Abstract 20653: A Novel Protein, Early Secreted Antigenic Target of 6 kDa, Promotes Cardiac Allograft Tolerance by Inducing CD4+FoxP3+ Tregs
Introduction: Cardiac transplant provides a cure for end-stage heart diseases. However, a cardiac allograft is always rejected by recipients without immunosuppression (IS). Inducing transplant tolerance without global IS is a highly desirable goal because long-term IS causes serious side-effects. This study was set to induce cardiac allograft tolerance without long-term IS. Early Secreted Antigenic Target of 6 kDa (ESAT-6) was originally identified as a T cell Ag in short-term culture filtrate of M. tuberculosis. Previous studies have shown that ESAT-6 is a virulence factor that promotes the pathogenesis of M. tuberculosis while weakening immunity.
Hypothesis: ESAT-6 prolongs allograft survival.
Methods: C57BL/6 mice were transplanted with a Balb/C heart and treated with ESTA-6 (0.05mg i.p. on days 0, 2, 4 and 6) and/or MR1 (anti-CD40L Ab) (0.25 mg on days 0, 2, 4 and 6). One-way MLRs were set up to determine T cell proliferation by 3H-TdR uptakes and in vitro CD4+CD25+FoxP3+ Treg generation from purified CD4+CD25-Thy1.1+ responders, while in vivo Treg generation was measured via quantification of Treg numbers in isolated graft-infiltrating cells.
Results: We found that ESAT-6 alone did not significantly extend acute cardiac allograft survival (MST = 7 vs. 6 days, n=7-8, P>0.05). However, treatments with both MR1 and ESAT-6 induced much longer cardiac allograft survival when compared to MR1 alone [MST > 120 versus 69 days, n=8-9], with 50% of recipients (MR1+ESAT-6) achieving allograft tolerance because they could not reject a new skin graft from a Balb/C donor. ESAT-6 plus MR1 suppressed in vitro T cell proliferation compared to MR1 alone (CPM: 7±1 vs. 13±2, x1000, n=4, P<0.05). Moreover, the combined treatments increased Thy1.1+FoxP3+ Treg numbers in vitro (9.7±0.6 vs 6.3±0.4, X1000, P<0.05) and in grafts (5.9±0.5 vs. 3.2±0.3, X10000/Heart, P<0.05).
Conclusion: for the first time, our studies reveal that ESAT-6 promotes cardiac allograft tolerance via enhancing Treg generation.
Author Disclosures: Z. Dai: None. Q. Li: None. H. Dai: None.
- © 2014 by American Heart Association, Inc.