**7. Summary and future prospects**

This particular report entails the use of transient microRNA manipulations to ensure acquis‐ ition of proper osteochondral phenotypes when engineering cells to replace damaged bone and cartilage in patients with inflammatory diseases targeting articular joints (in particular rheumatoid arthritis). We have shown that cell engineering, as a research field, needs to take into consideration how osteochondral cells affect osteoclasts directly, and that osteochondral cells may lose their acquired phenotypes upon exposure to cytokines (e.g. IL-1, IL-6, IL-17, and TNFα) or micro-RNA-containing exosome-like particles derived from activated Th17 cells. These detrimental effects can be counteracted by manipulating stem cell microRNA contents (the optimal minimal number and species of microRNAs are yet to be defined).

When refining the search for the minimal number of effective microRNAs, it is recommended that bioinformatics approaches are used along with micro-RNA micro-arrays and marker gene transcriptomes in engineered osteochondral cells, and that maximal compatibility score (Gordeladze 2011) between them are obtained. Assessment of phenotypes obtained should include analyses of how and to which extent these cells affect osteoclasts, and whether altered (i.e. enhanced) remodelling of bone formed within an *in vivo* model system (e.g. calcium deposits in the tibial muscle of SCID mice) of choice.
