Combined HDAC and BET inhibition to enhance cancer vaccine-elicited T-cell responses

e14632

Background: The combined inhibition of histone deacetylases (HDAC) and the proteins of the bromo and extra terminal (BET) family have recently shown therapeutic efficacy against pancreatic ductal adenocarcinoma, melanoma and lymphoma cancers in murine studies. However, in these studies the role of the immune system in therapeutically controlling these cancers was not explored. Methods: We sought to investigate the effect of the HDAC inhibitor romidepsin (RMD) and the BET inhibitor I-BET151, both singly and in combination, on vaccine elicited immune responses. C57Bl/6 mice were immunized with differing vaccines (Adenoviral, protein) in prime-boost regimens, under treatment with RMD, I-BET151, or RMD+I-BET151. Results: The combination RMD+I-BET151, administered during Adenoviral prime-boost vaccination, resulted in the significant increase in the frequency and number of antigen-specific CD8 T cells. RMD+I-BET151 treatment affected vaccine-elicited secondary T cell responses, significantly increasing the frequency of IFN-γ+ splenic CD8 T cells and maintaining their dual IFN-γ+TNFa+ polyfunctionality. These CD8 T cells maintained their protective ability against Listeria monocytogenes, and protected against B16-OVA challenge. The significant augmentation of vaccine elicited CD8 T cell responses under RMD+I-BET151 treatment was additionally observed following protein (OVA+CpG) prime-boost vaccination, resulting in greater protection against B16-OVA challenge and enhanced survival. T-regulatory cell (FoxP3+CD4+) frequency and total CD4 and CD8 cell numbers remained unaltered following RMD+I-BET151 treatment. Conclusions: Combined HDAC and BET inhibition resulted in greater vaccine-elicited CD8 T cell responses following immunization by multiple vaccine platforms, and enhanced protection against B16-OVA challenges. We are currently assessing immunological mechanisms of action for this combined HDAC and BET inhibition.

Adenovirus 5 vaccination elicits IL-27, which impairs CD4 and CD8 T cell functionality (VAC12P.1113)

In pre-clinical studies Ad26 has shown increased protective efficacy compared to Ad5. We hypothesize this is due, in part, to differences in phenotype and function of the elicited CD4 and CD8 T cell responses. Thus, our goal is to elucidate the phenotypic differences of the CD4 and CD8 T cell repertoire following Ad5 or Ad26 vaccination and the underlying mechanism. B6 mice vaccinated with Ad5 upregulate PD1 and Tim3 (p<0.01) expression on both CD4 and CD8 T cells 10 days post-immunization. On day 60, high PD1 and low CD226 expression (P<0.01) was observed following only Ad5 immunization. Ad5, but not Ad26, induced a population of regulatory CD4 T cells that co-produce IFN-γ and IL-10 (p<0.01). In Ad5 vaccinated non-human primates we also observed elevated expression of PD-1 and production of IL-10 (p<0.01), and less IL-2 expression by CD4 T cells. Mouse DCs stimulated in vitro with Ad5 showed a four-fold increase on Il27 mRNA compared to Ad26 stimulated cells. Immunization of IL-27ra KO mice with Ad5 resulted in downregulation of IL-10 (p<0.01), and up-regulation of IL-2 and CD226 (p<0.01) by CD4 T cells compared to WT. CD8 T cells from KO mice exhibited increased TNF-α and IL-2 polyfunctionality (p<0.01). These data demonstrate that Ad5 vaccination induces greater IL-27 production that drives inhibitory molecule expression and dysfunctional cytokine secretion by CD4 and CD8 T cells. These data suggest a mechanistic explanation for one reason why Ad5 is a suboptimal vector.

