Proportion of IL-17A Producing CD4+ Cells Increases in Response to Alloreactivity as Part of a Network Involving Memory and Regulatory Cells Post HSCT.
Authors: Lange Andrzej , Dlubek Dorota , Suchnicki Krzysztof , Madej Sylwia , Turlej Eliza 
Published: October 2019

Abstract
Abstract 1160
Poster Board I-182
Acute GvHD is a major factor affecting the outcome of hematopoietic stem cell transplantation (HSCT). In this study the focus was on the presence of IL-17-producing lymphocytes in patients post-HSCT with respect to FoxP3-positive lymphocytes and those with IFNgamma generation potential.
The cytoplasmic expressions of IL-17, FoxP3, and IFN-gamma were studied in stimulated PBMCs (brefeldin A, Ionomycin, and PMA) of alloHSCT patients (43 patients, median age: 45 yrs, range; 1.0-64 yrs, with 41 hematological malignancies and 2 SCID).The cells were labeled with CD4, IL-17A, IFN-gamma, and FoxP3 MoAbs and analyzed in the CD4+ lymphocyte subpopulation. Twenty patients received MUD and 23 SIB transplants. Twenty developed aGvHD, among them 7 patients with aGvHD seen at a later stage after hematological reconstitution and 4 patients with recurrent clinical manifestation of aGvHD.
It was found that: (1) the percentage of IL-17-producing CD4+ lymphocytes was higher in patients without aGvHD at the beginning of hematological reconstitution than in healthy controls (0.65±0.11% vs. 0.19±0.06%, p=0.02), (2) aGvHD cases with disease onset at the time of hematological reconstitution had lower proportions of IL-17A-producing CD4+ lymphocytes than those without aGvHD at a similar time after HSCT (0.31±0.1% vs. 0.65±0.11%, p=0.04), (3) when individual patients were followed it became apparent that the proportion of IL-17A-producing CD4+ lymphocytes, increased one week prior to aGvHD compared with the preceding observation (1.16±0.43% vs. 0.77±0.33%) and then a significant decrease was seen when symptoms became apparent (1.16±0.43% vs. 0.36±0.16%, p=0.017, Wilcoxon Test), (4) a high degree of correlation was found between the percentages of CD4+IL-17A+ and IFNgamma+CD4+ lymphocytes in blood at the time of hematological recovery (r=0.55, p=0.007), (5) patients with a higher percentage of IL-17A-producing cells in the CD4+ cell population more frequently had a higher proportion of FoxP3 in CD4+ cells (chi2=5.67, p=0.017), (6) the percentage of IFNgamma-producing CD4+ cells correlated with the proportion of FoxP3+ cells in the CD4+ cell population (r=0.48, p=0.02), and (7) the percentage of IL-17A-generating CD4+ cells rather inversely correlated with the proportion of CCR7+ lymphocytes in the blood of patients at the beginning of hematological recovery (r=-0.35, p=0.10).

In conclusion
Allogeneic HSCT induces the generation of IL-17A by CD4+ lymphocytes, especially in populations with lower proportions of naïve (CCR7+) lymphocytes, in response to alloantigens (the highest values were seen prior to the overt manifestation of aGvHD), which correlates with an increase in FoxP3+CD4+ cells. IL-17A-producing cells are likely to contribute to target organ lesions as they disappear from the blood at the time of overt manifestation of aGvHD. Supported by Grant no. 2P05E 037 30 from the Polish Ministry of Science & Higher Education.

Disclosures
No relevant conflicts of interest to declare.