Passive immunization with an extended half-life monoclonal antibody protects Rhesus macaques against aerosolized ricin toxin

Inhalation of ricin toxin (RT), a Category B biothreat agent, provokes an acute respiratory distress syndrome marked by pro-inflammatory cytokine and chemokine production, neutrophilic exudate, and pulmonary edema. The severity of RT exposure is attributed to the tropism of the toxin's B subunit (RTB) for alveolar macrophages and airway epithelial cells, coupled with the extraordinarily potent ribosome-inactivating properties of the toxin's enzymatic subunit (RTA). While there are currently no vaccines or treatments approved to prevent RT intoxication, we recently described a humanized anti-RTA IgG1 MAb, huPB10, that was able to rescue non-human primates (NHPs) from lethal dose RT aerosol challenge if administered by intravenous (IV) infusion within hours of toxin exposure. We have now engineered an extended serum half-life variant of that MAb, huPB10-LS, and evaluated it as a pre-exposure prophylactic. Five Rhesus macaques that received a single intravenous infusion (25 mg/kg) of huPB10-LS survived a lethal dose aerosol RT challenge 28 days later, whereas three control animals succumbed to RT intoxication within 48 h. The huPB10-LS treated animals remained clinically normal in the hours and days following toxin insult, suggesting that pre-existing antibody levels were sufficient to neutralize RT locally. Moreover, pro-inflammatory markers in sera and BAL fluids collected 24 h following RT challenge were significantly dampened in huPB10-LS treated animals, as compared to controls. Finally, we found that all five surviving animals, within days after RT exposure, had anti-RT serum IgG titers against epitopes other than huPB10-LS, indicative of active immunization by residual RT and/or RT-immune complexes.

Abnormally short serum half-lives of chimeric and human IgGs in NOD-SCID mice (P4184)

The immunodeficient mice are the standard animal model in antibody research, which include the inbred NOD-SCID strain. We report here the aberrant pharmacokinetics of chimeric and human IgGs with a human IgG1 Fc domain in NOD-SCID mice. These IgGs displayed very short in vivo half-lives (25.0±0.4 hrs and 27.6±1.3 hrs, respectively) when injected at a dose of 10 μg. At a dose of 500 μg the half-lives were extended (131.1±3.1 hrs and 220.3±14.3 hrs, respectively), but still shorter than those observed in other strains of mice. The half-lives of these IgGs in NOD MrkTac, BALB/c, Swiss Webster and another immunodeficient strain of mice, C.B-17 SC-R, were similar to previous reports (300-400 hrs). In contrast, no differences in half-lives were observed for murine, rat, bovine and goat IgGs in any mouse strain studied here. RT-PCR for FcRn cDNA showed no difference in FcRn gene sequence and the binding affinity of chimeric and human IgGs to the FcRn-positive intestinal brush border of suckling mice was similar for all mice. However, chimeric and human IgGs showed higher in vitro binding affinities for Fc gamma receptors on macrophages from NOD-SCID mice vs. other strains of mice studied, suggesting that at low doses, these antibodies might bind preferentially to Fc gamma receptors-expressing macrophages, impairing their pharmacokinetics. Taken together, the NOD-SCID mice and their derivatives may not be suitable models for studying the in vivo activity of chimeric and human IgGs.

A novel platform to generate peptoid-based mimetic vaccines (P4504)

The aim of this research is to generate vaccine candidates for any virus for which a neutralizing monoclonal antibody exists without prior knowledge of the protective epitope. We have developed a platform to generate such vaccine candidates and are working on a device to automate their identification. The platform consists of libraries of B cell epitopes prepared by displaying peptoid sequences on beads, screening with neutralizing monoclonal antibodies to select peptoids bound by the antigen binding site of the monoclonal antibody, and retaining the antibody-bound peptoids with protein G dynabeads and a magnet. Peptoids are similar to peptides but with the R group attached to the nitrogen instead of the carbon. They are haptens that can be attached to protein carriers to elicit anti-peptoid antibody responses. We have conducted platform optimization and proof-of-principle testing using FLAG peptide and anti-FLAG monoclonal antibody. We then applied the optimized platform to screen peptoid libraries with monoclonal anti-FLAG and identified two potential mimetics. Mice immunized with the peptoids have made FLAG peptide-reactive antibodies, thereby demonstrating proof of concept. Implementation of this platform with neutralizing monoclonal antibodies we have in hand against HIV, West Nile virus and hepatitis C virus can identify potential mimetic vaccine candidates without prior knowledge of important epitopes, and could represent an entirely new way to generate safe vaccines.

