*Purpose: Microparticles (MP) loaded with peptide antigen plus other immune signals and delivered directly into lymph nodes (LN) can result in either pro­inflammatory or anti­inflammatory responses. Confining MP delivery to single LN also induces systemic immune deviation. To demonstrate linkage between the modified LN and specificity of systemic tolerance, islet allografted mice received intra­LN delivery of MP encapsulating allopeptide plus rapamycin as a suppressive signal. We hypothesized that delivery of alloantigen plus regulatory signals into the LN could prolong allograft survival.

*Methods: MP were composed of poly (lactide­co­galactide). Rapamycin (Rapa) and/or class II alloantigen (I­E^d peptide (Ea)) were incorporated into the MP during assembly. A total of 400 freshly isolated BALB/c (H­2^d) islets were transplanted beneath the renal capsule of C57BL/6 (H­2^b) recipients made diabetic by streptozotocin. 2×10⁵ donor alloantigen specific CD4 T cell receptor transgenic TEa T cells were transferred i.v. into recipients. MP (1 μg in 10 μl of empty, Ea, Rapa, or Ea/Rapa loaded) were injected directly into inguinal LN after transplantation.

*Results: Neither empty MP nor Ea­MP (1.1 μg Ea peptide) prolonged graft survival, with all recipients rejecting between 10­15 days after transplant (mean survival time, empty MP 9.2 ± 2 days; Ea­MP 11 ± 3 days). The Rapa­MP (5.6 μg Rapa) prolonged graft survival and delayed rejection up to 28 days (23.6 ± 5 days, p<0.01). In contrast, the Ea/Rapa­MP synergistically prolonged islet graft survival up to 60 days (47.2 ± 6 days, p<0.001). Flow cytometry and histologic analyses showed that intra­nodal injection of Rapa and Ea/Rapa MPs induced more Treg (16% and 17%, respectively) and fewer activated CD4 T cells (15% and 12%) compared with control MPs (iTreg 12%, activated T cells 20%).

*Conclusions: MP can modify the LN microenvironment to promote regulatory T cell induction, and inhibition of effector cells. The results demonstrate that LN responses are important for systemic suppression, and that altering a single remote LN can prolong allograft survival at a distant site. These findings suggest a new therapeutic strategy to manipulate the LN environment with encapsulated, locally delivered antigen and regulatory signals to promote transplant tolerance.

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