A phase III study of belagenpumatucel-L, an allogeneic tumour cell vaccine, as maintenance therapy for non-small cell lung cancer.

BACKGROUND: Treatment options after first-line chemotherapy are limited in non-small cell lung cancer (NSCLC). Belagenpumatucel-L is a therapeutic vaccine comprised of 4 transforming growth factor (TGF)-ß2-antisense gene-modified, irradiated, allogeneic NSCLC cell lines that may be useful for maintenance after initial treatment. METHODS: Stage III/IV NSCLC patients who did not progress after platinum-based chemotherapy were randomised 1:1 to receive maintenance belagenpumatucel-L or placebo. Patients were eligible for randomisation between one and four months from the end of induction chemotherapy. The primary endpoint was overall survival. RESULTS: This phase III trial enrolled 270 patients in the belagenpumatucel-L arm and 262 in the control arm. Belagenpumatucel-L was well tolerated with no serious safety concerns. There was no difference in survival between the arms (median survival 20.3 versus 17.8months with belagenpumatucel-L versus placebo, respectively; hazard ratio (HR) 0.94, p=0.594). There were also no differences in progression-free survival (4.3months versus 4.0 for belagenpumatucel-L vs placebo, respectively; HR 0.99, p=0.947). A prespecified Cox regression analysis demonstrated that the time elapsed between randomisation and the end of induction chemotherapy had a significant impact on survival (p=0.002) and that prior radiation was a positive prognostic factor (median survival 28.4months with belagenpumatucel-L versus 16.0months with placebo; HR 0.61, p=0.032). CONCLUSIONS: Although the overall trial did not meet its survival endpoint, improved survival for belagenpumatucel-L is suggested in patients who were randomised within 12weeks of completion of chemotherapy and in those who had received prior radiation. Further studies of belagenpumatucel-L in NSCLC are warranted.

Phase I clinical trial of a TGF-beta antisense-modified tumor cell vaccine in patients with advanced glioma.

We performed a phase I clinical trial in grade IV astrocytoma to assess the safety of a whole-cell vaccine comprising autologous tumor cells genetically modified by a transforming growth factor-beta2 (TGF-beta2) antisense vector. Blocking secretion of the immunosuppressive molecule TGF-beta in this manner should inhibit one of the major mechanisms by which tumor cells evade immune surveillance and should lead to clinically effective antitumor immunity. Six patients with progressive WHO grade IV astrocytoma were enrolled in the trial. Patients received 2-7 subcutaneous injections of 5 x 10(6)-2 x 10(7) autologous tumor cells per injection. TGF-beta2 secretion by the tumor cells used to vaccinate patients was inhibited by 53-98%. Treatment was well tolerated with only low-grade, transient treatment-related toxicities reported. Two patients had partial regressions and two had stable disease following therapy. The overall median survival was 68 weeks. Median survival of the responding patients was 78 weeks, compared to a historic value of 47 weeks for glioma patients treated conventionally. There were indications of humoral and cellular immunity induced by the vaccine. These findings support further clinical evaluation of vaccines comprised of TGF-beta antisense-modified tumor cells.

Antigenic and immunologic characterization of an allogeneic colon carcinoma vaccine.

