CXCR5-Dependent Entry of CD8 T Cells into Rhesus Macaque B-Cell Follicles Achieved through T-Cell Engineering

ABSTRACT

Follicular helper CD4 T cells, T_FH, residing in B-cell follicles within secondary lymphoid tissues, are readily infected by AIDS viruses and are a major source of persistent virus despite relative control of viral replication. This persistence is due at least in part to a relative exclusion of effective antiviral CD8 T cells from B-cell follicles. To determine whether CD8 T cells could be engineered to enter B-cell follicles, we genetically modified unselected CD8 T cells to express CXC chemokine receptor 5 (CXCR5), the chemokine receptor implicated in cellular entry into B-cell follicles. Engineered CD8 T cells expressing human CXCR5 (CD8^hCXCR5) exhibited ligand-specific signaling and chemotaxis in vitro. Six infected rhesus macaques were infused with differentially fluorescent dye-labeled autologous CD8^hCXCR5 and untransduced CD8 T cells and necropsied 48 h later. Flow cytometry of both spleen and lymph node samples revealed higher frequencies of CD8^hCXCR5 than untransduced cells, consistent with preferential trafficking to B-cell follicle-containing tissues. Confocal fluorescence microscopy of thin-sectioned lymphoid tissues demonstrated strong preferential localization of CD8^hCXCR5 T cells within B-cell follicles with only rare cells in extrafollicular locations. CD8^hCXCR5 T cells were present throughout the follicles with some observed near infected T_FH. In contrast, untransduced CD8 T cells were found in the extrafollicular T-cell zone. Our ability to direct localization of unselected CD8 T cells into B-cell follicles using CXCR5 expression provides a strategy to place highly effective virus-specific CD8 T cells into these AIDS virus sanctuaries and potentially suppress residual viral replication.

IMPORTANCE AIDS virus persistence in individuals under effective drug therapy or those who spontaneously control viremia remains an obstacle to definitive treatment. Infected follicular helper CD4 T cells, T_FH, present inside B-cell follicles represent a major source of this residual virus. While effective CD8 T-cell responses can control viral replication in conjunction with drug therapy or in rare cases spontaneously, most antiviral CD8 T cells do not enter B-cell follicles, and those that do fail to robustly control viral replication in the T_FH population. Thus, these sites are a sanctuary and a reservoir for replicating AIDS viruses. Here, we demonstrate that engineering unselected CD8 T cells to express CXCR5, a chemokine receptor on T_FH associated with B-cell follicle localization, redirects them into B-cell follicles. These proof of principle results open a pathway for directing engineered antiviral T cells into these viral sanctuaries to help eliminate this source of persistent virus.