A method for monoclonal antibody isotype switching: anti-CD60 VH expression in a heavy chain-deficient hybridoma variant

Alteration of monoclonal antibody isotype is desirable for a variety of purposes, including obtaining an improved reagent for investigative or therapeutic use. A variety of approaches for isotype switching, particularly from IgM to various IgG subclasses, have been described. Antibodies that recognize carbohydrate determinants on glycoproteins, glycolipids, or polysaccharides are generally of the IgM isotype. This includes all available antibodies to the human CD60 antigen, a determinant with cell coactivating properties described on a subset of T lymphocytes and on other cell types. In this report a new method for monoclonal antibody isotype switching is presented. A plasmid containing the VH regions of anti-CD60 linked to C gamma 1 was transfected into a spontaneously arising variant of the CD60 hybridoma that produced kappa light chain but no heavy chain. This transfected hybridoma line maintains stable production of useful quantities of IgG1 monoclonal anti-CD60 in vitro and in vivo.

CT-SPECT fusion plus conjugate views for determining dosimetry in iodine-131-monoclonal antibody therapy of lymphoma patients

A method for performing 131I quantitative SPECT imaging is described which uses the superimposition of markers placed on the skin to accomplish fusion of computed tomography (CT) and SPECT image sets.

METHODS

To calculate mean absorbed dose after administration of one of two 131I-labeled monoclonal antibodies (Mabs), the shape of the time-activity curve is measured by daily diagnostic conjugate views, the y-axis of that curve is normalized by a quantitative SPECT measurement (usually intra-therapy), and the tumor mass is deduced from a concurrent CT volume measurement. The method is applied to six B-cell non-Hodgkin's lymphoma patients.

RESULTS

For four tumors in three patients treated with the MB1 Mab, a correlation appears to be present between resulting mean absorbed dose and disease response. Including all dosimetric estimates for both antibodies, the range for the specific absorbed dose is within that found by others in treating B-cell lymphoma patients. Excluding a retreated anti-B1 patient, the tumor-specific absorbed dose during anti-B1 therapy is from 1.4 to 1.7 mGy/MBq. For the one anti-B1 patient, where quantitative SPECT and conjugate-view imaging was carried out back to back, the quantitative SPECT-measured activity was somewhat less for the spleen and much less for the tumor than that from conjugate views.

CONCLUSION

The quantitative SPECT plus conjugate views method may be of general utility for macro-dosimetry of 131I therapies.

Imaging of lymphoma with PET with 2-[F-18]-fluoro-2-deoxy-D-glucose: correlation with CT

PURPOSE

To prospectively compare the accuracy of positron emission tomography (PET) with 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (FDG) in imaging thoracicoabdominal lymphoma to that of computed tomography (CT).

MATERIALS AND METHODS

Sixteen patients with lymphoma (11 with non-Hodgkin lymphoma [NHL] and five with Hodgkin disease) underwent FDG-PET and CT. Blinded, independent interpretations of PET and CT studies were followed by a direct comparison of the images. Measurement of tumor uptake of FDG was performed on positive PET studies.

RESULTS

Fifty-four foci of abnormal uptake were detected with PET in 13 patients. Forty-nine corresponding sites of lymphadenopathy and/or masses were detected with CT. All sites of adenopathy seen at CT were detected at PET. Three patients with Hodgkin disease had negative findings at abdominal PET, CT, and subsequent staging laparotomy. FDG uptake was comparable for both the low- and intermediate-grade lymphomas.

CONCLUSION

These preliminary data indicate excellent accuracy for FDG-PET imaging of thoracicoabdominal lymphoma. All grades of NHL were successfully imaged with FDG-PET. PET appears to be a useful method for imaging lymphoma.

Evaluation of dietary antioxidant levels and supplementation with ICAPS-Plus and Ocuvite

BACKGROUND

Oxidative damage caused by free radicals has been implicated in the development of age-related macular degeneration (ARMD). Recent studies suggest that antioxidant vitamins and minerals can be useful for the management and/or prevention of this condition.

METHODS

To assess the normal dietary intake of the antioxidants, 28 healthy subjects 55 years of age and over completed a diet survey. Then two over-the-counter (OTC) nutritional supplements that make claims about the antioxidant nutrients they contain (ICAPS-Plus and Ocuvite) were evaluated with respect to their ability to raise blood levels of two important antioxidant nutrients: zinc and beta-carotene.

