PS1328 ABNORMAL LEVELS OF FUNCTIONAL CTLS ON HIGH RISK MDS PATIENTS UNDER AZACYTIDINE TREATMENT
Authors: Lamprianidou E. , Papoutselis M. , Kotsianidis I. 
Published: June 2019

Background:CD3+CD8+ cytotoxic T cells (CTLs) play important role in antitumor immunity. Myelodysplastic Syndromes (MDS) are typically associated by immune dysregulation leading to compromised function of CTLs. The hypomethylating agent azacytidine (AZA) is the mainstay of high risk MDS treatment though its mechanism of action remains unclear. AZA appears to affect the antitumor immune response and its action could be, at least partially, immune‐mediated, but literature reports are often contradictory.Aims:We investigated both pretreatment and after treatment levels of functional subsets of CTLs in high‐risk MDS patients under AZA treatment and their association with various clinical parameters.Methods:Peripheral blood mononuclear cells from 72 patients and 13 healthy donors were obtained before, at Day15 and at the 6th cycle of AZA treatment. According to IWG criteria patients were characterized as responders (complete remission and hematologic improvement, 55%) and non‐responders (stable disease and failure, 45%). We utilized various protocols of multiparameter flow cytometry to assess the polarization, differentiation and functional states, by measuring the intracellular levels of Interferon γ, Interleukin 4, the levels of naïve CTLs (TN, CD27+CD45RA+), effector memory (TEM, CD27‐CD45RA‐), terminal effector memory (TEMRA, CD27‐CD45RA+) and central memory (TCM, CD27+CD45RA‐) and the levels of perforin, CD57 and program death receptor (PD1+ CTLs).Results:Pretreatment levels of CTLs were decreased in high‐risk MDS patients in comparison to healthy controls (p = 0.037). MDS patients had also decreased pretreatment levels of perforin+ CTL cells (p = 0.045) and increased levels of PD1+ TEMRA CTLs (p = 0.019) in comparison to healthy donors.The levels of perforin+ CTLs were positively associated with the levels of TEMRA CTLs (p = 0.041). Also, TEMRA CTL cells had higher levels of CD57 molecule (p < 0.001) and lower levels of PD1 (p < 0.001) in comparison with TEM, TN and TCM, indicating higher cytotoxic activity of that subset.In line with current literature, AZA treatment significantly upregulated CTL levels at the 6th cycle (p = 0.03). Non‐responders to AZA had reduced levels of pretreatment PD1+ TCM CTLs (p = 0.03) compared to responding patients but demonstrated a significant upregulation of the same subset at the 6th cycle of treatment (p = 0.028), whereas PD1 expression on all CTL subsets remained unchanged in responders. Moreover, the levels of perforin+ CTLs, both on responders and non‐responders, were not affected by AZA treatment.Summary/Conclusion:Collectively, our results demonstrate the CTL‐mediated antitumor immune response is defective in high‐risk MDS. AZA therapy increased CTL levels independently of response, without affecting their differentiation or functional state. PD‐1 expression on CTLs remained unaffected by AZA treatment in all patients but was upregulated in TCM cells of non‐responders potentially indicating a link, an undesirable compromise of antitumor immunity with failure to AZA.