5'-structural analysis of genes encoding polymorphic antigens of chemically induced tumors

Tumor immunotherapy based on tumor-derived heat shock proteins (Review)

Heat shock proteins (HSPs), the most important type of molecular chaperone, are expressed in all eukaryotic cells and have multiple functions, including the folding and unfolding of other proteins and peptides, the transport of proteins and peptides and the support of antigen presentation processes. Due to these important properties, the use of HSPs has been explored as a promising tumor immunotherapy strategy. It has been previously demonstrated that HSP peptide complex (HSP.PC) derived from tumors is the immunogenic entity that elicits powerful antitumor immune responses. Previous animal studies and phase III clinical trials have demonstrated the efficacy, safety and feasibility of HSP-based tumor vaccines. However, the limitations are also apparent and specific alternatives have been developed. The present review focused on the history of HSP-based immunotherapy, the mechanism of its immunogenicity and the previous efforts to promote the efficacy. The current review may be useful for antitumor studies based on the tumor-derived HSPs.

Vaccine strategies for glioblastoma: progress and future directions

Recent advances in glioblastoma therapy have led to optimism that more effective therapies will improve outcomes. Immunotherapy is a promising approach that has demonstrated the potential to eradicate cancer cells with cellular-level accuracy while minimizing damage to surrounding healthy tissue. Several vaccination strategies have been evaluated for activity against glioblastoma in clinical trials. These include peptide vaccines, polyvalent dendritic cell vaccines, heat shock protein vaccines and adoptive immunotherapy. In this review, we highlight clinical trials representative of each of these approaches and discuss strategies for integrating these therapies into routine patient care.

Active-specific immunotherapy of human cancers with the heat shock protein Gp96-revisited

The passive administration of specific antibodies that selectively target tumors is a well-known strategy in cancer treatment. Active immunotherapy using peptide vaccines, in contrast, is expected to induce specific, cytolytic T cells in the patient, which react against tumor antigens and destroy malignant cells. Although several concepts exist, the identification and low immunogenicity of tumor-specific peptides remain a serious problem. Heat shock proteins (HSPs), notably glycoprotein (Gp) 96, are of special interest, because they are able to take molecular peptide-fingerprints of the protein array characteristic for a particular cell. Association of Gp96 with peptides has been shown to be essential for crosspresentation and activation of T cells. Consequently, Gp96-peptide complexes extracted from cancer cells harbor the tumor-specific peptides and are immunogenic, thus offering a tool for active immunization against the tumor. Already, several immunotherapy studies of human cancers have been carried out, showing no severe adverse effects but unfortunately only limited improvement in the clinical outcome. Vitespen, a commercial HSP-peptide complex vaccine based on tumor-derived Gp96, seems to induce an improved overall survival for subsets of early stage melanoma and kidney cancer patients. The limited access to vaccine material derived from the autologous tumor requires the development of alternative protocols. Moreover, counteracting immunosuppressive mechanisms induced by the malignancy might further improve the efficacy of vaccinations. This review critically analyzes the current state of clinical immunotherapy with Gp96, with special attention to Vitespen.

Heat shock protein-peptide complex in the treatment of glioblastoma

Vaccination immunotherapies offer the promise of long-term tumor control, and preclinical trials have found promising results. Active immunotherapy uses the adaptive immune response to specifically kill tumor cells. Tumor-specific antigens are processed by antigen-presenting cells and recognized by specific effector lymphocytes. However, basic vaccination strategies with tumor lysates have been unsuccessful in inducing antiglioma immunity in clinical trials. Gliomas are known to modulate the activity of antigen-presenting cells to reduce antitumor immune activity. Recently, tumor-derived heat shock proteins have been found to more effectively activate the immune response. Widely expressed, heat shock proteins are thought to present protein peptide fragments in a format conducive to processing by antigen-presenting cells. As a part of the protein synthesis machinery, peptides complexed with heat shock proteins are effectively representative of antigens expressed by the cell; these peptides convey the specificity of this vaccination strategy. The heat shock protein-peptide vaccine is one of many promising immunotherapeutic strategies being evaluated in clinical trials. These can be broadly classified as active, passive and adoptive, each with advantages and disadvantages. Here, we compare and contrast heat shock protein-peptide vaccines with other immunotherapies and describe the outcomes of clinical trials to date.

