H60: A Unique Murine Hematopoietic Cell-Restricted Minor Histocompatibility Antigen for Graft-versus-Leukemia Effect

A brain-body feedback loop driving HPA-axis dysfunction in breast cancer

Breast cancer patients often exhibit disrupted circadian rhythms in circulating glucocorticoids (GCs), such as cortisol. This disruption correlates with reduced quality of life and higher cancer mortality 1-3 . The exact cause of this phenomenon - whether due to treatments, stress, age, co-morbidities, lifestyle factors, or the cancer itself remains unclear. Here, we demonstrate that primary breast cancer alone blunts host GC rhythms by disinhibiting neurons in the hypothalamus, and that circadian phase-specific neuromodulation of these neurons can attenuate tumor growth by enhancing anti-tumor immunity. We find that mice with mammary tumors exhibit blunted GC rhythms before tumors are palpable, alongside increased activity in paraventricular hypothalamic neurons expressing corticotropin-releasing hormone (i.e., PVN CRH neurons). Tumor-bearing mice have fewer inhibitory synapses contacting PVN CRH neurons and reduced miniature inhibitory post-synaptic current (mIPSC) frequency, leading to net excitation. Tumor-bearing mice experience impaired negative feedback on GC production, but adrenal and pituitary gland functions are largely unaffected, indicating that alterations in PVN CRH neuronal activity are likely a primary cause of hypothalamic-pituitary-adrenal (HPA) axis dysfunction in breast cancer. Using chemogenetics (hM3Dq) to stimulate PVN CRH neurons at different circadian phases, we show that stimulation just before the light-to-dark transition restores normal GC rhythms and reduces tumor progression. These mice have significantly more effector T cells (CD8+) within the tumor than non-stimulated controls, and the anti-tumor effect of PVN CRH neuronal stimulation is absent in mice lacking CD8+ T cells. Our findings demonstrate that breast cancer distally regulates neurons in the hypothalamus that control output of the HPA axis and provide evidence that therapeutic targeting of these neurons could mitigate tumor progression.

Granulocytic myeloid-derived suppressor cells to prevent and treat murine immune-mediated bone marrow failure

Myeloid-derived suppressor cells (MDSCs) are immature myeloid cells that originate in the bone marrow (BM) and have immunoregulatory functions. MDSCs have been implicated in the pathogenesis of several autoimmune diseases but have not been investigated in immune aplastic anemia (AA). We examined the roles of granulocytic-MDSCs (G-MDSCs) in murine models of human AA and BM failure (BMF). As both prophylaxis and therapy, BM-derived G-MDSCs improved pancytopenia and BM cellularity and suppressed BM T-cell infiltration in major histocompatibility complex (MHC)-matched C.B10 BMF mice. These effects were not obtained in the MHC-mismatched CByB6F1 AA model, likely because of MHC disparity between G-MDSCs and donor T cells. Single-cell RNA sequencing demonstrated that G-MDSCs downregulated cell cycle-related genes in BM-infiltrated T cells, consistent with suppression of T-cell proliferation by G-MDSCs through reactive oxygen species pathways. Clearance of G-MDSCs in the MHC-mismatched CByB6F1 model using anti-Ly6G antibody facilitated T cell-mediated BM destruction, suggesting an intrinsic immunosuppressive property of G-MDSCs. However, the same anti-Ly6G antibody in the MHC-matched C.B10 AA model mildly mitigated BMF, associated with expansion of an intermediate Ly6G population. Our results demonstrate that G-MDSC eradication and therapeutic efficacy are immune context-dependent.