Hematocrit of C57Bl/6 and Balb/c mice implanted with Epo-secreting C57Bl/6-derived MSCs. As detailed in “Materials and methods,” 10⁷ Epo⁺ C57Bl/6 MSCs (black dot) were implanted subcutaneously at day 0 in C57Bl/6 mice (black dot) and Balb/c mice (white dot) embedded either in a collagen-based matrix (A) or without a matrix (B), and the Hct of recipient mice was determined over time (n = 4-5 per group). Additional subcutaneous implantations of 10⁷ Epo⁺ C57Bl/6 MSCs were conducted in Balb/c mice only, at days 107 and 170 (A) or at days 69 and 132 (B), as indicated by asterisk (^*).