Antigen-loaded dendritic cell migration: MR imaging in a pancreatic carcinoma model

Results: Trypan blue assays showed no significant difference in mean viability indexes (unlabeled vs labeled dendritic cells, 4.32% ± 0.69 [standard deviation] vs 4.83% ± 0.76; P = .385). Thirty-five days after injection, the mean left and right flank tumor sizes, respectively, were 112.7 mm²± 16.4 and 109 mm² ± 24.3 for the 1-million dendritic cell group, 92.2 mm² ± 9.9 and 90.4 mm² ± 12.8 for the 2-million dendritic cell group, and 193.7 mm² ± 20.9 and 189.4 mm² ± 17.8 for the control group (P = .0001 for control group vs 1-million cell group; P = .00007 for control group vs 2-million cell group). There was a correlation between postinjection T2-weighted SNR decreases in the left popliteal LN 24 hours after injection and size changes at follow-up for tumors in both flanks (R = 0.81 and R = 0.76 for left and right tumors, respectively).

Conclusion: MR imaging approaches can be used for quantitative measurement of accumulated iron-labeled dendritic cell-based vaccines in draining LNs. The amount of dendritic cell-based vaccine in draining LNs correlates well with observed protective effects.

Purpose: To test the following hypotheses in a murine model of pancreatic cancer: (a) Vaccination with antigen-loaded iron-labeled dendritic cells reduces T2-weighted signal intensity at magnetic resonance (MR) imaging within peripheral draining lymph nodes (LNs) and (b) such signal intensity reductions are associated with tumor size changes after dendritic cell vaccination.

Materials and The institutional animal care and use committee approved Methods: this study. Panc02 cells were implanted into the flanks of 27 C57BL/6 mice bilaterally. After tumors reached 10 mm, cell viability was evaluated, and iron-labeled dendritic cell vaccines were injected into the left hind footpad. The mice were randomly separated into the following three groups (n = 9 in each): Group 1 was injected with 1 million iron-labeled dendritic cells; group 2, with 2 million cells; and control mice, with 200 mL of phosphate-buffered saline. T1- and T2-weight-ed MR imaging of labeled dendritic cell migration to draining LNs was performed before cell injection and 6 and 24 hours after injection. The signal-to-noise ratio (SNR) of the draining LNs was measured. One-way analysis of variance (ANOVA) was used to compare Prussian blue-positive dendritic cell measurements in LNs. Repeated-measures ANOVA was used to compare in vivo T2-weighted SNR LN measurements between groups over the observation time points.