Cell-permeable transgelin-2 as a potent therapeutic for dendritic cell-based cancer immunotherapy

Transgelin-2 is a 22 kDa actin-binding protein that has been proposed to act as an oncogenic factor, capable of contributing to tumorigenesis in a wide range of human malignancies. However, little is known whether this tiny protein also plays an important role in immunity, thereby keeping body from the cancer development and metastasis. Here, we investigated the functions of transgelin-2 in dendritic cell (DC) immunity. Further, we investigated whether the non-viral transduction of cell-permeable transgelin-2 peptide potentially enhance DC-based cancer immunotherapy.

To understand the functions of transgelin-2 in DCs, we utilized bone marrow-derived DCs (BMDCs) purified from transgelin-2 knockout (Tagln2^-/-) mice. To observe the dynamic cellular mechanism of transgelin-2, we utilized confocal microscopy and flow cytometry. To monitor DC migration and cognate T-DC interaction in vivo, we used intravital two-photon microscopy. For the solid and metastasis tumor models, OVA⁺ B16F10 melanoma were inoculated into the C57BL/6 mice via intravenously (i.v.) and subcutaneously (s.c.), respectively. OTI TCR T cells were used for the adoptive transfer experiments. Cell-permeable, de-ubiquitinated recombinant transgelin-2 was purified from Escherichia coli and applied for DC-based adoptive immunotherapy.

We found that transgelin-2 is remarkably expressed in BMDCs during maturation and lipopolysaccharide activation, suggesting that this protein plays a role in DC-based immunity. Although Tagln2^-/- BMDCs exhibited no changes in maturation, they showed significant defects in their abilities to home to draining lymph nodes (LNs) and prime T cells to produce antigen-specific T cell clones, and these changes were associated with a failure to suppress tumor growth and metastasis of OVA⁺ B16F10 melanoma cells in mice. Tagln2^-/- BMDCs had defects in filopodia-like membrane protrusion and podosome formation due to the attenuation of the signals that modulate actin remodeling in vitro and formed short, unstable contacts with cognate CD4⁺ T cells in vivo. Strikingly, non-viral transduction of cell-permeable, de-ubiquitinated recombinant transgelin-2 potentiated DC functions to suppress tumor growth and metastasis.

This work demonstrates that transgelin-2 is an essential protein for both cancer and immunity. Therefore, transgelin-2 can act as a double-edged sword depending on how we apply this protein to cancer therapy. Engineering and clinical application of this protein may unveil a new era in DC-based cancer immunotherapy. Our findings indicate that cell-permeable transgelin-2 have a potential clinical value as a cancer immunotherapy based on DCs.