Delivery of viral-vectored vaccines by B cells represents a novel strategy to accelerate CD8(+) T-cell recall responses.

Rapid boosting of memory CD8(+) T cells (TM) is essential in cancer immunotherapy and the control of certain infectious diseases. However, effector T cells (TE) are a barrier to booster vaccination because they can rapidly kill antigen-bearing antigen-presenting cells (APCs) before TM are engaged. We demonstrate that viral-vectored vaccines delivered by B cells elicit robust TM expansion in the presence of TE, enabling booster immunizations to bypass TE-mediated negative feedback regulation. Our data indicate that viral vector-loaded B cells home to the follicular regions in secondary lymphoid organs, which are anatomically separated from TE and in close proximity to TM. The B cells, however, do not serve as APCs in this area. Rather, classic CD11c(+) dendritic cells serve to stimulate the secondary CD8(+) T-cell response. Our data reveal that B cells represent a novel and readily accessible delivery system that can effectively engage secondary CD8(+) T-cell activation for prime-boost strategies.

CD8+ T-cell expansion and maintenance after recombinant adenovirus immunization rely upon cooperation between hematopoietic and nonhematopoietic antigen-presenting cells.

We have recently reported that CD8(+) T-cell memory maintenance after immunization with recombinant human adenovirus type 5 (rHuAd5) is dependent upon persistent transgene expression beyond the peak of the response. In this report, we have further investigated the location and nature of the cell populations responsible for this sustained response. The draining lymph nodes were found to be important for primary expansion but not for memory maintenance, suggesting that antigen presentation through a nonlymphoid source was required. Using bone marrow chimeric mice, we determined that antigen presentation by nonhematopoietic antigen-presenting cells (APCs) was sufficient for maintenance of CD8(+) T-cell numbers. However, antigen presentation by this mechanism alone yielded a memory population that displayed alterations in phenotype, cytokine production and protective capacity, indicating that antigen presentation through both hematopoietic and nonhematopoietic APCs ultimately defines the memory CD8(+) T-cell response produced by rHuAd5. These results shed new light on the immunobiology of rHuAd5 vectors and provide evidence for a mechanism of CD8(+) T-cell expansion and memory maintenance that relies upon both hematopoietic and nonhematopoietic APCs.

Combined mTOR inhibition and OX40 agonism enhances CD8(+) T cell memory and protective immunity produced by recombinant adenovirus vaccines.

The memory CD8(+) T cell population elicited by immunization with recombinant human adenovirus serotype 5 (rHuAd5) vaccines is composed primarily of effector and effector memory cells (T(EM)) with limited polyfunctionality. In this study, we investigated whether treatment with immunomodulators could enhance and/or redistribute the CD8(+) memory population elicited by rHuAd5. Vaccination in combination with both rapamycin (to modulate differentiation) and an OX40 agonist (to enhance costimulation) increased both the quantity and polyfunctionality of the CD8(+) memory T cell population, with expansion of the T(EM) and memory precursor populations. Furthermore, this intervention enhanced protection against multiple virus challenges. Attenuation of adenovirus transgene expression was required to enable the combination rapamycin + OX40 agonist immunomodulatory treatment to further enhance skewing towards central memory formation, indicating that persistence of antigen expression ultimately limits development of this memory population following rHuAd5 immunization. These results demonstrate that during the expansion phase following adenovirus immunization, the level of mammalian target of rapamycin (mTOR) activity, the amount of costimulation and the duration of antigen availability act together to define the magnitude, phenotype, and functionality of memory CD8(+) T cells. Modulation of these factors can be used to selectively manipulate memory formation.

Designed ankyrin repeat proteins are effective targeting elements for chimeric antigen receptors.

