INTRODUCTION: Graft-versus-host disease (GVHD) is a major complication following allogeneic bone marrow transplantation. Despite advances in understanding the etiology of GVHD it remains a formidable obstacle to the widespread application of BMT. T regulatory (Treg) cells have been shown to inhibit GVHD while preserving the beneficial graft-versus-leukemia (GVL) effect. Published studies by numerous groups, including our own, have shown the importance of Treg homing molecule expression in preventing GVHD. Of note, the Treg population that expressed high levels of the adhesion molecule L-Selectin (CD62L) was shown to be capable of promoting BM engraftment and inhibiting lethal acute GVHD, whereas the CD62Llo population was not. While these studies provided evidence that the phenotype of the CD62Lhi Treg population was responsible for inhibition of GVHD they did not directly assess the role of CD62L.
METHODS: To investigate the importance of CD62L in Treg mediated protection from GVHD we utilized a well-described parent into F1 model. We transferred Tregs (2×106) from CD62L deficient mice (CD62L−/−) or wild type (WT) C57BL/6 mice with WT naïve T cell effectors (5×106) into lethally irradiated B6D2 recipients. Our results demonstrated similar survival of recipient mice receiving CD62L−/− Tregs (40% survival) compared to those receiving WT Tregs (60% survival: p =0.66). In addition fluorescence microscopy revealed no difference in GFP+ T cell effector migration/accumulation in GVHD target organs (liver, lung, GI tract) or secondary lymphoid organs (spleen, mesenteric lymph node, inguinal lymph node, Peyers Patches) in the presence of CD62L−/− or WT Tregs. Also, we tracked the migration of GFP+ CD62L−/− Tregs in vivo by fluorescence microscopy and found they were able to efficiently migrate to secondary lymphoid organs and GVHD target organs. Surprisingly, GFP+ CD62L−/− Tregs were also able to home to peripheral lymph nodes.
CONCLUSIONS: These results suggest CD62L is dispensable for Treg mediated suppression of GVHD and that the function of the L-selectinhi Treg fraction may be due to the difference in the expression of other homing/migration molecules necessary for Treg migration into lymphoid and GVHD target organs.
Disclosure: No relevant conflicts of interest to declare.