Induction of anti-idiotypic (ab2) and anti-anti-idiotypic (ab3) antibodies in patients treated with the mouse monoclonal antibody 17-1A (ab1). Relation to the clinical outcome--an important antitumoral effector function?

Survival benefit associated with human anti-mouse antibody (HAMA) in patients with B-cell malignancies

BACKGROUND

About one-third of patients with relapsed B-cell malignancies develop human anti-mouse antibody (HAMA) following mouse antibody treatment. The purpose of this study was to assess the relationship between HAMA and survival in patients given a mouse anti-lymphoma monoclonal antibody (mAb), Lym-1, directed against a unique epitope of HLA-DR antigen that is up-regulated on malignant B-cells.

METHODS

ELISA was used to quantify HAMA in 51 patients with B-cell malignancies treated with iodine-131 (131I) labeled Lym-1. Sera were collected prior to and following radioimmunotherapy (RIT) with 131I-Lym-1 until documented to be HAMA negative or throughout lifetime. Univariate, then multivariate analyses including other risk factors, were used to analyze the relationship of HAMA to survival. The relationships of HAMA to prior chemotherapies and to absolute lymphocyte counts prior to RIT were also assessed.

RESULTS

Eighteen of 51 patients (35%) developed HAMA following RIT (range of ultimate maximum titers, 6.6-1,802 microg/ml). Using the time dependent Cox proportional hazards model, maximum HAMA titers were associated with survival (P=0.02). HAMA continued to be significant for survival in multivariate analyses that included known risk factors. In Landmark analysis of 39 patients that survived at least 16 weeks, median survival of patients with HAMA less than 5 microg/ml was 61 versus 103 weeks for patients with HAMA equal or greater than 5 microg/ml at 16 weeks (P=0.02). The median survival of the five patients with highest maximum HAMA titers was 244 weeks. At 16 weeks, there was an inverse correlation between the maximum HAMA titer and the number of previous chemotherapies (P<0.003). Absolute lymphocyte counts prior to 131I-Lym-1 treatment for patients that seroconverted were higher than those for patients that did not seroconvert (P=0.01).

CONCLUSIONS

Patients with B-cell malignancies that developed high HAMA titers had longer survival that was not explained by risk factors or histologic grade, suggesting the importance of the immune system.

Monoclonal antibodies as effective therapeutic agents for solid tumors

Monoclonal antibodies (mAbs) against growth factors or their receptors have been revealed to be effective therapeutic agents for solid tumors. Trastuzumab (humanized anti-HER2 mAb) is the first mAb approved for the treatment of a solid tumor, metastatic breast cancer. Large-scale phase III clinical trials are now ongoing to further evaluate the additive effects on chemotherapy and the efficacy as a maintenance monotherapy. Another anti-HER2 mAb CH401 that we developed also seems to have good potential. This chimeric mAb completely suppressed the growth of established human tumor xenografts in SCID mice after a single injection. Furthermore, CH401 characteristically showed much stronger induction of apoptosis in HER2-overexpressing gastric cancer cells compared to trastuzumab. Additional targets now being intensively evaluated are epidermal growth factor receptor (EGFR) and vascular endothelial growth factor (VEGF). Both cetuximab (chimeric anti-EGFR mAb) and bevacizumab (humanized anti-VEGF mAb) have recently been shown to be of clinical value for metastatic colorectal cancer. Anti-idiotype mAbs are unique as active immunotherapeutic agents, and survival benefits have been observed in clinical trials for solid tumors.

Recombinant antibodies for the diagnosis and treatment of cancer

The advent of recombinant antibody technology led to an enormous revival in the use of antibodies as diagnostic and therapeutic tools for fighting cancer. This review provides a brief historical sketch of the development of recombinant antibodies for the diagnosis and immunotherapy of cancer and summarizes the most significant clinical data for the best established reagents to date. It also discusses clinically relevant aspects of the use of recombinant antibodies in cancer patients.

