The TNF member LIGHT also known as TL4 or TNFSF14) can play a major role in cancer control via its two receptors; it induces tumor cell death through lymphotoxin-b receptor (LT-bR) and ligation to the herpes virus entry mediator (HVEM) amplifies the immune response. By studying the effect of LIGHT in the transcriptional profile of a lymphoid malignancy, we found that HVEM, but not LT-bR, stimulation induces a significant increase in the expression of chemokine genes such as IL-8, and an unexpected upregulation of apoptotic genes. This had functional consequences, since LIGHT, or HVEM mAb, thus far known to costimulate T-and B-cell activation, induced chronic lymphocytic leukemia cell death. Many of the mediators involved were identified here, with an apoptotic pathway as demonstrated by caspases activation, decrease in mitochondrial membrane potential, upregulation of the pro-apoptotic protein Bax, but also a role of TRAIL. Moreover, HVEM induced endogenous TNF-a production and TNF-a enhanced HVEM-mediated cell death. HVEM function was mainly dependent on LIGHT, since other ligands like HSV-glycoprotein D and B and T lymphocyte attenuator were essentially ineffective. In conclusion, we describe a novel, as yet unknown killing effect of LIGHT through HVEM on a lymphoid malignancy, and combined with induction of chemokine release this may represent an additional tool to boost cancer immunotherapy. 2502 IntroductionThe TNF and TNF receptor (TNFR) superfamilies have diverse and widespread physiological functions, including apoptosis, proliferation, differentiation, and immune system regulation. TNFR are schematically classified into two groups: those with a 80-amino acids death domain (DD) in the cytoplasmic region of the receptor, which signals cell death, and those without DD, which have been implicated in lymphoid cell proliferation and differentiation [1,2]. LIGHT also known as TL4 or TNFSF14) is a glycosylated, type II transmembrane protein of about 29 kDa, which can bind lymphotoxin-b receptor (LT-bR) and the herpes virus entry mediator (HVEM) both of which belong to the TNFR superfamily. HVEM is a type I transmembrane protein of 32 to 36 kDa, devoid of intracytoplasmic DD. To date, five ligands have been identified for HVEM. The first one is HSV glycoprotein D (HSV-gD), a structural component of the HSV envelope, essential for HSV entry into host cells [3]. Two of the ligands are members of the TNF superfamily: the trimeric lymphotoxin a (LTa3) and LIGHT [4]. Recently, it was also found that HVEM interacts with two immunoglobulin superfamily members B and T lymphocyte attenuator (BTLA) and CD160 [5][6][7]. HVEM is expressed in most immune cells such as monocytes, T and B lymphocytes, and natural killer cells whereas expression of LT-bR is restricted to stromal cells or non-lymphoid hematopoietic cells [8,9]. Functional differences between the two receptors of LIGHT have also been observed. LIGHT binding to HVEM confers mainly costimulatory effects; LIGHT has a potent, CD28-independent, co-stimulatory role in...

CD28 is a 44kDa homodimer present on T cells providing an important costimulatory signal for T cell proliferation, cytokine production and cytokine receptor expression. CD28 activation is mediated by interaction with its counter-receptors, B7.1/CD80 and B7.2/B70/CD86. The biochemical basis of these co-stimulatory signals are still poorly understood, particularly in resting T cells. However, various biochemical pathways such as tyrosine phosphorylation, phospholipase C, sphingomyelinase and phosphatidylinositol 3-kinase (PI3-K) activation have been reported to play a role in CD28 signaling in tumor T cell lines and CD28-transfected cells or pre-activated T cells. In addition, recent reports propose that CD28-B7.1 and B7.2 interaction could be involved in the production of Th1 and Th2 cytokines, respectively, but the putative biochemical basis for these different functions is still unknown. We have analyzed the functional and molecular consequences of CD28 activation by B7.1 and B7.2 in human resting T cells. We demonstrate in this report that both CD28-B7.1 and CD28-B7.2 interactions induce the association of PI3-K to CD28 in the CD4 subpopulation, whereas it was barely detectable in CD8 cells. This association involves the binding of the src homology domain 2 (SH2) of p85 to tyrosine-phosphorylated CD28 and does not require pre-activation by CD3-T cell receptor. Worthmannin, a specific inhibitor of PI3-K enzymatic activity within the nanomolar range also inhibits the interleukin-2 production induced by costimulation mediated by either the B7.1- and B7.2-transfected cells or CD28 monoclonal antibodies. The only slight difference between B7.1 and B7.2 costimulation is the IC50 of worthmannin being 25 and 110 nM, respectively, which could suggest differences in their activation of the T cell PI3-K.