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Cell‐intrinsic functions of Bhlhe40 in activated B cells and TFH cells restrain the GC reaction and prevent lymphomagenesis

ABSTRACT: The generation of high-affinity antibodies against pathogens and vaccines requires the germinal center (GC) reaction – a process that relies on a complex interplay between specialized effector subsets of B and CD4 T lymphocytes – GC B cells and T follicular helper (TFH) cells. Intriguingly, several key positive regulators of the GC reaction are common for both cell types. Here, we report that the transcription factor Bhlhe40 is a crucial cell-intrinsic negative regulator affecting both the B and T cell sides of the GC reaction. In activated CD4 T cells, Bhlhe40 was required to restrain proliferation thus limiting the number of TFH cells. In B cells, Bhlhe40 executed its function in the first days after immunization by selectively restricting the generation of the earliest GC B cells but not of early memory B cells or plasmablasts. Conditional Bhlhe40 inactivation confirmed cell-autonomous functions of Bhlhe40 in both GC B and TFH cells, while the GC phenotype was further enhanced upon loss of Bhlhe40 in both cell types. This negative regulation of the GC reaction by Bhlhe40 was of crucial importance, as Bhlhe40-deficient mice with progressing age succumbed to a B cell lymphoma characterized by the accumulation of monoclonal GC B-like cells and polyclonal TFH cells in various tissues.

ORGANISM(S): Mus musculus

PROVIDER: GSE186457 | GEO | 2021/10/25

REPOSITORIES: GEO

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Project description:The cell fate decisions between plasmablasts (PBs), germinal center B cells (GCBCs) and non-GC-derived early memory B cells (eMBCs) during early B cell activation determine the outcome of the immune responses to pathogens and vaccines. To characterize these poorly understood lineage choices, we dissected the early B cell responses to T-dependent antigen in mice by single-cell RNA-sequencing. Early after immunization, a homogenous population of activated precursors (APs) gave rise to a transient wave of PBs, followed a day later by the emergence of the first GCBCs, with the transcriptomes of both rapidly diverging from that of APs. The majority of APs started to withdraw from the cell cycle very early on and gave rise to eMBCs, a developmental transition that involved limited transcriptional changes. These events were controlled by antigen availability that rapidly declined soon after immunization, and provision of antigen excess interfered with the cell cycle exit of APs and induced a new wave of PBs. Fate mapping experiments revealed a prominent contribution of eMBCs to the overall MBC pool. Generation of the earliest GCBCs was tightly controlled by the transcriptional repressor Bhlhe40 in the absence of which this population was increased in numbers. Bhlhe40 also restrained in a cell intrinsic fashion the response of T follicular helper (TFH) cells, a specialized T helper cell subset required to mount the GC response. In B cells, Bhlhe40 executed its function in the first days after immunization by selectively restricting the generation of the earliest GCBCs but not of eMBCs or PBs. Conditional Bhlhe40 inactivation confirmed cell-autonomous functions of Bhlhe40 in both GCBCs and TFH cells, while the GC phenotype was further enhanced upon loss of Bhlhe40 in both cell types. This negative regulation of the GC reaction by Bhlhe40 was of crucial importance, as Bhlhe40-deficient mice with progressing age succumbed to a B cell lymphoma characterized by the accumulation of monoclonal GCBCs-like cells and polyclonal TFH cells in various tissues.

Project description:Using both global and conditional knockout mice, we demonstrated that the transcription factor Basic Helix-Loop-Helix Family Member E40 (BHLHE40/DEC1) is required in T cells for rejection of mouse syngeneic tumors upon immune checkpoint therapy (ICT) with anti-PD-1 or anti-CTLA-4 monoclonal antibody (mAb) treatment. Using single cell RNA sequencing (scRNAseq) we profiled intratumoral CD45+ cells from syngeneic mouse sarcomas that (a) grow progressively with control treatment in either Bhlhe40+/+ or Bhlhe40-/- tumor-bearing mice, (b) reject following anti-PD-1 or anti-CTLA-4 ICT in Bhlhe40+/+ tumor-bearing mice, or (c) grow progressively following anti-PD-1 or anti-CTLA-4 in Bhlhe40-/- mice. We performed two separate scRNAseq experiments with the same conditions but harvested tumors on either day 9 post-tumor transplant or day 11 post-tumor transplant. The groups were as follows: (1) Control mAb Bhlhe40+/+, (2) Control mAb Bhlhe40-/-, (3) anti-PD-1 Bhlhe40+/+, (4) anti-PD-1 Bhlhe40-/-, (5) anti-CTLA-4 Bhlhe40+/+, and (6) anti-CTLA-4 Bhlhe40-/-. scRNAseq of intratumoral immune cells in BHLHE40-deficient mice revealed differential ICT-induced immune cell remodeling. These BHLHE40-dependent gene expression alterations were associated with altered metabolism, NF-kB signaling, and IFN- response in subpopulations of intratumoral CD4+ and CD8+ T cells. Intratumoral T cells from tumor-bearing Bhlhe40-/- mice also had higher transcript expression of the inhibitory receptor gene Tigit, along with altered transcript expression of chemokine/chemokine receptor granzyme family members. Bhlhe40-/- CD4+ and CD8+ T cells also had reduced ICT-driven IFN- production. Furthermore, BHLHE40 was required for ICT-induced remodeling of macrophages from a CX3CR1+ CD206+ subpopulation to an iNOS+ subpopulation. While anti-PD-1 or anti-CTLA-4 ICT in tumor-bearing Bhlhe40-/- mice led to tumor outgrowth—several BHLHE40-dependent changes were specific to the ICT treatment that was administered.

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Cell‐intrinsic functions of Bhlhe40 in activated B cells and TFH cells restrain the GC reaction and prevent lymphomagenesis

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