Monoclonal antibody therapy for cancer

Monoclonal antibody therapy has emerged as an important therapeutic modality for cancer. Unconjugated antibodies show significant efficacy in the treatment of breast cancer, non-Hodgkin's lymphoma, and chronic lymphocytic leukemia. Promising new targets for unconjugated antibody therapy include cellular growth factor receptors, receptors or mediators of tumor-driven angiogenesis, and B cell surface antigens other than CD20. Immunoconjugates composed of antibodies conjugated to radionuclides or toxins show efficacy in non-Hodgkin's lymphoma. One immunoconjugate containing an antibody and a chemotherapy agent exhibits clinically meaningful antitumor activity in acute myeloid leukemia. Numerous efforts to exploit the ability of antibodies to focus the activities of toxic payloads at tumor sites are under way and show early promise. The ability to create essentially human antibody structures has reduced the likelihood of host-protective immune responses that otherwise limit the duration of therapy. Antibody structures now can be readily manipulated to facilitate selective interaction with host immune effectors. Other structural manipulations that improve the selective targeting properties and rapid systemic clearance of immunoconjugates should lead to the design of effective new treatments, particularly for solid tumors.

Generalization of single immunological experiences by idiotypically mediated clonal connections

Clonal interactions of B cells by idiotope-specific mutual recognition of their antigen receptors with the participation of T cells were assumed to form a web of unknown density, referred to as the idiotypic network. Although these clonal connections were proposed to fulfill important internal regulatory functions, their biological significance, especially in relation to antigen-induced immune responses, remained a mystery. In view of this, we postulate that the basic function of the idiotypic internal connection between B and T cell antigen receptors is to transform antigen-induced cellular activations, by idiotypic crossreactivity, into the regulation of cell clones with different antigen specificities. This process leads not only to the suppression of major clones but also to the activation of minor ones. The latter activating property may allow the generalization of single antigenic experiences, so that the immune system in its entirety benefits in its battle against environmental microbes. Such idiotypic clonal interactions are particularly effective in early ontogeny. During a short neonatal imprinting period, maternal immunological knowledge in the form of somatically mutated, high-affinity IgG antibodies, acquired through a continuous encounter with external antigens, guides the initial ontogenetic development of the immune system and so exerts long-lasting transgenerational advantageous effects in the offspring.

Clinical experience with edrecolomab: a monoclonal antibody therapy for colorectal carcinoma

Edrecolomab (monoclonal antibody 17-1A) is a murine monoclonal antibody that recognizes the human tumor-associated antigen Ep-CAM (otherwise known as 17-1A). It is being developed for the adjuvant treatment of colorectal cancer. In a study of 189 patients with resected stage III colorectal cancer, treatment with edrecolomab resulted in a 32% increase in overall survival compared with no treatment (P<0.01) and decreased the tumor recurrence rate by 23% (P<0.04). In terms of safety, edrecolomab was well tolerated. Based on these study results, edrecolomab is currently under investigation in large multicenter phase III studies both as monotherapy and in combination with 5-fluorouracil-based chemotherapy versus chemotherapy alone for the treatment of stage III colon cancer. Although these studies are still ongoing, an interim analysis of safety data indicated that the combination of edrecolomab with chemotherapy is well tolerated. In addition, edrecolomab monotherapy demonstrated a favorable safety profile compared with chemotherapy. Edrecolomab is also currently being tested in large multicenter adjuvant phase III studies in stage II/III rectal cancer and stage II colon cancer. Edrecolomab represents a novel therapeutic approach and has the potential to become a treatment of choice as monotherapy in stage II colon cancer and in combination with chemotherapy in stage II/III rectal and stage III colon cancer.

Update of clinical trials with edrecolomab: a monoclonal antibody therapy for colorectal cancer

Edrecolomab is a murine IgG2a monoclonal antibody that recognizes the tumor-associated antigen Ep-CAM. Its antitumor effects are mediated through antibody-dependent cellular cytotoxicity, complement-mediated cytolysis, and the induction of an anti-idiotypic network. An initial study of 189 patients with resected stage III colorectal cancer showed that edrecolomab reduced the relative risk of mortality by 32% compared with observation alone (P < .01). Edrecolomab has now been investigated in two large phase III studies of patients with stage III colon cancer, either as a single agent or in combination with 5-FU-based chemotherapy. Preliminary safety data have shown that edrecolomab is well tolerated when used as monotherapy and adds little to chemotherapy-related side effects when used in combination. Edrecolomab is also being studied as monotherapy following resection of stage II colon cancer, and in combination with chemotherapy in patients with resected stage II or III rectal cancer. In conclusion, edrecolomab is a novel biological therapy for the adjuvant treatment of colorectal cancer. Completed and ongoing trials may support its use as monotherapy in stage II colon cancer or in combination with chemotherapy in stage III colon cancer and stage II/III rectal cancer.