RESULTS

Based on the diet survey, 26 of the 28 subjects were found to have deficient intakes; zinc and selenium were the most commonly deficient nutrients. Following a 2-week administration period, both ICAPS-Plus and Ocuvite significantly raised mean serum zinc levels 24.7 percent and 18 percent respectively; ICAPS-Plus significantly raised mean beta-carotene levels by 21.4 percent, but Ocuvite did not change the mean level significantly.

CONCLUSIONS

Based on the probable relationship between antioxidant levels and diseases such as ARMD, these results suggest that OTC supplements might be useful for selected patients.

Free radicals and antioxidant supplementation: a review of their roles in age-related macular degeneration

BACKGROUND

Age-related macular degeneration (ARMD) is a major cause of blindness in the elderly. Unfortunately, no proven form of treatment is currently available for the dry, atrophic form of ARMD seen in more than 90 percent of patients with this condition.

METHODS

A recent theory suggests that ARMD is associated with damage to the retina caused by free radicals. If this is correct, it is possible that the damage could be prevented or moderated by supplementing the diet with specific antioxidant vitamins and minerals that enhance the body's natural defenses against free radicals.

RESULTS AND CONCLUSION

This paper reviews the literature regarding the pathogenesis of ARMD and presents a rationale for its management or prevention by the use of supplemental vitamins and minerals.

Radioimmunotherapy of B-cell lymphoma with [131I]anti-B1 (anti-CD20) antibody

BACKGROUND

Many patients with non-Hodgkin's lymphomas are not cured by current therapies, and new approaches to treatment are needed. As part of an ongoing phase 1 study, we examined the effect of radioimmunotherapy with 131I-labeled B-cell-specific anti-CD20 monoclonal antibody in 10 patients with CD20-positive B-cell lymphomas in whom primary chemotherapy had failed.

METHODS AND RESULTS

Anti-B1 (anti-CD20) mouse monoclonal antibody trace-labeled with 131I (15 mg containing 5 mCi) was given intravenously at approximately one-week intervals: first, without pretreatment with unlabeled anti-B1 antibody, to all 10 patients; then, with pretreatment with 135 mg of unlabeled antibody, to 8 patients; and then, with pretreatment with 685 mg, to 2 patients. Serial quantitative gamma-camera images and measures of whole-body radioactivity were obtained after each tracer dose. All known disease sites larger than 2 cm could be imaged. The effect of a pretreatment dose of unlabeled anti-B1 antibody on targeting of the tumor with the radiolabeled antibody was variable. The pretreatment dose of unlabeled antibody that produced the highest ratio of the tumor dose to the whole-body dose in tracer studies was then used to deliver higher doses of radioactivity for radioimmunotherapy in nine patients. Three patients received doses designed to deliver 25 cGy to the whole body (two patients treated twice, six to eight weeks apart), four patients received 35 cGy (one patient treated twice), and two patients received 45 cGy (one patient treated twice); each dose contained 34 to 66 mCi of activity. Six of the nine treated patients had tumor responses, including patients with bulky or chemotherapy-resistant disease: four patients had complete remissions, and two had partial responses. Three patients had objective responses to tracer infusions before they received radioimmunotherapeutic doses. Of the four patients with complete remissions, one remained in remission for eight months and the other three continue to have no disease progression (for 11, 9, and 8 months). There was mild or no myelosuppression.

CONCLUSIONS

Radioimmunotherapy with [131I]anti-B1 antibody is a promising new treatment for lymphoma.

Automated decision making: the role of expert computer systems in the future of optometry

BACKGROUND

Artificial intelligence (AI) refers to the ability of a machine, or system, or computer program to make intelligent decisions using the same methods that humans would use. By definition, and expert system (ES) is a computer program that uses knowledge and inference procedures to solve problems which would otherwise require the application of human expertise.

METHODS

The role of expert systems in current and future applications in a number of fields were reviewed.

RESULTS

Expert systems have and will be making an impact in many fields, including optometry in the future.

CONCLUSIONS

Expert systems present an opportunity for the profession of optometry to become more efficient or accurate, provided that their development cost could be justified.

