Molecular pathway-specific 99mTc-N-(3-bromo-2,4,6-trimethyacetanilide) iminodiacetic acid liver imaging to assess innate immune responses induced by cell transplantation.

OBJECTIVES: Inflammatory responses after cell transplantation impair engraftment of transplanted cells. We studied whether perturbations in specific molecular pathways after inflammation in a syngeneic cell transplantation model could be identified by noninvasive imaging.
METHODS: After transplanting hepatocytes into the liver of dipeptidyl peptidase IV-deficient Fischer 344 rats, we imaged hepatobiliary excretion of ppmTc-N-(3-bromo-2,4,6-trimethyacetanilide) iminodiacetic acid (99mTc-mebrofenin). Fractional retention of peak hepatic mebrofenin activity over 60-min periods was correlated with parameters of hepatic inflammation.
RESULTS: In healthy animals, 28+/-6% 99mTc-mebrofenin activity was in the liver after 60 min, whereas cell transplantation dose-dependently inhibited excretion of 99mTc-mebrofenin, P value of less than 0.001. Resolution of this abnormality in 99mTc-mebrofenin transport required 2 weeks in the setting of prolonged activation of Kupffer cells with increased TNF-alpha and IL-6 expression. Hepatic transport of 00mTc-mebrofenin was promptly restored by anti-inflammatory treatments, including inhibition of cyclooxygenase activity, depletion of neutrophils, or blocking of inflammatory cytokines before cell transplantation. Moreover, these treatments improved transplanted cell engraftment.
CONCLUSION: Molecular pathway-based imaging offers appropriate noninvasive means to address activation of innate immune responses. This will help in developing suitable strategies for characterizing and overcoming immune responses for cell and gene therapy.