Antibodies for neoplastic disease : solid tumors

The ease with which polyclonal, monoclonal, and engineered antibody fragments can be prepared allows access to a series of reagents with high selectivity and affinity. These reagents therefore have long held promise as a means of influencing the growth and spread of malignant disease. Over a number of decades therapeutic antibodies have been developed either as single entities or conjugated to a variety of potential disease-ameliorating agents.

Edrecolomab (monoclonal antibody 17-1A)

Edrecolomab is a mouse-derived monoclonal IgG2a antibody. It recognises the human tumour-associated antigen CO17-1A which is expressed on the cell surface of a wide variety of tumours and normal epithelial tissue. Edrecolomab is thought to destroy tumour cells by activating an array of endogenous cytotoxic mechanisms, including antibody-dependent cell-mediated cytotoxicity and possibly antibody-dependent complement-mediated cytotoxicity. Edrecolomab may induce antitumour activity indirectly by inducing a host anti-idiotypic antibody response. Adjuvant therapy with edrecolomab (500 mg initial dose followed by four 100 mg infusions administered at 4-weekly intervals) significantly improved survival and reduced the tumour recurrence rate in patients with resected Dukes' stage C colorectal cancer and minimal residual disease. Data from several small clinical trials suggest that edrecolomab given as monotherapy or in combination with other antineoplastic agents has limited efficacy in the treatment of advanced colorectal or pancreatic tumours. However, results from a small phase I study in patients with advanced breast cancer were more promising. Edrecolomab was generally well tolerated in clinical trials. In a postmarketing surveillance study, the most common adverse events associated with edrecolomab were flushing/erythema and gastrointestinal symptoms including diarrhoea, abdominal pain and nausea and vomiting. Because edrecolomab is of murine origin, anaphylactic reactions have developed in some patients treated with the drug.

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.

Are human anti-idiotypic anti-OC125 antibodies formed after immunization with the anti-CA125 antibody B43.13?

The two monoclonal antibodies (MAb) OC125 and B43.13 both recognize antigenic determinants on the cancer antigen 125 (CA125) molecule. The aim of the present study was to clarify how far antibodies formed by patients treated with B43.13 may cross-react with idiotopes of OC125. Serum samples from 15 ovarian cancer patients treated with B43.13 were tested for the presence of anti-idiotypic anti-OC125 antibodies; 4 of these patients previously had received OC125 F(ab')2 fragments. Six patients treated only with B43.13 and all patients pretreated with OC125 fragments developed a considerable increase of human anti-mouse anti-bodies after B43.13 infusion, indicating an immune response to antibody infusion. However, none of the patients treated only with B43.13 developed detectable levels of anti-idiotypic anti-OC125 antibodies, whereas in 2 patients pretreated with OC125 fragments, the pre-existing concentration of anti-idiotypic anti-OC125 antibodies further increased after B43.13 infusion. The binding of these newly formed antibodies to OC125 was not inhibited by the B43.13, but about 70% of the binding was inhibited by the CA125 antigen. The present data suggest that the idiotopes expressed on the antibodies B43.13 and OC125, respectively, are completely different. Thus, anti-idiotypic anti-B43.13 antibodies may not cross-react with OC125. A greater number of cases is needed to clarify how far the increase of anti-idiotypic anti-OC125 antibodies observed in 2 patients pretreated with OC125 fragments really is due to B43.13 infusion.

Anti-TAG-72 antibody B72.3--immunological and clinical effects in ovarian carcinoma

Based on the network theory, anti-tumor antibodies (Ab1) can trigger the immune system of the host into a response against tumor cells. Through an immunological cascade, anti-idiotypic antibodies bearing the internal image of epitopes of the nominal antigen (Ab2 beta) are produced that themselves can induce cellular and humoral cytotoxic effects against the antigen-expressing tumor cell. Formation of such antibodies has been shown to be associated with prolonged survival of melanoma, colorectal, and ovarian carcinoma patients. We studied anti-idiotypic antibody (Ab2) responses and clinical outcome of 31 ovarian cancer patients receiving the monoclonal antibody (MAb) B72.3, which targets the ovarian carcinoma associated antigen TAG-72. All patients were treated by surgery and polychemotherapy, which was followed by repeated (mean of 4) injections of 1 mg of the MAb B72.3. A remarkable anti-idiotypic anti-B72.3 response arose in 19 patients, with 9 of them showing a major response with Ab2 serum concentrations greater than 1,000 U/ml ("high-responders"). The median disease-free survival time, as well as the median survival time of these high-responders, was increased as compared to the low- or no responders. Evaluating our data, we conclude that monoclonal antibody treatment with the MAb B72.3 may induce humoral immunological responses in about two-thirds of our study group, although a positive clinical effect may only be expected in patients with excessive anti-idiotypic antibody formation.

