Characterisation of the Xenogeneic Immune Response to Microencapsulated Fetal Pig Islet-Like Cell Clusters Transplanted into Immunocompetent C57BL/6 Mice

Vijayaganapathy Vaithilingam,Sabina Ratnapala,Cherry Fung,Vijesh Vaghjiani,Bernard E. Tuch,Jayne Foster,Ursula Manuelpillai,Kathrin Maedler

doi:10.1371/journal.pone.0059120

Abstract

Xenotransplantation of microencapsulated fetal pig islet-like cell clusters (FP ICCs) offers a potential cellular therapy for type 1 diabetes. Although microcapsules prevent direct contact of the host immune system with the xenografted tissue, poor graft survival is still an issue. This study aimed to characterise the nature of the host immune cells present on the engrafted microcapsules and effects on encapsulated FP ICCs that were transplanted into immunocompetent mice. Encapsulated FP ICCs were transplanted into the peritoneal cavity of C57BL/6 mice. Grafts retrieved at days 1, 3, 7, 14 and 21 post-transplantation were analysed for pericapsular fibrotic overgrowth (PFO), cell viability, intragraft porcine gene expression, macrophages, myofibroblasts and intraperitoneal murine cytokines. Graft function was assessed ex vivo by insulin secretion studies. Xenogeneic immune response to encapsulated FP ICCs was associated with enhanced intragraft mRNA expression of porcine antigens MIP-1α, IL-8, HMGB1 and HSP90 seen within the first two weeks post-transplantation. This was associated with the recruitment of host macrophages, infiltration of myofibroblasts and collagen deposition leading to PFO which was evident from day 7 post-transplantation. This was accompanied by a decrease in cell viability and loss of FP ICC architecture. The only pro-inflammatory cytokine detected in the murine peritoneal flushing was TNF-α with levels peaking at day 7 post transplantation. This correlated with the onset of PFO at day 7 implying activated macrophages as its source. The anti-inflammatory cytokines detected were IL-5 and IL-4 with levels peaking at days 1 and 7, respectively. Porcine C-peptide was undetectable at all time points post-transplantation. PFO was absent and murine intraperitoneal cytokines were undetectable when empty microcapsules were transplanted. In conclusion, this study demonstrated that the macrophages are direct effectors of the xenogeneic immune response to encapsulated FP ICCs leading to PFO mediated by a combination of both pro- and anti-inflammatory cytokines.

Highlights

Porcine islet xenotransplantation offers a potential treatment for type 1 diabetes and a partial solution to the problem of human donor tissue shortage
Our results suggest macrophages and myofibroblasts as direct effectors of the xenogeneic immune response to encapsulated fetal pig islet-like cell clusters (FP ICCs) leading to pericapsular fibrotic overgrowth (PFO) and graft failure which is mediated by a combination of both pro- and anti-inflammatory cytokines
Previous studies with non-encapsulated FP ICCs transplanted into immunocompetent mouse recipients demonstrated heavy infiltration of CD4+ T cells and macrophages within day 5 posttransplantation and complete graft rejection within 8 to 14 days [23,24,25]

Summary

Introduction

Porcine islet xenotransplantation offers a potential treatment for type 1 diabetes and a partial solution to the problem of human donor tissue shortage. Adult porcine islets and NPCCs have been extensively studied in varied transplantation settings [1,2,3], FP ICCs have received less attention. A disadvantage of using FP ICCs is the low proportion of mature insulin-producing b cells at the time of transplantation compared to adult pig islets. Preclinical studies from our group have shown that FP ICCs can normalize blood glucose levels (BGLs) of diabetic recipients both when transplanted beneath the renal capsule of immunodeficient mice [7] and when allografted into an immunosuppressed pig [8]. Human trials with FP ICCs implanted into immunosuppressed diabetic recipients conferred neither a confirmed functional benefit nor any adverse consequences with some cells staining positive for insulin [9,10]. One of the major problems facing the use of porcine islet tissue is the xenograft rejection by the host immune system and the need for chronic immunosuppression to prolong graft survival

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