Date of Completion

3-3-2017

Embargo Period

3-3-2017

Keywords

LPS, Poly I:C, OX40, Type I IFN, CXCL9

Major Advisor

Dr Anthony Vella

Associate Advisor

Dr Andrei Medvedev

Associate Advisor

Dr Pramod Srivastava

Field of Study

Biomedical Science

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Most commonly used adjuvants in vaccines are effective at elevating serum antibody titers but do not elicit significant CD4 or CD8 T cell response. CD4 T cells are important in protection against challenging infectious diseases such as HIV, malaria and tuberculosis and also important for anti-tumor immunity. Therefore, our goal is to evaluate how adjuvants lipopolysaccharide (LPS) and polyinosinic:polycytidilic acid (poly I:C) induced mechanisms enhance the CD4 T cell immunity. LPS, a known Toll like receptor 4 (TLR4) ligand, when injected with or shortly after a T cell antigen, enhances T cell clonal expansion, long-term survival and Th1 differentiation. Importantly, LPS can synergize with a potent costimulatory agonist, OX40/CD134 (anti-CD134 mAb) to further enhance CD4 T cell expansion, survival, and memory. The mechanism behind this synergy is unknown. Our preliminary data suggests that Ag, LPS and anti-CD134 immunization results in enhanced production of type I IFN (IFN-β) which corresponds with the increased T cell expansion this vaccine induces. Therefore, we hypothesized that LPS and anti-CD134 mediated synergistic CD4 T cell response could depend on IFNαR signaling.

Depending on the model used, we show that absence of IFNαR signaling results in minor to major reduction in specific CD4 T cell expansion in peripheral lymph node (pLN) and liver tissue. More importantly, LPS induced type I IFN, promotes synthesis of chemokines, CXCL9 and CXCL10, suggesting their role in the LPS and CD134 costimulation response. Indeed, blocking CXCL9 highlighted the importance of this chemokine in promoting specific CD4 T cell accumulation in pLN and liver. CXCL9 impacted the T cell accumulation in spite of no difference in serum levels of type I IFN, suggesting that type I IFN induced downstream chemokines could play a more dominant role in promoting T cell accumulation.

We next evaluated the role of synthetic dsRNA analog, poly I:C in enhancing CD4 T cell immunity. Recent studies, have shown that poly I:C synergizes with CD40 agonist Ab, to promote enhanced effector CD4 T cell response, where poly I:C induced IFNαR signaling was shown to enhance CD134L expression on dendritic cells (DC’s). Therefore, we hypothesized that poly I:C could be directly combined with CD134 costimulation to promote enhanced CD4 T cell immunity. Indeed our results show that, administration of peptide Ag with poly I:C and anti-CD134 enhanced the Ag-specific CD4 expansion and Th1 differentiation and it was dependent on poly I:C induced IFNαR signaling. Thus, the vaccine combination of poly I:C and anti-CD134 should be evaluated for its efficacy in therapeutic vaccines against infectious diseases or cancer where CD4 Th1-type immunity is crucial. Additionally, we also show that CD134 costimulation induced CD4 Th1 response was also dependent on IFNαR signaling. Understanding, the mechanism of how CD134 costimulation triggers IFNαR signaling to promote CD4 T cell response will be important for the efficient targeting of CD134 in preclinical cancer trials.

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