Identification of HTLV-1-specific CTL directed against synthetic and naturally processed peptides in HLA-B*3501 transgenic mice

Human T-cell lymphotropic virus type 1 (HTLV-1) proposed vaccines: a systematic review of preclinical and clinical studies

BACKGROUND

Numerous vaccination research experiments have been conducted on non-primate hosts to prevent or control HTLV-1 infection. Therefore, reviewing recent advancements for status assessment and strategic planning of future preventative actions to reduce HTLV-1 infection and its consequences would be essential.

METHODS

MEDLINE, Scopus, Web of Science, and Clinicaltrials.gov were searched from each database's inception through March 27, 2022. All original articles focusing on developing an HTLV-1 vaccine candidate were included.

RESULTS

A total of 47 studies were included. They used a variety of approaches to develop the HTLV-1 vaccine, including DNA-based, dendritic-cell-based, peptide/protein-based, and recombinant vaccinia virus approaches. The majority of the research that was included utilized Tax, Glycoprotein (GP), GAG, POL, REX, and HBZ as their main peptides in order to develop the vaccine. The immunization used in dendritic cell-based investigations, which were more recently published, was accomplished by an activated CD-8 T-cell response. Although there hasn't been much attention lately on this form of the vaccine, the initial attempts to develop an HTLV-1 immunization depended on recombinant vaccinia virus, and the majority of results seem positive and effective for this type of vaccine. Few studies were conducted on humans. Most of the studies were experimental studies using animal models. Adenovirus, Cytomegalovirus (CMV), vaccinia, baculovirus, hepatitis B, measles, and pox were the most commonly used vectors.

CONCLUSIONS

This systematic review reported recent progression in the development of HTLV-1 vaccines to identify candidates with the most promising preventive and therapeutic effects.

The stationary distribution and extinction of a double thresholds HTLV-I infection model with nonlinear CTL immune response disturbed by white noise

This paper investigates the stochastic HTLV-I infection model with CTL immune response, and the corresponding deterministic model has two basic reproduction numbers. We consider the nonlinear CTL immune response for the interaction between the virus and the CTL immune cells. Firstly, for the theoretical needs of system dynamical behavior, we prove that the stochastic model solution is positive and global. In addition, we obtain the existence of ergodic stationary distribution by stochastic Lyapunov functions. Meanwhile, sufficient condition for the extinction of the stochastic system is acquired. Reasonably, the dynamical behavior of deterministic model is included in our result of stochastic model when the white noise disappears.

Development of a cytotoxic T-cell assay in rabbits to evaluate early immune response to human T-lymphotropic virus type 1 infection

Human T-lymphotropic virus type 1 (HTLV-1) infection causes adult T-cell lymphoma/leukemia (ATL) following a prolonged clinical incubation period, despite a robust adaptive immune response against the virus. Early immune responses that allow establishment of the infection are difficult to study without effective animal models. We have developed a cytotoxic T-lymphocyte (CTL) assay to monitor the early events of HTLV-1 infection in rabbits. Rabbit skin fibroblast cell lines were established by transformation with a plasmid expressing simian virus 40 (SV40) large T antigen and used as autochthonous targets (derived from same individual animal) to measure CTL activity against HTLV-1 infection in rabbits. Recombinant vaccinia virus (rVV) constructs expressing either HTLV-1 envelope surface unit (SU) glycoprotein 46 or Tax proteins were used to infect fibroblast targets in a (51)Cr-release CTL assay. Rabbits inoculated with Jurkat T cells or ACH.2 cells (expressing ACH HTLV-1 molecule clone) were monitored at 0, 2, 4, 6, 8, 13, 21, and 34 wk post-infection. ACH.2-inoculated rabbits were monitored serologically and for viral infected cells following ex vivo culture. Proviral load analysis indicated that rabbits with higher proviral loads had significant CTL activity against HTLV-1 SU as early as 2 wk post-infection, while both low- and high-proviral-load groups had minimal Tax-specific CTL activity throughout the study. This first development of a stringent assay to measure HTLV-1 SU and Tax-specific CTL assay in the rabbit model will enhance immunopathogenesis studies of HTLV-1 infection. Our data suggest that during the early weeks following infection, HTLV-1-specific CTL responses are primarily targeted against Env-SU.