Identification of peptide mimotopes of gp96 using single-chain antibody library

Heat shock proteins such as gp96 are immunogenic and are widely used as vaccines in immunotherapy of cancers. The present study focuses on the use of peptide mimotopes as immunotherapeutic vaccines for prostate cancer. To this end, we developed a 15-mer gp96 peptide mimotope specifically reactive to MAT-LyLu gp96-peptide complex using combinatorial single-chain antibody and peptide phage display library. The immunogenicity of the synthesized gp96 mimotope was analyzed initially in normal BALB/c mice in combination with various adjuvants such as complete Freund's adjuvant (CFA), aluminum salts (ALUM), granulocyte-macrophage colony-stimulating factor (GM-CSF), and liposome, of which CFA served as a positive control. The antibody response was determined and found that the gp96 mimotope with ALUM showed a significant increase in antibody titer, followed by GM-CSF and liposomes. Further, the T cell (CD4(+) and CD8(+)) populations from splenocytes, as well as IgG isotypes, interleukin-4, and interleukin-5 of gp96 mimotope with ALUM-immunized animals, were analyzed. The results suggest that the gp96 mimotope may elicit a potent and effective antitumor antibody response. Further, the study identifies ALUM and GM-CSF as adjuvant options to drive an appropriate protective immune response as these adjuvants have prior use in humans.

Autologous renal cell cancer vaccines using heat shock protein-peptide complexes

Investigations into the role of heat shock proteins (HSPs) in immune response have progressed well into a third decade, and indications of their use for the treatment of renal cell carcinoma (RCC) in the adjuvant setting will be revealed in the near future when a randomized phase III clinical trial is completed. Additional ongoing and planned randomized clinical trials will test the efficacy of HSP-based vaccines in more advanced stages of RCC. This review describes the compelling scientific rationale behind testing HSPs in RCC against the backdrop of other immunotherapeutic approaches in this indication.

Analysis of purified gp96 preparations from rat and mouse livers using 2-D gel electrophoresis and tandem mass spectrometry

The stress protein gp96 exhibits a number of immunological activities, the majority of studies into which have used gp96 purified from a variety of tissues. On the basis of 1-D gel electrophoresis, the purity of these preparations has been reported to range between 70% and 99%. This study analyzed gp96 preparations from rat and mouse livers using 2-D gel electrophoresis and liquid chromatography electrospray ionization tandem mass spectrometry (MS-MS). The procedure for purifying gp96 was reproducible, as similar protein profiles were observed in replicate gels of gp96 preparations. The purity of the preparations was typically around 70%, with minor co-purified proteins of varying molecular weights and mobilities being present. Dominant bands at 95-100 kDa in preparations from Wistar rats and C57BL/6 mice were identified as gp96 by ECL Western blotting. Multiple bands having similar, yet distinct molecular weights and differing pI mobility on ECL Western blots were confirmed as being gp96 in preparations from Wistar rats using MS-MS. The most striking feature of the 2-D gel analysis was the presence of additional dominant bands at 55 kDa in preparations from Wistar rats, and at 75-90 kDa in preparations from C57BL/6 mice. These were identified as gp96 by ECL Western blotting and, in the case of preparations from Wistar rats, by MS-MS. Although the lower molecular weight, gp96-related molecules might be partially degraded gp96, their reproducible presence, definition and characteristics suggest that they are alternative, species-specific isoforms of the molecule. A 55 kDa protein which exhibited a lower pI value than gp96 was present in all preparations and this was identified as calreticulin, another putative immunoregulatory molecule. This study confirms the reproducibility of the gp96 purification protocol and reveals the presence of multiple gp96 isoforms, some of which likely result from post-translational modifications such as differential glycosylation and phosphorylation.

Glycoprotein (gp) 96 expression: induced during differentiation of intestinal macrophages but impaired in Crohn's disease

BACKGROUND

The glycoprotein (gp) 96 links the adaptive with the innate immune system. It is a chaperone with a binding domain for peptides generated by proteasomal degradation. During cellular stress, peptide loaded gp96 can be released and presented to T cells by antigen presenting cells (APCs).

METHODS

mRNAs from in vitro differentiated macrophages (iv mac) and normal intestinal macrophages (IMACs) were compared by subtractive hybridisation and Affymetrix GeneChip analysis. Differentiation induced expression of gp96 was investigated in the multicellular spheroid (MCS) model. In vivo gp96 protein expression was detected by double labelling immunohistochemistry of human colon and in the CD4+ CD62L+ T cell transfer mouse model.

RESULTS

Five of 76 clones obtained by subtractive hybridisation revealed >99% sequence homology to gp96. Affymetrix GeneChip analysis confirmed induction of gp96 in IMACs. Gp96 mRNA was detected in IMACs from normal and intestinal bowel disease mucosa. Induction of gp96 protein was observed after seven days in the MCS model of IMAC differentiation. Immunohistochemistry confirmed the presence of gp96 protein in IMACs in normal mucosa as well as in mucosa from patients with ulcerative colitis and diverticulitis. In mucosa from Crohn's disease (CD) patients, gp96 protein was not detectable. In the CD4+ CD62L+ T cell transfer mouse model, gp96 was verifiable in non-activated IMACs.

