The impact of SARS-CoV-2 infection on infants and children is not well-defined. Children are typically asymptomatic or mildly symptomatic, although some can develop significant complications requiring intensive care. In order to capture the full range of SARS-CoV-2 infection in the pediatric population, a broad study design was implemented, including patients seen in urgent care clinics and hospital settings, neonates born to SARS-CoV-2-infected mothers, and asymptomatic children. Each study population required specific tailoring of study conduct to effectively and efficiently collect critical samples.
To establish a COVID-19 biorepository before the surge of cases, protocols were rapidly submitted to our Institutional Review Board (IRB, MGH IRB#2020P000955) and the Institutional Biosafety Committee (IBC, MGH IBC#2020B000061) for approval. The entire research team was properly trained on Biosafety Level 2-Plus (BSL2+) procedures, as required for handling SARS-CoV-2 specimens. Close collaborations with adult biorepositories within the hospital ensured consistency, and, harmonization in biospecimen collection and processing across patient cohorts, facilitating high-quality comparisons between patient groups. A coordinated effort by clinical research coordinators, laboratory technicians, graduate students, and postdoctoral fellows was essential for enrolling patients, coordinating sample collection with clinical teams, maintaining IRB approval, and for processing and storing high-quality biospecimens. Central to the operation, physician-scientists in Pediatrics, Neonatology, Medicine-Pediatrics, and Obstetrics-Gynecology collaborated to harmonize sample collection protocols, establish clinical connections, and provide clinical and scientific context to COVID-19-related research in the neonatal and pediatric population. Open communication, frequent quality checks, and accessible leadership was paramount, in addition to coordination with patients’ clinical care teams. Samples were collected in the clinical setting by the clinical team members to accommodate COVID-19 infection control guidelines and limit personal protective equipment (PPE) use. Cornerstones of the biorepository included open dialogue between research and clinical team members, a sensitivity to procedures required for specimen collection in children, and clear documentation of study participation and sample collection.
Patient enrollment and sample collection:
In order to include pediatric and neonatal patients from a range of clinical presentations for COVID-19, we established 4 cohorts of patients: 1) Pediatric patients with mild-moderate COVID-19, presenting to the MGH COVID-19 urgent care clinics, 2) Pediatric patients with severe COVID-19 or MIS-C requiring hospitalization, 3) Newborns born to mothers infected with SARS-CoV-2 at any point during their pregnancy, and, infants born to non-infected mothers, and 4) asymptomatic children at well-visits with possible SARS-CoV-2 exposure. Figure 1 provides a schematic of the recruitment strategy. Potential participants in all cohorts were contacted via telephone to verbally review the informed consent. Participants or their parent/guardian selected which biospecimens they would provide. One copy of the signed consent form was emailed to enrolled patients, and another was uploaded into the electronic medical record flagging the patient as a research participant, clearly documenting research participation for the clinical care teams. Participants were assigned a unique study ID number using REDCap, a secure, centralized online database platform that allows simultaneous recruitment at multiple sites without risking assigning the same number to multiple patients. The clinical team obtained biospecimens to minimize risk of SARS-CoV-2 transmission and limit PPE use.
1) Pediatric patients with mild-moderate COVID-19
As most children did not require hospital-level care, significant efforts were made to enroll patients in the outpatient setting. COVID-19 screening clinics, called Respiratory Infection Control clinics, were established at Massachusetts General Hospital. As COVID-19 symptoms are non-specific and current diagnostic reporting is time-delayed, all pediatric patients presenting to the COVID-19 screening clinics were eligible to participate in the biorepository.
In Respiratory Infection Control clinics, participants who signed informed consent could provide nasopharyngeal, oropharyngeal swabs and/or blood. Stool and urine were not collected given time limitations of clinic visits and patient flow patterns established to minimize potential COVID-19 exposures to clinical staff. Blood was collected into one tube with an EDTA anticoagulant (EDTA tube) (BD), one serum separator tube (SST) (BD), and a PAXgene RNA tube (BD). Blood volumes varied, depending on the age and weight of the patient, in accordance with limits established by the IRB. The aerosolizing procedure of collecting nasopharyngeal and oropharyngeal swabs into 15 mL falcon tubes, containing 3 mL phosphate buffered saline (PBS) (Gibco), was performed by clinical team members wearing N95 mask, face shield, protective outer gown and disposable gloves.
2) Patients with severe COVID-19 or Multisystem Inflammatory Syndrome in Children requiring hospitalization
Pediatric patients who were hospitalized with suspicion of SARS-CoV-2 exposure and/or symptoms concerning for SARS-CoV-2 infection or MIS-C were approached. Presenting symptoms included fever, rash, dyspnea, cough, nausea, vomiting or diarrhea. Patients were approached by the clinical team and upon declaring interest, a member of the research staff contacted the patient and family to obtain informed consent. Hospitalized patients could opt to provide urine, stool, sputum, or if intubated, tracheal aspirates, in addition to blood, nasopharyngeal and oropharyngeal swabs. Planned sample collection was discussed with the clinical team. Phlebotomy was aligned with clinical blood draws, when feasible, although participants had an option to undergo a separate venipuncture for research purposes. Blood was collected into an EDTA tube, an SST tube, and a PAXgene RNA tube. Repeat samples were collected on alternating days, as feasible. Based on daily coordination between the research and clinical teams, discarded blood from clinical labs were also obtained from hospitalized patients.
