Author ORCID Identifier


Date of Graduation


Document Type

Dissertation (PhD)

Program Affiliation


Degree Name

Doctor of Philosophy (PhD)

Advisor/Committee Chair

Dr. Michael Curran

Committee Member

Dr. Stephanie Watowich

Committee Member

Dr. Pamela Wenzel

Committee Member

Dr. Michael Davies

Committee Member

Dr. Matthew Gubin



Anupallavi Srinivasamani, M.S.

Advisory Professor: Michael A. Curran, Ph.D.

Therapeutic blockade of the Programmed cell death-1 (PD-1) receptor and its ligand Programmed death ligand-1 (PD-L1) has revolutionized the treatment of multiple cancers and made durable tumor regression a possibility in the clinic. PD-1 blockade prolonged progression-free survival and overall survival with lesser high-grade toxicity in patients with advanced melanoma when compared to the other FDA-approved checkpoint blockade target, CTLA-4. Unlike CTLA-4, PD-1 is unique in its ability to regulate T cell functions in lymphoid tissues as well as in non-lymphoid tissues like the tumor microenvironment. The comparatively lower incidence of immune-related adverse events associated with PD-1 blockade and its wide-ranging immune-modulatory functions makes PD-1 signaling axis especially favorable for next-generation of combination therapies aimed at increasing the clinical efficacy of immune checkpoint blockade beyond the current 20% of patients who are expected to positively respond to PD-1/PD-L1 blockade. The current and future development of novel therapeutics targeting the PD-1 signaling axis should be rationally guided by a comprehensive understanding of the immunobiology underlying PD-1 signaling. However, the highest affinity ligand of PD-1, PD-L2 remains understudied and has yet to be directly interrogated for therapeutic potential. Recent reports have begun to reveal the relevance of PD-L2 in tumor immunology, however, critical gaps in our knowledge about the function of PD-L2, particularly in humans, limit efforts to rationally harness its potential clinical benefit. We therefore investigated the distinct function of PD-L2 in the PD-1/PD-L1/PD-L2 signaling axis in human T cells. To this end, we established an in vitro experimental system using human Jurkat T cells that allowed us to study the T cell regulatory functions of PD-1/PD-L1 and PD-1/PD-L2 complexes, exclusive of other protein-protein interactions on the surface of T cells. We resolved the contention over the nature of T cell regulation mediated by PD-L2 in preclinical murine models and conclusively showed that PD-L2 is solely a co-inhibitory ligand of human T cells. We also discovered the capacity of PD-L1 and PD-L2 to heterodimerize and studied the functional consequence of this interaction on T cell signaling. Despite binding to the same receptor, we demonstrated that PD-L1 and PD-L2 differentially engage PD-1 to induce a distinct inhibitory signaling cascade downstream of PD-1 in human T cells. We characterized the differences in the molecular mechanisms of PD-1/PD-L1 and PD-1/PD-L2 mediated inhibition of primary human T cells and elucidated the physiological impact of the differential signaling induced by PD-ligands through PD-1 on T cell function. Taken together, our work provides a more solid immunobiological foundation for clinical translation of PD-L2 and defines its non-redundant role in regulating T cell immunity in humans.


Immune checkpoint inhibitors, PD-L2, T cell signaling, PD-L1, Immunotherapy

Available for download on Wednesday, June 05, 2024