Spontaneous transgenesis of human B lymphocytes

Heterologous vaccination targeting prostatic acid phosphatase (PAP) using DNA and Listeria vaccines elicits superior anti-tumor immunity dependent on CD4+ T cells elicited by DNA priming

Background. Sipuleucel T, an autologous cell-based vaccine targeting prostatic acid phosphatase (PAP), has demonstrated efficacy for the treatment of advanced prostate cancer. DNA vaccines encoding PAP and live attenuated Listeria vaccines have entered clinical trials for patients with prostate cancer, and have advantages in terms of eliciting predominantly Th1-biased immunity. In this study, we investigated whether the immunogenicity and anti-tumor efficacy of a DNA and Listeria vaccine, each encoding PAP, could be enhanced by using them in a heterologous prime/boost approach. Methods. Transgenic mice expressing HLA-A2.01 and HLA-DRB1*0101 were immunized alone or with a heterologous prime/boost strategy. Splenocytes were evaluated for MHC class I and II-restricted, PAP-specific immune responses by IFNγ ELISPOTs. Anti-tumor activity to a syngeneic, PAP-expressing tumor line was evaluated. Results. PAP-specific cellular immunity and anti-tumor activity were elicited in mice after immunization with DNA- or listeria-based vaccines. Greater CD4+ and CD8+ responses, and anti-tumor responses, were elicited when mice were immunized first with DNA and boosted with Listeria, but not when administered in the opposite order. This was found to be dependent on CD4+ T cells elicited with DNA priming, and was not due to inflammatory signals by Listeria itself or due to B cells serving as antigen-presenting cells for DNA during priming. Conclusions. Heterologous prime/boost vaccination using DNA priming with Listeria boosting may provide better anti-tumor immunity, similar to many reports evaluating DNA priming with vaccines targeting foreign microbial antigens. These findings have implications for the design of future clinical trials.

B lymphocytes as direct antigen-presenting cells for anti-tumor DNA vaccines

In spite of remarkable preclinical efficacy, DNA vaccination has demonstrated low immunogenicity in humans. While efforts have focused on increasing cross-presentation of DNA-encoded antigens, efforts to increase DNA vaccine immunogenicity by targeting direct presentation have remained mostly unexplored. In these studies, we compared the ability of different APCs to present antigen to T cells after simple co-culture with plasmid DNA. We found that human primary peripheral B lymphocytes, and not monocytes or in vitro derived dendritic cells (DCs), were able to efficiently encode antigen mRNA and expand cognate tumor antigen-specific CD8 T cells ex vivo. Similarly, murine B lymphocytes co-cultured with plasmid DNA, and not DCs, were able to prime antigen-specific T cells in vivo. Moreover, B lymphocyte-mediated presentation of plasmid antigen led to greater Th1-biased immunity and was sufficient to elicit an anti-tumor effect in vivo. Surprisingly, increasing plasmid presentation by B cells, and not cross presentation of peptides by DCs, further augmented traditional plasmid vaccination. Together, these data suggest that targeting plasmid DNA to B lymphocytes, for example through transfer of ex vivo plasmidloaded B cells, may be novel means to achieve greater T cell immunity from DNA vaccines.

DNA vaccines for prostate cancer

DNA vaccines offer many advantages over other anti-tumor vaccine approaches due to their simplicity, ease of manufacturing, and safety. Results from several clinical trials in patients with cancer have demonstrated that DNA vaccines are safe and can elicit immune responses. However, to date few DNA vaccines have progressed beyond phase I clinical trial evaluation. Studies into the mechanism of action of DNA vaccines in terms of antigen-presenting cell types able to directly present or cross-present DNA-encoded antigens, and the activation of innate immune responses due to DNA itself, have suggested opportunities to increase the immunogenicity of these vaccines. In addition, studies into the mechanisms of tumor resistance to anti-tumor vaccination have suggested combination approaches that can increase the anti-tumor effect of DNA vaccines. This review focuses on these mechanisms of action and mechanisms of resistance using DNA vaccines, and how this information is being used to improve the anti-tumor effect of DNA vaccines. These approaches are then specifically discussed in the context of human prostate cancer, a disease for which DNA vaccines have been and continue to be explored as treatments.