3) Newborns born to mothers with and without SARS-CoV-2 infection
Pregnant women with confirmed SARS-CoV-2 infection followed in the MGH obstetrics practice, presenting to the Labor and Delivery (L&D) Unit, or hospitalized for SARS-CoV-2 illness, were approached to enroll their infant in the Pediatric COVID-19 Biorepository following birth. When universal screening for SARS-CoV-2 infection was initiated on all pregnant women admitted to L&D, asymptomatic SARS-CoV-2 positive patients were identified and offered enrollment. Women who tested negative for SARS-CoV-2 were also approached as a control group. The pregnant mothers were simultaneously offered enrollment in the companion Obstetric COVID-19 Biorepository, which included collection of placental biopsies, umbilical cord blood, and other maternal samples. The clinical team assessed the patient’s interest in the Biorepository, then a member of the research staff contacted the patient to obtain informed consent. Parents could opt to have newborn blood, nasopharyngeal and oropharyngeal swabs, urine, stool, and (if intubated) tracheal aspirates collected. Blood was collected via heel stick between 24–36 hours of life, simultaneously with the heel stick for clinical newborn screening, into two EDTA microtainer tubes (BD). Research nasopharyngeal and/or oropharyngeal swabs were obtained after 24 hours of life, batched at the time of the nasopharyngeal swab for SARS-CoV-2 testing, if performed clinically. Stool and urine were collected on day of life 0 and 2. Stool was collected directly from the diaper. Urine was collected by placing cotton balls in the diaper, then transferring the urine-soaked cotton balls into a specimen cup for transport. If the recruited newborn was intubated for clinical indications, tracheal aspirates were collected at the time of clinical suctioning.
4) Asymptomatic children with potential SARS-CoV-2 exposure
Children presenting for their 2-, 3-, or 4-year annual well-child visit with their pediatrician for planned phlebotomy were eligible to participate in this cohort. Eligible patients were identified by study staff and clinicians. If appropriate, researchers contacted the parents via telephone prior to their visit to explain the research and obtain informed consent. Blood and saliva were collected during their clinical phlebotomy. Saliva collection is not considered an aerosolizing procedure; thus, these specimens could be collected in clinic without the need for N95 mask use. The specimens were immediately transported to the laboratory for processing.
Data collection:
REDCap databases were used to record all study data, including: 1) An enrollment log serving as the decoding log. Study ID numbers were assigned consecutively across all four patient groups; 2) A laboratory processing database with pertinent processing and freezer storage location information; 3) A chart review database, with demographic and clinical data, including COVID-19 exposures, SARS-CoV-2 polymerase chain reaction (PCR) results, symptoms, and outcomes; 4) A question-response database about COVID-19 exposures and risk factors, specifically for the well-visit cohort.
Specimen Transport and Processing:
In accordance with specimen transport guidelines, specimens were sealed in a leak-proof container labeled with subject’s study ID, then placed in a tight-sealed, biohazard-labeled, secondary container with a rigid outer container and lockable lid (e.g. Igloo cooler) for transport to the laboratory. Blood samples were processed following BSL2 safety guidelines, with a lab coat, nitrile/latex gloves, and a face shield or safety goggles. All other samples, including nasopharyngeal and oropharyngeal swabs, sputum, saliva, tracheal aspirates, stool, and urine were processed following BSL2 + safety guidelines. BSL2 + safety precautions require all samples to be processed in a certified biosafety cabinet (BSC), class II A2, with intake airflow. Well-trained laboratory personnel handling infectious specimens were required to wear closed-front water impermeable gowns, double nitrile/latex gloves, sleeve covers, and a face shield. Outer gloves were removed when moving away from the BSC and replaced with a new glove when returning to work in the BSC.
Plasma
Blood samples collected in tubes with an EDTA anticoagulant were stored at room temperature until processed, within 24 hours of collection. Tubes were spun at 1000 g for 10 minutes with brake activated. Plasma was then collected, aliquoted, stored at -80 °C, and logged in the REDCap database.
