Abstract

Classical dendritic cells (cDCs) are specialized antigen presenting cells that comprise distinct subsets distinguished by transcriptional developmental differences and in the types of immune responses they initiate. Classical type 1 dendritic cells (cDC1) are thought to perform antigen cross-presentation, which is required to prime CD8 T cells, whereas cDC2 have been suggested to be specialized for priming CD4 T cells. CD4 T cell help for CD8 T cell responses has been proposed to be mediated by CD40-dependent licensing of antigen-presenting cells. cDC1 have been suggested as the target of CD4 T cell help on the basis of in vitro analysis and intravital imaging during viral infection. However, despite extensive analysis, a requirement for cDC1 in mediating CD4 T cell help in vivo has not been directly established, and the downstream mechanism of CD40 help remains unclear. To evaluate the function of cDC1 in initiating CD4 and CD8 T cell responses in vivo, we generated a novel Xcr1-Cre mouse line that allows for inactivation of genes selectively in cDC1. We found that, in contrast to recent models, early priming of CD4+ T cells against tumor-derived antigens required cDC1 specifically for antigen presentation, as selective deletion of major histocompatibility class II (MHC II) molecules in cDC1 prevented early CD4 T cell priming. Deletion of either MHC II or CD40 in cDC1 impaired both tumor rejection and tumor-specific CD8 T cell priming, consistent with a role for cognate CD4 T cell interactions and CD40 signaling in cDC1 licensing. However, the precise mechanism by which CD40 signaling in cDC1 licenses the effective activation of tumor-specific CTL responses remained undefined. Therefore, we systematically identified CD40-induced genes in cDC1, including Cd70, Tnfsf9, Ptgs2, and Bcl2l1, and examined their contributions to anti-tumor immunity. We found that cDC1-specific inactivation of CD70 and COX-2, and global CD27 inactivation, only partially impaired tumor rejection or tumor-specific CD8 T-cell expansion. Loss of 4-1BB, alone or in Cd27-/- mice, did not further impair anti-tumor immunity. However, cDC1-specific CD40 inactivation reduced cDC1 mitochondrial transmembrane potential and increased caspase activation in tumor-draining lymph nodes, reducing migratory cDC1 numbers in vivo. Similar impairments occurred during in vitro antigen presentation by Cd40-/- cDC1 to CD8 T cells, which were reversed by re-expression of Bcl2l1. Thus, CD40 signaling acts as a control hub in cDC1, not only inducing co-stimulatory ligands for CD8 T cells, but also inducing Bcl2l1 that sustains cDC1 survival during priming of anti-tumor responses. These advances provide new insight into the cellular interactions and proteins involved in CD4 help for CD8 T cell anti-tumor responses.

Committee Chair

Kenneth Murphy

Degree

Doctor of Philosophy (PhD)

Author's Department

Biology & Biomedical Sciences (Immunology)

Author's School

Graduate School of Arts and Sciences

Document Type

Dissertation

Date of Award

5-8-2024

Language

English (en)

Author's ORCID

0000-0002-9521-1657

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