Methods
We treated four critically ill children actively infected with SARS-CoV-2 with CP at the Children’s Hospital of Philadelphia (CHOP) under emergency Investigational New Drug applications (eINDs) through the Food and Drug Administration (FDA). Patients were considered for CP if they met FDA guidance for life-threatening disease (Appendix S1). We prospectively screened and enrolled these patients into a larger SARS-CoV-2 biobanking protocol. Patients were enrolled on the biobank protocol if they had evidence of SARS-CoV-2 infection on reverse-transcriptase polymerase chain reaction (RT-PCR) testing from respiratory tract mucosa. This protocol was approved by the CHOP Institutional Review Board. Consent was obtained for both protocols from a legal authorized representative per the Declaration of Helsinki (written informed consent for CP; verbal consent for biobanking).
Clinical data were abstracted from patient charts to standardized forms by a research assistant using a REDCap database and verified by a physician. Blood samples were obtained from participants prior to CP infusion, following CP infusion and weekly thereafter until death or discharge. Remnant donor CP was retained.
SARS-CoV-2 specific antibodies were measured by ELISA as previously described.8 Antibodies in serially diluted plasma (starting at 1:50) were measured against RBD of the SARS-CoV-2 spike (S) protein,9 full-length S protein, and the N protein (Sino Biological, Wayne, PA). Reciprocal plasma dilutions were calculated from an optical density (OD) threshold from a set concentration. Standard curves were generated by diluting an RBD-specific monoclonal antibody (CR3022) starting at 0.5 µg/mL (RBD and S ELISAs) or serially diluted pooled serum from actively SARS-CoV-2 infected adults (N ELISAs). See Appendix S2 for detailed methods.