Development of the R263K Mutation to Dolutegravir in an HIV-1 Subtype D Virus Harboring 3 Class-Drug Resistance.

Dolutegravir (DTG), a second-generation integrase strand-transfer inhibitor (INSTI), is equivalent or superior to current non-nucleotide reverse transcriptase inhibitors (NNRTIs), protease inhibitors (PIs), and first-generation INSTI-based antiretroviral regimens (ARVs). It has the potential to make big improvements in HIV control globally and within patients. This is perhaps the most "precious" HIV drug available. The integrase mutation R263K has been observed in tissue culture experiments and in patients treated with dolutegravir monotherapy in clinical trials. Globally, adherence and monitoring may be less than optimal and therefore DTG resistance more common. This is particularly important in low-middle-income countries, where patients may remain on failing regimens for longer periods of time and accumulate drug resistance. Data on this mutation in non-subtype B infections do not exist. We describe the first report of the R263K integrase mutation in a dolutegravir-exposed subtype D-infected individual with vertically acquired HIV. We have used deep sequencing of longitudinal samples to highlight the change in resistance over time while on a failing regimen. The case highlights that poorly adherent patients should not be offered dolutegravir even as part of a combination regimen and that protease inhibitors should be used preferentially.

Extensively drug resistant tuberculosis in a HIV-infected patient in a UK hospital.

Tuberculosis (TB) is a major cause of mortality in the HIV-infected population, with growing concern about increasing incidence in extensively drug-resistant (XDR) TB worldwide. We describe the first published case of XDR TB and HIV co-infection in the UK. The case describes a patient newly diagnosed with smear-positive pulmonary TB and HIV. The isolate was found to be XDR TB, requiring use of third-line TB drugs alongside antiretroviral medication, causing multiple complications due to drug toxicity and interactions. After culture conversion was achieved directly observed treatment with close community support was organized for the patient. Despite these arrangements the patient required readmission for new-onset headaches after poor adherence to treatment. Investigations confirmed lymphocytic meningitis. The patient eventually deteriorated and died from acute cerebral infarction. This case highlights the complexity of managing drug-resistant TB in HIV-infected individuals, due to difficult adherence, drug toxicity and potential public health risks.

Fibroblasts as novel therapeutic targets in chronic inflammation.

A characteristic feature of many chronic inflammatory diseases is their persistence and predilection for certain sites. The molecular basis for such tissue tropism and failure of the inflammatory response to resolve has until relative recently remained obscure. Recent studies have strongly implicated fibroblasts as cells which contribute to disease persistence and which help define anatomical location. Therefore fibroblasts make an attractive therapeutic target as they help orchestrate the inflammatory infiltrate. Current anti-inflammatory therapies target immune cells in an attempt to inhibit the production of pro-inflammatory mediators. However an equally important target is the active induction of pro-resolution programmes responsible for the resolution of inflammation. Fibroblasts are likely to be an important source of these anti-inflammatory mediators. Therapeutic manipulation of fibroblasts and their biologically active products is an emerging concept in treating cancer and is likely to provide a novel method to achieve improved control of chronic inflammatory disease.

Therapy of human T-cell acute lymphoblastic leukaemia with a combination of anti-CD7 and anti-CD38-SAPORIN immunotoxins is significantly better than therapy with each individual immunotoxin.

