The multichain interleukin-2 receptor: a target for immunotherapy

Therapeutic Antibodies for Myeloid Neoplasms-Current Developments and Future Directions

Therapeutic monoclonal antibodies (mAbs) such as antibody-drug conjugates, ligand-receptor antagonists, immune checkpoint inhibitors and bispecific T cell engagers have shown impressive efficacy in the treatment of multiple human cancers. Numerous therapeutic mAbs that have been developed for myeloid neoplasms, including acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS), are currently investigated in clinical trials. Because AML and MDS originate from malignantly transformed hematopoietic stem/progenitor cells-the so-called leukemic stem cells (LSCs) that are highly resistant to most standard drugs-these malignancies frequently relapse and have a high disease-specific mortality. Therefore, combining standard chemotherapy with antileukemic mAbs that specifically target malignant blasts and particularly LSCs or utilizing mAbs that reinforce antileukemic host immunity holds great promise for improving patient outcomes. This review provides an overview of therapeutic mAbs for AML and MDS. Antibody targets, the molecular mechanisms of action, the efficacy in preclinical leukemia models, and the results of clinical trials are discussed. New developments and future studies of therapeutic mAbs in myeloid neoplasms will advance our understanding of the immunobiology of these diseases and enhance current therapeutic strategies.

Allogeneic hematopoietic cell transplantation after conditioning with 131I-anti-CD45 antibody plus fludarabine and low-dose total body irradiation for elderly patients with advanced acute myeloid leukemia or high-risk myelodysplastic syndrome

We conducted a study to estimate the maximum tolerated dose (MTD) of (131)I-anti-CD45 antibody (Ab; BC8) that can be combined with a standard reduced-intensity conditioning regimen before allogeneic hematopoietic cell transplantation. Fifty-eight patients older than 50 years with advanced acute myeloid leukemia (AML) or high-risk myelodysplastic syndrome (MDS) were treated with (131)I-BC8 Ab and fludarabine plus 2 Gy total body irradiation. Eighty-six percent of patients had AML or MDS with greater than 5% marrow blasts at the time of transplantation. Treatment produced a complete remission in all patients, and all had 100% donor-derived CD3(+) and CD33(+) cells in the blood by day 28 after the transplantation. The MTD of (131)I-BC8 Ab delivered to liver was estimated to be 24 Gy. Seven patients (12%) died of nonrelapse causes by day 100. The estimated probability of recurrent malignancy at 1 year is 40%, and the 1-year survival estimate is 41%. These results show that CD45-targeted radiotherapy can be safely combined with a reduced-intensity conditioning regimen to yield encouraging overall survival for older, high-risk patients with AML or MDS. This study was registered at www.clinicaltrials.gov as #NCT00008177.

Novel antibodies as anticancer agents

In recent years antibodies, whether generated by traditional hybridoma technology or by recombinant DNA strategies, have evolved from Paul Ehrlich's 'magic bullets' to a modern age 'guided missile'. In the recent years of immunologic research, we are witnessing development in the fields of antigen screening and protein engineering in order to create specific anticancer remedies. The developments in the field of recombinant DNA, protein engineering and cancer biology have let us gain insight into many cancer-related mechanisms. Moreover, novel techniques have facilitated tools allowing unique distinction between malignantly transformed cells, and regular ones. This understanding has paved the way for the rational design of a new age of pharmaceuticals: monoclonal antibodies and their fragments. Antibodies can select antigens on both a specific and a high-affinity account, and further implementation of these qualities is used to target cancer cells by specifically identifying exogenous antigens of cancer cell populations. The structure of the antibody provides plasticity resonating from its functional sites. This review will screen some of the many novel antibodies and antibody-based approaches that are being currently developed for clinical applications as the new generation of anticancer agents.

Serum level of soluble interleukin-2 receptor alpha correlates with the clinical course and activity of Wilms' tumour and soft tissue sarcomas in children

Wilms' tumour (WT) and soft tissue sarcomas (SA) in children lack reliable biochemical markers. This study was carried out to determine the clinical significance of serum soluble interleukin-2 receptor alpha (sIL-2Ralpha) in the diagnostics and treatment monitoring of children with WT and SA. The study included 48 children: ten with WT, eight with SA and 30 healthy controls. The sIL-2Ralpha levels (ELISA) and rates of elevated sIL-2Ralpha values were estimated prospectively at diagnosis and in complete remission during treatment and after therapy. As the dependence on age was determined, the levels of sIL-2Ralpha were expressed as multiplications of the upper value of the normal range for a particular age ( xN). Median pretreatment levels of sIL-2Ralpha in patients exceeded those of healthy controls (1.79 xN for WT and 1.53 for SA vs. 0.61 for controls; p < 0.001) as did the rates of elevated sIL-2Ralpha values (80% of WTand 87.5% of SA patients vs. 0% of controls). Good response to therapy was paralleled by a significant decline of pretreatment sIL-2Ralpha levels and its elevated rates. Thus, sIL-2Ralpha determination may be of some value in the diagnostics and treatment monitoring of childhood WT and SA.

131I-anti-CD45 antibody plus busulfan and cyclophosphamide before allogeneic hematopoietic cell transplantation for treatment of acute myeloid leukemia in first remission

In an attempt to improve outcomes for patients with acute myeloid leukemia (AML) after allogeneic hematopoietic cell transplantation (HCT), we conducted a phase 1/2 study in which targeted irradiation delivered by 131I-anti-CD45 antibody was combined with targeted busulfan (BU; area-under-curve, 600-900 ng/mL) and cyclophosphamide (CY; 120 mg/kg). Fifty-two (88%) of 59 patients receiving a trace 131I-labeled dose of 0.5 mg/kg anti-CD45 murine antibody had higher estimated absorbed radiation in bone marrow and spleen than in any other organ. Forty-six patients were treated with 102 to 298 mCi (3774-11 026 MBq) 131I, delivering an estimated 5.3 to 19 (mean, 11.3) Gy to marrow, 17-72 (mean, 29.7) Gy to spleen, and 3.5 Gy (n = 4) to 5.25 Gy (n = 42) to the liver. The estimated 3-year nonrelapse mortality and disease-free survival (DFS) were 21% and 61%, respectively. These results were compared with those from 509 similar International Bone Marrow Transplant Registry patients who underwent transplantation using BU/CY alone. After adjusting for differences in age and cytogenetics risk, the hazard of mortality among all antibody-treated patients was 0.65 times that of the Registry patients (95% CI 0.39-1.08; P = .09). The addition of targeted hematopoietic irradiation to conventional BU/CY is feasible and well tolerated, and phase 2 results are sufficiently encouraging to warrant further study.