Therapy with unlabeled and 131I-labeled pan-B-cell monoclonal antibodies in nude mice bearing Raji Burkitt's lymphoma xenografts

Clinical trials of radioimmunotherapy (RIT) of lymphoma have produced frequent tumor regressions and remissions, but it has been difficult to determine to what extent these tumor responses have been due to antibody-specific targeted radiation, nontargeted radiation, and/or cytotoxicity mediated by the carrier monoclonal antibody (MoAb). In this report, RIT was studied in athymic nude mice bearing s.c. Raji human Burkitt's lymphoma xenografts using two different pan-B-cell MoAbs, MB-1 (anti-CD37) and anti-B1 (anti-CD20), which differ in isotype (and thus the potential for interaction with host effector mechanisms) and isotype-matched control antibodies either in the unlabeled state or labeled with 131I. When a single i.p. injection of 300 microCi 131I-labeled MB-1 (IgG1) was compared to treatment with unlabeled MB-1 or 300 microCi 131I-labeled MYS control IgG1 MoAb, an antibody-specific targeted radiation effect of RIT was seen. 131I-labeled MB-1 produced a 44 +/- 19% (SEM) reduction in tumor size at 3 weeks posttreatment, while unlabeled MB-1 or 300 microCi 131I-labeled MYS control IgG1 antibody treatment resulted in continued tumor growth over this period of time. In vitro studies demonstrated that MB-1 was incapable of mediating antibody-dependent cellular cytotoxicity using Raji tumor cell targets and human peripheral blood mononuclear cells. Similar to the MB-1 studies, treatment with 300 microCi 131I-labeled anti-B1 produced a 64% reduction in mean tumor size, while 300 microCi of control antibody resulted in a 58% increase in tumor size over the same 3-week period. In contrast to MB-1, however, unlabeled anti-B1 (an IgG2a MoAb which in vitro studies showed to be capable of antibody-dependent cellular cytotoxicity) also had a substantial antitumor effect. Indeed, 300 microCi 131I-labeled anti-B1 and unlabeled anti-B1 treatment (using an equivalent amount of total protein in the treatment dose) produced a similar specific reduction in tumor size. Increasing the radionuclide dose of anti-B1 to 450 microCi in another experiment did not produce a significant difference in tumor regression compared to a 300-microCi dose. These results suggest that the antitumor effects of 131I-labeled anti-B1 treatment were dominated by antibody-mediated cytotoxicity mechanisms, such that an antibody-specific targeted radiation effect could not be distinguished. In contrast, antibody-specific targeting of radiation was the dominant mechanism of tumor killing with 131I-labeled MB-1.(ABSTRACT TRUNCATED AT 400 WORDS)

Imaging, dosimetry, and radioimmunotherapy with iodine 131-labeled anti-CD37 antibody in B-cell lymphoma

PURPOSE

This study was undertaken to evaluate the tumor targeting, toxicity, and therapeutic potential of the anti-B-cell-reactive monoclonal antibody MB-1 (anti-CD37) labeled with iodine 131 given in a nonmarrow ablative dose range in B-cell lymphoma patients who relapsed after chemotherapy.

PATIENTS AND METHODS

Twelve patients with MB-1-reactive tumors were infused first with 40 mg of trace-labeled (3 to 7 mCi) MB-1. Ten patients who had no serious toxicity postinfusion and who had successful tumor imaging on serial gamma scans then received at least one 40-mg radioimmunotherapy (RIT) dose (25 to 161 mCi). Tracer estimates of delivered whole-body dose (WBD) were used in prescribing a millicurie RIT dose for seven patients.

RESULTS

Eleven patients had positive tumor imaging after a tracer dose, including patients with bulky tumors and/or large tumor burdens (> or = 1 kg) +/- splenomegaly. However, overall sensitivity for the detection of known tumor sites was only 39%. In six of eight patients with dose-assessable tumors, the radiation dose to at least one tumor was 1.1 to 3.1 times higher than to any normal organ, excluding the spleen for a 40-mg tracer dose. Tracer-dose toxicities included reversible glossal edema in one patient, grade 3 hepatic transaminasemia in another, and early drops in both circulating B and T cells (with decreases in B cells more pronounced) in nearly all patients. RIT toxicity was primarily myelosuppression (especially thrombocytopenia), which had a delayed onset and protracted recovery (without significant recovery until at least 2 months post-RIT). Grade 3 myelosuppression in two of two patients who were treated at a tracer-projected 50-cGy WBD level (133 and 149 mCi) precluded further planned RIT dose escalation. Less myelosuppression was generally observed in patients who were treated at < or = 40-cGy WBD levels. Antimouse antibodies developed in two patients. Six patients had tumor responses post-RIT. Four had responses that lasted more than 1 month (2 to 6 months), which included one complete response, one partial response, one minor response, and one mixed response. Responses seemed to occur more frequently in imaged tumors than in nonimaged tumors. The most durable response occurred in a patient who had the best antibody targeting to tumor.

