Detection of keyhole limpet hemocyanin (KLH)-specific immune responses by intracellular cytokine assay in patients vaccinated with idiotype-KLH vaccine

Keyhole limpet hemocyanin (KLH) has been used as an immune potentiator to enhance antigen-specific responses against haptens and weak antigens including self-antigens. In the present study, we describe the optimization of the intracellular cytokine response to KLH in peripheral blood mononuclear cells (PBMC) of lymphoma and myeloma patients that were vaccinated with tumor-specific immunoglobulin (Id) conjugated to KLH. Addition of anti-CD28 antibody significantly enhanced cytokine-producing CD4-T cells. While fresh PBMC showed maximal cytokine response 14 h after antigen stimulation, the frozen PBMC showed maximal cytokine responses by 24 h. Supplementation of the culture medium with fetal bovine serum gave a better signal-to-noise ratio than human AB serum in the intracellular detection of cytokines. The intracellular cytokine responses correlated with the cytokine measurements by enzyme-linked immunosorbent assay (ELISA). Together these results indicate that the intracellular cytokine assay is very helpful to measure antigen-specific immune responses, and in subsequent studies, we have utilized this sensitive technique to detect immune responses against tumor antigens such as idiotype.

Grass immunotherapy induces inhibition of allergen-specific human peripheral blood mononuclear cell proliferation

The peripheral blood mononuclear cells (PBMC) from humans allergic to grass pollens (GR+ subjects) show strong in vitro proliferative responses to purified allergens from Lolium perenne pollen Lol p 1, and to a lesser extent to Lol p 2 and Lol p 3. By contrast, PBMC from grass allergic patients undergoing immunotherapy (GR + IT subjects) exhibit a very poor Lol p-specific proliferative response, similar to that observed in nongrass allergic subjects (GR-subjects). Unlike GR-subjects, both GR+ and GR + IT subjects have high levels of antigen-specific serum IgG and IgE antibodies to Lol p 1, Lol p 2 and Lol p 3. While GR+ subjects exhibit a significant correlation between antigen-specific serum antibody and PBMC responses, GR + IT subjects do not show a correlation between the two responses. The possible mechanisms by which immunotherapy may modulate allergen-specific T cell proliferative response are discussed.

Gene-modified tumor cells as cellular vaccine

The identification and characterization of many tumor antigens and the parallel explosion of knowledge of the cellular and molecular mechanisms of antigen recognition by the immune system have given renewed hopes that immunogenetherapy could be a promising modality to treat certain tumors. Many different novel strategies have been developed to derive genetically modified tumor cells and use them as cellular vaccines to induce useful antitumor immunity in a variety of animal tumor models. This review discusses induction of tumor immunity by injecting tumor cells that are genetically engineered to secrete various cytokines and to express major histocompatibility complex molecules and/or costimulatory molecules. While there has been a great success in inducing excellent antitumor immunity in a variety of tumor models, there are some difficulties and limitations in the application of these gene-modified tumor cells for the treatment of preexisting tumors. A number of improvements and modifications are already underway to overcome some of these problems.

Rejection of MHC class II-transfected tumor cells requires induction of tumor-encoded B7-1 and/or B7-2 costimulatory molecules

Many tumor cells that have been transfected with genes encoding B7 costimulatory molecules become effective cellular vaccines against wild-type tumor. The improved immunity is dependent on newly induced tumor-specific CD8+ and/or CD4+ T cells and presumably occurs because the B7 transfectants provide the requisite second signal for activation of T cells in conjunction with tumor cell-presented MHC class I/tumor peptide and/or MHC class II/tumor peptide complexes, respectively. Since B7 expression is such a potent enhancer of tumor immunity, and yet some tumors are immunogenic in the absence of B7 transfection, we have used class I+ class-II-transfected tumors to investigate whether costimulatory molecules are also involved in rejection of immunogenic, non-B7-transfected tumor. Blocking studies with B7 mAbs demonstrate that induction of tumor immunity in naive mice requires B7-1 and/or B7-2 expression, while experiments with tumor-primed mice indicate that once antitumor immunity is established, expression of B7 is not necessary. Flow cytometry analyses demonstrate that costimulatory molecules are expressed by the tumor cells via an in vivo induction process. Experiments with class II genes with truncated cytoplasmic tails indicate that the cytoplasmic region of the tumor-expressed class II heterodimer is involved in induction of B7. We therefore conclude that for this class I+ class II-transfected tumor, generation of tumor immunity requires induction of tumor cell-encoded B7 molecules that are mediated by the cytoplasmic region of the transfected class II heterodimer.

