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Memory CD8+ T cells confer long-term immunity against tumors, and anticancer vaccines therefore should maximize their generation. Multiple memory CD8+ T-cell subsets with distinct functional and homing characteristics exist, but the signaling pathways that regulate their development are ill defined. Here we examined the role of the serine/threonine kinase Akt in the generation of protective immunity by CD8+ T cells. Akt is known to be activated by the T-cell antigen receptor and the cytokine IL-2, but its role in T-cell immunity in vivo has not been explored. Using CD8+ T cells from pdk1K465E/K465E knockin mice, we found that decreased Akt activity inhibited the survival of T cells during the effector-to-memory cell transition and abolished their differentiation into C-X-C chemokine receptor 3 (CXCR3)loCD43lo effector-like memory cells. Consequently, antitumor immunity by CD8+ T cells that display defective Akt signaling was substantially diminished during the memory phase. Reduced memory T-cell survival and altered memory cell differentiation were associated with up-regulation of the proapoptotic protein Bim and the T-box transcription factor eomesodermin, respectively. These findings suggest an important role for effector-like memory CD8+ T cells in tumor immune surveillance and identify Akt as a key signaling node in the development of protective memory CD8+ T-cell responses. [ABSTRACT FROM AUTHOR]

A major contributing factor to the final magnitude and breadth of CD8+ T-cell responses to complex antigens is immunodomination, where CD8+ T cells recognizing their cognate ligand inhibit the proliferation of other CD8+ T cells engaged with the same APC. In this study, we examined how the half-life of cell surface peptide-MHC class I complexes influences this phenomenon. We found that primary CD8+ T-cell responses to DNA vaccines in mice are shaped by competition among responding CD8+ T cells for nonspecific stimuli early after activation and prior to cell division. The susceptibility of CD8+ T cells to 'domination' was a direct correlate of higher kinetic stability of the competing CD8+ T-cell cognate ligand. When high affinity competitive CD8+ T cells were deleted by self-antigen expression, competition was abrogated. These findings show, for the first time to our knowledge, the existence of regulatory mechanisms that direct the responding CD8+ T-cell repertoire toward epitopes with high-stability interactions with MHC class I molecules. They also provide an insight into factors that facilitate CD8+ T-cell coexistence, with important implications for vaccine design and delivery. [ABSTRACT FROM AUTHOR]

Purpose: PD-1 checkpoint blockade has revolutionized the field of cancer immunotherapy, yet the frequency of responding patients is limited by inadequate T-cell priming secondary to a paucity of activatory dendritic cells (DC). DC signals can be bypassed by CD27 agonists, and we therefore investigated if the effectiveness of anti-PD-1/L1 could be improved by combining with agonist anti-CD27 monoclonal antibodies (mAb). Experimental Design: The efficacy of PD-1/L1 blockade or agonist anti-CD27 mAb was compared with a dual-therapy approach in multiple tumor models. Global transcriptional profiling and flow cytometry analysis were used to delineate mechanisms underpinning the observed synergy. Results: PD-1/PD-L1 blockade and agonist anti-CD27 mAb synergize for increased CD8 + T-cell expansion and effector function, exemplified by enhanced IFNγ, TNFα, granzyme B, and T-bet. Transcriptome analysis of CD8 + T cells revealed that combination therapy triggered a convergent program largely driven by IL2 and Myc. However, division of labor was also apparent such that anti-PD-1/L1 activates a cytotoxicity-gene expression program whereas anti-CD27 preferentially augments proliferation. In tumor models, either dependent on endogenous CD8 + T cells or adoptive transfer of transgenic T cells, anti-CD27 mAb synergized with PD-1/L1 blockade for antitumor immunity. Finally, we show that a clinically relevant anti-human CD27 mAb, varlilumab, similarly synergizes with PD-L1 blockade for protection against lymphoma in human-CD27 transgenic mice. Conclusions: Our findings suggest that suboptimal T-cell invigoration in cancer patients undergoing treatment with PD-1 checkpoint blockers will be improved by dual PD-1 blockade and CD27 agonism and provide mechanistic insight into how these approaches cooperate for CD8 + T-cell activation. Clin Cancer Res; 24(10); 2383-94. ©2018 AACR ., (©2018 American Association for Cancer Research.)

A major contributing factor to the final magnitude and breadth of CD8(+) T-cell responses to complex antigens is immunodomination, where CD8(+) T cells recognizing their cognate ligand inhibit the proliferation of other CD8(+) T cells engaged with the same APC. In this study, we examined how the half-life of cell surface peptide-MHC class I complexes influences this phenomenon. We found that primary CD8(+) T-cell responses to DNA vaccines in mice are shaped by competition among responding CD8(+) T cells for nonspecific stimuli early after activation and prior to cell division. The susceptibility of CD8(+) T cells to 'domination' was a direct correlate of higher kinetic stability of the competing CD8(+) T-cell cognate ligand. When high affinity competitive CD8(+) T cells were deleted by self-antigen expression, competition was abrogated. These findings show, for the first time to our knowledge, the existence of regulatory mechanisms that direct the responding CD8(+) T-cell repertoire toward epitopes with high-stability interactions with MHC class I molecules. They also provide an insight into factors that facilitate CD8(+) T-cell coexistence, with important implications for vaccine design and delivery., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Antigen-specific CD4(+) T cells are central to natural and vaccine-induced immunity. An ongoing antigen-specific T-cell response can, however, influence surrounding T cells with unrelated antigen specificities. We previously observed this bystander effect in healthy human subjects following recall vaccination with tetanus toxoid (TT). Since this interplay could be important for maintenance of memory, we have moved to a mouse model for further analysis. We investigated whether boosting memory CD4(+) T cells against TT in vivo would influence injected CD4(+) TCR transgenic T cells (OT-II) specific for an unrelated OVA peptide. If OT-II cells were pre-activated with OVA peptide in vitro, these cells showed a bystander proliferative response during the ongoing parallel TT-specific response. Bystander proliferation was dependent on boosting of the TT-specific memory response in the recipients, with no effect in naive mice. Bystander stimulation was also proportional to the strength of the TT-specific memory T-cell response. T cells activated in vitro displayed functional receptors for IL-2 and IL-7, suggesting these as potential mediators. This crosstalk between a stimulated CD4(+) memory T-cell response and CD4(+) T cells activated by an unrelated antigen could be important in human subjects continually buffeted by environmental antigens.

The clonotypic T-cell antigen receptor (TCR) provides unique Valpha and Vbeta sequences with potential as idiotypic targets for immunoregulation. For T-cell malignancies, vaccination with the TCR could induce therapeutic anti-idiotypic responses. To facilitate this approach, we have developed DNA vaccines that include the genes encoding TCR sequences from a T-cell lymphoma (TCL). To combine requirements for stable folding with a simple minimized single-chain construction, we used a three-domain ValphaVbetaCbeta sequence. To promote anti-TCR immunity, we fused a pathogen-derived sequence from tetanus toxin to the 3'-end of the single-chain TCR. The fusion gene vaccine induced anti-idiotypic antibodies and generated protection against the TCL. The critical requirement for the conformational integrity of the delivered TCR antigen was highlighted by the observation that DNA fusion vaccines containing either ValphaVbeta or VbetaCbeta sequences failed to generate antibodies reactive with the native TCR or provide protection. This is the first report of a DNA vaccine able to induce anti-idiotypic immunity against TCL, and it presents a simple strategy for selectively eliminating T-cell clones in vivo.