Identification and Characterization of Human Aspergillus Fumigatus-Specific Tr1-(Like) Cells
Authors: Bedke Tanja , Lurati Sarah , Stuehler Claudia , Khanna Nina , Einsele Hermann , Topp Max S. 
Published: October 2019

Abstract
Abstract 181

Introduction:
The ubiquitous mold Aspergillus fumigatus (A. fumigatus) induces two forms of pathogenesis: invasive aspergillosis in neutropenic patients and allergic aspergillosis in patients with chronic obstructive lung disease as well as in immunosuppressed patients. Mouse models of aspergillosis suggest that not only effector T cells (Teff) but also regulatory T cells (Treg) play a crucial role for the regulation of a protective T cell-mediated immunity to A. fumigatus. However, it is little-known about the involvement of Treg during A. fumigatus infection in humans. In order to develop new therapeutical strategies for the treatment of aspergillosis this project aims to understand the influence of regulatory T cells on A. fumigatus infection in humans.
Material/Methods: A. fumigatus-specific CD4+ T cell clones were established from PBMC of healthy donors. Based on this clone pool Treg clones were identified due to their inability to proliferate in the absence of costimulation assessed by 3[H]-TdR incorporation as well as their Ag-specific cytokine production and phenotype determined by flow cytometry. Treg function was analyzed by their ability to suppress proliferation of autologous CD4+ T cells using CFSE dilution.

Results:
We identified A. fumigatus-specific T cell clones that exhibited marginal detectable proliferation after restimulation with immobilized anti-CD3 mAb in the absence of costimulation. However, these T cell clones vigorously proliferated in response to restimulation with their cognate antigen. A more detailed characterization showed that these suppressor T cell clones produced high amounts of IL-10 and moderate levels of IFN-gamma upon Ag-specific restimulation and expressed low amounts of Foxp3 but not Helios, a transcription factor that had recently been linked to natural occurring Treg. Most importantly, these T cell clones suppressed Ag-specific expansion of CD4+ Teff. This effect was contact-independent since suppression of Ag-specific CD4+ T cell expansion detected in transwell experiments was comparable to cocultures that enabled cellular-contact. Furthermore, anti-CD3/CD28-induced proliferation of naïve CD4+ T cells was not reduced in the presence of culture supernatants obtained from suppressor T cell clones after their antigen-specific restimulation in the absence of DCs.

Conclusions:
We identified for the first time A. fumigatus-specific CD4+ T cell clones with a Tr1(-like) IL-10+IFN-gamma+Foxp3lowHelios− phenotype. These cells suppressed expansion of A. fumigatus-specific Teff in an Ag-specific manner mediated by soluble factors released from Tr1(-like) cell clones. Since these factors did not affect CD4+ T cell proliferation in the absence of DCs our data suggest, that Tr1(-like) cell clones rather negatively regulate the stimulatory capacity of DCs leading to a reduced expansion of Ag-specific CD4+ T cells. Therefore these Tr1(-like) cells might play a protective role during A. fumigatus infection in humans. Thus, adoptive transfer of A. fumigatus-specific Treg could be useful to enhance protective immunity in patients with chronic A. fumigatus infection.

Disclosures:
Topp: Micromet: Consultancy, Honoraria.