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-2b) mice. CD4+CD25+Tregs were sorted by magnetic activated cell sorting (MACS) from BALB/C (H-2d) 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 × 105 B16-F10 (H-2b) cells via tail vein, the other were inoculated with 1 × 107 BALB/c expanded polyclonal Tregs and 5 × 105 B16-F10, the last with 1 × 107 antigen-specific BALB/c Tregs and 5 × 105 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-2b). 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.