Characterization of Infrapatellar Fat Pad-derived Cell Concentrates Obtained During Knee Arthroscopy: Nonenzymatic Versus Enzymatic Processing

Background: This exploratory laboratory study compared infrapatellar fat pad (IPFP)-derived cell concentrates obtained by non-enzymatic and collagenase-based processing with respect to cell yield, an adherent/proliferative fraction, selected mesenchymal stromal cell-associated markers, clonogenicity, and qualitative differentiation. Materials and Methods: Sixty independent patients were randomized to non-enzymatic or enzymatic processing (30 per group). Fresh concentrates were assessed for nucleated cell yield, attachment/proliferation, colony formation, and selected markers. Archived group-level summaries were reassessed with two-sided Welch t tests; marker comparisons were adjusted by the Benjamini-Hochberg procedure. Non-enzymatically isolated cells were culture-expanded for descriptive marker assessment and qualitative adipogenic, osteogenic, and chondrogenic staining. Results: Enzymatic processing produced a higher nucleated cell yield than non-enzymatic processing (8.86 ± 2.50 × 10 5 vs 1.19 ± 1.17 × 10 5 cells/g; P < .001) and a higher adherent/proliferative fraction (9.85% ± 2.36% vs 3.25% ± 1.23%; P < .001). This fraction was not a live/dead viability measurement. Seven of 8 marker-positive populations were higher after enzymatic processing following false-discovery-rate adjustment; CD105 + did not differ. Culture-stage marker findings and trilineage staining were descriptive and qualitative, respectively. Conclusion: Non-enzymatic processing yielded heterogeneous IPFP-derived cell concentrates that could be culture expanded, but enzymatic processing produced higher cell yield and higher proportions of most measured marker-positive populations. The findings do not establish equivalence, clinical efficacy, complete International Society for Cell and Gene Therapy characterization, or quantitative viability.