CSF1R inhibition promotes neuroinflammation and behavioral deficits during graft-versus-host disease in mice

Microglia specific Csf1r haploinsufficiency induces depressive-like behaviors by promoting NLRP6/caspase-1 signaling in mice

Depression is an early clinical manifestation of adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP), although the underlying molecular mechanisms remain poorly elucidated. The objective of this study was to investigate the mechanisms underpinning depressive behavior in the context of ALSP, utilizing microglial-specific Csf1r haploinsufficient mice. Our findings indicate that these mice exhibited depressive-like behaviors, as well as microglial hyper-ramification and aberrant synaptic pruning capacity. Blockade of CSF1R signaling with PLX3397 resulted in significant amelioration of depressive symptoms and restoration of normal microglial morphology and function. RNA sequencing analysis of microglia isolated from the medial prefrontal cortex (mPFC) of the brain indicated that NLRPs signaling pathways may play a significant role in the observed alterations in microglial Csf1r haploinsufficient mice. Notably, NLRP6, rather than NLRP3, was found to be upregulated, and the expression of caspase-1 exhibited colocalization with the microglial marker Iba1. Pharmacological inhibition of caspase-1 using VX-765 improved depressive-like behaviors, as well as microglial function. Taken together, our findings delineate a causal relationship between microglial Csf1r haploinsufficiency-induced activation of the NLRP6/caspase-1 signaling pathway and the manifestation of depressive-like behaviors in ALSP mice.

CuO-NPs Induce Apoptosis and Functional Impairment in BV2 Cells Through the CSF-1R/PLCγ2/ERK/Nrf2 Pathway

Copper oxide nanoparticles (CuO-NPs) induce neurological diseases, including neurobehavioral defects and neurodegenerative diseases. Direct evidence indicates that CuO-NPs induce inflammation in the central nervous system and cause severe neurotoxicity. However, the mechanism of CuO-NP-induced damage to the nervous system has rarely been studied, and the toxicity of different CuO-NP particle sizes and their copper ion (Cu2+) precipitation in microglia (BV2 cells) is worth exploring. Therefore, this study investigated CuO-NPs with different particle sizes (small particle size: S-CuO-NPs; large particle size: L-CuO-NPs), Cu2+ with equal molar mass (replaced by CuCl2 [Equ group]), and Cu2+ precipitated in a cell culture solution with CuO-NPs (replaced by CuCl2 [Pre group]), and examined the mechanism of action of each on BV2 microglia after co-culture for 12 h and 24 h. The activity of BV2 cells decreased, the morphology was damaged, and the apoptosis rate increased in all the exposed groups. Toxicity increased time- and dose-dependently, and was highest in the Equ group, followed by the S-CuO-NPs, L-CuO-NPs, and Pre groups, respectively. Subsequently, we investigated the mechanism of S-CuO-NP-induced cell injury, and revealed that S-CuO-NPs induced oxidative stress and inflammatory response and increased the membrane permeability of BV2 cells. Moreover, S-CuO-NPs reduced the ratio of p-CSF-1R/CSF-1R, p-PLCγ2/PLCγ2, p-extracellular signal-regulated kinase (ERK)/ERK, p-Nrf2/Nrf2, and Bcl-2/Bax protein expression in microglia, and elevated cleaved caspase-3 expression. The CSF-1R/PLCγ2/ERK/Nrf2 apoptotic pathway was activated. The downregulation of CX3CR1, CSF-1R, brain-derived neurotrophic factor (BDNF), and IGF-1 protein expression indicates impairment of the repair and protection functions of microglia in the nervous system. In summary, our results reveal that CuO-NPs promote an increase in inflammatory molecules in BV2 microglia through oxidative stress, activate the CSF-1R/PLCγ2/ERK/Nrf2 pathway, cause apoptosis, and ultimately result in neurofunctional damage to microglia.