Combined targeting of exposed phosphatidylserine, CD47 and CD54 on human pancreatic tumor cells in a mouse xenograft model of human pancreatic cancer (P4455)

Phosphatidylserine (PS) is normally intracellular but becomes exposed on the luminal surface of vascular endothelium in tumors and can also be expressed on tumor cells themselves. Studies have shown that targeting PS with an antibody enhances the antitumor effect of chemotherapy or radiation on several tumors, and induces antitumor immunity in mice. Combination of this anti-vascular and antitumor antibody with an antibody (anti-CD47) that blocks the “don’t eat me” signal CD47 commonly expressed on human tumors may lead to synergistic antitumor activity. Similarly, synergistic antitumor activity might be obtained by combining the PS-targeting antibody with anti-CD54, an antibody that has been demonstrated to have pan antitumor activity in xenograft models and is safe in humans. Our objective is to evaluate combinations of these antibodies in a xenograft model of human cancer. Studying these combinations requires determining the expression of CD47 and CD54 on several cancer cell lines. To this end, MDA-MB-231 (breast), NCI-H157 (lung), Du145 (prostate), PANC-1 and BxPC-3 (pancreatic) were analyzed for surface expression of CD47 and CD54. All five cell lines expressed CD47 (>87% of cells positive). All tested cell lines were also highly CD54 positive (>84% of cells positive) except for MDA-MB-231 (~50% positive). The effects of anti-PS antibody in conjunction with anti-CD47 or anti-CD54 on tumor growth are currently being analyzed in SCID mice bearing BxPC-3 pancreatic tumors.

The development of a novel anti-peptoid antibody for a peptoid-based vaccine platform (P4506)

Peptoids are synthetic molecules that share structure with peptides, but bear side groups on the backbone nitrogen. They are protease resistant and relatively cheap to synthesize. Since many amines can form peptoid side groups, peptoids are more diverse than peptides and can take on various shapes, making them good B cell epitopes or haptens. We aim to develop peptoid-based vaccines by screening on-bead peptoid libraries we have made with broadly neutralizing monoclonal antibodies against pathogens. Resulting peptoids can be attached to carrier proteins (which provide T cell epitopes) to elicit antibodies that should mimic the screening antibody. To test the immunogenicity of peptoid haptens, we generated the first affinity-purified anti-peptoid antibody by immunizing rabbits with a peptoid linked to a carrier and adsorbed to an adjuvant, alum. Antibodies were produced against the hapten, carrier and linker. After affinity purification, an enzyme-linked immunosorbent assay demonstrated a robust, specific response against the peptoid. This vaccine platform will now be applied using broadly neutralizing monoclonal antibodies against West Nile and hepatitis C viruses, mouse norovirus-1 and HIV. Candidate peptoids will be tested for the ability to induce neutralizing antibodies against the pathogen. If successful, this platform could be applied to any pathogen for which a broadly neutralizing monoclonal antibody is available, without structural knowledge of the native epitope.

A retrospective analysis of early and late outcome of biodegradable stent placement in the management of refractory anastomotic colorectal strictures

BACKGROUND

Benign colorectal strictures are treated conventionally by endoscopic dilation. Experience using SEMS for benign colonic strictures is limited, and outcomes to date have been disappointing. Refractory colorectal strictures remain challenging to be treated with surgery. Polydioxanone-based stent are biodegradable (BD) stent CE approved for esophageal strictures. This study was designed to investigate retrospectively the safety and the efficacy of these stents for the management of strictures refractory to multiple sessions of dilation.

METHODS

Patients with postsurgical benign strictures located within 20 cm from anal verge, refractory to mechanical or pneumatic dilation (at least 3 sessions) were included in this analysis. Clinical success was defined as the absence of occlusive symptoms and the ability to pass through the stricture with a regular size colonoscope. All patients were predilated before stent placement. Stents were released under fluoroscopic control. All patients were under stool softeners for 3 months. Follow-up was scheduled with endoscopic and fluoroscopic controls within 90 days from stent deployment and afterwards by telephone interview and/or ambulatory consultation.