BACKGROUND: Adoptive cell transfer of tumor-specific T lymphocytes (T cells) is proving to be an effective strategy for treating established tumors in cancer patients. One method of generating these cells is accomplished through engineering bulk T cell populations to express chimeric antigen receptors (CARs), which are specific for tumor antigens. Traditionally, these CARs are targeted against tumor antigens using single-chain antibodies (scFv). Here we describe the use of a designed ankyrin repeat protein (DARPin) as the tumor-antigen targeting domain. METHODS: We prepared second generation anti-HER2 CARs that were targeted to the tumor antigen by either a DARPin or scFv. The CARs were engineered into human and murine T cells. We then compared the ability of CARs to trigger cytokine production, degranulation and cytotoxicity. RESULTS: The DARPin CARs displayed reduced surface expression relative to scFv CARs in murine cells but both CARs were expressed equally well on human T cells, suggesting that there may be a processing issue with the murine variants. In both the murine and human systems, the DARPin CARs were found to be highly functional, triggering cytokine and cytotoxic responses that were similar to those triggered by the scFv CARs. CONCLUSIONS: These findings demonstrate the utility of DARPins as CAR-targeting agents and open up an avenue for the generation of CARs with novel antigen binding attributes.

Indigenous enteric eosinophils control DCs to initiate a primary Th2 immune response in vivo.

Eosinophils natively inhabit the small intestine, but a functional role for them there has remained elusive. Here, we show that eosinophil-deficient mice were protected from induction of Th2-mediated peanut food allergy and anaphylaxis, and Th2 priming was restored by reconstitution with il4(+/+) or il4(-/-) eosinophils. Eosinophils controlled CD103(+) dendritic cell (DC) activation and migration from the intestine to draining lymph nodes, events necessary for Th2 priming. Eosinophil activation in vitro and in vivo led to degranulation of eosinophil peroxidase, a granule protein whose enzymatic activity promoted DC activation in mice and humans in vitro, and intestinal and extraintestinal mouse DC activation and mobilization to lymph nodes in vivo. Further, eosinophil peroxidase enhanced responses to ovalbumin seen after immunization. Thus, eosinophils can be critical contributors to the intestinal immune system, and granule-mediated shaping of DC responses can promote both intestinal and extraintestinal adaptive immunity.

Combined vaccination and immunostimulatory antibodies provides durable cure of murine melanoma and induces transcriptional changes associated with positive outcome in human melanoma patients.

We have developed a recombinant adenovirus vaccine encoding dopachrome tautomerase (rHuAd5-hDCT) that produces robust DCT-specific immunity, but only provides modest suppression of murine melanoma. In the current study, an agonist antibody against 4-1BB was shown to enhance rHuAd5-hDCT efficacy and evoke tumor regression, but most tumors ultimately relapsed. The vaccine triggered upregulation of the immune inhibitory PD-1 signaling pathway and PD-1 blockade dramatically enhanced the rHuAd5-hDCT + anti-4-1BB strategy, resulting in complete regression of growing tumors in > 70% of recipients. The impact of the combined anti-4-1BB/anti-PD-1 treatment did not manifest as a dramatic enhancement in either the magnitude or functionality of DCT-specific tumor infiltrating lymphocytes relative to either treatment alone. Rather, a synergistic enhancement in intratumoral cytokine expression was observed, suggesting that the benefit of the combined therapy was a local event within the tumor. Global transcriptional analysis revealed immunological changes within the tumor following the curative vaccination, which extended beyond the T cell compartment. We identified an immune signature of 85 genes associated with clearance of murine melanoma that correlated with improved survival outcome in two independent cohorts of human melanoma patients. Our data reinforce the concept that successful vaccination must overcome local hurdles in the tumor microenvironment that are not manifest within the periphery. Further, tumor rejection following vaccination involves more than simply T cells. Finally, the association of our immune signature with positive survival outcome in human melanoma patients suggests that similar vaccination strategies may be promising for melanoma treatment.

Optimizing vaccine-induced CD8(+) T-cell immunity: focus on recombinant adenovirus vectors.

Recombinant adenoviruses have emerged as promising viral vectors for CD8(+) T-cell vaccines. Our studies have indicated that unlike most acute infections, the CD8(+) T-cell memory population elicited by recombinant human adenovirus serotype 5 (rHuAd5) displays a dominant effector memory phenotype. Persistent, low-level transgene expression from the rHuAd5 vector sustains the CD8(+) T-cell memory population and a nonhematopoietic cell compartment appears to be involved in long-term presentation of adenoviral antigens. Although we are beginning to learn more about the factors that control the maintenance and functionality of memory CD8(+) T cells, we do not yet fully understand what comprises a protective CD8(+) T-cell response. Results from upcoming Phase II clinical trials will be important for determining whether rHuAd5 T-cell vaccines are effective in humans and should help identify correlates of CD8(+) T-cell protection.