Immunological identification of human T cells intracranially and tracing of neuronal projections by magnetic resonance imaging

This report describes the preparation and utilization of paramagnetically labelled proteins to trace neural projections in vivo, and to distinguish between human T cells and bovine T cells implanted into canine brain. The proteins are covalently coupled to the chelator (DTPA), then labelled with gadolinium and visualized in vivo by magnetic resonance imaging (MRI) techniques. Gadolinium labelled horseradish peroxidase (HRP) was injected into the auditory cortex of adult cats (1-7 μ1 containing 50 μg HRP per μ1) and 48-72 hours later the brain was imaged by MRI. The HRP was labelled with an average of 20 DTPA per HRP. MRI unambiguously identified the HRP injection sites and the sites of neural projections in the medical geniculate body (MGB). MGB localization of HRP-Gd was confirmed histologically demonstrating that MRI can distinguish between paramagnetically labelled protein and local environment effects in the brain (i.e. gray vs white matter). Two monoclonal antibodies against human T cells were labelled with gadolinium. The distinguished by MRI, human from bovine T cells implanted into canine brains (each implant contained 10 million cells in 40 μ1). The T1 weighted and calculated images readily identified the human T cells as a lesion of <4 mm while the bovine T cells did not yield a significant MRI signal. The ratio of DTPA to protein during the coupling procedure, affects the formation of protein aggregates by crosslinking