[Short-term use of rapamycin combined with Tregs prolongs mouse cardiac graft survival but attenuates recipient’s anti-tumor immunity].

Objective: To study the effect of short-term use of rapamycin( Rap) combined with regulatory T cells( Tregs)on the long-time survival of allogeneic mouse cardiac transplant,and its impact on the anti-tumor immunity of recipient.

Methods: Mouse Tregs were purified from recipients’ spleen by magnetic activated cell sorting( MACS),and expanded by CD3 / CD28 monoclonal antibody immunomagnetic beads and 2000 U / m L recombinant mouse IL-2( rm IL-2) ex vivo. The purity was tested by fluorescence-activated cell sorting( FACS). Allogeneic mouse cardiac transplanted models were established( H-2~bto H-2~d),and the mice were divided into three groups: control group( transplant only),Rap group,and Rap combined with Tregs group. In the Rap group,the mice were treated with Rap [1 mg /( kg·d),ip] for 14 consecutive days,and the mice in the Rap plus Tregs group received the same treatment,and 1 × 107 Tregs were adoptively transferred through the tail vein on the day of transplantion. Meanwhile,the syngeneic transplanted group was set up( H-2~dto H-2~d). Allograft survival was monitored daily and the graft was harvested on the indicated day and histologically evaluated. In the experiment of recipient’s anti-tumor immunity,the similar three groups of allogeneic cardiac transplanted models were established( H-2~bto H-2~d),and B16-F10 cells( recipient derived) were transferred through the tail vein, another three groups of allogeneic cardiac transplanted mice( H-2~dto H-2~b) were also transferred with B16-F10 cells( donor derived). Two weeks later,the tumor nodules of the lung were compared.

Results: The median survival time( MST) of the graft was 7 days in the control group,15 days in the Rap group,and 93 days in the Rap combined with Tregs group. Histologic analysis of long-time survival grafts showed lymphocyte infiltration and chronic vasculopathy. For donor-derived tumor,there was no tumor nodule in the control group,and tumor nodules significantly increased to 15 ± 8 in the Rap group and 14 ± 7 in the Rap combined with Tregs group,with no significant difference between the later two groups; for recipient-derived tumor,the tumor nodules in the Rap combined with Tregs group were 146 ± 12,which were significantly elevated compared with the control group( 70 ± 12) and the Rap group( 28 ± 9).

Conclusion: Short-term use of low-dose Rap combined with Tregs can significantly prolong the survival of transplanted mouse heart,but cannot inhibit tumorigenesis of the recipient.