Antileukemic effect of daclizumab in CD25 high-expressing leukemias and impact of tumor burden on antibody dosing

Humanized anti-CD25 antibody, daclizumab, was applied in a pilot study of 10 patients with CD25(+) leukemias and pharmacokinetic/pharmacodynamic properties were characterized. Two widely held concepts - tumor sink accelerating pharmacokinetics and higher antigen expression correlating with target cell clearance - were supported by this first systematic evaluation of these questions with actual human clinical data. A flexi-dosing regimen was validated for maintaining target drug levels in vivo with a wide range of tumor burdens. Daclizumab induced clearance of peripheral leukemic cells when highly positive for CD25, but durable responses were not obtained. If daclizumab will have a role in antileukemic therapy, it may be in minimal disease settings or as a component of a combination regimen, but only when CD25 expression is high.

Anti-Interleukin-2 Receptor Antibodies in Transplantation

Two monoclonal antibody preparations against the alpha-chain of the interleukin-2 receptor (IL-2Ralpha) are available for use, basiliximab and daclizumab, a chimeric and a humanised antibody, respectively. The first clinical studies have demonstrated the efficacy of these agents as induction therapy to reduce the rate of acute rejection after organ transplantation. Basiliximab and daclizumab have a similar effect on prevention of acute rejection. Likewise, incidence of infections and malignancies are not different between the two treatment options. Anti-IL-2Ralpha therapy was very well tolerated in clinical trials. Phase III studies with basiliximab have been undertaken with a two-dose regimen, consisting of two doses of 20mg, in an attempt to saturate the IL-2Ralpha on peripheral blood T lymphocytes for an average of 4-6 weeks. In contrast, the daclizumab dose is corrected for bodyweight and the goal is to achieve IL-2Ralpha blockade for 12 weeks. Phase III efficacy trials with daclizumab have, therefore, been developed with five doses of 1 mg/kg every 2 weeks in the first 2 months after transplantation. Whether or not it is a benefit to have blockade of the IL-2Ralpha for 10-12 weeks (daclizumab) compared with 4-6 weeks (basiliximab) remains unknown. Assuming 4-6 weeks would be sufficient for prevention of acute rejection, many centres have changed the protocol of daclizumab administration to two doses, the first dose given at the time of transplantation, the second 10 or 14 days after, with good success. Therefore, it seems feasible to limit the dose of daclizumab, which increases the ease of administration and probably also the cost effectiveness of this agent. There are no controlled studies comparing basiliximab and daclizumab, nor have different dose regimens been directly compared in renal transplantation. The data available suggest the differences are small, if present at all, and it is unlikely that such a trial will ever be done. With both compounds, a significant reduction in the number of acute rejection episodes following solid organ transplantation can be obtained without an increase in adverse effects or infectious complications.

Immunotoxin therapy of hematologic malignancies

Patients with chemotherapy relapsed or refractory hematologic malignancies may be effectively treated with allogeneic or autologous stem cell transplants. However, many patients cannot be transplanted due to age, comorbidities, or lack of suitable donors. Further, a fraction of patients relapse post-transplant. Novel therapeutic agents that can kill multidrug-resistant malignant stem cells and are not myelosuppressive are needed. One class of such agents is immunotoxins. Immunotoxins consist of cell-selective ligands covalently linked to peptide toxins. The ligand delivers the molecule to specific cell surface receptors on malignant cells. The toxin triggers cell death either by reaching the cytosol and catalytically inactivating vital cell processes or by modifying the tumor cell surface membrane. We have synthesized immunotoxins for therapy of chemoresistant hematologic diseases. In this review, we will detail the synthesis of a number of these drugs and describe their preclinical and clinical activity. Several of these agents have shown dramatic antitumor effects in patients with hematologic neoplasms, and one immunotoxin has been approved for use by the US Food and Drug Administration (FDA). Over the next several decades, a growing number of these agents should reach the clinic.

Pretarget radiotherapy with an anti-CD25 antibody-streptavidin fusion protein was effective in therapy of leukemia/lymphoma xenografts

Although radioimmunotherapy with radiolabeled intact monoclonal antibodies has demonstrated efficacy in the treatment of lymphoma, it provides low tumor-to-normal-tissue radionuclide target ratios and unwanted prolonged radiation exposure to the bone marrow. To overcome these obstacles, the administration of the radionuclide was separated from that of the antibody by using an anti-IL-2 receptor alpha antibody single chain Fv-streptavidin fusion protein, followed by radiolabeled biotin to treat lymphoma or leukemia xenografted mice. This Pretarget approach provided extremely rapid and effective tumor targeting, permitting the use of short-lived alpha-emitting radionuclides. With the beta-emitter (90)Y, all of the 10 lymphoma-xenografted mice were cured. With the alpha-emitter (213)Bi, significant efficacy was obtained in treating leukemic mice, and, furthermore, when combined with immunotherapy, 7 of 10 leukemic mice were cured. Thus, Pretarget radioimmunotherapy is very promising and could represent the next generation in the treatment of lymphoma and leukemia.

Pretargeting radioimmunotherapy of a murine model of adult T-cell leukemia with the alpha-emitting radionuclide, bismuth 213

We used a pretargeting technique to treat a nonobese diabetic/severe combined immunodeficient murine model of human adult T-cell leukemia with an anti-Tac antibody-streptavidin (HAT-SA) conjugate, which recognizes CD25, followed by bismuth 213 ((213)Bi)-1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid (DOTA)- biotin. In the 3-step pretargeting radioimmunotherapy protocol, HAT-SA (140 or 400 microg) was administered intravenously (i.v.) to bind to the interleukin 2 receptor alpha (IL-2R alpha; CD25)-expressing tumor cells. After 24 hours, 100 microg of a synthetic clearing agent was administered i.v. to remove unbound circulating HAT-SA conjugate from the circulation. Four hours later, (213)Bi-DOTA-biotin was administered i.v. for therapy. Tumor growth was significantly inhibited in 3 trials by using 250 microCi (9.25 MBq) of (213)Bi-DOTA-biotin with a pretargeting technique as monitored by serum levels of soluble IL-2R alpha and/or human beta-2-microglobulin (P <.05, t test) and by survival of tumor-bearing mice in the treatment groups (P <.02, log rank test) as compared with the control groups. No prolongation of survival was observed with a nonspecific antibody-SA conjugate or in the absence of the radionuclide. Additionally, no prolongation of survival resulted from administration of (213)Bi directly linked to intact HAT. Furthermore, there was no prolongation of survival when the beta-emitting radionuclide yttrium 90 instead of the alpha-emitting radionuclide (213)Bi was used. The pretargeting approach with (213)Bi inhibited tumor growth more effectively than did immunotherapy with unmodified HAT. The best results were obtained with combination therapy that involved (213)Bi-DOTA-biotin with a pretargeting technique supplemented by 4 weekly doses of HAT. The findings of this study support the use of this combination approach in a clinical trial in patients with IL-2R alpha-expressing leukemias.

