Spleen but not tumor infiltration by dendritic and T cells is increased by intravenous adenovirus-Flt3 ligand injection.

Dendritic cell (DC) expansion is regulated by the hematopoietic growth factor fms-like tyrosine kinase 3 ligand (Flt3L). DCs are critical to the control of tumor growth and metastasis, and there is a positive correlation between intratumoral DC infiltration and clinical outcome. In this report, we first demonstrate that single intravenous (i.v.) injections of adenovirus (Adv)-Flt3L significantly increased splenic dendritic, B, T and natural killer (NK) cell numbers in both normal and mammary tumor-bearing mice. In contrast, the numbers of DCs and T cells infiltrating the tumors were not increased. Consistent with the minimal effect on immune cell infiltration, i.v. Adv-Flt3L injections had no therapeutic activity against orthotopic mammary tumors. In addition, we noted tumor and Adv-Flt3L expansion of Gr1(+)CD11b(+) immature myeloid suppressor cells (IMSCs), which may inhibit the therapeutic efficacy of Adv-Flt3L-expanded DCs.

Central nervous system expression of IL-10 inhibits autoimmune encephalomyelitis.

Multiple sclerosis, an inflammatory, demyelinating disease of the CNS currently lacks an effective therapy. We show here that CNS inflammation and clinical disease in experimental autoimmune encephalomyelitis, an experimental model of multiple sclerosis, could be prevented completely by a replication-defective adenovirus vector expressing the anti-inflammatory cytokine IL-10 (replication-deficient adenovirus expressing human IL-10), but only upon inoculation into the CNS where local infection and high IL-10 levels were achieved. High circulating levels of IL-10 produced by i. v. infection with replication-deficient adenovirus expressing human IL-10 was ineffective, although the immunological pathways for disease are initiated in the periphery in this disease model. In addition to this protective activity, intracranial injection of replication-deficient adenovirus expressing human IL-10 to mice with active disease blocked progression and accelerated disease remission. In a relapsing-remitting disease model, IL-10 gene transfer during remission prevented subsequent relapses. These data help explain the varying outcomes previously reported for systemic delivery of IL-10 in experimental autoimmune encephalomyelitis and show that, for optimum therapeutic activity, IL-10 must either access the CNS from the peripheral circulation or be delivered directly to it by strategies including the gene transfer described here.

Transgenic mice expressing human HLA and CD8 molecules generate HLA-restricted measles virus cytotoxic T lymphocytes of the same specificity as humans with natural measles virus infection.

Control of primary measles virus (MV) infection in humans and continued maintenance of immune memory that protects against reinfection are mediated primarily through the anti-MV T cell response, as judged by observations of children with defects in antibody formation but competency in making T cells. Further, the failure of T cell responses in those infected with MV most often leads to overwhelming infection. To better define and manipulate the elements involved in human T cell responses to MV, we analyzed the generation of HLA-restricted cytotoxic T lymphocytes (CTL) in a small animal model. Transgenic mice expressing the human class I MHC antigen HLA-B27 in conjunction with human CD8 molecules produced vigorous HLA-restricted CTL responses to MV antigens, paralleling those in MV infection of humans. In addition, such humanized mice generated human CD8 coreceptor-dependent HLA-B27-restricted CTL with the same specificity for recognition of MV fusion (F) peptide RRYPDAVYL as reported for humans during natural MV infection. Neither murine beta(2)-microglobulin nor murine CD8 substituted adequately as coreceptors for the HLA-B27 heavy chain. By contrast, HLA-A2.1-restricted responses to measles could be generated in the absence of expression of human beta(2)-microglobulin or CD8(+) molecules in HLA-A2.1/K(b) transgenic mice. Thus a small animal model is now available for studying strategies for optimizing human CD8(+) T cell responses and for testing vaccines. This model offers the potential, when combined with the newly reported CD46 transgenic mouse model in which MV replicates in cells of the immune system, for uncoding the molecular mechanism of MV-induced immunosuppression.

Human CD8 transgene regulation of HLA recognition by murine T cells.

