Role of immune cell-specific receptor glycosylation in immunotherapy response (Schatton and Barthel Lab)
In my current project, I am investigating the consequences of immune cell type-specific receptor glycosylation in therapy response. It is often noticed that while immunotherapies are designed to target a specific cell type it often brings about their therapeutic response by integrating responses from other cells as well. Overall, the aim of my research is to identify innovative glyco-based combinatorial therapy to enhance disease response to immunotherapy in melanoma. I am currently standardizing protocols for modulating the glycome of immune cells isolated from patients to assess alterations in immune checkpoint inhibitor interactions. In parallel, I am developing molecular and functional assays with different immune cell populations and melanoma cells to decipher the mechanistic basis of glycome-dependent signaling crosstalk between immune and cancer cells. Furthermore, the differences in key glycan structures on immune checkpoint receptors are being characterized by immunoprecipitation followed by glycoproteomics.
Melanoma glycome in disease progression (Dimitroff Lab)
Metastatic melanoma (MM) has a dismal 5-year survival rate of 25%. Hence, there is a dire need for novel biomarkers to predict metastasis and forecast efficacious therapies. My research is aimed at elucidating the metastatic consequences of elevated fetal i-linear glycans and related loss of I-branching enzyme GCNT2 in MM and investigating whether loss of GCNT2 can predict disease progression. Preliminary data indicate that increased expression of i-linear glycans (GCNT2 downregulation) enhances tumor-initiating cell (TIC) generation and increases stem marker CD271 and invasion and colony-forming activities. Further, hypoxia-induced decreases in GCNT2 and differentiation marker MITF and an increase in stem marker KLF4 were observed and implicate GCNT2 as a regulator of TIC generation. Additionally, depressed GCNT2 levels corresponded with significantly reduced melanoma patient survival and a marked reduction in response to immune checkpoint (ICI) therapy. We, therefore, hypothesize that hypoxia-dependent GCNT2 downregulation drive MM immune evasion and disease progression. Utilizing genetically-engineered mouse (GEM) models of MM and GCNT2 gene regulation methods in patient-derived MM organoids will allow for analysis of GCNT2 downregulation in melanoma progression and ICI therapy resistance. In all, my research will underscore the development of new biomarkers for MM and unveil how MM glycome can be therapeutically targeted to boost ICI therapy.
Galectins and immune modulation (Dimitroff Lab)
Humoral immunity is reliant on the efficient recruitment of circulating naïve B cells from the blood into peripheral lymph nodes (LN) and the timely transition of naïve B cells to high-affinity antibody (Ab)-producing cells. The current understanding of factor(s) coordinating B cell adhesion, activation, and differentiation within LN, however, is incomplete. Prior studies on naïve B cells reveal remarkably strong binding to putative immunoregulator, galectin (Gal)-9, which attenuates BCR activation and signaling, implicating Gal-9 as a negative regulator in B cell biology. My recent publication investigated Gal-9 localization in human tonsils and LNs and unearthed conspicuously high expression of Gal-9 on high endothelial and post-capillary venules. Adhesion analyses showed that Gal-9 can bridge human circulating and naïve B cells to vascular endothelial cells (EC), while decelerating transendothelial migration. Moreover, Gal-9 interactions with naïve B cells induced global transcription of gene families related to the regulation of cell signaling and membrane/cytoskeletal dynamics. Signaling lymphocytic activation molecule F7 (SLAMF7) was among the key immunoregulators elevated by Gal-9-binding, while SLAMF7’s cytosolic adapter EAT-2, which is required for cell activation, was eliminated. Gal-9 also activated phosphorylation of the pro-survival factor, ERK. Together, these data suggest that Gal-9 promotes B cell – EC interactions while delivering anergic signals to control B cell reactivity.
Altered pancreatic cancer glycome and disease prognosis (Bellis Lab)
My dissertation research identified the addition of α2-6 linked sialic acid addition by sialyltransferase ST6Gal-I as a determinant of gemcitabine resistance in PDAC. ST6Gal-I was shown to hinder chemotherapy-dependent DNA damage and lead to the dysregulation of genes involved in gemcitabine metabolism. In the next part of my thesis, I analyzed the role of ST6Gal-I in PDAC progression. I generated a novel mouse of PDAC by pancreases specific knock-in of ST6Gal-I along with oncogenic K-Ras. Oncogenic K-Ras is the driving mutation of PDAC. ST6Gal-I knock-in significantly reduced survival along with increased metastasis. Mechanistic investigation depicted crosstalk between increased sialylation with increased Sox9, key ductal marker, and expression. Sox9 is a driver of acinar to ductal metaplasia, which is one of the earliest steps in disease progression. To study initiation we mimicked pancreatitis by caerulein treatment in our mouse model. ST6Gal-I knock-in mice had significantly increased ADM compared to the control. Single-cell RNA sequencing depicted increased ductal as well as acinar gene expression in mice pancreas with increased ST6Gal-I expression. Interestingly Sox9, the ductal fate determinant gene was aberrantly overexpressed in acinar nuclei of ST6Gal-I knock-in mice. These striking observations of ST6Gal-I-dependent aggravation of PDAC progression depicted the heavy dependence of PDAC on altered sialylation of surface receptors. This opens up a plethora of questions for further investigation. Together my work placed ST6Gal-I as a key player in PDAC initiation, pathogenesis, and therapy resistance.