RESULTS

Eleven patients (7 males, mean age 62.3 ± 8.5 years) were included. Technical success was achieved in all the patients. Stent migration was observed in four patients within the first 2 weeks after stent placement. Stent migration was followed by recurrence of stricture and obstructive symptoms in all the cases. Among the seven patients who completed the process of stent biodegradation, five of them had complete resolution of the stricture and relief of symptoms. Two of 11 patients required surgical treatment during the follow-up period (mean 19.8 (range 42-15) months). The overall success rate of the BD stent was 45 %.

CONCLUSIONS

This retrospective analysis of a limited number of patients demonstrated that nondedicated esophageal BD stents are associated with high risk of migration and clinical success in less than 50 % of patients. Dedicated stents with large diameter and antimigration findings could potentially improve the outcome of patients with refractory benign colorectal strictures.

Randomised clinical trial: low-volume bowel preparation for colonoscopy - a comparison between two different PEG-based formulations

BACKGROUND

Low-volume bowel preparations with polyethylene glycol (PEG) have been shown to provide an equivalent cleansing with improved tolerability as compared with standard PEG bowel preparation for colonoscopy. A new iso-osmotic sulphate-free formulation of PEG-Citrate-Simethicone (PEG-CS) in combination with bisacodyl has been recently developed.

AIM

To compare the quality of bowel cleansing with PEG-CS with bisacodyl vs. PEG-Ascorbate (PEG-ASC) in adult out-patients undergoing colonoscopy.

METHODS

Randomised, observer-blind, parallel group study in adult out-patients undergoing colonoscopy in five Italian centres. Both preparations were taken the evening before the procedure. Subjects were instructed to take 2-4 tablets of 5 mg bisacodyl at 16:00 hours and 2 L of PEG-CS at 20:00 hours or 2 L of PEG-ASC plus 1 L of additional water the day before colonoscopy. Bowel cleansing was evaluated according to the Boston Bowel Preparation Scale (≥6 scores were considered as 'clinical success'), and mucosal visibility according to a 3-point scale. Tolerability, acceptability and compliance were also evaluated.

RESULTS

Four hundred and eight patients were randomly allocated to PEG-CS and bisacodyl (n = 204, male patient 48%, mean age 59.1 years) or PEG-ASC (n = 204, male patient 51%, age 59.4 years). In the planned per-protocol analysis, the rate of successful preparation was 79.1% following PEG-CS with bisacodyl, and 70% following PEG-ASC (P < 0.05). Mucosal visibility was evaluated as optimal in 56.1% in the PEG-CS and bisacodyl and 46.3% in the PEG-ASC group (P < 0.05). There were no serious adverse events (AE) in each of the two experimental groups. Two subjects in the PEG-ASC group discontinued the study because of AE.

CONCLUSIONS

Polyethylene glycol-Citrate-Simethicone in combination with bisacodyl was more effective for bowel cleansing than PEG-ASC for out-patient colonoscopy. Tolerability, safety, acceptability and compliance of the two low-volume bowel preparations were similar.

Safety of cold polypectomy for <10mm polyps at colonoscopy: a prospective multicenter study

BACKGROUND

Cold polypectomy techniques (without electrocautery) by means of biopsy forceps or snare are widely adopted for the removal of subcentimetric polyps. However, few data are available on the safety of this approach. The aim of this study was to assess the safety of cold polypectomy for subcentimetric polyps, as well as the rate of advanced neoplasia in these lesions.

PATIENTS AND METHODS

In a prospective multicenter trial, consecutive patients with at least one < 10-mm polyp at colonoscopy were prospectively included. All of the < 10-mm polyps detected within the study period were removed by cold polypectomy. The rates of immediate or delayed bleeding and other complications were assessed at 7 and 30 days after cold polypectomy by telephone calls. The rate of advanced histology was also assessed. Predictive variables of postpolypectomy bleeding or advanced neoplasia were identified by multivariate analysis.

