Lymphocytes are pivotal to microbial immunity, tumor surveillance and tissue homeostasis. In contrast to T, B and Natural Killer (NK) cells, the in vivo development and function of helper-like innate lymphoid cells (ILCs) remain to be fully unveiled in humans. In this study, we aimed, first, to study the kinetics of ILC recovery in adults and children following allogeneic HSCT for the curative treatment of a broad range of diseases that included tumor pathologies. Second, we aimed to assess the correlation between the reconstitution of different ILC subsets and the occurrence of GVHD.
We performed a prospective study of ILC reconstitution after HSCT in 58 patients in collaboration with the pediatric oncohematology unit of the Timone Hospital in Marseille. The retrospective study included 91 adult patients from the CRYOSTEM cohort. Quantifications of circulating T, B, NK and ILC subsets were performed by flow cytometry using BD Canto 2 and Fortessa analysers.
We found that, unlike NK cells, helper-like ILCs recovered slowly, mirroring the pattern observed for T cells, with normalization at one year. The graft type and the proportion of CD34+cells in the graft did not significantly affect ILC reconstitution. As HSCT is often complicated by graft-versus-host disease (GVHD), we also analyzed the potential role of ILC subsets in maintaining tissue integrity in these conditions. We found that GVHD was associated with lower levels of activated and gut-homing ILC3.
These data support a non-redundant role of this ILC subset in lymphopenic conditions for preventing these life-threatening damages.