Exosomes are a heterogenous subpopulation of extracellular vesicles 30–150 nm in range and of endosome-derived origin. We explored the exosome formation through different systems, including the endosomal sorting complex required for transport (ESCRT) and ESCRT-independent system, looking at the mechanisms of release. Different isolation techniques and specificities of exosomes from different tissues and cells are also discussed. Despite more than 30 years of research that followed their definition and indicated their important role in cellular physiology, the exosome biology is still in its infancy with rapidly growing interest. The reasons for the rapid increase in interest with respect to exosome biology is because they provide means of intercellular communication and transmission of macromolecules between cells, with a potential role in the development of diseases. Moreover, they have been investigated as prognostic biomarkers, with a potential for further development as diagnostic tools for neurodegenerative diseases and cancer. The interest grows further with the fact that exosomes were reported as useful vectors for drugs.

The repair of bone defects caused by trauma, infection or tumor resection is a major clinical orthopedic challenge. The application of bone grafts in orthopedic procedures is associated with a problem of inadequate vascularization in the initial phase after implantation. Meanwhile, the survival of cells within the implanted graft and its integration with the host tissue is strongly dependent on nutrient and gaseous exchange, as well as waste product removal, which are effectuated by blood microcirculation. In the bone tissue, the vasculature also delivers the calcium and phosphate indispensable for the mineralization process. The critical role of vascularization for bone healing and function, led the researchers to the idea of generating a capillary-like network within the bone graft in vitro, which could allow increasing the cell survival and graft integration with a host tissue. New strategies for engineering pre-vascularized bone grafts, that apply the co-culture of endothelial and bone-forming cells, have recently gained interest. However, engineering of metabolically active graft, containing two types of cells requires deep understanding of the underlying mechanisms of interaction between these cells. The present review focuses on the best-characterized endothelial cells—human umbilical vein endothelial cells (HUVECs)—attempting to estimate whether the co-culture approach, using these cells, could bring us closer to development and possible clinical application of prevascularized bone grafts.

Recent studies have demonstrated that treatment with alphabeta-T-cell receptor (TCR) monoclonal antibody and cyclosporine A (CsA) can extend survival in composite tissue allografts (CTA). The purpose of this study was to induce tolerance in fully major histocompatibility complex (MHC)-mismatched rat limb allografts under 7 days of a combined alphabeta-TCR-CsA protocol. The authors performed 30 hind-limb allotransplantations across the MHC barrier between Brown Norway donors (BN; RT1n) and Lewis recipients (LEW; RT1l). Isograft and allograft controls received no treatment. The experimental groups received monotherapy of alphabeta-TCR and CsA or a combination of alphabeta-TCR and CsA for 7 days only. Donor-specific tolerance and immunocompetence were determined by standard skin grafting in vivo and mixed lymphocyte reaction (MLR) in vitro. The efficacy of immunosuppressive therapy and the level of donor-specific chimerism were determined by flow cytometry. Long-term survival (>350 days) was achieved in allograft recipients (n=6) under the 7-day protocol of combined alphabeta-TCR-CsA. Donor-specific tolerance and immunocompetence of long-term chimeras were confirmed by acceptance of skin grafts from the donors and rejection of the third-party alloantigens (AxC Irish). At day 120, MLR demonstrated unresponsiveness to the host and donor antigens but strong reactivity against third-party alloantigens. Flow cytometry confirmed the high efficacy of immunosuppressive treatment and the development of donor-specific chimerism (7.6% of CD4+-RT1n+ cells, 1.3% of CD8+-RT1n+ cells, and 16.5% of CD45RA+-RT1n+ cells) in the periphery of tolerated recipients. Combined therapy of alphabeta-TCR-CsA for 7 days resulted in tolerance induction in fully MHC-mismatched rat hind-limb allografts. Tolerance was directly associated with stable, donor-specific chimerism.

Background. Transplantation of composite-tissue allograft (CTA) such as the human hand recently became a clinical reality. The high risks associated with the use of lifelong immunosuppression have been the prohibiting factor in the routine use of the CTA transplants. In this article, we present a new approach of inducing long-term, donor-specific tolerance to CTAs without recipient preconditioning and need for chronic immunosuppression. Methods. We have developed a clinically applicable 35-day protocol that induces donor-specific tolerance in a rat hindlimb-transplantation model across major histocompatibility complex (MHC) barrier [Lewis-Brown-Norway (LBN, RT1^l/n→F1) to Lewis (LEW, RT1^l) by using cyclosporine A (CsA) and a mouse monoclonal antibody against rat αβ-T-cell receptor (TCR) to systemically eliminate alloresponsive cells. Standard skin grafting, flow cytometry (FC), and mixed lymphocyte reaction (MLR) were used to assess efficacy of immunodepletion and confirm donor-specific tolerance and chimerism. Results. Under this protocol long-term tolerance (>720 days) was induced in all (n=5) CTA recipients across the MHC barrier without further need for immunosuppression. Tolerance was confirmed in all limb-allograft recipients by skin grafting in vivo and by MLR in vitro. The animals rejected third-party grafts, indicating immunocompetence. Conclusions. In this CTA model, combined protocol of αβ-TCR monoclonal antibody and CsA resulted in induction of donor-specific tolerance across the MHC barrier without recipient conditioning. We believe that our findings will foster development of new therapeutic strategies and expand clinical applications for composite-tissue transplantation.

The diagnosis of cancer is a family experience that changes the lives of all its members, bringing an immense amount of stress and many challenging situations. The daily routine, common activities and distribution of duties all have to change. Family members follow the phases of the disease,...