Abstract
The noninvasive imaging of dendritic cells (DCs) migrated into lymph nodes (LNs) can provide helpful information on designing DCs-based immunotherapeutic strategies. This study is to investigate the influence of transduction of human ferritin heavy chain (FTH) and green fluorescence protein (GFP) genes on inherent properties of DCs, and the feasibility of FTH as a magnetic resonance imaging (MRI) reporter gene to track DCs migration into LNs. FTH-DCs were established by the introduction of FTH and GFP genes into the DC cell line (DC2.4) using lentivirus. The changes in the rate of MRI signal decay (R2*) resulting from FTH transduction were analyzed in cell phantoms as well as popliteal LN of mice after subcutaneous injection of those cells into hind limb foot pad by using a multiple gradient echo sequence on a 9.4 T MR scanner. The transduction of FTH and GFP did not influence the proliferation and migration abilities of DCs. The expression of co-stimulatory molecules (CD40, CD80 and CD86) in FTH-DCs was similar to that of DCs. FTH-DCs exhibited increased iron storage capacity, and displayed a significantly higher transverse relaxation rate (R2*) as compared to DCs in phantom. LNs with FTH-DCs exhibited negative contrast, leading to a high R2* in both in vivo and ex vivo T2*-weighted images compared to DCs. On histological analysis FTH-DCs migrated to the subcapsular sinus and the T cell zone of LN, where they highly expressed CD25 to bind and stimulate T cells. Our study addresses the feasibility of FTH as an MRI reporter gene to track DCs migration into LNs without alteration of their inherent properties. This study suggests that FTH-based MRI could be a useful technique to longitudinally monitor DCs and evaluate the therapeutic efficacy of DC-based vaccines.
Highlights
The noninvasive tracking of the migration of dendritic cells (DCs) into the draining lymph node (LN) where DCs activate T cells, is critical to determine the efficacy of DC-based vaccines [1,2]
To further investigate the changes of mouse ferritin heavy chain (FTH), mouse transferrin receptor and mouse transferrin, which were involved in the control of cellular iron metabolism, RT-PCR were assessed in the DCs and ferritin heavy chain-transduced DC (FTH-DC) treated with or without 25 μM and 250 μM ferric ammonium citrate (FAC)
As shown in S2 Fig, the expression levels of mouse ferritin heavy chain (mFTH) and mouse transferrin receptor (mTfR) were similar between DCs and FTH-DCs. mFTH was slightly increased whereas mTfR was decreased dose-dependently in both cells treated with an increasing FAC (S2 Fig)
Summary
The noninvasive tracking of the migration of dendritic cells (DCs) into the draining lymph node (LN) where DCs activate T cells, is critical to determine the efficacy of DC-based vaccines [1,2]. A clinically approved superparamagnetic iron oxides (SPIOs) such as Feridex and Resovist has been safely used for the evaluation of in vivo DC migration without the alteration of characteristics of the DCs [4,5]. Stable transduction of ferritin heavy chain (FTH) which stores iron in a soluble, non-toxic form, has recently been applied to track diverse cells, evaluate the therapeutic effect and quantify transplanted cells non-invasively [8,9,10,11,12]. In order to assess MRI and optical imaging of DCs migration into LNs, we here established FTH-DCs transduced with imaging reporter genes, FTH and green fluorescence protein (GFP), using lentivirus system. In vitro and in vivo MRIs of FTH-DCs were performed using a 9.4 Tesla (T) scanner and an optical imaging system. Our results suggest that assessment by MRI of FTH-transduced DCs would be a useful tool to maximize and control the effects of DCs-based immunotherapy
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