Malaya Bhattacharya-Chatterjee

Summary: In the present study, we have analysed the detailed cellular immune mechanisms involved in tumour rejection in carcinoembryonic antigen (CEA) transgenic mice after immunization with dendritic cells (DC) pulsed with an anti‐idiotype (Id) antibody, 3H1, which mimics CEA. 3H1‐pulsed DC vaccinations resulted in induction of CEA specific cytotoxic T lymphocyte (CTL) responses in vitro and the rejection of CEA‐transfected MC‐38 murine colon carcinoma cells, C15, in vivo (Saha et al.,Cancer Res 2004; 64: 4995–5003). These CTL mediated major histocompatibility complex (MHC) class I‐restricted tumour cell lysis, production of interferon‐γ (IFN‐γ) and tumour necrosis factor‐α (TNF‐α), and expression of Fas ligand (FasL) and TNF‐related apoptosis‐inducing ligand (TRAIL) in response to C15 cells. CTL used perforin‐, FasL‐, and TRAIL‐mediated death pathways to lyse C15 cells, although perforin‐mediated killing was the predominant lytic mechanism in vitro. The cytokines IFN‐γ and TNF‐α synergistically enhanced surface expression of Fas, TRAIL receptor, MHC class I and class II on C15 cells that increased the sensitivity of tumour cells to CTL lysis. CTL activity generated in 3H1‐pulsed DC immunized mice was directed against an epitope defined by the idio‐peptide LCD‐2, derived from 3H1. In vivo lymphocyte depletion experiments demonstrated that induction of CTL response and antitumour immunity was dependent on both CD4⁺ and CD8⁺ T cells. The analysis of splenocytes of immunized mice that had rejected C15 tumour growth revealed up‐regulated surface expression of memory phenotype Ly‐6C and CD44 on both CD4⁺ and CD8⁺ T cells. The adoptive transfer experiments also suggested the role of both CD4⁺ and CD8⁺ T cells in this model system. Furthermore, mice that had rejected C15 tumour growth, developed tumour‐specific immunological memory.

A murine monoclonal anti-idiotype (Id) antibody, 3H1 has been developed and characterized previously. Anti-Id 3H1 mimics a specific epitope of carcinoembryonic antigen (CEA) and can be used as a surrogate antigen for CEA. 3H1 induced anti-CEA immunity in different species of animals as well as humans and showed promise as a potential vaccine candidate in phase I/II clinical trials for colon cancer patients. One area of interest to us has been the development of new immune adjuvants that may augment the potency of 3H1 as a tumor vaccine. Oligodeoxynucleotides containing unmethylated CpG motifs (CpG ODN) are potent immunostimulatory agents capable of enhancing the Ag-specific Th1 response when used as immune adjuvants. In this study, we have evaluated the efficacy of 3H1 as a tumor vaccine when admixed with a select CpG ODN 1826 in transgenic mice that express human CEA. The vaccine potential of 3H1 was also assessed in the presence of another widely used adjuvant, QS-21. 3H1 coupled to keyhole limpet hemocyanin (KLH) and mixed with Freund’s adjuvant (FA) was used as a gold standard in this system. 3H1 vaccination with different adjuvants induced both humoral and cellular anti-3H1, as well as anti-CEA immunity in CEA transgenic mice. The immune sera could lyse CEA-transfected murine colon carcinoma cells, C15 effectively in an antibody-dependent cellular cytotoxicity assay. The anti-CEA antibody responses were somewhat comparable in each adjuvant-treated group of mice, whereas cellular immune responses were significantly greater when CpG was used as an adjuvant. Splenocytes obtained from 3H1–CpG-immunized mice showed an increased proliferative CD4⁺ Th1-type T-cell response when stimulated in vitro with 3H1 or CEA and secreted elevated levels of Th1 cytokines (IL-2, IFN-γ). This vaccine also induced MHC class I antigen-restricted CD8⁺ T-cell responses. In a solid tumor model, C15 tumor growth was significantly inhibited by 3H1 vaccinations. In 3H1–CpG-vaccinated mice, the duration of survival was, however, longer compared to the 3H1–QS21-vaccinated mice. These findings suggest that 3H1-CpG vaccinations can break peripheral tolerance to CEA and induce protective antitumor immunity in this murine model transgenic for human CEA.

In this report, we have studied the immunogenicity of the nominal antigen, carcinoembryonic antigen (CEA), and that of an anti-idiotype antibody, 3H1, which mimics CEA and can be used as a surrogate for CEA. We have demonstrated that immunization of CEA transgenic mice with bone marrow-derived mature dendritic cells (DC) loaded with anti-idiotype 3H1 or CEA could reverse CEA unresponsiveness and result in the induction of CEA-specific immune responses and the rejection of CEA-transfected MC-38 colon carcinoma cells, C15. Immunized mice splenocytes proliferated in an antigen-specific manner by a mechanism dependent on the functions of CD4, MHC II, B7–2, CD40, CD28, and CD25. However, immune splenic lymphocytes isolated from 3H1-DC-vaccinated mice when stimulated in vitro with 3H1 or CEA secreted significantly higher levels of Th1 cytokines than did CEA-DC vaccinated mice. DC vaccination also induced antigen-specific effector CD8⁺ T cells capable of expressing interluekin-2, IFN-γ, and tumor necrosis factor (TNF)-α and displayed cytotoxic activity against C15 cells in an MHC class I-restricted manner. 3H1-DC vaccination resulted in augmented CTL responses and the elevated expression of CD69, CD25, and CD28 on CD8⁺ CTLs. The immune responses developed in 3H1-DC-immunized mice resulted in rejection of C15 tumor cells in nearly 100% of experimental mice, whereas only 40% of experimental mice immunized with CEA-DC were protected from C15 tumor growth. These findings suggest that under the experimental conditions used, 3H1-DC vaccination was better than CEA-DC vaccination in breaking immune tolerance to CEA and inducing protective antitumor immune responses in this murine model transgenic for human CEA.

