The aim of the study is to assess the effect of polyvalent mechanical bacterial lysate (PMBL, Ismigen) on the clinical course of grass pollen-induced allergic rhinitis (using: total nasal symptom score, visual analogue scale, peak nasal inspiratory flow measurement) in children aged 5 to 17 and to assess changes in the concentration of iNKT cells under the influence of the therapy. Half of the 80 participants will receive PMBL while the other half will receive placebo.

Seasonal allergic rhinitis (SAR) is caused by the allergens of wind-pollinated plants, and in Poland mainly by grass pollen allergens. During the grass pollen season, patients may suffer from fatigue, weakness, lack of fitness, difficulty in sleeping and reduced performance at school. In people allergic to the above-mentioned pollen, the disease significantly reduces the quality of life and requires intensive treatment in the pollen period.

Due to the high incidence of allergic rhinitis, the negative impact of the disease on the quality of life, and incomplete effectiveness of previously available therapeutic methods, new methods of treatment are being developed. Recent research highlights the immunoregulatory potential of bacterial lysates, indicating the possibility of their future use in the prevention and treatment of allergic diseases, including atopic dermatitis, allergic rhinitis, and asthma. However, the mechanism of action of these drugs in allergic diseases is still not entirely clear.

iNKT (Invariant Natural Killer T) are a conserved line of T cells with unique features expressing the invariant TCR alpha chain and recognizing glycolipids presented in the context of the non-classical MHC molecule, CD1d. As a result of TCR stimulation, iNKT cells are able to quickly secrete a variety of cytokines, thus stimulating various immune processes and playing an immunoregulatory role. iNKT cells are a small percentage of all T cells, however numerous studies indicate their possible participation in the pathogenesis of allergic diseases.The ambivalence of the activity of iNKT cells may result from the heterogeneity of this subpopulation. iNKT cells, like T lymphocytes, can be divided into further subpopulations: iNKT1, iNKT2, iNKT10, iNKT17 and iNKTreg. Individual subpopulations have a different cytokine profile, and thus may play opposite functions in the pathomechanism of many diseases, including allergic ones.

The main aim of this study is to evaluate the clinical course of the pollen allergic rhinitis, caused by grass pollen allergens in children during the grass pollen season, treated with polyvalent mechanical bacterial lysate (PMBL) and to assess the impact of PMBL on changes in the concentrations of the iNKT cell subpopulation. The approval of the Bioethics Committee at the Medical University in Lublin was obtained for the study.

Eighty children with SAR will be enrolled to this study and randomly assigned to the PMBL group (n=40) and placebo group (n=40). The study will include six visits, 2 site visits (before the grass pollen season and at the peak of the grass pollen season) and 4 telephone visits.The first site visit will be the randomization visit. The second site visit will take place after the end of the drug intake period. Telephone contact with the patient will take place twice during the period of taking the drug, and twice after the end of this period (follow-up visits).The time frame of the grass pollen season for south-eastern Poland will be determined using the "95%" method on the basis of measurements of grass pollen concentration in the atmospheric air, which will be obtained from the Environmental Allergy Research Centre in Warsaw. Patients will start taking sublingual tablets at the beginning of the April 2021.

Nasal SAR symptoms will be recorded by parents of children in the daily patient diary according to the standard scoring system (TNSS, total nasal symptom score), and their intensity will be also evaluated during six visits using VAS (visual analogue scale). At each site visit, peak nasal inspiratory flow (PNIF) will be also measured.

In order to determine the mechanism responsible for the possible effects of PMBL, blood samples (8 ml) will be taken from patients for additional tests during two site visits. The following iNKT cell subpopulations will be measured in the blood: iNKT1, iNKT2, iNKT10, iNKT17 and iNKTreg.

Inclusion Criteria:

• Children of both genders aged 5 to 17 years.
• Children with grass pollen-induced allergic rhinitis recognized and treated according to current ARIA (Allergic Rhinitis and its Impact on Asthma) recommendations.
• Positive skin prick test to grass pollen allergens or positive specific IgE (defined as ≥ class 2, ≥ 0,70 kU/l) against timothy grass pollen allergens.
• Presentation of clinical symptoms of the allergic rhinitis (rhinorrhea, nasal congestion, nasal itching, sneezing) in at least two recent grass pollen seasons in Poland before inclusion in the study.
• Proper use of polyvalent mechanical bacterial lysate sublingual tablets.
• Not using drugs to alleviate the symptoms of allergic rhinitis in the last 7 days prior to enrollment in the study: intranasal glucocorticosteroids, intranasal, oral and ophthalmic antihistamines, intranasal and oral alpha-mimetics, intranasal anticholinergics, antileukotrienes and cromones.
• Written informed consent obtained from parents/guardians before any study related procedures are performed.

Exclusion Criteria:

• Patient received mechanical bacterial lysate immunostimulation within the previous 12 months before randomisation visit.
• Patient received chemical bacterial lysate immunostimulation within the previous 6 months before randomisation visit.
• Patient received oral/subcutaneous allergen-immunotherapy within the previous 3 years before the start of the study.
• Other chronic conditions of the nose or nasal sinuses.
• Severe nasal septum deviation.
• Acute respiratory infection in the 2 weeks prior to randomization visit.
• Treatment with systemic corticosteroids within the last 6 months before the start of the study.
• History of transfusion of blood, blood components or blood products.
• Pregnant or breastfeeding woman.
• Other chronic, uncontrolled diseases of the respiratory tract, gastrointestinal tract, urinary system, hematological diseases, immunodeficiency, cancer, cystic fibrosis.