Recognition of autoantigens by patients with melanoma

A DNA vaccine for multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) is a disease in which safety is of paramount importance when developing a potential therapeutic. Antigen-specific treatments provide a method for achieving efficacy while maintaining safety. DNA vaccines are one such form of treatment that have been tested in clinical trials

OBJECTIVE

To determine if a DNA vaccine is a viable method of antigen-specific treatment of MS.

RESULTS/CONCLUSION

Phase I and II trials of BHT-3009, a DNA vaccine encoding myelin basic protein, demonstrated that it was safe, well-tolerated, and caused antigen-specific immune tolerance. BHT-3009 showed efficacy in reducing brain lesion activity as well as clinical relapses in patients that were immunologically active at baseline. BHT-3009 is a promising therapy in development for MS, and may prove to be one of the first antigen-specific treatments for this disease.

Adoptive T-Cell Therapy of Cancer

Adoptive therapy involves the transfer of ex vivo expanded immune effector cells to patients as a means of augmenting the antitumor immune response. In general, this transfer is accomplished by harvesting cells from the peripheral blood, tumor sites, or draining lymph nodes and expanding effector cells in a specific or nonspecific fashion for adoptive transfer. This article describes the rationale for adoptive T-cell therapy, the developments that have led to the translational application of this strategy for the treatment of cancer, the challenges that have been addressed, and future approaches to the development of adoptive therapy as a treatment modality.

A single heteroclitic epitope determines cancer immunity after xenogeneic DNA immunization against a tumor differentiation antigen

Successful active immunization against cancer requires induction of immunity against self or mutated self Ags. However, immunization against self Ags is difficult. Xenogeneic immunization with orthologous Ags induces cancer immunity. The present study evaluated the basis for immunity induced by active immunization against a melanoma differentiation Ag, gp100. Tumor rejection of melanoma was assessed after immunization with human gp100 (hgp100) DNA compared with mouse gp100 (mgp100). C57BL/6 mice immunized with xenogeneic full-length hgp100 DNA were protected against syngeneic melanoma challenge. In contrast, mice immunized with hgp100 DNA and given i.p. tolerizing doses of the hgp100 D(b)-restricted peptide, hgp100(25-33), were incapable of rejecting tumors. Furthermore, mice immunized with DNA constructs of hgp100 in which the hgp100(25-27) epitope was substituted with the weaker D(b)-binding epitope from mgp100 (mgp100(25-27)) or a mutated epitope unable to bind D(b) did not reject B16 melanoma. Mice immunized with a minigene construct of hgp100(25-33) rejected B16 melanoma, whereas mice immunized with the mgp100(25-33) minigene did not develop protective tumor immunity. In this model of xenogeneic DNA immunization, the presence of an hgp100 heteroclitic epitope with a higher affinity for MHC created by three amino acid (25 to 27) substitutions at predicted minor anchor residues was necessary and sufficient to induce protective tumor immunity in H-2(b) mice with melanoma.

Immunization with DNA coding for gp100 results in CD4 T-cell independent antitumor immunity

BACKGROUND

Xenogeneic DNA immunization can exploit small differences in expressed protein sequence resulting in immune recognition of self-molecules. We hypothesized that immunizing mice with xenogeneic DNA coding for the human melanosomal membrane glycoprotein gp100 would overcome immune ignorance or tolerance and result in tumor immunity. We also investigated the immunologic mechanisms of the antitumor immunity.

METHODS

C57BL/6 mice were immunized with DNA coding for human gp100, mouse gp100, or control vector by gene gun. After immunization, mice were challenged with a syngeneic melanoma expressing gp100, and tumor growth was analyzed. Mice deficient in major histocompatibility complex class I or class II molecules were similarly studied to assess the immunologic mechanism of the tumor protection.

RESULTS

There was significant tumor protection after vaccination with xenogeneic human gp100 DNA. Class I, but not class II, major histocompatibility complex molecules were required for tumor immunity. In addition, mice immunized with human gp100 demonstrated autoimmunity manifested as coat color depigmentation.

CONCLUSIONS

Immunization with xenogeneic DNA coding for the melanosomal glycoprotein gp100 results in tumor protection and autoimmune depigmentation. These results show that xenogeneic DNA vaccines can lead to cancer immunity without CD4(+) T-cell help with potential implications for rational vaccine design.

Liposomes containing interferon-gamma as adjuvant in tumor cell vaccines

PURPOSE

Liposomal systems may be useful as a cytokine supplement in tumor cell vaccines by providing a cytokine reservoir at the antigen presentation site. Here, we examined the effect of liposome incorporation of mIFNgamma on its potency as adjuvant in an established tumor cell vaccination protocol in the murine B16 melanoma model. Adjuvanticity of the mIFNgamma-liposomes was compared to that achieved by mIFNgamma-gene transfection of the B16 tumor cells. Furthermore, we studied whether liposomal incorporation of mIFNgamma indeed increases the residence time of the cytokine at the vaccination site.

