In-Vivo Detection and Tracking of T Cells in Various Organs in a Melanoma Tumor Model by (19)F-Fluorine MRS/MRI

BACKGROUND: (19)F-MRI and (19)F-MRS can identify specific cell types after in-vitro or in-vivo (19)F-labeling. Knowledge on the potential to track in-vitro (19)F-labeled immune cells in tumor models by (19)F-MRI/MRS is scarce. AIM: To study (19)F-based MR techniques for in-vivo tracking of adoptively transferred immune cells after in-vitro (19)F-labeling, i.e. to detect and monitor their migration non-invasively in melanoma-bearing mice. METHODS: Splenocytes (SP) were labeled in-vitro with a perfluorocarbon (PFC) and IV-injected into non-tumor bearing mice. In-vitro PFC-labeled ovalbumin (OVA)-specific T cells from the T cell receptor-transgenic line OT-1, activated with anti-CD3 and anti-CD28 antibodies (T(act)) or OVA-peptide pulsed antigen presenting cells (T(OVA-act)), were injected into B16 OVA melanoma-bearing mice. The distribution of the (19)F-labelled donor cells was determined in-vivo by (19)F-MRI/MRS. In-vivo (19)F-MRI/MRS results were confirmed by ex-vivo (19)F-NMR and flow cytometry. RESULTS: SP, T(act), and T(OVA-act) were successfully PFC-labeled in-vitro yielding 3x10(11)-1.4x10(12 19)F-atoms/cell in the 3 groups. Adoptively transferred (19)F-labeled SP, T(OVA-act), and T(act) were detected by coil-localized (19)F-MRS in the chest, abdomen, and left flank in most animals (corresponding to lungs, livers, and spleens, respectively, with highest signal-to-noise for SP vs T(OVA-act) and T(act), p<0.009 for both). SP and T(act) were successfully imaged by (19)F-MRI (n = 3; liver). These in-vivo data were confirmed by ex-vivo high-resolution (19)F-NMR-spectroscopy. By flow cytometric analysis, however, T(OVA-act) tended to be more abundant versus SP and T(act) (liver: p = 0.1313; lungs: p = 0.1073; spleen: p = 0.109). Unlike (19)F-MRI/MRS, flow cytometry also identified transferred immune cells (SP, T(act), and T(OVA-act)) in the tumors. CONCLUSION: SP, T(act), and T(OVA-act) were successfully PFC-labeled in-vitro and detected in-vivo by non-invasive (19)F-MRS/MRI in liver, lung, and spleen. The portion of (19)F-labeled T cells in the adoptively transferred cell populations was insufficient for (19)F-MRS/MRI detection in the tumor. While OVA-peptide-activated T cells (T(OVA-act)) showed highest infiltration into all organs, SP were detected more reliably by (19)F-MRS/MRI, most likely explained by cell division of T(OVA-act) after injection, which dilutes the (19)F content in the T cell-infiltrated organs. Non-dividing (19)F-labeled cell species appear most promising to be tracked by (19)F-MRS/MRI.