CONCLUSIONS

Although 131I-MB-1 has limited diagnostic value, it can produce tumor responses at nonmarrow ablative RIT doses. Further studies that focus on improving tumor targeting with this or other B-cell-reactive radiolabeled antibodies and on ameliorating the myelosuppression associated with the RIT-dosing approach used in this trial are warranted.

Improved delivery of radiolabeled anti-B1 monoclonal antibody to Raji lymphoma xenografts by predosing with unlabeled anti-B1 monoclonal antibody

A human B-cell lymphoma xenograft model was used to test whether the administration of unlabeled MoAb prior to injection of radiolabeled monoclonal antibody (MoAb) improves delivery of the radiolabeled MoAb to tumor prior to testing in clinical radioimmunotherapy trials. The anti-B1/CD20 pan-B-cell MoAb reactive with human B-cell lymphomas and leukemias but not reactive with mouse B-cells was used in this study. Athymic nude mice bearing human Raji Burkitt lymphoma xenografts were given injections of 2.5 muCi (0.3 microgram) 131I-labeled anti-B1 with or without a 2-h prior single injection of 100 micrograms of unlabeled anti-B1 antibody. Four days later the animals given injections of 131I-labeled anti-B1 and the unlabeled anti-B1 predose had a tumor uptake of 12.72 +/- 1.17% (SEM) of injected dose/g which was 44% greater than the animals receiving the 131I-labeled anti-B1 alone (P = 0.014). The uptake in most normal tissues was unchanged, although the blood level of 131I-labeled anti-B1 appeared to be greater following unlabeled anti-B1 predosing (P = 0.067). Predosing with isotype matched irrelevant MoAb did not result in a greater tumor uptake or blood concentration of 131I-labeled anti-B1 compared to the administration of 131I-labeled anti-B1 alone. In studies using 111In-labeled anti-B1, the effect of unlabeled antibody predosing was more pronounced. For animals given injections of 4.5 muCi (0.4 microgram) 111In-labeled anti-B1 and the unlabeled anti-B1 predose, the uptake in tumor was 12.37 +/- 2.07% of injected dose/g which was 162% greater than the animals receiving the 111In-labeled anti-B1 alone (P = 0.009). Predosing decreased 111In-labeled anti-B1 uptake in spleen, while the blood level was significantly greater. Predosing was more effective than simultaneous injection in improving tumor delivery. When tumor-bearing mice were either simultaneously given injections of 36 micrograms of unlabeled anti-B1 and 4 micrograms 111In-labeled anti-B1 or were given preinjections of 36 micrograms unlabeled anti-B1 3 h prior to injection of 4 micrograms 111In-labeled anti-B1, tumor uptake 3 days later was 1.3-fold higher in the animals which received the preinjection of unlabeled antibody (P = 0.011). As the quantity of unlabeled anti-B1 was increased (36, 96, 996 micrograms) in the predose, significantly greater uptake in tumor was observed, although this uptake appeared to plateau at the highest predoses.(ABSTRACT TRUNCATED AT 400 WORDS)

Hsp27 is a mediator of sustained smooth muscle contraction in response to bombesin

We have identified the low MW 27 kD heat shock protein as a major phosphoprotein constituent of smooth muscle and have investigated its potential role in agonist induced smooth muscle contraction. The neuropeptides bombesin and substance P, which are present in neurons of the anorectal region, induce contraction of isolated smooth muscle cells from this region by activating different intracellular pathways. Substance P-induced contraction is 1,4,5-inositol trisphosphate (IP3)/calmodulin dependent, while contraction induced by bombesin is mediated by a protein kinase C (PKC)-dependent pathway. The sustained contraction induced by bombesin or exogenous PKC was blocked by preincubation of cells with monoclonal antibodies to hsp27, while the transient contraction induced by substance P or IP3 was unaffected by the antibodies. Preincubation with isotype matched control antibodies had no inhibitory effect on contraction induced in response to the agents used. These data support a novel role for hsp27 in the non calmodulin mediated sustained contraction induced by bombesin or PKC.