Severe combined immunodeficient (SCID) mice injected i.v. with the human T-ALL cell line CCRF CEM (SCID-CEM mice) develop within 50 days life-threatening multi-organ growth of leukaemia cells. The development of leukaemia in SCID-CEM mice treated with three 10 microg i.v. doses of the anti-CD7 immunotoxin (IT) HB2-SAPORIN or the anti-CD38 IT OKT10-SAPORIN was significantly delayed compared with PBS sham-treated animals but 90% of animals treated with either IT eventually developed disseminated leukaemia cell growth. In contrast treatment of SCID-CEM mice with a combination of both ITs led not only to a significantly greater delay in time to leukaemia development but also in the numbers of animals remaining leukaemia free (60%). The native HB2 and OKT10 antibodies (both murine IgG1antibodies) exerted significant, though relatively weak therapeutic effects, probably mediated through an antibody-dependent cellular cytotoxicity (ADCC) mechanism. Moreover, there was no in vivo additivity of therapeutic effect when both antibodies were used in combination. Apparent, however, was that the combination of HB2-SAPORIN IT with OKT10 antibody led to an intermediate therapeutic effect that was significantly greater than that obtained when either was used alone but significantly less than that obtained when the two IT combination was utilized. This was similarly the case for the combination of OKT10-SAPORIN IT with HB2 antibody though the effect was less pronounced in this instance. This result suggests that the therapeutic effect of IT + antibody treatment results from an additivity between antibody-mediated delivery of saporin combined with a SCID mouse NK cell-mediated ADCC attack on the target cell directed through target cell bound antibody Fc engagement with FcgammaRIII on the NK cell surface. The combination of both ITs however gave the best therapeutic outcome in SCID-CEM mice probably as the result of (i) delivery of greater amounts of saporin to target CEM cells positive for both CD7 and CD38, (ii) delivery of an effective dose of saporin to CEM cells downregulated or negative for one of the target antigens and (iii) through ADCC mechanisms that interact additively with IT action. We have previously proposed that combination IT therapy would be one means of overcoming the problem of heterogeneity of antigen expression within a global tumour cell population and these additional findings support this and provide a further strengthening of the rationale for employing cocktails of ITs for the treatment of human malignancies.

Anti-CD7 antibody and immunotoxin treatment of human CD7(+)T-cell leukaemia is significantly less effective in NOD/LtSz-scid mice than in CB.17 scid mice.

Groups of 8 to ten SCID (CB.17 scid/scid) or NOD/SCID (NOD/LtSz- scid/scid) mice were injected i.v. with two million human HSB-2 T-ALL cells on day 1 (SCID-HSB-2 and NOD/SCID-HSB-2 mice) and treated later with 3 i.v. 10 microg doses of the anti-CD7 antibody HB2 on days 7, 9 and 11 or with a single 10 microg dose of HB2-SAPORIN or a 7.4 microg dose of HB2-F(ab)(2)-SAPORIN immunotoxin (IT) on day 7. Treatment of SCID-HSB-2 mice with HB2-SAPORIN led to a significant prolongation in the time to development of signs and symptoms of disease compared with PBS sham-treated controls with 80% of animals surviving disease-free. In contrast treatment with HB2-F(ab)(2)-SAPORIN was significantly less effective in SCID-HSB-2 mice with 80% of animals in this treatment group developing leukaemia over the course of the study. HB2 antibody treatment of SCID-HSB-2 mice also led to a significant prolongation in time to leukaemia development compared with sham-treated controls with 37% of animals in this treatment group disease-free at termination of the study. In contrast HB2 antibody treatment of NOD/SCID-HSB-2 mice had no therapeutic effect in these animals and the therapeutic effectiveness of both HB2-SAPORIN and HB2-F(ab)(2)-SAPORIN ITs was similar and significantly reduced compared to the effect observed in SCID-HSB-2 mice. It was initially thought that the lack of therapeutic effect of antibody and IT in NOD-SCID-HSB-2 mice might relate to their putative lack of NK cells but flow cytometric and functional studies with NOD-SCID mouse splenocytes revealed that these animals do have some functional NK cells though fewer in number and possibly lower in functionality than those of SCID mice. We reason that the complete lack of therapeutic effect of HB2 antibody and the reduced effect of HB2-SAPORIN in NOD/SCID mice is due to the reduced cytolytic activity of NOD/SCID NK cells which is probably below a certain critical threshold value in these animals. We conclude from this that immunotherapeutics like HB2-SAPORIN would be more accurately assessed for intrinsic potency in NOD/SCID mice where the effects of NK cell and possibly other non-adaptive immune mechanisms would not have a significant influence.

Host-mediated antibody-dependent cellular cytotoxicity contributes to the in vivo therapeutic efficacy of an anti-CD7-saporin immunotoxin in a severe combined immunodeficient mouse model of human T-cell acute lymphoblastic leukemia.

