Improving Tumor Retention of Effector Cells in Adoptive Cell Transfer Therapies by Magnetic Targeting

Abstract

Adoptive cell transfer therapy is a promising anti-tumor immunotherapy in which effector immune cells are transferred to patients to treat tumors. However, one of its main limitations is the inefficient trafficking of inoculated effector cells to the tumor site and the small percentage of effector cells that remain activated when reaching the tumor. Multiple strategies have been attempted to improve the entry of effector cells into the tumor environment, often based on tumor types. It would be, however, interesting to develop a more general approach, to improve and facilitate the migration of specific activated effector lymphoid cells to any tumor type. We and others have recently demonstrated the potential for adoptive cell transfer therapy of the combined use of magnetic nanoparticle-loaded lymphoid effector cells together with the application of an external magnetic field to promote the accumulation and retention of lymphoid cells in specific body locations. The aim of this review is to summarize and highlight the recent findings in the field of magnetic accumulation and retention of effector cells in tumors after adoptive transfer, and to discuss the possibility of using this approach for tumor targeting with chimeric antigen receptor (CAR) T-cells.

Keywords: adoptive cell transfer therapy; cancer immunotherapy; chimeric antigen receptor (CAR) T-cells; magnetic targeting.

Figure 1

Main barriers that restrict the efficient traffic of effector cells towards tumors. The tumor microenvironment is a hostile environment for antitumor effector cell infiltration. This is achieved through multiple mechanisms such as: (1) mismatch between the chemokine receptors and chemokine pool in the tumor microenvironment; (2) decrease in the expression of adhesion molecule on the tumor endothelium; (3) aberrant vasculature that leads to inefficient traffic of immune cells; (4) tumor endothelium acting as a barrier.

Figure 2

MNP treatment increases the presence of mitochondria in naïve T cells. Representative images obtained by transmission electronic microscopy from murine naïve T cells with MNPs. Arrowheads indicate the mitochondria within the cells. TEM methodology is described in [78].

Figure 3

Subcellular localization of the APS-MNPs in different lymphoid cell models. Representative images obtained by transmission electronic microscopy. Arrowheads indicate the MNPs associated with the cell membrane.

Figure 4

Conjugation of murine NK cells with the RMA/S cell target in presence of MNPs. NK cells were treated with MNPs (+ APS-MNPs) or left untreated (− APS-MNPs) and incubated with RMA/S target cells for different lengths of time. Representative images of their conjugation at different incubation times, acquired by confocal microscopy (actin (red), microtubules (blue), perforin (green), MNPs (gray)). Scale: 10 μm. Dark-field confocal imaging is described in [78] and conjugation technique in [79].

Figure 5

Analysis of the migratory capacity of murine T cells after association with MNPs and in presence of an EMF, in in vitro “under agarose” migration assays. Coverslips were coated with recombinant murine Intercellular Adhesion Molecule 1 (ICAM-1) and CCL21 and overlaid with agarose. Primary murine T cells were labelled with CellTracker orange dye (Invitrogen), injected under the agarose layer with a micropipette and allowed to polarize for 30 min prior to the EMF application. Five positions (1 to 5) were selected with the microscope at increasing distance of the applied magnet (position 1 being the closest to the magnet and position 5 being the furthest from the magnet), and T cell movement was tracked over time. Mean displacement versus time graphs of T cells in the “under agarose” assay (A) at increasing distances from an EMF and (B) in the absence of an EMF. On one hand, these results indicate that MNP treatment by itself produces alterations in the migratory capacity of murine T cells, which show a reduction in the displacement along the time compared to untreated cells. On the other hand, EMF impairs migration in both MNP-treated and untreated murine T cells in a distance-dependent manner. Quantification of (C) cell speed and (D) percentage of cells that migrate in all conditions after analyzing the movies using Imaris software. The results shown (mean ± SD) are representative of two independent experiments. Student’s t-test, *** p < 0.001. These results show that both MNP treatment and EMF application reduce the velocity of murine T cells. However, no differences in the number of cells that was able to migrate were found in the different conditions.

Figure 6

In vivo behavior of MNP-loaded or unloaded murine DCs in the popliteal LN in the presence or absence of an EMF. (A) Representative captures of multiphoton microscopy movies obtained in presence or absence of EMF (blue: MNP-free DCs, red: MNP-associated DCs, gray: high endothelial venules (HEVs)). (B) Quantification of cell speed after movie analysis using Imaris software. The results shown (mean ± SD) are representative of two–three independent experiments. Student’s t-test, *** p < 0.001. (C) Paths followed by MNP-treated or untreated DCs inside the LN during the multiphoton microscopy assays in the absence or presence of EMF placed on the left (overall DC displacement to the left in red; to the right in blue), analyzed with the software provided by Ibidi (Chemotaxis and Migration tool). The methodology and ethic committee permits for these experiments are detailed in [78].