Based on the current literature, there is no consensus on how to demarcate “immature,” “intermediate,” and “mature” TANs. Terminology often overlaps, obscuring distinctions in developmental states
3–7. Studies interchangeably invoke TANs, polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs), and low-density neutrophils (LDNs). Morphologic labels, such as band versus segmented nuclei, are applied with non-aligned gates and composite immunophenotypes differ across platforms and cohorts
8. Phase assignment typically integrates nuclear morphology with markers in humans, including CD10, CD16, CD62L, C-X-C chemokine receptor 2 (CXCR2), and lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) but the precise thresholds of expression and gating hierarchies vary between laboratories, which hinders a cross-study comparison
4. CD101 is commonly used to distinguish immature from mature granulocytes in mice, often combined with Ly6G, CXCR2, and C-X-C chemokine receptor 4 (CXCR4)
3, yet case-to-case mapping between CD101-defined murine states and human stages remains unsatisfactory. Methodologic variability adds further ambiguity. Specifically, density-gradient separation can artifactually partition LDN/high-density neutrophil (HDN) pools. Delayed processing or cryopreservation alters CD62L/CD10 and degranulation status and sorting itself can activate neutrophils, creating spurious “new” subpopulations
1,7,9. Single-cell RNA-seq (scRNA-seq) helps reveal a continuum of maturation status, however the sparse capture of surface proteins complicates the back-annotation of developmental phases and integration across datasets. To enable reproducible interpretation, we adopt practical working definitions. Neutrophils progress from promyelocytes (PMs), myelocytes (MCs), metamyelocytes (MMs), band/seg-competent (Band/SC), and finally to segmented neutrophils (Seg) in humans; MC/MM neutrophils are considered immature
4. CD101
− denotes immature and CD101
+ denotes mature TANs in mice, while the functional pattern to human stages could be more complex
3. Finally, neutrophil development in the TME is unlikely to follow a strictly linear developmental trajectory
5. Emergency granulopoiesis can accelerate output and skew lineage specification.