Ubiquitous LEA29Y Expression Blocks T Cell Co-Stimulation but Permits Sexual Reproduction in Genetically Modified Pigs

We have successfully established and characterized a genetically modified pig line with ubiquitous expression of LEA29Y, a human CTLA4-Ig derivate. LEA29Y binds human B7.1/CD80 and B7.2/CD86 with high affinity and is thus a potent inhibitor of T cell co-stimulation via this pathway. We have characterized the expression pattern and the biological function of the transgene as well as its impact on the porcine immune system and have evaluated the potential of these transgenic pigs to propagate via assisted breeding methods. The analysis of LEA29Y expression in serum and multiple organs of CAG-LEA transgenic pigs revealed that these animals produce a biologically active transgenic product at a considerable level. They present with an immune system affected by transgene expression, but can be maintained until sexual maturity and propagated by assisted reproduction techniques. Based on previous experience with pancreatic islets expressing LEA29Y, tissues from CAG-LEA29Y transgenic pigs should be protected against rejection by human T cells. Furthermore, their immune-compromised phenotype makes CAG-LEA29Y transgenic pigs an interesting large animal model for testing human cell therapies and will provide an important tool for further clarifying the LEA29Y mode of action

The isolation of primary hepatocytes from human tissue: optimising the use of small non-encapsulated liver resection surplus

Two-step perfusion is considered the gold standard method for isolating hepatocytes from human liver tissue. As perfusion may require a large tissue specimen, which is encapsulated and has accessible vessels for cannulation, only a limited number of tissue samples may be suitable. Therefore, the aim of this work was to develop an alternative method to isolate hepatocytes from non-encapsulated and small samples of human liver tissue. Healthy tissue from 44 human liver resections were graded for steatosis and tissue weights between 7.8 and 600 g were used for hepatocyte isolations. Tissue was diced and underwent a two-step digestion (EDTA and collagenase). Red cell lysis buffer was used to prevent red blood cell contamination and toxicity. Isolated hepatocyte viability was determined by trypan blue exclusion. Western blot and biochemical analyses were undertaken to ascertain cellular phenotype and function. Liver tissue that weighed ≥50 g yielded significantly higher (P < 0.01) cell viability than tissue <50 g. Viable cells secreted urea and displayed the phenotypic hepatocyte markers albumin and cytochrome P450. Presence of steatosis in liver tissue or intra-hepatocellular triglyceride content had no effect on cell viability. This methodology allows for the isolation of viable primary human hepatocytes from small amounts of “healthy” resected liver tissue which are not suitable for perfusion. This work provides the opportunity to increase the utilisation of resection surplus tissue, and may ultimately lead to an increased number of in vitro cellular studies being undertaken using the gold-standard model of human primary hepatocytes

Targeting CD28, CTLA-4 and PD-L1 costimulation differentially controls immune synapses and function of human regulatory and conventional T-cells.

CD28, CTLA-4 and PD-L1, the three identified ligands for CD80/86, are pivotal positive and negative costimulatory molecules that, among other functions, control T cell motility and formation of immune synapse between T cells and antigen-presenting cells (APCs). What remains incompletely understood is how CD28 leads to the activation of effector T cells (Teff) but inhibition of suppression by regulatory T cells (Tregs), while CTLA-4 and PD-L1 inhibit Teff function but are crucial for the suppressive function of Tregs. Using alloreactive human T cells and blocking antibodies, we show here by live cell dynamic microscopy that CD28, CTLA-4, and PD-L1 differentially control velocity, motility and immune synapse formation in activated Teff versus Tregs. Selectively antagonizing CD28 costimulation increased Treg dwell time with APCs and induced calcium mobilization which translated in increased Treg suppressive activity, in contrast with the dampening effect on Teff responses. The increase in Treg suppressive activity after CD28 blockade was also confirmed with polyclonal Tregs. Whereas CTLA-4 played a critical role in Teff by reversing TCR-induced STOP signals, it failed to affect motility in Tregs but was essential for formation of the Treg immune synapse. Furthermore, we identified a novel role for PD-L1-CD80 interactions in suppressing motility specifically in Tregs. Thus, our findings reveal that the three identified ligands of CD80/86, CD28, CTLA-4 and PD-L1, differentially control immune synapse formation and function of the human Teff and Treg cells analyzed here. Individually targeting CD28, CTLA-4 and PD-L1 might therefore represent a valuable therapeutic strategy to treat immune disorders where effector and regulatory T cell functions need to be differentially targeted