Temporal Changes in Innate and Adaptive Immunity During Sepsis as Determined by ELISpot.

Background: The inability to evaluate host immunity in a rapid quantitative manner in patients with sepsis has severely hampered development of novel immune therapies. The ELISpot assay is a functional bioassay that measures the number of cytokine-secreting cells and the relative amount of cytokine produced at the single-cell level. A key advantage of ELISpot is its excellent dynamic range enabling a more precise quantifiable assessment of host immunity. Herein, we tested the hypothesis on whether the ELISpot assay can detect dynamic changes in both innate and adaptive immunity as they often occur during sepsis. We also tested whether ELISpot could detect the effect of immune drug therapies to modulate innate and adaptive immunity. Methods: Mice were made septic using sublethal cecal ligation and puncture (CLP). Blood and spleens were harvested serially and ex vivo IFN-γ and TNF-α production were compared by ELISpot and ELISA. The capability of ELISpot to detect changes in innate and adaptive immunity due to in vivo immune therapy with dexamethasone, IL-7, and arginine was also evaluated. Results: ELISpot confirmed a decreased innate and adaptive immunity responsiveness during sepsis progression. More importantly, ELISpot was also able to detect changes in adaptive and innate immunity in response to immune-modulatory reagents, for example dexamethasone, arginine, and IL-7 in a readily quantifiable manner, as predicted by the reagents known mechanisms of action. ELISpot and ELISA results tended to parallel one another although some differences were noted. Conclusion: ELISpot offers a unique capability to assess the functional status of both adaptive and innate immunity over time. The results presented herein demonstrate that ELISpot can also be used to detect and follow the in vivo effects of drugs to ameliorate sepsis-induced immune dysfunction. This capability would be a major advance in guiding new immune therapies in sepsis.

Retroviral vectors for the transduction of autoregulated, bidirectional expression cassettes.

Regulated transgene expression is increasingly used in research but is also needed for certain therapies. Regulatory systems are usually composed of two expression units, one bearing the gene of interest under control of a regulatable promoter and the other, a constitutively expressed transactivator that modulates the activity of the regulatable promoter. Because the cotransfer of two independent elements is not efficient in primary cells, single transduction step vectors conferring regulatable gene expression cassettes would be helpful. We have developed retroviral vectors containing an autoregulatory bidirectional expression cassette that encodes all components necessary for regulated expression of a gene of interest. The influence of the orientation of the reporter gene with respect to the viral long terminal repeat (LTR) and the effect of transcriptionally inactive LTRs were investigated using mouse leukemia virus (MLV) and self-inactivating (SIN)-based retroviral vectors. Strict regulation was observed when the reporter was inserted in antisense orientation with respect to the LTR, whereas a sense arrangement of the reporter resulted in a loss of regulation capacity. Expression and regulation of the antisense-orientated reporter gene were homogenous in infected cell pools and investigated cell clones. Long-term observations of infected cells over a period of 30 passages revealed stable expression and regulation. These autoregulated, bidirectional retroviral vectors combine the advantages of single-step transduction with strict regulation of the gene of interest in the infected target cells.

New approaches towards ex vivo and in vivo gene therapy.

A number of hurdles have to be overcome for efficient and specific gene therapy approaches. Here, we report on two different strategies that should lead to an improvement of current protocols. A strategy is presented to tag unique chromosomal integration sites by means of retroviral infection, which can be reused for exchange with the gene of interest by action of site-specific recombinases. Targeting exchange is achieved in one step with 100% efficiency by a stringent positive selection, which makes further screening superfluous. With this strategy a predictable gene expression is obtained for foreign genes integrated into a predefined chromatin structure. A second approach aims at the stabilization of mouse retroviruses towards human serum which is a prerequisite for in vivo gene therapy protocols. To stabilize murine leukemia virus-based retroviruses against human serum, complement regulatory proteins were fused to the retroviral ENV proteins. This resulted in infectious and human complement-protected particles.

Polyvalent DNA vaccines with bidirectional promoters.

The hepatitis B surface antigen (HBsAg) and core antigen (HBcAg) were coexpressed from a synthetic bidirectional promoter with the tetracycline-inactivated transactivator (tTA). The function of this autoregulative system was evaluated following either transfer into established cell lines or intramuscular and intradermal injection of high or low doses of DNA into mice. We measured in vitro antigen expression and in vivo the induction of specific humoral and cellular immune responses. Successful regulation of antigen expression was observed in cultured cells. DNA vaccination with these constructs efficiently primed hepatitis B virus (HBV) specific immunity. However, immunogenic concentrations of the antigens were expressed even in the absence of the transactivator, indicating that low expression level is sufficient to prime an immune response. The bidirectional promoter allows coexpression of either both HBV antigens or a HBV antigen and enhanced green fluorescent protein leading to efficient priming of stable immunity against both antigens. This study demonstrates the potential of synthetic polyvalent plasmids in DNA vaccination.