Epitopes of the mycobacterial heat shock protein 65 for human T cells comprise different structures

Generation of anti-tumor immunity using mammalian heat shock protein 70 DNA vaccines for cancer immunotherapy

In this study, we explored the protective anti-tumor potency of mouse (self) Hsp70 or Hsp110-based DNA vaccination approach targeting a tumor-associated antigen, human papilloma virus (HPV) type 16 E7 protein. Linkage of E7 to the N-terminus of the mouse Hsp70 not only elicits an E7-specific cytotoxic T cell (CTL) response, but also protects mice against challenge with E7 expressing tumors. CD8+ T-cells are crucial in both priming and effector phases for the induction of tumor immunity, whereas CD4+ T-cells and NK cells do not appear to play a major role. Furthermore, the ATP-binding domain deletion mutant Hsp70(382-641), when fused to E7, was immunologically effective, suggesting that the peptide-binding region, not the ATPase domain of Hsp70, is required for the vaccine activity of the E7-Hsp70 DNA. This study demonstrates that autologous Hsp70 is highly potent in enhancing antigen-specific immune responses. Functional domain mapping and orientation of the E7 and Hsp70 in the fusion gene may have clinical implications for the design and optimization of Hsp70-based DNA vaccines.

Identification of promiscuous epitopes from the Mycobacterial 65-kilodalton heat shock protein recognized by human CD4(+) T cells of the Mycobacterium leprae memory repertoire

By using a synthetic peptide approach, we mapped epitopes from the mycobacterial 65-kDa heat shock protein (HSP65) recognized by human T cells belonging to the Mycobacterium leprae memory repertoire. A panel of HSP65 reactive CD4(+) T-cell lines and clones were established from healthy donors 8 years after immunization with heat-killed M. leprae and then tested for proliferative reactivity against overlapping peptides comprising both the M. leprae and Mycobacterium tuberculosis HSP65 sequences. The results showed that the antigen-specific T-cell lines and clones established responded to 12 mycobacterial HSP65 peptides, of which 9 peptides represented epitopes crossreactive between the M. tuberculosis and M. leprae HSP65 (amino acids [aa] 61 to 75, 141 to 155, 151 to 165, 331 to 345, 371 to 385, 411 to 425, 431 to 445, 441 to 455, and 501 to 515) and 3 peptides (aa 343 to 355, 417 to 429, and 522 to 534) represented M. leprae HSP65-specific epitopes. Major histocompatibility complex restriction analysis showed that presentation of 9 of the 12 peptides to T cells were restricted by one of the 2 HLA-DR molecules expressed from self HLA-DRB1 genes, whereas 3 peptides with sequences completely identical between the M. leprae and M. tuberculosis HSP65 were presented to T cells by multiple HLA-DR molecules: peptide (aa 61 to 75) was presented by HLA-DR1, -DR2, and -DR7, peptide (aa 141 to 155) was presented by HLA-DR2, -DR7, and -DR53, whereas both HLA-DR2 and -DR4 (Dw4 and Dw14) were able to present peptide (aa 501 to 515) to T cells. In addition, the T-cell lines responding to these peptides in proliferation assays showed cytotoxic activity against autologous monocytes/macrophages pulsed with the same HSP65 peptides. In conclusion, we demonstrated that promiscuous peptide epitopes from the mycobacterial HSP65 antigen can serve as targets for cytotoxic CD4(+) T cells which belong to the human memory T-cell repertoire against M. leprae. The results suggest that such epitopes might be used in the peptide-based design of subunit vaccines against mycobacterial diseases.

Immune responses to stress proteins: applications to infectious disease and cancer

Heat shock proteins, or stress proteins have been identified as part of a highly conserved cellular defence mechanism mediated by multiple, distinct gene families and corresponding gene products. As intracellular chaperones, stress proteins participate in many essential biochemical pathways of protein maturation and function active during times of stress and during normal cellular homeostasis. In addition to their well-characterized role as protein chaperones, stress proteins are now realized to possess another important biological property: immunogenicity. Stress proteins are now understood to play a fundamental role in immune surveillance of infection and malignancy and this body of basic research has provided a framework for their clinical application. As key targets of both humoral and cellular immunity during infection, stress proteins have accordingly received considerable research interest as prophylactic vaccines for infectious disease applications. The unique and potent immunostimulatory properties of stress proteins have similarly been applied to the development of new approaches to cancer therapy, including both protein and gene-based modalities.