We have investigated the anti-leukemia effect that is exerted by the murine anti-CD7 antibody HB2 in a severe combined immunodeficient (SCID) mouse model of human T-cell acute lymphoblastic leukemia (T-ALL) and determined the contribution that this antibody effect makes to the therapeutic potency of a saporin immunotoxin (IT) constructed with the same antibody. The anti-leukemia effect is not exerted through complement-mediated lysis or through direct growth-inhibitory signaling after binding of antibody to the CD7 molecule on the T-ALL cell surface but rather through antibody-dependent cellular cytotoxicity (ADCC). Thus, the in vivo depletion of SCID mice of their natural killer cells almost completely abolishes the therapeutic effect of native HB2 anti-CD7 antibody and moreover significantly reduces the in vivo therapeutic performance of the anti-CD7 HB2-SAPORIN IT. Furthermore, an IT constructed with the F(ab')2 fragment of the same anti-CD7 antibody (HB2-F(ab')2-SAPORIN), which is incapable of recruiting natural killer cells, performed significantly less well therapeutically than HB2-SAPORIN IT. There was also a significant improvement in the therapeutic performance of the HB2-F(ab')2-SAPORIN IT in SCID-HSB-2 mice when used in combination with intact HB2 antibody, presumably through restoration of an ADCC attack on the target HSB-2 cell. These combined data indicate that ADCC in the SCID mouse does contribute additively together with toxin to the in vivo therapeutic potency of the HB2-SAPORIN IT directed against this human T-ALL cell line and that this has potentially important implications for the utility of this and other related classes of immunotherapeutic in human therapy.

Systemic therapy with 3BIT, a triple combination cocktail of anti-CD19, -CD22, and -CD38-saporin immunotoxins, is curative of human B-cell lymphoma in severe combined immunodeficient mice.

We demonstrate in these preclinical studies that all severe combined immunodeficient mice injected with the human B-cell lymphoma cell line Ramos are cured when treated with a combination of anti-CD19, -CD22, and -CD38-saporin immunotoxins (ITs; termed 3BIT). Each component IT used individually did not cure the majority of animals but did significantly prolong their survival compared with PBS sham-treated controls, although the majority succumbed eventually to disease. The very significant improvement obtained with the three-IT combination 3BIT was not due to an antibody or antibody-plus-IT effect. We postulate that by targeting against these three cell surface molecules, we have effectively ensured delivery of saporin to each lymphoma cell with growth potential within the tumor, thus overcoming the problems of heterogeneity of target antigen expression that can limit the therapeutic efficacy of single-IT therapy or even two-IT combination therapy. These "proof of principle" findings have an obvious important bearing on antibody-based therapies for cancer and provide the rationale needed for the design and implementation of clinical trials with such combinations.

Comparison of the potency and therapeutic efficacy of the anti-CD7 immunotoxin HB2-saporin constructed with one or two saporin moieties per immunotoxin molecule.

Immunotoxins that carry two toxin molecules to the target cell should in theory have a greater anti-tumour effect than those that carry just one. We have investigated the therapeutic efficacy of two anti-CD7-saporin immunotoxins constructed with one saporin (HB2-Sap 1-mer) or two saporin molecules (HB2-Sap 2-mer) per immunotoxin molecule. In vitro, the 2-mer immunotoxin was 5.6 times more effective than the 1-mer immunotoxin at inhibiting protein synthesis in the CD7+ human T-cell acute lymphoblastic leukaemia (T-ALL) cell line HSB-2 and was also more effective at inhibiting HSB-2 cell proliferation. Flow cytometry revealed that the 2-mer immunotoxin had a reduced binding capacity to HSB-2 cells compared with the 1-mer immunotoxin or native HB2 antibody. In therapy studies in SCID mice with disseminated HSB-2 human leukaemia, the 2-mer immunotoxin performed marginally better than the 1-mer immunotoxin, but log-rank analysis did not reveal any significant differences between the two therapy groups. We therefore conclude that, although the 2-mer immunotoxin performed better than the 1-mer immunotoxin against target HSB-2 cells in vitro, this improved performance was not reflected as an improved in vivo therapeutic outcome in the SCID mouse model.

Preclinical studies with the anti-CD19-saporin immunotoxin BU12-SAPORIN for the treatment of human-B-cell tumours.

