There have been an increased number of clinical trials with the use of intracerebral grafts for the treatment of neurological disorders. However, once the graft is deposited intracerebrally, the patient's immune response and the possible influence of that response on graft functionality is unknown. Imaging of neuroinflammation, such as with MRI in multiple sclerosis, is based on increased relative water content (edema) and/or measurements of a blood brain barrier (BBB) breach. Inflammation within cellular grafts, due to the small size, high cellularity, and the BBB that is affected by the injection needle, cannot be monitored by the same methods. In our extensive experience with cell transplantation in rodents, we have observed a great variability of graft infiltration by immune cells between individual animals, and a similar variability likely occurs in patients. This could explain the striking difference in outcomes between patients, including the unexpected severe side effects observed in a few patients, which frustrates both patients and clinical researchers. Thus, the aim of this proposal is to develop novel, clinically applicable approaches to the non-invasive detection of immune cell infiltration of the cellular graft. We have already established an experimental platform that is ideally suited to address the aims of this proposal. The immune deficient rag2-/- mice, characterized by absolute tolerance to all types of cellular grafts, will b employed as a reference for experimental, immune- competent hosts. Graft viability within the brain will be repeatedly evaluated by non-invasive bioluminescent imaging. The use of dysmyelinating shiverer mice (both rag2-/- and wild-type) as transplant recipients will enable the behavioral assessment of compromised graft functionality due to infiltration of immune cells, and will also enable post mortem assessment of graft differentiation using immunohistochemistry against MBP. Our preliminary studies have demonstrated that the survival of cells grafted into immunocompetent hosts is highly dependent on the implantation site. We will employ both rejection-prone and rejection-resistant target sites, to validate the applicability of the proposed non-invasive rejection monitoring readouts. We hypothesize that immune cell infiltration results in an alteration of the local microenvironment. Thus, we will employ novel MRI techniques, such as CEST, which has been recognized as a powerful tool for the non-invasive acquisition of molecular information in living tissues, and FLEX, which is complementary and adds information about rapidly exchanging protons. We will use these techniques for the detection of the molecular signature of graft rejection and to monitor the effects of immunosuppression on graft infiltration with regard to behavioral outcomes and post mortem analysis of graft differentiation and infiltration by immune cells. Upon the successful completion of this proposal, we anticipate that we will have established an efficient method by which to evaluate the immune response against transplanted cells, with the intention to translate this technique further as a diagnostic tool for patients with intracerebral grafts.
After the graft is deposited intracerebrally, the patient's immune response and the possible influence of that response on the graft is unknown. We have observed a great variability of graft infiltration by immune cells between individual animals, and a similar variability likely occurs in the clinic, which may explain the striking difference in outcomes between patients. Thus, the aim of this proposal is to develop novel, clinically applicable approaches to the non-invasive detection of immune cell infiltration of the cellular graft.
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