CD38 in Monocytes Drives Myelofibrosis and Points to New Treatments
Elevated CD38 in monocytes depletes NAD+ and fuels fibrosis in myeloproliferative neoplasms — blocking CD38 or boosting NAD+ may reverse disease.
Summary
Researchers discovered that CD38, an enzyme that degrades NAD+, is significantly overexpressed in monocytes during the fibrotic progression of myeloproliferative neoplasms (MPNs). Using a mouse model engineered to develop myelofibrosis, the team found that inflammatory monocytes with high CD38 activity differentiate into fibrocytes — cells that deposit scar tissue in bone marrow. The same CD38 elevation was confirmed in human patients with myelofibrosis. Critically, restoring NAD+ levels either by blocking CD38 pharmacologically or supplementing NAD+ precursors reduced fibrocyte formation in the lab and prevented fibrosis onset in mice. These findings position CD38 both as a biomarker for monitoring fibrotic progression and as a promising therapeutic target in myelofibrosis.
Detailed Summary
Myelofibrosis (MF) is a serious blood cancer in which inflammatory signaling drives progressive scarring of the bone marrow, leading to anemia, organ dysfunction, and shortened survival. Understanding what triggers this fibrotic process is critical for developing better therapies. Monocytes — a type of white blood cell — have been implicated in producing inflammatory cytokines and fibrocyte precursors, but the molecular mechanisms have remained unclear.
To investigate, researchers created a dual-mutation mouse model (NrasG12D/+Jak2V617F/+) that reliably develops myelofibrosis with early anemia and monocytosis. Transplanting these mice's bone marrow into recipients recapitulated MF features, and the team confirmed that Ly6c-high inflammatory monocytes were the primary source of collagen-producing fibrocytes driving bone marrow scarring.
RNA sequencing of these monocytes revealed a striking upregulation of CD38, an NAD+-consuming enzyme. Elevated CD38 activity caused a pronounced drop in intracellular NAD+ levels, which appears to fuel the pro-fibrotic differentiation program. Importantly, the same pattern held in humans: CD14+ monocytes from MF patients had significantly higher CD38 expression than healthy controls, and monocytes from polycythemia vera patients with early fibrosis had higher CD38 than those without fibrosis.
Pharmacological inhibition of CD38 or supplementation with NAD+ precursors successfully blocked fibrocyte differentiation in cell culture and, crucially, prevented the onset of fibrosis in the mouse model. This dual validation — cellular and in vivo — strengthens the case considerably.
These findings establish CD38 as both a potential biomarker for tracking fibrotic progression in MPNs and a druggable target. Anti-CD38 therapies already exist in oncology (e.g., daratumumab), raising the possibility of repurposing them for MF. NAD+ precursor supplementation represents another accessible avenue worth exploring in clinical trials.
Key Findings
- CD38 is significantly overexpressed in Ly6c-high monocytes in myelofibrosis mice and CD14+ monocytes in human MF patients.
- Elevated CD38 depletes intracellular NAD+, promoting differentiation of monocytes into pro-fibrotic fibrocytes.
- CD38 expression in monocytes correlates with fibrotic grade in polycythemia vera patients.
- Pharmacological CD38 inhibition or NAD+ precursor supplementation blocks fibrocyte formation in vitro.
- Targeting CD38 in vivo effectively prevented fibrosis onset in the NrasG12D/+Jak2V617F/+ mouse model.
Methodology
The study used an inducible dual-oncogene mouse model (NrasG12D/+Jak2V617F/+) with bone marrow transplantation to recapitulate myelofibrosis. RNA sequencing of sorted monocyte populations identified CD38 upregulation, which was validated in human patient samples. In vitro fibrocyte differentiation assays and in vivo pharmacological interventions confirmed CD38 and NAD+ as functional targets.
Study Limitations
The study is based primarily on a mouse model with two specific oncogenic mutations, which may not fully capture MF heterogeneity in humans. Human data is correlational and derived from a limited patient cohort; prospective trials are needed to validate CD38 as a clinical biomarker or therapeutic target. The long-term safety and efficacy of CD38 inhibition specifically in MF patients remains untested.
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