RESULTS

A total of 1015 < 10-mm polyps in 823 patients (15.5 % on antiplatelet agents) were removed. Of these, 822 (81 %) were ≤ 5 mm and 193 (19 %) were 6 - 9 mm. Immediate postpolypectomy bleeding occurred in 18 patients, corresponding to a per-patient and per-polyp bleeding rate of 2.2 % (95 % confidence interval [CI] 1.2 % - 3.2 %) and 1.8 % (95 %CI 1 % - 2.6 %), respectively. Therapy with antiplatelet agents (odds ratio [OR] 4; 95 %CI 1.5 - 10.6) and larger polyp size (OR 2; 95 %CI 1.1 - 6.9) were independent predictors of bleeding. Bleeding was successfully treated by endoscopic hemostasis in all cases and required no further medical intervention. Advanced neoplasia prevalence in polyps ≤ 5 mm was as high as 8.7 %.

CONCLUSIONS

The results from this study showed the high safety of a cold polypectomy approach for subcentimetric polyps. This was due to the low rate of postpolypectomy bleeding and to the high efficacy of endoscopic hemostasis in its treatment. The high rate of advanced neoplasia in polyps ≤ 5 mm should prompt some caution on the management of these lesions following detection at computed tomography colonography or colon capsule endoscopy.

A phase I study of a combination of anti-CD19 and anti-CD22 immunotoxins (Combotox) in adult patients with refractory B-lineage acute lymphoblastic leukaemia

Novel agents are needed for patients with refractory and relapsed acute lymphoblastic leukaemia (ALL). Combotox is a 1:1 mixture of two immunotoxins (ITs), prepared by coupling deglycosylated ricin A chain (dgRTA) to monoclonal antibodies directed against CD22 (RFB4-dgRTA) and CD19 (HD37-dgRTA). Pre-clinical data demonstrated that Combotox was effective in killing both pre-B-ALL cell lines and cells from patients with pre-B ALL. A clinical study of paediatric patients in which 3 of 17 patients with ALL experienced complete remission, supported the preclinical work and motivated this study. This study was a Phase I, dose-escalation trial using Combotox in adults with refractory or relapsed B-lineage-ALL. A cycle consisted of three doses, with one dose given every other day. Dose levels were 3, 5, 6, 7 and 8 mg/m(2) per dose. Seventeen patients, aged 19-72 years, were enrolled in this multi-institution study. The maximum tolerated dose was 7 mg/m(2) /dose (21 mg/m(2) /cycle) and vascular leak syndrome was the dose-limiting toxicity. Two patients developed reversible grade 3 elevations in liver function tests. One patient achieved partial remission and proceeded to allogeneic stem cell transplantation. All patients with peripheral blasts experienced decreased blast counts following the administration of Combotox. Thus, Combotox can be safely administered to adults with refractory leukaemia.

Rituximab but not Other anti-CD20 Antibodies Reverses Multidrug Resistance in 2 B lymphoma Cell Lines, Blocks the Activity of P-glycoprotein (P-gp), and Induces P-gp to Translocate out of Lipid Rafts

The objective of this study was to investigate the ability of the anti-CD20 antibody, Rituximab (RTX), to inhibit the activity of P-glycoprotein (P-gp), and reverse multidrug resistance (MDR) in 2 P-gp/CD20 lymphoma cell lines. We determined whether RTX would chemosensitize the 2 P-gp cell lines in vitro, and inhibit the ability of the cells to efflux Rhodamine 123. One cell line was infected with an MDR1 vector and the other was generated by drug selection. We also determined whether RTX induced P-gp to translocate out of lipid rafts. RTX chemosensitized 2 different MDR cell lines, inhibited the activity of P-gp in both, and induced P-gp to translocate out of lipid rafts in the 1 cell line that was studied in greater detail. In contrast, 3 other anti-CD20 antibodies did not chemosensitize, inhibit the activity of P-gp, or induce it to translocate out of rafts, despite the fact that 1 antibody recognized the same epitope on CD20. Our results suggest that RTX can chemosensitize 2 CD20/P-gp cell lines in vitro by inhibiting the activity of the P-gp pump. The inhibition of P-gp activity correlated with the ability of RTX to induce P-gp to translocate out of lipid rafts. Although the mechanisms by which RTX effects P-gp translocation and activity are not yet known, they are not associated with acid-sphingomyelinase activation in raft microdomains, as described for the antiproliferative activity of RTX.

