Development of a Cu-⁶⁴Cu-labeled CD4(+) T cell targeting PET tracer: evaluation of CD4 specificity and its potential use in collagen-induced arthritis

Background CD4(+) T cells are central inflammatory mediators in the pathogenesis of autoimmune rheumatoid arthritis (RA), as they are one of the dominating cell types in synovial inflammation. Molecular imaging of CD4(+) T cells has potential role for early detection and monitoring of RA. Here, we developed a new radiotracer for in vivo immunoPET imaging of murine CD4(+) T cells and tested it in the collagen-induced arthritis (CIA) mouse model of human RA. Results The tracer, [Cu-64]Cu-NOTA-CD4-F(ab)'2 ([Cu-64]Cu-NOTA-CD4), was generated from F(ab)'2 fragments of R-anti-mouse CD4 antibodies conjugated to the 2-S-(isothiocyanatbenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (p-SCN-Bn-NOTA) chelator and radiolabeled with copper-64. Accumulation of the tracer and isotype control was evaluated in the CIA model and mice receiving whole-body irradiation (WBI) (5 Gy). The potential of [Cu-64]Cu-NOTA-CD4 for response assessment was evaluated in CIA induced mice treated with dexamethasone (DXM). Imaging data were compared with flow cytometry and immunohistochemistry (IHC) of inflammatory cells including CD4(+) T cells. [Cu-64]Cu-NOTA-CD4 showed increased accumulation in T cell-rich tissues compared with isotype control (p < 0.0001). In addition, reduced accumulation of [Cu-64]Cu-NOTA-CD4 was observed in T cell-depleted tissue (p < 0.0001). Flow cytometry and IHC confirmed the increased infiltration of CD4(+) T cells in CIA mice. Conclusions We developed and evaluated a new radiotracer, [Cu-64]Cu-NOTA-CD4, for immunoPET imaging of murine CD4(+) T cells. [Cu-64]Cu-NOTA-CD4 was successfully synthesized by F(ab)'2 fragments of R-anti-mouse CD4 antibodies conjugated to a chelator and radiolabeled with copper-64. We found that our novel CD4 PET tracer can be used for noninvasive visualization of murine CD4(+) T cells.