Immune recognition of exposed xenoantigens on the surface of PEGylated bovine red blood cells

Bioengineered skin allografts: a new method to prevent humoral response

We previously reported that a bioengineered interface consisting of a nano-barrier membrane (NB-LVF4) used as an artificial interface between skin allografts and wound surfaces significantly prolonged graft survival without immunosuppression. We now evaluated whether NB-LVF4 could serve as a targeted drug delivery system to further improve outcomes. Fibroblast growth factor-1 (FGF-1) was selected for its known function as a wound hormone. Full-thickness 8-mm skin grafts were cross-transplanted between out-bred mice. Controls were transplanted without treatment. In test groups, the NB-LVF4, with or without FGF-1, was applied to both basolateral skin and wound surfaces with polymerization resulting in a tridimensional transparent membrane. The mice were evaluated for T-cell activation and development of donor-specific antibody. Rejection occurred in controls by 7 days. NB-LVF4 treatment, with or without FGF-1, was found to significantly prolong allograft survival (27 and 28 days, respectively [p < 0.05]). Untreated controls stimulated 10-fold shift in the number of circulating CD4+ cells while test groups exhibited substantially reduced shifts in CD4+ cells. The group treated with FGF-1 did not develop donor-specific antibody. Treatment with the NB-LVF4 membrane delays the onset of allograft rejection in the absence of systemic immunosuppression. FGF-1 appears to prevent the development of a humoral response by preventing B cell activation.

Pretransplant kidney-specific treatment to eliminate the need for systemic immunosuppression

BACKGROUND

Despite significant side effects, chronic systemic immunosuppression remains the backbone of clinical transplantation. We investigated the feasibility of preventing early allorecognition in canine renal allografts using a nonsystemic pretreatment.

METHODS

The renal vasculature was treated with a bioengineered interface consisting of a nano-barrier membrane during 3 hr of ex vivo warm perfusion.

RESULTS

Preliminary feasibility of the immunocloaking technology was established by the following criteria: it is possible to achieve approximately 90% coverage of the vasculature with nano-barrier membrane after 3 hr of ex vivo warm perfusion; covering the luminal surfaces prevents allorecognition as determined by mixed lymphocyte-vascular endothelial reaction; covering the luminal surfaces does not negatively affect renal function as determined by autotransplant outcomes; and graft rejection is significantly postponed in canine kidneys treated with the immunocloaking technology. In the absence of systemic immunosuppression, untreated control dogs experienced a mean onset of rejection on day 6, whereas in the treated dogs with modified renal vascular luminal surfaces, the mean onset of rejection was significantly delayed until day 30.

CONCLUSIONS

The ability to postpone, or eventually eliminate, the allorecognition that occurs immediately on reperfusion could provide a new window of opportunity to introduce adjunct therapies to support tolerance induction. To our knowledge, this is the first time significantly prolonged canine renal allograft survival has been achieved in the absence of systemic immunosuppression or immunologic manipulation of the recipient.

Drug delivery by red blood cells: vascular carriers designed by mother nature

IMPORTANCE OF THE FIELD

Vascular delivery of several classes of therapeutic agents may benefit from carriage by red blood cells (RBC), for example, drugs that require delivery into phagocytic cells and those that must act within the vascular lumen. The fact that several protocols of infusion of RBC-encapsulated drugs are now being explored in patients illustrates a high biomedical importance for the field. AREAS COVERED BY THIS REVIEW: Two strategies for RBC drug delivery are discussed: encapsulation into isolated RBC ex vivo followed by infusion in compatible recipients and coupling therapeutics to the surface of RBC. Studies of pharmacokinetics and effects in animal models and in human studies of diverse therapeutic enzymes, antibiotics and other drugs encapsulated in RBC are described and critically analyzed. Coupling to RBC surface of compounds regulating immune response and complement, affinity ligands, polyethylene glycol alleviating immune response to donor RBC and fibrinolytic plasminogen activators are described. Also described is a new, translation-prone approach for RBC drug delivery by injection of therapeutics conjugated with fragments of antibodies providing safe anchoring of cargoes to circulating RBC, without need for ex vivo modification and infusion of RBC.

WHAT THE READER WILL GAIN

Readers will gain historical perspective, current status, challenges and perspectives of medical applications of RBC for drug delivery.

TAKE HOME MESSAGE

RBC represent naturally designed carriers for intravascular drug delivery, characterized by unique longevity in the bloodstream, biocompatibility and safe physiological mechanisms for metabolism. New approaches for encapsulating drugs into RBC and coupling to RBC surface provide promising avenues for safe and widely useful improvement of drug delivery in the vascular system.