A simple and sensitive assay for determination of human anti-idiotypic anti-B72.3 antibodies, which is not affected by the presence of tumour-associated glycoprotein 72

An immunoradiometric assay is described for the determination of human anti-idiotypic anti-B72.3 IgG. The latter is formed in ovarian cancer patients after treatment with the murine monoclonal antibody B72.3, which is directed against the tumour-associated glycoprotein 72 (TAG-72). A gel coupled with Fc-specific anti-human IgG antibodies is used as a solid phase for the extraction of serum IgG. The anti-B72.3 IgG is then specifically detected by incubation with radiolabelled B72.3 detector antibodies. Calibration standards were prepared from serum obtained from a patient repeatedly treated with B72.3 antibodies. The concentration of anti-idiotypic anti-B72.3 antibodies was expressed as TAG-72-like arb.units/1. The assay performed with two 60-minute incubation steps is characterized by a high sensitivity (detection limit: 3 x 10(3) arb.units/1) and precision (coefficients of variation: intra-assay = 6.4% and 5.8% at 80 x 10(3) arb. units/1 and 217 x 10(3) arb.units/1, inter-assay = 8.7% and 7.1% at 91 x 10(3) arb.units/1 and 212 x 10(3) arb.units/1) and a good linearity of dilution (recovery after dilution between 99% and 107%). The assay is more specific than previously described methods; no interference was observed by TAG-72 up to 3.3 x 10(7) arb.units/1. Also, non-specific human anti-mouse antibodies did not cross-react up to 34.8 mg/l. The test may be modified for detection of anti-idiotypic antibodies, which are formed after treatment with other monoclonal antibodies.

A comparison of the anti-idiotypic responses generated by antibodies to a protein and a hapten: a common interspecies idiotype on antibodies against human albumin induces an idiotypic network in rabbits

Idiotypic networks have the capacity to exert significant influences on immune responses and an understanding of the ways to manipulate these networks may lead to new modalities in immunotherapy. In order to gain further insights into the nature of the immune responses stimulated by immunoglobulin idiotypes, rabbits were immunized with a mAb (Ab1) against a large globular protein, human albumin, or a mAb against a hapten, TNP. All rabbits developed anti-idiotypic antibodies (Ab2) and the rabbits immunized with anti-human albumin concomitantly developed antibodies to human albumin (Ab3). Ab2 prepared from these rabbits blocked binding of Ab1 to antigen and the anti-human albumin Ab2 reacted with all species of anti-human albumin including sheep, rabbit, rat and goat. The anti-TNP Ab2 reacted only with the mouse anti-TNP Ab1. This TNP Ab2 bound only to intact Ab1 whereas the human albumin Ab2 reacted with the Ab1 heavy chain. To compare the relative efficiencies of anti-idiotypic antibodies and antigen in inducing antibody, mice were immunized with rabbit Ab2 or antigen. All mice immunized with Ab2 developed anti-idiotypic Ab3, but only the human albumin Ab2 preparations elicited antigen specific Ab3; the amount of antibody produced was less than 1% of that found by immunization with antigen. The type of antibody induced in the Ab2-immunized mice was compared with that found in the antigen-immunized mice and in the Ab1-immunized rabbits. The mouse anti-albumin Ab3 was comparable to mouse Ab1 in terms of affinity and specificity for proteolytic fragments of human albumin. The Ab3 which arose in Ab1-immunized rabbits had a higher affinity and broader epitope specificity and was similar to antibodies raised against antigen. These results show considerable differences in the ability of similar anti-idiotypic antibodies to induce immune responses as well as considerable differences in the nature of a response seen within an intact network compared to an artificially induced network.

