Anke Redeker

Vaccine-Induced Effector-Memory CD8+ T Cell Responses Predict Therapeutic Efficacy against Tumors

CD8+ T cells have the potential to attack and eradicate cancer cells. The efficacy of therapeutic vaccines against cancer, however, lacks defined immune correlates of tumor eradication after (therapeutic) vaccination based on features of Ag-specific T cell responses. In this study, we examined CD8+ T cell responses elicited by various peptide and TLR agonist-based vaccine formulations in nontumor settings and show that the formation of CD62L−KLRG1+ effector-memory CD8+ T cells producing the effector cytokines IFN-γ and TNF predicts the degree of therapeutic efficacy of these vaccines against established s.c. tumors. Thus, characteristics of vaccine-induced CD8+ T cell responses instill a predictive determinant for the efficacy of vaccines during tumor therapy.

Dendritic cells process synthetic long peptides better than whole protein, improving antigen presentation and T-cell activation

The efficiency of antigen (Ag) processing by dendritic cells (DCs) is vital for the strength of the ensuing T‐cell responses. Previously, we and others have shown that in comparison to protein vaccines, vaccination with synthetic long peptides (SLPs) has shown more promising (pre‐)clinical results. Here, we studied the unknown mechanisms underlying the observed vaccine efficacy of SLPs. We report an in vitro processing analysis of SLPs for MHC class I and class II presentation by murine DCs and human monocyte‐derived DCs. Compared to protein, SLPs were rapidly and much more efficiently processed by DCs, resulting in an increased presentation to CD4+ and CD8+ T cells. The mechanism of access to MHC class I loading appeared to differ between the two forms of Ag. Whereas whole soluble protein Ag ended up largely in endolysosomes, SLPs were detected very rapidly outside the endolysosomes after internalization by DCs, followed by proteasome‐ and transporter associated with Ag processing‐dependent MHC class I presentation. Compared to the slower processing route taken by whole protein Ags, our results indicate that the efficient internalization of SLPs, accomplished by DCs but not by B or T cells and characterized by a different and faster intracellular routing, leads to enhanced CD8+ T‐cell activation.

Long lasting p53‐specific T cell memory responses in the absence of anti‐p53 antibodies in patients with resected primary colorectal cancer

Colorectal carcinoma is commonly associated with mutation and overexpression of p53, making this antigen a potential target for immune intervention. We analyzed humoral and proliferative immunity against p53 in the blood of patients with resected primary colorectal cancer. The majority of these patients displayed anti‐p53 T helper (Th) immunity in the absence of measurable p53 specific antibody levels. The Th responses were long‐lasting since they could be detected up to several years after resection of the primary tumor. In a number of cases the Th responses were highly sensitive, reflected by the recognition of naturally processed p53 protein. Our data argue that boosting of these responses in patients with minimal residual disease through p53‐specific vaccination, may be employed for improving the chance of disease‐free survival of these patients.

Safety of intravenous administration of a canarypox virus encoding the human wild-type p53 gene in colorectal cancer patients

Overexpression of p53 occurs in more than 50% of colorectal cancers. Therefore, p53 represents an attractive target antigen for immunotherapy. We assessed the safety of a canarypox virus encoding the human wild-type p53 gene given intravenously to end-stage colorectal cancer patients in a three-step dose escalation study aimed at inducing p53 immune responses. Patients with metastatic disease of p53-overexpressing colorectal cancers were vaccinated three times at 3-week intervals, each time with 106.5 CCID50 (CCID50=cell culture infectious dose 50%; group 1, n=5), 107.0 CCID50 (group 2, n=5) or 107.5 CCID50 (group 3, n=6). Vital signs and the occurrence of adverse events were monitored and blood was analyzed for biochemical and hematological parameters as well as signs of auto-immune safety. In all, 16 patients were enrolled and 15 patients completed three vaccinations. No anaphylactic reaction or unwanted auto-immune reactions were observed. A total of 16 serious adverse events (SAEs) occurred: 10 in group 1, three in group 2 and three in group 3. All SAEs were tumor-related complications. There was no difference in the frequency of adverse events between the three groups, except for fever. Fever was the only vaccination-related adverse event consistently observed and was most frequent and outspoken in the group 3 patients. The majority was a grade 1 or 2 fever (93%) and grade 3 fever (7%) was observed in three patients of group 3. Some patients showed humoral and cellular responses against p53, following vaccinations. After having completed his initial treatment cycle, one patient (group 2) received a second treatment cycle of three doses of 107.5 CCID50 and subsequently showed stable disease. All other patients showed progressive disease. We conclude that ALVAC-p53 can be administered intravenously to colorectal cancer patients without serious toxicity or pathological autoimmunity and can induce immune responses against p53.