Importance of intra-therapy single-photon emission tomographic imaging in calculating tumour dosimetry for a lymphoma patient

The dosimetry for two, similarly sized tumours in a lymphoma patient being treated with non-bone marrow ablative, monoclonal antibody therapy is reported. The 45-year-old man was infused with 2.48 GBq (67 mCi) of 131I-labelled MB-1. Prior to therapy, a time series of diagnostic conjugate-view images and a radionuclide transmission scan were obtained and processed to obtain time-activity curves. Starting 2 days after the therapeutic infusion of radioactivity, a second conjugate-view time series was obtained. At that time, a quantitative single-photon emission tomography (SPET) acquisition was also carried out. Pre- and post-therapy X-ray computed tomography scans demonstrated a percentage reduction in volume for the right tumour which was 3.8 times that for the left tumour. In contrast, diagnostic conjugate views by themselves estimated the absorbed dose to be the same for the two tumours. Addition of therapy conjugate-view data increased the right-over-left ratio but only to 1.22. Normalizing either time-activity series by the intra-therapy SPET results increased the ratio to greater than 1.5. We assume here that a differential dose is correct according to the differential tumour shirnkage. One can further assume that the largest ratio corresponds most certainly to the most accurate dosimetric method. Other assumptions are possible. While additional study is essential, data from this patient suggest that the preferred dosimetric method is intra-therapy SPET normalization of either time series.

The potential of 2-deoxy-2[18F]fluoro-D-glucose (FDG) for the detection of tumor involvement in lymph nodes

To assess the potential of FDG for PET imaging of nodal tumor metastases, we evaluated its uptake into normal lymph nodes, tumor-involved lymph nodes, and subcutaneous tumor xenografts in rodents. Normal lymph nodes in mice and rats accumulate FDG moderately, developing node/blood ratios of 1.3-11.9/1 at 2 hr following i.v. injection. By contrast, FDG given subcutaneously to healthy Sprague Dawley rats developed very high normal draining lymph node/blood ratios (272/1) versus 7.7/1 by i.v. injection. In nude mice, subcutaneous human ovarian cancer xenografts had 1.27-fold more uptake relative to blood than did normal popliteal lymph nodes. Subcutaneous tumor xenografts of rat breast cancer developed tumor/normal node uptake ratios of 4.91 +/- 0.43/1 and tumor/blood ratios of 6.6 +/- 0.9 at 2 hr postinjection. Mouse nodes involved with 38C13 murine B-cell lymphoma had mean node/blood ratios of 42.9 +/- 6.7/1 and tumored node/normal lymph node uptake of 6.3/1. Thus, FDG given intravenously but not subcutaneusly (due to high normal nodal uptake) has potential as an agent for the detection of metastatic tumors in regional lymph nodes using PET scanning.

Molecular characterization of anti-idiotype antibody-resistant variants of a murine B cell lymphoma

We have previously identified Id- tumor vaiants that emerge after anti-Id mAb therapy of the murine B cell lymphoma 38C13. This report characterizes the molecular basis for these variants. By using a modification of the polymerase chain reaction (PCR), mu and kappa Ig loci were sequenced from nine Id- variants derived directly by anti-Id immunoselection in vivo. Ig kappa loci sequence analysis was also performed from 10 additional variants amplified directly from tumor cells in vitro without immunoselection. We demonstrate that the molecular mechanism underlying tumor cell escape in this model is the spontaneous emergence of variants that have undergone kappa L chain gene "re-rearrangement" before positive selection by the anti-Id antibody. A second round of re-rearrangement was also demonstrated to occur within primary tumor variants. Re-rearrangement of the 38C13 tumor cell Ig kappa locus is strongly biased toward use of variable kappa genes within the conserved V kappa-Ox1 gene family, although their use is not exclusive. With the use of RNA PCR re-rearrangement was documented to occur in vitro at a frequency of approximately 1.0 x 10(-5)/cell. These findings may have important implications for the application of anti-Id antibodies as a therapeutic approach for human lymphomas and for understanding of the Ig gene rearrangement process.

