Mitochondrial genetics cooperate with nuclear genetics to selectively alter immune cell development/trafficking.

The nuclear genome drives differences in immune cell populations and differentiation potentials, in part regulated by changes in metabolism. Despite this connection, the role of mitochondrial DNA (mtDNA) polymorphisms (SNP) in this process has not been examined. Using mitochondrial nuclear exchange (MNX) mice, we and others have shown that mtDNA strongly influences varying aspects of cell biology and disease. Based upon an established connection between mitochondria and immune cell polarization, we hypothesized that mtDNA SNP alter immune cell development, trafficking, and/or differentiation. Innate and adaptive immune cell populations were isolated and characterizated from the peritoneum and spleen. While most differences between mouse strains are regulated by nuclear DNA (nDNA), there are selective changes that are mediated by mtDNA differences (e.g., macrophage (CD11c) differentiation), These findings highlight how nuclear-mitochondrial crosstalk may alter pathology and physiology via regulation of specific components of the immune system.

Antigen-specific blockade of T cells in vivo using dimeric MHC peptide.

Ag-specific immune tolerance in clinical organ transplantation is currently an unrealized but critical goal of transplant biology. The specificity and avidity of multimerized MHC-peptide complexes suggests their potential ability to modulate T cell sensitization and effector functions. In this study, we examined the ability of MHC-peptide dimers to modulate T cell function both in vitro and in vivo. Soluble MHC dimers induced modulation of surface TCR expression and inhibited T cell cytolytic activity at nanomolar concentrations in vitro. Furthermore, engagement of TCR by soluble dimers resulted in phosphorylation of the TCR zeta-chain and recruitment and phosphorylation of zeta-associated protein-70 to the signaling complex, the latter of which increased upon dimer cross-linking. Significantly, Ag-specific inhibition of an alloreactive TCR-transgenic T cell population in vivo resulted in consequent outgrowth of an allogeneic tumor. The prolonged Ag-specific suppression of expansion and/or effector function of cognate T cells in vivo suggests that soluble MHC dimers may be a means of inducing sustained Ag-specific T cell unresponsiveness in vivo.

Epitope spreading upon P815 tumor rejection triggered by vaccination with the single class I MHC-restricted peptide P1A.

Epitope spreading has been best characterized as an exacerbating factor in CD4(+) T cell-dependent autoimmune disease models and is believed to occur via presentation of antigens liberated by tissue destruction initiated by CD4(+) T cells specific for a primary epitope. The growing evidence that exogenous antigens can also be processed and presented by class I MHC molecules has suggested that epitope spreading could occur for CD8(+) cytotoxic T lymphocyte (CTL) responses as well. In the context of anti-tumor immunity, expansion of a CTL response to include secondary epitopes could improve the efficacy of therapeutic vaccines. To determine directly whether epitope spreading can occur during an anti-tumor immune response, two defined class I MHC-binding peptides in the P815 tumor model were utilized. We observed that immunization against the single tumor peptide, P1A, followed by rejection of a P1A(+) tumor, subsequently yielded CTL activity and tumor protection against a P1A(-) tumor variant. P1A immunized mice that subsequently rejected tumor challenge developed CTL against a second defined epitope, P1E. These results indicate that, as for class II-restricted peptides in autoimmune disease, epitope spreading can occur for class I-restricted peptides during tumor rejection. A broadened CTL response may help eliminate outgrowth of antigen-negative tumor variants.

The effect of isolated soy protein on plasma biomarkers in elderly men with elevated serum prostate specific antigen.

PURPOSE: We performed a randomized double-blind crossover pilot study in elderly men with elevated prostate specific antigen (PSA) on the effects of the daily consumption of 2 soy beverages, each containing 20 gm. of isolated soy protein, on the isoflavone concentration in blood and urine, and on the 3 serum biomarkers cholesterol, PSA and the soluble p105 component of the p185erbB-2 proto-oncogene. MATERIALS AND METHODS: A total of 34 men supplemented their diet by consuming 1 of 2 soy protein beverages assigned randomly twice daily for a 6-week period. In a second 6-week period they consumed the other soy protein beverage. The beverage ISP+ provided 42 mg. of genistein and 27 mg. of daidzein daily, whereas the other beverage, ISP-, provided only 2.1 and 1.3 mg. of these isoflavones daily, respectively. Blood and 24-hour urine samples were obtained before the study, at 2-week intervals during the study and 2 weeks after study completion. RESULTS: ISP+ and to a lesser extent ISP- substantially increased the serum concentration and urinary output of the isoflavones and their metabolites. Serum cholesterol was significantly decreased by ISP+ irrespective of the order in which the 2 soy beverages were administered and in apparent correlation with the total isoflavone concentration. There was no significant effect of the soy beverages on serum PSA and p105erbB-2 values. CONCLUSIONS: This study reveals that short-term exposure of elderly men with elevated serum PSA values to soy protein containing isoflavones decreases serum cholesterol but not the serum biomarkers PSA and p105erbB-2.

