Full Donor Chimerism in Both Plasma and Mononuclear Cell after Haematopoietic Stem Cell Transplant (HSCT) at D28 Is Predictive of Acute Graft-Versus-Host Disease but Not Disease Relapse or Graft Failure.

Mononuclear cell mixed donor/recipient chimerism has been shown extensively to have high predictive value in disease relapse and graft rejection. Recently, donor DNA in plasma of transplant recipient has been suggested as a potential tool for post HSCT monitoring for disease relapse and graft rejection but its role has not been defined. Moreover, the impact of GVHD on plasma donor DNA remains unknown. In the current study, both the plasma and mononuclear cell donor chimerism of 40 patients post HSCT (mean age = 40; 35 myeloablative, 5 non-myeloablative) were analyzed at D28. Each patient was followed-up for one year or when disease relapse/graft rejection occurred. GVHD of grade II or above was also recorded to establish its correlation with the chimerism status. At D28, all patients were engrafted and alive. 5 (13%) patients had full donor chimerism in both plasma and mononuclear cell (Group A), 7 (18%) patients had full donor chimerism in the mononuclear cell only but not the plasma (Group B) and 28 (70%) patients failed to have full chimerism in both plasma and mononuclear cell (Group C). The sex, age, HLA-matching, donor relationship and ABO blood group matching had no impact on the chimerism status. None of the Group A patient had disease relapse/graft rejection at 1 year when compared to 13/35 (37%) of Group B and C patients (p=0.154, not significant).However, all the patients in Group A had acute GVHD which was significantly more than those in Group B and C (5/5 vs 12/35, p=0.009) and the acute GVHD would not alter the chimerism status. These results provide a foundation for further research on the potential role of plasma donor chimerism in predicting disease relapse/graft rejection and GVHD so that early intervention can be instituted.