HLA class I transgenic mice: development, utilisation and improvement

Classical major histocompatibility complex (MHC) class I antigens are trimeric molecules found on the surface of nucleated cells in all jawed vertebrates. MHC I are recognised by two families of receptors: clonotypic T cell receptors expressed on the surface of CD8+ cytotoxic T lymphocytes (CTLs), and monomorphic receptors expressed by both natural killer cells and CTLs. The production of MHC I molecules within the cells is a sequential process performed with the help of interacting proteins: proteases, chaperones, transporters and so on. Although largely homologous in their structure, organisation and function, the human and mouse MHC I antigen processing and presentation machineries show fine differences. Transgenesis and 'knockout' or 'knock-in' technologies permit the addition of relevant human genes or the replacement of mouse genes by their human orthologues in order to produce immunologically humanised mice. Such experimental animals are especially relevant for the comparative evaluation of immunotherapies and for the characterisation of MHC I peptide epitopes. This review presents the similarities and differences between mouse and human MHC I antigen processing machinery, and describes the development and utilisation of improving mouse models of human cytotoxic T cell immunity.

Intrathymic inoculation of donor HLA class I-derived peptide generates donor-specific CD4+CD25+ regulatory T cells

CD4(+)CD25(+) regulatory T cells are selected in the thymus to control autoreactive thymic escapees preventing autoimmunity that cannot be achieved by negative selection or deletion alone, thus playing an important role in the maintenance of immunological homeostasis. Not only significant in preventing autoimmunity, CD4(+)CD25(+) regulatory T cells have also been shown to be involved in allograft tolerance in organ transplantation. We have formerly introduced two lines of HLA class I transgenic mice to elucidate the role of HLA class I molecules in transplantation biology. Using a heterotopic cardiac transplantation model, we show herein that intrathymic inoculation of donor HLA class I-derived synthetic peptide results in the generation of CD4(+)CD25(+) regulatory T cells, which induce graft specific tolerance without any preconditioning of the recipient or use of immunosuppressive drugs. This study provides evidence of the novel therapeutic potential of CD4(+)CD25(+) regulatory T cells for clinical transplantation.

Derivation of HLA-B*0702 transgenic mice: functional CTL repertoire and recognition of human B*0702-restricted CTL epitopes

Transgenic mice expressing chimeric human leukocyte antigen (HLA)-B*0702 and murine H-2K(b) class I molecules were evaluated as a model system to study the immunogenicity of human cytotoxic T lymphocyte epitopes. Immunization of these mice with six known HLA-B*0702-restricted cytotoxic T lymphocyte epitopes emulsified in incomplete Freund's adjuvant induced significant immune responses specific for all six epitopes. A comparison of the immune responses between HLA-B*0702/K(b) and HLA-A*0201/K(b) transgenic mice demonstrated that the HLA-B*0702/K(b) mice possess a T-cell receptor repertoire capable of recognizing human B*0702 epitopes. However, the magnitude of B*0702-specific responses induced in B*0702/K(b) mice were approximately tenfold lower than A*0201-specific responses induced in HLA-A*0201/K(b) transgenic mice. A panel of 24 B*0702 motif-bearing peptides was used to examine the relationship between immunogenicity and HLA-B*0702 binding capacity. All seven peptides with high binding affinities of 50% inhibitory concentration < or =50 NM (IC(50) 50 nM or less) were immunogenic. Similarly, 75% (9 of 12) of the intermediate binders (IC(50) nM of 50-500) were also immunogenic. Finally, only two of five peptides with binding capacity > 500 nM were found to have marginal immunogenicity, whereas the other three were completely negative. HLA-B*0702/K(b) transgenic mice were found to induce B*0702-specific responses after immunization with whole DNA genes or minigenes, suggesting that, at least to some degree, B*0702 epitopes were generated as a result of natural in vivo processing and presentation.