Rejection of MHC class II-transfected tumor cells requires induction of tumor-encoded B7-1 and/or B7-2 costimulatory molecules

Many tumor cells that have been transfected with genes encoding B7 costimulatory molecules become effective cellular vaccines against wild-type tumor. The improved immunity is dependent on newly induced tumor-specific CD8+ and/or CD4+ T cells and presumably occurs because the B7 transfectants provide the requisite second signal for activation of T cells in conjunction with tumor cell-presented MHC class I/tumor peptide and/or MHC class II/tumor peptide complexes, respectively. Since B7 expression is such a potent enhancer of tumor immunity, and yet some tumors are immunogenic in the absence of B7 transfection, we have used class I+ class-II-transfected tumors to investigate whether costimulatory molecules are also involved in rejection of immunogenic, non-B7-transfected tumor. Blocking studies with B7 mAbs demonstrate that induction of tumor immunity in naive mice requires B7-1 and/or B7-2 expression, while experiments with tumor-primed mice indicate that once antitumor immunity is established, expression of B7 is not necessary. Flow cytometry analyses demonstrate that costimulatory molecules are expressed by the tumor cells via an in vivo induction process. Experiments with class II genes with truncated cytoplasmic tails indicate that the cytoplasmic region of the tumor-expressed class II heterodimer is involved in induction of B7. We therefore conclude that for this class I+ class II-transfected tumor, generation of tumor immunity requires induction of tumor cell-encoded B7 molecules that are mediated by the cytoplasmic region of the transfected class II heterodimer.

Expression of MHC Class II and B7-1 and B7-2 costimulatory molecules accompanies tumor rejection and reduces the metastatic potential of tumor cells

Mouse tumor cells transfected with syngeneic MHC class II genes are highly immunogenic in the autologous host, and induce a potent tumor-specific immunity against wild type tumor. Previous studies with sarcoma tumor cells expressing transfected class II gene products with truncated cytoplasmic domains suggested that during the process of tumor rejection costimulatory molecules are induced on the tumor cells, contributing to the cells' ability to stimulate immunity. In the present study we directly demonstrate that tumor cells containing full-length class II heterodimers are induced to express B7-1 and B7-2 costimulatory molecules during the rejection process. In contrast, tumor cells expressing class II heterodimers truncated for their cytoplasmic tails are not induced to express B7-1 and/or B7-2. Blocking the interaction of the induced costimulatory molecules with their corresponding receptors on T cells prevents tumor rejection. These results support the hypothesis that the cytoplasmic domain of the MHC class II molecule is involved in induction of costimulatory molecule expression, perhaps via intracellular signalling pathways. Because class II, B7 transfected tumor cells are such effective immunogens against ascites and solid tumors, they have also been tested in metastatic disease. K1735 and B16BL6 mouse melanomas, when transfected with syngeneic MHC class II and B7-1 genes, are significantly less metastatic than parental cells, and immunization with the transfectants protects against subsequent challenge with wild type tumor.

Major histocompatibility complex class II+B7-1+ tumor cells are potent vaccines for stimulating tumor rejection in tumor-bearing mice

Mice carrying large established major histocompatibility complex (MHC) class 1+ sarcoma tumors can be successfully treated by immunization with genetically engineered sarcoma cells transfected with syngeneic MHC class II plus B7-1 genes. This approach is significantly more effective than previously described strategies using cytokine- or B7-transduced tumor cells which are only effective against smaller tumor loads, and which cannot mediate regression of longer-term established tumors. The most efficient tumor rejection occurs if both the class II and B7-1 molecules are coexpressed on the same tumor cell. Immunity induced by immunization with class II+B7-1(+)-transfected sarcoma cells involves CD4+ and CD8+ T cells, suggesting that the increased effectiveness of the transfectants is due to their ability to activate both of these T cell populations.

