Clinical islet transplantation is today an established alternative treatment for a selected group of type 1 diabetes patients. The predominant technique for transplantation is infusion of islets in the liver via the portal vein. Obstacles to advancing islet transplantation include limited engraftment resulting from an immediate blood-mediated inflammatory reaction (IBMIR), a life-long need for immunosuppression and the shortage of organs available. In this thesis, innate and adaptive immunity were explored in allogeneic and xenogeneic settings, with the long-term goal of preventing islet graft destruction. Methods for studying immune responses to islets in blood and engrafted islets in liver tissue (intragraft gene expression) were developed and refined. The innate response to human islets and exocrine tissue in ABO-compatible blood was characterized up to 48 h using a novel whole-blood model. Physiological changes in the blood during incubations were explored and adjusted to allow prolonged experiments. Increased production of chemokines targeting CXCR1/2, CCR2 and CXCR3 was observed, accompanied by massive intra-islet neutrophil infiltration. Notably, endocrine and exocrine tissue triggered a similarly strong innate immune response. Two studies of adult porcine islet transplantation to non-human primates (NHPs) were performed. Expression of immune response genes induced in liver tissue of non-immunosuppressed NHPs (≤72 h) was evaluated after porcine islet transplantation. Up-regulation of CXCR3 mRNA, together with IP-10, Mig, MIP-1α, RANTES, MCP-1 and cytotoxic effector molecule transcripts, was associated with T-cell and macrophage infiltration at 48-72 h. Long-term survival (>100 days) of adult porcine islets in a NHP model was later demonstrated using T-cell-based immunosuppression, including co-stimulatory blockade (anti-CD154 mAb). Graft failure was associated with increased levels of circulating, indirectly activated T cells, non-Gal pig-specific IgG and gene transcripts of inflammatory cytokines. Microarray analysis of the response to inflammatory cytokines in cultured porcine islets identified genes involved in cell death, immune responses and oxidative stress; this gene pattern coincided with physiological changes (decrease in insulin and ATP content). In summary, allogeneic whole-blood experiments and xenogeneic in vivo studies underscored the importance of preventing early inflammation and cell-recruitment to avoid islet graft loss in islet transplantation. Long-term survival of porcine islets in NHPs was shown to be feasible using T-cell-directed immunosuppression, including anti-CD154 mAb.

Adenovirus-mediated gene therapy is a potential complement to standard cancer treatments. Advantages are that vectors can be used to target tumors and that replicating viruses lead to increased therapeutic dosage. In this thesis, an oncolytic serotype 5 adenovirus (Ad5), Ad[i/PPT-E1A, E3], was developed where viral replication is controlled by the insulator-shielded (i) prostate-specific PPT promoter. The adenoviral E3 region was inserted for its immune regulatory and lysis functions. Ad[i/PPT-E1A, E3] had improved cytotoxic abilities both in vitro and in a prostate cancer xenograft mouse model compared to a virus lacking the E3 region. To further improve adenoviral vectors, the histone deacetylase inhibitor (HDACi) FK228 was studied. FK228 has been proposed to enhance the effect of adenoviral therapy by upregulation of CAR, the primary receptor for Ad5 infection. In the present study, we observed that FK228 promotes transgene expression even better when administered after viral transduction, indicating a post-transductional enhancement of transgene expression. Another interesting finding was that FK228 reduced transgene expression from the PPT promoter in the prostate cancer cell line LNCaP. This is explained by the fact that different HDACi have the ability to provoke a neuroendocrine phenotype of LNCaP. A potential drawback with adenoviral gene therapy is the rapid clearance of the virus from the circulation. Viral particles have been coated with polyethylene glycol (PEG) to evade immune recognition, a strategy that works well in mouse models. However, less is known about the effects of adenoviral PEGylation in human blood. We have studied cell interactions and immune responses to PEGylated and uncoated Ad5 vectors in human whole blood using a blood loop model with constant blood flow. Limited effects of PEGylation were observed in human blood, which were associated with the neutralizing ability of the donor blood. An important finding that donors with high neutralizing ability in whole blood do not necessarily have neutralizing antibodies against the virus strongly implies that neutralization should be measured in whole blood.

Weaning piglets are susceptible to the invasive Streptococcus (S.) suis infection, which can result in septicemia. The aim of this study was to investigate the cytokine profile induced upon S. suis infection of blood, to determine the cellular sources of those cytokines, and to study the potential effects of the induced cytokines on bacterial killing. We measured TNF-α, IL-6, IFN-γ, IL-17A and IL-10 after an experimental intravenous infection with S. suis serotype 2 in vivo, and analyzed whole blood, peripheral blood mononuclear cells (PBMC) and separated leukocytes to identify the cytokine-producing cell type(s). In addition, we used a reconstituted whole blood assay to investigate the effect of TNF-α on bacterial killing in the presence of different S. suis-specific IgG levels. An increase in IL-6 and IL-10, but not in IFN-γ or IL-17A, was observed in two of three piglets with pronounced bacteremia 16 to 20 h after infection, but not in piglets with controlled bacteremia. Our results confirmed previous findings that S. suis induces TNF-α and IL-6 and could demonstrate that TNF-α is produced by monocytes in vitro. We further found that IL-10 induction resulted in reduced secretion of TNF-α and IL-6. Rapid induction of TNF-α was, however, not crucial for in vitro bacterial killing, not even in the absence of specific IgG.