In future studies, it will be interesting to see if targeting more than two checkpoint pathways simultaneously in myeloma and other hematologic malignancies can further improve anti-tumor immunity without generating unacceptable autoimmunity

In future studies, it will be interesting to see if targeting more than two checkpoint pathways simultaneously in myeloma and other hematologic malignancies can further improve anti-tumor immunity without generating unacceptable autoimmunity. multiple myeloma model. Myeloma-bearing mice were treated with a low dose of whole body irradiation and combinations of blocking antibodies to PD-L1, LAG-3, TIM-3, CD48 (the ligand for 2B4) and CTLA4. Results Temporal phenotypic analysis of bone GSK-3b marrow from myeloma-bearing mice exhibited that elevated percentages of PD-1, 2B4, LAG-3 and TIM-3 proteins were expressed on T cells. When PD-L1 blockade was combined with blocking antibodies to LAG-3, TIM-3 or CTLA4, synergistic or additive increases in survival were observed (survival rates improved from ~30% to 80%). The increased survival rates correlated with increased frequencies of tumor-reactive CD8 and CD4 T cells. When stimulated in vitro with myeloma cells, CD8 T cells from treated mice produced elevated levels proinflammatory cytokines. Cytokines were spontaneously released from CD4 T cells isolated from mice treated with PD-L1 plus CTLA4 blocking antibodies. Conclusions These data indicate that blocking PD-1/PD-L1 interactions in conjunction with other immune checkpoint proteins provides synergistic anti-tumor efficacy following lymphodepletive doses of whole body irradiation. This strategy is a promising combination strategy for myeloma and other hematologic malignancies. GSK-3b Electronic supplementary material The online version of this article GSK-3b (doi:10.1186/s40425-014-0043-z) contains supplementary material, which is available to authorized users. strong class=”kwd-title” Keywords: Low dose whole body irradiation, Immune checkpoint proteins, Blockade, PD-L1, TIM-3, LAG-3, CTLA4, 2B4, Myeloma Background Reports of immunotherapy-induced clinical responses have brought the study of tumor immunity front and center in the mission to eliminate cancer. Central to tumor immunity is the killing potential of activated tumor-specific T cells. Tumor-specific T cells can be detected in both preclinical animal models and cancer patients, but due to multiple immune suppressive factors within the tumor microenvironment, T cells fail to maintain an activated state against progressing tumor and are rendered tolerant or exhausted. T cell activation is initiated through tumor antigen recognition by the T cell receptor (TCR) and is regulated by a balance of activation and inhibitory intracellular signals. These signals are initiated by engagement of co-stimulatory and co-inhibitory receptors with their cognate ligands. One of the promising approaches to induce and maintain tumor-specific T cells in an activated state is to interfere with signaling through inhibitory (also referred to as immune checkpoint) receptors. There are multiple known T cell checkpoint receptors, and there is evidence that blocking interaction of these receptors with their respective ligands can increase anti-tumor immune responses. One of the most studied checkpoint receptors is usually CTLA4. Cell surface CTLA4 expression is usually rapidly upregulated when T cells are activated, and it is constitutively expressed on Foxp3+ regulatory T cells [1]. Signaling through CTLA4 arrests T cell activation by outcompeting co-stimulatory receptors (CD80 and CD86) for binding to CD28. CTLA4 binding to CD28 results in reduced T cell survival, cytokine production and T cell cycle arrest [2]. Testament to the importance of CTLA4 in dampening GSK-3b T cell activation is the occurrence of a lethal polyclonal lymphoproliferative disease that occurs DRIP78 in GSK-3b CTLA4 knockout mice [3]. Antagonistic anti-CTLA4 antibodies have been extensively tested in cancer models as a strategy to activate anti-tumor immunity, and CTLA4 was the first immune checkpoint targeted in the clinic for cancer therapy. The anti-tumor effects associated with blocking CTLA4 in vivo have been shown to involve depletion of regulatory T cells as well as restoring effector T cell function [4,5]. Notably, CTLA4 blockade results in increased ratios of effector CD8 T cells to regulatory T cells in tumors, possibly due to higher levels of CTLA4 expression by regulatory T cells [4]. In 2010 2010, a phase III randomized controlled clinical trial showed prolonged survival of metastatic melanoma patients when treated with the anti-CTLA4 antibody ipilimumab [6]. In melanoma patients, blocking CTLA4 produced a host of immune-related toxic side effects (referred to as immune-related adverse events). However, based on the promising responses in melanoma patients, ipilimumab was the first checkpoint-blocking antibody to be FDA approved (for the treatment of melanoma). Our laboratory has focused on blocking the checkpoint receptor programmed death receptor-1 (PD-1) pathway in the treatment of myeloma. PD-1.