- Background aims Clinical trials have documented beneficial effects of mesenchymal stromal cells from bone marrow and adipose tissue (ASCs) as treatment in patients with ischemic heart disease. However, retention of transplanted cells is poor. One potential way to increase cell retention is to inject the cells in an in situ cross-linked alginate hydrogel. Methods ASCs from abdominal human tissue were embedded in alginate hydrogel and alginate hydrogel modified with Arg-Gly-Asp motifs (RGD-alginate) and cultured for 1 week. Cell viability, phenotype, immunogenicity and paracrine activity were determined by confocal microscopy, dendritic cell co-culture, flow cytometry, reverse transcriptase quantitative polymerase chain reaction, Luminex multiplex, and lymphocyte proliferation experiments. Results ASCs performed equally well in alginate and RGD-alginate. After 1 week of alginate culture, cell viability was >93%. Mesenchymal markers CD90 and CD29 were reduced compared with International Society for Cellular Therapy criteria. Cells sedimented from the alginates during cultivation regained the typical level of these markers, and trilineage differentiation was performed by standard protocols. Hepatocyte growth factor mRNA was increased in ASCs cultivated in alginates compared with monolayer controls. Alginates and alginates containing ASCs did not induce dendritic cell maturation. ASCs in alginate responded like controls to interferon-gamma stimulation (licensing), and alginate culture increased the ability of ASCs to inhibit lymphocyte proliferation. Discussion ASCs remain viable in alginates; they transiently change phenotype in alginate hydrogel but regain the phenotype of monolayer controls upon release. Cells maintain their paracrine potential while in alginates; the combination of ASCs and alginate is non-immunogenic and, in fact, immunosuppressive.