Allogeneic hematopoietic cell transplantation (HCT) is a curative therapy for relapsed hematological malignances (i.e. leukemia) due to graft-versus-leukemia (GVL) activity mediated by alloreactive T cells. However, alloreactive T cells also mediate graft-versus-host disease (GVHD), which remains the major obstacle for wide-spread application of allogeneic HCT. The long-term goal of our study is to develop novel regimens that prevent GVHD while preserving GVL activity. PD-L1 interacts with CD80 and PD-1. Although PD-L1/PD-1 regulation of immune responses plays an important role in animal models and humans, the role of PD-L1/CD80 remains largely unknown. Our recent publication in JCI has shed light on the importance of PD- L1/CD80 interactions. Our studies indicate that the outcome of PD-L1-mediated signaling in CD8+ T cells depends on the presence or absence of CD4+ T cells, the nature of the interacting receptors (i.e. CD80 versus PD-1) expressed by CD8+ T cells and the tissue environment (i.e. lymphoid versus parenchymal tissues) in which the signaling occurs. We observed that, in the absence of donor CD4+ T cells, CD8+ T-T interactions via PD-L1/CD80 augmented nave/activating CD8+ T proliferation and survival in lymphoid tissues, leading to strong GVL activity. In contrast, host-tissue PD-L1 interactions with PD-1 and CD80 on CD8+ T cells in GVHD target tissues induced their proliferation and apoptosis, leading to prevention of GVHD. Donor CD4+ T cells helped CD8+ T cells via IL-2 become resistant against tissue PD-L1-mediated tolerance. Agonistic PD-L1-Ig binding to both CD80 and PD-1 augmented activated T cell proliferation and apoptosis. Conflicting results have been reported regarding the effects of glycolysis and oxidative phosphorylation (OXPHOS) in alloreactive T cells during the pathogenesis of acute GVHD. In kinetic studies, we observed that expression of CD80 and PD- 1 was associated with shift from glycolysis to OXPHOS. Therefore, we hypothesize that 1) PD-L1/CD80 and PD-L1/PD-1 interactions reciprocally regulate T cell glycolysis and OXPHOS, and the outcome depends on the tissue environment, due to differential T cell expression of CD80, PD-1, and PD-L1; 2) Reduction of serum IL-2 will increase the sensitivity of T cells towards tissue PD-L1-mediated or agonistic PD-L1- Ig-mediated tolerance in association with metabolic profile changes. The proposed studies will dissect the mechanisms by which PD-L1/CD80 interactions regulate glycolysis and OXPHOS in nave/activating and activated T cells in lymphoid and GVHD target tissues (Aim 1). We will also design a regimen of sequentially administered anti-IL-2 and agonistic PD-L1-Ig to prevent GVHD and preserve strong GVL activity (Aim 2). These studies will reveal novel insights into T cell biology and GVHD pathogenesis and could lead to development of novel regimens that prevent GVHD while preserving GVL activity in humans. 1

Public Health Relevance

Allogeneic hematopoietic cell transplantation (HCT) is a curative therapy for hematological malignancies due to the graft versus leukemia/lymphoma (GVL) effects mediated by alloreactive T cells. However, alloreactive T cells also mediate a severe side effect, graft versus host disease (GVHD), which remains the major obstacle for a wide-spread application of allogeneic HCT. Prevention of GVHD while preserving GVL effects remains the holy grail of allogeneic HCT. We have observed that immune check points PD-L1/CD80 and PD-L1/PD-1 not only can be manipulated to augment but also can be manipulated to down-regulate immune response. The proposed studies will explore in depth mechanisms how PD-L1/CD80 and PD-L1/PD-1 signaling regulates alloreactive T cell metabolism, proliferation, and apoptosis, as well as explore how to manipulate these pathways for prevention of GVHD while preserving GVL effects.

National Institute of Health (NIH)
National Cancer Institute (NCI)
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Transplantation, Tolerance, and Tumor Immunology Study Section (TTT)
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Mccarthy, Susan A
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Beckman Research Institute/City of Hope
United States
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