Recombinant immunotoxins in targeted cancer cell therapy

Targeted cancer therapy in general and immunotherapy in particular combines rational drug design with the progress in understanding cancer biology. This approach takes advantage of our recent knowledge of the mechanisms by which normal cells are transformed into cancer cells, thus using the special properties of cancer cells to device novel therapeutic strategies. Recombinant immunotoxins are excellent examples of such processes, combining the knowledge of antigen expression by cancer cells with the enormous developments in recombinant DNA technology and antibody engineering. Recombinant immunotoxins are composed of a very potent protein toxin fused to a targeting moiety such as a recombinant antibody fragment or growth factor. These molecules bind to surface antigens specific for cancer cells and kill the target cells by catalytic inhibition of protein synthesis. Recombinant immunotoxins are developed for solid tumors and hematological malignancies and have been characterized intensively for their biological activity in vitro on cultured tumor cell lines as well as in vivo in animal models of human tumor xenografts. The excellent in vitro and in vivo activities of recombinant immunotoxins have lead to their preclinical development and to the initiation of clinical trail protocols. Recent trail results have demonstrated potent clinical efficacy in patients with malignant diseases that are refractory to traditional modalities of cancer treatment: surgery, radiation therapy, and chemotherapy. The results demonstrate that such strategies can be developed into a separate modality of cancer treatment with the basic rationale of specifically targeting cancer cells on the basis of their unique surface markers. Efforts are now being made to improve the current molecules and to develop new agents with better clinical efficacy. This can be achieved by development of novel targeting moieties with improved specificity that will reduce toxicity to normal tissues. In this review, the design, construction, characterization, and applications of recombinant immunotoxins are described. Results of recent clinical trails are presented, and future directions for development of recombinant immunotoxins as a new modality for cancer treatment are discussed.

Adult T-cell leukemia/lymphoma: a rare case in the USA and review of the literature

Adult T-cell leukemia/lymphoma (ATLL), in its acute stage, is a uniformly fatal disease. ATLL is caused by the human T-cell lymphotropic virus I (HTLV-1), a retrovirus endemic in numerous areas throughout the world including Japan, the Caribbean, Central and South America and certain areas of the United States. Although the progression from HTLV-1 carrier status to ATLL occurs only rarely, ATLL is incurable and thus prevention of HTLV-1 transmission should be a primary goal. With the development of new anti-retroviral and monoclonal therapies, there exist potential cures or at least prolonged remissions for patients diagnosed with ATLL. We present a case of ATLL that, to our knowledge, is only the third reported case in Georgia. In addition, we present a brief review of the literature, including potential new treatment regimens that appear to have promise in the treatment of ATLL.

Synergism of cytotoxic T lymphocyte-associated antigen 4 blockade and depletion of CD25(+) regulatory T cells in antitumor therapy reveals alternative pathways for suppression of autoreactive cytotoxic T lymphocyte responses

Therapeutic efficacy of a tumor cell-based vaccine against experimental B16 melanoma requires the disruption of either of two immunoregulatory mechanisms that control autoreactive T cell responses: the cytotoxic T lymphocyte-associated antigen (CTLA)-4 pathway or the CD25(+) regulatory T (Treg) cells. Combination of CTLA-4 blockade and depletion of CD25(+) Treg cells results in maximal tumor rejection. Efficacy of the antitumor therapy correlates with the extent of autoimmune skin depigmentation as well as with the frequency of tyrosinase-related protein 2(180-188)-specific CTLs detected in the periphery. Furthermore, tumor rejection is dependent on the CD8(+) T cell subset. Our data demonstrate that the CTL response against melanoma antigens is an important component of the therapeutic antitumor response and that the reactivity of these CTLs can be augmented through interference with immunoregulatory mechanisms. The synergism in the effects of CTLA-4 blockade and depletion of CD25(+) Treg cells indicates that CD25(+) Treg cells and CTLA-4 signaling represent two alternative pathways for suppression of autoreactive T cell immunity. Simultaneous intervention with both regulatory mechanisms is therefore a promising concept for the induction of therapeutic antitumor immunity.

Potential biologic agents for treating rheumatoid arthritis

The encouraging clinical results observed in trials using anti-TNF therapy clearly warrant further studies to determine whether TNF inhibitors are capable of modifying the destructive component of this disease in long-term follow-up studies as well as to assess the safety of long-term use (see the article by Keystone in this issue). It is also reasonable to propose that interfering with the cytokine cascade earlier in the course of disease may be of even greater therapeutic benefit. As the pathogenetic mechanisms in RA are more clearly defined, especially in early disease and in those individuals destined to develop severe disease, the potential of other biologic agents to specifically inhibit these critical pathways may provide better treatments for our patients. Many potential targets in the immune-mediated process of RA are currently being rigorously evaluated in clinical trials. Use of combinations of biologic therapies, perhaps in human patients with RA, should be of considerable interest in future trials.

Monoclonal antibodies in lymphoid neoplasia: principles for optimal combined therapy

Rituximab and other monoclonal antibody therapies now in development have the potential to markedly impact the treatment of non-Hodgkin's lymphoma (NHL). These agents have significant single-agent activity, distinct mechanisms of action, and, in the case of rituximab and other unconjugated antibodies, favorable toxicity profiles that are nonoverlapping with the adverse effects associated with conventional chemotherapy. These properties may allow for the use of novel combination therapies with enhanced outcomes for patients. Systematic evaluation of rationally designed combinations through randomized, prospective trials is required to determine the clinical utility of these novel agents and combinations will live up to their potential.

Viral Disease in Hematology

As part of the international outreach of the American Society of Hematology, this review addresses some aspects of the genetics, biology, epidemiology, and clinical relevance of viruses that cause a variety of hematopoietic disorders in human populations. The viruses described here have a different pattern of geographical distribution, and the disease manifestations may vary according to environmental and/or genetic characteristics of the host. Epstein-Barr virus, a linear double-stranded DNA virus (herpesvirus), and the human T-cell leukemia virus, a retrovirus with a single-stranded diploid RNA genome, are associated among other diseases with lymphoma and leukemia/lymphoma, respectively. Both viruses cause a lifelong infection, but only a small percentage of infected individuals develop hematopoietic neoplasms. Epidemiological data suggest that the time of infection may be important in determining disease outcome in both HTLV-I and EBV infection. The pathogenic mechanisms used by these viruses are of most interest since they may recapitulate growth dysregulation steps also occurring in other hematopoietic malignancies.

In Section I Dr. Franchini reviews the biology, genetics and diseases associated with HTLV-I and HTLV-II. In Section II, Dr. Ambinder reviews the biology of EBV infection and its relationship to the pathogenesis of Hodgkin's disease and other malignancies.

In Section III, Dr. Barry reviews the viral hemorrhagic fevers caused by RNA viruses such as Arenaviridae, Bunyaviridae, Filoviridae, and Flaviviridae, which can lead to acute syndromes that can be fatal. However, prompt diagnosis is key for patient management as well as for limiting their spread to others. These syndromes have become the focus of public concern and represent not only a clinical challenge, since in most cases no specific antiviral treatment is available, but also a challenge for future basic research on their biology and pathogenesis since little is known at present.

