B-108 Germinal center CD8 T cells can be redirected to eliminate HIV-expressing T follicular helper cells

Abstract

Background: T follicular helper CD4 T cells are located within the germinal centers (GC) of lymph nodes (LN). They are a source of residual viral replication during antiretroviral therapy and a contributor to the latent reservoir. Bispecific antibodies that target HIV Env and CD3 are being developed to purge the latent reservoir by activating HIV from CD4 T cells and inducing killing of those cells by CD8 T cells. We characterized the localization, frequency, and function of CD8 T cells in GCs to determine if they were present and capable of killing HIV-expressing cells in the context of HIV Env/CD3-targeting bispecific antibodies. Methods: We analyzed the phenotype, localization and function of CD8 T cells in tonsils and LNs from non-infected and HIV-infected viremic individuals. Polychromatic flow cytometry was used for phenotypic analysis and confocal imaging for spacial localization. Function (IFNγ, TNF, MIP-1α, and GzB production) was assessed by intracellular staining after 5 hour anti-CD3 stimulation. In vitro cytolytic activity of sorted CD8 T cell populations was tested in a killing assay using an anti-HIV Env/anti-CD3 bispecific-antibody. Results: Phenotypic analysis of tonsillar cells revealed a memory population of CD8 T cells expressing a CCR7lowCXCR5high profile compatible with follicular localization, while confocal imaging confirmed the presence of a small population of CD8 T cells within the GC. These GC CD8 T cells were expanded in HIV-infected LNs compared to non-infected tonsils. Functional activity in response to TCR stimulation occurred almost exclusively in CD8 T cells localized to the GC (defined by CXCR5 expression and loss of CCR7). Production of MIP-1α and GzB predominated over IFNγ and TNF production in GC CD8 T cells. Of all tissue CD8 T cell populations tested, GC localized CD8 T cells had the greatest ability to mediate killing of HIV-infected target cells after cross-linking with an anti-HIV Env/anti-CD3 bispecific antibody. Conclusions: HIV infection is characterized by accumulation of CD8 T cells within LN follicles. These CD8 T cells are functionally capable of mediating bispecific antibody-mediated killing of HIV-infected CD4 T cells. These data add credence to the use of bispecific antibody therapy to purge the LN reservoir.