TREG and Tcon Dynamics after Allo-HSCT: Cgvhd Is Associated to Decreased NaïVe and Stem Cell Memory Subsets with a Concomitant Increase in Terminally Differentiated T Cell Subsets

• Published in: Blood 2016-12, Vol.128 (22), p.2229-2229
• Main Authors: Soares, Maria V.D., Azevedo, Rita I, Ferreira, Ines A, Bucar, Sara Ventura, Alho, Ana Cristina, Espada, Eduardo L, Clara, Juncal, Camacho, Nadia, Martins, Carlos M., Carmo, José A, Lourenço, Fernanda, Moreno, Raul, Vaz, Carlos, Campos, Antonio M., Campilho, Fernando, Ferreira, Rosa, Ritz, Jerome, Lacerda, Joao F
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V128.22.2229.2229

Chronic Graft versus Host disease (cGVHD) is a major limiting factor for the success of allo-HSCT. In this prospective study we aimed to evaluate the association between the kinetics of Regulatory T cells (TREG) and Conventional CD4+T cells (TCON) reconstitution and the emergence of cGVHD. We performed a detailed phenotypic analysis by multiparametric flow cytometry using fresh blood from 39 patients undergoing unrelated donor HSCT after a reduced intensity conditioning regimen containing ATG over a 2 year period, representing a total of 213 samples analyzed. GVHD prophylaxis consisted of cyclosporine plus mycophenolate mofetil. 11 patients were excluded due to disease relapse and/or death due to infection or acute GVHD in the first 9 months post-HSCT. We observed indiscriminately low numbers of TREG (CD4+CD127lowFoxp3+CD25bright) until mo 6 after HSCT and reduced TREG numbers in patients developing cGVHD (GVHD+) versus those who did not (GVHD-) (p=0.02 at mo 9). We further studied the dynamics of TREG subset reconstitution. CM TREG (CD45RA-CD62L+) was the predominant population in both patient groups. EM (CD45RA-CD62L-) was the second most abundant TREG subset. CM and EM TREG numbers were similar between patient groups. EMRA (CD45RA+CD62L-) TREG remained very low throughout the follow-up but were significantly increased at mo 9 in GVHD+ (p= 0.03). Interestingly, Naïve TREG (CD45RA+CD62L+CD95-) started to emerge at mo 9 and were significantly reduced in GVHD+ patients at mo 12 (0.71 vs 0.14 cells/µl; p=0.02) The Stem Cell Memory subset (SCM), identified as CD45RA+CD62L+CD95+, is thought to be self renewing and multipotent, being able to differentiate into CM, EM and TEMRA memory subsets. While in GVHD- SCM TREG started to emerge at mo 9, this subset remained low in GVHD+. Statistically significant differences were observed at mo 18 (0.91 vs 0.15 cells/µl; p=0.02). To ascertain the role of thymic output in TREG reconstitution we quantified CD31+ naïve TREG. Recent Thymic Emigrant cells (RTE) TREG were significantly reduced in GVHD+ at mo 12 (0.8 vs 0.16cells/µl; p=0.02) and at mo 18 (1.93 vs 0.28 cells/µl; p=0.02). In order to clarify whether both thymic output and peripheral expansion were contributing factors to decreased Naïve TREG, we quantified proliferation using Ki-67. TREG from GVHD+ patients proliferated less from months 2 to 18 reaching statistical significance at mo 9 and 12 (p= 0.003 and 0.02, respectively), suggesting that decreased TREG number