Brief Summary: This study investigates whether donors with previous exposure to COVID-19 can pass their immunity by hematopoietic (blood) stem cell transplant (HCT) donation to patients that have not been exposed. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the virus that causes the COVID19 infection. This study may provide critical information for medical decision-making and possible immunotherapy interventions in immunocompromised transplant recipients, who are at high risk for COVID19 severe illness.

Detailed Description: PRIMARY OBJECTIVE: I. To establish the possibility of anti-SARS-CoV-2 adaptive immunity transfer from matched related (MRD) or unrelated (MUD) HCT donor to HCT recipient. SECONDARY OBJECTIVES: I. To explore anti-SARS-CoV-2 adaptive immunity transfer in the haploidentical (haplo) HCT setting. II. To assess the prevalence and change over time of SARS-CoV-2 seropositive donors among all consented donors. OUTLINE: DONORS: Prior to HCT, sibling donors (MRD and haplo) undergo a nasopharyngeal swab per standard of care for SARS-Cov-2 testing. For MUD donors, initial testing may consist of a questionnaire. All donors undergo collection of blood and saliva at the time of granulocyte-colony stimulating factor (G-CSF). Donors' medical charts are also reviewed. RECIPIENTS: Patients undergo a nasopharyngeal swab for SARS-Cov-2 testing at 30, 60, 90, 120 days post-HCT, and afterwards as deemed necessary by the treating physician. Patients also undergo the collection of blood and saliva specimens at days 30, 60, 90, 120, 150, and 180 post-HCT. Recipients' medical charts are also reviewed.