AS Culture Condition for MSC led to co-cultured MPC
    At the end of 20th century, the evidence of the multipotency of an easily expandable progenitor of the mesenchymal lineage with apparent "stem" properties, the MSCs \cite{Pittenger_1999,Bruder_1994}, attracted a great interest from the scientific community and pulled the trigger on a decade of great efforts translating MSCs "from the bench to the bed-side" \cite{Bunpetch_2017}. In parallel to the increasing evidences of the great therapeutical value of in vitro expanded MSCs, serious concerns regarding the safety of the cell manufacturing procedures have been expressed. In particular, as mentioned above the use of FBS has been indicated as one of the principal possible source of morbidity in MSC-based cell therapies \cite{Spees_2004,Heiskanen2007}. The straightforward substitute firstly took in consideration was human-derived autologous and allogeneic sera (HS). However, large scale production of MSC in HS has significant limitations affecting manufacturing, regulatory issues, and the quality assurance. Specifically, even if considerable number of studies demonstrated the feasibility of HS in culturing MSC, the great biological variability of the produced HS batches led to contradictory results \cite{Sotiropoulou_2006,Dimarakis2006,Berger2006}.  From 2006, promising results were obtained firstly applying platelet-rich plasma (PRP) then adding trombin (tPRP) to maximize the reales of growth factors from the platelet granules. However, also the use of media supplementation with PRP or tPRP have some drawbacks as incomplete reales of granules content and mainly the presence of fibrinogen leading to possible clot activation. These aspects could be ameliorated applying human platelet lysate (hPL) \cite{Schallmoser_2007}, AGGIORNARE BIBLIO  PL which production and application could be standardized \cite{Shih_2015}. Moreover,  it has been demonstrated that hBM-MSC could be expanded with increased population doublings and growth rate in hPL-supplemented cultures compared with FBS, HS, or tPRP \cite{Bieback2009,Kinzebach2013}. Consequently, even with some issues to face off, hPL has been widely considered most feasible substitute of FBS in MSC GMP-grade expansion for clinical applications \cite{Altaie_2016}, this brought to a progressive reduction of the number of studies applying HS culturing bone marrow MSCs. Nonetheless our identification of the mesangiogenic potential retained by co-isolated MPC, only in HS-containing cultures of hBM-MNCs, led us to more deeply investigate the neglected application of HS. As described above, we especially applied pooled human AB-type serum (PhABS) in order to isolate purified MPC, representing an upstream approach in culturing bone marrow derived cells, usually intended to amplifying MSC instead  \cite{Trombi_2009}. AGGIORNARE BILBIO SU GMP SUPPLEMENTS
    Interestingly, our first observation of "contaminating" rounded and highly rifrangent cells in hBM-MNCs cultured with hAS (Figure XXX A) but not detected in FBS-supplemented cultures, was not a singular observation, indeed some Authors reported similar results applying human plasma or serum. In 1998, Koller et al. noted that applying human serum- or plasma-supplemented media did not produce a confluence of stromal cells but instead showed numerous large and adherent cells ,that were not observed in animal serum-containing medium, resembling the MPC morphology (Figure XXXX B)\cite{Koller1998}. Later Stute et al. described from 0.5 to 4.0% of "monocytes" and other, not better specified, rounded cells co-isolated with classical spindle-shaped MSC cells, in primary cultures of hBM-MNCs (Figure XXX C.1\cite{Stute2004}. Very similar to our first identification and characterization of MPCs  \cite{Petrini_2009}. Authors reported that passaging produced e drastic reduction of these "contaminating" cells, as they remained firmly adhered after trypsin digestion of the primary cultures (Figure XXX A and Figure XXX C left). More recently, also Takeda et al. reported a "non uniform morphology" of adherent cells at the primary culture of human bone marrow-derived cells applying hAS, in comparison to FBS-containing medium \cite{Takeda_2012}. Photomicrographs also from this latest paper clearly show MPC-like cells in the autologous serum-containing cultures (Figure XXX D). 
    When not more specifically described, these trypsin-resistant rounded cells were generically identified of hemopoietic origin and considered undesired contaminating cells, which were lost during passaging of MSC cultures \cite{Stute2004,Codinach_2016}. Surprisingly, basing on the results reported by our group in the last ten years, these "unwanted" cells, if characterized as MPCs,  could retain a great biological value and been of great interest in the field of MSC-based clinical application \cite{Pacini2014}. Moreover, it has been also hypothesized that the presence of MPCs could be responsible for the controversial data regarding the mesengenic but also angiogenic potential of MSCs cultured in HS, where different culture conditions could select or simply promote the persistence of co-isolated MPC as well as their direct progenies \cite{Pacini_2014}.
    Even if we strongly believe that MPCs should not be considered "undesired contaminating cells" but possibly increasing the regenerative potential of the BM cell preparations \cite{Giannotti_2013}, their hemopoietic origin should not be excluded. MPC morphology evokes that of cultured macrophages (Mϕ) or dendritic cells (DCs) and some of the expressed markers (i.e. CD31), and functions (Ac-LDL uptake, trans-endothelial migration, ECM degradation) reported in order to demonstrate the early angiogenic potential of MPCs are also shared by these latest cells (REF. Nonetheless, the consolidated data regarding in vitro and in vivo mesangiogenic potential of MPCs and the expression of pluripotency-associated genes suggest a possible plasticity of these BM-derived Mϕ-like cells. Retention of this mesangiogenic potential in hemopoietic cell lineages, in particular belonging to the moncytic/macrophagic subsets, is surprisingly but not completely unprecedented. This hypothesis has been supported by interesting data reported by several groups mainly during the first decade of 2000s, and discussed in the next paragraph, about both mesengenic and angiogenic potential retained by specialized and specific tissue-resident Mϕ and even by specifically stimulated circulating monocyte-derived Mϕ.