CONCLUSION

Gp96 is induced during differentiation of normal IMACs but is not detected in IMACs in CD mucosa. As gp96 has been described as having a role in tolerance induction, this may be relevant for loss of tolerance against luminal bacteria found in CD patients.

Re-evaluating the role of heat-shock protein-peptide interactions in tumour immunity

Early investigations into the immune surveillance of chemically-induced sarcomas led to two important concepts in tumour immunobiology: one, tumour rejection can be elicited by immune recognition of tumour antigens; and two, tumours express unique sets of antigens, which are known as tumour-specific antigens. The pioneering studies of Srivastava and colleagues led to the proposal that heat-shock proteins (HSPs) function as ubiquitous tumour-specific antigens, with the specificity residing in a population of bound peptides that identify the tissue of origin of the HSP. However, recent findings, including new data on the cell biology of peptide generation and trafficking, have called into question the specificity of tumour rejection that is induced by HSPs.

Identification of the peptide-binding site in the heat shock chaperone/tumor rejection antigen gp96 (Grp94)

Heat shock protein (HSP)-peptide complexes from tumor cells elicit specific protective immunity when injected into inbred mice bearing the same specific type of tumor. The HSP-mediated specific immunogenicity also occurs with virus-infected cells. The immune response is solely due to endogenous peptides noncovalently bound to HSP. A vesicular stomatitis virus capsid-derived peptide ligand bearing a photoreactive azido group was specifically bound by and cross-linked to murine HSP glycoprotein (gp) 96. The peptide-binding site was mapped by specific proteolysis of the cross-links followed by analysis of the cross-linked peptides using a judicious combination of SDS-gel electrophoresis, mass spectrometry, and amino acid sequencing. The minimal peptide-binding site was mapped to amino acid residues 624-630 in a highly conserved region of gp96. A model of the peptide binding pocket of gp96 was constructed based on the known crystallographic structure of major histocompatibility complex class I molecule bound to a similar peptide. The gp96-peptide model predicts that the peptide ligand is held in a groove formed by alpha-helices and lies on a surface consisting of antiparallel beta-sheets. Interestingly, in this model, the peptide binding pocket abuts the dimerization domain of gp96, which may have implications for the extraordinary stability of peptide-gp96 complexes, and for the faithful relay of peptides to major histocompatibility complex class I molecule for antigen presentation.

Cutting Edge: Tumor Secreted Heat Shock-Fusion Protein Elicits CD8 Cells for Rejection

The endoplasmic reticulum resident heat shock protein gp96 chaperons peptides, including those derived from tumor Ags, on their way to presentation by MHC class I. Replacement of the endoplasmic reticulum retention signal of gp96 with the Fc portion of murine IgG1 generated a secretory form of gp96, gp96-Ig. Tumor cells secreting gp96-Ig exhibited decreased tumorigenicity and increased immunogenicity in vivo and were rejected after initial growth. Rejection required CD8 T cells during the priming and effector phase. CD4 T cells were not required for rejection in either phase. Carrageenan, a compound known to inactivate macrophages in vivo, did not diminish CD8-mediated tumor rejection. Therefore, immunization with tumors secreting gp96-Ig generates efficient tumor-rejecting CD8 CTL without requirement for CD4 or macrophage help. In contrast, immunization with purified, tumor-derived gp96 or with irradiated tumor cells requires both.

Retroviral insertions in Evi12, a novel common virus integration site upstream of Tra1/Grp94, frequently coincide with insertions in the gene encoding the peripheral cannabinoid receptor Cnr2

The common virus integration site (VIS) Evi11 was recently identified within the gene encoding the hematopoietic G-protein-coupled peripheral cannabinoid receptor Cnr2 (also referred to as Cb2). Here we show that Cnr2 is a frequent target (12%) for insertion of Cas-Br-M murine leukemia virus (MuLV) in primary tumors in NIH/Swiss mice. Multiple provirus insertions in Evi11 were cloned and shown to be located within the 3' untranslated region of the candidate proto-oncogene Cnr2. These results suggest that proviral insertion in the Cnr2 gene is an important step in Cas-Br-M MuLV-induced leukemogenesis in NIH/Swiss mice. To isolate Evi11/Cnr2 collaborating proto-oncogenes, we searched for novel common VISs in the Cas-Br-M MuLV-induced primary tumors and identified a novel frequent common VIS, Evi12 (14%). Interestingly, 54% of the Evi11/Cnr2-rearranged primary tumors contained insertions in Evi12 as well, which suggests cooperative action of the target genes in these two common VISs in leukemogenesis. By interspecific backcross analysis it was shown that Evi12 resides on mouse chromosome 10 in a region that shares homology with human chromosomes 12q and 19p. Sequence analysis demonstrated that Evi12 is located upstream of the gene encoding the molecular chaperone Tra1/Grp94, which was previously mapped to mouse chromosome 10 and human chromosome 12q22-24. Thus, Tra1/Grp94 is a candidate target gene for retroviral activation or inactivation in Evi12. However, Northern and Western blot analyses did not provide evidence that proviral insertion had altered the expression of Tra1/Grp94. Additional studies are required to determine whether Tra1/Grp94 or another candidate proto-oncogene in Evi12 is involved in leukemogenesis.

