Protective Role of Myeloid Cells Expressing a G-CSF Receptor Polymorphism in an Induced Model of Lupus

Contribution of Dendritic Cell Subsets to T Cell-Dependent Responses in Mice

BATF3-deficient mice that lack CD8⁺ dendritic cells (DCs) showed an exacerbation of chronic graft-versus-host disease (cGVHD), including T follicular helper (Tfh) cell and autoantibody responses, whereas mice carrying the Sle2c2 lupus-suppressive locus with a mutation in the G-CSFR showed an expansion of CD8⁺ DCs and a poor mobilization of plasmacytoid DCs (pDCs) and responded poorly to cGVHD induction. Here, we investigated the contribution of CD8⁺ DCs and pDCs to the humoral response to protein immunization, where CD8^neg DCs are thought to represent the major inducers. Both BATF3^-/- and Sle2c2 mice had reduced humoral and germinal center (GC) responses compared with C57BL/6 (B6) controls. We showed that B6-derived CD4⁺ DCs are the major early producers of IL-6, followed by CD4^-CD8^- DCs. Surprisingly, IL-6 production and CD80 expression also increased in CD8⁺ DCs after immunization, and B6-derived CD8⁺ DCs rescued Ag-specific adaptive responses in BATF3^-/- mice. In addition, inflammatory pDCs (ipDCs) produced more IL-6 than all conventional DCs combined. Interestingly, G-CSFR is highly expressed on pDCs. G-CSF expanded pDC and CD8⁺ DC numbers and IL-6 production by ipDCs and CD4⁺ DCs, and it improved the quality of Ab response, increasing the localization of Ag-specific T cells to the GC. Finally, G-CSF activated STAT3 in early G-CSFR⁺ common lymphoid progenitors of cDCs/pDCs but not in mature cells. In conclusion, we showed a multilayered role of DC subsets in priming Tfh cells in protein immunization, and we unveiled the importance of G-CSFR signaling in the development and function pDCs.

Immunomodulatory effects of G-CSF in cancer: Therapeutic implications

Numerous preclinical studies have reported a pro-tumour role for granulocyte colony-stimulating factor (G-CSF) that is predominantly mediated by neutrophils and MDSCs, the major G-CSF receptor expressing populations. In the presence of G-CSF (either tumour-derived or exogenous) these myeloid populations commonly exhibit a T cell suppressive phenotype. However, the direct effects of this cytokine on other immune lineages, such as T and NK cells, are not as well established. Herein we discuss the most recent data relating to the effect of G-CSF on the major immune populations, exclusively in the context of cancer. Recent publications have drawn attention to the other tumour-promoting effects of G-CSF on myeloid cells, including NETosis, promotion of cancer stemness and skewed differentiation of bone marrow progenitors towards myelopoiesis. Although G-CSF is safely and commonly used as a supportive therapy to prevent or treat chemotherapy-associated neutropenia in cancer patients, we also discuss the potential impacts of G-CSF on other anti-cancer treatments. Importantly, considerations for immune checkpoint blockade are highlighted, as many publications report a T cell suppressive effect of G-CSF that may diminish the effectiveness of this immunotherapy.

CD38 Deficiency Ameliorates Chronic Graft-Versus-Host Disease Murine Lupus via a B-Cell-Dependent Mechanism

The absence of the mouse cell surface receptor CD38 in Cd38^−/− mice suggests that this receptor acts as a positive regulator of inflammatory and autoimmune responses. Here, we report that, in the context of the chronic graft-versus-host disease (cGVHD) lupus inducible model, the transfer of B6.C-H2bm12/KhEg(bm12) spleen cells into co-isogenic Cd38^−/− B6 mice causes milder lupus-like autoimmunity with lower levels of anti-ssDNA autoantibodies than the transfer of bm12 spleen cells into WT B6 mice. In addition, significantly lower percentages of Tfh cells, as well as GC B cells, plasma cells, and T-bet⁺CD11c^hi B cells, were observed in Cd38^−/− mice than in WT mice, while the expansion of Treg cells and Tfr cells was normal, suggesting that the ability of Cd38^−/− B cells to respond to allogeneic help from bm12 CD4⁺ T cells is greatly diminished. The frequencies of T-bet⁺CD11c^hi B cells, which are considered the precursors of the autoantibody-secreting cells, correlate with anti-ssDNA autoantibody serum levels, IL-27, and sCD40L. Proteomics profiling of the spleens from WT cGVHD mice reflects a STAT1-driven type I IFN signature, which is absent in Cd38^−/− cGVHD mice. Kidney, spleen, and liver inflammation was mild and resolved faster in Cd38^−/− cGVHD mice than in WT cGVHD mice. We conclude that CD38 in B cells functions as a modulator receptor that controls autoimmune responses.

A Variant of the Histone-Binding Protein sNASP Contributes to Mouse Lupus

The Sle2c1rec1c (rec1c) sublocus is derived from the mouse lupus susceptibility 2 (Sle2) locus identified in the NZM2410 model. Our current study dissected the functional characters and the genetic basis of the rec1c locus relative to lupus when co-expressed with the Fas^lpr mutation, an established inducer of autoimmunity. The rec1c.lpr mice exhibited mild expansion of lymph nodes and had a normal T cell cellularity, but developed significantly kidney and lung inflammation, indicating that the rec1c amplifies lpr-induced autoimmune pathogenesis. A variant of somatic nuclear autoantigenic sperm protein (sNASP) was identified from the rec1c interval as a substitution of two consecutive amino acid residues in the histone-binding domain, resulting in an increased binding affinity to histone H4 and H3.1/H4 tetramer. To determine the role of the sNASP rec1c allele in mouse lupus, a novel strain was generated by introducing the rec1c mutations into the B6 genome. In this transgenic model, the sNASP allele synergized with the lpr mutation leading to moderate autoimmune phenotypes and aggravating inflammatory pathology alterations in kidney and lung that were similar to those observed in the rec1c.lpr mice. These results establish that the sNASP allele is a pathogenic genetic element in the rec1c sublocus, which not only promotes autoimmunity, but also exacerbates the inflammation reaction of end organs in mouse lupus pathogenesis. It also shows the complexity of the Sle2c locus, initially mapped as the major locus associated with B1a cell expansion. In addition to Cdkn2c, which regulates this expansion, we have now identified in the same locus a protective allele of Csf3r, a variant of Skint6 associated with T cell activation, and now a variant of sNASP that amplifies autoimmunity and tissue damage.