Adoptive immunotherapy with allodepleted donor T-cells improves immune reconstitution after haploidentical stem cell transplantation

Poor T lymphocyte reconstitution limits the use of haploidentical stem cell transplantation (SCT) because it results in a high mortality from viral infections. One approach to overcome this problem is to infuse donor T cells from which alloreactive lymphocytes have been selectively depleted, but the immunologic benefit of this approach is unknown. We have used an anti-CD25 immunotoxin to deplete alloreactive lymphocytes and have compared immune reconstitution after allodepleted donor T cells were infused at 2 dose levels into recipients of T-cell-depleted haploidentical SCT. Eight patients were treated at 10(4) cells/kg/dose, and 8 patients received 10(5) cells/kg/dose. Patients receiving 10(5) cells/kg/dose showed significantly improved T-cell recovery at 3, 4, and 5 months after SCT compared with those receiving 10(4) cells/kg/dose (P < .05). Accelerated T-cell recovery occurred as a result of expansion of the effector memory (CD45RA(-)CCR-7(-)) population (P < .05), suggesting that protective T-cell responses are likely to be long lived. T-cell-receptor signal joint excision circles (TRECs) were not detected in reconstituting T cells in dose-level 2 patients, indicating they are likely to be derived from the infused allodepleted cells. Spectratyping of the T cells at 4 months demonstrated a polyclonal Vbeta repertoire. Using tetramer and enzyme-linked immunospot (ELISPOT) assays, we have observed cytomegalovirus (CMV)- and Epstein-Barr virus (EBV)-specific responses in 4 of 6 evaluable patients at dose level 2 as early as 2 to 4 months after transplantation, whereas such responses were not observed until 6 to 12 months in dose-level 1 patients. The incidence of significant acute (2 of 16) and chronic graft-versus-host disease (GVHD; 2 of 15) was low. These data demonstrate that allodepleted donor T cells can be safely used to improve T-cell recovery after haploidentical SCT and may broaden the applicability of this approach.

HER-2 gene amplification can be acquired as breast cancer progresses

Amplification and overexpression of the HER-2 oncogene in breast cancer is felt to be stable over the course of disease and concordant between primary tumor and metastases. Therefore, patients with HER-2-negative primary tumors rarely will receive anti-Her-2 antibody (trastuzumab, Herceptin) therapy. A very sensitive blood test was used to capture circulating tumor cells (CTCs) and evaluate their HER-2 gene status by fluorescence in situ hybridization. The HER-2 status of the primary tumor and corresponding CTCs in 31 patients showed 97% agreement, with no false positives. In 10 patients with HER-2-positive tumors, the HER-2/chromosome enumerator probe 17 ratio in each tumor was about twice that of the corresponding CTCs (mean 6.64 +/- 2.72 vs. 2.8 +/- 0.6). Hence, the ratio of the CTCs is a reliable surrogate marker for the expected high ratio in the primary tumor. Her-2 protein expression of 10 CTCs was sufficient to make a definitive diagnosis of the HER-2 gene status of the whole population of CTCs in 19 patients with recurrent breast cancer. Nine of 24 breast cancer patients whose primary tumor was HER-2-negative each acquired HER-2 gene amplification in their CTCs during cancer progression, i.e., 37.5% (95% confidence interval of 18.8-59.4%). Four of the 9 patients were treated with Herceptin-containing therapy. One had a complete response and 2 had a partial response.

Selective depletion of donor alloreactive T cells without loss of antiviral or antileukemic responses

