Hepes buffer

RM 1 and RM 2 were prepared by GBD mbH by diluting the SARS-CoV-2 positive cell culture supernatant as follows:
Dilution was performed using cell culture medium (Minimal Essential Medium, PanBioTech, Aidenbach, Germany) supplemented with non-essential amino acids (PanBioTech); HEPES buffer (PanBioTech) and fetal bovine serum (PanBioTech, gamma irradiated; 15% v/v for supplemented cell culture medium).
In total 2,300 vials each of RM 1 and RM 2 (1.1 mL per vial) were aliquoted in screw cap micro tubes (2.0 mL; Sarstedt, Nuermbrecht, Germany). Before lyophilization, primary freezing of the filled micro tubes was performed at -30 °C (4–12 hours) followed by freezing at -70 °C over night.
Process controlled lyophilization was performed in an Epsilon 2-10D LSC freeze dryer (Martin Christ Gefriertrocknungsanlagen GmbH, Osterode, Germany). The gradual lyophilization profile over a period of 72 hours included: (i) a temperature change from -70 °C to 20 °C and (ii) a pressure change from atmospheric pressure to 6 x 10⁻² bar. At the end of lyophilization, the micro tubes were manually topped with screw caps. The RMs were stored at <-20 °C until they were shipped to the laboratories at ambient temperature.

The monocytic cell line THP-1 and alveolar epithelium cell line A549 were used to quantify the toxicity of the irradiation on human cells. Both cell lines were incubated at 37 °C in a 5% CO₂ atmosphere in ambient humidified air. THP-1 cells were grown in RPMI 1640 (Gibco™ RPMI 1640 Medium, GlutaMAX™, Life Technologies Limited, Paisley, UK) containing phenol red, supplemented with 0.01 M HEPES Buffer (PAN-Biotech, Aidenbach, Germany), 10% v/v fetal bovine serum (FBS superior stabil, Bio&Sell, Feucht, Germany) and 0.2% v/v 2-mercaptoethanol (SERVA Electrophoresis, Heidelberg, Germany). The A549 cells were incubated in DMEM medium (DMEM, high glucose, Life Technologies Limited, Paisley, UK) containing phenol red, supplemented with 10% v/v fetal bovine serum (FBS superior stabil, Bio&Sell, Feucht, Germany) and 1 mM sodium pyruvate (Life Technologies Limited, Paisley, UK). Both cell culture media were supplemented with 1% v/v Penicillin–Streptomycin (PAN-Biotech, Aidenbach, Germany).

KMS 18 (University of Leeds, Leeds, England) and U-266 (DSMZ, Braunschweig, Germany) are both cell lines derived from patients suffering from multiple myeloma. Both cell lines were cultured in 75 cm ${}^2$ culture flasks using RPMI-medium (PAN Biotech, Aidenbach, Germany) supplemented with 10% fetal calf serum (FCS) (Gibco Life Technologies, Darmstadt, Germany) and 1% penicillin/streptomycin (P/S) (Life Technologies, Darmstadt, Germany). Cells were kept at 37 °C and 5% CO₂. New Medium was added every 3 days and completely replaced at least once a week or whenever deemed necessary. Cells were split weekly or whenever splitting was required.
CIK cells were cultured in RPMI-medium supplemented with 10% FCS and 1% P/S. Additionally the medium was buffered with 2.5% HEPES buffer (PAN Biotech). Every 3 days part of the medium was renewed and 300 U·mL ${}^{-1}$ interleukin-2 (IL-2) (Immuno Tools, Friesoythe, Germany, and, Novartis Pharma GMBH, Nuernberg, Germany) was added to the culture flask. CIK cells were not centrifuged, unless part of the culture was harvested for further experiments.