METHODS

C57B1/6 mice were immunized with i) irradiated IFNgamma-gene transfected B16 melanoma cells or ii) irradiated wild type B16 cells supplemented with (liposomal) mIFNgamma, followed by a challenge with viable B16 cells. The residence time of the (liposomal) cytokine at the subcutaneous (s.c.) vaccination site was monitored using radiolabeled mIFNgamma and liposomes.

RESULTS

Immunization with irradiated tumor cells admixed with liposomal mIFNgamma generated comparable protection against B16 challenge as immunization with mIFNgamma-gene modified tumor cells. Irradiated tumor cells admixed with soluble mIFNgamma did not generate any protective responses. Radiolabeling studies indicated that free mIFNgamma rapidly cleared from the s.c. injection site. Association of [125I]-mIFNgamma with liposomes increased the local residence time substantially: liposomal association of mIFNgamma resulted in a prolonged local residence time of the cytokine as reflected by a 4-fold increase of the area under the curve. The amount of released cytokine in the optimal dose range corresponds to the amount released by the gene-transfected cells. Moderate but significant CTL-activity against B16 cells was found for mice immunized with irradiated cells supplemented with mIFNgamma-liposomes compared to untreated control animals.

CONCLUSIONS

Prolonged presence of mIFNgamma at the site of antigen presentation is crucial for the generation of systemic immune responses in the B16 melanoma model. These studies show that liposomal encapsulation of cytokines is an attractive strategy for paracrine cytokine delivery in tumor vaccine development.

Heteroclitic immunization induces tumor immunity

In tumor transplantation models in mice, cytotoxic T lymphocytes (CTLs) are typically the primary effector cells. CTLs recognize major histocompatibility complex (MHC) class I-associated peptides expressed by tumors, leading to tumor rejection. Peptides presented by cancer cells can originate from viral proteins, normal self-proteins regulated during differentiation, or altered proteins derived from genetic alterations. However, many tumor peptides recognized by CTLs are poor immunogens, unable to induce activation and differentiation of effector CTLs. We used MHC binding motifs and the knowledge of class I:peptide:TCR structure to design heteroclitic CTL vaccines that exploit the expression of poorly immunogenic tumor peptides. The in vivo potency of this approach was demonstrated using viral and self-(differentiation) antigens as models. First, a synthetic variant of a viral antigen was expressed as a tumor antigen, and heteroclitic immunization with peptides and DNA was used to protect against tumor challenge and elicit regression of 3-d tumors. Second, a peptide from a relevant self-antigen of the tyrosinase family expressed by melanoma cells was used to design a heteroclitic peptide vaccine that successfully induced tumor protection. These results establish the in vivo applicability of heteroclitic immunization against tumors, including immunity to poorly immunogenic self-proteins.

Cytokine-modified tumor vaccines: an antitumor strategy revisited in the age of molecular medicine

Technological advances and improved understanding of the biology of the immune response have resulted in a resurgence of interest in the use of tumor vaccination as a means to control cancer. Tumor vaccines genetically modified with cytokine genes comprise the greatest proportion of gene therapy approaches to cancer. Tumor cells obtained at resection of the primary tumor are grown in tissue culture and genetically modified with cytokine genes such that the vaccine cells, after injection, may stimulate immune recognition of tumor cells and generate immunologic memory to prevent future tumor recurrence. There are many unanswered questions regarding tumor vaccination including the optimal dose, optimal cytokine, injection technique including route and site of vaccine delivery, and methods of evaluating the immune response. Oncology nurses have an integral role in these areas as well as in evaluating patients for as yet undetermined side effects. As tumor vaccines receive increasing attention by the lay media, oncology nurses, especially those in the clinical research setting, must learn new terminology and concepts relevant to this new treatment approach in order to effectively translate the information to patients.

Immunomodulation and enhancement of antitumor activity by co-administration of 1,3-bis(2-chloroethyl)-1-nitrosourea and thymidine

The antitumor activity of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) has been shown previously to be enhanced markedly by the co-administration of pyrimidine deoxyribonucleosides (Lin and Prusoff, Cancer Res 47: 394-397, 1987). In the present study, we examined the cellular mechanisms underlying the augmentation effect of thymidine, one of the pyrimidine deoxyribonucleosides. It was found that thymidine did not increase the cytotoxicity of BCNU for B16/F10 melanoma cells in vitro. Instead, thymidine appeared to produce modulatory actions on the immune system of the tumor-bearing mice. More than 40% of the BCNU/ thymidine-cured mice specifically rejected secondary rechallenge with the B16/F10 tumor. Furthermore, these cured mice developed extensive depigmentation of their natural black hair, suggesting immune reactions to normal melanocytes. When spleen cells from normal mice were treated with BCNU alone, their response to T-cell mitogen phytohemagglutinin was suppressed markedly. This suppression was ablated by co-administration of BCNU with thymidine. Such BCNU/thymidine treatment also augmented the activity of tumor-specific cytotoxic T-cells in tumor-bearing mice. Taken together, these results suggest that the enhanced antitumor activity of combined BCNU and thymidine may result from the action of thymidine on the immune effector mechanisms, which facilitate the development of antitumor immune responses in the presence of immunosuppression induced by BCNU.