In this study, using the carcinoembryonic antigen (CEA)-expressing C15 murine colon carcinoma system in syngeneic C57BL/6 mice, we have evaluated the efficacy of bone marrow-derived dendritic cells (DCs) pulsed with the murine anti-idiotype antibody 3H1 as a tumor vaccine. Anti-idiotype 3H1 mimics a distinct and specific epitope of CEA and can generate anti-CEA immunity in mice, rabbits, monkeys, and humans when used with a conventional immune adjuvant. Our goal was to determine whether the use of DC as direct antigen-presenting cells would improve the potency of 3H1 as vaccine. Bone marrow-DC pulsed with 3H1 and injected into naïve mice induced both humoral and cellular anti-3H1, as well as anti-CEA immunity. Specific killing of C15 cells in in vitro antibody-dependent cellular cytotoxicity has been observed by immune sera. Immune-splenic lymphocytes when stimulated in vitro with 3H1 or CEA, showed increased proliferative CD4(+) Th1 type T-cell response and secreted significantly high levels of Th1 cytokines [IFN-gamma, interleukin (IL)-2] and low levels of Th2 cytokines (IL-4, IL-10). This vaccine also induced MHC class I antigen-restricted CD8(+) T-cell responses. The up-regulation of activation markers CD69 and CD25 on CD8(+) CTLs correlated with antigen-specific strong CTL responses in vitro. The immunity induced in mice resulted in a complete rejection of CEA-expressing C15 tumor cells in 100% of experimental mice, whereas no protection was observed when 3H1-pulsed DC-vaccinated mice were challenged with CEA-negative MC-38 cells. The tumor rejection in 3H1-pulsed DC-treated mice was associated with the induction of a memory response that helped those mice to survive a second challenge with a lethal dose of C15 cells.

We have developed and characterized a monoclonal anti-idiotype (Id) antibody, designated 3H1, which mimics a specific epitope of carcinoembryonic antigen (CEA) and can be used as a surrogate for CEA. Anti-Id 3H1 induced anti-CEA immunity in different species of animals as well as humans and showed promise as a potential vaccine candidate in phase I/II clinical trials for colorectal cancer patients. One area of interest to us has been the development of new immune adjuvants that may augment the potency of 3H1 as a tumor vaccine. Immunostimulatory oliogonucleotides containing the unmethylated CpG motif (CpG ODN) are potent inducers of both innate and adaptive immunity and can serve as suitable vaccine adjuvants. In this study, using the CEA-transduced MC-38 murine colon carcinoma model in syngeneic C57BL/6 mice, we assessed whether a select CpG ODN (1826) can function as immune adjuvant in immunization of mice with anti-Id 3H1. Complete Freund's adjuvant (FA) was used as a gold standard in this system. A single immunization of 3H1 mixed with CpG ODN 1826 was sufficient to induce measurable anti-CEA immunity in naïve mice. However, 3 immunizations every other week were necessary to obtain and sustain peak immune reactivity over a long period of time. With FA and 3H1, single immunization was ineffective and multiple immunizations (5 to 6) were needed to achieve and sustain peak immunity. Anti-CEA antibody reactivity was comparable in both groups, but cellular immune reactivity as measured by immune splenic lymphocyte T cell proliferation and cytoxicity assay was slightly higher in the CpG ODN group. Mice immunized with 3H1 and either CpG ODN or FA were protected from challenge by lethal doses of MC-38-CEA cells. However, the degree of protection was slightly higher and the duration of survival was somewhat longer in the group of mice treated with 3H1 plus CpG ODN. Thus, CpG ODN 1826 was faster than FA in increasing anti-tumor immunity induced by anti-Id 3H1 immunization in this prophylactic model.

The use of anti-idiotype (Id) antibodies as vaccines to stimulate antitumour immunity is one of several promising immunologic approaches to the therapy of cancer. Extensive studies in animal tumour models have demonstrated the efficacy of anti-Id vaccines in preventing tumour growth and curing mice with established tumours. A number of monoclonal anti-Id antibodies that mimic distinct human tumour-associated antigens (TAAs) have been developed and tested in the clinic, and demonstrate encouraging results. In general, the antigen mimicry by anti-Id antibodies has reflected structural homology in the majority of the cases, and amino acid sequence homology in a few of them. The greatest challenge of immunotherapy by means of anti-Id vaccines is to identify the optimal anti-Id antibody that will function as a true surrogate antigen for a TAA system, and ideally will generate both humoral and cellular immune responses. Although several clinical studies have shown enhanced survival of patients receiving anti-Id...

Certain anti-idiotypic antibodies that bind to the antigen-combining sites of antibodies can effectively mimic the three-dimensional structures and functions of the external antigens and can be used as surrogate antigens for active specific immunotherapy. Extensive studies in animal models have demonstrated the efficacy of these vaccines for triggering the immune system to induce specific and protective immunity against bacterial, viral and parasitic infections as well as tumors. Several monoclonal anti-idiotype antibodies that mimic distinct human tumor-associated antigens have been developed and characterized. Encouraging results have been obtained in recent clinical trials using these anti-idiotype antibodies as vaccines. In this article, we will review the current literature and discuss the potential of this novel therapeutic approach for various human cancers.