ALBERT

Description: CD4+CD25+ regulatory T cells (Tregs) suppress immune responses to alloantigens. The in vivo circulation and tissue localization of Tregs during an adaptive immune response remain unclear. We noninvasively tracked luciferase-expressing Tregs over time in an allogeneic bone marrow transplant model and demonstrated colocalization with effector T cells and initial expansion in secondary lymphoid organs before migration into inflamed tissues. Inflammation induced by irradiation and the allogeneic setting provided crucial stimuli for early Treg expansion and migration, leading to parallel reduction of effector T-cell proliferation in lymphoid organs and peripheral tissues. Treg transplants conferred long-term protection from systemic inflammatory challenge consistent with Treg in vivo survival. Suppression occurred during multiple phases of inflammation, but is optimal in the initial phase, providing protection from graft-versus-host disease while maintaining the graft-versus-tumor effect even at physiologic doses of Tregs due to their in vivo expansion, hence overcoming a major barrier to potential clinical applications of Tregs given their rarity.

Description: CD4+CD25+ Regulatory T cells (Treg) reduce the incidence and severity of acute graft-versus-host disease (GvHD) in murine models of allogeneic bone marrow transplantation (BMT) when given at the time of transplantation at a 1:1 ratio with donor effector T cells (Tcon). In our previous study with Treg trafficking, bioluminescene imaging (BLI) indicated a persistence of signal consistent with a prolonged survival of Treg in vivo following allogeneic BMT. In the current study, we evaluated the duration of Treg suppression and the impact of Treg on evolving and established GvHD. Lethally irradiated Balb/c (H2d) hosts received 5x106 T-cell depleted bone marrow (TCD-BM) cells from wild-type FVB mice (H2q) on day 0. On day 2, 3x106 splenocytes, or 1x106 purified CD4+/CD8+ T cells (Tcon) from luciferase+ transgenic mice (FVB) were infused to induce GvHD. Treg, purified from wt-FVB mice, in a 1:1 dose ratio with Tcon, were infused either on day 0, 2, 9, or 23 post-transplantation. Bioluminescence imaging was used to localize and quantitate the proliferation of Tcon in the absence or presence of Treg. Signal intensity, measured by photons/second/mouse, was significantly decreased in animals which received Treg at day 0, 2, or 9 (p-value 〈 0.05). More importantly, the greatest reduction in signal intensity occurred when Treg were given prior to the induction of GvHD by Tcon. This reduction was associated with a significantly lower clinical score for GvHD. Studies in which Treg are given up to 10 days prior to the addition of Tcon show similar findings. At day 23, when clinical GvHD was fully established in mice which received Tcon, the addition of Treg did not alter the increasing BLI signal level or the clinical course such that all animals died of GvHD (p-value=0.38). Lymphoid reconstitution was not affected by the addition of Treg prior to the induction of GvHD. In dose titration studies whereby Treg are given two days prior to the induction of GvHD, a 10-fold dose reduction in Treg was sufficient to significantly reduce Tcon proliferation and suppress clinical GvHD. We next assessed the duration of Treg suppressive effect by inducing GvHD on day 7, 14, 19 with luc+ Tcon following the infusion of Treg on day 0 of allogeneic BMT. Treg provided protection from the Tcon challenge at all 3 time points, leading to improved survival (p-value 〈 0.05). We conclude that Treg provide prolonged protection due to their ability to proliferate in vivo in an allogeneic setting. The capacity of Treg to proliferate in vivo permits a significant reduction in the number of Treg needed for adoptive transfer to induce a clinical response, a practical finding given the rarity of Treg. In addition, we conclude that Treg suppress the early proliferation of Tcon, allowing them to prevent and control evolving but not established GvHD.

Description: No abstract available