Antibody-based immunotherapeutic strategies in colorectal cancer

Monoclonal antibodies may well be on their way to becoming an integral part of therapy after the most recent success in prolonging overall and recurrence-free survival in patients with stage III colorectal cancer after potentially curative surgery. After a median follow-up of 5 years, antibody treatment reduced the overall death rate by 30% and decreased the recurrence rate by 27%. These results are similar with regard to efficacy but there is less toxicity with those obtained in contemporary and more recent chemotherapy trials. The key to success with high-molecular-weight substances such as immunoglobulines lies in the careful selection of the appropriate target population, i.e., patients with minimal residual disease, where only isolated tumor cells which are readily accessible to therapy are present. An argument for combining immunotherapy with chemotherapy can be made on the basis of the phenotype of individual disseminated tumor cells, which by immunocytochemistry were found to only rarely express proliferation-associated antigens and therefore are independent of the cell cycle. Further efforts to improve immunotherapy have also led to the combined clinical use of antibodies with biologic response modifiers which are known to enhance effector cell-mediated antibody-dependent cytotoxicity. Additional rationally designed clinical trials are ongoing in which specific immunotherapy is directed towards known, readily accessible, and abundant cell target structures, either alone or combined with treatment modalities which employ different action mechanisms.

Granulocyte/macrophage-colony-stimulating factor augments the induction of antibodies, especially anti-idiotypic antibodies, to therapeutic monoclonal antibodies

A group of 86 patients with advanced colorectal carcinoma were treated with the mouse (m) (IgG2A) or chimeric (c) monoclonal antibody (mAb) 17-1A. Prior to therapy, no patient had detectable levels of antibodies to mAb17-1A. All mmAb17-1A-treated patients (n = 76) developed antibodies against both idiotypic and isotypic determinants. Addition of granulocyte/macrophage-colony-stimulating factor (GM-CSF) to mmAb17-1A significantly enhanced the induction of anti-idiotypic (ab2) as well as anti-isotypic antibodies. Of the mmAb17-1A-treated patients, 16 developed type I allergic reactions. These patients had significantly higher concentrations of anti-(mouse Ig) antibodies than patients without type I reactions. Of these 16 patients, 5 had received mmAb17-1A alone; they constituted 9% of this group (5/56). The remaining 11 patients had been given mmAb17-1A together with GM-CSF, and represented 55% of this treatment group (11/20). The difference was statistically significant (P < 0.001). Of 10 patients, 9 (90%) treated with cmAb17-1A and GM-CSF developed ab2. The ab2 concentration in this patient group was significantly lower compared to those treated with mmAb-17A. Anti-(mouse Ig) antibodies caused clinical symptoms requiring therapeutic intervention in fewer than 10% of the patients treated with mmAb17-1A alone. With the addition of GM-CSF, the antibody concentration as well as the frequency of allergic side-effects calling for medical action increased significantly. Significantly more patients with a high ab2 concentration (at least 15 micrograms/ml) 1 month after completion of mAb therapy responded to mAb treatment as compared to those with a low ab2 concentration (P < 0.05). Moreover, patients with a high ab2 concentration (at least 15 micrograms/ml) had a median survival time of 15 months while those with a lower concentration survived for a median time of 9 months (P = 0.01).

Human anti-idiotypic antibodies induced a humoral and cellular immune response against a colorectal carcinoma-associated antigen in patients

Induction of immunity against antigens expressed on tumor cells might prevent or delay recurrence of the disease. Six patients operated on for colorectal carcinoma were immunized with human monoclonal anti-idiotypic antibodies (h-Ab2) against the mouse 17-1A anti-colon carcinoma antibody, mimicking a nominal antigen (GA733-2). All patients developed a long-lasting T-cell immunity against the extracellular domain of GA733-2 (GA733-2E) (produced in a baculovirus system) and h-Ab2. This was shown in vitro by specific cell proliferation (DNA-synthesis) assay as well as by interleukin 2 and interferon gamma production and in vivo by the delayed-type hypersensitivity reaction. Five patients mounted a specific humoral response (IgG) against the tumor antigen GA733-2E (ELISA) and tumor cells expressing GA733-2. Epitope mapping using 23 overlapping peptides of GA733-2E revealed that the B-cell epitope was localized close to the N terminus of GA733-2. Binding of the antibodies to the tumor antigen and to one 18-aa peptide was inhibited by h-Ab2, indicating that the antibodies were able to bind to the antigen as well as to h-Ab2. The results suggest that our h-Ab2 might be able to induce an anti-tumor immunity which may control the growth of tumor cells in vivo.

