SPINK2 in hematopoiesis and cancer: Biology and clinical implications.

Serine protease inhibitors are essential regulators of tissue homeostasis, immunity, and cell survival, where they modulate tightly controlled proteolytic signaling networks that influence cell fate and microenvironmental interactions in diverse biological systems. Among them, Kazal-type inhibitors constitute a structurally distinct group defined by a compact, disulfide-rich domain that confers exceptional stability and potent inhibitory activity against a range of serine proteases. SPINK2, a relatively understudied member of this family, has recently gained increasing attention due to its emerging functional roles in haematopoiesis and hematological cancers, as well as for its known function in reproductive biology. Initially identified in the testis as a key regulator of protease-driven germ-cell maturation, SPINK2 expression has since been found in bone marrow-derived hematopoietic stem and progenitor cells (HSPCs), where it contributes to the fine-tuning of protease-mediated signaling, cellular stress responses, and early lineage decisions. Growing evidence now implicates aberrant SPINK2 expression in leukemogenesis, therapy resistance, and bone marrow failure syndromes, highlighting its potential importance as both a mechanistic determinant and a clinically relevant biomarker in hematologic disorders.