be useful to treat different disorders and diseases of the gastrointestinal tract. With the increasing interest in the development of functional foods for a healthy life, the non-psychoactive phytocannabinoids are hoped to find a place as nutraceuticals and food ingredients also for a healthy gastrointestinal tract function.

Prediction of response to biological treatment with monoclonal antibodies in severe asthma

In recent years, major developments have occurred in severe asthma management. Different asthma phenotypes and subgroups have been identified and new treatment options have become available. A total of five monoclonal antibodies are currently approved in severe asthma treatment: omalizumab, mepolizumab, reslizumab, benralizumab and dupilumab. These drugs have been shown to reduce exacerbations and to have an oral corticosteroid-sparing effect in many severe asthma patients. However, biological treatment is not successful in all patients and should be discontinued in non-responsive patients. Treating the right patient with the right biologic, and therefore biologic response prediction, has become a major point of interest in severe asthma management. A variety of response outcomes is utilized in the different clinical trials, as well as a huge range of potential predicting factors. Also, regarding the timing of the response evaluation, there are considerable differences between studies. This review summarizes the results from studies on predicting responses and responders to biological treatment in severe asthma, taking into account clinical, functional and inflammatory parameters assessed prior to the start of treatment as well as following a few months of therapy. In addition, future perspectives are discussed, highlighting the need for more research to improve patient identification and treatment responses in the field of biological treatment in severe asthma.