Poor immune reconstitution after haploidentical stem cell transplantation results in a high mortality from viral infections and relapse. One approach to overcome this problem is to selectively deplete the graft of alloreactive cells using an immunotoxin directed against the activation marker CD25. However, the degree of depletion of alloreactive cells is variable following stimulation with recipient peripheral blood mononuclear cells (PBMCs), and this can result in graft versus host disease (GVHD). We have refined this approach using recipient Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines (LCLs) as stimulators to activate donor alloreactive T cells. Our studies demonstrate that allodepletion with an anti-CD25 immunotoxin following stimulation with HLA-mismatched host LCLs more consistently depleted in vitro alloreactivity than stimulation with host PBMCs, as assessed in primary mixed lymphocyte reactions (MLRs). Allodepletion using this approach specifically abrogates cytotoxic T-cell responses against host LCLs. In interferon-gamma (IFN-gamma) enzyme-linked immunospot (ELISPOT) assays, antiviral responses to adenovirus and cytomegalovirus (CMV) were preserved following allodepletion. Likewise, using HLA-A2-pp65 tetramers, we have shown that the frequency of CMV-specific T cells is unaffected by allodepletion. Moreover, the donor anti-EBV response is partially retained by recognition of EBV antigens through the nonshared haplotype. Finally, we studied whether allodepletion affects the response to candidate tumor antigens in myeloid malignancies. Using HLA-A2-PR1 tetramer analysis, we found that the frequency of T cells recognizing the PR1 epitope of proteinase 3 was not significantly different in allodepleted and unmanipulated PBMCs from patients with chronic myeloid leukemia (CML) undergoing transplantation. Based on these data, we have embarked on a phase 1 clinical trial of addback of allo-LCL-depleted donor T cells in the haplo-identical setting.

Immune reconstitution without graft-versus-host disease after haemopoietic stem-cell transplantation: a phase 1/2 study

BACKGROUND

Allogeneic haemopoietic stem-cell transplantation (HSCT) is the treatment of choice for many haematological malignancies and inherited disorders. When stem cells for transplantation come from a human leucocyte antigen matched unrelated donor, or from a partly mismatched related donor, ex-vivo T-cell depletion of the graft can prevent development of graft-versus-host disease, but lead in turn to a delay in immune reconstitution and a concordant increase in incidence of opportunistic infections and leukaemic relapses. We aimed to infuse T cells selectively depleted in allogeneic T cells that cause graft-versus-host disease using an ex-vivo procedure designed to eliminate alloactivated donor T cells, with an immunotoxin that reacts with a cell surface activation antigen, CD25.

METHODS

We did a phase 1/2 study, in which 1-8 x 10(5) allodepleted T cells/kg were infused between days 15 and 47 into 15 paediatric patients who had acquired or congenital haemopoietic disorders and who received HSCT on day 0. Occurrence of graft-versus-host disease and time to immune reconstitution were assessed. No treatment for graft-versus-host disease was given.

FINDINGS

Less than 1% residual anti-host alloreactivity was recorded in 12 of 16 procedures. Other immune responses were preserved by the allodepletion procedure in 12 cases. No cases of severe (greater than grade II) graft-versus-host disease arose. Evidence for early T-cell expansion was shown in three patients with continuing viral infections. Specific antiviral responses, such as strong cytolytic activity, were noted.

INTERPRETATION

Our results show that ex-vivo selective depletion of T cells that cause graft-versus-host disease is efficient and feasible, even in haploidentical settings.

Treatment of refractory Hodgkin's lymphoma patients with an anti-CD25 ricin A-chain immunotoxin

The anti-CD25 immunotoxin RFT5.dgA was constructed by coupling the monoclonal antibody RFT5 via a sterically hindered disulfide linker to deglycosylated ricin A-chain and was administered to patients with relapsed Hodgkin's lymphoma in four bolus infusions over 7 days (day 1, 3, 5 and 7). The maximum tolerated dose in these patients as defined in a previous phase I study was 15 mg/m2. Subsequently, further patients were enrolled at the maximum tolerated dose and a total of 18 patients were treated at this level. All patients had signs of progressive disease and were heavily pretreated. Side-effects in this trial were moderate and related to vascular leak syndrome. Five of 18 patients experienced NCI grade III toxicities including weakness, edema, dyspnea, and myalgia. Eleven of 16 (69%) patients receiving two or more cycles produced human anti-ricin antibodies and human anti-mouse antibodies (>/=1.0 microg/ml). Seventeen of 18 patients were evaluable for clinical response. These included two partial remissions. One patient demonstrated minor response and five patients stable diseases. We conclude that RFT5.dgA is of moderate clinical efficacy in this group of heavily pretreated refractory patients. Leukemia (2000) 14, 129-135.