Viral Disease in Hematology

As part of the international outreach of the American Society of Hematology, this review addresses some aspects of the genetics, biology, epidemiology, and clinical relevance of viruses that cause a variety of hematopoietic disorders in human populations. The viruses described here have a different pattern of geographical distribution, and the disease manifestations may vary according to environmental and/or genetic characteristics of the host. Epstein-Barr virus, a linear double-stranded DNA virus (herpesvirus), and the human T-cell leukemia virus, a retrovirus with a single-stranded diploid RNA genome, are associated among other diseases with lymphoma and leukemia/lymphoma, respectively. Both viruses cause a lifelong infection, but only a small percentage of infected individuals develop hematopoietic neoplasms. Epidemiological data suggest that the time of infection may be important in determining disease outcome in both HTLV-I and EBV infection. The pathogenic mechanisms used by these viruses are of most interest since they may recapitulate growth dysregulation steps also occurring in other hematopoietic malignancies.

In Section I Dr. Franchini reviews the biology, genetics and diseases associated with HTLV-I and HTLV-II. In Section II, Dr. Ambinder reviews the biology of EBV infection and its relationship to the pathogenesis of Hodgkin's disease and other malignancies.

In Section III, Dr. Barry reviews the viral hemorrhagic fevers caused by RNA viruses such as Arenaviridae, Bunyaviridae, Filoviridae, and Flaviviridae, which can lead to acute syndromes that can be fatal. However, prompt diagnosis is key for patient management as well as for limiting their spread to others. These syndromes have become the focus of public concern and represent not only a clinical challenge, since in most cases no specific antiviral treatment is available, but also a challenge for future basic research on their biology and pathogenesis since little is known at present.

Phase I Study of 131I-Anti-CD45 Antibody Plus Cyclophosphamide and Total Body Irradiation for Advanced Acute Leukemia and Myelodysplastic Syndrome

Delivery of targeted hematopoietic irradiation using radiolabeled monoclonal antibody may improve the outcome of marrow transplantation for advanced acute leukemia by decreasing relapse without increasing toxicity. We conducted a phase I study that examined the biodistribution of 131I-labeled anti-CD45 antibody and determined the toxicity of escalating doses of targeted radiation combined with 120 mg/kg cyclophosphamide (CY) and 12 Gy total body irradiation (TBI) followed by HLA-matched related allogeneic or autologous transplant. Forty-four patients with advanced acute leukemia or myelodysplasia received a biodistribution dose of 0.5 mg/kg131I-BC8 (murine anti-CD45) antibody. The mean ± SEM estimated radiation absorbed dose (centigray per millicurie of 131I) delivered to bone marrow and spleen was 6.5 ± 0.5 and 13.5 ± 1.3, respectively, with liver, lung, kidney, and total body receiving lower amounts of 2.8 ± 0.2, 1.8 ± 0.1, 0.6 ± 0.04, and 0.4 ± 0.02, respectively. Thirty-seven patients (84%) had favorable biodistribution of antibody, with a higher estimated radiation absorbed dose to marrow and spleen than to normal organs. Thirty-four patients received a therapeutic dose of 131I-antibody labeled with 76 to 612 mCi131I to deliver estimated radiation absorbed doses to liver (normal organ receiving the highest dose) of 3.5 Gy (level 1) to 12.25 Gy (level 6) in addition to CY and TBI. The maximum tolerated dose was level 5 (delivering 10.5 Gy to liver), with grade III/IV mucositis in 2 of 2 patients treated at level 6. Of 25 treated patients with acute myeloid leukemia (AML)/myelodysplastic syndrome (MDS), 7 survive disease-free 15 to 89 months (median, 65 months) posttransplant. Of 9 treated patients with acute lymphoblastic leukemia (ALL), 3 survive disease-free 19, 54, and 66 months posttransplant. We conclude that 131I-anti-CD45 antibody can safely deliver substantial supplemental doses of radiation to bone marrow (∼24 Gy) and spleen (∼50 Gy) when combined with conventional CY/TBI.

Phase I Study of 131I-Anti-CD45 Antibody Plus Cyclophosphamide and Total Body Irradiation for Advanced Acute Leukemia and Myelodysplastic Syndrome

Delivery of targeted hematopoietic irradiation using radiolabeled monoclonal antibody may improve the outcome of marrow transplantation for advanced acute leukemia by decreasing relapse without increasing toxicity. We conducted a phase I study that examined the biodistribution of 131I-labeled anti-CD45 antibody and determined the toxicity of escalating doses of targeted radiation combined with 120 mg/kg cyclophosphamide (CY) and 12 Gy total body irradiation (TBI) followed by HLA-matched related allogeneic or autologous transplant. Forty-four patients with advanced acute leukemia or myelodysplasia received a biodistribution dose of 0.5 mg/kg131I-BC8 (murine anti-CD45) antibody. The mean ± SEM estimated radiation absorbed dose (centigray per millicurie of 131I) delivered to bone marrow and spleen was 6.5 ± 0.5 and 13.5 ± 1.3, respectively, with liver, lung, kidney, and total body receiving lower amounts of 2.8 ± 0.2, 1.8 ± 0.1, 0.6 ± 0.04, and 0.4 ± 0.02, respectively. Thirty-seven patients (84%) had favorable biodistribution of antibody, with a higher estimated radiation absorbed dose to marrow and spleen than to normal organs. Thirty-four patients received a therapeutic dose of 131I-antibody labeled with 76 to 612 mCi131I to deliver estimated radiation absorbed doses to liver (normal organ receiving the highest dose) of 3.5 Gy (level 1) to 12.25 Gy (level 6) in addition to CY and TBI. The maximum tolerated dose was level 5 (delivering 10.5 Gy to liver), with grade III/IV mucositis in 2 of 2 patients treated at level 6. Of 25 treated patients with acute myeloid leukemia (AML)/myelodysplastic syndrome (MDS), 7 survive disease-free 15 to 89 months (median, 65 months) posttransplant. Of 9 treated patients with acute lymphoblastic leukemia (ALL), 3 survive disease-free 19, 54, and 66 months posttransplant. We conclude that 131I-anti-CD45 antibody can safely deliver substantial supplemental doses of radiation to bone marrow (∼24 Gy) and spleen (∼50 Gy) when combined with conventional CY/TBI.