Molecular characterization of anti-idiotype antibody-resistant variants of a murine B cell lymphoma

We have previously identified Id- tumor vaiants that emerge after anti-Id mAb therapy of the murine B cell lymphoma 38C13. This report characterizes the molecular basis for these variants. By using a modification of the polymerase chain reaction (PCR), mu and kappa Ig loci were sequenced from nine Id- variants derived directly by anti-Id immunoselection in vivo. Ig kappa loci sequence analysis was also performed from 10 additional variants amplified directly from tumor cells in vitro without immunoselection. We demonstrate that the molecular mechanism underlying tumor cell escape in this model is the spontaneous emergence of variants that have undergone kappa L chain gene "re-rearrangement" before positive selection by the anti-Id antibody. A second round of re-rearrangement was also demonstrated to occur within primary tumor variants. Re-rearrangement of the 38C13 tumor cell Ig kappa locus is strongly biased toward use of variable kappa genes within the conserved V kappa-Ox1 gene family, although their use is not exclusive. With the use of RNA PCR re-rearrangement was documented to occur in vitro at a frequency of approximately 1.0 x 10(-5)/cell. These findings may have important implications for the application of anti-Id antibodies as a therapeutic approach for human lymphomas and for understanding of the Ig gene rearrangement process.

Anti-idiotypic antibodies recognizing stable epitopes limit the emergence of idiotype variants in a murine B cell lymphoma

The emergence of Id variants is a major escape mechanism from anti-Id therapy of human B cell malignancies and of the murine B cell lymphoma 38C13. To determine what impact the epitope specificity of anti-Id antibodies has on the prevention of emergence of such Id variants in the 38C13 lymphoma, anti-Id mAb of varying epitope specificity for the Id of 38C13 tumor cells were produced and studied. Some antibodies, produced by immunizing mice with both the wild-type 38C13 IgM and variant IgM, cross-reacted with wild-type 38C13 IgM and with all four members of a panel of variant IgM. These anti-Id did not react with separated 38C13 IgM H or L chains by Western blot, but did react with the cytoplasmic H chain of the surface Ig- variant cell line T2D that expresses the same H chain as wild-type 38C13 in its cytoplasm but does not express any associated L chain. In contrast, anti-Id of narrower specificity did not react with this H chain. This indicated that the broadly cross-reactive antibodies recognized a stable epitope on 38C13 H chain. When a broadly cross-reactive antibody MS11G6 was compared to S1C5, an antibody of narrower specificity, MS11G6, was superior at preventing tumor growth in mice inoculated with 38C13 cells. Moreover, no surface Ig+ variants emerged in escaping tumors in the MS11G6-treated group, whereas such variants were common in the S1C5 treated group. Both anti-Id were of equal efficacy in eliminating wild-type 38C13 cells by using 38C13 cells in tumor inoculums that had just been cloned in vitro, but MS11G6 was also capable of preventing the growth of several surface Ig+ variant cell lines in vivo. We conclude that anti-Id recognizing more stable Id determinants can limit the emergence of Id variants and therefore be more effective therapeutic agents. This finding is of additional importance as additional in vivo and immunophenotypic studies demonstrated that the generation of Id variants was an ongoing process both in cloned parental 38C13 cells and its variants.

Anti-idiotypic antibodies recognizing stable epitopes limit the emergence of idiotype variants in a murine B cell lymphoma