Properties of internalization factors contributing to the uptake of extracellular DNA into tumor-initiating stem cells of mouse Krebs-2 cell line

Background

Previously, we demonstrated that poorly differentiated cells of various origins, including tumor-initiating stem cells present in the ascites form of mouse cancer cell line Krebs-2, are capable of naturally internalizing both linear double-stranded DNA and circular plasmid DNA.

Methods

The method of co-incubating Krebs-2 cells with extracellular plasmid DNA (pUC19) or TAMRA-5’-dUTP-labeled polymerase chain reaction (PCR) product was used. It was found that internalized plasmid DNA isolated from Krebs-2 can be transformed into competent Escherichia coli cells. Thus, the internalization processes taking place in the Krebs-2 cell subpopulation have been analyzed and compared, as assayed by E. coli colony formation assay (plasmid DNA) and cytofluorescence (TAMRA-DNA).

Results

We showed that extracellular DNA both in the form of plasmid DNA and a PCR product is internalized by the same subpopulation of Krebs-2 cells. We found that the saturation threshold for Krebs-2 ascites cells is 0.5 μg DNA/10⁶ cells. Supercoiled plasmid DNA, human high-molecular weight DNA, and 500 bp PCR fragments are internalized into the Krebs-2 tumor-initiating stem cells via distinct, non-competing internalization pathways. Under our experimental conditions, each cell may harbor 340–2600 copies of intact plasmid material, or up to 3.097 ± 0.044×10⁶ plasmid copies (intact or not), as detected by quantitative PCR.

Conclusion

The internalization dynamics of extracellular DNA, copy number of the plasmids taken up by the cells, and competition between different types of double-stranded DNA upon internalization into tumor-initiating stem cells of mouse ascites Krebs-2 have been comprehensively analyzed. Investigation of the extracellular DNA internalization into tumor-initiating stem cells is an important part of understanding their properties and possible destruction mechanisms. For example, a TAMRA-labeled DNA probe may serve as an instrument to develop a target for the therapy of cancer, aiming at elimination of tumor stem cells, as well as developing a straightforward test system for the quantification of poorly differentiated cells, including tumor-initiating stem cells, in the bulk tumor sample (biopsy or surgery specimen).

Microfluidic squeezing for intracellular antigen loading in polyclonal B-cells as cellular vaccines

B-cells are promising candidate autologous antigen-presenting cells (APCs) to prime antigen-specific T-cells both in vitro and in vivo. However to date, a significant barrier to utilizing B-cells as APCs is their low capacity for non-specific antigen uptake compared to “professional” APCs such as dendritic cells. Here we utilize a microfluidic device that employs many parallel channels to pass single cells through narrow constrictions in high throughput. This microscale “cell squeezing” process creates transient pores in the plasma membrane, enabling intracellular delivery of whole proteins from the surrounding medium into B-cells via mechano-poration. We demonstrate that both resting and activated B-cells process and present antigens delivered via mechano-poration exclusively to antigen-specific CD8⁺T-cells, and not CD4⁺T-cells. Squeezed B-cells primed and expanded large numbers of effector CD8⁺T-cells in vitro that produced effector cytokines critical to cytolytic function, including granzyme B and interferon-γ. Finally, antigen-loaded B-cells were also able to prime antigen-specific CD8⁺T-cells in vivo when adoptively transferred into mice. Altogether, these data demonstrate crucial proof-of-concept for mechano-poration as an enabling technology for B-cell antigen loading, priming of antigen-specific CD8⁺T-cells, and decoupling of antigen uptake from B-cell activation.

Early and repeated IgG1Fc-pCons chimera vaccinations (GX101) improve the outcome in SLE-prone mice

A previous study showed that a tolerogenic gene vaccine based on a IgG1Fc-pCons chimera (here named GX101) protects NZB/NZW mice from SLE development. The present study was aimed at identifying the most effective schedule of immunization and the possible involvement of CD4(+) Foxp3(+) Treg in the mechanism of action, in view of its eventual translation to the human studies. NZB/NZW mice were vaccinated with B lymphocytes made transgenic by spontaneous transgenesis with a gene coding for a chimeric IgG1Fc-pCons construct. Different schedules of vaccination were set in relation to the timing and number of administrations. Survival, proteinuria levels, and CD4(+) Foxp3(+) Treg frequency were monitored during the full experiments. GX101-treated mice showed delayed disease onset and delayed mortality than controls. GX101 effects were implemented by early as well as repeated vaccine administrations. GX101 vaccination was associated with increased frequencies of CD4(+) CD25(+) Foxp3(+) Treg with respect to controls. This study demonstrates that early and repeated immunizations with GX101 vaccine provide a better outcome than late or single vaccine administration regarding onset/development in SLE-prone mice, acting as a possible disease-modifying approach. Vaccine effects are likely related to CD4(+) Foxp3(+) Treg cell expansion.

