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Designing better TLR-based agonists and antagonists suitable for immunotherapeutic applications

In its broadest sense, immune system is divided into two major arms, innate and adaptive immunity. Among the activators of innate immune system, Toll Like Receptors (TLRs hereafter), are the most widely studied and understood family of innate sensors. Of note, the contribution of TLRs to modulate vaccine response and also its interplay during initiation of protective adaptive immune response was crowned as a Nobel Prize in Medicine and Physiology (2011). Of TLR family receptors, nucleic acid sensors comprise the sub-family of TLRs and are implicated to play a pivotal role dictating innate and educating adaptive immunity against anti-pathogenic response. When mouse experience was attempted to be translated to human via initiation of phase-I clinical trials, the outcome was a total disappointment due to the fact that mouse TLRs vs human TLRs did not share 100% sequence homology, and studies demonstrated that there were up to 25% non-homologous regions in man.

Bacterial DNA is quite different from mammalian DNA, since unmetylated CpG dinucleotides are 25x more frequently expressed in prokaryotes compared to eukaryotes and furthermore unmethylated CpG motifs are suppressed in mammalian genome and most of the time they exist in methylated rather than unmethylated forms. These distinct structural and functional features were sufficient to regard bacterial genome as “Non-Self” by mammalian innate immune system. Among our innate immune system sensors, TLR9 senses the existence of free prokaryotic DNA in the biological milieu and initiates a concerted activation leading to a robust pro-inflammatory or inflammatory immune cascade, as well as leading to a pronounced Th1-biased immunity.

We were among the pioneering groups describing for the first time that a CpG ODN sequence known to perform optimally in mouse system is not suitable for human applications. This opened the window of opportunity to design better and more effective CpG ODN sequences suitable for human clinical trials ranging from vaccine adjuvants to anti-cancer or anti-allergic therapeutic agents. These studies led to filing of several international patents under our names as the co-inventors (see patent list). Most of these sequences went into clinical trials or were offered to scientific community as research grade materials by US companies.

The labile nature of these nucleic acids hampered their clinical performance. Again, we were the first to offer an innovative approach to modulate innate immunity via formulating these sequences and delivering them to the site of relevant cells unharmed, thus extending their biological performance. NIH and FDA jointly patented these ideas. This technology was later licensed by US biopharmaceutical companies to pursue clinical trials against cancer therapy, either as a standalone agent or in combination therapy.

In 2003, opposite to the logic followed that led to the identification of immune stimulatory CpG motifs that presented in bacterial genome, we embarked on a project to describe the existence of immune suppressive motifs patterned in mammalian genome. We reported for the first time that G-run motifs, such as TTAGGG repeats, are highly abundant in mammalian DNA compared to bacterial genome, and these G-rich sequences are secreted to the environment by host cells probably during apoptosis and may help to down-regulate over-exuberant immune activation. We and others later went on documenting that these immunosuppressive motifs are potent nucleic-acid based agents against auto-immune or auto-inflammatory response. The findings of this work, not only led to other international patents, but also reported from the cover when it was published in the Journal of Immunology.

Currently, in our research laboratory in MBG, our major research focus encompasses these themes. We are tasked to develop more effective next generation nucleic acid sequences along with developing novel nano-delivery systems mainly from natural sources, therefore, improving the biological performance as well as expanding potential immunotherapeutic applications of these two distinct classes of immunomodulatory DNA. Moreover, my Lab. is dedicated to provide cutting-edge research solutions to companies in Turkey who intend to extend their competitiveness around the globe.

I strongly believe that understanding the basis of the activating or suppressing mechanisms of the innate immune system, we would be better equipped to develop more effective and more innovative biotherapeutic applications. While this will help combat bacterial and viral diseases and generate more effective/potent anti-cancer response, it will also help to control autoimmune symptoms in near future. In order to achieve these goals modifying and achieving sustained and targeted delivery of these ligands (or antagonists) to the site of innate immune sensors in a nanoparticulate form is vital since it will achieve more effective/efficient instruction of adaptive immune system.