Transfer of the ability of HIV-1 Tat to raise an adjuvant-free humoral immune response to unrelated antigens

Heparan sulfates targeting increases MHC class I- and MHC class II-restricted antigen presentation and CD8(+) T-cell response

Heparan sulfates (HS) are carbohydrate moieties of HS proteoglycans (HSPGs). They often represent alternative attachment points for proteins or microorganisms targeting receptors. HSPGs, which are ubiquitously expressed, thereby participate in numerous biological processes. We previously showed that MHC class II-restricted antigen presentation is increased when antigens are coupled to HS ligands, suggesting that HSPGs might contribute to adaptive immune responses. Here, we examined if HSPG targeting influences other aspects of immune responses. We found that coupling of an HS ligand to the antigen increases antigen presentation to CD4(+) and CD8(+) T-cells after antigen targeting to membrane immunoglobulins or to MHC-II molecules. Moreover, this increased stimulating capacity correlates with an enhanced CD8(+) immune response in mice. Last, animals control more effectively the growth of Ova-expressing tumour cells when they are immunized with an Ova construct targeting HSPGs and MHC-II molecules. Our results indicate that ubiquitous molecules can influence both MHC class I- and MHC class II-restricted antigen presentation and behave as co-receptors during T-cell stimulation. Moreover, they suggest that tumour-antigens endowed with the ability to target both HSPGs and MHC-II molecules could be of value to increase CD8(+) immune response and control tumour-growth, opening new perspectives for the design of highly immunogenic protein-based vaccines.

Production of antigen-specific human IgGs by in vitro immunization

Background

We previously developed in vitro immunization based on a fusion protein containing the transcriptional transactivator (Tat) of human immunodeficiency virus and a double domain, called ZZ, derived from protein A of Staphylococcus aureus. In this approach, naïve human peripheral blood mononuclear cells (PBMCs) trigger a specific IgM antibody (Ab) response in the presence of ZZTat. In the present study, we attempted to raise a specific IgG Ab response.

Results

We found that PBMCs incubated with ZZTat and a mixture containing anti-CD40, IL4 and IL21 secrete anti-Tat IgG Abs in their supernatants, indicating that the cytokine cocktail provides an isotypic switch. Then, we deciphered the Tat determinant involved in the phenomenon and found that it is located in the region 22–57 and that, within this region, the cysteine-rich domain and the basic residues play a crucial role. Finally, we prepared a fusion protein containing a fragment derived from the NY-ESO-1 cancer/testis antigen (Ag) and showed that PBMCs incubated with ZZfNY-ESO-1Tat trigger a specific anti-fNY-ESO-1 IgG Ab response, which demonstrates the possibility of transferring immunizing ability to an Ag unrelated to Tat.

Conclusion

Our ZZTat-based in vitro immunization approach that offers the possibility to raise an IgG Ab response against NY-ESO-1 might represent a valuable first stage for the generation of fully human IgG specific Abs.

Obtaining anti-type 1 melatonin receptor antibodies by immunization with melatonin receptor-expressing cells

Antibodies (Abs) specific to cell-surface receptors are attractive tools for studying the physiological role of such receptors or for controlling their activity. We sought to obtain such antibodies against the type 1 receptor for melatonin (MT1). For this, we injected mice with CHO cells transfected with a plasmid encoding human MT1 (CHO-MT1-h), in the presence or absence of an adjuvant mixture containing Alum and CpG1018. As we previously observed that the immune response to a protein antigen is increased when it is coupled to a fusion protein, called ZZTat101, we also investigated if the association of ZZTat101 with CHO-MT1-h cells provides an immunogenic advantage. We measured similar levels of anti-CHO and anti-MT1-h Ab responses in animals injected with either CHO-MT1-h cells or ZZTat101/CHO-MT1-h cells, with or without adjuvant, indicating that neither the adjuvant mixture nor ZZTat101 increased the anti-cell immune response. Then, we investigated whether the antisera also recognized murine MT1 (MT1-m). Using cloned CHO cells transfected with a plasmid encoding MT1-m, we found that antisera raised against CHO-MT1-h cells also bound the mouse receptor. Altogether our studies indicate that immunizing approaches based on MT1-h-expressing CHO cells allow the production of polyclonal antibodies against MT1 receptors of different origins. This paves the way to preparation of MT1-specific monoclonal antibodies.

