Date of Award

January 2025

Document Type

Thesis

Degree Name

Medical Doctor (MD)

Department

Medicine

First Advisor

Harriet M. Kluger

Abstract

Immune checkpoint inhibitors have become the standard of care treatment for local and systemic clear cell renal cell carcinoma (RCC). However, a subset of patients fail these therapies due to the development of disease refractory to such treatments. Therefore, it is imperative that we study the potential mechanisms of resistance to immune checkpoint inhibition within the tumor microenvironment. Likewise, establishing biomarkers indicative of treatment resistance may benefit clinicians and patients when it comes to the initial selection of treatment. Moreover, biomarkers of resistance might also serve as potential drug targets. In this study we analyzed expression of TIGIT and GDF-15, two proteins expressed within the tumor microenvironment, as potential biomarkers for increased immune tolerance in RCC. TIGIT is believed to act as a coinhibitory immune checkpoint promoting T cell anergy and increased tumor immune tolerance, while GDF-15 is a secreted cytokine hypothesized to downregulate tumor infiltration by immune and pro-inflammatory cells, though its mechanism is not yet fully elucidated. We hypothesized a role for these proteins in metastatic seeding, and thus increased expression at metastatic sites. Additionally, we expected worsened clinical outcomes such as overall survival and response to therapy with increased TIGIT and GDF-15. We used both quantitative immunofluorescence and immunohistochemistry to identify and quantify the expression of these proteins in tissue microarrays of renal cell carcinoma, including primary tumors, metastases, and normal renal tissue. We found no significant differences in TIGIT positivity in T cells between primary RCC tumors and patient matched metastases, and found that TIGIT positivity in RCC is comparable to lung cancer, but lower than in other malignancies such as cervical, melanoma, and head and neck cancer. We revealed an inverse association between TIGIT positivity and two other checkpoint proteins PD-1 and LAG3. Immunological staining of patient tumors for GDF-15 did not reveal differences in expression when comparing primary tumor versus metastatic sites or normal renal parenchyma. However, quantification of GDF-15 using quantitative immunofluorescence revealed an association with poorer therapeutic response, including decreased progression free survival in patients with high GDF-15 expression at metastatic sites. Furthermore, correlation studies with previously published spatial proteomic data revealed a decrease in tumor B and T cell infiltration with increased GDF-15 expression. The expression of TIGIT and GDF-15 in immune checkpoint inhibitor resistant tumors has made these proteins conceivable targets for novel therapies with neutralizing monoclonal antibodies or small molecule inhibitors. As patients continue to be enrolled in basket clinical trials targeting TIGIT or GDF-15 in conjunction with other immune checkpoint inhibitors, our findings support continued consideration for evaluating these markers in patients with RCC. We showed that in RCC expression of GDF-15 and TIGIT was variable and thus blockading therapies may require selective employment in this patient population.

Comments

This thesis is restricted to Yale network users only. It will be made publicly available on 05/14/2026

Download

Share

COinS