MHC class II-transfected tumor cells induce long-term tumor-specific immunity in autologous mice

Many tumors express peptides that are potentially immunogenic; however, the host's immune system is often not sufficiently stimulated to mediate tumor rejection. The inability to mount a potent antitumor immune response has often been attributed to the lack of generation of sufficient tumor-specific T cell help. Efforts in this laboratory to improve tumor-specific immunity have therefore focused on improving the generation of tumor-reactive T helper cells. Previous studies have suggested that immunity to the murine SaI sarcoma can be significantly improved if the tumor is engineered to express syngeneic MHC class II molecules, and thereby directly present tumor peptides to Th lymphocytes. In the present study we demonstrate that vaccination with class II+ SaI transfectants results in immunity that is extremely effective against high-dose challenges of wild-type SaI tumor. The immunity induced by immunization with these transfectants is also exceptionally long-lived (greater than 6 months) and radiation resistant, suggesting that tumor-specific memory T cells are generated. The resulting immunity is specific for the immunizing tumor and protects autologous mice against challenges of both ascites and solid SaI variants. Depletion and adoptive transfer studies confirm the role of CD4+ T cells in the induced immunity, supporting the hypothesis that improving the generation of Th cells enhances the antitumor immune response. Inasmuch as irradiated or paraformaldehyde-fixed transfectants are as effective as live transfectants in stimulating tumor rejection, these genetically engineered tumor cells may serve as useful vaccines against wild-type neoplasms.

Tumor cells expressing major histocompatibility complex class II and B7 activation molecules stimulate potent tumor-specific immunity

In previous studies we have shown that the highly malignant mouse SaI sarcoma can be converted into an immunogenic tumor that is immunologically rejected by the autologous host if the tumor cells are transfected with and express syngeneic major histocompatibility complex (MHC) class II genes. Tumor cells expressing class II heterodimers truncated for the cytoplasmic regions of the alpha and beta chains, however, are as malignant as wild-type class II- tumors. These studies have contributed to the hypothesis that T-cell activation requires two signals: the engagement of the MHC class II/peptide complex of the antigen-presenting cell (APC) by the T cell receptor for antigen of the responding T cell and the transmittal of a second, or costimulatory, signal by the APC to the responding T cell. In this report we show that induction of tumor-specific immunity is facilitated by delivery of a costimulatory signal provided by the B7 activation molecule. Mice challenged with SaI cells bearing truncated class II molecules and transfected with B7 cDNA are immune to the transfectants and are protected against a challenge of wild-type class II-B7- ascites or solid SaI tumor. The induced immunity requires CD4+ T cells and is specific for the immunizing sarcoma cells. These results highlight the critical role of the B7 costimulatory pathway in stimulating long-term, tumor-specific immunity that is effective against high doses of challenging wild-type tumor and suggest a strategy for enhancing tumor rejection.

Constitutive expression of B7 restores immunogenicity of tumor cells expressing truncated major histocompatibility complex class II molecules

The inability of the autologous host to reject resident tumor cells is frequently the result of inadequate generation of tumor-specific T cells. Specific activation of T cells occurs after delivery of two signals by the antigen-presenting cell. The first signal is antigen-specific and is the engagement of the T-cell antigen receptor by a specific major histocompatibility complex antigen-peptide complex. For some T cells, the second or costimulatory signal is the interaction of the T-cell CD28 receptor with the B7 activation molecule of the antigen-presenting cell. In the present study, we demonstrate that mouse sarcoma cells genetically engineered to provide both T-cell activation signals stimulate potent tumor-specific CD4+ T cells that cause rejection of both engineered and wild-type neoplastic cells. Two other recent studies have also demonstrated that costimulation via B7 can improve tumor immunity. However, our study differs from these reports by two important observations. (i) One of these studies utilized mouse tumor cells expressing xenogenic viral antigens, and hence, the results are not applicable to wild-type resident tumors. Our study, however, demonstrates that coexpression of B7 by major histocompatibility complex class II+ tumor cells induces immunity in the autologous host that is specific for naturally occurring tumor antigens of poorly immunogenic tumors. (ii) In both earlier studies, only CD8+ T cells were activated after coexpression of B7, whereas in the present report, tumor-specific CD4+ T cells are generated. This report therefore illustrates the role of B7 activation molecule in stimulating potent tumor-specific CD4+ T cells that mediate rejection of wild-type tumors and provides a theoretical basis for immunotherapy of established tumors.

