*2.7.3 Results*

The chimerism analysis of transplant patients was done for the first time no later than 1 month after allo-hSCT and further on 1–4 weekly intervals up to day +200 after transplantation and then according to the chimerism result and the timing of clinical controls. Patients who showed no evidence of autologous (recipient) DNA at any time in the post-transplantation follow-up were considered to have complete chimerism (CC). Patients with both donor and recipient DNA in any of the samples analysed were defined as having mixed chimerism (MC). An example of patient's mixed chimerism is presented in **Figure 1**. The average quantity of donor alleles 30.2 and 31.2 is 77%. The average quantity of recipient's alleles 16 and 25.2 is 23%, which means patient's mixed chimerism is 23% (MC = 23%). Patients who showed an increase (5% or more) in the proportion of recipient DNA or who changed from CC to any level of MC between two consecutive assessments were referred as having increasing MC. Those patients with decreasing recipient DNA content (5% or more) or transforming from MC to CC in two successive samples were categorised

*Monitoring of Chimerism in Rare Haematological Malignant Diseases after Allogeneic… DOI: http://dx.doi.org/10.5772/intechopen.89845*

**Figure 1.** *Mixed chimerism (MC) in a patient after allo-hSCT*

as having decreasing MC [26, 31]. Patients from our cohort with CC, stable MC, and decreasing MC showed a significantly better (p = 0.005) overall survival rate (OSR = 0.83) after allo-hSCT (**Figure 2**), compared to those with increasing MC (OSR = 0.25) after allo-hSCT (**Figure 3**) detected at any time after allo-hSCT.

#### *2.7.4 Conclusion*

Our observation shows that chimerism analysis gives clear information about engraftment, its failure, or graft rejection but is not a sufficiently sensitive method to detect an imminent relapse in acute lymphoblastic leukaemia patients. According to the changes in chimerism status after transplantation, early implementation of immunotherapeutic measures such as rapid cessation of immunosuppression and donor lymphocyte infusion (DLI) with or without cytokine coadministration can be delivered as prophylaxis and seems to be highly efficacious in restoring CC and decreasing autologous cell contents [18, 27, 32].

*Kaplan-Meier analysis of overall survival in patients with complete chimerism (CC), decreasing, stable mixed chimerism (MC) after allo-hSCT.*

**Figure 3.** *Kaplan-Meier analysis of overall survival in patients with increasing mixed chimerism (MC) after allo-hSCT*