We report the immunological characterization of three colon carcinoma cell lines, COLO 205, SW620 and SW403, which we selected to combine with cytokine-secreting fibroblasts for the development of an allogeneic tumour cell vaccine. The cell lines expressed HLA-A2 as well as shared tumour-associated antigens (TAAs) representative of colon carcinomas: CEA, Ep-CAM, MUC1, HER2/neu and MAGE antigens. They did not secrete high levels of the immunosuppressive factors TGF-beta, IL-10 or prostaglandins. The lines presented TAAs in a manner recognized by immune effector cells, which was demonstrated by the lysis of SW620 by HLA-A2-restricted anti-p53 cytotoxic T lymphocytes (CTL). COLO 205 and SW620 were genetically modified to express the co-stimulatory molecule CD80 (B7.1), which increased the ability of the cells to stimulate CTL in vitro. CTL clones derived from HLA-A2+ peripheral blood mononuclear cells stimulated with the CD80-expressing lines lysed the stimulator cell and an HLA-A2+ colon cancer cell line, but did not lyse an isogeneic fibroblast line or an HLA-A2- colon cancer cell line. CTL clones derived from colon carcinoma patients immunized with an allogeneic vaccine containing these lines demonstrated killing of autologous tumour cells, the vaccine cell lines and other HLA-A2+ colon cancer cell lines, but not fibroblasts isogeneic to certain of the target cell lines. Our studies demonstrate that these colon carcinoma cell lines express shared TAAs that can induce CTLs which recognize and lyse other colon carcinoma cells, and support the continued clinical evaluation of the CD80 gene modified allogeneic colon cell/cytokine-secreting fibroblast carcinoma vaccine.

Interleukin 2 gene therapy of colorectal carcinoma with autologous irradiated tumor cells and genetically engineered fibroblasts: a Phase I study.

The purpose of this study was to determine the safety, toxicity, and antitumor immune response following S.C. immunizations with a mixture of irradiated, autologous tumor cells and autologous fibroblasts that were genetically modified to express the gene for interleukin 2 (IL-2) in patients with colorectal carcinoma. Ten patients were treated with a fixed dose of tumor cells (10(7)) and escalating doses of fibroblasts secreting IL-2 (per 24 h): 100 units (three patients), 200 units (three patients), 400 units (three patients), and 800 units (one patient). Pre- and posttreatment peripheral blood mononuclear cells were evaluated for evidence of antitumor immune responses. Fatigue and/or flu-like symptoms were experienced by seven patients and delayed-type hypersensitivity-like skin reactions were observed at the sites of the second or subsequent vaccinations in five patients. Low frequencies of tumor cytotoxic T-cell precursors (range, 1/190,000-1/1,320,000 peripheral blood mononuclear cells) were detected prior to therapy in four of seven patients. There was a 5-fold increase following treatment in the frequency of tumor cytotoxic T-cell precursors in two of six evaluable patients. Some patients with colorectal cancer have low frequencies of tumor cytotoxic T-cell precursors that may be increased by this well-tolerated form of IL-2 gene therapy, which warrants continued clinical evaluation.

Combination of transforming growth factor beta antisense and interleukin-2 gene therapy in the murine ovarian teratoma model.

The immunosuppressive protein transforming growth factor beta (TGF-beta) inhibits the activation of various immune effector cells including cytotoxic T lymphocytes and may therefore inhibit the efficacy of immunostimulatory interleukin-2 (IL-2) gene therapy. In this study, we investigated the effect of TGF-beta downregulation on IL-2 gene therapy in the intraperitoneal model of murine ovarian teratoma (MOT). MOT cells, like many human ovarian carcinomas, were found to produce TGF-beta. Production of TGF-beta by MOT cells was suppressed using a TGF-beta antisense plasmid vector (pCEP4/TGF-beta antisense). Subcutaneous immunization of C3H mice with a mixture of IL-2 gene-transduced fibroblasts and TGF-beta antisense-modified MOT cells induced significantly better protection against a subsequent intraperitoneal tumor challenge compared with immunization with unmodified MOT cells alone [11/16 (69%) vs 4/21 (19%) tumor-free animals, P < 0.01]. Immunization with either a mixture of IL-2 gene modified fibroblasts and unmodified MOT cells [2/12 (17%) tumor-free animals] or TGF-beta antisense-modified MOT cells alone (0/13 tumor free animals) failed to induce significant protection compared with immunization with unmodified MOT cells. These data show that combined TGF-beta antisense and IL-2 gene therapy is required to generate effective antitumor responses in the MOT model. Our findings suggest that tumor cell expression of immunosuppressive factors may inhibit cytokine immunogene therapy and may have potential implications for the development of future clinical immunogene therapy protocols.

