Visualization of antigen-specific T cell activation in vivo in response to intracerebral administration of a xenopeptide

Porcine Fetal Ventral Mesencephalic Cells are Targets for Primed Xenoreactive Human T Cells

Xenotransplantation of porcine fetal ventral mesencephalic (pfVM) cells to overcome the dopamine shortage in the striatum of patients with Parkinson's disease seems a viable alternative to allotransplantion of human fetal donor tissue, especially because the latter is complicated by both practical and ethical issues. There is, however, little known about the xenospecific immune responses involved in such an intracerebral xenotransplantation. The aim of our study was to investigate whether 1) naive human peripheral blood mononuclear cells (PMBC) display cytotoxicity against pfVM cells of E28 pig fetuses, and 2) priming of human PBMC by xenogeneic antigen presenting cells (APC) modulates pfVM-directed cellular cytotoxicity. For this purpose fresh PMBC from nine individual donors were primed by incubation with either irradiated pfVM cells or porcine spleen cells (PSC) as APC in the presence of IL-2 for 1 week before assessing cytotoxicity in a 51Cr release assay. Also, direct NK reactivity and antibody-dependent cellular cytotoxicity (ADCC) of fresh PMBC against pfVM cells was assessed. No direct cytotoxicity of naive cells (either NK reactivity or ADCC) against pfVM cells could be determined. Only PMBC primed with PSC were capable of lysing pfVM cells. PBMC primed with pfVM cells did not show cytolytic capacity towards pfVM. Interestingly, large differences in xenospecific T-cell responses exist between individual donor PBMC. Thus, human T cells are capable of killing pfVM cells in a xenoreactive response, but only after priming by donor APC. The large interindividual differences between human donors in their xenoreactive response may influence patient selection for xenotransplantation and chances of graft survival for individual patients.

Immunotherapy for human glioma: innovative approaches and recent results

The outcome for malignant glioma patients remains dismal despite treatment with surgical resection, radiation and chemotherapy. The goal of immunotherapy is to eradicate or suppress the residual infiltrative component of these tumors. Although there is clinical evidence for cell-mediated antiglioma activity, there are special considerations that need to be accounted for in the design of immunotherapeutics for CNS tumors, such as possible differences in antigen-presenting cells, trafficking of effector T-cells and immunosuppression. Previously characterized immunosuppression in glioma patients has included low peripheral blood lymphocyte counts, reduced delayed type hypersensitivity reactions to recall antigens, impaired mitogen-induced blastogenic responses by peripheral blood mononuclear cells, increased CD8+ suppressor T-cells, decreased CD4+ T-cell activity in vitro, diminished immunoglobulin synthesis by B-cells and impaired transmembrane signaling through the T-cell receptor/CD3 complex. Recent impairments that are being identified include anergy, failure of costimulation, lack of sufficient numbers of functional effector T-cells and the presence of T-suppressor cells within the tumor microenvironment. It is proposed that these inherent problems will need to be overcome in order for immunotherapies to realize their potential. Paradoxically, the efficacy of recent clinical immunotherapies for glioma patients appears equivalent to that seen in other cancer immunotherapeutic approaches. This review will provide an overview of the juxtaposition of the immune system and CNS, and will discuss the most recent and ongoing immunotherapeutic clinical trials that are demonstrating promising results.

Transgenic expression of CTLA4-Ig by fetal pig neurons for xenotransplantation

The transplantation of fetal porcine neurons is a potential therapeutic strategy for the treatment of human neurodegenerative disorders. A major obstacle to xenotransplantation, however, is the immune-mediated rejection that is resistant to conventional immunosuppression. To determine whether genetically modified donor pig neurons could be used to deliver immunosuppressive proteins locally in the brain, transgenic pigs were developed that express the human T cell inhibitory molecule hCTLA4-Ig under the control of the neuron-specific enolase promoter. Expression was found in various areas of the brain of transgenic pigs, including the mesencephalon, hippocampus and cortex. Neurons from 28-day old embryos secreted hCTLA4-Ig in vitro and this resulted in a 50% reduction of the proliferative response of human T lymphocytes in xenogenic proliferation assays. Transgenic embryonic neurons also secreted hCTLA4-Ig and had developed normally in vivo several weeks after transplantation into the striatum of immunosuppressed rats that were used here to study the engraftment in the absence of immunity. In conclusion, these data show that neurons from our transgenic pigs express hCTLA4-Ig in situ and support the use of this material in future pre-clinical trials in neuron xenotransplantation.

Compartmentalization of TCR repertoire alteration during rejection of an intrabrain xenograft

Xenograft rejections of embryonic pig neural cells implanted into the adult rat striatum occurs within 3-4 weeks, following a dramatic T cell infiltration. Little is known about the cross-talk between the brain and peripheral lymphoid tissues which results in this recruitment and lymphocyte homing. To better characterize the dynamics of the T cell response against xenogeneic neural cells implanted into the brain parenchyma, we used both qualitative and quantitative methods to follow the alterations of the CDR3 length distribution (CDR3-LD) of the TCR (T cell receptor) beta chain in the transplanted striatum and compared this response to that observed in the deep cervical lymph nodes, spleen, and blood. Data showed that the T cell repertoire diversity was highly altered in the recipient brain during xenograft rejection. Comparison of the alterations of the CDR3-LD between several animals revealed a single public alteration in the Vbeta20 family, and many private alterations of the CDR3-LD which differed from one infiltrated brain to another. Alterations of the T cell repertoire were also observed in lymphocytes homed into the deep cervical lymph nodes. However, they differed from the alterations detected in the infiltrated brains. Conversely, no significant alteration of the CDR3-LD was detected in the spleen or in the blood. These data suggest that the deep cervical lymph nodes play an active role in the process of xenograft recognition or/and rejection. However, they also indicate that the fate of T cells homed in the brain and deep cervical lymph nodes differs.

Trafficking of superparamagnetic iron oxide particles (Combidex) from brain to lymph nodes in the rat

Central nervous system (CNS) drainage may occur via connections to the vasculature, but in animal models up to 50% occurs via perivascular, perineural and primitive lymphatic drainage to cervical lymph nodes. We evaluated efflux of particles from the brain to cervical lymph nodes in normal rats, using Combidex iron oxide-based magnetic resonance imaging (MRI) agent. After intracerebral, intraventricular, intracarotid or intravenous injection of Combidex in normal Long Evans rats, particle localization was assessed by MRI and histochemistry for iron and the dextran coat (n = 27). Intraventricular or intracerebral injection, but not intracarotid administration of Combidex (100 micro g), resulted in MRI signal changes in the deep cervical lymph nodes around the carotid artery, and, less strongly, in the superficial cervical nodes. Within 2 h of Combidex administration, iron was histologically localized in cervical lymph nodes, with patched staining of capsule and peripheral sinus consistent with delivery via multiple afferent lymphatic vessels. Lymph node staining in groups receiving CNS Combidex was significantly different from controls (P < 0.0001) and was significantly localized in the deep vs. superficial cervical lymph nodes (P = 0.0003). The trafficking of the superparamagnetic iron particles from the CNS in the rat could be visualized by MRI and histology. Combidex provides a powerful tool to rapidly assess drainage of virus-sized particles from the CNS.