Clinical trials with an anti-CD25 ricin A-chain experimental and immunotoxin (RFT5-SMPT-dgA) in Hodgkin's lymphoma

Immunotoxins (ITs) consisting of a cell-binding component and a potent toxin were developed as a new class of biological anti-tumor agents to improve adjuvant therapy. Hodgkin's lymphoma (HL) has been demonstrated to be an excellent target for ITs because high concentrations of lymphocyte activation markers such as CD25 and CD30 are expressed on Hodgkin and Reed-Sternberg (H-RS). Several ITs against these antigens have shown potent antitumor effects against H-RS cells in vitro and in different HL animal models. On the basis of its superiority in preclinical models, the anti-CD25 IT RFT5-SMPT-dgA was subsequently evaluated in a phase I study in patients with refractory Hodgkin's lymphoma. The IT was constructed by linking the monoclonal antibody (Moab) RFT5 via a sterically hindered disulfide linker (SMPT) to deglycosylated ricin A-chain (dgA). All 15 patients enrolled in this trial were heavily pretreated with a mean of five different prior therapies. The IT was administered intravenously over four hours on days 1-3-5-7 for total doses per cycle of 5, 10, 15, or 20 mg/m2. Side effects were reversible and related to the vascular leak syndrome (VLS), i.e. decrease in serum albumin, edema, weight gain, hypotension, tachycardia, myalgia, and weakness. In all three patients receiving 20 mg/m2 NCI toxicity grade III was observed. Thus, 15 mg/m2 is the maximal tolerated dose (MTD) of RFT5-SMPT-dgA. 50% of the patients developed human anti-ricin A-chain antibodies (HARA) and/or human anti-mouse antibodies (HAMA). Clinical results included two partial remissions (PR), one minor response (MR), three stable disease (SD) and nine progressive disease (PD). In an extension of the phase I trial, five additional patients have been treated at the MTD.

The emerging role of ricin A-chain immunotoxins in leukemia and lymphoma

Since MRD is the major cause for relapses of malignant diseases, strategies utilizing ITs to target tumor cells surviving conventional treatment have attracted scientific and clinical interest. Many different ITs against various blood-borne as well as solid malignancies have demonstrated specific potent anti-tumor effects in vitro and in animal models. Some of these have already undergone clinical phase I/II-trials. The dose-limiting toxicities of RTA ITs include manifestation of VLS presenting as decreased urinary sodium excretion, hypoalbuminemia, fatigue, hypotonia, myalgia, pulmonary edema, or rhabdomyolysis. Problems encountered clinically include the development of HAMA, HARA, and HACA and the selection of antigen-deficient malignant clones. Most clinical trials performed with ITs so far were conducted in heavily pretreated patients presenting with high tumor burdens. Thus, the responses observed with ITs in these trials are very encouraging and warrant further exploration.

A phase-I study of an anti-CD25 ricin A-chain immunotoxin (RFT5-SMPT-dgA) in patients with refractory Hodgkin's lymphoma

The anti-CD25 immunotoxin (IT), RFT5-SMPT-dgA, was used in a phase I dose escalation trial in patients with refractory Hodgkin's lymphoma. The IT was constructed by linking the monoclonal antibody RFT5 via a sterically hindered disulfide linker to deglycosylated ricin-A. All patients in this trial were heavily pretreated with a mean of 5 (range, 2 to 8) different prior therapies, including autologous bone marrow transplantation in 8 of 15. The mean age was 29 years (range, 19 to 34 years). Thirteen of 15 patients had advanced disease (stage IV) with massive tumor burdens and 6 of 15 had B symptoms. The IT was administered intravenously over 4 hours on days 1, 3, 5, and 7 for total doses per cycle of 5, 10, 15, or 20 mg/m2. Patients received one to four cycles of treatment. The peak serum concentration of intact IT varied from 0.2 to 9.7 micrograms/mL. The serum half life (T1/2) of the IT ranged from 4.0 to 10.5 hours (mean, 6.1 hours). Side effects were related to vascular leak syndrome (VLS), ie, decreases in serum albumin, edema, weight gain, hypotension, tachycardia, myalgia, and weakness. Two patients had a National Cancer Institute (NCI) grade 2 allergic reaction with generalized urticaria and mild bronchospasm. At 15 mg/m2, 1 patient experienced a grade 3 myalgia. All 3 patients receiving 20 mg/m2 experienced NCI grade 3 toxicities (edema, nausea, dyspnea or tachycardia) and 1 patient had NCI grade 4 myalgia. Thus, the maximal tolerated dose was 15 mg/m2. Seven of 15 patients made human antiricin antibodies (> or = 1.0 microgram/mL) and 6 of 15 developed human antimouse antibodies (> or = 1.0 microgram/mL). Clinical response included 2 partial remissions, 1 minor response, 3 stable diseases, and 9 progressive diseases. As has been predicted from the preclinical tests, these data seem to indicate clinical efficacy of this new IT in heavily pretreated Hodgkin's patients, thus warranting further clinical investigation.