Construction and characterization of retroviral vectors for interleukin-2 gene therapy.

Several investigators have employed interleukin-2 (IL-2) gene transfer to enhance the immunogenicity of tumor cell vaccines. We describe in this report the construction and characterization of retroviral vectors for IL-2 gene therapy. Human IL-2 cDNA with a chimeric rat preproinsulin/IL-2 DNA leader sequence was subcloned into the pLXSN (long terminal repeat promoter) and pLNCX (cytomegalovirus [CMV] promoter) vectors to generate the plasmids pLXSN-iIL2 and pLNCX-iIL2, respectively. Human IL-2 cDNA with a chimeric human tissue factor/IL-2 DNA leader sequence was utilized to construct the vector pLXSN-tIL2. The levels of IL-2 secreted by transduced tumor cells and fibroblasts were evaluated by enzyme-linked immunosorbent assay (ELISA) of culture supernatants and compared with those of normal peripheral blood mononuclear cells (PBMC) activated in vitro with calcium ionophore and phorbol 12-myristate 13-acetate. The highest levels of IL-2 secreted by transduced tumor cells (760 units/10(6) cells/24 h), adult fibroblasts (625 units/10(6) cells/24 h), and embryonic fibroblasts (3,975 units/10(6) cells/24 h) were 150- to 1,000-fold higher than than secreted by the activated PBMC (4 units/10(6) cells/24 h). Similar levels of IL-2 were expressed by human fibroblasts transduced with pLXSN vectors employing the preproinsulin (pLXSN-iIL2) or tissue factor (pLXSN-tIL2) leader sequences (range in IL-2 units/10(6) cells/24 h pLXSN-iIL2 = 375-625 vs. pLXSN-tIL2 = 90-440). Because IL-2-transduced cells for clinical applications are generally irradiated to prevent cellular proliferation, we evaluated the effects of radiation on IL-2 production. Radiation doses between 1,500 and 10,000 cGy resulted in gradual decreases in IL-2 secretion by transduced cells. The range of the decrease in IL-2 secretion was 7-11% by day 7, 0-29% by day 14, and 25-50% by day 35. For clinical applications, stable production of the vector in high concentrations is an important consideration. The retroviral vector pLXSN-tIL2 produced the highest viral titer and was chosen for further characterization. Southern blot analysis of SacI-digested genomic DNA from the LXSN-tIL2 producer cell line and SacI-digested pLXSN-tIL2 plasmid DNA revealed the expected 3.2-kbp fragment, suggesting the absence of transgene rearrangement and the suitability of this vector as a candidate for clinical applications.

Radioimmunotherapy of relapsed B-cell lymphoma with yttrium 90 anti-idiotype monoclonal antibodies.

Tumor-specific anti-idiotype (anti-Id) monoclonal antibodies (MoAbs) to B-cell lymphomas have been administered to patients, resulting in significant clinical responses. However, clinical responses have been limited by the emergence of Id-negative lymphoma. To overcome the problem of tumor heterogeneity, we conducted a pilot evaluation of the safety and effectiveness of yttrium 90 (90Y)-labeled anti-Id and shared Id (sId) MoAbs in non-Hodgkin's B-cell lymphoma. Nine patients with relapsed B-cell lymphoma in whom tumor was successfully targeted with 111In-labeled anti-Id MoAb were treated with 90Y-labeled anti-Id MoAb. A total of 19 courses (one to four per patient) were administered using 1,000 to 2,320 mg unlabeled clearing MoAb and 10 to 54 mCi 90Y MoAb per patient. Two of nine patients had a complete response, one a partial response, three stable disease, and three disease progression. Time to progression varied from 1 to 12 months. Toxicities were predominately hematologic, and only one patient developed infection and required transfusion. At progression, three of five assessable patients had Id-positive lymphoma and two had Id-negative lymphoma. Human antimouse antibodies (HAMA) did not develop in the patients after treatment. 90Y anti-Id MoAbs demonstrated excellent in vivo stability, produced significantly tumor regression in three of nine patients, exhibited acceptable toxicities, and elicited no HAMA formation. Further investigation of repetitive, low-dose 90Y anti-Id and MoAb therapy is warranted; however, the advantages of a pan B MoAb may prove the latter to be the agent of choice for the radio immunotherapy of B-cell lymphoma.

