Haploidentical and matched donor HCT patients treated with PTCy underwent serial sample collection before and after receiving a transplant. Established and exploratory analytes along with key immune cell subsets were measured. A subset of mechanistically relevant immune cells were sort purified and interrogated via RNA sequencing, and machine learning was used to correlate with key transplantation-related outcomes including GVHD and survival. The CXCR3-CXCL9 axis was implicated as being important for the development of aGVHD, and quantitative NK-cell deficits during recovery were associated with inferior OS. The figure was created (in part) with BioRender.com.