Substrates for protein kinase CK2 in insulin receptor preparations from rat liver membranes: identification of a 210-kDa protein substrate as the dimeric form of endoplasmin

Chromatography of extracts from rat liver membranes on wheat-germ lectin-Sepharose resulted in a partial resolution of the insulin receptor from other phosphorylatable proteins. Among the latter, a protein (p210, with an apparent M(r) of 210 kDa on SDS/PAGE under nonreducing conditions) was found to be phosphorylated by protein kinase CK2 on Thr and Ser residues. Under reducing conditions p210 was resolved into two phosphopolypeptides with apparent M(r) of 95 and 105 kDa. Neither the 95-kDa nor the 105-kDa polypeptides were recognized by antibodies against the beta-subunit of the insulin receptor. Both polypeptides gave identical phosphopeptide maps after protease V8 digestion and contained the same N-terminal amino acid sequence. This sequence coincided with that of endoplasmin, and both polypeptides as well as p210 were recognized by antibodies against this protein. This shows that p210 corresponds to the dimeric form of rat liver endoplasmin. DEAE-Sepharose chromatography of p210 preparations removed most other contaminating proteins and revealed the presence of a protein kinase activity that coeluted with p210. This protein kinase possessed the properties (substrate specificity and inhibition by heparin) that are characteristic of the protein kinase CK2 enzymes. Furthermore, phosphoamino acid analysis and phosphopeptide maps of the 95/105-kDa polypeptides phosphorylated either by the endogenous protein kinase or by exogenous protein kinase CK2 gave similar results. The phosphorylation of p210/endoplasmin by protein kinase CK2 and its coelution gives support to the involvement of this protein kinase in membrane-associated processes.

Isolation of an immunodominant viral peptide that is endogenously bound to the stress protein GP96/GRP94

Heat shock protein gp96 primes class I restricted cytotoxic T cells against antigens present in the cells from which it was isolated. Moreover, gp96 derived from certain tumors functions as an effective vaccine, causing complete tumor regressions in in vivo tumor challenge protocols. Because tumor-derived gp96 did not differ from gp96 isolated from normal tissues, a role for gp96 as a peptide carrier has been proposed. To test this hypothesis, we analyzed whether such an association of antigenic peptides with gp96 occurs in a well-defined viral model system. Here we present the full characterization of an antigenic peptide that endogenously associates with the stress protein gp96 in cells infected with vesicular stomatitis virus (VSV). This peptide is identical to the immunodominant peptide of VSV, which is also naturally presented by H-2Kb major histocompatibility complex class I molecules. This peptide associates with gp96 in VSV-infected cells regardless of the major histocompatibility com- plex haplotype of the cell. Our observations provide a biochemical basis for the vaccine function of gp96.

Molecular heterogeneity of tumor rejection antigen/heat shock protein GP96

Glycoproteins of 96 kDa (gp96) have been shown to mediate tumor-specific immunogenicity of a number of murine sarcomas. The purity of gp96 preparations used in these studies was originally demonstrated by their homogeneity on silver-stained gels and the observation that a single amino acid terminus was detected by micro-sequencing. Results reported here show that gp96 preparations consist of 3-4 closely spaced bands. However, each of the bands is recognized by well-characterized monoclonal or monospecific antibodies to gp96. We have obtained purified preparations of a slowly migrating 110-kDa and a faster migrating 96-kDa band of the gp96 cluster from the Meth A sarcoma and have observed both species to be immunogenic in a dose-restricted manner. In addition to the size-based heterogeneity, purified 96-kDa molecules are found to contain 2 major populations, which share the same amino and carboxy termini but differ in the region recognized by an anti-grp94 monoclonal antibody (MAb). The heterogeneity in gp96 preparations does not result from differences in glycosylation but may result from differential phosphorylation, conformation or the antigenic peptides associated with gp96. It has been suggested that the tumor-specific immunogenicity of gp96 preparations does not derive from gp96 but from a 110-kDa protein which co-purifies with gp96 and is distinct from it. Our observations show instead that the presence of a number of bands in purified gp96 preparations is due to heterogeneity within gp96 molecules rather than to contamination with unrelated proteins.