Invariant chain alters the malignant phenotype of MHC class II+ tumor cells

T lymphocytes usually recognize endogenously encoded Ag in the context of MHC class I molecules, whereas exogenous Ag is usually presented by MHC class II molecules. In vitro studies in model systems suggest that presentation of endogenous Ag by class II molecules is inhibited by the association of class II with its invariant chain (Ii). In the present study we test this hypothesis in an in vivo system in which endogenously encoded tumor peptides are presented by tumor cell MHC class II molecules. In this system, transfection of syngeneic MHC class II genes (Aak and Abk) into a highly malignant, Ii negative, mouse tumor (SaI sarcoma) produces an immunogenic tumor (SaI/Ak) that is rejected by the autologous host. The class II+ transfectants also effectively immunize autologous A/J mice against a subsequent challenge of wild-type class II- tumor cells. We have hypothesized that the SaI/Ak transfectants induce protective immunity because they function as APC for endogenously synthesized tumor peptides, and thereby stimulate tumor-specific Th cells, by-passing the need for professional APC. To test the role of Ii as an inhibitor of presentation of endogenous peptides, SaI/Ak tumor cells were supertransfected with Ii gene (SaI/Ak/Ii cells), and the tumorigenicity of the resulting cells determined. Nine SaI/Ak/Ii clones were tested, and their malignancy compared with that of SaI/Ak and SaI cells. Seven of the nine class II+/Ii+ tumor cells are more malignant than class II+/Ii- tumor cells in autologous A/J mice. Expression of Ii therefore restores the malignant phenotype, presumably by preventing presentation of endogenously synthesized tumor peptides. Ii therefore regulates Ag presentation and can be a critical parameter for in vivo tumor immunity.

Invariant chain alters the malignant phenotype of MHC class II+ tumor cells

T lymphocytes usually recognize endogenously encoded Ag in the context of MHC class I molecules, whereas exogenous Ag is usually presented by MHC class II molecules. In vitro studies in model systems suggest that presentation of endogenous Ag by class II molecules is inhibited by the association of class II with its invariant chain (Ii). In the present study we test this hypothesis in an in vivo system in which endogenously encoded tumor peptides are presented by tumor cell MHC class II molecules. In this system, transfection of syngeneic MHC class II genes (Aak and Abk) into a highly malignant, Ii negative, mouse tumor (SaI sarcoma) produces an immunogenic tumor (SaI/Ak) that is rejected by the autologous host. The class II+ transfectants also effectively immunize autologous A/J mice against a subsequent challenge of wild-type class II- tumor cells. We have hypothesized that the SaI/Ak transfectants induce protective immunity because they function as APC for endogenously synthesized tumor peptides, and thereby stimulate tumor-specific Th cells, by-passing the need for professional APC. To test the role of Ii as an inhibitor of presentation of endogenous peptides, SaI/Ak tumor cells were supertransfected with Ii gene (SaI/Ak/Ii cells), and the tumorigenicity of the resulting cells determined. Nine SaI/Ak/Ii clones were tested, and their malignancy compared with that of SaI/Ak and SaI cells. Seven of the nine class II+/Ii+ tumor cells are more malignant than class II+/Ii- tumor cells in autologous A/J mice. Expression of Ii therefore restores the malignant phenotype, presumably by preventing presentation of endogenously synthesized tumor peptides. Ii therefore regulates Ag presentation and can be a critical parameter for in vivo tumor immunity.