Eradication of established intracranial rat gliomas by transforming growth factor beta antisense gene therapy.

Like human gliomas, the rat 9L gliosarcoma secretes the immunosuppressive transforming growth factor beta (TGF-beta). Using the 9L model, we tested our hypothesis that genetic modification of glioma cells to block TGF-beta expression may enhance their immunogenicity and make them more suitable for active tumor immunotherapy. Subcutaneous immunizations of tumor-bearing animals with 9L cells genetically modified to inhibit TGF-beta expression with an antisense plasmid vector resulted in a significantly higher number of animals surviving for 12 weeks (11/11, 100%) compared to immunizations with control vector-modified 9L cells (2/15, 13%) or 9L cells transduced with an interleukin 2 retroviral vector (3/10, 30%) (P < 0.001 for both comparisons). Histologic evaluation of implantation sites 12 weeks after treatment revealed no evidence of residual tumor. In vitro tumor cytotoxicity assays with lymph node effector cells revealed a 3- to 4-fold increase in lytic activity for the animals immunized with TGF-beta antisense-modified tumor cells compared to immunizations with control vector or interleukin 2 gene-modified tumor cells. These results indicate that inhibition of TGF-beta expression significantly enhances tumor-cell immunogenicity and supports future clinical evaluation of TGF-beta antisense gene therapy for TGF-beta-expressing tumors.

Comparison of gene therapy with interleukin-2 gene modified fibroblasts and tumor cells in the murine CT-26 model of colorectal carcinoma.

We compared the efficacy of gene therapy mediated by interleukin-2 (IL-2) gene-modified tumor cells to gene therapy mediated by IL-2 transduced fibroblasts in the CT-26 model of murine colorectal carcinoma. We transduced CT-26 tumor cells and BALB/c 3T3 fibroblasts with three different retroviral vectors using three different promoters for the human IL-2 gene: DC/TKIL-2 (thymidine kinase promoter), LXSN-iIL2 (long terminal repeat promoter), and LNCX-iIL2 (cytomegalovirus promoter). These transductions resulted in CT-26 and 3T3 subclones that secreted different amounts of IL-2. Immunization of animals with either CT-26/IL-2 cells or with fibroblast/IL-2 cells mixed with CT-26 induced similar levels of immunity that protected 62-82% of animals against a subsequent tumor challenge with parental CT-26. However, mice developed tumors at the site of inoculation in 46% of the animals immunized with CT-26/IL-2 cells. In a separate experiment, CT-26/IL-2 cells were exposed to 6,000 cGy of gamma irradiation to prevent tumor growth at the site of inoculation. Although the CT-26/IL-2 cells continued to secrete IL-2 after irradiation, they were no longer effective at inducing antitumor immunity. In contrast, both irradiated and nonirradiated fibroblast/IL-2 cells, mixed with irradiated CT-26, were equally effective at inducing antitumor immunity. These data suggest that in the CT-26 model, fibroblast-mediated IL-2 gene therapy has advantages for the induction of antitumor immunity and abrogation of tumorigenic potential at the site of inoculation compared with tumor cell-mediated IL-2 gene therapy.

Cytokine gene therapy with interleukin-2-transduced fibroblasts: effects of IL-2 dose on anti-tumor immunity.

