Treg Downregulation Was Associated with Augmentation of T Cell Responses Against Immunogenic Antigens and Clinical Responses in Patients with Hematological Malignancies after Donor Lymphocyte Infusion (DLI)

In order to maintain remission and to prolong overall-survival after allogeneic stem cell transplantation (allo-SCT) and donor lymphocyte infusion (DLI), cytotoxic T-cell responses against malignant cells play a pivotal role, however they are not well characterized so far. In this study, we focused on the detection of immune responses in patients before and after DLI. A broader epitope-specific T cell activity is associated with clinical response of patients treated with DLI and a concurrent reduction of regulatory T cell frequency may contribute to clinical response in patients after DLI.

For a better characterization of the T cell responses, frequency and diversity of leukemia-associated antigen (LAA)-specific cytotoxic T cells was assessed using ELISpot and pMHC multimer assays. Furthermore, the frequency of regulatory T cells (Treg) before and after DLI was analyzed. Results were correlated to the clinical course of the patients.

Independently of their clinical response, 7/11 patients (63.6%) showed an immunological response through an increase in the number of recognized epitopes over the course of DLI. There was a significant increase (p=0.02) in epitope recognition comparing early screening and maximum response after DLI and a significant increase in the mean augmentation from 1 to 4 of the spotted epitopes in the course of DLI was detected in the cohort of clinical responders (R) compared to non-responders (NR) who did not show any dynamics in epitope recognition with a median of 3 to 4 recognized LAA.

The proportion of the CD4+CD25^highFoxP3+ Treg within the CD4+CD25^high T cell fraction decreased significantly in R from a median of 72.9% to 54.6% when comparing the variation at the time points before and after DLI (p=0.04). In NR there was no significant change in the Treg fraction in the course of DLI.

In general, significantly more LAA-derived T cell epitopes (p=0.02) were recognized in R when compared to NR. Moreover, the frequency of Treg in R decreased significantly (p=0.008) while remaining stable in NR.

Taken together, an increase of specific CTL responses against several LAA after DLI was detected. This study suggests that decreasing numbers of Treg as well as enhanced LAA diversity in T cell responses contribute to clinical outcome of patients treated with DLI.