Dendritic Cells Restore CD8⁺T Cell Reactivity to Autologous HIV-1

Abstract

Recall T cell responses to HIV-1 antigens are used as a surrogate for endogenous cellular immune responses generated during infection. Current methods of identifying antigen-specific T cell reactivity in HIV-1 infection use bulk peripheral blood mononuclear cells (PBMC) yet ignore professional antigen-presenting cells (APC) that could reveal otherwise hidden responses. In the present study, peptides representing autologous variants of major histocompatibility complex (MHC) class I-restricted epitopes from HIV-1 Gag and Env were used as antigens in gamma interferon (IFN-␥) enzyme-linked immunosorbent spot (ELISpot) and polyfunctional cytokine assays. Here we show that dendritic cells (DC) enhanced T cell reactivity at all stages of disease progression but specifically restored T cell reactivity after combination antiretroviral therapy (cART) to early infection levels. Type 1 cytokine secretion was also enhanced by DC and was most apparent late post-cART. We additionally show that DC reveal polyfunctional T cell responses after many years of treatment, when potential immunotherapies would be implemented. These data underscore the potential efficacy of DC immunotherapy that aims to awaken a dormant, autologous, HIV-1-specific CD8 ؉ T cell response. IMPORTANCEAssessment of endogenous HIV-1-specific T cell responses is critical for generating immunotherapies for subjects on cART. Current assays ignore the ability of dendritic cells to reveal these responses and may therefore underestimate the breadth and magnitude of T cell reactivity. As DC do not prime new responses in these assays, it can be assumed that the observed responses are not detected without appropriate stimulation. This is important because dogma states that HIV-1 mutates to evade host recognition and that CD8 ؉ cytotoxic T lymphocyte (CTL) failure is due to the inability of T cells to recognize the autologous virus. The results presented here indicate that responses to autologous virus are generated during infection but may need additional stimulation to be effective. Detecting the breadth and magnitude of HIV-1-specific T cell reactivity generated in vivo is of the utmost importance for generating effective DC immunotherapies.

HIV-1 Reservoir Dynamics after Vaccination and Antiretroviral Therapy Interruption Are Associated with Dendritic Cell Vaccine-Induced T Cell Responses

“…Finally, despite all the factors that we found to be associated with viral reservoir replenishment during cART interruption (inflammation markers, CD4 T cell subsets, and HIV-1-specific T cell immune responses induced by the vaccine), the specific antiviral immune response seems to be the best independent predictor of viral load replenishment in a multivariate analysis. This finding could be partially explained by data recently reported by Smith et al (30). These authors showed that dendritic cells can restore CD8 T cell reactivity to autologous HIV-1 in subjects on cART at all stages of disease progression and support the use of DC immunotherapy in subjects on cART.…”

“…These authors showed that dendritic cells can restore CD8 T cell reactivity to autologous HIV-1 in subjects on cART at all stages of disease progression and support the use of DC immunotherapy in subjects on cART. Moreover, Smith et al (30) argue that DC immunotherapy that uses an antigen that is similar to but not the exact antigen to which the subject's T cells were originally primed may not induce an effective cytotoxic T lymphocyte response and may actually hinder viral clearance (31). These results could be an explanation for the findings that, despite the fact that HIV-1-specific immune responses have been elicited in all DCbased vaccine clinical trials, a partial virological response has only been observed in the studies using autologous HIV antigens (32).…”

HIV-specific CD8+ T cells and HIV eradication

“…Dendritic cells (DCs) are also likely to play critical roles in refocusing the immune response. In vitro studies have demonstrated the ability of DCs to expose and boost CD8 + T cell responses against subdominant autologous variants of HIV epitopes in cART-treated subjects (111). DC vaccines involving the ex vivo manipulation and reinfusion of HIV antigen-loaded DCs have also been shown to boost HIV-specific T cell responses in cART-treated patients, resulting in significantly reduced viral load set points following cART interruption Additional immunotherapeutics.…”

Programming T cell Killers for an HIV Cure: Teach the New Dogs New Tricks and Let the Sleeping Dogs Lie

“…We propose that the key objective of a DC-based immunotherapy to treat HIV-1 infection should be to specifically target naïve T cell precursors in order to prime CTLs de novo (teach the new dogs new tricks), and avoid or even inhibit activation of the existing, dysfunctional memory T cell population (let the sleeping dogs lie), as their presence prior to cART 32,33 already supports the notion that they are incapable of controlling the virus. This is problematic, however, as studies have revealed decreases in the prevalence and function of naïve T cells following HIV-1 infection compared to uninfected controls.…”

“…While only a small fraction of PBMC and purified CD8 + T cells from these subjects secrete IFN-γ in response to HIV-1 peptide antigens, DCs loaded with these same antigens reveal broad and robust T cell responses. 22,33,69 Additionally, peptide-loaded DCs enhance the percent of T cells that secrete multiple type 1 cytokines, including IL-2, IFN-γ, TNFα, MIPip-1β, and CD107a, and stimulate proliferation of T cells in response to MHC class I-restricted HIV-1 peptide epitopes. 20,22,33 As the assays used in these studies range from 6 h 18 h, it is highly unlikely that DCs are inducing primary responses, but are rather revealing T cell responses that were undetectable with standard assay procedures.…”