Immunotoxins in the therapy of cancer: from bench to clinic

This review presents only those contributions that have progressed from the bench to the clinic using murine monoclonal antibodies coupled chemically to toxins, their subunits or ribosome-inactivating proteins. The rationale and progress in the development, characterization, preclinical testing and clinical trials are discussed.

The relationship between surface immunoglobulin isotype and the immune function of murine B lymphocytes. V. High affinity secondary antibody responses are transferred by both IgD-positive and IgD-negative memory B cells

We examined the adoptive secondary anti-DNP responses restored by surface IgD+ and IgD- memory B cells. Several parameters that might affect the affinity and magnitude of the adoptive responses were studied: 1) time after priming of cell donors, 2) source of anti-IgD antibodies used for immunofluorescent cell staining, 3) adjuvant used for priming, 4) carrier protein used for priming, 5) amount of antigen used for the challenge of adoptive hosts, and 6) the strain of ice used as donors and recipients. In contrast to previous reports, the present results demonstrate that the selection of cells with high affinity antigen receptors can occur to the same extent in both the delta + and delta - memory cell pools. This suggests that the loss of surface IgD is not a necessary intermediate stage in the maturation of memory B cells.

The relationship between surface immunoglobulin isotype and the immune function of murine B lymphocytes. V. High affinity secondary antibody responses are transferred by both IgD-positive and IgD-negative memory B cells

We examined the adoptive secondary anti-DNP responses restored by surface IgD+ and IgD- memory B cells. Several parameters that might affect the affinity and magnitude of the adoptive responses were studied: 1) time after priming of cell donors, 2) source of anti-IgD antibodies used for immunofluorescent cell staining, 3) adjuvant used for priming, 4) carrier protein used for priming, 5) amount of antigen used for the challenge of adoptive hosts, and 6) the strain of ice used as donors and recipients. In contrast to previous reports, the present results demonstrate that the selection of cells with high affinity antigen receptors can occur to the same extent in both the delta + and delta - memory cell pools. This suggests that the loss of surface IgD is not a necessary intermediate stage in the maturation of memory B cells.

Induction of murine B cell proliferation by insolubilized anti-immunoglobulins

This study demonstrates that intact antibodies specific for mu, delta, or light chains when coupled to Sepharose are effective in delivering proliferative signals to B cells. Furthermore, using Sepharose-coupled anti-delta antibodies, we have shown that hybridoma anti-delta (that is not active as soluble protein) is as effective as rabbit anti-delta in activating murine B cells. However, antibodies directed against two other surface molecules, I-A and H-2K, were not mitogenic. Thus, sIgM and sIgD are comparable in their ability to transmit a proliferative signal to the B cell and sIg seems to play a unique role in this regard.

Induction of murine B cell proliferation by insolubilized anti-immunoglobulins

This study demonstrates that intact antibodies specific for mu, delta, or light chains when coupled to Sepharose are effective in delivering proliferative signals to B cells. Furthermore, using Sepharose-coupled anti-delta antibodies, we have shown that hybridoma anti-delta (that is not active as soluble protein) is as effective as rabbit anti-delta in activating murine B cells. However, antibodies directed against two other surface molecules, I-A and H-2K, were not mitogenic. Thus, sIgM and sIgD are comparable in their ability to transmit a proliferative signal to the B cell and sIg seems to play a unique role in this regard.

Molecular similarities between the Qa-2 alloantigen and other gene products of the 17th chromosome of the mouse

The alloantigen Qa-2, whose gene is located on the 17th chromosome between H-2D and Tla, is identified as a molecule of 43,000 daltons which is associated with beta 2-microglobulin. Qa-2 comprises approximately 0.15% of the iodinateable cell surface protein of lymph node cells. Sequential precipitations demonstrated that Qa-2 is distinct from H-2D and H-2K molecules.