Cytotoxic agents directed to peptide hormone receptors: defining the requirements for a successful drug

In principle, cell surface receptors that are overexpressed in tumor tissue could serve as targets for anticancer drugs attached to receptor ligands. The purpose of this paper is to identify the necessary elements for a successful receptor-targeted drug. We used the gastrin/cholecystokinin type B receptor as a model delivery system, and we report on the synthesis, trafficking, and in vitro and in vivo evaluation of heptagastrin, the C-terminal heptapeptide of gastrin, linked via an appropriate linker to a potently cytotoxic ellipticine derivative, 1-[3-[N-(3-aminopropyl)-N-methylamino]propyl]amino-9-methoxy-5, 11-dimethyl-6H-pyrido[4,3-b]carbazole. These data, and previous work from our laboratory, show that the drug-complexed ligand is sorted to lysosomes whereas the receptor is recycled to the plasma membrane. The lysosomal processing of the ligand/drug construct depends on the linker between the ligand sequence and the cytotoxic moiety. We show that heptagastrin linked to ellipticine via a succinoyl-substituted pentapeptide, AlaLeuAlaLeuAla, is at least 10(3) more toxic to cholecystokinin type B receptor-positive NIH/3T3 cells than to isogenic NIH/3T3 cells lacking the receptor. The conjugated drug eradicated all receptor-positive tumor cells in vivo without producing any general toxicity. The data indicate that the density of the cell surface receptor, the properties of the cytotoxic moiety, and the correct processing of the drug-conjugated ligand in lysosomes are crucial to the effectiveness of a receptor-targeted drug.

Anti-GM-CSF monoclonal antibody therapy for refractory acute leukemia

Several phase I trials and pilot studies using Monoclonal Antibody (MoAb) have been performed in B-cell neoplasms, but this approach has not until now been extensively tested in myeloid leukemias. Recently, we evaluated the use of anti-Granulocyte-Macrophage Colony-Stimulating Factor MoAb (Anti-GM-CSF MoAb) in acute myeloid leukemia (AML). Eight patients fulfilled inclusion criteria and received a single course of Anti-GM-CSF MoAb infusion during 5 to 15 days. Anti-GM-CSF MoAb was well tolerated and was detectable in pharmacokinetics studies. Using Human Anti-Rat Antibodies (HARA), we also observed an immunological response to the MoAb. Despite sufficient levels detected in the serum and biological activity of Anti-GM-CSF MoAb in vivo, no anti-leukemic effect was noted, except for one patient who had a decrease of 50% in the marrow blast cell mass. These observations indicate that leukemic proliferation in vivo involves a complex network spanning many mechanisms, and inhibition of leukemia is not effective if only one of these key targets is attacked. The development of these new approaches may be more effective in the future.

Rationale for the use of immunotoxins in the treatment of HIV-infected humans

The first step in the replication of human immunodeficiency virus (HIV) is selective binding of the envelope glycoprotein (gp120) to CD4 receptors on T cells or macrophages. After penetration in these cells, the genome of the virus is integrated in the human genome. HIV-infection causes depletion of CD4-positive cells resulting in a severe immunosuppression. It is believed that eliminating HIV-infected cells is crucial in limiting further reduction of CD4-positive cells and thus, preventing disease progression. The most commonly used drugs, such as zidovudine (AZT), appeared to be not completely effective. Therefore many investigators are searching for alternative treatment modalities. The use of immunotoxins (ITs) to eliminate HIV-infected cells is discussed. ITs are chimeric molecules in which cell-binding ligands are coupled to toxins and can specifically eliminate undesired cells. The cell-binding carriers of anti-HIV ITs have been directed against different regions of the HIV envelope glycoprotein (gp120 and gp41) and surface antigens (e.g CD4, CD25). The ITs have been composed of different ribosome-inactivating proteins (RIPs) like pokeweed antiviral protein (PAP), Pseudomonas exotoxin (PE), Diphtheria toxin (DT), or ricin. In in vitro studies, several of these ITs have been shown to be effective and specific in killing acute and persistently HIV-infected cells. The ITs were effective at concentrations (ID50 range from 10(-9) M to 10(-12) M) that were not toxic to uninfected cells or cells without the antigen. The IT CD4(178)PE40, a fusion protein directed against the CD4 binding site of gp120, has been investigated in two in vivo trials. The results were disappointing considering the antiviral activity in vitro. This was thought to be due to the rapid clearance of the IT and the differential resistance of clinical HIV isolates. Use of a panel of ITs is likely to be more effective because multiple approaches cover the intrinsic variability of HIV and the presence of IT-resistant or latently infected cells, as well as the blocking presence of neutralizing anti-HIV antibodies and the immunogenicity of most ITs. It may be possible to control the virus completely with a panel of ITs in combination with other antiviral or immunosuppressive agents such as RT inhibitors (e.g AZT), interferon alpha, or cyclosporine. More research will be necessary to develop such a combined therapy.

Impact of antigenemia on the bioactivity of infused anti-Tac antibody: implications for dose selection in antibody immunotherapies

In patients with malignancies and immune disorders expressing Tac (alpha chain of the interleukin 2 receptor; CD25), physiologic shedding of this receptor may lead to high blood levels of the soluble form (sTac). This system was used to model the interaction of soluble antigen with antibody in therapeutic settings and to develop rational principles to optimize the delivery of antibody to tumor target cells. First, we confirmed that sTac in vivo can block anti-Tac binding sites and diminish antibody binding to Tac+ cells. Second, the bioactivity of antibody in vivo correlated directly with the amount of antibody infused and inversely with the sTac concentration. Third, bindability of antibody declined in the hours and days after anti-Tac infusion in patients. Finally, tumor targeting was achieved even in the presence of excess sTac, demonstrating a partition of antibody between soluble and cell-bound antigen. A role is proposed for the Brambell receptor (FcRB) to delay saturation of human or chimeric antibodies via differential catabolism of antigen-antibody complexes. Principles are developed for predicting activity of administered antibody in the presence of soluble antigen to assist in dose selection in passive, radioimmuno and immunotoxin therapies.

Preparation of 211At-labeled humanized anti-Tac using 211At produced in disposable internal and external bismuth targets

These studies describe the production and purification of 211At as well as the procedure for labeling humanized anti-Tac, the antibody to the alpha-chain of the IL-2 receptor (IL-2R alpha), which has been shown to be a useful target for immunotherapy. The optimized protocol combines the advantages of the two-stage dry distillation procedure with the astatination of trialkylstannyl substances as labeling compounds for proteins. The 211At was produced by bombarding either an external or a recently developed disposable internal bismuth target with alpha-particles from a Cyclotron Corporation CS-30 cyclotron. The 211At was found to contain less than 0.01% 210At. The production rate for the external target was 0.15 mCi +/- 0.056 microA(-1) h(-1) (n = 9) (5.55 MBq mcroA[-1] h[-1]). The production rate for the internal target was 0.44 +/- 0.14 mCi microA(-1) h(-1) (n = 16) (16.28 MBq mcroA[-1] h[-1]).

