The unmethylated CpG motifs present in bacterial DNA interact with toll-like receptor 9 to trigger a pro-inflammatory immune response. CpG DNA also improves antigen presenting cell function, thereby facilitating the development of adaptive immunity. Over the past several years, my laboratory established that synthetic oligonucleotides expressing immunostimulatory CpG motifs (CpG ODN) reduced host susceptibility to infection and allergic inflammation, were effective as vaccine adjuvants, and had a role in the treatment of cancer. Most recently, we demonstrated that they also accelerated wound repair in mice and non-human primates. These pre-clinical studies suggest that CpG ODN may be used to both treat established diseases and speed wound healing after trauma or (oncologic) surgery. Based in part on this pre-clinical data, a number of phase I through III clinical trials exploring the safety and efficacy of CpG ODN have been initiated by groups who have licensed our technology. Ongoing pre-clinical research in my lab is designed to identify the optimal therapeutic window for CpG ODN delivery, and examine whether the protective immune responses they elicit can be accelerated and/or magnified by combining them with other immunomodulatory agents (such as additional TLR ligands and small molecule agonistic immune potentiators). One of the model systems used by my lab to examine the adjuvant activity of CpG ODN involves AVA, the licensed anthrax vaccine. Our recent results show that adding CpG ODN to AVA significantly prolongs the duration of protective immunity via two distinct mechanisms. First, CpG-adjuvanted AVA elicits a faster and stronger initial Ab response, with anti-anthrax Ab levels persisting in the protective range for more than one year after a single vaccination (significantly longer than AVA alone). Second, CpG-adjuvanted AVA induces the generation of a high affinity memory B cell population that persists long-term. These B cells respond to anthrax infection so rapidly that they confer resistance to the host even after serum Ab levels have waned. This represents a novel mechanism for providing long-term protection against bioterror pathogens. Efforts to optimize the therapeutic utility of CpG ODN require a detailed understanding of the cells they activate (both directly and indirectly), their duration of action, and the regulatory pathways involved in mediating these responses. To clarify these issues, we are using microarray technology to identify the genes and networks central to the immune stimulation elicited by CpG ODN. Such experiments are conducted in vitro on highly purified cell subpopulations and in vivo to monitor gene expression under physiologic conditions. Results indicate that significant changes in gene expression are detectable within 15 minutes of ODN administration and persist for at least 9 days. TNFa, IL-1b, and IFNg were identified as playing key roles in the initial up-regulation of CpG mediated gene activation (which eventually spreads to involve the expression of nearly 700 genes). The magnitude with which individual genes are up-regulated is influenced by additional co-regulators that are predominantly activated within 24 hr of CpG ODN stimulation. Unexpectedly, we observed two peaks of gene activation following CpG ODN delivery to mouse or human cells. An initial peak at 3 hr primarily involves genes associated with immune regulation/activation while genese in the second peak (at day 5) a largely associated with cell division. This second peaks help explain the prolonged activity of CpG ODN in vivo. By three days post CpG ODN administration, the number of up-regulated genes had decreased by greater than 85%. This effect is largely mediated by a group of down-regulators (including MYC, FOS, and SOCS) that actively suppress CpG-induced gene expression. These suppressors target the critical up-regulatory genes described above, thereby shutting down entire stimulatory networks. The other major therapeutic goal of this project is to improve the induction of tumor-specific immunity. We recently demonstrated conjugating CpG ODN to killed tumor cells improved the uptake of the cancer vaccine by professional APCs, and boosted the induction of humoral and cell mediated immune responses. In multiple murine models, we found that vaccination with CpG conjugated killed cell vaccines significantly reduced susceptibility to tumor challenge. This effect is not only observed in mice pre-vaccinated and then challenged, but in animals immunized with our CpG-killed tumor vaccine up to 5 weeks post challenge. The addition of agents known to boost NK and T cell activation, such as 4-1BB MAb, synergistically enhanced the anti-tumor effect of CpG ODN.
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