The emergence of Id variants is a major escape mechanism from anti-Id therapy of human B cell malignancies and of the murine B cell lymphoma 38C13. To determine what impact the epitope specificity of anti-Id antibodies has on the prevention of emergence of such Id variants in the 38C13 lymphoma, anti-Id mAb of varying epitope specificity for the Id of 38C13 tumor cells were produced and studied. Some antibodies, produced by immunizing mice with both the wild-type 38C13 IgM and variant IgM, cross-reacted with wild-type 38C13 IgM and with all four members of a panel of variant IgM. These anti-Id did not react with separated 38C13 IgM H or L chains by Western blot, but did react with the cytoplasmic H chain of the surface Ig- variant cell line T2D that expresses the same H chain as wild-type 38C13 in its cytoplasm but does not express any associated L chain. In contrast, anti-Id of narrower specificity did not react with this H chain. This indicated that the broadly cross-reactive antibodies recognized a stable epitope on 38C13 H chain. When a broadly cross-reactive antibody MS11G6 was compared to S1C5, an antibody of narrower specificity, MS11G6, was superior at preventing tumor growth in mice inoculated with 38C13 cells. Moreover, no surface Ig+ variants emerged in escaping tumors in the MS11G6-treated group, whereas such variants were common in the S1C5 treated group. Both anti-Id were of equal efficacy in eliminating wild-type 38C13 cells by using 38C13 cells in tumor inoculums that had just been cloned in vitro, but MS11G6 was also capable of preventing the growth of several surface Ig+ variant cell lines in vivo. We conclude that anti-Id recognizing more stable Id determinants can limit the emergence of Id variants and therefore be more effective therapeutic agents. This finding is of additional importance as additional in vivo and immunophenotypic studies demonstrated that the generation of Id variants was an ongoing process both in cloned parental 38C13 cells and its variants.

Production of mammastatin, a tissue-specific growth inhibitor, by normal human mammary cells

The growth of human mammary cells may be regulated by a balance between growth stimulatory and growth inhibitory pathways. Polypeptides of 47 and 65 kilodaltons (mammastatin) were isolated from conditioned medium of normal human mammary cells. Monoclonal antibodies against mammastatin were generated that blocked its activity and were used for purification and further characterization of the protein. Mammastatin inhibited the growth of 5 transformed human mammary cell lines, but had no effect on the growth of 11 transformed human cell lines derived from nonmammary tissues. Mammastatin appeared to be a heat-labile protein distinct from transforming growth factor-beta (TGF-beta). By immunoperoxidase staining it was detected in cultured normal human mammary cells, but was decreased in transformed mammary cells.

Isotype switch variant anti-idiotype monoclonal antibodies: comparative radiolabeling and in vitro binding

The influence of antibody isotype on radiolabeling efficacy and immunoreactivity has been difficult to systematically examine as antibodies of different isotypes generally vary in both constant and variable regions. The recent ability to isolate class or isotype switch monoclonal antibodies that have identical binding regions but different constant regions allows for such a comparison to be undertaken. Two isotype switch variant families of murine anti-idiotypic monoclonal antibodies were studied for radioiodination efficacy and immunoreactivity following labeling. In one of the families (S3H5), the IgG2a isotype switch variant derived from an IgG2b parent had nearly 70% greater iodine incorporation and over 50% greater immunoreactivity than the IgG2b parent. In the other family (S5A8), the IgG2a isotype switch variant had virtually identical efficacy of iodine incorporation and binding to antigen after labeling as did its IgG2b parent. Differences in relative heavy and light chain iodine incorporation were seen among isotype switch variants and their parents regardless of alterations in quantitative iodine incorporation or immunoreactivity. We conclude that in certain instances, cloning of an isotype switch variant antibody can result in an antibody offspring that has superior radiolabeling characteristics to its parent antibody. This isotype switching approach may find utility in converting highly-specific, but difficult to label antibodies, to more useful agents.

Idiotype variants emerging after anti-idiotype monoclonal antibody therapy of a murine B cell lymphoma

One of the difficulties encountered with the treatment of human B cell malignancies with anti-Id antibodies is the emergence of Id variants. The current study was designed to investigate this phenomenon further by using the murine B cell lymphoma model 38C13. Tumors were harvested that developed despite treatment with the anti-Id antibody S1C5 in mice inoculated with 38C13 cells and evaluated by immunofluorescence. Various phenotypes were found among escaping tumor cells. Some cells continued to react with S1C5 whereas others lost S1C5 reactivity. Among these latter cells, some continued to express surface IgM kappa, whereas others no longer expressed surface mu or kappa. After Id variant cell lines were established, immunofluorescence and ELISA of cell lysates from the surface IgM kappa- lines revealed persistent intracellular mu H chain but no detectable kappa. Surface IgM kappa+ lines were fused with myeloma cells and the Ig proteins secreted by the resultant hybridomas analyzed. The apparent m.w. of the mu-chains of these rescued Ig was the same as wild-type 38C13, whereas the kappa-chains were either the same or different in m.w. from the wild type. The IgM kappa of the variant line, T3C, weakly reacted with S1C5 and did not react with other anti-Id antibodies. The IgM kappa of the other variants were nonreactive with all the antibodies. Immunofluorescence of these surface Ig+ variants confirmed this finding. Some of the surface Ig+ and Ig- variant lines grew identically to wild-type tumor in vivo, but only the weakly S1C5-reactive variant T3C was inhibited in its growth by S1C5. Moreover, T3C was the only one of these lines capable of being lysed in vitro with S1C5 by antibody-dependent cellular cytotoxicity. Further studies revealed that surface Ig+ and Ig- variants emerge in escaping tumors with similar frequency and that these variants represent a major mode of tumor escape from anti-Id treatment in this model.

