Integrating MRI and Chemokine Receptor CXCR4-Targeted PET for Detection of Leukocyte Infiltration in Complicated Urinary Tract Infections After Kidney Transplantation.

Abstract

Complicated urinary tract infections (UTIs) are frequent in immunosuppressed patients after kidney transplantation and may lead to allograft failure or urosepsis. Noninvasive detection of allograft involvement as well as localization of the primary site of infection are challenging. Therefore, we sought to determine whether molecularly targeted PET, combined with diffusion-weighted MRI, enables detection of leukocytes in renal allografts. <b>Methods:</b> Thirteen kidney transplant recipients with complicated UTIs underwent both PET with a specific CXCR4 ligand, ⁶⁸Ga-pentixafor, and diffusion-weighted MRI. The spatial distribution and intensity of CXCR4 upregulation in renal allografts as determined by SUVs on PET and diffusion restriction as determined by apparent diffusion coefficients (ADCs) on MRI were analyzed and compared with urinalysis, clinical chemistry and bacteriology, and biopsy, if available. <b>Results:</b> Combined PET/MRI detected acute allograft infection in 9 patients and lower UTI/nonurologic infections in the remaining 4 patients. Leukocyte infiltration was identified by areas of CXCR4 upregulation compared with unaffected parenchyma in PET (SUV_mean, 4.6 vs. 3.7; <i>P</i> < 0.01), corresponding to areas with increased cell density in MRI (ADC_min, 0.89 vs. 1.59 × 10^-3 mm²/s, <i>P</i> < 0.01). Allograft CXCR4 signal was paralleled by CXCR4 upregulation in lymphoid organs. Histopathologic evaluation supported a correlation between CXCR4 signal and presence of leukocytes. <b>Conclusion:</b> Combined CXCR4-targeted PET/MRI with ⁶⁸Ga-pentixafor may enable the noninvasive detection of leukocytes in renal allografts. This novel methodology may refine the characterization of infectious and inflammatory kidney diseases and may serve as a platform for future clinical studies targeting allograft infection.