We evaluated the effects of different doses of interleukin-2 (IL-2)-transduced fibroblasts in the treatment of colorectal carcinoma in the CT-26 murine tumor model. Immunization with a mixture of irradiated tumor cells and IL-2-transduced fibroblasts (100 units of IL-2/24 hr) induced significantly greater protection against a live tumor challenge compared to irradiated tumor cells alone (22/35, 65% vs. 10/30, 33%, p < 0.02). Protective effects were observed with doses of IL-2-transduced fibroblasts secreting from 5 to 100 units of IL-2/24 hr. Parallel experiments in nude mice produced no protection, indicating that the effects of immunization were mediated by a T-cell-dependent mechanism. In animals with established tumors, complete tumor remissions were observed following immunization with a mixture of irradiated tumor cells and IL-2-transduced fibroblasts secreting 100 units of IL-2/24 hr, but not after immunization with irradiated tumor cells alone (7/16 vs. 0/11 complete remissions, p < 0.02). Fibroblasts secreting higher doses of IL-2 were ineffective in generating systemic immunity, but were required to prevent tumor implantation. A statistically significant difference in the prevention of tumor implantation was observed between groups inoculated with a mixture of live tumor cells and IL-2-transduced fibroblasts (1,750 units of IL-2/24 hr) compared to control fibroblasts (6/8 vs. 0/12, p < 0.001). Similar results were observed in nude mice, suggesting that the implantation rejection response is mediated in part by cells other than thymus-derived T cells. Our data support the utility of IL-2-transduced fibroblasts and indicate that the level of IL-2 expression is an important variable in activating different effector components of antitumor immune responses in IL-2 gene therapy.

Characterization of a new human glioblastoma cell line that expresses mutant p53 and lacks activation of the PDGF pathway.

We have established and characterized a new glioblastoma cell line, termed GT9, from a biopsy sample of a female adult patient with glioblastoma multiforme. The line has now undergone over 60 passages and has been successfully cultured after cryopreservation. Immunofluorescence analyses with a panel of monoclonal antibodies were positive for glial fibrillary acidic protein and vimentin, and negative for neurofilament, galactocerebroside, and fibronectin, a pattern typical of glial cells. Based on a tetraploid, the composite karyotype of GT9 cells included the loss of chromosome 10, gain of chromosome 7, and the presence of double minute chromosomes, three of the most common karyotypic abnormalities in glioblastoma. Sequence analysis of p53 cDNA revealed a homozygous double mutation at codon 249 (commonly mutated in aflatoxin-associated hepatocellular carcinoma) and codon 250. Moreover, there was a complete absence of wild-type p53. However, unlike the majority of human glioblastomas previously described, the expression of platelet-derived growth factor-B (PDGF-B), a potent mitogenic autocrine factor, was low in GT9 cells. The expression and phosphorylation of c-Jun and Jun-B, downstream mediators of the PDGF pathway, were also low. Thus, deregulation of the PDGF pathway does not appear to be involved in the pathogenesis of the GT9 glioblastoma. Conversely, Jun-D, a negative regulator of cell growth, was also low. In addition, Phosphorylated Egr-1, a recently reported suppressor of PDGF-B/v-sis-transformed cells, was also low, suggesting that the lack of activation of the PDGF pathway was not due to these suppressive mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Human anti-mouse antibody response in cancer patients following single low-dose injections of radiolabeled murine monoclonal antibodies.

We examined the human anti-mouse antibody (HAMA) response in 61 cancer patients following a single, diagnostic injection of any one of ten 111In conjugated murine monoclonal antibodies. Between 1 and 22 mg of antibody containing 1-5 mCi 111In was administered. The populations studied included 30 patients with colorectal carcinoma (four different antibodies), 22 with malignant melanoma (four antibodies), and nine with prostate cancer (two antibodies). Forty-one percent of the patients developed HAMA within 14 days. Three patients (5%) developed an IgM response, five patients (8%) developed an IgG response, and 17 patients (28%) developed both IgM and IgG. Only 27% of the patients with colon cancer developed HAMA, compared to 55% of the melanoma patients and 56% of the prostate cancer patients. There were no correlations among injected dose, various clinical parameters, and HAMA response. There were variations in the HAMA response to different monoclonal antibodies, but population samples were too small to infer significance. Most of the HAMA responses had a significant proportion of idiotypic or isotypic specificity. Only 1/6 patients who were HAMA negative after the first infusion developed HAMA following subsequent infusions of the same monoclonal antibody. Our data demonstrate that a significant percent of cancer patients develop HAMA following a single, low-dose injection of a radiolabeled monoclonal antibody for diagnostic purposes. This may have important implications for the future therapeutic use of monoclonal antibodies in such patients.

