Biodistribution of 99Tcm-labelled 5-thio-D-glucose.

We studied the biodistribution and tumour localization of 99Tcm-labelled-5-thio-D-glucose (99Tcm-TG). 5-Thio-D-glucose was labelled with 99Tcm by direct stannous ion reduction. The biodistribution of 99Tcm-TG was investigated in normal rabbits and in mice bearing experimental tumours. In rabbits, the plasma and clearance of 99Tcm-TG was 14.5 +/- 2.0 and 11.3 +/- 3.0 ml.min-1 respectively. Urinary excretion at 1 h was 53 +/- 5%. 99Tcm-TG was injected intravenously in mice bearing MC26 colon carcinoma and tissue samples were analysed by gamma scintillation counting at various times. Uptake of 99Tcm-TG in tumour at 1 and 3 h was 1.6 +/- 0.3% and 1.2 +/- 0.3%; the tumour to muscle ratios were 2.7:1 and 4:1 respectively. The autoradiographic biodistribution of 99Tcm-TG in MX-1 human breast xenografted nude mice showed more persistent tumour uptake of 99Tcm-TG than 14C-2-deoxyglucose (14C-DG). 99Tcm-TG accumulated in the centre of the tumours; 14C-DG was decreased in this central region probably because of zones of infarction on necrosis. The discordance between the tumour uptake of 99Tcm-TG and 14C-DG indicates that 99Tcm-TG does not act like a glucose analog, suggesting 99Tcm-TG avidity for zones of infarction or necrosis. The further study of 99Tcm-TG in tumours and ischaemic injury is warranted.

Bolus injection of aqueous antigen leads to a high density of T-cell-receptor ligand in the spleen, transient T-cell activation and anergy induction.

In vivo anergy can be modelled by administration of soluble peptide to T-cell receptor (TCR) transgenic mice specific for the moth cytochrome c peptide 88-103 (MCCp). Two weeks after initial peptide treatment, T cells were present in normal numbers but were unresponsive to antigen stimulation in vitro. Only bolus injections of peptide, either subcutaneous or intravenous, were effective at inducing tolerance, while slowly released antigen administered via mini-osmotic pump failed to result in anergy. Examination of T cells soon after bolus peptide administration revealed that anergy induction was preceded by a transient hyperactivation of T cells in vivo. Within 2 hr of peptide treatment, interleukin-2 was detectable in the plasma of the transgenic mice. Interestingly, only bolus injections of peptide led to high levels of T-cell activation, while adjuvant emulsified and pump-administered peptide resulted in very low stimulation in vivo. When the dose of bolus-injected peptide used for tolerization was titrated, the extent of anergy induction directly correlated with the intensity of early T-cell activation. Indirect measurements of TCR-ligand density on the surface of antigen-presenting cells following peptide administration revealed that aqueous peptide delivered via bolus injection generated a large number of major histocompatibility complex-peptide complexes, while pump-delivered and adjuvant-emulsified peptide did not. These data suggest that high levels of TCR ligand are required for in vivo T-cell hyperactivation and induction of anergy.

Experimental autoimmune encephalomyelitis induced with a combination of myelin basic protein and myelin oligodendrocyte glycoprotein is ameliorated by administration of a single myelin basic protein peptide.

Multiple sclerosis is an autoimmune disease of the central nervous system in which T cell reactivity to several myelin proteins, including myelin basic protein (MBP), proteolipid protein, and myelin oligodendrocyte glycoprotein (MOG), has been implicated in the perpetuation of the disease state. Experimental autoimmune encephalomyelitis (EAE) is used commonly as a model in which potential therapies for multiple sclerosis are evaluated. The ability of T cell epitope-containing peptides to down-regulate the disease course is well documented for both MBP- and proteolipid protein-induced EAE, and recently has been shown for MOG-induced EAE. In this study, we describe a novel EAE model, in which development of severe disease symptoms in (PL/J x SJL)F1 mice is dependent on reactivity to two different immunizing Ags, MBP and MOG. The disease is often fatal, with a relapsing/progressive course in survivors, and is more severe than would be predicted by immunization with either Ag alone. The MOG plus MBP disease can be treated postinduction with a combination of the MOG 41-60 peptide (identified as the major therapeutic MOG epitope for this strain) and the MBP Ac1-11[4Y] peptide. A significant treatment effect can also be obtained by administration of the MBP peptide alone, but this effect is strictly dose dependent. This MBP peptide does not treat the disease induced only with MOG. These results suggest that peptide immunotherapy can provide an effective means of mitigating disease in this model, even when the treatment is targeted to only one component epitope or one component protein Ag of a diverse autoimmune response.

Peripheral tolerance in T cell receptor-transgenic mice: evidence for T cell anergy.

T cell tolerance can be induced in adult mice by injection of soluble antigenic peptide. The underlying mechanism has been difficult to establish in normal mice due to the low precursor frequency of T cells specific for any given antigen. Therefore, we examined peripheral tolerance in mice transgenic for a T cell receptor specific for a cytochrome c peptide bound to I-Ek. Antigen-specific hyporesponsiveness could be induced in the transgenic mice. We followed the transgene-bearing T cells with a clonotypic monoclonal antibody and found similar numbers of clonotypic T cells in tolerized and control mice. To prevent de novo differentiation of T cells we analyzed thymectomized mice in which antigen-specific hyporesponsiveness was induced. Our analysis of thymectomized transgenic mice showed that antigen-specific T cell hyporesponsiveness following injection of peptide intravenously is not caused by gross elimination of T cells. These data provide evidence for the role of anergy in peripheral tolerance.

Autoradiography and radioscintigraphy of technetium-99m-sestamibi in c-neu transgenic mice.

UNLABELLED: Intratumor distribution patterns of 99mTc-sestamibi and 14C-2-deoxy-D-glucose were compared in the c-neu OncoMouse, a transgenic mouse that spontaneously develops breast tumors. METHODS: Thirty or 60 min after intravenous injection of 5 muCi 14C-2-deoxy-D-glucose and 3 mCi 99mTc-sestamibi into mice (n = 3 per time point) bearing mammary tumors (0.3-1.5 cm), the animals were analyzed for organ and tumor distribution using dual-label, whole-body autoradiography. The retention patterns of the two compounds were related to tumor morphology and viability, based on H&E-stained adjacent sections. For imaging studies, the transgenic mice (n = 9) were anesthetized with pentobarbital, injected intravenously with 5-20 mCi 99mTc-sestamibi and imaged for 60 min using a gamma camera equipped with a 1-mm pinhole collimator. RESULTS: All positively stained tumors retained both agents, with a mean 99mTc-sestamibi tumor retention of 0.38% +/- 0.2% ID/g at 30 min compared to 4.18% +/- 0.62% ID/g for 14C-2-deoxy-D-glucose. Tumor retention of the agents remained the same at 60 min, and neither compound localized within necrotic or cystic regions of the neoplasms. Repeat imaging at 2-8-day intervals indicated a predicted sensitivity to detect a 30% difference in tumor retention of a test versus reference compound in preclinical screening. CONCLUSION: The c-neu OncoMouse is a useful model for in vivo imaging and provides a spontaneous tumor model for preclinical screening of breast tumor imaging agents.