Antiidiotypic antibodies in ovarian cancer patients treated with the monoclonal antibody B72.3

Immunotherapy with monoclonal antibodies has become a hopeful approach to the adjuvant therapy of cancer patients. Recently, formation of antiidiotypic antibodies (Ab2) has been demonstrated in ovarian cancer patients after immunization with F(ab')2 fragments of the monoclonal antibody OC 125 (MAb OC 125). Preliminary results suggested that patients with high Ab2 serum concentrations had better survival rates compared to those where low or no Ab2 serum levels were detected. Beginning in 1992, 23 patients with advanced ovarian adenocarcinomas have been treated with repeated intravenous applications of the MAb B72.3, which is directed against the ovarian carcinoma associated antigen TAG-72. Five of them had been pretreated with several F(ab')2 MAb OC 125 infusions. Blood sample analysis revealed a remarkable antiidiotypic antibody (Ab2) response in 14 patients, with five patients developing high serum levels > 1000 U/ml. Ab2 serum concentrations increased with increasing number of Mab B72.3 applications. In terms of serum levels, corresponding antiidiotypic antibody responses in patients who received both the F(ab')2 MAb OC 125 and the MAb B72.3 differed considerably. We conclude that the use of MAb B72.3 may be an additional beneficial approach to the immunological therapy of ovarian cancer. Subsequent MAb B72.3 application after failure of the F(ab')2 MAb OC 125 may induce appreciable Ab2 serum concentrations and vice versa.

Monospecific polyclonal anti-anti-idiotypic antibodies to the carboxyterminal undecapeptide of the SV40 large tumour antigen

The murine monoclonal antibody PAb1605 defines an epitope, peptide Lys(698)-Thr(708) (KT), on the carboxyterminus of the tumour(T)antigen of SV40-transformed cells. In vivo and in vitro experiments had shown that this sequence represents an epitope for both humoral and cellular immune responses. When injected into rabbits PAb1605 induces anti-idiotypic antibodies (Ab-2). Ab-2 beta (internal image type) was purified by adsorption chromatography and characterized by the ability of KT to compete with the binding of ab-2 with ab-1. Murine anti-anti-idiotypic antibodies (ab-3) were obtained by immunization of mice with ab-2 beta. Both ab-1 and ab-3 JgG showed affinities to immunoprecipitated SV40 T antigen by immunoblot analysis and to nuclear SV40 T antigen by the immunofluorescence assay. The binding of ab-3 to SV40 T antigen was completely inhibited by competition with KT. We conclude that the polyclonal ab-3 is of the ab-3 subtype and specific for only one epitope which is represented by KT and defined by ab-1. The results demonstrate that the specificity for a defined peptide epitope of an antibody was conserved even after two consecutive steps of anti-idiotypic-antibody formation in two host species. Since this postulate of network theory could be verified for a sequence of a tumour-associated antigen which represents a B- and T cell epitope, this model is of great interest for further tumour immunological studies.

Induction of an immune network cascade in cancer patients treated with monoclonal antibodies (ab1). II. Is induction of anti-idiotype reactive T cells (T3) of importance for tumor response to mAb therapy?

The antitumor effector functions of unconjugated monoclonal antibodies (mAb) in cancer therapy are not fully understood. Direct cytotoxic mechanisms such as antibody-dependent cellular cytotoxicity, complement-dependent cytolysis and apoptosis have been suggested. Induction of anti-idiotypic (ab2) and anti-anti-idiotypic (ab3) antibodies as well as the corresponding T cells (T2 and T3) has also been proposed to be of therapeutic significance. In this study induction of an immune network cascade in ten patients with colorectal carcinoma, treated with mAb 17-1A (ab1) was assessed. After treatment, all ten patients had anti-idiotypic antibodies and anti-anti-idiotypic antibodies with ab1-like binding specificity while only five of ten patients had T cells corresponding to ab3 (T3) as assessed by a proliferation assay (DNA synthesis), and an assay of interferon gamma production (ELISPOT) (Enzyme-linked immuno SPOT) in vitro or by a delayed-type hypersensitivity reaction in vivo. Purified T cells from four of the five patients with a positive T3 test responded with DNA synthesis after stimulation using human anti-mAb 17-1A anti-idiotypic monoclonal antibodies. These four patients had a clinical response showing a tumor reduction after therapy, while all six patients lacking a proliferative response failed to show tumor regression. Induction of a cell-mediated immune network cascade might accordingly be an important antitumor effector function of mAb and should be considered in the future design of mAb-based therapy protocols in cancer patients.