CpG oligodeoxynucleotides discriminately enhance binding capacity of human naïve B cells to Hepatitis B virus epitopes

CpG oligodeoxynucleotides (CpG ODN) have the potential to enhance the antigen-presenting cells function of human naïve B cells. In this study, we aim to define the effect of CpG ODNs on the binding capacity of human naïve B cells for different Hepatitis B virus (HBV) epitopes. Three HLA-A2 restricted epitopes were selected to incubate with CpG ODN-primed human naïve B cells. Binding capacity for each epitope and expression of CD80, CD86, class I major histocompatibility complex (MHC), and class II MHC of naïve B cells was tested, respectively, by flow cytometry. CpG ODNs, especially ODN 2216, enhanced the binding capacity of human naïve B cells for HBV epitopes (p < 0.01), and induced markedly higher expression of CD80, CD86, class I MHC, and class II MHC. The binding capacity of CpG-treated naive B cells for each epitope was significantly different. In all the 3 subjects, CpG ODN 2216-primed naïve B cells showed the highest binding ability for Env172-180 compared with the other epitopes with a high expression of co-stimulatory and MHC molecules. CpG ODN showed the potential to selectively enhance the binding capacity of human naïve B cells for HBV epitopes. These results suggest new strategies for development of vaccine design.

Presentation of soluble antigens to CD8+ T cells by CpG oligodeoxynucleotide-primed human naive B cells

Naive B lymphocytes are generally thought to be poor APCs, and there is limited knowledge of their role in activation of CD8(+) T cells. In this article, we demonstrate that class I MHC Ag presentation by human naive B cells is enhanced by TLR9 agonists. Purified naive B cells were cultured with or without a TLR9 agonist (CpG oligodeoxynucleotide [ODN] 2006) for 2 d and then assessed for phenotype, endocytic activity, and their ability to induce CD8(+) T cell responses to soluble Ags. CpG ODN enhanced expression of class I MHC and the costimulatory molecule CD86 and increased endocytic activity as determined by uptake of dextran beads. Pretreatment of naive B cells with CpG ODN also enabled presentation of tetanus toxoid to CD8(+) T cells, resulting in CD8(+) T cell cytokine production and granzyme B secretion and proliferation. Likewise, CpG-activated naive B cells showed enhanced ability to cross-present CMV Ag to autologous CD8(+) T cells, resulting in proliferation of CMV-specific CD8(+) T cells. Although resting naive B cells are poor APCs, they can be activated by TLR9 agonists to serve as potent APCs for class I MHC-restricted T cell responses. This novel activity of naive B cells could be exploited for vaccine design.

Ex VivoProgramming of Antigen-Presenting B Lymphocytes: Considerations on DNA Uptake and Cell Activation

Plasmids used in DNA vaccination not only serve as a source of antigen, but also have an important adjuvant effect. This review focuses on recent advancements made in understanding how cells internalize DNA, and how internalized DNA activates immune response pathways. We also comment on the role of B cells in both of these processes.

Gene vaccination for the induction of immune tolerance

DNA vaccination is a strategy of immunization based on the injection of a gene encoding for a target protein with the goal of eliciting a potentially protective immune response in the host. Compared to traditional immunization procedures, DNA vaccination offers several advantages: increased availability of antigenic peptides because of the endogenous and long-term synthesis of the gene product, improved antigen processing and presentation, possibility of antigen structure modeling through molecular engineering, coexpression of immunologically relevant agents, and low cost of vaccine production. Although the choice of the most appropriate vector for gene transfer may still be controversial, the application of DNA vaccination to the treatment of autoimmune diseases in different experimental animal models has demonstrated the great potential of this procedure for therapeutic purposes. DNA vaccination has been successful in protecting mice from the development of organ-specific autoimmunity (experimental allergic encephalomyelitis (EAE), autoimmune diabetes, experimental arthritis, experimental uveitis) as well as systemic autoimmune disease (systemic lupus erythematosus (SLE), antiphospholipid syndrome). The protection appears to be highly influenced by the capacity of DNA vaccination to modulate immune responses affecting the Th1, Th2 and, importantly, the T cell immunoregulatory arms. We review here the experimental evidence and most recent data supporting the use of DNA vaccination in the induction of immune tolerance.

