T CELL MIXED CHIMERISM IS SIGNIFICANTLY CORRELATED TO A DECREASED RISK OF ACUTE GRAFT-VERSUS-HOST DISEASE AFTER ALLOGENEIC STEM CELL TRANSPLANTATION 1

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Abstract
It has been debated whether mixed chimerism (MC) is correlated to a decreased incidence of graft-versus-host disease (GVHD) after allogeneic stem cell transplantation (SCT). Between September 1996 and April 1999 we analyzed 102 patients for MC in the T-cell fraction post allogeneic SCT, using PCR amplification of variable numbers of tandem repeat (VNTR) loci. All samples, taken regularly post SCT, were cell separated using anti-CD3 immunomagnetic beads. T-cell mixed chimerism was detected in 58 out of 102 patients (57%). Patient characteristics were comparable in the T-cell MC- and donor chimeric-group (DC). The median follow-up time for the MC group was 714 days (range 58 - 1248) as compared to 427 days (range 45 - 1042) for the DC group. Overall probability of acute GVHD grades II-IV was significantly higher in the DC group as compared to the MC group (52% vs. 5%, P<0.001). In multivariate analysis T-cell DC proved to be the most significant risk factor for acute GVHD grades II-IV. The cumulative incidence of relapse, among patients with malignant disease, did not show any statistical difference between the T-cell MC patients and the DC-group. There was a tendency for better overall survival in the T-cell MC group compared to the DC group (2 yrs; 73% vs. 54%, P=0.06). Among DC patients, 14/20 (70%) deaths were due to GVHD versus none in the MC-group(P<0.001). T-cell mixed chimerism was significantly correlated to a decreased risk of moderate to severe acute GVHD and death by GVHD.