Idiotype variants emerging after anti-idiotype monoclonal antibody therapy of a murine B cell lymphoma

One of the difficulties encountered with the treatment of human B cell malignancies with anti-Id antibodies is the emergence of Id variants. The current study was designed to investigate this phenomenon further by using the murine B cell lymphoma model 38C13. Tumors were harvested that developed despite treatment with the anti-Id antibody S1C5 in mice inoculated with 38C13 cells and evaluated by immunofluorescence. Various phenotypes were found among escaping tumor cells. Some cells continued to react with S1C5 whereas others lost S1C5 reactivity. Among these latter cells, some continued to express surface IgM kappa, whereas others no longer expressed surface mu or kappa. After Id variant cell lines were established, immunofluorescence and ELISA of cell lysates from the surface IgM kappa- lines revealed persistent intracellular mu H chain but no detectable kappa. Surface IgM kappa+ lines were fused with myeloma cells and the Ig proteins secreted by the resultant hybridomas analyzed. The apparent m.w. of the mu-chains of these rescued Ig was the same as wild-type 38C13, whereas the kappa-chains were either the same or different in m.w. from the wild type. The IgM kappa of the variant line, T3C, weakly reacted with S1C5 and did not react with other anti-Id antibodies. The IgM kappa of the other variants were nonreactive with all the antibodies. Immunofluorescence of these surface Ig+ variants confirmed this finding. Some of the surface Ig+ and Ig- variant lines grew identically to wild-type tumor in vivo, but only the weakly S1C5-reactive variant T3C was inhibited in its growth by S1C5. Moreover, T3C was the only one of these lines capable of being lysed in vitro with S1C5 by antibody-dependent cellular cytotoxicity. Further studies revealed that surface Ig+ and Ig- variants emerge in escaping tumors with similar frequency and that these variants represent a major mode of tumor escape from anti-Id treatment in this model.

Idiotype vaccination against murine B cell lymphoma. Inhibition of tumor immunity by free idiotype protein

A murine B cell lymphoma (38C13) was used as a model to study the induction of idiotype (Id)-specific tumor immunity. Immunization of syngeneic mice with Id protein derived from the tumor resulted in the production of anti-Id antibodies by the host and in the induction of a state of resistance to tumor growth. Tumor immunity could be established only if the Id protein was conjugated to a strongly immunogenic carrier protein such as keyhole limpet hemocyanin or thyroglobulin, and if the conjugate was administered at least 1 week prior to tumor challenge. Free Id protein, such as that present in tumor bearing animals, was found to inhibit tumor immunity in a dose-dependent manner. Although tumor immunity could be induced in animals with pre-existent serum Id protein, the expression of the immune state was inhibited by the presence of the soluble protein.

Idiotype vaccination against murine B cell lymphoma. Inhibition of tumor immunity by free idiotype protein

A murine B cell lymphoma (38C13) was used as a model to study the induction of idiotype (Id)-specific tumor immunity. Immunization of syngeneic mice with Id protein derived from the tumor resulted in the production of anti-Id antibodies by the host and in the induction of a state of resistance to tumor growth. Tumor immunity could be established only if the Id protein was conjugated to a strongly immunogenic carrier protein such as keyhole limpet hemocyanin or thyroglobulin, and if the conjugate was administered at least 1 week prior to tumor challenge. Free Id protein, such as that present in tumor bearing animals, was found to inhibit tumor immunity in a dose-dependent manner. Although tumor immunity could be induced in animals with pre-existent serum Id protein, the expression of the immune state was inhibited by the presence of the soluble protein.