[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. MethodsMouse Tregs were purified from recipients' spleen by magnetic activated cell sorting (MACS), and expanded by CD3/CD28 monoclonal antibody immunomagnetic beads and 2000 U/mL recombinant mouse IL-2 (rmIL-2) ex vivo. The purity was tested by fluorescence-activated cell sorting (FACS). Allogeneic mouse cardiac transplanted models were established (H-2(b) to 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 1×10(7) Tregs were adoptively transferred through the tail vein on the day of transplantion. Meanwhile, the syngeneic transplanted group was set up (H-2(d) to 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(b) to 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(d) to 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.