A series of human CD8 transgenic (hCD8 Tg) mice with differential expression in the thymus and periphery were produced to investigate CD8 coreceptor regulation of repertoire selection and T cell responses. Expression of hCD8 markedly enhanced responses to both HLA class I molecules and hybrid A2/Kb molecules providing functional evidence for a second interaction site, outside of the alpha 3 domain, which is essential for optimal coreceptor function. Peripheral T cell expression of hCD8 was sufficient to augment responsiveness to HLA class I, as hCD8 Tg mice which lacked thymic expression responded as well as mice expressing hCD8 in the thymus and periphery. Both murine CD8+ and CD4+ T cells expressing hCD8 transgenes exhibited markedly enhanced responses to foreign HLA class I, revealing the ability of T cell receptor repertoires selected on either murine class I or class II to recognize human class I major histocompatibility complex (MHC). In contrast to recognition of foreign class I, thymic expression of hCD8 transgenes was absolutely required to enhance recognition of antigenic peptide restricted by self-HLA class I. Thus, our studies revealed disparate requirements for CD8 coreceptor expression in the thymus for selection of a T cell repertoire responsive to foreign MHC and to antigenic peptides bound to self-MHC, providing a novel demonstration of positive selection that is dependent on human CD8.

Early redistribution of plasma membrane phosphatidylserine is a general feature of apoptosis regardless of the initiating stimulus: inhibition by overexpression of Bcl-2 and Abl.

A critical event during programmed cell death (PCD) appears to be the acquisition of plasma membrane (PM) changes that allows phagocytes to recognize and engulf these cells before they rupture. The majority of PCD seen in higher organisms exhibits strikingly similar morphological features, and this form of PCD has been termed apoptosis. The nature of the PM changes that occur on apoptotic cells remains poorly defined. In this study, we have used a phosphatidylserine (PS)-binding protein (annexin V) as a specific probe to detect redistribution of this phospholipid, which is normally confined to the inner PM leaflet, during apoptosis. Here we show that PS externalization is an early and widespread event during apoptosis of a variety of murine and human cell types, regardless of the initiating stimulus, and precedes several other events normally associated with this mode of cell death. We also report that, under conditions in which the morphological features of apoptosis were prevented (macromolecular synthesis inhibition, overexpression of Bcl-2 or Abl), the appearance of PS on the external leaflet of the PM was similarly prevented. These data are compatible with the notion that activation of an inside-outside PS translocase is an early and widespread event during apoptosis.

Reciprocal allogeneic bone marrow transplantation between NOD mice and diabetes-nonsusceptible mice associated with transfer and prevention of autoimmune diabetes.

Reciprocal allogeneic bone marrow transplantations were carried out between diabetes-susceptible nonobese diabetic (NOD) and diabetes-nonsusceptible C57BL/6 or B10.BR/cd mice to examine the role of the immune system and host environment in the development of autoimmune diabetes. Serotyping of lethally irradiated hosts reconstituted with allogeneic bone marrow showed the hematopoietically derived cells to be of donor origin. Our results showed that lethally irradiated NOD mice reconstituted with a B10.BR/cd hematopoietic cell system remained totally free of insulitis, failed to develop diabetes, and thrived to old age. In contrast, lethally irradiated C57BL/6 or B10.BR/cd mice reconstituted with an NOD hematopoietic cell system all developed insulitis, but only approximately 10% progressed to overt diabetes. Direct adoptive transfer of insulitis and diabetes by mature T-lymphocytes apparently was not required; analogous results were obtained when diabetes-nonsusceptible hosts were reconstituted with NOD hematopoietic cells containing T-lymphocytes or devoid of Thy-1+ cells. The difference in frequency for the development of insulitis versus insulitis plus overt diabetes in C57BL/6 and B10.BR/cd mice suggests that the hematopoietically derived immune cells from NOD mice were sufficient to induce anti-islet reactivity but may require the diabetogenic host environment to develop the frequency and severity of diabetes observed in NOD mice.

Successful semiallogeneic and allogeneic bone marrow reconstitution of lethally irradiated adult mice mediated by neonatal spleen cells.

Spleens of fetal/newborn mice less than 3-4 days of age contain a naturally occurring cell population capable of suppressing T-dependent and T-independent immune responses of third-party adult cells both in vitro and in vivo. We have utilized newborn spleen cells to prevent acute graft-versus-host (GVH) disease in lethally irradiated adult hosts reconstituted with semiallogeneic or even allogeneic bone marrow cells. Pretreatment of reconstituting cell populations with newborn spleen cells reduced the incidence of GVH disease from 100% to 20% in semiallogeneic and from 100% to 40% in allogeneic combinations. Long-term-surviving reconstituted hosts proved immunologically unresponsive to both donor and host histocompatibility antigens, yet possessed a fully chimeric lymphoid system responsive to T and B cell mitogens, as well as unrelated third-party alloantigens.