Novel Highly Homeostatic B Cells induced by Immunomodulatory Oligonucleotide IMT504

Cellular homeostasis depends on endoplasmic reticulum (ER) function and is highly sensitive to ER stress typically triggered by protein-folding overload. To restore balance, eukaryotic cells engage the unfolded protein response (UPR), a network of signaling pathways that enhances resistance to stress by upregulating chaperones, reducing global translation, and promoting degradation of unfolded proteins via autophagy. Additional stress-sensing pathways, including the NRF2 antioxidant response and the AMPK energy-sensing axis, converge to reinforce cellular homeostasis. In pathological conditions, reinforcing immune homeostasis constitutes a promising therapeutic strategy. Among emerging pharmacological agents that activate endogenous protective pathways, the synthetic immunomodulatory oligonucleotide IMT504 has shown favorable pharmacokinetics and stability in preclinical models, although its mechanisms of action remain unclear. Using purified human CD19 B cells, we investigated the cellular, molecular, and transcriptional responses to IMT504 stimulation, to uncover new insights into its mode of action and broader implications for immune-mediated homeostasis. We discovered that incubation of CD19CD27- B cells with IMT504 directly induces a-previously unreported-subpopulation of human B cells, which we termed B homeostatic cells (Bhom). These Bhom cells display a distinctive phenotype (CD27-CD24CD38CD138-MUC1) and upregulate genes associated with mitochondrial metabolism, proteostasis, antioxidant defense, and survival. Promoter analysis of the most highly upregulated genes revealed an Invariant Gene Transcriptional Regulator (IGTR) signature with binding motifs for MYC, CREB1, CTCF, EP300 and NRF1/NRF2, suggesting a coordinated transcriptional control of the involved homeostatic programs. Network analysis linked NRF1 to SIRT1/PGC1 metabolic axis and NRF2 to IGTR-regulated factors. Furthermore, we found that IMT504 binds ATP-citrate lyase (ACLY), an endogenous repressor of AMPK, indicating that IMT504 may activate AMPK-dependent autophagy and downstream NRF1/NRF2 signaling. Altogether, these findings identify Bhom cells as a novel B-cell subset that embodies homeostatic features and reveal IMT504 as a potent inducer of B-cell-mediated homeostasis through AMPK-driven transcriptional reprogramming. This mechanism strongly supports IMT504 as a promising candidate for immune-modulatory therapies aimed at restoring immune homeostasis. SIGNIFICANCE STATEMENTThe discovery of a novel B-cell subset, termed B homeostatic cells (Bhom), reveals a previously unrecognized axis of immune response. Incubation of human CD19CD27-B cells with the immunomodulatory oligonucleotide IMT504 directly induces Bhom cells. Its differentiation engages a conserved transcriptional network centered on AMPK-NRF1/NRF2 signaling, highlighting a potential therapeutic pathway to restore or enhance immune homeostasis.