Temporal regulation of adenovirus vector-elicited antibody responses by CD4 T cells (VAC4P.1111)

BACKGROUND: Recombinant adenovirus (Ad) vectors have recently garnered interest as vaccine platforms to elicit robust antibody (Ab) responses. In this study we seek to determine the timing of CD4 T cell help for the induction of these Ab responses. METHODS: B6 mice were immunized intramuscularly with 1010 vp of Ad serotype 26 expressing SIVmac239 Env. Anti-CD4 Ab (GK1.5) was used to deplete CD4 T cells. Serum Env-specific IgG was quantified by ELISA. Statistical analysis was performed by Mann-Whitney U test. RESULTS: Depletion of CD4 T cells at immunization completely abolished SIV Env-specific Ab responses at day 30 post-immunization. Surprisingly, by day 60 post-immunization Env-specific IgG responses spontaneously developed in these mice, and by day 90 these responses were of equal titer to those in control mice (Endpoint titer of 18225 for untreated vs. 12150 for anti-CD4 treated mice; P=0.9). Delayed Ab responses coincided temporally with the recovery of CD4 T cells following anti-CD4 Ab treatment. Recovery of CD4 T cells was necessary for this phenomenon, as repeated administration of anti-CD4 Ab blocked the development of Env-specific Ab responses long term. CONCLUSION: These data demonstrate that CD4 T cells actively promote the development of Ad vector-elicited Ab responses even when CD4 T cells are absent at the time of immunization. These data have potential implications for the utility of Ad vectors in immunocompromised individuals, such as AIDS patients.

LCMV-specific CD4 T cells induce immunopathology and impair immune protection following chronic LCMV infection (VIR1P.1132)

CD4 T cells promote memory immune responses, but it is unclear whether vaccine-induced CD4 T cells contribute to immune protection. We interrogated if virus-specific CD4 T cells would protect mice against infection with chronic lymphocytic choriomeningitis virus (LCMV). Immunization with vaccines that induced CD4 T cell responses resulted in mortality following infection with persistent strains of LCMV. Immunopathology was associated with high levels of virus-specific CD4 T cells, generalized inflammation and collapse of adaptive immunity. Interestingly, virus-specific CD8 T cells or antibodies abrogated these lethal effects of CD4 T cell vaccines. Our data demonstrate the importance of tightly regulating CD4 T cell responses following vaccination, and suggest that CD4 T cells in the absence of effective antiviral immune responses could induce lethal immunopathology.

Aberrant differentiation and exhaustion of adenovirus vaccine-elicited CD8 T cells primed in the absence of CD4 T cells (VAC3P.940)

Replication-incompetent recombinant adenovirus (Ad) vectors have garnered considerable interest as candidate vaccine platforms for an array of diseases. However, the efficacy of such vaccines in settings of impaired CD4 T cell function remains poorly understood. We demonstrate that monoclonal antibody-mediated depletion of CD4 T cells prior to Ad immunization of C57BL/6 mice impaired expansion of responding CD8 T cells and led to aberrant differentiation and exhaustion. The absence of CD4 T cells resulted in a failure of antigen-specific CD8 T cells to differentiate into KLRG1hiCD127lo effector cells. This phenotypic defect corresponded to reduced ex vivo cytotoxicity and decreased expression of IFN-γ and TNF-α. Strikingly, CD8 T cells primed in the absence of CD4 T cells expressed elevated levels of the inhibitory molecules PD-1, LAG-3, and Tim-3. Consistent with this, these cells were identified as exhausted using gene expression profiling and gene set enrichment analysis. Blockade of PD-1 signaling by administration of anti-PDL-1 antibody at the time of immunization rescued expansion of antigen-specific CD8 T cells primed in the absence of CD4 T cells. This treatment also rescued differentiation into KLRG1hiCD127lo effector cells, and corrected defects in expression of IFN-γ and TNF-α. Collectively, these data suggest a novel mechanism of CD4 T cell help whereby CD4 T cells prevent the exhaustion of vaccine-elicited CD8 T cells by modulating PD-1 signaling during priming.

Ad5 but not Ad26 induces an IFN-γ+IL-10+ CD4+ T cell population following immunization (VAC12P.1023)