Protection against renal disease in (NZB x NZW)F(1) lupus-prone mice after somatic B cell gene vaccination with anti-DNA immunoglobulin consensus peptide

OBJECTIVE

Ig molecules contain epitopes that can induce T cell-mediated immune responses. B cells can process and present such epitopes and activate T cells. The purpose of the present study was to test our hypothesis that T cells that recognize an Ig consensus sequence presented by B cells will modulate lupus-like disease in mice.

METHODS

(NZB x NZW)F(1) (NZB/NZW) lupus mice received somatic B cell gene transfer of a DNA plasmid encoding a consensus sequence of T cell determinants of murine anti-DNA IgG or control plasmids. Treated animals were monitored for the production of antibody, the development of renal disease, and the phenotype, number, and function of T cells.

RESULTS

Treatment of mice with Ig consensus plasmid induced transforming growth factor beta-producing CD8+,CD28- T cells that suppressed the antigen-specific stimulation of CD4+ T cells in a cell-contact-independent manner, reduced antibody production, retarded the development of nephritis, and improved survival. Significantly, adoptive transfer of CD8+,CD28- T cells from protected mice into hypergammaglobulinemic NZB/NZW mice effectively protected the transferred mice from the development of renal disease.

CONCLUSION

Gene expression of anti-DNA Ig consensus sequence induces immunoregulatory T cells that delay the development of lupus nephritis by suppressing hypergammaglobulinemia and renal disease.

Plasmid DNA and IL-4 modulate expression of mHC class I and costimulatory molecules in B lymphocytes

B lymphocytes are capable of spontaneous internalization of plasmid (p)DNA, an event that set in motion the antigen-presenting function in this class of hemopoietic cells. Previously, we showed that priming of CD8 T lymphocytes by spontaneously transgenic B lymphocytes requires T-cell help, and that this can be replaced by soluble IL-4. To better understand this phenomenon we studied the relative role of pDNA and IL-4 on the expression of MHC-I and a panel of critical costimulatory molecules (CD40, CD80, CD86, OX40L, and LAG-3). Whereas upregulation of MHC-I is contributed by pDNA, IL-4 mainly upregulates CD86 and to a lesser degree CD40. The two effects appear to be independent. In addition, however, it was found that IL-4 stabilizes MHC-I transcription in lymphocytes after spontaneous transgenesis with pDNA. These results further our understanding of events that take place in specialized mammalian cells after exposure to pDNA. They also point to the fact after pDNA internalization that the antigen-presenting function of B lymphocytes can be complemented by IL-4, a cytokine normally produced by activated CD4 T cells.

Telomerase immunity from bench to bedside: round one

Telomerase, a reverse transcriptase primarily devoted to the elongation of telomeres in mammalian cells, is also the first bona fide common tumor antigen. In fact, telomerase is over-expressed in > 85% of tumor cells irrespective of origin and histological type. In the past seven years, there has been considerable interest in assessing telomerase as substrate for vaccination in cancer patients to induce CD8 T cell responses. Because the activation of T cells is restricted by the MHC molecules on antigen presenting cells or tumor cells, the identification of telomerase peptides immunogenic for humans is tightly linked with HLA types. To date, a handful of peptides have been identified through a variety of screening procedures, including bioinformatics prediction, in vivo immunization of HLA transgenic mice, in vitro immunization of PBMC from normal donors and cancer patients, and processing in human tumor cells. Currently, there exist putative peptides for five major HLA types (A2, A1, A3, A24 and B7). Due to the complexity of the HLA system, trials have been performed focusing on the most prevalent HLA type, HLA-A2. Here, we summarize this collective effort and highlight results obtained in Phase 1 trials including a Phase 1 trial performed at the UCSD Cancer Center.

