Immunological Responses to Injury and Grafting in the Central Nervous System of Nonhuman Primates

Experimental Models to Study Immune Dysfunction in the Pathogenesis of Parkinson's Disease

Parkinson's disease (PD) is a chronic, age-related, progressive multisystem disease associated with neuroinflammation and immune dysfunction. This review discusses the methodological approaches used to study the changes in central and peripheral immunity in PD, the advantages and limitations of the techniques, and their applicability to humans. Although a single animal model cannot replicate all pathological features of the human disease, neuroinflammation is present in most animal models of PD and plays a critical role in understanding the involvement of the immune system (IS) in the pathogenesis of PD. The IS and its interactions with different cell types in the central nervous system (CNS) play an important role in the pathogenesis of PD. Even though culture models do not fully reflect the complexity of disease progression, they are limited in their ability to mimic long-term effects and need validation through in vivo studies. They are an indispensable tool for understanding the interplay between the IS and the pathogenesis of this disease. Understanding the immune-mediated mechanisms may lead to potential therapeutic targets for the treatment of PD. We believe that the development of methodological guidelines for experiments with animal models and PD patients is crucial to ensure the validity and consistency of the results.

The immunogenicity of midbrain dopaminergic neurons and the implications for neural grafting trials in Parkinson's disease

Dopaminergic (DA) cell replacement therapies are a promising experimental treatment for Parkinson’s disease (PD) and a number of different types of DA cell-based therapies have already been trialled in patients. To date, the most successful have been allotransplants of foetal ventral midbrain but even then, the results have been inconsistent. This coupled to the ethical and logistical problems with using this tissue has meant that an alternative cell source has been sought of which human pluripotent stem cells (hPSCs) sources have proven very attractive. Robust protocols for making mesencephalic DA (mesDA) progenitor cells from hPSCs now exist and the first in-human clinical trials have or are about to start. However, while their safety and efficacy are well understood, relatively little is known about their immunogenicity and in this review, we briefly summarise this with reference mainly to the limited literature on human foetal DA cells.

Immunological Responses to Transgene-Modified Neural Stem Cells After Transplantation

Neural stem cell (NSC) therapy is a promising therapeutic strategy for stroke. Researchers have frequently carried out genetic modification or gene editing of stem cells to improve survival or therapeutic function. However, NSC transplantation carries the risk of immune rejection, and genetic modification or gene-editing might further increase this risk. For instance, recent studies have reported on manipulating the stem cell genome and transplantation via the insertion of an exogenous gene derived from magnetotactic bacteria. However, whether transgene-modified stem cells are capable of inducing immunological reactions has not been explored. Although NSCs rarely express the major histocompatibility complex (MHC), they can still cause some immunological issues. To investigate whether transgene-modified NSCs aggravate immunological responses, we detected the changes in peripheral immune organs and intracerebral astrocytes, glial cells, and MHC-I and MHC-II molecules after the injection of GFP-labeled or mms6-GFP-labeled NSCs in a rat model. Xenogeneic human embryonic kidney (HEK-293T) cells were grafted as a positive control group. Our results indicated that xenogeneic cell transplantation resulted in a strong peripheral splenic response, increased astrocytes, enhanced microglial responses, and upregulation of MHC-I and MHC-II expression on the third day of transplantation. But they decreased obviously except Iba-1 positive cells and MHC-II expression. When injection of both mms6-GFP-labeled NSCs and GFP-labeled NSCs also induced similar responses as HEK-293T cells on the third days, but MHC-I and MHC-II expression decreased 3 weeks after transplantation. In addition, mms6 transgene-modified NSCs did not produce peripheral splenic response responses as well as astrocytes, microglial cells, MHC-I and MHC-II positive cells responses when compared with non-modified NSCs. The present study provides preliminary evidence that transgenic modification does not aggravate immunological responses in NSC transplantation.

Clinical correlation of peripheral CD4+‑cell sub‑sets, their imbalance and Parkinson's disease

Emerging evidence suggests that the peripheral immune system has an active role in the progression of Parkinson's disease (PD). The finding of T‑helper (Th; CD4+) cells infiltrating into the substantia nigra in PD patients demonstrated that Th cells are involved in PD. However, the association between peripheral T‑helper cell sub‑sets (Th1, Th2, Treg and Th17) and the sub‑set balance (Th1/Th2 and Th17/Treg) and PD has remained elusive. In the present study, sixty PD patients of the First Affiliated Hospital of Bengbu Medical College as well as 40 age‑ and environment‑matched healthy individuals were enrolled. The fraction of CD4+ T cells in the peripheral blood was assessed by automated hematology analysis and its sub‑sets (Thl, Th2, Thl7, Treg) were quantified by flow cytometry. The results showed that in the PD group, the proportion of Th1 and Th17 cells was increased, while that of Th2 and Treg cells was decreased. Compared with the control group, the Th1/Th2 and Th17/Treg ratios were significantly enhanced, and shifted towards Th1 and Th17, respectively. Furthermore, this Th1‑type response (Th1/Th2 balance shifting towards Th1) were associated with motor function scores determined by Unified Parkinson's Disease Rating Scale III (UPDRS‑III) scores. However, no correlation was found between the change in the Th17/Treg cell balance (Th17/Treg balance shifting towards Th1) and UPDRS‑III scores. These data supported that chronic immune stimulation, specifically CD4+‑cell sub‑set imbalance, is linked to PD pathobiology and disease severity. CD4+‑cell sub‑sets and their imbalance may therefore represent novel biomarkers or therapeutic targets for PD.

