Imaging intraplaque inflammation in carotid atherosclerosis with 11C-PK11195 positron emission tomography/computed tomography.

AIMS: We sought to determine whether intraplaque inflammation could be measured with positron emission tomography/computed tomography angiography (PET/CTA) using (11)C-PK11195, a selective ligand of the translocator protein (18 kDa) (TSPO) which is highly expressed by activated macrophages. METHODS AND RESULTS: Patients (n = 32; mean age 70 ± 9 years) with carotid stenoses (n = 36; 9 symptomatic and 27 asymptomatic) underwent (11)C-PK11195 PET/CTA imaging. (11)C-PK11195 uptake into carotid plaques was measured using target-to-background ratios (TBR). On CTA images, plaque composition was assessed by measuring CT attenuation of the carotid plaque. Eight patients underwent carotid endarterectomy and ultrathin contiguous sections were processed for TSPO and CD68 (using immunohistochemical staining, (3)H-PK11195 autoradiography, and confocal fluorescence microscopy). Carotid plaques associated with ipsilateral symptoms (stroke or transient ischaemic attack) had higher TBR (1.06 ± 0.20 vs. 0.86 ± 0.11, P = 0.001) and lower CT attenuation [(median, inter-quartile range) 37, 24-40 vs. 71, 56-125 HU, P = 0.01] than those without. On immunohistochemistry and confocal fluorescence microscopy, CD68 and PBR co-localized with (3)H-PK11195 uptake at autoradiography. There was a significant correlation between (11)C-PK11195 TBR and autoradiographic percentage-specific binding (r = 0.77, P = 0.025). Both TBR and CT plaque attenuation had high negative predictive values (91 and 92%, respectively) for detecting symptomatic patients. However, the best positive predictive value (100%) was achieved when TBR and CT attenuation were combined. CONCLUSION: Imaging intraplaque inflammation in vivo with (11)C-PK11195 PET/CTA is feasible and can distinguish between recently symptomatic and asymptomatic plaques. Patients with a recent ischaemic event had ipsilateral plaques with lower CT attenuation and increased (11)C-PK11195 uptake.

[¹8F]GE-180: a novel fluorine-18 labelled PET tracer for imaging Translocator protein 18 kDa (TSPO).

A series of tricyclic compounds have been synthesised and evaluated in vitro for affinity against Translocator protein 18 kDa (TSPO) and for preferred imaging properties. The most promising of the compounds were radiolabelled and evaluated in vivo to determine biodistribution and specificity for high expressing TSPO regions. Metabolite profiling in brain and plasma was also investigated. Evaluation in an autoradiography model of neuroinflammation was also carried out for the best compound, 12a ([(18)F]GE-180).

Safety and Efficacy of OXB-202, a Genetically Engineered Tissue Therapy for the Prevention of Rejection in High-Risk Corneal Transplant Patients.

Due to both the avascularity of the cornea and the relatively immune-privileged status of the eye, corneal transplantation is one of the most successful clinical transplant procedures. However, in high-risk patients, which account for >20% of the 180,000 transplants carried out worldwide each year, the rejection rate is high due to vascularization of the recipient cornea. The main reason for graft failure is irreversible immunological rejection, and it is therefore unsurprising that neovascularization (NV; both pre and post grafting) is a significant risk factor for subsequent graft failure. NV is thus an attractive target to prevent corneal graft rejection. OXB-202 (previously known as EncorStat®) is a donor cornea modified prior to transplant by ex vivo genetic modification with genes encoding secretable forms of the angiostatic human proteins, endostatin and angiostatin. This is achieved using a lentiviral vector derived from the equine infectious anemia virus called pONYK1EiA, which subsequently prevents rejection by suppressing NV. Previously, it has been shown that rabbit donor corneas treated with pONYK1EiA substantially suppress corneal NV, opacity, and subsequent rejection in an aggressive rabbit model of cornea graft rejection. Here, efficacy data are presented in a second rabbit model, which more closely mirrors the clinical setting for high-risk corneal transplant patients, and safety data from a 3-month good laboratory practice toxicology and biodistribution study of pONYK1EiA-modified rabbit corneas in a rabbit corneal transplant model. It is shown that pONYK1EiA-modified rabbit corneas (OXB-202) significantly reduce corneal NV and the rate of corneal rejection in a dose-dependent fashion, and are tolerated with no adverse toxicological findings or significant biodistribution up to 13 weeks post surgery in these rabbit studies. In conclusion, angiogenesis is a valid target to prevent corneal graft rejection in a high-risk setting, and transplanted genetically modified corneas are safe and well-tolerated in an animal model. These data support the evaluation of OXB-202 in a first-in-human trial.

Functional repair of the corticospinal tract by delayed transplantation of olfactory ensheathing cells in adult rats.

Adult rats were trained to use their forepaws to retrieve a piece of food. Destruction of the dorsal corticospinal tract on one side at the level of the first cervical segment abolished the use of the ipsilateral forepaw for retrieval for at least 6 months after operation. Where a variable amount of the corticospinal tract was spared, there was a proportionate persistence of retrieval. In lesioned rats that had shown no retrieval for 8 weeks after operation, a suspension of olfactory ensheathing cells was injected into the lesion site. Starting between 1 and 3 weeks after transplantation, all rats with transplants bridging the lesion site resumed retrieval by the ipsilateral forepaw. Biotin dextran anterograde tracing shows regenerating corticospinal axons crossing the bridge, traveling caudally for approximately 10 mm in the distal part of the corticospinal tract and forming terminal arborizations in the spinal gray matter. Functional recovery can occur when only approximately 1% of the corticospinal tract axons are present.

Delayed repair of corticospinal tract lesions as an assay for the effectiveness of transplantation of Schwann cells.

We have previously shown that cultured adult olfactory ensheathing cells injected after 8 weeks into functionally complete unilateral lesions of the rat corticospinal tract induce restoration of paw reaching function to about 50% of normal, starting at around 10 days after transplantation. This provides an assay for determining the effectiveness of different methods of cell preparation or different cell types. We report that transplantation of cultured adult peripheral nerve Schwann cells also restores function, but the effect is delayed until around 30 days after transplantation and reaches only around 5-10% of normal. The presence of fibroblasts in the Schwann cell cultures neither improves, nor impairs the reparative effect, but fibroblasts alone (without Schwann cells) have no reparative effect. Without transplantation of exogenous Schwann cells, the ingrowth of endogenous Schwann cells which occurs spontaneously into these lesions does not restore function.