A p16INK4a-insensitive CDK4 mutant targeted by cytolytic T lymphocytes in a human melanoma

A mutated cyclin-dependent kinase 4 (CDK4) was identified as a tumor-specific antigen recognized by HLA-A2. 1-restricted autologous cytolytic T lymphocytes (CTLs) in a human melanoma. The mutated CDK4 allele was present in autologous cultured melanoma cells and metastasis tissue, but not in the patient's lymphocytes. The mutation, an arginine-to-cysteine exchange at residue 24, was part of the CDK4 peptide recognized by CTLs and prevented binding of the CDK4 inhibitor p16INK4a, but not of p21 or of p27KIP1. The same mutation was found in one additional melanoma among 28 melanomas analyzed. These results suggest that mutation of CDK4 can create a tumor-specific antigen and can disrupt the cell-cycle regulation exerted by the tumor suppressor p16INK4a.

Autophosphorylation of grp94 (endoplasmin)

The 94-kDa glucose-regulated protein (endoplasmin, grp94) is an abundant member of the 90-kDa molecular chaperone family in the endoplasmic reticulum. We have found earlier that the 50% homologous 90-kDa heat shock protein, hsp90, has ATP-binding site(s) and autophosphorylating activity (Csermely, P., and Kahn, C. R. (1991) J. Biol. Chem. 266, 4943-4950). In the present paper we demonstrate that highly purified grp94 is also able to autophosphorylate itself on serine and threonine residues. grp94 can be freed from the co-purifying casein kinase II by concanavalin A affinity chromatography, and its phosphorylation is unaffected by activators and inhibitors of numerous protein kinases known to associate with the homologous hsp90. The autophosphorylation persists in immunoprecipitates and in SDS-polyacrylamide gel-purified and renatured grp94. Autophosphorylation displays a monomolecular kinetics, is activated by micromolar calcium concentrations, has an extreme heat stability, and can utilize both ATP and GTP with relatively high km values of 243 +/- 14 microM and 116 +/- 23 microM, respectively. Sequence analysis of grp94 shows the presence of two ATP-binding sites. The major product of limited proteolysis of grp94 by chymotrypsin or papain is an N-terminal 85-kDa fragment that can bind to ATP-agarose but does not show autophosphorylation. Our data suggest that grp94 has an enzymatic function analogous in many respects to the similar activity of hsp70, hsp90, and grp78 (BiP). Autophosphorylation may participate in/regulate the complex formation of these proteins, so it may be involved in their chaperone function.

Purification and characterization of an adenotin-like adenosine binding protein from human platelets

A low-affinity adenosine binding protein (adenotin) was purified from human platelet membranes by a four-step procedure. Purification was achieved after extraction from human platelet membranes with 0.3% 3-[3-(cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS). Further purification included Sepharose CL6B gel filtration, DEAE-Sepharose CL6B, and hydroxylapatite chromatography. The protein was purified 884-fold to homogeneity with a 25% yield of binding activity from the membranes. 5'-[8(n)-3H]-N-ethylcarboxamidoadenosine ([3H]NECA) binds to the purified protein with a KD of 155 (144-167) nmol/l and a Bmax of 1.85 +/- 0.10 nmol/mg of protein. Sodium dodecylsulfate polyacrylamide gel electrophoresis of purified protein revealed a single band at 98 kDa. The 2-chloro-substituted adenosine analogs 2-chloro-5'-N-methylcarboxamidoadenosine (CIMECA) and 2-chloro-5'-N-ethylcarboxamidoadenosine (CINECA) were identified as new high affinity ligands of the purified protein showing Ki values of 18 nmol/l and 28 nmol/l, respectively. The low-affinity adenosine binding protein showed a pharmacological profile as follows: CIMECA > 5'-N-ethylcarboxamidoadenosine (NECA) > 2-chloroadenosine (CIA) > 2-[4-(2-carboxyethyl)phenethylamino]-5'-N-ethylcarboxamidoadenosin e (CGS 21,680) > R-N6-phenylisopropyl-adenosine (R-PIA). Amino-terminal sequence analysis revealed homologies to endoplasmin, glucose regulated protein (GRP94), tumor rejection antigen precursor (GP96), and some stress related proteins.

Immunoselection of GRP94/endoplasmin from a KNRK cell-specific lambda gt11 library using antibodies directed against a putative heparanase amino-terminal peptide

