Date of Award
8-7-2024
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Immune checkpoint therapies (ICT) have shown promise in treating solid tumors, providing cures and durable protection in some cases. However, only a subset of patients benefits from ICT, indicating a need for a deeper understanding of the requirements for successful therapy. In both mice and humans, αβ T cells are key mediators of spontaneous and ICT-induced anti-tumor responses. While the anti-tumor roles of CD8+ T cells are well-studied, the role of CD4+ T cells, particularly in ICT for MHC-II negative tumors, is less understood. New insights into how CD4+ T cells modulate CD8+ T cells during ICT may lead to new therapeutic avenues for enhancing CD8+ T cell responses in patients for whom ICT is currently ineffective. Thus, the primary aim of this thesis was to define the key cellular and molecular aspects governing CD4+ T cell-driven enhancement of tumor-specific CD8+ T cells within the tumor microenvironment (TME) during successful ICT. We focused primarily on αPD-1/αCTLA-4 ICT using our well-characterized MHC-II negative T3 sarcoma model. In the first part of the study, we demonstrated that CD4+ T cell help is crucial both for priming and during the effector phase within the TME for successful ICT. We discovered that while the CD40/CD40L pathway is necessary for priming CD8+ T cells, it is dispensable during the effector stage, where cytokines IFN-γ and IL-2 play critical roles. Effector-phase CD4+ T cell help mediated three major ICT-induced changes in CD8+ tumor-infiltrating lymphocytes (TILs): (i) downregulation of inhibitory receptors, (ii) enhancement of pro-inflammatory cytokine production, and (iii) increased cytotoxic potential. Additionally, effector-phase CD4+ T cell help indirectly enhanced CD8+ TILs by upregulating MHC-I on tumor cells and facilitating the elimination of immunosuppressive macrophages, thus fostering a tumor milieu conducive for their cytolytic activity. The second part of this thesis explored the dynamics of MHC-II neoantigen presentation by host antigen-presenting cells, crucial for activating CD4+ T cells in MHC-II negative tumors. We generated a TCR-mimic monoclonal antibody (1G10) specific for the dominant T3 CD4+ T cell neoepitope (mItgb1) bound to MHC-II (I-Ab). Time course flow cytometry staining of tumors and tumor-draining lymph nodes (TDLNs) from T3 tumor-bearing mice revealed that 1G10 predominantly stained macrophages and cDC2 cells in both untreated and ICT-treated mice. These findings suggest that macrophages and cDC2s comprise a major fraction of the cellular interaction network associated with CD4+ T cell activation in T3 tumors. However, the contribution of cDC1 cells could not be formally ruled out due to the detection limit of flow cytometry. Furthermore, in RAG2-/- T3 tumor-bearing mice, the 1G10 mAb inhibited the capacity of adoptively transferred neoantigen vaccine-elicited CD4+ and CD8+ T cells to drive tumor rejection, indicating that the effector phase CD4+ T cell help program depends on continuous MHC-II neoantigen presentation beyond the initial priming phase. The specific identity of the necessary antigen-presenting cells in this context warrants further investigation. Collectively, our findings reveal the dynamic complexities of helper CD4+ T cell-driven anti-tumor immunity and underscore the necessity of CD4+ T cell assistance for effective CD8+ T cell anti-tumor responses in immunotherapy. The insights gained advocate for the inclusion of CD4+ T cell-modulating agents in immunotherapy modalities that aim to maximally unleash the cytolytic potential of tumor-specific CD8+ T cells, such as ICT and neoantigen vaccines.
Language
English (en)
Chair and Committee
Robert Schreiber
Committee Members
Carl DeSelm; Kenneth Murphy; Marco Colonna; Maxim Artyomov; Sheila Stewart
Recommended Citation
Ameh, Samuel Oche, "Cellular and Molecular Basis of CD4+ T Cell Help at the Effector Phase During Immunotherapy of MHC-II Negative Tumors" (2024). Arts & Sciences Electronic Theses and Dissertations. 3279.
https://openscholarship.wustl.edu/art_sci_etds/3279