WY 18,251 (Tilomisole), an analog of levamisole: tolerability, and immune modulating effects in cancer patients.

Wy 18,251 (Tilomisole; Wyeth Laboratories, Philadelphia, PA, USA) is a benzimidazole that is structurally similar to the antihelminth levamisole that has recently been approved for the adjuvant treatment of colon cancer. In preclinical models, Tilomisole caused less agranulocytosis than levamisole, but retained immunomodulating capabilities. We examined the effects of Tilomisole administered to cancer patients in four different dose schedules: 60 mg/m2 orally (p.o.) weekly, and 60, 300, or 960 mg/m2 p.o. daily for 1 month. All patients were immunosuppressed when treatment was initiated as defined by standardized assays of phytohemagglutinin, concanavalin A, pokeweed mitogen, and mixed lymphocyte responses. Tilomisole was well tolerated with no significant side effects in 25 patients. There were no antitumor responses noted in this setting of metastatic cancer. There was no improvement in concanavalin A or pokeweed mitogen assays at any dose or schedule, but there was sustained improvement in mixed lymphocyte reaction and phytohemagglutinin assays at the 60 mg/m2 daily dose. This drug may have favorable biological response modifying effects in vivo and be a suitable alternative to levamisole in cancer treatment, especially if agranulocytosis is a significant problem associated with widespread use of levamisole.

Expression of shared idiotypes in chronic lymphocytic leukemia and small lymphocytic lymphoma.

The expression of shared idiotypes (Slds) has been studied on malignant CD5+B cells from patients with chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL) using a panel of 37 murine monoclonal antibodies previously demonstrated to be reactive with Slds derived from follicular B-cell lymphomas. Thirteen anti-Slds identified tumor cells from 31 of 105 (30%) CLL patients and 4 of 6 SLL patients. In comparison, the same panel of anti-Slds is reactive with 33% of follicular and diffuse B-cell lymphomas. Ten of these anti-Slds reacted with CLL cases at similar frequencies to that of the B-cell lymphomas. Two anti-Slds, which are known to react with autoantibodies, were significantly more prevalent in CLL than in B-cell lymphomas. These data confirm the presence of Slds in CLL and provide further evidence of an association between CLL and autoimmunity. The identification of a panel of antibodies reactive with a significant number of CLL and SLL patients will facilitate the application of anti-idiotype antibody therapy in these diseases.

Preclinical trials using an immunoconjugate of T101 and methotrexate in an athymic mouse/human T-cell tumor model.

We made an immunoconjugate (IC) using the anti-CD5 monoclonal antibody T101 and the chemotherapeutic drug methotrexate. Methotrexate was conjugated to T101 using an active ester intermediate, yielding a drug: antibody molar ratio of 12.4. Although T101 immunoreactivity was not significantly altered by conjugation, the IC did not demonstrate antigen-specific cytotoxicity in vitro. Methotrexate activity, assayed in vitro, decreased approximately 100-fold following conjugation. The IC was tested for in vivo efficacy in athymic mice bearing human T-cell (MOLT 4) xenografts. Experimental arms used in the study included i.p. injections of saline, T101, methotrexate, the IC, and a mixture of T101 and methotrexate. Doses ranged from 500 micrograms T101 (17.5 micrograms methotrexate) to 2 mg T101 (70 micrograms methotrexate). Injections were administered only after palpable tumors were established. In experiments at all doses, totaling 66 animals per arm, injection of the IC significantly inhibited tumor growth, and resulted in more tumor regressions and fewer animal deaths than the other four experimental arms. These data demonstrate that the IC promotes a potential advantage over the use of methotrexate through an increase in the therapeutic index.

