A strong association between CD4 T-cells and chronic GVHD was found in HLA-matched sibling donor recipients (p <0.001) but not for recipients of alternative donors. Among patients who received reduced-intensity conditioning and PBSC from a matched-sibling donor, higher CD4 dose was strongly associated with more chronic GVHD (p=0.001) with HR of 2.43 for quartile 4 (Q4) vs. quartile 1 (Q1) (p=0.002). We found no association between CD8 cell dose and chronic GVHD.