Induction of an invasive phenotype by metastatic tumour cells results in part from inappropriate expression of extracellular matrix-degrading enzymes normally involved in embryonic morphogenesis, tissue remodelling, angiogenesis and wound healing. Such enzymes include endoglycosidases that degrade heparan sulfate (HS) in endothelial basement membrane, as well as better characterized proteases. Heparanase, an endo-beta-D-glucuronidase initially detected in B16 melanoma cells, has been described as a M(r) 96,000 glycoprotein with pI of 5.2, and has been immunolocalized to the cell surface and cytoplasm. We have utilized a polyacrylamide-gel-based HS degradation assay to demonstrate that KNRK, a rat kidney fibroblast cell line transformed by v-K-ras, exhibits HS-degrading activity similar to that of B16F10 mouse melanoma cells. To immunoselect heparanase-expressing clones from a KNRK-cell-specific lambda gt11 cDNA library, we have also prepared a rabbit anti-serum directed against a putative amino-terminal peptide of B16F10 cellular heparanase. Lysogens from one clone expressed a beta-galactosidase fusion protein whose staining with peptide anti-serum was inhibited by competition with excess peptide. Dideoxy-mediated sequencing of the insert termini of this recombinant revealed that it represents a rat homologue of M(r) 94,000 glucose-regulated protein (GRP94/endoplasmin), a molecular chaperone that contains the exact amino-terminal sequence previously attributed to heparanase. Our results call into question the specificity of this peptide sequence, as well as previous immunolocalization studies of heparanase carried out using such anti-sera.

Heat shock proteins transfer peptides during antigen processing and CTL priming

Recently emerging evidence indicates that the heat shock proteins (HSPs) gp96, hsp90, and hsp70 associate with antigenic peptides derived from cellular proteins. This evidence forms the basis of the following two hypotheses: 1) that HSPs constitute a relay line in which the peptides, after generation in the cytosol by the action of proteases, are transferred from one HSP to another, until they are finally accepted by MHC class I molecules in the endoplasmic reticulum, and 2) that the binding of peptides by HSPs constitutes a key step in the priming of cytotoxic T lymphocytes (CTLs) in vivo. The following chain of events is suggested: HSPs are released from virus-infected cells or tumor cells in vivo during lysis of cells during infection or by the action of antibodies or nonspecific effectors. The HSPs, which are now complexed with antigenic peptides derived from the cognate cells, are taken up by macrophage or other specialized antigen-presenting cells, possibly by a receptor-mediated mechanism. The HSP-borne peptide is then routed to the endogenous presentation pathway in the antigen-presenting cell and is displayed in the context of that cell's MHC class I, where it is finally recognized by the precursor CTLs. Thus it is suggested that, as with antigen presentation by MHC class II molecules, presentation by MHC class I molecules is also carried out primarily by the host antigen-presenting cells. This mechanism explains the phenomenon of cross-priming and has implications for the development of immunological strategies against cancer and infectious diseases.

A pathogen-induced gene of barley encodes a HSP90 homologue showing striking similarity to vertebrate forms resident in the endoplasmic reticulum

The full-length nucleotide sequence of a barley (Hordeum vulgare L.) leaf mRNA, found to increase rapidly in amount during infection attempts by the powdery mildew fungus (Erysiphe graminis DC. ex Mérat), is reported. The mRNA encodes a polypeptide of 809 amino acid residues which, by sequence comparison, was identified as a member of the 90 kDa heat shock protein (HSP90) family. The encoded protein most resembles the endoplasmic reticulum (ER) resident HSP90 protein, the 94 kDa glucose-regulated protein (GRP94) of vertebrates, as it possesses both the characteristic N-terminal domain including a signal peptide sequence and the C-terminal ER retention signal (Lys-Asp-Glu-Leu). A transcript cross-hybridizing at high stringency accumulated rapidly in leaves upon heat shock treatment. Genomic DNA blot analysis indicated the presence of a family of related genes in the barley genome.

Mapping of the genes for human endoplasmic reticular heat shock protein gp96/grp94

The murine tumor rejection antigen gp96 (TRA1, mapped to mouse chromosome 10) is a member of the heat shock protein family. Using a fragment of the murine gp96 cDNA as a probe, three gp96-related human genes have been isolated and structurally characterized. They have been mapped to human chromosomes 1 (p22), 12 (q24.2-->q24.3), and 15 (q25-->q26) by Southern blot hybridization and in situ hybridization of gene-specific probes. Only one of the genes, designated TRA1 (human chromosome 12) is a coding gene; the other genes (TRA1P1 and TRAP2) appear to be independently derived, processed pseudogenes.

Inhibition of B6RV2 leukemia growth by immunization with purified unique antigen

Monoclonal antibody (mAb) NU7-99 reacted with only B6RV2 cells, not with 28 other leukemia cell lines, fibroblasts or normal tissues. Biochemical analyses of the unique antigen on B6RV2 cells that reacted with NU7-99 mAb indicated its relationship to xenotropic murine leukemia virus gp70. The antigen that reacted with NU7-99 mAb was extracted from the surface of B6RV2 cells with n-butanol and purified by ion-exchange chromatography and affinity chromatography. Growth of B6RV2 tumors in semi-syngeneic mice was inhibited by immunization of the mice with a purified preparation of this unique antigen.

