Host immune determinants of stromal vascular fraction graft survival: Toward a concept of SVF therapy resistance - A systematic narrative review.

Stromal vascular fraction (SVF)-based therapies and autologous fat grafting have emerged as promising regenerative strategies due to their pro-angiogenic, immunomodulatory, and trophic properties. However, despite encouraging preclinical and clinical findings, therapeutic outcomes remain highly heterogeneous, with marked variability in graft retention and functional efficacy between patients. Increasing evidence suggests that this variability cannot be explained solely by procedural factors or cellular composition, but may also depend on host-related immune and microenvironmental determinants. This review explores the biological mechanisms governing SVF engraftment and introduces the emerging concept of "SVF therapy resistance," defined as the failure of autologous regenerative therapies resulting from maladaptive interactions between transplanted stromal cells and the host tissue environment. Particular attention is given to sterile inflammation, innate immune activation, and early graft-host interactions. Following transplantation, tissue injury and ischemia induce the release of danger-associated molecular patterns (DAMPs), triggering neutrophil recruitment, macrophage activation, complement signaling, and inflammatory remodeling. While controlled inflammatory responses may support tissue repair and angiogenesis, excessive neutrophil activation, neutrophil extracellular trap (NET) formation, persistent pro-inflammatory macrophage polarization, and impaired vascular adaptation may compromise graft survival and regenerative efficacy. The review further discusses how SVF processing, inflammatory priming, stromal cell heterogeneity, and donor-related factors-including obesity, aging, metabolic dysfunction, and chronic inflammation-may influence therapeutic responsiveness. Emerging evidence from mesenchymal stromal cell biology suggests that stromal cells are highly sensitive to inflammatory licensing and microenvironmental cues. Candidate biomarkers and immune profiling strategies capable of identifying responders and non-responders to SVF-based therapies are also reviewed. Finally, these mechanisms are discussed in spinal cord injury, a condition characterized by chronic inflammation and vascular dysfunction. Overall, this review proposes a translational framework linking innate immunity, sterile inflammation, angiogenesis, and stromal cell heterogeneity to the variability of SVF therapy outcomes, highlighting the need for personalized regenerative medicine approaches.