Higher Proportion of a Novel PD-1+ Foxp3+ γδ Regulatory T Cell Subset in De Novo and Recurrent AML

T cell immunodeficiency may be a common characteristic in acute myeloid leukemia (AML) and adoptive T cellular immunotherapy has a broad prospect for clinical treatment. γδ T cells is essential to anti-leukemia function through perforin (Perf) / granzyme B (Grmb) pathway and may become a new strategy for leukemia immunotherapy. However, γδ T cells have different functional subsets like regulatory cell subsets and relevant regulatory mechanism is still unknown. Programmed death-1 (PD-1) which is one of T cell inhibitory receptors may mediate T cell suppression and dysfunction in leukemia and relate to general regulatory T cells which express transcription factor forkhead box P3 (Foxp3). It would be interesting whether PD-1 pathway might involve in regulation of regulatory Foxp3+ γδ T cells. In this study, we first investigated the regulatory cell subsets of γδ T cells in patients with AML. The flow cytometry (FCM) was used to detect the expression proportions of γδ T cells and their subfamilies in peripheral blood of AML patients (including 15 cases of de novo AML, 5 cases of recurrent AML and 4 cases in complete remission (CR)). Real-time quantitative PCR(RQ-PCR)was used to detect the expression levels of PD-1, Foxp3, Grmb and Perf genes in the γδ T cells sorting by MACS technique from peripheral blood of de novo AML patients. Fifteen health individuals (HI) served as controls. The results showed decreasing trend of γδ T cell counts in AML patients. Compared with HI groups, higher expression levels of PD-1 gene in γδ T cells were found in de novo AML patients, while Grmb and Perf gene presented lower expression levels by RQ-PCR ( P <0.05) (Figure A). The expression levels of PD-1 gene had a positive correlation to the Foxp3 gene in de novo AML group. It was noteworthy that we firstly found a novel PD-1+ Foxp3+ γδ T subset in peripheral blood of AML patients and HI controls with different frequencies. The proportions of Foxp3+ γδ T cells, PD1+ γδ T cells, and PD-1+ Foxp3+ γδ T cells were significantly higher either in de novo or the recurrent AML patients, respectively ( P <0.05). The PD1+ Foxp3+ γδ T cells counts in AML patients showed the pattern as the recurrent AML > the de novo AML > the AML-CR groups (Figure B and C). In conclusion, a novel regulatory PD1+ Foxp3+ γδ T subset with lower expression levels of Grmb and Perf genes was found in peripheral blood of AML patients. Higher proportion of PD1+ Foxp3+ γδ T cells might influence the occurrence and development of AML.

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