The influence of immunosuppressive drugs on neural stem/progenitor cell fate in vitro

In allogenic and xenogenic transplantation, adequate immunosuppression plays a major role in graft survival, especially over the long term. The effect of immunosuppressive drugs on neural stem/progenitor cell fate has not been sufficiently explored. The focus of this study is to systematically investigate the effects of the following four different immunotherapeutic strategies on human neural progenitor cell survival/death, proliferation, metabolic activity, differentiation and migration in vitro: (1) cyclosporine A (CsA), a calcineurin inhibitor; (2) everolimus (RAD001), an mTOR-inhibitor; (3) mycophenolic acid (MPA, mycophenolate), an inhibitor of inosine monophosphate dehydrogenase and (4) prednisolone, a steroid. At the minimum effective concentration (MEC), we found a prominent decrease in hNPCs' proliferative capacity (BrdU incorporation), especially for CsA and MPA, and an alteration of the NAD(P)H-dependent metabolic activity. Cell death rate, neurogenesis, gliogenesis and cell migration remained mostly unaffected under these conditions for all four immunosuppressants, except for apoptotic cell death, which was significantly increased by MPA treatment.

Transplantation of neural stem cells in a rat model of stroke: assessment of short-term graft survival and acute host immunological response

The use of progenitors and stem cells for neural grafting is promising, as these not only have the potential to be maintained in vitro until use, but may also prove less likely to evoke an immunogenic response in the host, when compared to primary (fetal) grafts. We investigated whether the short-term survival of a grafted conditionally immortalised murine neuroepithelial stem cell line (MHP36) (2 weeks post-implantation, 4 weeks post-ischaemia) is influenced by: (i) immunosuppression (cyclosporin A (CSA) vs. no CSA), (ii) the local (intact vs. lesioned hemisphere), or (iii) global (lesioned vs. sham) brain environment. MHP36 cells were transplanted ipsi- and contralateral to the lesion in rats with middle cerebral artery occlusion (MCAo) or sham controls. Animals were either administered CSA or received no immunosuppressive treatment. A proliferation assay of lymphocytes dissociated from cervical lymph nodes, grading of the survival of the grafted cells, and histological evaluation of the immune response revealed no significant difference between animals treated with or without CSA. There was no difference in survival or immunological response to cells grafted ipsi- or contralateral to the lesion. Although a local upregulation of immunological markers (MHC class I, MHC class II, CD45, CD11b) was detected around the injection site and the ischaemic lesion, these were not specifically upregulated in response to transplanted cells. These results provide evidence for the low immunogenic properties of MHP36 cells during the initial period following implantation, known to be associated with an acute host immune response and ensuing graft rejection.

Cyclosporine A-induced hyperactivity in rats: is it mediated by immunosuppression, neurotrophism, or both?

Cyclosporine A (CsA) immunosuppressive treatment has become an adjunctive therapy in neural transplantation of dopamine-secreting cells for treatment of Parkinson's disease (PD). Recently, CsA and its analogues have been shown to promote trophic effects against neurodegenerative disorders, and therefore CsA may have direct beneficial effects on dopaminergic neurons and dopamine-mediated behaviors. The present study examined the interaction between the reported CsA-induced hyperactivity and the possible alterations in nigral tyrosine hydroxylase (TH)-immunoreactive neurons in rats with damaged blood-brain barrier. CsA was administered at a therapeutic dose (10 mg/kg/day, IP, for 9 days) used in neural transplantation protocol for PD animal models. CsA-treated animals displayed significantly higher general spontaneous locomotor activity than control animals at drug injection days 7 and 9. Histological assays at day 9 revealed that there was a significant increase in TH-immunoreactive neurons in the nigra of CsA-treated rats compared to that of the vehicle-treated rats. The nigral TH elevation was accompanied by suppressed calcium-phosphotase calcineurin activity, indicating an inhibition of host immune response. This is the first report of CsA exerting simultaneous immunosuppressive and neurotrophic effects, as well as increasing general spontaneous locomotor behavior. These results support the utility of CsA as a therapeutic agent for PD and other movement disorders.