TLR9-independent activation of B lymphocytes by bacterial DNA

The intracellular Toll-like receptor 9 (TLR9) is unique in its ability to recognize single-stranded DNA unmethylated at CpG motifs. Work from this laboratory showed that plasmid DNA is spontaneously internalized in B lymphocytes. This event is followed by the upregulation of costimulatory molecules and the acquisition of antigen presenting function by these cells. However, it is not known whether this phenomenon depends on TLR9. Because of the relevant role played by DNA-based drugs in immunotherapy and vaccination, and the central role of TLR9 signaling by CpG motifs, we decided to investigate whether signaling through TLR9 is a prerequisite for spontaneous transgenesis of lymphocytes. Here we found that transgene expression and upregulation of CD40 and CD86 costimulatory molecules was not inhibited by chloroquine treatment. Spontaneous transgenesis also occurred in B lymphocytes from TLR9-/- mice, and the injection of TLR9-/- transgenic B lymphocytes in C57Bl/6 mice induced both CD4 and CD8 T cell responses comparable to those induced by wild-type B lymphocytes. Collectively, these results suggest that plasmid DNA activates mammalian B lymphocytes through a TLR9 independent pathway.

Genetically programmed B lymphocytes are highly efficient in inducing anti-virus protective immunity mediated by central memory CD8 T cells

The hallmarks of specific T cell immunity include proliferative expansion, acquisition of effector function and memory T cell formation. Here, we used priming with B lymphocytes transgenic for the dominant epitope (NP366-374) of the influenza virus nucleoprotein, to study the characteristics of the CD8 T cell memory response in C57Bl/6 mice and elucidate which subset of CD8 T cells memory mediates protection from disease. We found that (i) the size of the memory CTL response is independent of the priming dose and is similar to that induced by the live virus, (ii) priming with a low dose (3 x 10(2)cells/inoculum) of transgenic B lymphocytes confers a protective memory CTL response, and (iii) protection from disease is mediated by central memory (T(CM)) CD8 T cells.

B lymphocytes as antigen-presenting cell-based genetic vaccines

Inoculation of plasmid DNA is a simple way to immunize, but it is characterized by low immunogenicity, which has hampered the development of effective DNA vaccines for human use. Here, we discuss how poor immunogenicity can be solved and present our proposal: genetically programmed B lymphocytes as antigen-presenting cell (APC) vaccines. First, we demonstrate that mature B lymphocytes take up plasmid DNA spontaneously, i.e., in the absence of any facilitating molecule or event, spontaneous lymphocyte transgenesis. Second, we demonstrate that transgenic B lymphocytes are easily and reproducibly turned into functional APCs with dual characteristics: upregulation of costimulatory molecules and endogenous synthesis of antigen. Used as immunogens in mice, transgenic B lymphocytes induce robust and long-lasting T-cell immunity after single intravenous injection. Surprisingly, immunity and protection against lethal virus challenge can be obtained with a single intravenous injection of 3 x 10(2) transgenic lymphocytes. The new approach is discussed relative to the advantage of targeting secondary lymphoid organs with genetically programmed B lymphocytes and the advantage offered with respect to low antigen dose. We suggest that these properties reflect on simple characteristics, such as time synchronization and initial localization to secondary lymphoid organs of APCs endowed with protracted synthesis and presentation of antigen to T cells.

T cell immunity using transgenic B lymphocytes

Adaptive immunity exists in all vertebrates and plays a defense role against microbial pathogens and tumors. T cell responses begin when precursor T cells recognize antigen on specialized antigen-presenting cells and differentiate into effector cells. Currently, dendritic cells are considered the only cells capable of stimulating T lymphocytes. Here, we show that mature naïve B lymphocytes can be genetically programmed by using nonviral DNA and turned into powerful antigen-presenting cells with a dual capacity of synthesis and presentation of antigen to T cells in vivo. A single i.v. injection of transgenic lymphocytes activates T cell responses reproducibly and specifically even at very low cell doses (approximately 10(2)). We also demonstrate that T cell priming can occur in the absence of dendritic cells and results in immunological memory with protective effector functions. These findings disclose aspects in the regulation of adaptive immunity and indicate possibilities for vaccination against viruses and cancer in humans.