Lung allograft VCAM-1: a ligand for graft targeting of nanoparticles post-lung transplantation

Introduction: Lung transplantation (LTx) necessitates lifelong systemic immunosuppression (SI), which carries substantial toxicities that impair quality of life and long-term survival. Although SI is essential for preventing allograft rejection, advances in nanotechnology offer the potential to deliver immunosuppressive agents more selectively, thereby reducing off-target toxicity while maintaining graft protection. In this study, we leveraged the upregulation of VCAM-1 during ischemia and rejection within the lung allograft to direct targeted delivery of otherwise subtherapeutic immunosuppressive doses compared to standard.
Methods: Allogeneic orthotopic left LTx were performed using Balb/c donors and C57BL/6 recipients. To define the minimum effective free rapamycin dose, mice received a single post-transplant tail vein injection of escalating rapamycin doses (100–1200 ng), with grafts harvest on day 7 post LTx and ISHLT rejection grade assessed. Dose-finding studies identified 300 ng as a subtherapeutic free rapamycin dose, which was subsequently used as the payload dose for VCAM-1–targeted PEG-PLGA rapamycin nanoparticles (VCAM-NP) to test whether targeted delivery could improve graft immune protection while reducing SI exposure. A separate arm evaluated reversal of established rejection. Subtherapeutic VCAM-NP-delivered rapamycin on day 5 post-LTx and grafts harvested on day 10. VCAM-NP binding was assessed using CyAl-5.5–labeled VCAM-1–NP under conditions of continuous flow perfusion of TNF-α–stimulated human microvascular endothelial cell organ chips. VCAM-1 immunostaining and NP colocalization was assessed by spinning-disk confocal imaging.
Results: Delivery of a subtherapeutic rapamycin dose (300ng) delivered by VCAM-1 targeted NP was associated with a significant reduction in rejection grade, as compared to free drug (1.3 ± 0.5 vs 3.6 ± 0.6, respectively). Interestingly, VCAM-1 targeted NPs, used as targeting controls, also produced a modest but significant reduction in rejection (2.3 ± 0.5 (p<0.05;).

Next, we assessed whether VCAM targeted delivery of sub-therapeutic rapamycin could reverse established rejection.  Administration of VCAM-NPs at day 5, significantly ameliorated graft rejection, with treatment associated with a rejection score of 2 ± 0, as compared with 4 ± 0 in free rapamycin controls (p<0.05;). VCAM mediated NP uptake was tested in-vitro using a novel endothelial perfused organ chip model. We demonstrate visual aggregation of VCAM-1 around VCAM-1 CyAl-5.5 conjugated NPs.

Conclusion: VCAM-1–targeted PEG-PLGA nanoparticles improved the efficacy of low-dose rapamycin in reducing and reversing acute rejection after lung transplantation. VCAM-1 targeted nanoparticles also showed unexpected anti-rejection effects, supporting further mechanistic study and development of targeted nanotherapeutic immunosuppression.