Identification and characterization of a rat protein (p 105) auto-antigenic in rats bearing a progressive syngeneic colon carcinoma

Sera from BDIX rats inoculated with 2 tumor clones derived from a single syngeneic colon carcinoma were assayed by Western blotting for the presence of antibodies against the grafted tumor. The PROb clone is progressive and produces metastases. We observed that rats bearing this tumor developed antibodies against an unglycosylated water-soluble protein of 105 kDa. The magnitude of this humoral response, as assessed by the intensity of the signal on immunoblots, was inversely correlated with survival of the rats. Furthermore, rats inoculated with the REGb clone, which is immunologically rejected, never developed detectable antibodies against the tumor. Antisera from rats injected with PROb tumor detected p105 antigen in cellular extracts from the REGb clone and from a series of rat and human cell lines. This protein was also detected in variable amounts in some normal adult and fetal tissues. Treatment of PROb or REGb cells by either interferon-gamma or heat shock did not significantly alter the expression of the p105 auto-antigen.

Stress-induced proteins in immune response to cancer

Chemically induced tumors of inbred mice elicit immunity in animals in which the tumors are induced and in other animals of the same inbred stock. The immunity is specific for each tumor: even two tumors induced in one animal with the same carcinogen are not cross-reactive. Immunity to cancer has since been observed in the case of sarcomas and carcinomas induced by a number of chemical and physical carcinogens and in several species, including mice, rats, and guinea pigs. The nature of molecules which mediate immunity to tumors is a central question in cancer immunology. A small number of such molecules have been biochemically defined. Of these, some are viral antigens expressed in tumor cells, while the relationship of some others to viral antigens is unclear. A surprising majority of nonviral tumor antigens have turned out to bear homology with stress-induced proteins. Four families of such molecules are discussed: the gp96 (hsp100) and p84/86 (hsp90) antigens of chemically induced mouse sarcomas, hsp70 antigens of tumors obtained by transfection of normal rat fetal fibroblasts with an H-ras oncogene, and the albuminoid antigens of murine melanomas and a rat histiocytoma. (Albumin-like antigens are included among the stress-induced proteins because albumin, though constitutively expressed in adult tissues, is heat shock inducible in fetal liver.) Each of these antigens is a moderately abundant protein, present not only in tumors but also in normal tissues. Administration of each of these antigen preparations from the tumor, but not from normal tissue, renders the animal immune to challenge with live cells of the tumor from which the antigens are prepared. And yet, no structural differences in the antigens have been observed between normal tissues and tumors. It is suggested that these stress-induced proteins may not be tumor antigens per se, but may be carriers of immunogenic moieties such as short peptides. The stress-induced proteins may therefore serve either as antigen-presenting molecules like the MHC-encoded molecules or as accessory molecules in the presentation of antigens by MHC molecules. The ability of stress-induced proteins to bind to a variety of molecules, including peptides, is consistent with this possibility.

Human homologue of murine tumor rejection antigen gp96: 5'-regulatory and coding regions and relationship to stress-induced proteins

Cell-surface glycoproteins of 96 kDa (gp96) have been implicated in immunogenicity of methylcholanthrene-induced mouse sarcomas in syngeneic hosts. In view of the potential immunogenicity of gp96-related molecules in human tumors, we have defined the 5'-regulatory and complete coding regions of a human gp96 transcript. The 5'-regulatory region contains an imperfect heat shock element apart from other regulatory sequences. The amino acid sequence of human gp96 is 96% homologous to its murine counterpart and genes for the two molecules show significant homology between untranslated regions. Comparison of gp96 sequences to other sequences in DNA and protein data bases indicates significant homology with the stress proteins 94-kDa glucose-regulated protein (grp94) and 108-kDa heat shock protein (hsp108) and 99-kDa endoplasmic reticular protein (ERp99). These molecules are either identical or represent a family of closely related molecules. With regard to their role in tumor immunity, it needs to be determined whether gp96 molecules are tumor antigens per se or whether they serve as carriers of other immunogenic moieties.

Soluble and membrane-associated human low-affinity adenosine binding protein (adenotin): properties and homology with mammalian and avian stress proteins

