Myeloid Bias in the Bone Marrow of Septic Patients and Its Correlation With Disease Severity and Prognosis: A Single-Center, Prospective Cohort Study

Myeloid Bias in the Bone Marrow of Septic Patients

Sepsis remains a leading cause of critical illness worldwide, yet the underlying mechanisms driving its profound and persistent immune dysfunction are incompletely understood. The bone marrow, as the birthplace of all immune cells, plays a central role in orchestrating systemic immune responses. Emerging evidence from animal models suggests that sepsis triggers emergency myeloid-biased hematopoiesis in the bone marrow, characterized by expansion of myeloid progenitors and myeloid-derived suppressor cells (MDSCs) at the expense of lymphoid and erythroid lineages. This bone marrow remodeling precedes peripheral immune alterations and may represent the initiating event of sepsis-induced immunosuppression. However, direct clinical evidence in humans is scarce. This prospective, single-center cohort study aims to systematically characterize bone marrow hematopoietic remodeling in patients with septic shock, compared to critically ill non-septic patients and healthy volunteers, and to determine whether the degree of myeloid lineage bias correlates with disease severity, immunosuppression, and adverse clinical outcomes.

This study will enroll three cohorts. Bone marrow aspirates and peripheral blood samples will be collected at 48-72 hours post-enrollment for flow cytometric immunophenotyping of hematopoietic stem/progenitor cells, MDSC subsets, and PD-L1 expression, as well as cytokine profiling and exploratory single-cell transcriptomics. Rectal swabs will be collected synchronously for 16S rRNA sequencing and untargeted metabolomics to investigate the association between gut microbiota, microbial metabolites, and bone marrow myeloid skewing, testing the gut-bone marrow-immune axis hypothesis. Clinical severity (SOFA/APACHE II), secondary infections, and 90-day mortality will be assessed to evaluate prognostic value. By integrating bone marrow hematopoiesis, gut microbiome, and clinical outcomes, this study seeks to provide novel mechanistic insights into sepsis-induced immunoparalysis and identify potential biomarkers or therapeutic targets for immune restoration.

1. Inclusion Criteria

(1) Sepsis-Associated Critical Illness Cohort

• Age 18-80 years, both genders;

• Meets the Sepsis-3.0 criteria: confirmed or suspected infection with an acute increase in SOFA score of ≥2 points;

• Admitted to the intensive care unit (ICU) for 48-72 hours at the time of enrolment;

• Expected ICU length of stay ≥7 days;

• Written informed consent provided by the patient or their legally authorized representative.

  (2) Non-Septic Critical Illness Cohort

• Age 18-80 years, both genders;

• Admitted to the ICU for 48-72 hours with a diagnosis of non-infectious critical illness, including but not limited to: (a) severe acute pancreatitis; (b) major trauma (Injury Severity Score ≥16); (c) post-major surgery (e.g., cardiovascular surgery, hepatectomy); (d) acute cerebrovascular disease (ischaemic stroke, intracerebral haemorrhage); (e) other critical conditions requiring ICU support;

• Expected ICU length of stay ≥7 days;

• Written informed consent provided by the patient or their legally authorized representative.

  (3) Healthy Volunteer Control Cohort

• Age 18-80 years, both genders.

• No acute or chronic medical history; recent health check-up results are normal.

• Normal complete blood count: white blood cell count, haemoglobin, and platelet count within the normal reference ranges;

• Willing and able to provide written informed consent.

  2. Exclusion Criteria

  (1) Sepsis-Associated Critical Illness Cohort

• Haematological disorders: previous or current primary haematological diseases affecting bone marrow haematopoiesis, including leukaemia, myelodysplastic syndromes, aplastic anaemia, multiple myeloma, lymphoma, etc;

• Active malignancy or receipt of chemotherapy/radiotherapy within the past 3 years;

• Immunosuppressed state: (a) use of immunosuppressive agents within the past 3 months (including glucocorticoids ≥0.5 mg/kg/day for ≥2 weeks); (b) history of solid organ or haematopoietic stem cell transplantation; (c) HIV infection or AIDS; (d) congenital immunodeficiency;

• Blood transfusion or bone marrow transplantation within the past 3 months;

• Severe chronic organ dysfunction: (a) Child-Pugh Class C liver disease; (b) end-stage renal disease (eGFR <30 mL/min) without regular dialysis;

• Abnormalities at the puncture site: infection, rash, trauma, or anatomical deformity at the posterior superior iliac spine;

• Pregnancy or breastfeeding;

• Moribund state with expected survival <24 hours;

• Participation in another interventional clinical trial within 3 months before or at enrolment;

• Refusal to sign informed consent by the patient or legal representative.

  (2) Non-Septic Critical Illness Cohort

• Evidence of infection: confirmed or suspected active infection (including pneumonia, intra-abdominal infection, urinary tract infection, bloodstream infection, etc.) within 48 hours of ICU admission;

• All other exclusion criteria listed for the Sepsis-Associated Critical Illness Cohort (items 1-10) apply.

  (3) Healthy Volunteer Control Cohort

• History of infection within the past 1 month;

• Abnormalities at the puncture site: infection, rash, trauma, or anatomical deformity at the posterior superior iliac spine;

• Pregnancy or breastfeeding.