Noninvasive Approach to Detection of T-Cell Mediated Graft Rejection through Antibody-Tagged Nanoparticles Using SQUID Detection.

Organ transplantation is a life-saving procedure for patients. However, acute T-cell mediated graft rejection occurs in a significant quantity of recipients, which is a potentially life-threatening condition. Current diagnostic criteria for transplant rejection rely on invasive tissue biopsies and relatively non-specific clinical features. We hypothesized that nanoparticles could be developed that specifically bind to T-cells. Furthermore, we postulated that these nanoparticles could be detected non-invasively by a Superconducting Quantum Interference Device (SQUID). Nanoparticles were conjugated through either amino or carboxy termini to either anti-CD2 or anti-CD3 antibodies. All three cell types were found to bind exclusively to specifically targeted antibody-tagged nanoparticles as identified through light microscopy and SQUID detection. Using receptor site densities determined by flow cytometry and the magnetic moment per nanoparticle results, SQUID is capable of determining the number of labeled cells in a sample. Our results indicate that T-cells bind approximately 1×10⁴ nanoparticles per cell. A SQUID sensor array also allows for in vitro localization of discrete sources of labeled T-cells. Using a phantom as a surrogate for organ or soft tissue, we also demonstrate that discrete signals of 10⁵ T- cells can be detected at 10 cm from the SQUID detector. These results demonstrate the potential utility of antibody-tagged nanoparticles as a contrast agent and SQUID as a noninvasive and sensitive detection device in patients who may be undergoing T-cell mediated graft rejection. In addition, the extreme sensitivity of this technique may provide not only a means of early, non-invasive detection of impending T-cell mediated rejection, but also an approach to titrating chemotherapeutics for treating rejection.