A low-affinity adenosine binding protein has recently been distinguished from the adenosine A2 receptor and purified from human placental membranes. Soluble human placental extracts contain an adenosine binding activity that has properties similar to those of the membrane low-affinity adenosine binding protein. The binding protein was purified from soluble human placental extracts 134-fold to 89% purity with a Bmax of 2.5 nmol/mg. It comprises 0.7-0.9% of the soluble protein. The major purified soluble protein has a subunit molecular mass of 98 kDa and a Stokes radius identical with that of the membrane-bound adenosine binding protein. Competition analysis of the soluble protein revealed similar affinities and an identical potency order for displacement of 5'-(N-ethylcarbamoyl)[2,8-3H]adenosine ([3H]NECA) as follows: NECA greater than 2-chloroadenosine greater than adenosine greater than (R)-N6-(2-phenylisopropyl)adenosine. The soluble binding protein was more acidic than the membrane binding protein as revealed by a comparison of the elution properties during ion exchange chromatography. A second form of soluble adenosine binding activity comprised 17% of the major form and had a charge similar to that of the membrane binding protein, a smaller Stokes radius, and a subunit molecular mass of 74 kDa. Carbohydrate composition analysis revealed that the major soluble form has 4.3% carbohydrate by weight as compared to the membrane-associated form, which has 5.5% carbohydrate by weight.(ABSTRACT TRUNCATED AT 250 WORDS)

The tumor-rejection antigens of the 1591 ultraviolet fibrosarcoma. Potential origin and evolutionary implications

Previously, we cloned and sequenced the three novel MHC class I genes expressed by the C3H UV fibrosarcoma, 1591. We have extended the analysis of the polymorphic nature of these genes relative to the C3H strain. Scattered nucleotide differences among the tumor genes as compared with the C3H H-2 and Qa sequences make it highly unlikely that the novel tumor genes were generated by recombination between endogenous C3H sequences. Given that two of the tumor clones, A149 and A166, are remarkably similar in amino acid and DNA sequence to H-2Lq and H-2Dq, respectively, we also examined the 1591 RP2 and GUS loci for evidence of polymorphism. Compared with C3H and B10.AKM, 1591 appears to be heterozygous at each of these loci, consistent with an H-2q origin for the two novel 1591 class I genes. Interestingly, the third tumor gene, designated A216, shares certain characteristics with the H-2Ks antigen, reminiscent of the naturally occurring combination of H-2Ks, H-2Dq, and H-2Lq antigens found in some Swiss mouse strains. As a result, we propose that the non-C3H/HeN characteristics displayed by the 1591 tumor point to a non-C3H origin for the novel tumor class I genes of 1591.

The expression of tumor rejection antigen on rat fetus fibroblasts transformed by the ras oncogene

The expression of tumor rejection antigens (TRA) was analyzed on clones of rat fetus-derived fibroblasts, WFB, transformed or transfected by oncogenes. It was shown that a tumorigenic W14 clone, which is an activated H-ras transformant of parental WFB, expressed TRA in transplantation experiments using syngeneic WKA rats. The data also showed that W14 TRA was acquired in the event of cell transformation, since it was not detected on parental non-transformed WFB cells or Wmyc-4 clone which is a transfectant of WFB by mouse plasmacytoma-derived c-myc DNA. However, TRA was not expressed or at least was not detected on highly tumorigenic W31, another clone of H-ras transformants of parental WFB, in the transplantation experiments. We also assessed the level of expression of major histocompatibility antigens (MHC) class I molecules on these cells by using R4-8B1 Mab that reacts specifically with rat class I antigen. The data indicated that it was decreased on W14, W31, and Wmyc-4, but not on parental WFB. Although this molecule was weakly positive on W14 cells, W31 and Wmyc-4 showed even greater decreases. These data may indicate that the TRA expression and its recognition by syngeneic hosts are dependent upon the transformed clones, although their parental cell is the same. We discuss in detail this difference of expression and recognition of TRA in the context of the cell transforming process.

Immunogenic (tum-) variants of mouse tumor P815: cloning of the gene of tum- antigen P91A and identification of the tum- mutation

Mutagen treatment of mouse P815 tumor cells produces tum- variants that are rejected by syngeneic mice because these variants express new surface antigens. These "tum- antigens" are recognized by cytolytic T lymphocytes but induce no detectable antibody response. Transfection of P815 cell line P1.HTR with DNA of tum- variant P91 yielded transfectants expressing tum- antigen P91A. They were detected by their ability to stimulate proliferation of cytolytic T lymphocytes [Wölfel, T., Van Pel, A., De Plaen, E., Lurquin, C., Maryanski, J. L. & Boon, T. (1987) Immunogenetics 26, 178-187]. A cosmid library of a cell line expressing antigen P91A was transfected into P1.HTR. Transfectants expressing the antigen were obtained. By packaging directly the DNA of a transfectant with lambda phage extracts, we obtained a small cosmid population containing as major component a cosmid that transferred the expression of P91A. The assay of various restriction fragments of this cosmid led to the isolation of an 800-base-pair fragment containing the P91A sequence required for transfection. Comparison with a homologous cDNA showed that this fragment contained only one of the several exons of the P91A gene. The normal and the tum- forms of the gene differ by one nucleotide located in this 137-base-pair exon. The essential role of this mutation, which produces an amino acid change, was confirmed by site-directed mutagenesis. No significant sequence similarity was found between the 800-base-pair fragment and any recorded gene.