library_construction_protocol: For the first UTX sample (UTX#1), targeted Fluorescence-activated single cell (FACS) sorting was used to obtain leukocyte subsets (B cells from donor peripheral blood, monocytes from recipient peripheral blood, T and NK cells from recipient tissue). Alive CD45+ sorted mononuclear cells were obtained from the remaining UTX and HSCT samples. All samples were then processed with the 10x Genomics single cell gene expression kit according to manufacturer's instructions to obtain gene expression libraries. 10x Genomics Gene Expression libraries were converted to single-stranded circular DNA from 50 ng using the Universal Library Conversion Kit (App-A; MGI Tech) according to the manufacturer's instructions. Libraries were pooled and 60 fmol of the pool was used to generate DNA nanoballs directly prior to sequencing on two FCL flow cells on the DNBSEQ G400RS platform (MGI Tech).