Increase of donor derived tumor occurrence by transfer of ex vivo expanded antigen specific regulatory T cells

Objectives: Using regulatory T cells (Tregs) as a cellular therapy to control rejection is an attractive immunosuppressive strategy in transplantation, but immunosuppression mediated by Tregs need to be investigated before application. Methods: In our experiment, mature Dendritic Cells (DCs) were generated through inducing bone marrow cells of C57BL/6 (H-2(b)) mice. CD4(+)CD25(+) Tregs were sorted by magnetic activated cell sorting (MACS) from BALB/C (H2(d)) mice, and Tregs were expanded ex vivo with anti-CD3/CD28 microbeads and high concentration of recombinant murine (rm) IL-2 for 14 days, after that, expanded polyclonal Tregs were collected and cocultured with mature DCs (H-2b) in the presence of lower concentration of rmIL-2 for 7 days to get antigen-specific Tregs. Subsequently, BALB/C mice were randomly divided into three groups: BALB/c mice were inoculated with 5 x 10(5) B16-F10 (H-2(b)) cells via tail vein, the other were inoculated with 1 x 10(7) BALB/c expanded polyclonal Tregs and 5 x 10(5) B16-F10, the last with 1 x 10(7) antigen-specific BALB/c Tregs and 5 x 10(5) B16-F10 cells. After 14 days, mice were sacrificed and the black tumor nodules in lungs were counted. Results: Adoptive transfer of ex vivo expanded polyclonal Tregs rendered BALB/c mice (recipient) susceptible to MHC-mismatched tumor (B16-F10 cells, H-2(b)). If ex vivo expanded polyclonal Tregs from BALB/c were cocultured with mature DCs from C57BL/6 after expansion, suppression of tumor immunity against B16-F10 cells was further. Conclusion: We suggested that ex vivo expanded antigen-specific Tregs could more dampen recipient tumor immunity compare with polyclonal Tregs, and the increased risk of donor derived tumor should be considered.