Atypical lymphoid infiltrates arising in cutaneous lesions of connective tissue disease

Atypical lymphoid infiltrates occurring in the setting of connective-tissue disease (CTD) comprise malignant neoplasms of B-cell or T-cell phenotypes and various reactive lymphoid hyperplasias, such as myoepithelial sialadenitis, lymphocytic thyroiditis, and lymphocytic interstitial pneumonitis. We describe 17 patients with atypical lymphoid infiltrates arising in cutaneous lesions of CTD, the spectrum of which included lupus erythematosus, dermatomyositis, relapsing polychondritis, and lichen sclerosus et atrophicus. There were two principal categories, pseudolymphoma and malignant lymphoma, the former representing 15 of the 17 cases. The clinical and histologic features and possible pathogenetic mechanisms are discussed.

Therapy of patients with T-cell lymphomas and leukemias using an anti-CD7 monoclonal antibody-ricin A chain immunotoxin

Anti-CD7-dgA, DA7, consists of deglycosylated ricin A chain coupled to a mouse monoclonal anti-human CD7 antibody. This study determined the maximally tolerated dose (MTD) of this immunotoxin administered as a one hour infusion over five days to 11 patients with T-cell lymphoma (>30% CD7+ malignant cells). The MTD was 0.2 mg/kg/day or 1 mg/kg/120 hours (maximal toxicity grade 3) with vascular leak syndrome (VLS) as dose-limiting toxicity (DLT). Predictors of severe VLS included age and absence of circulating lymphoma cells. Two partial responses and one minimal response were seen. Patients with minimal lymphoma burden or T-cell large granular lymphocyte (LGL) leukemia showed the best responses. The mean maximal serum concentration of immunotoxin at the MTD was 2.5 ug/ml. The mean alpha-phase half-life was 1.5 hours and the mean beta-phase half-life was 8 hours. Repeated dosing had minimal effects on either peak serum immunotoxin concentrations or serum half-lives. While human antimouse antibodies were observed, they were low in concentration (<55 ng/ml). Human anti-ricin antibody was elevated in one patient (190 ng/ml). VLS presented with hypoalbuminemia, dyspnea, pulmonary edema, aphasia, and peripheral edema and cleared over a two week period. Serum fibronectin levels were measured in three patients and were very low in one patient who developed VLS. No specific binding of DA7 immunotoxin was seen with vascular endothelium in various human tissues.

The biological therapy of acute and chronic leukemia

With the increasing knowledge of the mechanisms of immune-mediated cytotoxicity, immunotherapeutic strategies are rapidly being incorporated into chemotherapy treatment schemes for acute and chronic leukemias. This includes the use of mAbs, immunotoxins, tumor-specific T cells, and, most recently, vaccines. Much of the new information is derived from bone marrow transplant data, where immune enhancement from IL-2 and donor T-cell infusions are being studied. Trials using humanized mAbs that permit prolonged and repeated dosing will allow better evaluation of the effectiveness of mAb therapy. More sophisticated molecular tests have been developed, allowing the detection of minimal residual disease to a greater degree. It is likely that biological and immunological therapy of leukemia will have its greatest impact here.

Engineering antibody Fv fragments for cancer detection and therapy: disulfide-stabilized Fv fragments

Disulfide-stabilized Fv fragments of antibodies (dsFv) are molecules in which the VH-VL heterodimer is stabilized by an interchain disulfide bond engineered between structurally conserved framework positions distant from complementarity-determining regions (CDRs). This method of stabilization is applicable for the stabilization of many antibody Fvs and has also been applied to a T-cell receptor Fv. A summary of the design strategy, and the construction and production of various dsFvs and dsFv-fusion proteins is presented. Included in the discussion are the biochemical features of dsFvs in comparison with scFvs, the effect of disulfide stabilization on Fv binding and activity, and various applications of dsFvs and dsFv-immunotoxins for tumor imaging and the treatment of solid tumors in animal models.

Identification and characterization of two alternative splice variants of human interleukin-2

Our previous work showed that alternative splicing is used to make an inhibitory variant of human interleukin (IL)-4. Because of homology between IL-4 and IL-2 proteins and receptors, we tested whether alternative splicing is used to generate similar inhibitory variants of human IL-2. Messenger RNA from peripheral blood mononuclear cells was subjected to reverse transcription-polymerase chain reaction using IL-2 exon 1- and exon 4-specific primers. Two amplification products, named IL-2delta2 and IL-2delta3, were found in addition to the native IL-2 product. The IL-2delta2 cDNA sequence was identical to IL-2 cDNA throughout the entire coding region, except exon 2 was omitted by alternative splicing. In IL-2delta3 cDNA, the third exon of IL-2 was omitted by alternative splicing. Unlike IL-2, IL-2delta2 and IL-2delta3 did not stimulate T cell proliferation. However, both inhibited IL-2 costimulation of T cell proliferation, and both inhibited cellular binding of rhIL-2 to high affinity IL-2 receptors. Thus, IL-2 is the second cytokine that uses alternative splicing to generate variants that are competitive inhibitors.

A randomized trial comparing safety and efficacy of OKT3 and a monoclonal anti-interleukin-2 receptor antibody (BT563) in the prevention of acute rejection after heart transplantation

In a prospective randomized trial, BT563, a murine IgG, anti-interleukin-2 receptor antibody, was compared with OKT3 for use as an early rejection prophylaxis after heart transplantation. Patients received either BT563 (n=31) or OKT3 (n=29) during the first 7 days after transplantation; cyclosporine was started on day 3. Median follow-up was 34 months. A cytokine release syndrome occurred in the majority of patients of the OKT3-treated group but in none of the BT563 recipients. The mean duration of electrical stimulation of the heart in the BT563 group was longer than in the OKT3 group (5.1 vs. 2.1 days). In both groups, one patient required insertion of a permanent pacemaker. Freedom from acute rejection at 3 months was not significantly different between the two groups (BT563: 5/29, 17%; OKT3: 6/29, 21%). In the BT563 group, however, rejection tended to occur earlier after transplantation. There was no difference in the overall incidence of rejection. The incidence of infectious complications was evenly distributed in both groups. Malignancies occurred in two patients, both in the OKT3 group. In conclusion, the use of this anti-interleukin-2 receptor monoclonal antibody in heart transplant recipients is safe and devoid of the side effects that accompany the use of OKT3. OKT3 and BT563 result in a similar freedom from rejection at 3 and 12 months after heart transplantation.