The contribution of the monocyte-macrophage lineage to immunotherapy outcomes

ABSTRACT

Macrophages execute core functions in maintaining tissue homeostasis, in which their extensive plasticity permits a spectrum of functions from tissue remodeling to immune defense. However, perturbations to tissue-resident macrophages during disease, and the subsequent emergence of monocyte-derived macrophages, can hinder tissue recovery and promote further damage through inflammatory and fibrotic programs. Gaining a fundamental understanding of the critical pathways defining pathogenic macrophage populations enables the development of targeted therapeutic approaches to improve disease outcomes. In the setting of chronic graft-versus-host disease (cGVHD), which remains the major complication of allogeneic hematopoietic stem cell transplantation, colony-stimulating factor 1 (CSF1)-dependent donor-derived macrophages have been identified as key pathogenic mediators of fibrotic skin and lung disease. Antibody blockade of the CSF1 receptor (CSF1R) to induce macrophage depletion showed remarkable capacity to prevent fibrosis in preclinical models and has subsequently demonstrated impressive efficacy for improving cGVHD in ongoing clinical trials. Similarly, macrophage depletion approaches are currently under investigation for their potential to augment responses to immune checkpoint inhibition. Moreover, both monocyte and tissue-resident macrophage populations have recently been implicated as mediators of the numerous toxicities associated with chimeric antigen receptor T-cell therapy, further highlighting potential avenues of macrophage-based interventions to improve clinical outcomes. Herein, we examine the current literature on basic macrophage biology and contextualize this in the setting of cellular and immunotherapy. Additionally, we highlight mechanisms by which macrophages can be targeted, largely by interfering with the CSF1/CSF1R signaling axis, for therapeutic benefit in the context of both cellular and immunotherapy.

FDA-approved therapies for chronic GVHD

ABSTACT

Despite novel prophylactic regimens, chronic graft-versus-host disease (cGVHD) remains a challenging complication after allogeneic hematopoietic cell transplantation. cGVHD can affect multiple organs and reduces quality of life, and treatment can cause serious adverse effects. In the past 10 years, the drugs ibrutinib, ruxolitinib, belumosudil, and axatilimab were approved by the US Food and Drug Administration (FDA) for cGVHD. Here, we discuss which signaling pathways and cell types are targeted, the clinical studies that were the basis for FDA approval, and future directions for clinical research.

Axatilimab in Recurrent or Refractory Chronic Graft-versus-Host Disease

BACKGROUND

Colony-stimulating factor 1 receptor (CSF1R)-dependent monocytes and macrophages are key mediators of chronic graft-versus-host disease (GVHD), a major long-term complication of allogeneic hematopoietic stem-cell transplantation. The CSF1R-blocking antibody axatilimab has shown promising clinical activity in chronic GVHD.

METHODS

In this phase 2, multinational, pivotal, randomized study, we evaluated axatilimab at three different doses in patients with recurrent or refractory chronic GVHD. Patients were randomly assigned to receive axatilimab, administered intravenously, at a dose of 0.3 mg per kilogram of body weight every 2 weeks (0.3-mg dose group), at a dose of 1 mg per kilogram every 2 weeks (1-mg dose group), or at a dose of 3 mg per kilogram every 4 weeks (3-mg dose group). The primary end point was overall response (complete or partial response) in the first six cycles; the key secondary end point was a patient-reported decrease in chronic GVHD symptom burden, as assessed by a reduction of more than 5 points on the modified Lee Symptom Scale (range, 0 to 100, with higher scores indicating worse symptoms). The primary end point would be met if the lower bound of the 95% confidence interval exceeded 30%.

RESULTS

A total of 241 patients were enrolled (80 patients in the 0.3-mg dose group, 81 in the 1-mg dose group, and 80 in the 3-mg dose group). The primary end point was met in all the groups; an overall response was observed in 74% (95% confidence interval [CI], 63 to 83) of the patients in the 0.3-mg dose group, 67% (95% CI, 55 to 77) of the patients in the 1-mg dose group, and 50% (95% CI, 39 to 61) of the patients in the 3-mg dose group. A reduction of more than 5 points on the modified Lee Symptom Scale was reported in 60%, 69%, and 41% of the patients in the three dose groups, respectively. The most common adverse events were dose-dependent transient laboratory abnormalities related to CSF1R blockade. Adverse events leading to discontinuation of axatilimab occurred in 6% of the patients in the 0.3-mg dose group, 22% in the 1-mg dose group, and 18% in the 3-mg dose group.

CONCLUSIONS

Targeting CSF1R-dependent monocytes and macrophages with axatilimab resulted in a high incidence of response among patients with recurrent or refractory chronic GVHD. (Funded by Syndax Pharmaceuticals and Incyte; AGAVE-201 ClinicalTrials.gov number, NCT04710576.).