Changes in expression of putative antigens encoded by pigment genes in mouse melanomas at different stages of malignant progression

Cutaneous melanomas of Tyr-SV40E transgenic mice (mice whose transgene consists of the tyrosinase promoter fused to the coding regions of simian virus 40 early genes) strikingly resemble human melanomas in their development and progression. Unlike human melanomas, the mouse tumors all arise in genetically identical individuals, thereby better enabling expression of specific genes to be characterized in relation to advancing malignancy. The products of pigment genes are of particular interest because peptides derived from these proteins have been reported to function as autoantigens with immunotherapeutic potential in some melanoma patients. However, the diminished pigmentation characteristic of many advanced melanomas raises the possibility that some of the relevant products may no longer be expressed in the most malignant cells. We have therefore investigated the contributions of several pigment genes in melanotic vs. relatively amelanotic components of primary and metastatic mouse melanomas. The analyses reveal marked differences within and among tumors in levels of mRNAs and proteins encoded by the wild-type alleles at the albino, brown, slaty, and silver loci. Tyrosinase (the protein encoded by the albino locus) was most often either absent or undetectable as melanization declined. The protein encoded by the slaty locus (tyrosinase-related protein 2) was the only one of those tested that was clearly present in all the tumor samples. These results suggest that sole reliance on targeting tyrosinase-based antigens might selectively favor survival of more malignant cells, whereas targeting the ensemble of the antigens tested might contribute toward a more inclusive and effective antimelanoma strategy.

A human melanoma cell line, recognized by both HLA class I and class II restricted T cells, is capable of initiating both primary and secondary immune responses

We have characterized a melanoma cell line, FM3, established from a metastasis of a 75 year old female patient (HLA-A2, HLA-DQ7) with malignant melanoma. This cell line expresses both HLA class I and class II antigens, as well as several important accessory molecules at high levels. FM3 cells were shown to function as a stimulator of both allogeneic as well as autologous mixed lymphocyte tumour cell culture (MLTC). From these autologous MLTC we were able to generate cytotoxic T cell clones indicating that FM3 is capable of processing and presenting endogenous antigens. We have used this cell line in a model system to investigate whether these cells were able to initiate and support an immune response with specificity for selected peptide antigens. The FM3 cell line was capable of presenting a HLA-DQ7 restricted ras derived peptide (5-21, 13Gly- >Asp) to a previously established T cell clone, RM70. The ability of FM3 to function as an antigen presenting cell (APC) was comparable to that of an autologous Epstein Barr virus (EBV) transformed B cell line. The CD4+ T cell clone RM70 showed a peptide-specific anti-proliferative effect on FM3 cells. This growth inhibition was not due to cytotoxicity as measured in a standard 4 h chromium release assay. The FM3 cell line also presented a HLA-A2 restricted nonapeptide derived from the influenza matrix protein, M1(58-66) to a CD8+ T cell line specific for this peptide. This resulted in an effective killing of the melanoma cells. Together, these data suggest that some melanomas may initiate an immune response by presenting their own specific antigens in an immunogenic context, and subsequently serve as targets for T cells of both the CD4+ and CD8+ phenotype.

Differentiation of cultured human melanoma cells induced by the aromatic fatty acids phenylacetate and phenylbutyrate

The increasing incidence of melanoma and the poor responsiveness of disseminated disease to conventional treatments call for the development of new therapeutic approaches. Phenylacetate, a nontoxic differentiation inducer, can suppress the growth of other neuroectodermal tumors, i.e., gliomas, in laboratory models and in humans. This finding led us to explore the efficacy of phenylacetate and related aromatic fatty acids in melanoma. Phenylacetate and phenylbutyrate were found to a) induce selective cytostasis and maturation of cultured human melanoma cells, b) modulate the expression of genes implicated in tumor metastasis (type IV collagenase and tissue inhibitor of metalloproteinases-2) and immunogenicity (HLA class I); and c) enhance the efficacy of other agents of clinical interest, including retinoids, interferon-alpha, suramin, and 5-aza-2'-deoxycytidine. Reflecting on the phenotypic heterogeneity of melanoma, the degree of biologic alterations induced by phenylacetate/phenylbutyrate varied significantly among the tumor cell lines tested. Although losing invasive capacity and tumorigenicity in athymic mice, poorly differentiated cells exhibited only a marginal change in morphology, remained amelanotic, and resumed growth after treatment was discontinued. By contrast, treatment of melanoma cells that were in a more advanced stage of maturation resulted in profound alterations in cell growth, morphology, and pigmentation consistent with terminal differentiation. The in vitro antitumor activity was observed with nontoxic, pharmacologic concentrations of phenylacetate and phenylbutyrate, suggesting potential clinical use of these drugs in the treatment of melanomas.