Adenovirus-based vaccines have arisen as an attractive method to elicit robust cellular and humoral immune responses. Multiple vector serotypes have been developed, but the CD4+ regulatory T cell responses generated by these vectors have not previously been compared. We therefore, compared the functionality of antigen-specific CD4+ regulatory T cells induced following Ad5 or Ad26 immunization. C57BL/6 mice were immunized intramuscularly with 1010vp of Ad5-SIVgag or Ad26-SIVgag. Spleen cells were harvest at day 10, and SIVgag-specific CD4+ regulatory T cell responses were evaluated. Immunization with 1010vp of Ad5-SIVgag induced a population of IL-10+ producing cells that comprised 30% of gag-specific IFN-γ+ CD4+ T cells. In contrast, the number of CD4+ T cells that co-produced IFN-γ and IL-10 was 8 times lower following Ad26 immunization. These cells were T-bet+ and FoxP3-. In addition, Ad5 immunization induced a substantially larger fraction of IL-10+ cells that co-express PD-1 than Ad26 immunization. Moreover, a larger fraction of IFN-γ+ CD4+ T cells were Tim-3+ following Ad5 versus Ad26 immunization. We also observed increasing frequency of IFN-γ+IL-10+ CD4+ T cells with increasing doses of Ad5. These data suggest that Ad5 vectors, but not Ad26 vectors, induce a large population of CD4+ T cells that co-produce IFN-γ and IL-10, an immunosuppressive cytokine that may potentially limit vaccine efficacy.

CD4 T cells control the induction, magnitude, and phenotype of the primary CD8 T cell response following adenovirus vector immunization (P4465)

Despite the widespread use of replication-incompetent recombinant Adenovirus (Ad) vectors as candidate vaccine platforms for the elicitation of CD8 T cell responses, the mechanism by which these vectors elicit a CD8 T cell response remains poorly understood. Our data demonstrate that the induction of a primary CD8 T cell response by Ad immunization is dependent on CD4 T cell help. CD4 and MHC class II knockout mice had substantial defects in the primary CD8 T cell response following Ad vaccination. Furthermore, The CD8 T cell response generated in the absence of CD4 T cells exhibited a less effector-like phenotype, as assessed by surface staining, cytokine production, and expression of transcription factors. The unhelped CD8 T cell population also exhibited increased apoptosis and increased PD-1 expression. Intriguingly, longitudinal removal of the CD4 T cell population by monoclonal antibody depletion demonstrated that CD4 T cell help is required for at least eight days post-immunization to facilitate normal expansion and effector differentiation of the responding CD8 T cell population. Collectively, these data suggest that CD4 T cell help is needed not only at the time of initial antigen exposure but also during the first week of induction of CD8 T cell responses. Future experiments will aim to identify the mechanism(s) by which CD4 T cell help is provided in this system.

Allograft rejection is restrained by short-lived TIM-3+PD-1+Foxp3+ Tregs

Tregs play a pivotal role in inducing and maintaining donor-specific transplant tolerance. The T cell immunoglobulin and mucin domain-3 protein (TIM-3) is expressed on many fully activated effector T cells. Along with program death 1 (PD-1), TIM-3 is used as a marker for exhausted effector T cells, and interaction with its ligand, galectin-9, leads to selective death of TIM-3+ cells. We report herein the presence of a galectin-9-sensitive CD4+FoxP3+TIM-3+ population of T cells, which arose from CD4+FoxP3+TIM-3- proliferating T cells in vitro and in vivo and were often PD-1+. These cells became very prominent among graft-infiltrating Tregs during allograft response. The frequency and number of TIM-3+ Tregs peaked at the time of graft rejection and declined thereafter. Moreover, these cells also arise in a tolerance-promoting donor-specific transfusion model, representing a pool of proliferating, donor-specific Tregs. Compared with TIM-3- Tregs, TIM-3+ Tregs, which are often PD-1+ as well, exhibited higher in vitro effector function and more robust expression of CD25, CD39, CD73, CTLA-4, IL-10, and TGF-β but not galectin-9. However, these TIM-3+ Tregs did not flourish when passively transferred to newly transplanted hosts. These data suggest that a heretofore unrecognized graft-infiltrating, short-lived subset of Tregs can restrain rejection.

In vivo imaging of Treg cells providing immune privilege to the haematopoietic stem-cell niche

