CD19-B Cell Depletion in PAIS-ME/CFS Patients

Inclusion Criteria: * Male/female/diverse adults who are 18-65 years old at time of enrollment * Subject is able and willing to give informed consent * Signed informed consent prior to initiation of any trial related measure * Diagnosis of PAIS as defined by WHO for PCS, wi th other infectious triggers * Diagnosis of ME/CFS according to CCC criteria with PEM \> 14 hours = PAIS/CFS * Detection of autoantibodies (elevated ß2R adrenergic AAB) prior to immunoadsorption or prior to inclusion to PIONEER * Pre-treatment with immunoadsorption in the immunoadsorption studies at least 6 months before study inclusion * Documented clinical response to immunoadsorption (minimum increase in SF-36 PF of 10 points at week 8) followed by consecutive worsening of symptoms (minimum decrease in SF-36 PF of 10 points for at least 3 months) * Evidence of activated pro inflammatory immune cell status * Bell score at screening visit: 30-60 * Normal thyroid function or sufficiently medicated dysfunction * For women of childbearing potential (WOCBP): 1. Confirmed post-menopausal state, defined as amenorrhea for at least 12 months, or 2. If being of childbearing potential: Negative highly sensitive urine or serum pregnancy test before randomization, and practicing a highly effective birth control method (failure rate of less than 1%) Exclusion Criteria: * Contraindication against IMP or AMP * Hypersensitivity to the active substance or any of the other ingredients * Vaccination less or up to 4 weeks before first visit * Immunomodulative therapy \< 3 month before screening visit * Concomitant and previous use of IMP * Known SARS-CoV-2 or other infection related organ damage/comorbidity * Pre-infection history of chronic fatigue syndrome or other fatigue syndromes that are due to associated diseases (e.g., cancer, autoimmune diseases \[patients with a preexcisting Hashimoto thyroiditis and/or fibromyalgia without fatigue syndromes can be included\]) * Serious infections, including active or latent and chronic infections such as tuberculosis, HIV, Lues, hepatitis B and C * Immune- and immunoglobulin-deficiency or severely immunocompromised condition * Any other severe or unstable medical conditions (immune, cardiovascular, respiratory, endocrine, gastrointestinal, hematological, neurological, psychiatric, systemic) or any other condition deemed by the Investigator to pose unacceptable risk, interfere with IP evaluation, or confound study results. * At screening : aspartate transaminase (AST) \> 2.5 × upper limit of normal (ULN), alanine transaminase (ALT) \> 2.5 × ULN, total bilirubin \> 1.5 × ULN (unless due to Gilbert's syndrome), platelet count \< 75,000/µL, hemoglobin \< 8 g/dL, eGFR\<30 mL/min/1.73 m², total immunoglobulin \< 900 mg/dL, absolute neutrophil count \< 1200 cells/µL, CD4 T lymphocyte count \< 300 cells/µL * Concomitant diseases or health constellations causing general physical weakness or fatigue, like: i) renal insufficiency with eGR\< 15 or diyalsis, ii) impaired liver function with elevated liver enzymes a) Aspartate aminotransferase (AST) and b) Alanin-Aminotransferase (ALT), both \>35 U/l for women or \> 50 U/l for men, iii) anemia with low hemoglobin-concentrations \<13,0 g/dL for males and \<12,0 g/dL for females, and iv) adipositas grades II or higher (BMI: ≥ 35 kg/m 2) at screening * Subject is pregnant or breastfeeding * Subject is institutionalized by order of court or public authority * Subject who might be dependent on the sponsor, the investigator, or the trial site * Participation in another clinical trial with a medical device or an investigational medicinal product within 3 Months or 5 half-lives (whichever is longer) before screening visit