mtDNA is released by MM cells. (A-B) Schematic of experimental design. Human MM1s (2 × 10⁶) were injected IV into busulfan (25 mg/kg)–pretreated NSG mice. PB samples were taken via IV tail vein bleed at 7 and 14 days after engraftment. (C) Cell-free serum was extracted from PB via centrifugation, and DNA was extracted and analyzed via qPCR for the presence of murine and human mtDNA, using human and mouse ND1 primers. (D) Percentage of human CD38⁺ cells in the BM of control NSG mice (n = 4) and NSG-MM1s mice (n = 4). (E) In a separate experiment, human MM1s (2 × 10⁶) were injected IV into busulfan (25 mg/kg)–pretreated NSG mice. At 21 days, PB and BM samples were taken, cell-free serum was taken, and DNA was extracted and analyzed via qPCR for mtDNA. (F-G) A total of 1 × 10⁶ murine 5TGM1^{(GFP+ LUCI+)} cells were injected into C57BL/KaLwRij mice. Mice were euthanized at 21 days, and PB serum samples were extracted and analyzed via qPCR for mtDNA. Data indicate mean ± SD. Statistics are presented as Mann-Whitney U test. ∗P < .05.