Induction of delayed-type hypersensitivity responses by monoclonal anti-idiotypic antibodies to tumor cells expressing carcinoembryonic antigen and tumor-associated glycoprotein-72

Phylogenetic discordance of human and canine carcinoembryonic antigen (CEA, CEACAM) families, but striking identity of the CEA receptors will impact comparative oncology studies

Comparative oncology aims at speeding up developments for both, human and companion animal cancer patients. Following this line, carcinoembryonic antigen (CEA, CEACAM5) could be a therapeutic target not only for human but also for canine (Canis lupus familiaris; dog) patients. CEACAM5 interacts with CEA-receptor (CEAR) in the cytoplasm of human cancer cells. Our aim was, therefore, to phylogenetically verify the antigenic relationship of CEACAM molecules and CEAR in human and canine cancer.

Anti-human CEACAM5 antibody Col-1, previously being applied for cancer diagnosis in dogs, immunohistochemically reacted to 23 out of 30 canine mammary cancer samples. In immunoblot analyses Col-1 specifically detected human CEACAM5 at 180 kDa in human colon cancer cells HT29, and the canine antigen at 60, 120, or 180 kDa in CF33 and CF41 mammary carcinoma cells as well as in spontaneous mammary tumors. While according to phylogenicity canine CEACAM1 molecules should be most closely related to human CEACAM5, Col-1 did not react with canine CEACAM1, -23, -24, -25, -28 or -30 transfected to canine TLM-1 cells. By flow cytometry the Col-1 target molecule was localized intracellularly in canine CF33 and CF41 cells, in contrast to membranous and cytoplasmic expression of human CEACAM5 in HT29. Col-1 incubation had neither effect on canine nor human cancer cell proliferation. Yet, Col-1 treatment decreased AKT-phosphorylation in canine CF33 cells possibly suggestive of anti-apoptotic function, whereas Col-1 increased AKT-phosphorylation in human HT29 cells. We report further a 99% amino acid similarity of human and canine CEA receptor (CEAR) within the phylogenetic tree. CEAR could be detected in four canine cancer cell lines by immunoblot and intracellularly in 10 out of 10 mammary cancer specimens from dog by immunohistochemistry. Whether the specific canine Col-1 target molecule may as functional analogue to human CEACAM5 act as ligand to canine CEAR, remains to be defined. This study demonstrates the limitations of comparative oncology due to the complex functional evolution of the different CEACAM molecules in humans versus dogs. In contrast, CEAR may be a comprehensive interspecies target for novel cancer therapeutics.

CDR substitutions of a humanized monoclonal antibody (CC49): contributions of individual CDRs to antigen binding and immunogenicity

One of the major obstacles in the successful clinical application of monoclonal antibodies has been the development of host immune responses to murine Ig constant and variable regions. While the CDR grafting of MAbs may alleviate many of these problems, the potential remains that one or more murine CDRs on the human Ig backbone of a "humanized" MAb may still be immunogenic. Studies were undertaken employing a MAb of potential clinical utility, CC49, to define those CDRs that are essential for antigen binding and those that may be immunogenic in humans. We previously developed a humanized CC49 (HuCC49) by grafting the MAb CC49 hypervariable regions onto frameworks of human MAbs. To identify those CDRs essential for binding, a panel of variant HuCC49 MAbs was generated here by systematically replacing each of the murine CDRs with their human counterparts. The relative affinity constant of each variant was determined. Serum from a patient who received murine CC49 was used to determine the potential immunogenicity of each CDR in humans. The serum was shown to react with the anti-CC49 variable region. Results showed that patients' anti-idiotypic responses are directed mainly against LCDR3 and moderately against LCDR1 and HCDR2. These studies demonstrate for the first time that variants containing individual CDR substitutions of a humanized MAb can be constructed, and each CDR can be defined for the two most important properties for potential clinical utility: antigen binding and immunogenicity.

Clinical and immunologic effects of monoclonal antibody CC49 and interleukin-2 in patients with metastatic colorectal cancer

We examined the possibility that prior exposure to the murine monoclonal antibody (mAb), CC49, which recognizes the pancarcinoma antigen, TAG-72, would modify the clinical activity of interleukin-2 (IL-2) in patients with metastatic colorectal cancer. Fourteen patients received 2 mg of unconjugated CC49 on Day 1; on Day 22, they began human recombinant IL-2 at 1 mg/m2/day for 4 days by continuous IV infusion. Four-day cycles of IL-2 were repeated weekly for 8 weeks unless there was evidence of unacceptable toxicity or progressive disease. Therapy was well tolerated. Proliferative responses of peripheral blood mononuclear cells (PBMC) to CC49, its Fab fragment, isotype matched murine immunoglobulin, and CC49 complexed with TAG-72+ mucin increased after CC49 administration (Day 21). These proliferative responses decreased after IL-2 administration. PBMC proliferative responses to AI49, an anti-CC49 idiotype antibody (Ab2), and TAG-72+ mucin was not induced. No complete or partial clinical responses were observed; one patient manifested a transient mixed response. A single infusion of CC49 does have biologic activity; it is, however, unlikely to substantially modify tumor response rates effected by IL-2 in patients with metastatic colorectal cancer.