Stem cells reside in a specialized regulatory microenvironment or niche, where they receive appropriate support for maintaining self-renewal and multi-lineage differentiation capacity. The niche may also protect stem cells from environmental insults including cytotoxic chemotherapy and perhaps pathogenic immunity. The testis, hair follicle and placenta are all sites of residence for stem cells and are immune-suppressive environments, called immune-privileged sites, where multiple mechanisms cooperate to prevent immune attack, even enabling prolonged survival of foreign allografts without immunosuppression. We sought to determine if somatic stem-cell niches more broadly are immune-privileged sites by examining the haematopoietic stem/progenitor cell (HSPC) niche in the bone marrow, a site where immune reactivity exists. We observed persistence of HSPCs from allogeneic donor mice (allo-HSPCs) in non-irradiated recipient mice for 30 days without immunosuppression with the same survival frequency compared to syngeneic HSPCs. These HSPCs were lost after the depletion of FoxP3 regulatory T (T(reg)) cells. High-resolution in vivo imaging over time demonstrated marked co-localization of HSPCs with T(reg) cells that accumulated on the endosteal surface in the calvarial and trabecular bone marrow. T(reg) cells seem to participate in creating a localized zone where HSPCs reside and where T(reg) cells are necessary for allo-HSPC persistence. In addition to processes supporting stem-cell function, the niche will provide a relative sanctuary from immune attack.

Allogeneic apoptotic thymocyte-stimulated dendritic cells expand functional regulatory T cells

Dendritic cells (DCs) play an important role in the clearance of apoptotic cells. The removal of apoptotic cells leads to peripheral tolerance, although their role is still not clear. We show that the uptake of apoptotic thymocytes by DCs converts these cells into tolerogenic DCs resistant to maturation by lipopolysaccharide, modulating the production of interleukin-12 and up-regulating the expression of transforming growth factor-β(1) latency associated peptide. We also observed that DCs pulsed with apoptotic cells in the allogeneic context were more efficient in the expansion of regulatory T cells (Tregs), and that this expansion requires contact between DCs and the T cell. The Tregs sorted from in vitro culture suppressed the proliferation of splenocytes in vitro in a specific and non-specific manner. In the in vivo model, the transfer of CD4(+) CD25(-) cells to Nude mice induced autoimmunity, with cell infiltrate found in the stomach, colon, liver and kidneys. The co-transfer of CD4(+) CD25(-) and CD4(+) CD25(+) prevented the presence of cell infiltrates in several organs and increased the total cell count in lymph nodes. Our data indicate that apoptotic cells have an important role in peripheral tolerance via induction of tolerogenic DCs and CD4(+) CD25(+) Foxp3(+) cells that present regulatory functions.

Maximal inflammatory response benefits syngeneic skin graft acceptance

OBJECTIVE AND DESIGN

We investigated the influence of acute inflammation in skin isograft acceptance.

METHODS

Two mouse lines selected for maximal (AIRMAX) or minimal inflammatory response (AIRMIN) were transplanted with syngeneic skin. Cellular infiltrates and cytokine production were measured 1, 3, 7 or 14 days post-transplantation. The percentage of CD4+CD25+Foxp3+ cells in the lymph nodes was also evaluated.

RESULTS

Grafts were totally accepted in 100% of AIRMAX and in 26% of AIRMIN mice. In the latter, partial acceptance was observed in 74% of the animals. Emigrated cells were basically PMN and were enhanced in AIRMAX transplants. IL-10 production by graft infiltrating cells showed no interline differences. IFN-gamma was increased in AIRMIN grafts at day 14 and lower percentages of CD4+CD25+Foxp3+ cells in the lymph nodes were observed in these mice.

CONCLUSIONS

Our data suggest that differences in graft acceptance might be due to a lack of appropriate regulation of the inflammatory response in AIRMIN mice compromising the self/non-self recognition.

Effect of Evans blue and trypan blue on syncytia formation and infectivity of human immunodeficiency virus type I and type II in vitro

Polyanionic compounds were used to inhibit infectivity of human immunodeficiency virus in vitro. Suramin, Evans blue, and Trypan blue were shown to inhibit syncytia formation normally observed when HIV-1-infected cells are cocultured with CD4+ cells. The inhibition was more pronounced with Evans blue than with any of the other polyanions studied. The inhibitory effect was significantly weaker in HIV-2 systems. However, the reverse transcriptase activities of both types of viruses were inhibited by Evans blue. Another polyanionic compound, phosphorothioate 28-mer cytidine homopolymer (SdC28) was shown to inhibit syncytium formation induced by HIV-1-and HIV-2-infected cells in an identical manner. Evans blue showed partial blocking of gp120 binding to CD4 in a solid-phase enzyme-linked immunosorbent assay (ELISA). These results suggest that the polyanionic dyes may exert their antiviral effects, at least in part, by interfering with the binding and fusion of HIV with susceptible T cells.