Treatment of Presymptomatic (Stage 1) Type 1 Diabetes Pediatric Patients With Treg Cell Preparations and Anti-CD20 Antibody

Inclusion Criteria: 1. Age 3-18 2. 5 ≤ BMI ≤ 95 percentile (acc. to OLAF, or WWF in the case of children under six years old) with a lower weight threshold of 20 kg 3. Venous plasma glucose levels \< 100mg% at fasting (70 to 100 mg/dl) and normal glucose tolerance test (at 120 minutes glycaemia \<140 mg/dl) (acc. to PTD) 4. Insulin independence 5. C-peptide levels ≥ 1.0 ng/ml (central laboratory limit of normal) in fasting and post-stimulation tests increase ≥ 100% 6. Participant has not yet been diagnosed with stage 2 or 3 type 1 diabetes mellitus (no history of dysglycemia, no history of clinical symptoms of type 1 diabetes mellitus) 7. HbA1c level (%) \<5,7% (acc. to ADA) 8. Positive autoantibody titres (ICA, IAA, GAD, IA-2/ICA512, ZnT8) - low titers of two or more antibodies (2 times the normal\* or higher); if high titer of one of the antibodies (≥ 4 times the norm, not applicable to ICA) re-screening allowed (the participant can be included in the trial only after confirming two or more antibodies) 9. Ability to give informed consent by the child's legal representatives (and the child himself or herself if he or she is over the age of 13 at the time of the trial \[according to local law\]) 10. Ability of the child's legal representatives to manage diabetes, defined as blood glucose levels control at least three times a day and the ability to dose insulin correctly. 11. Venous access to guarantee blood donation \* Standard defined depending on the method used Exclusion Criteria: 12. Refusal to participate in the trial or lack of a signed informed consent form 13. Suspicion or diagnosis for a type of diabetes other than type 1 diabetes mellitus 14. Age under 3 or above 18 15. IgA deficiency or history of other diagnosed immunodeficiency (max. 7 infections/year allowed, and the prognosis should indicate that the patient will remain in the study throughout its duration) 16. C-peptide levels \< 1.0 ng/ml fasting and in post-stimulation tests increase \< 100% 17. Glucose levels in venous blood ≥ 100mg% fasting 18. Glucose levels in venous blood after 1 and 2 hours in OGTT ≥ 200mg% 19. Glycated hemoglobin level (HbA1c) in venous blood ≥ 5,7% 20. BMI \< 5th percentile or \> 95th percentile for age, or body weight \< 20 kg 21. History of hypersensitivity to anti-CD20 or other components of the preparation 22. History of hypersensitivity to penicillin and/or streptomycin 23. Past or active infection with HBV, HCV, HIV, HTLV I/II, mycobacterium tuberculosis, syphilis. Laboratory evidence of infection without the need for clinical signs and symptoms is sufficient for diagnosis. 24. Active infection with the EBV or CMV virus (positive IgM) 25. Any fungal, parasitic, viral, or bacterial infection 26. History of past or active cancer 27. Anemia, lymphopenia, neutropenia, or thrombocytopenia defined as a blood cell count below the lower limit of normal for age found within the last 6 weeks prior to trial inclusion 28. Elevated thrombotic activity/history of thrombosis episode 29. Any disease prior to inclusion in the trial currently requiring medication for more than 3 months in history 30. Diagnosed autoimmune disease other than type 1 diabetes mellitus, including a history of Hashimoto's disease and coeliac disease 31. Taking anti-diabetic medication (including insulin) in the last 4 weeks prior to trial inclusion 32. History of retinopathy 33. History of hypertension 34. Current or history of albuminuria 35. For women in childbearing potential/menstruating women: pregnancy (from medical interview) or unwillingness to exercise sexual restraint or use effective forms of contraception for the duration of the trial and up to 4 months after completion, if applicable. The following contraceptive methods are acceptable: bilateral fallopian tube closure, sterilization in men, appropriate use of hormonal contraception that inhibits ovulation, hormone-releasing IUDs, and copper IUDs, male or female condoms with spermicide; and cap, uterine disc, or sponge with spermicide. 36. Breastfeeding 37. For males over 15 years of age: expressed intention to have offspring or donate sperm during the trial or within 4 months after the end of the trial, if applicable 38. Excessive anxiety of the participant or his/her legal representatives regarding the procedures used in the trial 39. Any medical problem that, in the opinion of the investigator, may adversely affect the participant's health if included in the trial 40. Legal representatives and/or children over the age of 15 with an identified alcohol and/or psychoactive substance addiction 41. History of disease of unknown etiology 42. History of Creutzfeldt-Jacob disease 43. History of progressive dementia or degenerative neurological disease, including of unknown origin 44. History of taking hormones derived from the human pituitary gland (e.g., growth hormone) 45. Treatment with immunosuppressants 46. History of corneal, scleral, and dural transplant or undocumented neurosurgery 47. History of occurrence of risk factors related to the participant's travel, where there is a possibility of exposure to regional infectious diseases 48. Physical signs that indicate the risk of an infectious disease 49. History of xenogeneic transplant