Monoclonal anti-idiotypic antibody functionally mimics the human gastrointestinal carcinoma epitope GA733

Anti-idiotypic antibodies (Ab2) that bind to the antigen-combining region of anti-tumor antibodies (Ab1) may functionally, and even structurally, mimic tumor antigen. We have previously demonstrated that polyclonal goat Ab2 directed against anti-human gastrointestinal carcinoma Ab1 GA733 induces anti-anti-idiotypic antibodies (Ab3) in animals that are Ab1-like in their binding specificity and idiotope expression. To obtain more defined Ab2 vaccines with potentially increased specificity and efficacy, a monoclonal Ab2 (FG1) was produced against Ab1 GA733 in rats. The monoclonal Ab2 FG1, similar to the polyclonal Ab2 described previously, induced Ab3 in rabbits that were Ab1-like in their idiotope expression and binding specificity to tumor cells and antigen. Antigen-specific Ab3 induced by Ab2 FG1 were easily detected in unprocessed rabbit sera, whereas the demonstration of such Ab3 after polyclonal Ab2 immunization required purification of the Ab3 from the rabbit sera. In addition, Ab2 FG1 induced antigen-specific humoral and cellular immunity in mice. Murine Ab3 bound specifically to antigen-positive tumor cells. Ab2-immunized mice showed antigen-specific delayed-type hypersensitivity (DTH) reaction, and cultured splenocytes from the immune mice demonstrated specific proliferation and cytokine (interferon-gamma and interleukin-4) secretion upon stimulation with GA733 antigen. However, immune mice were not protected against a challenge with syngeneic GA733 antigen-expressing colon carcinoma cells.

Immune response to the carcinoembryonic antigen in patients treated with an anti-idiotype antibody vaccine

We have generated an IgG1 murine monoclonal anti-idiotype antibody (Ab2) designated 3H1, which mimics a specific epitope on the carcinoembryonic antigen (CEA). Patients with CEA positive tumors are immunologically "tolerant" to CEA. We used 3H1 as a surrogate for CEA for vaccine therapy of 12 patients with advanced colorectal cancer. Each of the patients received a minimum of four intracutaneous injections of aluminum hydroxide precipitated 3H1 at either 1, 2, or 4 mg dosage per injection. 9 of 12 patients demonstrated anti-anti-idiotypic (Ab3) response to 3H1. All nine patients generated specific anti-CEA antibody demonstrated by reactivity with radiolabeled purified CEA; some cases were confirmed by immunoprecipitation of purified CEA. We also demonstrated Ab3 stained both autologous and allogeneic colonic tumors. 7 of 12 patients demonstrated idiotype specific T cell proliferative responses and four also showed T cell proliferation to CEA. Toxicity was limited to local reaction with mild fever and chills. All 12 patients eventually progressed after finishing 4-13 dosages. This is the first report demonstrating that a vaccine therapy is capable of breaking "immune tolerance" to CEA in patients with CEA positive tumors. Future studies will focus on treating patients with minimal residual disease.

Mimicry of a carcinoembryonic antigen epitope by a rat monoclonal anti-idiotype antibody

Anti-idiotype antibodies (Ab2) that immunologically mimic tumor antigens are auspicious agents for the active immunization of cancer patients. We have developed W12, a rat monoclonal IgG1 Ab2 to MN-14, a murine anti-carcinoembryonic antigen (CEA) monoclonal antibody. W12 is specific for MN-14 and does not react with other isotype-matched anti-CEA monoclonal antibodies. Moreover, W12 inhibits the binding between MN-14 and CEA. Anti-CEA antibodies can be induced by immunization with W12 (but not with control rat IgG) in xenogenic animals (mice or rabbits). Immunoblotting studies indicate that the internal image determinant borne by W12 is conformational and requires the association of the heavy and light chains of the Ab2 molecule. This study indicates that W12 is a potential idiotype vaccine in patients with CEA-producing cancers.