Programmed cell death-1 (PD-1) targeted therapies enhance T cell responses and show efficacy in multiple cancers but the role of costimulatory molecules in this T cell rescue remains elusive. Here we demonstrate that the CD28/B7 costimulatory pathway is essential for effective PD-1 therapy during chronic viral infection of mice. Conditional gene deletion showed a cell-intrinsic requirement of CD28 for CD8 T cell proliferation after PD-1 blockade. B7-costimulation was also necessary for effective PD-1 therapy in tumor-bearing mice. In addition, we found that CD8 T cells proliferating in blood after PD-1 therapy of lung cancer patients were predominantly CD28 positive. Taken together these data demonstrate CD28-costimulation requirement for CD8 T cell rescue and suggest an important role for CD28/B7 pathway in PD-1 therapy of cancer patients.

Memory CD8 T cells that circulate in the blood and are present in lymphoid organs are an essential component of long-lived T cell immunity. These resting memory CD8 T cells remain poised to rapidly elaborate effector functions upon re-exposure to pathogen, but also have many properties in common with naïve cells, including the ability to migrate to lymph nodes and spleen, and their pluri-potency. Thus, memory cells embody features of both naïve and effector cells, fueling a long-standing debate centered on whether memory T cells develop from effector cells or directly from naïve cells1–4. To better define the developmental path of memory CD8 T cells we investigated changes in DNA methylation programming at naïve and effector genes in virus specific CD8 T cells during acute LCMV infection of mice. Methylation profiling of effector CD8 T cell subsets at day 4 and 8 after infection showed that, rather than retaining a naïve epigenetic state, the subset of cells that gives rise to memory cells acquired de novo DNA methylation programs at naïve-associated genes and became demethylated at loci of classically defined effector molecules. Conditional deletion of the de novo methyltransferase, Dnmt3a, at an early stage of effector differentiation strikingly reduced methylation of naïve-associated genes and resulted in faster re-expression of these naïve genes, accelerating memory cell development. Longitudinal phenotypic and epigenetic characterization of virus-specific memory-precursor CD8 T cells transferred into antigen-free mice revealed that their differentiation into memory cells was coupled to cell-division independent erasure of de novo methylation programs and re-expression of naïve-associated genes. These data provide evidence that epigenetic repression of naïve-associated genes in effector CD8 T cells can be reversed in cells that develop into long-lived memory CD8 T cells supporting a differentiation model where memory T cells arise from a subset of fate-permissive effector T cells.

T reg cells effectively maintain CD8 T cell exhaustion during chronic LCMV infection, but blockade of PD-1 is critical for elimination of infected cells.

؉ T cell responses were further enhanced when the duration between priming and boosting was extended from 30 to 60 days. Our results demonstrate that heterologous prime-boost vaccine regimens with alternative-serotype Ad vectors elicited more functional memory CD8 ؉ T cells than any of the regimens containing Ad5. In summary, these results suggest that alternative-serotype Ad vectors will prove useful as candidates for vaccine development against human immunodeficiency virus type 1 and other pathogens and also emphasize the importance of a longer rest period between prime and boost for generating optimal CD8 ؉ T cell immunity.

Human papillomaviruses are causative agents in around 5% of all cancers, with no specific antiviral therapeutics available for treating infections or resultant cancers. In this report, we demonstrate that phosphorylation of HPV16 E2 by CK2 promotes formation of a complex with the cellular protein TopBP1 in vitro and in vivo .

