Impact of gamma/delta TCR⁺, Foxp3⁺ and Toll-Like Receptor Expressing T-Cells on the Outcome of Patients Receiving Unrelated Peripheral Blood Stem Cell Transplantation.

Introduction: The role of gamma/delta (GD), foxp3 (regulatory, TREGs) and Toll-like receptor (TLR) expressing T-cells contained in the graft for the induction of graft versus host disease (GVHD) in patients after unrelated peripheral blood stem cell transplantation (PBSCT) is unknown.

Methods and patients: We therefore determined by flowcytometry and PCR the content of these T-cell subsets within the graft of 63 patients with hematological malignancies receiving unrelated PBSCT followed by cyclosporine A and methotrexate as GVHD prophylaxis and correlated these data with clinical endpoints. Patient and donor pairs were matched at least in nine out of ten characteristics (n=17), whereas a complete match (10 out of 10) was observed in 46 (73%) patients.

Results: The grafts contained a median of 11.25 x 10⁶/kg (2.7–33.5) CD4+foxp3 T-cells and 9.79 x 10⁶/kg (1.4–36.2) GD T-cells. Patients receiving lower amounts of CD4+foxp3+ cells had an increased risk of acute GVHD II–IV (65% vs. 44%, p=0.03). Whereas the overall CD3⁺ cell dose was not associated with the incidence of GVHD, increased counts of gdTCR expressing CD3⁺ cells showed significant correlation with an increased risk of GVHD II–IV (66% vs. 40%, p=0.028). A lower CD34⁺ cell dose was also significantly associated with an increased risk of GVHD II–IV (63% vs. 38%, p=0.04). Interestingly, there was a positive correlation between CD34+ and CD4+foxp3 cell dose (r=0.34, p=0.007).

In contrast to the blood of healthy donors, TLR2 and 4 were both expressed on up to 11 % of CD4+ and CD8+ cells within the graft but had no influence on the severity of GVHD. Interestingly, a higher expression of TLR2 and 4 on CD4+ but not CD8+ T-cells was associated with a higher treatment-related mortality (CD4: 17% for TLR2low vs. 45% for TLR2high, 13% for TLR4low vs. 52% for TLR4high, p=0.002).

Conclusion: Strategies aiming at selective manipulation of graft composition or add-back of distinct T-cell subsets after unrelated PBSCT might be a promising strategy in order to modulate the extent of clinical GVHD. Furthermore, up-regulation of TLR2 and 4 on T-cells and their role for non-relapse mortality warrants further investigation.