Biophysical characterization of a recombinant soluble interleukin 2 receptor (Tac). Evidence for a monomeric structure

The interleukin 2 receptor (IL2R) plays a prominent role in the biology of T cells, B cells, and NK cells during activation. Of the three chains described, the alpha-chain of the receptor (Tac; IL2R alpha; CD25) is the most subject to regulation and is shed from the surface of activated cells to generate a soluble form in serum and tissues. Conflicting results have been reported on the native structure of soluble Tac, suggesting variously a monomer, a dimer, or higher noncovalent forms, spawning different models for its mechanism of action. We similarly show a large M(r)(app) by HPLC sieving chromatography, suggesting a tetrameric form. However, stoichiometry-ordered size (SOS) analysis of antibody-antigen complexes indicated only a single epitope per Tac molecule, compatible with a monomeric form. This larger M(r)(app) also conflicted with prior in vivo data showing rapid filtration of soluble Tac through the renal glomerulus that was not expected of a larger complex. Using different solvents, denaturants, and columns in the chromatography suggested that the elevated M(r)(app) values were an artifact of solute-column interactions, termed "ionic exclusion", rather than reflecting larger native structures. Analytical ultracentrifugation using a new type of analysis specific to glycoproteins demonstrated monomeric masses under all salt conditions with no tendency to form dimers or higher aggregates. Finally, circular dichroism spectroscopy showed no salt-dependent changes to suggest conformational alterations that might correlate with mobility changes on high pressure liquid chromatography. We conclude therefore that Tac is monomeric under physiologic conditions. Assessments of higher molecular weight for the purified soluble protein by other methods may be explained by the highly acidic nature of the molecule, which hampers matrix penetration with chromatographic media and by the high carbohydrate content and low partial specific volumes that accelerate the molecule in sedimentation media relative to pure protein standards.

Metabolism of Tac (IL2Ralpha): physiology of cell surface shedding and renal catabolism, and suppression of catabolism by antibody binding

The interleukin 2 receptor alpha (IL2Ralpha; CD25; Tac) is the prototypic model for soluble receptor studies. It exists in vivo as a transmembrane complete molecule (TM-Tac) on cell surfaces and as a truncated soluble form (sTac; sIL2R alpha). sTac has been used as a serum marker of T cell activation in immune disorders and of tumor burden in Tac-expressing malignancies. In vivo, serum levels of all soluble proteins depend on the balance between production and catabolism, but little is known about the metabolic features of this class of molecules. We have developed a model for Tac metabolism that incorporates new insights in its production and catabolism. Tac was shed from the surface of malignant and activated human T cells with a model half-life (t1/2) of 2-6h, but which was prolonged under certain circumstances. The rate of shedding is first order overall and nonsaturable over a two order of magnitude range of substrate (TM-Tac) expression. Once shed from cells Tac is subject to catabolic activities in the host. In vivo studies in mice showed that 90% of Tac was catabolized by the kidney with a t1/2 of 1 h and a filtration fraction of 0.11 relative to creatinine. The remaining 10% of catabolism was mediated by other tissues with a t1/2 of 10 h. Approximately 1-3% of sTac is excreted intact as proteinuria with the remaining 97-99% catabolized to amino acids. Antibody to the receptor induced a marked delay in sTac catabolism by preventing filtration of the smaller protein through the renal glomerulus and additionally suppressing other nonrenal catabolic mechanisms. A discrepancy between the catabolic rats for Tac and anti-Tac in the same complex was interpreted as a previously unrecognized differential catabolic mechanism, suggesting features of the Brambell hypothesis and immunoglobulin G transport and catabolism, in which the antigen-in-complex in intracellular vesicles is relatively less protected from catabolism than the associated antibody. In light of the pivotal role played by the kidney in sTac catabolism and the impact of administered antibody, the serum concentration of Tac in the settings of renal dysfunction or antibody therapy is not a suitable surrogate of activated T cells or of the body burden of tumor. These results provide parameters for assessing soluble receptor-ligand interactions generally.

Interleukin-2 as a neuroregulatory cytokine

Interleukin-2 (IL-2), the cytokine also known as T-cell growth factor, has multiple immunoregulatory functions and biological properties not only related to T-cells. In the past decade, substantial evidence accumulated to suggest that IL-2 is also a modulator of neural and neuroendocrine functions. First, extremely potent effects of IL-2 on neural cells were discovered, including activities related to cell growth and survival, transmitter and hormone release and the modulation of bioelectric activities. IL-2 may be involved in the regulation of sleep and arousal, memory function, locomotion and the modulation of the neuroendocrine axis. Second, the concept that IL-2 could act as a neuroregulatory cytokine has been supported by reports on the presence in rodent and human brain tissues of IL-2-like bioactivity, IL-2-like immunoreactivity, IL-2-like mRNA, IL-2 binding sites, IL-2 receptor (IL-2R alpha) and beta chain mRNA and IL-2R immunoreactivity. IL-2 and/or IL-2R molecules mainly localize to the frontal cortex, septum, striatum, hippocampal formation, hypothalamus, locus coeruleus, cerebellum, the pituitary and fiber tracts, such as the corpus callosum, where they are likely expressed by both neuronal and glial cells. Although the molecular biology of the brain IL-2/IL-2R system (including its relation to IL-15/IL-15R alpha) is not yet fully established by cloning and complete sequencing of all respective components, similarities (and to some extent differences) to peripheral counterparts are now apparent. The ability of IL-2 to readily penetrate the blood-brain barrier further suggests that this cytokine could regulate interactions between peripheral tissues and the central nervous system. Taken together, these data suggest that IL-2 of either immune and CNS origin can have access to functional IL-2R molecules on neurons and glia under normal conditions. Additionally, dysregulation of the IL-2/IL-2 receptor system could lead or contribute to functional and pathological alterations in the brain as in the immune system. Understanding the neurobiology of the IL-2/IL-2 receptor system should also help to explain neurologic, neuropsychiatric and neuroendocrine side effects occurring during IL-2 treatment of peripheral and brain tumors. Immunopharmacological manipulation either aiming at the activation or suppression of IL-2 signaling should consider functional interference with constitutive and inducible IL-2 receptors on brain cells in order to fulfil the high expectations associated with the use of this cytokine as a promising agent in immunotherapies, especially of brain tumors.

Radioimmunodetection of human leukemia with anti-interleukin-2 receptor antibody in severe combined immunodeficiency mice

Anti-Tac monoclonal antibody recognizes human interleukin-2 receptor, which is overexpressed in leukemic cells of most adult T-cell leukemia (ATL) patients. To examine the potency of anti-Tac for targeting of ATL, biodistributions of intravenously administered 125I- and 111In-labeled anti-Tac were examined in severe combined immunodeficiency (SCID) mice inoculated with ATL cells. Significant amounts of radiolabeled anti-Tac were found in the spleen and thymus. The trafficking of ATL cells in SCID mice was detected using 111In-oxine-labeled ATL cells. These results were coincident with the histologically confirmed infiltration of ATL cells. The radiolabeled anti-Tac seemed potent for targeting of ATL.

Phase II trial of 131I-B1 (anti-CD20) antibody therapy with autologous stem cell transplantation for relapsed B cell lymphomas

25 patients with relapsed B-cell lymphomas were evaluated with trace labelled doses (2.5 mg/kg, 185-370 MBq [5-10 mCi]) of 131I-labelled anti-CD20 (B1) antibody in a phase II trial. 22 patients achieved 131I-B1 biodistributions delivering higher doses of radiation to tumour sites than to normal organs and 21 of these were treated with therapeutic infusions of 131I-B1 (12.765-29.045 GBq) followed by autologous haemopoietic stem cell reinfusion. 18 of the 21 treated patients had objective responses, including 16 complete remissions. One patient died of progressive lymphoma and one died of sepsis. Analysis of our phase I and II trials with 131I-labelled B1 reveal a progression-free survival of 62% and an overall survival of 93% with a median follow-up of 2 years. 131I-anti-CD20 (B1) antibody therapy produces complete responses of long duration in most patients with relapsed B-cell lymphomas when given at maximally tolerated doses with autologous stem cell rescue.

