Myeloid cells dominate most profiles, with 2 distinct subgroups: a larger group with mainly granulocytes (potentially NETosis) and a smaller group enriched for monocyte. In 1 CART19-treated patient, a B cell cfDNA signal was observed, consistent with CART-19 targeting B cells. Several patients with ARDS and controls displayed signal from liver cells, suggesting liver damage. A neuron/glial cell signal was detected in 1 sample, potentially reflecting brain injury, and 1 sample exhibited a strong signal from erythrocyte progenitors.