The p815 mastocytoma tumor model.

This unit presents an experimental tumor model which has led to pivotal advances in tumor immunology culminating in the preclinical development of human cancer vaccines for melanoma. The model employs the use of the P815 mastocytoma cell line. Although the P815 cell line belongs to the mast cell lineage, it offers several advantages for in vivo experimentation of the tumor-host relationship. It grows progressively in the majority of syngeneic DBA/2 mice and can be implanted either intraperitoneally or subcutaneously. Moreover, immunogeneic variants have been created yielding tumors that are spontaneously rejected BB a behavior that has provided a context in which to study the immunologically relevant molecules and cells that dictate a successful anti-tumor response.

Cutting edge: spontaneous rejection of poorly immunogenic P1.HTR tumors by Stat6-deficient mice.

Experimental evidence suggests that a type 1 T cell response may result in optimal tumor rejection in vivo. This phenotype is determined in part by cytokines that influence T cell differentiation. In transplantable tumor models such as P1.HTR, tumors grow progressively despite expression of defined tumor Ags. We hypothesized that this failure to reject may be due to poor generation of a type 1 phenotype, through a dominant influence of the type 2-promoting cytokines IL-4 and/or IL-13. This hypothesis was tested by implanting P1.HTR tumors into mice deficient in Stat6. In contrast to progressive growth of P1.HTR tumors in wild-type mice, and aggressive growth even of IL-12-transfected P1.HTR in Stat1(-/-) mice, P1.HTR was spontaneously rejected by Stat6(-/-) mice. Rejection was accompanied by augmented tumor-specific IFN-gamma production and CTL activity. These results suggest that pharmacologic inhibition of Stat6 signaling could potentiate anti-tumor immunity in vivo.

The immune system as anti-tumor sentinel: molecular requirements for an anti-tumor immune response.

The concept behind immune surveillance against cancer is that tumor cells continuously develop, but that there may not be clinical evidence of their presence because the immune system recognizes the cells as foreign and destroys them. A clear role for the immune system in preventing and/or eliminating tumors is emerging as insights into the molecular requirements for the induction and effector function of cytolytic T lymphocytes (CTL) have been gained. Using murine tumor rejection models, the role of particular molecular components of the immune system in controlling tumor growth has been defined. However, tumor rejection does not always occur spontaneously in vivo, indicating that defects in the generation or execution of an anti-tumor immune response may be common. Understanding defects when they arise should allow for development of new therapeutic approaches in tumor-bearing individuals. Many clinical studies are underway to test strategies to induce or heighten an antitumor immune response in cancer patients.

Long-term T cell memory requires the surface expression of self-peptide/major histocompatibility complex molecules.

How memory T cells are maintained in vivo is poorly understood. To address this problem, a male-specific peptide (H-Y) was identified and used to activate female anti-H-Y T cells in vitro. Anti-H-Y T cells survived in vivo for at least 70 days in the absence of antigen. This persistence was not because of the intrinsic ability of memory T cells to survive in vivo. Instead, the survival and function of adoptively transferred memory cells was found to require transporter of antigen protein 1-dependent expression of self-peptide/major histocompatibility complex class I molecules in recipient animals. Therefore, it appears that the level of T cell receptor engagement provided by transporter of antigen protein 1-dependent, self-peptide/major histocompatibility complexes is sufficient to maintain the long-term survival and functional phenotype of memory cells in the absence of persistent antigen. These data suggest that positive selection plays a role not only in T cell development but also in the maintenance of T cell memory.

Novel pharmacological strategies in the treatment of life-threatening cytomegalovirus infections. Clinical experience with continuous infusion 9-(1,3-dihydroxy-2-propoxymethyl) guanine.

Two novel antiviral pharmacologic strategies were used for therapy of life- and sight-threatening cytomegalovirus (CMV) infection; these were continuous drug infusion by portable pump and individualized patient regimen. 9-(1,3-Dihydroxy-2-propoxymethyl)-guanine (DHPG), an active and recently licensed antiviral drug against cytomegalovirus infection, was administered to five immunocompromised patients with chorioretinitis (all patients), colitis (two), and pneumonitis (three). Through dosage escalation, correlations between plasma levels, toxicity (i.e., myelosuppression), and clinical benefit were ascertained for therapy of acute disease (pneumonitis) as well as long-term therapy (chorioretinitis). Resolution of viremia, pneumonitis, colitis, and chorioretinitis was accomplished with steady-state plasma levels of DHPG approximating the mean ID50 of CMV isolates. The most notable clinical benefit was survival from CMV pneumonia and stabilization of vision. Although no adverse toxicity occurred during the DHPG continuous long-term therapy, survival was limited by the underlying disease.