Induction of an immune network cascade in cancer patients treated with monoclonal antibodies (ab1). I. May induction of ab1-reactive T cells and anti-anti-idiotypic antibodies (ab3) lead to tumor regression after mAb therapy?

The antitumor effector functions of unconjugated monoclonal antibodies in cancer therapy are complex. Direct cytotoxic mechanisms such as antibody-dependent cellular cytotoxicity, complement-dependent cytolysis and apoptosis have been suggested. Induction of anti-idiotypic (ab2) and anti-anti-idiotypic (ab3) antibodies as well as T cell (T2 and T3 respectively) responses have also been proposed to be of clinical importance. In this study induction of an immune network cascade in patients with colorectal carcinoma, treated with mAb 17-1A (ab1) was assessed. All patients developed anti-idiotypic antibodies (ab2) of the IgG class after treatment with ab1 and four of nine patients showed induction of mouse Ig reactive T cells [a proliferative response to F(ab')2 fragments of ab1]. Patients with such a T cell response developed anti-anti-idiotypic antibodies (ab3), while those lacking the T cell reactivity failed to mount an ab3 response. Three of four patients with a T cell response achieved a tumor response to mAb therapy. Thus, all responding patients belonged to the group of individuals developing ab3. Induction of mAb(ab1)-reactive T cells as well as an immune network cascade might be important antitumor effector functions of mAb and should be considered in the future design of mAb-based therapy protocols in cancer patients.

The clinical significance of HAMA in patients treated with mouse monoclonal antibodies

Twenty-four patients were analyzed for the development of HAMA (human antimouse antibodies) after being treated with repeated doses (200-500 mg) of the mouse monoclonal antibody (MAb) 17-1A. All patients developed anti-17-1A IgG antibodies, and most of them also developed IgM antibodies. In only two patients could immune complexes be demonstrated. Allergic reactions were rare (1.9%). In an extended study, a further 19 patient were analyzed for an idiotypic response. Forty-one out of 43 patients developed antiidiotypic antibodies (ab2), and 20 of these also anti-anti-idiotypic antibodies (ab3). Ab3+ patients responded significantly better (p = 0.01) and survived longer (p < 0.001) compared to ab3- patients. In this study, we showed that MAb 17-1A could be repeatedly given on a safe basis. The development of high titers of HAMA did not cause significant clinical problems when further repeated infusions of MAb 17-1A were given. The development of an idiotypic response also indicate that the induction of HAMA might be beneficial and not harmful to the patient.

Chemotherapy and immunotherapy of colorectal cancer

More than 50% of the patients with large bowel cancer develop disseminated disease and invariably succumb. Adjuvant chemotherapy with 5-FU and levamisole have been shown to be more efficient than 5-FU alone or in combination with cytostatics. The combination of 5-FU, leukovorin and methotrexate induces prolonged survival with a good quality of life in metastatic colorectal cancer (CRC). During the last decade tumor immunotherapy has been an alternative facilitated by isolation and large scale production of cytokines and monoclonal antibodies. The mouse monoclonal antibody (MAb) 17-1A recognizes a tumor-associated antigen (TAA), present in high concentrations on the surface of gastrointestinal tumor cells. Injections of MAb 17-1A in patients with metastatic CRC induced generation of anti-idiotypic (ab2) in 90% and anti-anti-idiotypic (ab3) antibodies in 47% of the treated patients. The development of ab3 correlated significantly with survival (mean 80 weeks) while ab3- patients survive only 38 weeks. One of 52 patients treated with MAb 17-1A is a complete remission after 66 months, 3 had minor regression and 6 had a stable disease (19% RR). Based on in vitro findings showing increased antibody-dependent cellular cytotoxicity (ADCC) by the combination of granulocyte-macrophage colony stimulating factor (GM-CSF) and MAb 17-1A, 16 CRC patients have been treated with subcutaneously injections of GM-CSF for 10 days and intravenous infusions of MAb 17-1A at day 3. Two of 16 are in CR, 1 in MR and 3 in SD (37.5% RR). Minor side-effects were registered. A further development of immunotherapy of CRC might imply vaccination by injection of specific human anti-idiotypic antibodies (ab2) which mimics the nominal antigen, in order to induce a specific immunity.