Disease-Specific Recovery of Regulatory T Cell After Allogenic Stem Cell Transplantation

Allogenic stem cell transplantation (allo SCT) offers a potential curative approach for many malignant and non malignant haematological diseases. Despite its therapeutic benefit, long term immunodeficiency, poor immune reconstitution and Graft vs. Host Disease (GvHD) can often be limiting drawbacks. Since the nineties, regulatory T cell subsets (Treg) have been described and several lines of evidence indicated their implication on GvHD occurrence and progression. We analysed the immune reconstitution of 184 patients who underwent allo SCT at our Transplant Center from 2007 till 2009.

Differential lymphocyte subsets were analysed by flow cytometry. Antigens were stained by usage of the following mAb: CD3, CD4, CD8, CD19, HLA-DR, CD56/CD16, CD45RA, CD45RO, CD45, γδ TCR, CD25, and CD127. Tregs were evaluated on simultaneous expression of CD4/CD25hi/CD127low. Data were obtained in monthly intervals for the first six months and thereafter every six months for the next 3 years. Data were analysed for three different subgroups: Multiple Myeloma (MM: n=83), Myelofibrosis (PMF: n=22) and AML/MDS (n=51). Smaller number subgroups of patients with CML (n=11), NHL (n=10) and ALL (n=7) were included into the overall analysis but not evaluated separately.

The mean value of Treg cell number before allo SCT was 2,5% of the total leukocyte number in all patients. There was no significant difference in the Treg level in any of the three major groups (MM: 2,2%; PMF: 2,1% and AML/MDS: 2,03%). All patients exhibited a significant reduced number of Treg cells during the first 30 days after allo SCT (MM: 0,79%; p= 0,009; PMF: 0,41%; p= 0,01; MDS/AML: 0,6%; p=0,01). Between day 30 and 60 after allo SCT patients with MM had a transient Treg recovery to baseline level (2,4%) while Tregs of patients with PMF or MDS/AML remained significantly lower in comparison to baseline value (PMF: 0,72%, p=0,002 and MDS/AML 0,81%, p=0,01 respectively). One year after allo SCT a faster Treg recovery (1,3% and 1,8% respectively) was observed in MM and MDS/AML patients while patients with PMF still maintained a significant reduction (0,65%; p=0,01). Interestingly, in the second year after allo SCT, Treg cell levels were decreased in all investigated subgroups (MM: 1,1%, p=0,008; PMF: 0,7%, p=0,02 and MDS/AML: 0,7%, p<0,0001), while after 3 years Treg cell number achieved pretransplant level. In contrast to Treg cells, total T cells are only transiently but significantly reduced within the first 180 days.

A highly dynamic Treg cell recovery after allo SCT was observed in our group of patients. Even one year after allo SCT Treg reconstitution is still ongoing. Our data highlight that there is a distinctive difference in Treg recovery among the various fore mentioned diseases. Treg reconstitution appeared to be prolonged in patients with PMF in comparison to the other subgroups. Our data provide a basis for further analysis towards differential Treg reconstitution and its potential impact on allo SCT complications.

No relevant conflicts of interest to declare.