Transgenic mice expressing human HLA and CD8 molecules generate HLA-restricted measles virus cytotoxic T lymphocytes of the same specificity as humans with natural measles virus infection

Control of primary measles virus (MV) infection in humans and continued maintenance of immune memory that protects against reinfection are mediated primarily through the anti-MV T cell response, as judged by observations of children with defects in antibody formation but competency in making T cells. Further, the failure of T cell responses in those infected with MV most often leads to overwhelming infection. To better define and manipulate the elements involved in human T cell responses to MV, we analyzed the generation of HLA-restricted cytotoxic T lymphocytes (CTL) in a small animal model. Transgenic mice expressing the human class I MHC antigen HLA-B27 in conjunction with human CD8 molecules produced vigorous HLA-restricted CTL responses to MV antigens, paralleling those in MV infection of humans. In addition, such humanized mice generated human CD8 coreceptor-dependent HLA-B27-restricted CTL with the same specificity for recognition of MV fusion (F) peptide RRYPDAVYL as reported for humans during natural MV infection. Neither murine beta(2)-microglobulin nor murine CD8 substituted adequately as coreceptors for the HLA-B27 heavy chain. By contrast, HLA-A2.1-restricted responses to measles could be generated in the absence of expression of human beta(2)-microglobulin or CD8(+) molecules in HLA-A2.1/K(b) transgenic mice. Thus a small animal model is now available for studying strategies for optimizing human CD8(+) T cell responses and for testing vaccines. This model offers the potential, when combined with the newly reported CD46 transgenic mouse model in which MV replicates in cells of the immune system, for uncoding the molecular mechanism of MV-induced immunosuppression.

CD8+ T cells are necessary for recognition of allelic, but not locus-mismatched or xeno-, HLA class I transplantation antigens

Although HLA transgenic mice (HLA TgM) could provide a powerful approach to investigate human MHC-specific T cell responsiveness, the extent to which these molecules are recognized by the mouse immune system remains unclear. We established TgM expressing HLA class I alleles A2, B7, or B27 in their fully native form (HLAnat) or as hybrid molecules (HLAhyb) of the HLA alpha1/alpha2 domains linked to the H-2Kb alpha3, transmembrane, and cytoplasmic domains (i.e., to maintain possible species-specific interactions). Comparison of each as xeno- (i.e., by non-TgM) vs allo- (i.e., by TgM carrying an alternate HLA allele) transplantation Ags revealed the following: 1) Although HLAhyb molecules induced stronger xeno-CD8+ T cell responses in vitro, additional effector mechanisms must be active in vivo because HLAnat skin grafts were rejected faster by non-TgM; 2) gene knockout recipients showed that xenorejection of HLAnat and, unexpectedly, HLAhyb grafts doesn't depend on CD8+ or CD4+ T cells or B cells; 3) each HLAhyb strain developed tolerance to "self" but rejected allele- (-B27 vs -B7) and locus- (-B vs -A) mismatched grafts, the former requiring CD8+ T cells, the latter by CD8+ T cell-independent mechanisms. The finding that recognition of xeno-HLAhyb does not require CD8+ T cells while recognition of the identical molecule in a strictly allo context does, demonstrates an alpha1/alpha2 domain-dependent difference in effector mechanism(s). Furthermore, the CD8+ T cell-independence of locus-mismatched rejection suggests the degree of similarity between self and non-self alpha1/alpha2 determines the effector mechanism(s) activated. The HLA Tg model provides a unique approach to characterize these mechanisms and develop tolerance protocols in the context of human transplantation Ags.

Cell-mediated graft rejection observed in two lines of human histocompatibility leukocyte antigen class I transgenic mice

BACKGROUND

Human histocompatibility leukocyte antigen (HLA) class I molecules are essential for graft rejection. However, to determine the specific role of these molecules in clinical situations is difficult. We investigated the applicability of HLA class I transgenic mice (C3H.B35 and C3H.B51) for elucidation of the role of HLA class I molecules.

METHODS

Skin or heart grafts were transplanted. Cytotoxic T cells (CTL) of C3H.B51 against C3H.B35 were generated and their cytotoxicity against various transfectant cell lines was determined.