Improved Innate and Adaptive Immunostimulation by Genetically Modified HIV-1 Protein Expressing NYVAC Vectors

Attenuated poxviruses are safe and capable of expressing foreign antigens. Poxviruses are applied in veterinary vaccination and explored as candidate vaccines for humans. However, poxviruses express multiple genes encoding proteins that interfere with components of the innate and adaptive immune response. This manuscript describes two strategies aimed to improve the immunogenicity of the highly attenuated, host-range restricted poxvirus NYVAC: deletion of the viral gene encoding type-I interferon-binding protein and development of attenuated replication-competent NYVAC. We evaluated these newly generated NYVAC mutants, encoding HIV-1 env, gag, pol and nef, for their ability to stimulate HIV-specific CD8 T-cell responses in vitro from blood mononuclear cells of HIV-infected subjects. The new vectors were evaluated and compared to the parental NYVAC vector in dendritic cells (DCs), RNA expression arrays, HIV gag expression and cross-presentation assays in vitro. Deletion of type-I interferon-binding protein enhanced expression of interferon and interferon-induced genes in DCs, and increased maturation of infected DCs. Restoration of replication competence induced activation of pathways involving antigen processing and presentation. Also, replication-competent NYVAC showed increased Gag expression in infected cells, permitting enhanced cross-presentation to HIV-specific CD8 T cells and proliferation of HIV-specific memory CD8 T-cells in vitro. The recombinant NYVAC combining both modifications induced interferon-induced genes and genes involved in antigen processing and presentation, as well as increased Gag expression. This combined replication-competent NYVAC is a promising candidate for the next generation of HIV vaccines.

CD27-CD70 Costimulation Controls T Cell Immunity during Acute and Persistent Cytomegalovirus Infection

ABSTRACT Cytomegaloviruses (CMVs) establish lifelong infections that are controlled in part by CD4+ and CD8+ T cells. To promote persistence, CMVs utilize multiple strategies to evade host immunity, including modulation of costimulatory molecules on infected antigen-presenting cells. In humans, CMV-specific memory T cells are characterized by the loss of CD27 expression, which suggests a critical role of the costimulatory receptor-ligand pair CD27-CD70 for the development of CMV-specific T cell immunity. In this study, the in vivo role of CD27-CD70 costimulation during mouse CMV infection was examined. During the acute phase of infection, the magnitudes of CMV-specific CD4+ and CD8+ T cell responses were decreased in mice with abrogated CD27-CD70 costimulation. Moreover, the accumulation of inflationary memory T cells during the persistent phase of infection and the ability to undergo secondary expansion required CD27-CD70 interactions. The downmodulation of CD27 expression, however, which occurs gradually and exclusively on inflationary memory T cells, is ligand independent. Furthermore, the IL-2 production in both noninflationary and inflationary CMV-specific T cells was dependent on CD27-CD70 costimulation. Collectively, these results highlight the importance of the CD27-CD70 costimulation pathway for the development of CMV-specific T cell immunity during acute and persistent infection.

Differential B7–CD28 Costimulatory Requirements for Stable and Inflationary Mouse Cytomegalovirus-Specific Memory CD8 T Cell Populations

CMV establishes a lifelong persistent infection, and viral immune-modulating strategies are important in facilitating this. A particularly diverse CD8 T cell response develops as a result of this host-virus détente, with the CMV-specific memory T cell pool displaying unique functions and phenotypes. To gain insight into the factors that regulate CMV-specific CD8 T cell responses, we examined the influence of the B7–CD28 costimulatory pathway on magnitude, kinetics, and phenotype. Initial expansion of mouse CMV-specific CD8 T cells that establish stable memory pools was severely lower in mice lacking B7–CD28 signaling, and the resulting memory levels also remained reduced during persistent/latent infection. In contrast, expansion of CD8 T cells that undergo memory inflation during chronic infection was less affected in the absence of B7–CD28 costimulatory signals, eventually reaching the levels seen in wild-type mice at later times. Regardless of their differential requirements for B7–CD28 signals, both stable and inflationary memory T cell populations showed normal cytotoxic capacity. These results reveal that B7–CD28 costimulation differentially regulates the magnitude and kinetics of the multifaceted CD8 T cell response that develops during CMV infection.