Superiority of an acid-labile daunorubicin-monoclonal antibody immunoconjugate compared to free drug.

We conjugated the chemotherapy agent daunorubicin to the anti-T-cell monoclonal antibody T101 using an active ester intermediate of the acid-labile linker cis-aconitate anhydride. By converting carbohydrate hydroxyl groups on the antibody to amines prior to conjugation, average drug to antibody ratios of 25:1 were achieved with retention of cytotoxicity and only minimal loss of immunoreactivity. The pH sensitivity of the linkage was confirmed. The preparation was cytotoxic for antigen-bearing cells but not antigen-negative cells, even up to 48-h incubation in vitro. Specific cytotoxicity was apparently mediated through the endocytosis of the intact T101 immunoconjugate and the release of the active drug in the lysosomal compartment. Athymic mice bearing human tumor xenografts who received a single injection of the immunoconjugate had less tumor growth and more tumor regressions than animals receiving antibody alone, drug alone, or a mixture of drug plus antibody. This approach appears promising for further investigation.

Inhibition of human T-cell tumor growth by T101-ricin A-chain in an athymic mouse model.

An immunotoxin prepared with the pan-T-cell, anti-CD5, antibody T101, and purified ricin A-chain (RTA) was selectively cytotoxic in vitro, inactivating protein synthesis in the human T-cell line MOLT-4 but not in the human B-cell line 8392. Modulation studies showed that the immunoconjugate was more rapidly cleared from the cell surface than unconjugated T101. Preclinical evaluation of T101-RTA was conducted in a human T-cell, athymic mouse model (Dillman et al., Cancer Res., 45:5632-5336, 1985). Tumor-bearing mice received single i.p. injections of saline, T101, UPC-10 (irrelevant IgG2a), unconjugated RTA, an irrelevant conjugate, UPC-10-RTA, a mixture of T101 plus RTA, or T101-RTA. T101-RTA was the most effective reagent. Thirty animals given injections of 33 micrograms of T101 showed reductions in tumor growth (compared to tumor growth in animals receiving phosphate-buffered saline) but no complete regressions. No decrease in tumor growth was observed with UPC-10. Animals given 12 micrograms of free RTA exhibited reduced tumor growth but only one complete regression was observed; similar results were obtained with mice given 45 micrograms of UPC-10-RTA or a mixture of 33 micrograms of T101 plus 12 micrograms of RTA. Eleven complete regressions and 18 partial regressions were produced in the 46 animals given injections of 45 micrograms of T101-RTA and tumor growth was almost completely blocked. No toxicity was observed in any experimental arm. These results suggest that T101-RTA may be administered safely and with significant antitumor effect.

Mechanisms of human CD5 modulation and capping induced by murine monoclonal antibody T101.

We have previously demonstrated that the murine monoclonal antibody T101 induces antigenic modulation when infused into patients with chronic lymphocytic leukemia and cutaneous T-cell lymphoma. In this paper, we extend our studies of T101-induced modulation and compare it to T101-induced capping. We found that, in contrast to antigenic modulation, capping occurred only in the presence of secondary anti-mouse IgG antisera and was altered by drugs that affect the cellular cytoskeleton or energy metabolism. F(ab')2 fragments of T101 induced antigenic modulation with kinetics similar to those of intact T101, but Fab-induced modulation proceeded more slowly and required the continual presence of Fab throughout the incubation. Experiments with radioiodinated T101 demonstrated that initial internalization of the antibody is followed by rapid efflux of intact, immunoreactive T101 from the cells. These data indicate important differences between capping and modulation and suggest that these two phenomena proceed by different mechanisms. More importantly, the data have implications for the potential therapeutic use of monoclonal antibody immunoconjugates.