RESULTS

C3H.B35 skin and heart grafted to C3H.B51 were rejected within 17 and 28 days, respectively. Cytotoxic T cells generated from C3H.B51 showed cytotoxicity against a HLA-B*3501-transfectant cell line that did not express H-2 molecule, which indicates that these cytotoxic T cells recognize HLA-B35 molecules directly without H-2 restriction.

CONCLUSION

Our results suggest that C3H.B51 recognize C3H.B35 grafts as allo-MHC class I-incompatible grafts, and these mice are valuable to elucidate the role of HLA class I molecules in transplantation.

Mechanisms of T-cell activation by human T-cell lymphotropic virus type I

The interactions between human T-cell lymphotropic virus type I (HTLV-I) and the cellular immune system can be divided into viral interference with functions of the infected host T cell and the subsequent interactions between the infected T cell and the cellular immune system. HTLV-I-mediated activation of the infected host T cell is induced primarily by the viral protein Tax, which influences transcriptional activation, signal transduction pathways, cell cycle control, and apoptosis. These properties of Tax may well explain the ability of HTLV-I to immortalize T cells. It is not clear, though, how HTLV-I induces T-cell transformation (interleukin-2 [IL-2] independence). Recent evidence suggests that Tax may promote the G1- to S-phase transition, although this may involve additional proteins. A role for other viral proteins that may constitutively activate the IL-2 receptor pathway has also been suggested. By virtue of their activated state, HTLV-I-infected T cells can nonspecifically activate resting, uninfected T cells via virus-mediated upregulation of adhesion molecules. This may favor viral dissemination. Moreover, the induction of a remarkably high frequency of antiviral CD8(+) T cells does not appear to eliminate the infection. Indeed, individuals with a high frequency of virus-specific CD8(+) T cells have a high viral load, indicating a state of chronic immune system stimulation. Thus, while an activated immune system is needed to eradicate the infection, the spread of the HTLV-I is also accelerated under these conditions. A detailed knowledge of the molecular interactions between virus-specific CD8(+) T cells and immunodominant viral epitopes holds promise for the development of specific antiviral therapy.

Assessment of Immunogenicity of Human Melan-A Peptide Analogues in HLA-A*0201/Kb Transgenic Mice

Previous studies have shown that substitution of single amino acid residues in human Melan-A immunodominant peptides Melan-A27–35 and Melan-A26–35 greatly improved their binding and the stability of peptide/HLA-A*0201 complexes. In particular, one Melan-A peptide analogue was more efficient in the generation of Melan-A peptide-specific and melanoma-reactive CTL than its parental peptide in vitro from human PBL. In this study, we analyzed the in vivo immunogenicity of Melan-A natural peptides and their analogues in HLA-A*0201/Kb transgenic mice. We found that two human Melan-A natural peptides, Melan-A26–35 and Melan-A27–35, were relatively weak immunogens, whereas several Melan-A peptide analogues were potent immunogens for in vivo CTL priming. In addition, induced Melan-A peptide-specific mouse CTL cross-recognized natural Melan-A peptides and their analogues. More interestingly, these mouse CTL were also able to lyse human melanoma cell lines in vitro in a HLA-A*0201-restricted, Melan-A-specific manner. Our results indicate that the HLA-A*0201/Kb transgenic mouse is a useful animal model to perform preclinical testing of potential cancer vaccines, and that Melan-A peptide analogues are attractive candidates for melanoma immunotherapy.

The use of human leucocyte antigen class I transgenic mice to investigate human immune function

HLA class I transgenic mice are a powerful research tool which have been used as models for human immune responses. This review describes the generation of the different HLA class I transgenic mice, the techniques used to improve expression of the transgene and use of the transgene product in immune responses. It also illustrates how HLA class I transgenic mice have provided insights into the nature of the allogeneic and xenogeneic response, the generation of CTL responses, the development of autoimmune diseases, and their use for the generation of anti-HLA class I antibodies. Despite these advances, the use of available HLA class I transgenic mice as models for human disease and immune responses has been limited. The development of new transgenic strains incorporating multiple human transgenes may allow the potential of HLA class I transgenic mice to be realised.