Abstract

Immunotherapy with checkpoint blockade has revolutionized cancer treatment, sparking the search for other immune cell inhibitory receptors as novel immunotherapeutic targets. Among those, TIGIT has been the most promising based on strong initial results with multiple therapeutic antibodies under clinical development. Yet, first results of two phase III trials of anti-TIGIT, tiragolumab, in combination with anti-PD-L1 in lung cancer were disappointing, prompting a search for answers. Tiragolumab and many other candidate antibodies include an Fc-active domain, which binds to Fc receptors on effector cells, including to FcγRIII on Natural Killer (NK) cells. This induces killing of opsonized TIGIT+-cells by antibody-dependent cellular cytotoxicity (ADCC). The Fc-active domain of anti-TIGIT is associated with enhanced efficacy over Fc-silent versions due to ADCC-based clearance of unwanted TIGIT+ exhausted effector lymphocytes and Tregs. Yet, TIGIT is also expressed on NK cells, which potentially could result in their depletion through fratricide and negatively affect treatment outcomes. NK cells are innate immune cells that upon activation directly kill cancer and coordinate anti-tumor immunity and are being pursued as adoptive cell therapy. Prior studies in mice showed that NK cells play an essential role in the efficacy of anti-TIGIT, while TIGIT expression on NK cells was associated with exhaustion. Despite this, TIGIT expression and signaling on human, activated and expanded NK cells and the effect of Fc-active vs. silent anti-TIGIT in the context of NK cell function and fratricide have not been studied and are the subject of this dissertation. This study found that activation of NK cells upregulates TIGIT, and in fact, TIGIT+ NK cells had superior anti-tumor function compared to TIGIT- NK cells. However, chronic TIGIT engagement by its ligand PVR during tumor exposure induced dysfunction in NK cells. TIGIT blockade with Fc-silent anti-TIGIT restored NK cell effector function while Fc-active anti-TIGIT resulted in NK cell depletion via fratricide and reduced killing compared to Fc-silent. To overcome this, NK cells were expanded with clinically relevant PM21-particle method and engineered using CRISPR/Cas-9 to generate TIGIT knockout (KO) PM21-NK cells. TIGIT KO not only improved PM21-NK metabolic fitness and cytotoxicity during long-term tumor exposure, importantly, it prevented PM21-NK cell depletion and decrease in cytotoxicity when combined with Fc-active anti-TIGIT. Overall, these findings suggest that Fc-active anti-TIGIT therapeutics can deplete activated TIGIT+ NK cells. This study also demonstrated the therapeutic potential of fratricide-resistant expanded TIGIT KO PM21-NK cells alone or in combination with Fc-active anti-TIGIT to improve treatment outcomes.

Notes

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Graduation Date

2023

Semester

Summer

Advisor

Copik, Alicja

Degree

Doctor of Philosophy (Ph.D.)

College

College of Medicine

Department

Burnett School of Biomedical Sciences

Degree Program

Biomedical Sciences

Identifier

CFE0009882

Language

English

Release Date

February 2029

Length of Campus-only Access

5 years

Access Status

Doctoral Dissertation (Campus-only Access)

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Restricted to the UCF community until February 2029; it will then be open access.

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