An attenuated herpes simplex virus type 1 (HSV1) encoding the HIV-1 Tat protein protects mice from a deadly mucosal HSV1 challenge

Herpes simplex virus types 1 and 2 (HSV1 and HSV2) are common infectious agents in both industrialized and developing countries. They cause recurrent asymptomatic and/or symptomatic infections, and life-threatening diseases and death in newborns and immunocompromised patients. Current treatment for HSV relies on antiviral medications, which can halt the symptomatic diseases but cannot prevent the shedding that occurs in asymptomatic patients or, consequently, the spread of the viruses. Therefore, prevention rather than treatment of HSV infections has long been an area of intense research, but thus far effective anti-HSV vaccines still remain elusive. One of the key hurdles to overcome in anti-HSV vaccine development is the identification and effective use of strategies that promote the emergence of Th1-type immune responses against a wide range of epitopes involved in the control of viral replication. Since the HIV1 Tat protein has several immunomodulatory activities and increases CTL recognition of dominant and subdominant epitopes of heterologous antigens, we generated and assayed a recombinant attenuated replication-competent HSV1 vector containing the tat gene (HSV1-Tat). In this proof-of-concept study we show that immunization with this vector conferred protection in 100% of mice challenged intravaginally with a lethal dose of wild-type HSV1. We demonstrate that the presence of Tat within the recombinant virus increased and broadened Th1-like and CTL responses against HSV-derived T-cell epitopes and elicited in most immunized mice detectable IgG responses. In sharp contrast, a similarly attenuated HSV1 recombinant vector without Tat (HSV1-LacZ), induced low and different T cell responses, no measurable antibody responses and did not protect mice against the wild-type HSV1 challenge. These findings strongly suggest that recombinant HSV1 vectors expressing Tat merit further investigation for their potential to prevent and/or contain HSV1 infection and dissemination.

Production of human antibodies by in vitro immunization using a fusion protein containing the transcriptional transactivator of HIV-1

Antigen-specific activation of human B cells represents a key step for the production of monoclonal antibodies. Several approaches have been developed over the last thirty years in order to improve the process of lymphocyte activation in vitro. In the present study, we investigated whether the transcriptional transactivator (Tat) of human immunodeficiency virus, which possesses numerous biological activities, is able to trigger antibody secretion when incubated with human peripheral blood mononuclear cells. No such effect was observed when using Tat as a free protein. However, we found a significant IgM antibody production when Tat was previously fused to a double domain, called ZZ, derived from protein A of Staphylococcus aureus. The effect was also observed when the fusion protein, called ZZTat101, was incubated with purified B cells, indicating that the phenomenon does not require T-cell help. Antibody secretion was observed in the absence of cytokines that are usually used during in vitro immunization experiments, indicating that ZZTat101 provides the signals required for the initiation of the immune response. Antibody secretion was observed using a ZZTat mutant, containing only the Tat residues 22 to 57, called ZZTat22-57, indicating that this region is sufficient to initiate the immune response. In contrast, the effect was not found with a ZZTat22-57 mutant devoid of the seven Tat cysteines located between residues 22 and 37, demonstrating that these residues play a crucial role in the phenomenon. Our results pave the way to the development of a new in vitro immunization method based on antigens associated with ZZTat.

The effects of HIV Tat DNA on regulating the immune response of HIV DNA vaccine in mice

BACKGROUND

HIV trans-activator protein (Tat) is the crucial factor to control HIV transcription, and is usually considered as an important immunogen for the design of HIV vaccine. Recent studies reported some special bio-activities of Tat protein on immunoregulation. However, to date, few studies have focused on exploring the effects of Tat expression plasmid (pTat) on regulating the immune responses induced by HIV DNA vaccines. In this study, our main objective is to investigate the immunoregulation mediated by pTat in mice.

METHODS

Four gene-coding plasmids (pTat, pGag, pEnv and pPol) were constructed, and the gene expression was detected by western blot method. The effects of pTat on regulating the immune responses to antigens Gag, Env, Pol were assessed by enzyme-linked immunospot and enzyme-linked immunosorbent assay. The data was analysed by one-way analysis of variance.

RESULTS

After two immunizations, mice vaccinated with antigen expressing plasmid (pGag, pEnv or pPol) plus pTat exhibited significantly stronger IFN-gamma response than that vaccinated with the corresponding antigen alone. Moreover, mice receiving two injections of antigen plus pTat exhibited the same strong IFN-gamma response as those receiving three injections of antigen alone did. Furthermore, addition of pTat not only induced a more balanced Th1 and Th2 response, but also broadened IgG subclass responses to antigens Gag and Pol.

CONCLUSION

pTat exhibited the appreciable effects on modulating immune responses to HIV antigens Gag, Env and Pol, providing us interesting clues on how to optimize HIV DNA vaccine.