BackgroundRadiotherapy (RT) has been shown to stimulate an antitumor immune response in irradiated tumors as well as unirradiated distant sites (abscopal effect). Previous studies have demonstrated a role for the tumor-draining lymph node (LN) in mediating an anti-programmed death-1 (PD-1)/programmed death ligand-1 (PD-L1) stimulated antitumor immune response. Here, we investigated whether the LN is also important in mediating a RT alone stimulated abscopal response.MethodsWe used a subcutaneous modified B16F10 flank tumor model injected bilaterally. Our B16F10 cell line has an inserted viral glycoprotein which facilitated identification of tumor-specific T-cells. RT was directed at one flank tumor alone or one flank tumor and the tumor-draining LN. We evaluated response by tumor growth measurements and flow cytometry of both tumor-infiltrating and LN T-cells.ResultsWe show that local tumor irradiation improves distant tumor control (abscopal effect). Depletion of CD8+ T-cells significantly reduced this abscopal response. We have previously shown, in a chronic lymphocytic choriomeningitis virus (LCMV) infection, that the T-cell proliferative burst following blockade of PD-1/L1 is provided by a ‘stem-like’ CD8+ T-cell subset which then differentiate into terminally differentiated effectors. These terminally differentiated effectors have the potential to kill virally infected or tumor cells following PD-1/L1 blockade. In the chronic LCMV infection, stem-like CD8+ T-cells were found exclusively in secondary lymphoid organs. Similarly, here we found these cells at high frequencies in the tumor-draining LN, but at low frequencies within the tumor. The effect of RT on this T-cell subset in unknown. Interestingly, tumor irradiation stimulated total CD8+ and stem-like CD8+ T-cell proliferation in the LN. When the LN and the tumor were then targeted with RT, the abscopal effect was reduced, and we found a concomitant reduction in the number of total tumor-specific CD8+ T-cells and stem-like CD8+ T-cells in both the irradiated and unirradiated tumor.ConclusionsThese correlative results suggest the tumor-draining LN may be an important mediator of the abscopal effect by serving as a stem-like CD8+ T-cell reservoir, a site for stem-like T-cell expansion, and a site from which they can populate the tumor.

Immunodominance limits the TCR diversity of specific antiviral CD8 T cell responses elicited by vaccination or infection. To prime multispecific T cell responses, we constructed DNA vaccines that coexpress chimeric, multidomain Ags (with CD8 T cell-defined epitopes of the hepatitis B virus (HBV) surface (S), core (C), and polymerase (Pol) proteins and/or the OVA Ag as stress protein-capturing fusion proteins. Priming of mono- or multispecific, HLA-A*0201- or Kb-restricted CD8 T cell responses by these DNA vaccines differed. Kb/OVA257–264- and Kb/S190–197-specific CD8 T cell responses did not allow priming of a Kb/C93–100-specific CD8 T cell response in mice immunized with multidomain vaccines. Tolerance to the S- Ag in transgenic Alb/HBs mice (that express large amounts of transgene-encoded S- Ag in the liver) facilitated priming of subdominant, Kb/C93–100-specific CD8 T cell immunity by multidomain Ags. The “weak” (i.e., easily suppressed) Kb/C93–100-specific CD8 T cell response was efficiently elicited by a HBV core Ag-encoding vector in 1.4HBV-Smut tg mice (that harbor a replicating HBV genome that produces HBV surface, core, and precore Ag in the liver). Kb/C93–100-specific CD8 T cells accumulated in the liver of vaccinated 1.4HBV-Smut transgenic mice where they suppressed HBV replication. Subdominant epitopes in vaccines can hence prime specific CD8 T cell immunity in a tolerogenic milieu that delivers specific antiviral effects to HBV-expressing hepatocytes.

Human herpesviruses are important causes of potentially severe chronic infections for which T cells are believed to be necessary for control. In order to examine the role of virus-specific CD8 T cells against Varicella Zoster Virus (VZV), we generated a comprehensive panel of potential epitopes predicted in silico and screened for T cell responses in healthy VZV seropositive donors. We identified a dominant HLA-A*0201-restricted epitope in the VZV ribonucleotide reductase subunit 2 and used a tetramer to analyze the phenotype and function of epitope-specific CD8 T cells. Interestingly, CD8 T cells responding to this VZV epitope also recognized homologous epitopes, not only in the other α-herpesviruses, HSV-1 and HSV-2, but also the γ-herpesvirus, EBV. Responses against these epitopes did not depend on previous infection with the originating virus, thus indicating the cross-reactive nature of this T cell population. Between individuals, the cells demonstrated marked phenotypic heterogeneity. This was associated with differences in functional capacity related to increased inhibitory receptor expression (including PD-1) along with decreased expression of co-stimulatory molecules that potentially reflected their stimulation history. Vaccination with the live attenuated Zostavax vaccine did not efficiently stimulate a proliferative response in this epitope-specific population. Thus, we identified a human CD8 T cell epitope that is conserved in four clinically important herpesviruses but that was poorly boosted by the current adult VZV vaccine. We discuss the concept of a “pan-herpesvirus” vaccine that this discovery raises and the hurdles that may need to be overcome in order to achieve this.