Viral inoculum dose impacts memory T-cell inflation.

Memory T‐cell inflation develops during certain persistent viral infections and is characterized by the accumulation and maintenance of large numbers of effector‐memory T cells, albeit with varying degrees in size and phenotype among infected hosts. The underlying mechanisms that control memory T‐cell inflation are not yet fully understood. Here, we dissected CMV‐specific memory T‐cell formation and its connection to the initial infectious dose by varying the inoculum size. After low dose inoculum with mouse CMV, the accumulation of inflationary memory T cells was severely hampered and correlated with reduced reservoirs of latent virus in nonhematopoietic cells and diminished antigen‐driven T‐cell proliferation. Moreover, lowering of the initial viral dose turned the characteristic effector memory‐like inflationary T cells into more central memory‐like cells as evidenced by the cell‐surface phenotype of CD27high, CD62L+, CD127+, and KLRG1−, and by improved secondary expansion potential. These data show the impact of the viral inoculum on the degree of memory T‐cell inflation and provide a rationale for the observed variation of human CMV‐specific T‐cell responses in terms of magnitude and phenotype.

Magnitude and polarization of P53-specific T-helper immunity in connection to leukocyte infiltration of colorectal tumors

The tumor antigen p53 is mutated frequently and overexpressed in colorectal cancer. As a result, patients with this type of cancer commonly display p53‐specific T‐helper (Th) immunity. Examination of the cytokines produced by these Th‐cells showed that a majority of the proliferative p53‐specific T cell cultures produced none of the key cytokines (IFNγ, TNFα, IL‐4, IL‐5 or IL‐10), indicating that these p53‐specific Th‐responses are not polarized. In patients who exhibited p53‐specific reactivity against multiple p53‐epitopes, non‐polarized responses could be found side by side with polarized Th‐responses that produced INFγ or other cytokines such as IL‐10. Patients who exhibited p53‐specific IFNγ‐producing Th cell‐immunity before surgical excision of the tumor displayed higher numbers of tumor infiltrating intraepithelial leukocytes (p = 0.04) than patients lacking such responses, suggesting that the systemic presence of p53‐specific Th‐cells positively affects local tumor‐immunity. Our data concerning the polarization‐state of p53‐specific Th immunity in colorectal cancer patients support the use of vaccine formulations that induce strong Th1‐polarized p53‐specific immunity to ensure proper (re‐)programming of the anti‐tumor response.

Polyfunctional CD4+ T Cell Responses to Immunodominant Epitopes Correlate with Disease Activity of Virulent Salmonella

Salmonella enterica serovars are intracellular bacteria capable of causing typhoid fever and gastroenteritis of significant morbidity and mortality worldwide. Current prophylactic and therapeutic treatment is hampered by the emergence of multidrug-resistant (MDR) strains of Salmonella, and vaccines provide only temporal and partial protection in vaccinees. To develop more effective Salmonella vaccines, it is important to understand the development of protective adaptive immunity to virulent Salmonella. Here we report the identification of novel CD4+ T cell peptide epitopes, which are conserved among Salmonella serovars. Immunization of Salmonella-infected mice with these peptide epitopes reduces the burden of Salmonella disease. Furthermore, we show that distinct polyfunctional (interferon-γ+, tumor necrosis factor+, and interleukin-2+) Salmonella-specific CD4+ T cell responses develop with respect to magnitude and kinetics. Moreover, we found that CD4+ T cell responses against immunodominant epitopes are predictive for active Salmonella disease. Collectively, these data could contribute to improved diagnosis of Salmonella-related diseases and rational design of Salmonella vaccines.