2B4 (CD244) Induced By Selective CD28 Blockade Functionally Regulates Allograft-Specific CD8+ T Cell Responses.

Abstract

Mounting evidence in models of both autoimmunity and chronic viral infection suggests that the outcome of T cell activation is critically impacted by the constellation of costimulatory and coinhibitory receptors expressed on the cells' surface. Here, we identified a critical role for the coinhibitory SLAM family member 2B4 (CD244) in attenuating primary donor-reactive CD8+ T cell responses in the presence of immune modulation with selective CD28 blockade. Our results reveal a specific upregulation of 2B4 on donor-reactive CD8+ T cells in animals in which CD28 signaling was blocked. However, 2B4 upregulation was not observed in animals treated with CTLA-4 Ig (abatacept) or CD28 blockade in the presence of anti-CTLA-4 mAb, indicating that CTLA-4 coinhibitory signals are required for 2B4 upregulation. Skin graft experiments revealed a dramatic prolongation in survival in animals treated with CD28 dAbs, in which CTLA-4 coinhibitory signaling is maintained and 2B4 coinhibitory signaling is induced, as compared to CTLA-4 Ig in both major and minor histocompatibility models. Interestingly, the increased efficacy of CD28 dAbs in attenuating donor-reactive CD8+ T cell responses as compared to CTLA-4 Ig was not an effect of preserved PD-L1/CD80 coinhibitory signals, as blockade of PD-L1 did not abrogate the ability of CD28 dAb to inhibit donor-reactive CD8+ T cell responses or induce 2B4 upregulation. In order to directly assess the functional role of the 2B4 coinhibitory pathway in prolonging allograft survival, we assessed donor-reactive CD8+ T cell responses in 2B4-/- mice. 2B4 upregulation following CD28 blockade was functionally significant, as the inhibitory impact of CD28 blockade was diminished when donor-reactive CD8+ T cells were deficient in 2B4. In contrast, 2B4 deficiency had no effect on CD8+ T cell responses during unmodified rejection or in the presence of CTLA-4 Ig. We conclude that blockade of CD28 signals in the presence of preserved CTLA-4 signals results in the unique upregulation of 2B4 on primary CD8+ effectors, and that this 2B4 expression plays a critical functional role in controlling donor-reactive CD8+ T cell responses during transplantation. DISCLOSURES:Schneeweis, L.: Employee, Bristol Myers-Squibb. Stetsko, D.: Employee, Bristol Myers-Squibb. Suchard, S.: Employee, Bristol Myers-Squibb. Nadler, S.: Employee, Bristol Myers-Squibb.