MSC effect on pathologic FVIII response. (A) Faster clearance of hFVIII IgG on MSC injection in hemophilic mice. hFVIII-immunized hemophilic B6 mice were injected with MSCs intraperitoneally after the same scheme as in panel A. The IgG profile shows high IgG clearance compared with the nontreated group. (B) ELISPOT assay using FVIII-derived splenocytes. In vitro ELISPOT performed with immunized hemophilic B6 mice splenocytes demonstrates that CCL2 neutralization rescues approximately 75% of the IgG secretion ability by PC, whereas simultaneous inhibition of CCL2/7 completely restored Ig secretion. Lane 1 indicates negative; lane 2, positive; lane 3, MSC CM + isotype; lane 4, MSC CM + CCL2 neutralizing antibody; lane 5, MSC CM + neutralizing CCL2/7 antibodies; lane 6, CCL2^−/− MSC CM + isotype; lane 7, CCL2^−/− MSC CM + CCL7 neutralizing antibody.