Peripheral blood mononuclear cells (PBMCs)
Immediately following the removal of plasma, samples with greater than 2 mL initial volume were processed for PBMC isolation using a Ficoll density gradient[2]. Briefly, blood was transferred into a 50 mL conical tube, then diluted 1:1 with Hanks’ Balanced Salt Solution without calcium or magnesium (HBSS minus) (Gibco). This diluted blood was then gently layered on top of Ficoll-Paque Plus (GE Healthcare) at 2:1 ratio (2 volumes of blood diluted with HBSS minus to 1 volume Ficoll). Careful attention was made to avoid any mixing of blood with the Ficoll layer. The conical tube was then centrifuged at 1000 g for 30 minutes at room temperature with brake inactivated to allow adequate layering of cellular components. The cloudy ring below the plasma and above the Ficoll (i.e. the PBMC layer) was collected and transferred to a new 15 mL conical tube, with HBSS minus added to bring the volume to 15 mL (Fig. 2a). This tube was then centrifuged at 330 g for 10 minutes, with high brake activated. The supernatant was removed, the PBMC pellet was again washed with HBSS minus, and then resuspended in 10 mL HBSS minus for counting. Cell count was obtained by diluting 10 µL of sample with 90 µL of trypan blue, mixed, and sampled on a hemocytometer. Cells were then frozen in freshly-prepared freezing medium (RPMI 1640 Medium with 1% penicillin-streptomycin, L-glutamine, 1% sodium pyruvate, 1% non-essential amino-acids, and 20% Fetal Bovine Serum (FBS) (Sigma)) with 10% DMSO (Sigma) for a goal concentration range of 5–10 million cells/vial, placed in a chilled Mr. Frosty filled with isopropanol, then immediately placed at -80 °C. Final concentration (5–10 million cells per 1 mL of freezing medium) and number of aliquot vials were logged. The following day, PBMC cryovials were moved to a liquid nitrogen freezer for long term storage, and location was recorded in specimen log.
PBMCs were isolated within 24 hours of phlebotomy, although higher cell counts were obtained if isolated within 3–4 hours of collection. If less than 5 mL blood was collected, a 15 mL conical tube, rather than a 50 mL conical tube could be used for Ficoll layering. Fresh freezing media were made throughout the day for each sample batch.
Neutrophils
Neutrophils were extracted from the red blood cell layer that remained following the collection of PBMCs (Fig. 2a). Neutrophils were isolated using EasySep Direct Human Neutrophil Isolation Kit (StemCell Technologies). The remaining blood layer was incubated with EasySep Direct RapidSpheres and EasySep Direct Human Neutrophil Isolation Cocktail, then diluted in EasySep Buffer. Neutrophils were isolated by successive negative magnet selection using EasySep magnets, then counted using a hemocytometer and aliquoted into Eppendorf tubes for RNA extraction (1 × 105 cells/tube) or DNA analysis (5 × 106 cells/tube). Neutrophils designated for RNA extraction were resuspended in 100 µL of RNA lysis buffer (TCL) (Qiagen) with 1% β-mercaptoethanol (Sigma), immediately stored at -80 °C and logged. Neutrophils planned for DNA analysis were pelleted then directly stored at -80 °C and logged.
For RNA extraction steps, a cleaning agent, such as RNaseZAP should be used to remove RNAse from the working surface. RNA lysis buffer should be newly made for each sample using a 10:1 TCL to β-mercaptoethanol ratio.
Serum
Serum samples were collected from blood drawn into serum separator tubes without any anticoagulant (BD). Blood was kept at room temperature, standing upright for 30–60 minutes, then spun at 1200 g for 10 minutes with brake activated. Serum was then collected, aliquoted, stored, and logged (Fig. 2b).
Nasopharyngeal and Oropharyngeal Swabs
Swab samples were delivered in phosphate buffered saline (PBS)[3]. Samples were directly aliquoted into 1 mL aliquots, then immediately stored at -80 °C and logged (Fig. 3a).
Sputum/Saliva
Samples collected into a collection cup were mixed well at 1:1 ratio with 500 mM DL-Dithiothreitol (DTT) (Sigma)/PBS solution according to CDC recommendations. Diluted samples were then divided into 1 mL aliquots, volume permitting, immediately stored at -80 °C and logged (Fig. 3b).
Tracheal aspirates
Aspirates collected into a sterile collection cup were divided into 1 mL aliquots (1 mL/vial), immediately stored at -80 °C and logged (Fig. 3c).
Stool
Stool samples collected from a diaper or specimen cup were divided using a micro spatula volume permitting, into cryovials with 1 mL RNAlater (Invitrogen), empty cryovials without any additive/reagent, up to the 1.5 mL tube mark, and cryovials with 1 mL Buffered Glycerol Saline (Fisher). Stool samples were fully submerged in RNAlater or glycerol solution prior to immediate storage at − 80 °C. Samples were logged onto database (Fig. 3d).
Urine
Urine samples collected with cotton balls placed inside baby diapers were transferred using forceps, to a 10 mL syringe to dispense at most 1 mL of fluid into cryovials and immediately stored at − 80 °C. Samples collected into a tube or a sterile collection cup were aliquoted into cryovials (at 1 mL at most/vial) and immediately stored at − 80 °C (Fig. 3e).
Supplies required for specimen collection and processing are listed in Supplemental Table 1.