Human T cell responses to purified pollen allergens of the grass, Lolium perenne. Analysis of relationship between structural homology and T cell recognition

The in vitro proliferative response to purified allergens of the grass, Lolium perenne pollens was studied using PBMC from individuals allergic to grass pollens and Ag-specific T cell lines and T cell clones derived from them. The PBMC from all 10 subjects studied showed a strong response to Lol p I and most of them (8 of 10) also responded to Lol p III. Although Lol p II induced a moderate response in 4 of 10 individuals, it did not induce any response in others at all the Ag concentrations tested. However, one of the subjects (JH) responded to, besides Lol p I, both Lol p II and Lol p III equally well. Analysis of Ag-specific T cell lines and clones derived from three individuals showed varied pattern of reactivity to the Lol p allergens. Some of the Lol p III-specific T cell lines and clones were also stimulated by Lol p I and similarly, some of the Lol p I-specific T cell clones (derived from four other subjects) were stimulated by Lol p III; thus showing a two-way cross-reactivity between those T cells. In both cases, the cross-reactivity to Lol p II, when observed, was lower than that seen with Lol p I and Lol p III. Comparison of amino acid sequences of the three Lol p proteins revealed a significant level of structural similarity among them, including several segments of identical sequences. Although one of the synthetic peptides of Lol p III sharing appreciable sequence homology with other proteins stimulated PBMC from two subjects, three other peptides did not. Nevertheless, these studies indicated the possible existence of cross-reactive T cell epitope(s) among the grass pollen allergens. Based on these results, the relationship between amino acid sequence homology among the Lol p proteins and their recognition by T cells is discussed.

Human T cell responses to purified pollen allergens of the grass, Lolium perenne. Analysis of relationship between structural homology and T cell recognition

The in vitro proliferative response to purified allergens of the grass, Lolium perenne pollens was studied using PBMC from individuals allergic to grass pollens and Ag-specific T cell lines and T cell clones derived from them. The PBMC from all 10 subjects studied showed a strong response to Lol p I and most of them (8 of 10) also responded to Lol p III. Although Lol p II induced a moderate response in 4 of 10 individuals, it did not induce any response in others at all the Ag concentrations tested. However, one of the subjects (JH) responded to, besides Lol p I, both Lol p II and Lol p III equally well. Analysis of Ag-specific T cell lines and clones derived from three individuals showed varied pattern of reactivity to the Lol p allergens. Some of the Lol p III-specific T cell lines and clones were also stimulated by Lol p I and similarly, some of the Lol p I-specific T cell clones (derived from four other subjects) were stimulated by Lol p III; thus showing a two-way cross-reactivity between those T cells. In both cases, the cross-reactivity to Lol p II, when observed, was lower than that seen with Lol p I and Lol p III. Comparison of amino acid sequences of the three Lol p proteins revealed a significant level of structural similarity among them, including several segments of identical sequences. Although one of the synthetic peptides of Lol p III sharing appreciable sequence homology with other proteins stimulated PBMC from two subjects, three other peptides did not. Nevertheless, these studies indicated the possible existence of cross-reactive T cell epitope(s) among the grass pollen allergens. Based on these results, the relationship between amino acid sequence homology among the Lol p proteins and their recognition by T cells is discussed.

Competition among class II major histocompatibility molecules for presentation of tyrosine-azobenzenearsonate occurs in vivo and in vitro

We have compared by functional assays the relative preference among Ia molecules for their ability to present tyrosine-azobenzenearsonate (ABA-Tyr) to T cells. Immunization of B10.BR mice (IAk, IEk) with ABA-Tyr resulted in the induction of IAk-restricted T cells only. Immunization of B10.A(5R) mice (IAb, IEb/k) gave only IEb/k-restricted T cell clones even though IAb-restricted responses could be induced in C57BL/6 mice (IAb). These results indicated that IAk was preferred over IEk and IEb/k was preferred over IAb for presentation of ABA-Tyr. A comparison between IAk and IEb/k made by immunizing [B10.BR x B10.A(5R)]F1 mice (IAk, IEk, IAb, IEb/k), showed that IEb/k was favored over IAk. No IAb- or IEk-restricted response was seen. Further attempts were made to compare Ia preference for ABA-Tyr presentation by competitive inhibition assays. It could be shown that the presence of IEb/k molecules on an accessory cell interfered with the ability of IAb molecules on the same cell to present ABA-Tyr to an IAb-restricted T cell clone by direct competition. Such a competition was not observed between IAk and IEk. Finally, it could be shown that addition of ABA-Tyr inhibited the presentation of moth cytochrome-c peptide (81-103) by IEb/k but did not influence its presentation by IEk. From these functional studies we suggest that the binding affinity of ABA-Tyr with the Ia molecules will fall in the order: IEb/k greater than IAk greater than IAb greater than IEk.