HLA-DR4-restricted T-cell epitopes from the mycobacterial 60,000 MW heat shock protein (hsp 60) do not map to the sequence homology regions with the human hsp 60

The mycobacterial 60,000 MW heat shock protein (hsp 60) is a major antigen recognized by mycobacteria-reactive human CD4+ T cells with lymphokine profiles and effector functions consistent with protective immunity. In addition, the presence of a large number of T-cell epitopes presented by several HLA class II molecules makes this antigen relevant to subunit vaccine design. However, the results from animal models as well as human studies suggest that the mycobacterial hsp 60 may induce T-cell-mediated autoimmune conditions. In humans, the expression of HLA-DR4 represents a risk factor for some autoimmune diseases. These observations suggest that the epitopes from the mycobacterial hsp 60 presented to T cells in the context of HLA-DR4 could be relevant to autoimmunity. This is the first report on identification of HLA-DR4-restricted T-cell epitopes from the mycobacterial antigen hsp 60. In total, five epitopes recognized in the context of HLA-DR4 by the M. leprae hsp 60-reactive CD4+ T-cell clones from a subject immunized with M. leprae were defined by synthetic peptides. Two of the epitopes were M. leprae-specific (aa 343-355, aa 522-534), whereas three epitopes were common to M. leprae and M. tuberculosis (aa 331-345, aa 441-455, aa 501-515). However, all of these epitopes belong to the regions that are highly divergent between the mycobacterial hsp 60 and the homologous human hsp 60 sequence, suggesting that the T cells recognizing the mycobacterial hsp 60 in the context of HLA-DR4 may not necessarily induce autoreactivity.

Heat shock proteins as immunological carriers and vaccines

HSPs are among the major targets of the immune response to bacterial, fungal and parasitic pathogens. The antigenic nature of HSPs is emphasized by evidence that mammals are capable of recognizing multiple B- and T cell epitopes in these proteins. The powerful immunological features of HSPs have led to their experimental use as immunomodulators and as subunit vaccine candidates. Mycobacterial hsp70 and hsp60 have been found to be excellent immunological carriers of molecules against which an immune response is desired; in the absence of adjuvants, the HSPs can stimulate strong and long-lasting immune responses against molecules which have been covalently attached to the HSPs. When used as subunit vaccines, HSPs derived from a variety of bacterial and fungal pathogens have been found to stimulate protective immunity in animal models. These studies suggest that HSPs might be used as immunomodulators or subunit vaccines against infectious disease in man.

Mycobacterium tuberculosis expresses two chaperonin-60 homologs

A 65-kDa protein and a 10-kDa protein are two of the more strongly immunoreactive components of Mycobacterium tuberculosis, the causative agent of tuberculosis. The 65-kDa antigen has homology with members of the GroEL or chaperonin-60 (Cpn60) family of heat shock proteins. The 10-kDa antigen has homology with the GroES or chaperonin-10 family of heat shock proteins. These two proteins are encoded by separate genes in M. tuberculosis. The studies reported here reveal that M. tuberculosis contains a second Cpn60 homolog located 98 bp downstream of the 10-kDa antigen gene. The second Cpn60 homolog (Cpn60-1) displays 61% amino acid sequence identity with the 65-kDa antigen (Cpn60-2) and 53% and 41% identity with the Escherichia coli GroEL protein and the human P60 protein, respectively. Primer-extension analysis revealed that transcription starts 29 bp upstream of the translation start of the Cpn60-1 homolog and protein purification studies indicate that the cpn60-1 gene is expressed as an approximately 60-kDa polypeptide.

Heat-shock protein 60: implications for pathogenesis of and protection against bacterial infections

In this review we have focused on antigenic features of hsp 60 related to: its ubiquitous distribution in the biosphere; its extraordinary homology among various bacteria; its high conservation from prokaryotic to eukaryotic cells; and its abundant expression under stress situations occurring during infection. These unique features make hsp 60 an excellent candidate antigen relevant to protection and pathogenesis of bacterial infections and, perhaps in a broader sense, to surveillance and autoimmunity. We will briefly discuss these possibilities in the following. Acquired resistance. If we assume that bacterial organisms contain some thousand different proteins which all represent potential antigens, the frequency of T cells with specificity for mycobacterial hsp 60 appears surprisingly high. Although, during the course of infection, high levels of hsp may be induced in bacteria, mere abundance appears to be an important though insufficient explanation. In addition, constant boosting by similar hsp 60 cognates from various microbes with which humans come into contact may contribute to dominance. This could easily explain the occurrence of hsp 60-specific T cells in healthy individuals with no clinical history of mycobacterial infections. Involvement of more sophisticated mechanisms, such as the affinity of hsp to other proteins, cannot be excluded (Flynn et al. 1989). Yet dominance does not necessarily mean protection and definite proof that hsp are protective antigens is lacking. Perhaps the immune response against epitopes shared by various mycobacterial pathogens represents a first line of defence preceding a more specific immune response. Such broadly reactive antigens would not qualify as prime candidates for vaccine design. Immunesurveillance. T cells with specificity for epitopes shared by bacterial and human hsp 60 are readily demonstrable and stressed host cells are recognized by hsp 60-specific T cells. Such T lymphocytes are endowed with the capacity to identify host cells stressed by a variety of assaults such as inflammation, infection, trauma, or transformation. Although it has been claimed that hsp-reactive gamma/delta T cells are particularly destined for such surveillance functions (Born et al. 1990, Asarnow et al. 1988), alpha/beta T cells could also participate. Pathogenesis. The mechanisms causing pathogenesis should be similar to those underlying protection and surveillance. In the former case bacterial hsp would be responsible for both induction of immunity and expression of pathogenic reactions; in the latter case an immune response stimulated by conserved regions of bacterial hsp 60 would be converted against a host-derived cognate.(ABSTRACT TRUNCATED AT 400 WORDS)