A novel chimeric protein composed of interleukin 13 and Pseudomonas exotoxin is highly cytotoxic to human carcinoma cells expressing receptors for interleukin 13 and interleukin 4

Chimeric proteins provide a unique opportunity to target therapeutic bacterial toxins to a subset of specific cells. We have generated a new recombinant chimeric toxin composed of human interleukin 13 (hIL13) and a Pseudomonas exotoxin A (PE) mutant, PE38QQR. The hIL13-PE38QQR chimera is highly cytotoxic to cell lines derived from several human epithelial carcinomas such as adenocarcinoma of stomach, colon, and skin. The cytotoxic action of hIL13-PE38QQR, which can only occur upon internalization of ligand-receptor complex, is blocked by an excess of hIL13 but not of hIL2. This action is not solely hIL13-specific because an excess of hIL4 also blocks the cytotoxicity of hIL13-toxin. Conversely, hIL13 blocks the cytotoxicity of a hIL4-PE38QQR chimera. Binding studies showed that hIL13 displaces competitively 125I-labeled hIL4-PE38QQR on carcinoma cells. These results indicate that IL4 and IL13 compete for a common binding site on the studied human cell lines. Despite this competition, hIL4 but not hIL13 decreased protein synthesis in malignant cells susceptible to the cytotoxicity of both hIL13- and hIL4-PE38QQR. Our results suggest that a spectrum of human carcinomas express binding sites for IL13. Furthermore, hIL13 and hIL4 compete reciprocally for a form of the receptor that is internalized upon binding a ligand. Thus, cancer cells represent an interesting model for studying receptors for these two growth factors. Finally, hIL13-PE38QQR may be a useful agent in the treatment of several malignancies.

Phenotypic knockout of the high-affinity human interleukin 2 receptor by intracellular single-chain antibodies against the alpha subunit of the receptor

The experimental manipulation of peptide growth hormones and their cellular receptors is central to understanding the pathways governing cellular signaling and growth control. Previous work has shown that intracellular antibodies targeted to the endoplasmic reticulum (ER) can be used to capture specific proteins as they enter the ER, preventing their transport to the cell surface. Here we have used this technology to inhibit the cell surface expression of the alpha subunit of the high-affinity interleukin 2 receptor (IL-2R alpha). A single-chain variable-region fragment of the anti-Tac monoclonal antibody was constructed with a signal peptide and a C-terminal ER retention signal. Intracellular expression of the single-chain antibody was found to completely abrogate cell surface expression of IL-2R alpha in stimulated Jurkat T cells. IL-2R alpha was detectable within the Jurkat cells as an immature 40-kDa form that was sensitive to endoglycosidase H, consistent with its retention in a pre- or early Golgi compartment. A single-chain antibody lacking the ER retention signal was also able to inhibit cell surface expression of IL-2R alpha although the mechanism appeared to involve rapid degradation of the receptor chain within the ER. These intracellular antibodies will provide a valuable tool for examining the role of IL-2R alpha in T-cell activation, IL-2 signal transduction, and the deregulated growth of leukemic cells which overexpress IL-2R alpha.

Detection of homing, proliferation, and infiltration sites of adult T cell leukemia cells in severe combined immunodeficiency mice using radiometric techniques

To clarify the mechanism of in vivo proliferation of adult T cell leukemia (ATL) cells, we examined the organ distribution of ATL-43T cell line cells derived from original leukemic cells in severe combined immunodeficiency (SCID) mice using radiometric techniques. First, we injected 111In-oxine-labeled ATL-43T cells into SCID and CB17 mice. On day 6, significant accumulation of radioactivity was found in the spleen and thymus of SCID mice (33.3 +/- 9.4 and 10.0 +/- 3.6% injected dose/g of tissue [%ID/g], respectively) in comparison with that in CB17 mice (19.1 +/- 2.5 and 3.7 +/- 0.9%ID/g, respectively). Next, we injected radiolabeled anti-Tac monoclonal antibody (MoAb) recognizing human interleukin-2 receptor (IL-2R) alpha chain or isotype-matched control MoAb RPC5 in SCID mice bearing ATL-43T cells 4 weeks after cell inoculation. The amounts of radioactivity found in the spleen and thymus of SCID mice injected with 125I-labeled anti-Tac MoAb (22.5 +/- 6.9 and 22.8 +/- 9.6 %ID/g, respectively) were significantly higher than those in the corresponding organs of SCID mice injected with 125I-labeled RPC5 MoAb (12.0 +/- 5.1 and 7.5 +/- 4.6 %ID/g, respectively). Similar results were obtained with 111In-labeled anti-Tac MoAb. These results were consistent with the histological findings of SCID mice bearing ATL-43T cells, indicating that ATL-43T cells infiltrated preferentially into the lymphoid organs, such as the spleen and thymus, and proliferated there. Thus, the radiometric techniques employed in this study were very useful to evaluate the proliferation sites of ATL-43T cells in SCID mice. Furthermore, this murine model could give us an opportunity to test the feasibility of therapeutic application of radiolabeled anti-Tac MoAb.

Stimulus-dependent production of cytokines and pterins by peripheral blood mononuclear cells

The cytokine profiles produced by peripheral blood mononuclear cell (PBMC) cultures were dependent upon the nature of the stimulus used. Powerful lymphocyte activators such as mitogens induced rapid cell proliferation together with the production of both inflammatory (IL-1 alpha, IL-1 beta, IL-6 and TNF alpha) and immune (IFN-gamma, TNF-alpha and TNF-beta) cytokines, and immune activation markers (soluble IL-2 receptor, neopterin and xanthopterin). Bacterial endotoxin failed to induce cell proliferation but resulted in the rapid production of inflammatory cytokines together with a short burst of IFN-gamma production, without the production of the other immune cytokines or activation markers. Alloantigen stimulation gave a typical immune cytokine and marker profile, with little or no production of inflammatory cytokines. Re-call antigens (candida and PPD) induced maximal cell proliferation at days 5 to 6, but induced little or no production of inflammatory cytokines. Markedly different immune cytokine profiles were obtained with these re-call antigens. Candida induced an early burst of IFN-gamma production on day 1 followed by later production of TNF-alpha. In cultures stimulated with PPD, both IFN-gamma and TNF-alpha were detected from day 2. With both re-call antigens, the levels of production of the activation markers were equivalent to the proliferative responses obtained.