The amino boronic dipeptide, PT-100 (Val-boro-Pro), a dipeptidyl peptidase (DPP) inhibitor, has been shown to up-regulate gene expression of certain cytokines in hematopoietic tissue via a high-affinity interaction, which appears to involve fibroblast activation protein. Because fibroblast activation protein is also expressed in stroma of lymphoid tissue and tumors, the effect of PT-100 on tumor growth was studied in mice in vivo. PT-100 has no direct cytotoxic effect on tumors in vitro. Oral administration of PT-100 to mice slowed growth of syngeneic tumors derived from fibrosarcoma, lymphoma, melanoma, and mastocytoma cell lines. In WEHI 164 fibrosarcoma and EL4 and A20/2J lymphoma models, PT-100 caused regression and rejection of tumors. The antitumor effect appeared to involve tumor-specific CTL and protective immunological memory. PT-100 treatment of WEHI 164-inoculated mice increased mRNA expression of cytokines and chemokines known to promote T-cell priming and chemoattraction of T cells and innate effector cells. The role of innate activity was further implicated by observation of significant, although reduced, inhibition of WEHI 164 and A20/2J tumors in immunodeficient mice. PT-100 also demonstrated ability to augment antitumor activity of rituximab and trastuzumab in xenograft models of human CD20 ؉ B-cell lymphoma and HER-2 ؉ colon carcinoma where antibody-dependent cytotoxicity can be mediated by innate effector cells responsive to the cytokines and chemokines up-regulated by PT-100. Although CD26/ DPP-IV is a potential target for PT-100 in the immune system, it appeared not to be involved because antitumor activity and stimulation of cytokine and chemokine production was undiminished in CD26 Ϫ/Ϫ mice.

Objective Poor condition at birth may impact on IQ, although its effect on other measures of neurodevelopment is unclear. The authors' aim was to determine whether infants receiving resuscitation after birth have reduced scores in measures of attention, memory and language skills or the need for educational support at school even in the absence of clinical encephalopathy. Methods Three groups of term infants were identifi ed from the Avon longitudinal study of parents and children: infants resuscitated at birth but asymptomatic for encephalopathy (n=612), infants resuscitated who developed symptoms of encephalopathy (n=40) and the reference infants who were not resuscitated and had no further neonatal care (n=8080). Measures of attention, language, memory and the need for educational support were obtained for children between 8 years and 11 years. Test results (standardised to a mean of 100 and SD of 15) were adjusted for clinical and social covariates. Missing covariate data were imputed using chained equations. Results Infants asymptomatic after resuscitation had similar scores to those not requiring resuscitation for all measures while infants who developed encephalopathy had lower working memory (−6.65 (−12.34 to −0.96)), reading accuracy (−7.95 (−13.28 to −2.63)) and comprehension (−9.32 (−14.47 to −4.17) scores and increased risk of receiving educational support (OR 6.24 (1.52 to 26.43)) than infants thought to be well at birth, although there was little evidence for an association after excluding infants who developed cerebral palsy. Conclusions The authors found no evidence that infants who were resuscitated but remained well afterwards differed from those not requiring resuscitation in the aspects of neuropsychological functioning assessed in this study. Infants who developed neonatal encephalopathy had evidence of worse functioning, particularly in language skills and were more likely to receive educational support at school.

In hematopoiesis, cytokine levels modulate blood cell replacement, self-renewal of stem cells, and responses to disease. Feedback pathways regulating cytokine levels and targets for therapeutic intervention remain to be determined. Amino boronic dipeptides are orally bioavailable inhibitors of dipeptidyl peptidases. Here we show that the high-affinity inhibitor Val-boro-Pro (PT-100) can stimulate the growth of hematopoietic progenitor cells in vivo and can accelerate neutrophil and erythrocyte regeneration in mouse models of neutropenia and acute anemia. Hematopoietic stimulation by PT-100 correlated with increased cytokine levels in vivo. In vitro, PT-100 promoted the growth of primitive hematopoietic progenitor cells by increasing granulocyte–colony-stimulating factor (G-CSF), interleukin-6 (IL-6), and IL-11 production by bone marrow stromal cells. Two molecular targets of PT-100 are expressed by stromal cells— CD26/DPP-IV and the closely related fibroblast activation protein (FAP). Because PT-100 was active in the absence of CD26, FAP appears to be the hematopoietic target for PT-100. Interaction of PT-100 with the catalytic site seems to be required because amino-terminal acetylation of PT-100 abrogated enzyme inhibition and hematopoietic stimulation. PT-100 is a therapeutic candidate for the treatment of neutropenia and anemia. The data support increasing evidence that dipeptidyl peptidases can regulate complex biologic systems by the proteolysis of signaling peptides.

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Efficient activation and regulation of the cellular immune response requires engagement of T cell accessory molecules as well as the antigen-specific T cell receptor. The lymphocyte function-associated antigen (LFA) 3 (CD58)/CD2 accessory pathway, one of the first discovered, has been extensively characterized in terms of structure and function of the CD2 molecule, which is present on all T lymphocytes and natural killer cells of the human immune system. The binding site of human CD2 for LFA-3 has been localized to two epitopes on one face of the first immunoglobulin (Ig)-like domain of this two-domain, Ig superfamily molecule. Human LFA-3 is genetically linked and is 21% identical in amino acid sequence to CD2, suggesting that this adhesive pair may have evolved from a single ancestral molecule. We have aligned the amino acid sequences of LFA-3 and CD2 and mutagenized selected amino acids in the first domain of LFA-3 that are analogous to those implicated in the binding site of CD2. The data show that K30 and K34, in the predicted C-C' loop, and D84, in the predicted F-G loop of LFA- 3, are involved in binding to CD2, suggesting that two complementary sites on one face of the first domain of each molecule bind to each other.

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Cell-surface gangliosides are presumed to play a role in cell growth and differentiation. With the use of monoclonal antibodies directed against GD3, a disialoganglioside expressed predominantly by cells of neuroectodermal origin, we have found that GD3 is expressed by a subpopulation of cells of the immune system including: 1) fetal thymocytes in subcortical regions and near vessels, 2) lymph node lymphocytes in interfollicular areas and near vessels, and 3) a small subset of T cells in the peripheral blood. Mouse monoclonal antibodies (two IgGs, one IgM, and F(ab')2 fragments) reacting with GD3 were found to stimulate proliferation of T cells derived from peripheral blood. Proliferation of T cells was observed even in cultures depleted of macrophages, suggesting that activation by anti-GD3 was not dependent on the presence of accessory cells. T cell proliferation was maximum between days 5 and 7 of stimulation and was preceded by expression of interleukin 2 receptors. No stimulation was observed with control antibodies of the identical isotype or with monoclonal antibodies recognizing the gangliosides GD2 or GM2. During stimulation by anti-GD3 monoclonal antibodies, there was an expansion of the GD3+ pool of T cells, but depletion of GD3+ T cells prior to stimulation abrogated the response. Proliferation induced by binding to GD3 could be augmented by exogenous interleukin 2 and phytohemagglutinin. Anti-CD3 (T3) monoclonal antibodies had little or no effect. These results demonstrate that binding to GD3 on the surface of T cells can elicit signals for T cell proliferation.

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