Short-Term Anti-CD40 Ligand Costimulatory Blockade Induces Tolerance to Peripheral Nerve Allografts, Resulting in Improved Skeletal Muscle Function

CD40-CD40L in Neurological Disease

Immune-inflammatory conditions in the central nervous system (CNS) rely on molecular and cellular interactions which are homeostatically maintained to protect neural tissue from harm. The CD40–CD40L interaction upregulates key proinflammatory molecules, a function best understood in the context of infection, during which B-cells are activated via CD40 signaling to produce antibodies. However, the role of CD40 in neurological disease of non-infectious etiology is unclear. We review the role of CD40–CD40L in traumatic brain injury, Alzheimer’s Disease, Parkinson’s Disease, stroke, epilepsy, nerve injury, multiple sclerosis, ALS, myasthenia gravis and brain tumors. We also highlight therapeutic advancements targeting the CD40 system to either attenuate the neuroinflammatory response or leverage the downstream effects of CD40 signaling for direct tumor cell lysis.

Engendering allograft ignorance in a mouse model of allogeneic skin transplantation to the distal hind limb

OBJECTIVE

The aim of this study was to demonstrate lymphatic isolation in a model of hind limb lymph node (LN) excision, consisting of ipsilateral popliteal and inguinal LN excision and to evaluate the immunologic response to allogeneic skin transplanted onto this region of lymphatic isolation.

METHODS

To study lymphatic flow, C57BL/6 mice underwent lymphadenectomy (n = 5), sham lymphadenectomy (n = 5), or no intervention (n = 5), followed by methylene blue injection. Mice were dissected to determine whether methylene blue traveled to the iliac LN. To study host response to skin transplantation, C57BL/6 mice underwent allogeneic skin transplantation with LN excision (n = 6), allogeneic skin transplantation alone (n = 6), or syngeneic skin transplantation (n = 4). Skin grafts were placed distal to the popliteal fossa and mice were euthanized at day 10. Grafts were stained for endothelial cell and proliferation markers (CD31 and Ki67, respectively). Secondary lymphoid tissues (spleen, ipsilateral axillary LN, and contralateral inguinal LN) were removed and rechallenged with BALB/c alloantigen in vitro with subsequent assay of interferon-γ and interleukin 4 cell expression using ELISPOT technique.

RESULTS

Mice that underwent LN excision had no evidence of methylene blue in the iliac nodes; mice without surgical intervention or with sham LN excision consistently had methylene blue visible in the ipsilateral iliac nodes. Mice treated with allogeneic skin transplantation and LN excision had lower expression of interferon-γ and interleukin 4 in the secondary lymphoid tissues.

CONCLUSIONS

Lymph node excision completely interrupts lymphatic flow of the hind limb. This model of lymphatic isolation impairs the ability of the transplant recipient to acutely mount a Th1 or Th2 response to allogeneic skin transplants.

The role of T helper cell differentiation in promoting nerve allograft survival with costimulation blockade

OBJECT

Peripheral nerve allografts provide a temporary scaffold for host nerve regeneration and allow for the repair of significant segmental nerve injuries. Despite this potential, nerve allograft transplantation requires temporary systemic immunosuppression. Characterization of the immunological mechanisms involved in the induction of immune hyporesponsiveness to prevent nerve allograft rejection will help provide a basis for optimizing immunomodulation regimens or manipulating donor nerve allografts to minimize or eliminate the need for global immunosuppression.

METHODS

The authors used C57Bl/6 mice and STAT4 and STAT6 gene BALB/c knockout mice. A nonvascularized nerve allograft was used to reconstruct a 1-cm sciatic nerve gap in the murine model. A triple costimulatory blockade of the CD40, CD28/B7, and inducible costimulatory (ICOS) pathways was used. Quantitative assessment was performed at 3 weeks with nerve histomorphometry, walking track analysis, and the enzyme-linked immunospot assay.

RESULTS

The STAT6 -/- mice received 3 doses of costimulation-blocking antibodies and had axonal regeneration equivalent to nerve isografts, while treated STAT4 -/- mice demonstrated moderate axonal regeneration but inferior to the T helper cell Type 2-deficient animals. Enzyme-linked immunospot assay analysis demonstrated a minimal immune response in both STAT4 -/- and STAT6 -/- mice treated with a costimulatory blockade.

CONCLUSIONS

The authors' findings suggest that Type 1 T helper cells may play a more significant role in costimulatory blockade-induced immune hyporesponsiveness in the nerve allograft model, and that Type 2 T helper differentation may represent a potential target for directed immunosuppression.

Inhibition of allergic responses by CD40 gene silencing

BACKGROUND

Gene silencing using small interfering RNA (siRNA) is a potent method of specifically knocking down molecular targets. Small interfering RNA is therapeutically promising, however, treatment of allergic diseases with siRNA has not been explored in vivo. The aim of this study was to evaluate therapeutic effects of CD40 siRNA on inhibition of allergic responses.

METHODS

Mice sensitized with ovalbumin (OVA) and alum were treated with CD40 siRNA, scrambled siRNA, or phosphate buffer saline (PBS) alone, and then challenged intranasally with OVA.

RESULTS

A significant reduction in nasal allergic symptoms was observed in the CD40 siRNA treated OVA-allergic mice compared to the controls of scrambled siRNA and PBS alone, which is correlated with the decrease of local eosinophil accumulation. CD40 siRNA treatment knocked down CD40 expression on dendritic cells (DCs) in vivo and impaired their antigen presenting function. Treatment with CD40 siRNA resulted in inhibition of OVA-specific T cell response and decrease of interleukin-4 (IL-4), IL-5, and interferon-gamma production from T cells stimulated with OVA. Administration of CD40 siRNA also suppressed CD40 expression on B cells, resulting in down-regulation of OVA-specific immunoglobulin E (IgE), IgG1, and IgG2a levels. Additionally, increased regulatory T cells were observed in the CD40 siRNA treated mice.

CONCLUSIONS

The present study demonstrates a novel therapeutic use for siRNA in allergy. CD40 siRNA attenuated allergy through inhibition of DC and B cell functions and generation of regulatory T (Treg) cells.

Novel vaccination for allergy through gene silencing of CD40 using small interfering RNA

Small interfering RNA (siRNA) is a potent means of inducing gene-specific silencing. Gene silencing strategies using siRNA have demonstrated therapeutic benefits in animal models of various diseases, and are currently in clinical trials. However, the utility of gene silencing as a treatment for allergic diseases has not yet been reported. In this study, we report a novel therapy for allergy through gene silencing of CD40, a critical costimulatory molecule and a key factor in allergic immune responses. Silencing CD40 resulted in generation of immunoregulatory dendritic cells (DCs). Administration of CD40 siRNA remarkably reduced nasal allergic symptoms and local eosinophil accumulation in the OVA-induced allergic mice. The OVA-specific T cell response was inhibited after the CD40 siRNA treatment. Additionally, anti-OVA specific IgE and production of IL-4 and IL-5 of T cells stimulated by OVA were significantly decreased in CD40 siRNA-treated mice. Furthermore, we demonstrated that the therapeutic effects by CD40 siRNA were associated with impaired Ag-presenting functions of DCs and B cells, and generation of regulatory T cells. The present study highlights a therapeutic potential of siRNA-based treatment for allergic diseases.