An intracellular pathway is required for ABA-tyrosine presentation to T cells

Although tyrosine-azobenzenearsonate (ABA-Tyr) is not degraded by proteolytic enzymes, its presentation by accessory cells is inhibited by lysosomotropic agents such as chloroquine. Presentation of ABA-poly-L-glutamic, alanine, tyrosine (ABA-GAT) is similarly inhibited by chloroquine, but in contrast to ABA-Tyr it is also inhibited by leupeptin. Finally formaldehyde fixation of accessory cells after pulsing with ABA-Tyr but not before permits successful stimulation of ABA-specific hybridoma cells. These results suggest that a lysosomal pathway but not digestion is necessary for the association of ABA-Tyr and la molecules for presentation.

The presentation of L-tyrosine-azobenzenearsonate by different mouse Ia molecules uses a common agretope

The T cell response to L-tyrosine-azobenzenearsonate (ABA-tyr) has been studied using T cell lines and clones derived from three different mouse strains, B10.BR, B10.A (5R) and C57B1/6. In all cases, the arsonate group in conjunction with the amino group of tyrosine formed the functional T cell epitope. Molecules without any one or both of these groups are non-stimulatory. The hydrophobic moiety consisting of the azo-linked benzene rings forms the agretope of the molecule, as is evident from competitive inhibition of T cell stimulation by non-stimulatory analogues lacking the epitope. Substitutions on the benzene ring at ortho or meta positions resulted in decreases in ability to compete, indicating the likelihood of steric inhibition of binding of the agretope with the Ia molecule. This pattern was observed for clones and lines restricted by IAk, IAb and IEb/k MHC class II molecules. Peptides from lambda repressor protein, P84-98 and P73-88, showed haplotype specificity in their ability to inhibit ABA-tyr-induced proliferation of T cell clones, BRTC-4 and B6TC, respectively. The binding constants of ABA-tyr analogues were considered to be comparable to those of lambda repressor peptides because equimolar concentrations resulted in similar levels of competition. A cluster of aromatic amino acids on the floor of most MHC class II molecule binding sites might provide strong hydrophobic interaction with azo-linked benzene rings of ABA-tyr, thus accounting for its immunogenicity in all strains of mice studied.

Fish oil and tocopherol-induced changes in natural killer cell-mediated cytotoxicity and PGE2 synthesis in young and old mice

Natural killer cell (NK) activity decreases and prostaglandin E2 (PGE2) level increases in aged mice. Because PGE2 is involved in control of NK activity this study was conducted to investigate whether or not decreasing PGE2 level by changing the type of dietary fat or increasing the level of vitamin E (vit. E) modulates NK activity of young and old mice. Mice were fed either a corn oil (CO) or a fish oil (FO) diet supplemented with 30 or 500 mg/kg diet of vit. E for 6 wk. To study the effect of vit. E during active immune response and oxidative stress, groups of old mice fed CO and either 30 or 500 mg/kg diet of vit. E were injected with sheep red blood cells (SRBC) prior to assessment of their NK activity. As reported by others regarding mice fed a nonpurified diet, the old mice in all dietary groups had significantly less NK activity and tended to synthesize more PGE2 than young mice. FO-fed mice synthesized less PGE2 than CO-fed mice; however, their NK activity was not higher than that of CO-fed mice. By contrast young mice fed FO had a moderately lower NK activity than those fed CO. Vit. E supplementation did not change NK activity in nonimmunized mice but was effective in preventing SRBC-induced decrease in NK activity of old mice.