The immunotoxin BU12-SAPORIN was constructed by covalently coupling the single-chain ribosome-inactivating protein saporin to the anti-CD19 monoclonal antibody BU12 via a disulphide linker using the heterobifunctional reagent SPDP. The immunoreactivity and specificity of BU12-SAPORIN was identical to that of unmodified native BU12 antibody. BU12-SAPORIN was selectively cytotoxic in vitro in a dose-dependent manner for the CD19+ human common acute lymphoblastic leukaemia (cALL) cell line NALM-6 but exhibited no toxicity for the CD19- T-cell acute lymphoblastic leukaemia (T-ALL) cell line HSB-2. The survival of severe combined immunodeficient (SCID) mice with disseminated NALM-6 leukaemia was significantly prolonged compared with sham-treated control animals by a course of therapy with BU12-SAPORIN but not with the irrelevant anti-CD7 immunotoxin HB2-SAPORIN. BU12-SAPORIN had no therapeutic effect in SCID mice with disseminated CD19- HSB-2 leukaemia. These preclinical studies have clearly demonstrated the selective cytotoxicity of BU12-SAPORIN for CD19+ target cells both in vitro and in vivo. This, taken together with the lack of expression of the CD19 molecule by any normal life-sustaining tissue and its ubiquitous and homogeneous expression by the majority of cALL and B-NHL cells, provides the rationale for undertaking a phase I trial of systemic therapy with BU12-SAPORIN.

Comparison of the performance of anti-CD7 and anti-CD38 bispecific antibodies and immunotoxins for the delivery of saporin to a human T-cell acute lymphoblastic leukemia cell line.

We have investigated the cytotoxic performance of two different anti-CD7/anti-saporin BsAb's (HB2 x DB7-18 and Q1.1), three anti-CD38/anti-saporin BsAb's (OKT10 x RabSap, OKT10 x DB7-18 and Q4.1) and an anti-CD7 (HB2-Sap) and anti-CD38-saporin (OKT10-Sap) immunotoxin for delivering the ribosome inactivating protein (rip) to the human T-cell acute lymphoblastic leukemia cell line HSB-2. In the case of CD7 as target molecule the immunotoxin outperformed both anti-CD7 BsAb's being six times more effective than HB2 x DB7-18 and 98 times more so than Q1.1 at effectively inhibiting protein synthesis in a dose dependent manner. The chemically constructed HB2 x DB7-18 BsAb was more effective at inhibiting protein synthesis and cell growth in target HSB-2 cells in a dose dependent manner than the quadroma produced BsAb Q1.1. Both BsAb demonstrated a prozone effect used at concentrations above 0.1 nM though this was more pronounced for Q1.1 than for HB2 x DB7-18. The prozone effect was partially though not completely reversed by increasing the concentration of saporin in the system. In the case of CD38 as target molecule the anti-CD38 IT OKT10-Sap performed poorly, never actually achieving its IC50. Two BsAb's constructed with monoclonal anti-saporin Fab arms each recognizing a different epitope on the saporin molecule also performed poorly. In contrast the BsAb OKT10 x RabSap constructed with Fab derived from a rabbit polyclonal anti-saporin antiserum performed in a dose dependent manner achieving its IC50 at a concentration of 1.3 nM. This BsAb also exhibited a prozone effect. These results exemplify the importance of cross linking adjacent target molecules on the cell surface in order to achieve effective delivery of saporin to the cell interior.

Therapy of human B-cell lymphoma bearing SCID mice is more effective with anti-CD19- and anti-CD38-saporin immunotoxins used in combination than with either immunotoxin used alone.

The CD19+ CD38+ human Burkitt's lymphoma cell line Ramos grows aggressively when injected intravenously (i.v.) into severe combined immunodeficient (SCID) mice, killing 100% of animals within a 33-42 day period with widely disseminated disease. Treatment commencing 7 days after i.v. injection of Ramos cells, with 3 doses of an anti-CD19 immunotoxin (IT; BU12-SAPORIN) or an anti-CD38IT (OKT10-SAPORIN) led to a significant prolongation of survival compared with sham-treated controls; the anti-CD38 IT gave the greatest prolongation of survival, but all treated animals eventually succumbed to disease. When both ITs were used in combination at equivalent dose levels, the therapeutic outcome was significantly improved over that obtained for single IT therapy, with 20% of animals surviving disease-free to 300 days. When anti-CD38 IT was given in combination with anti-CD19 antibody there was no therapeutic improvement over anti-CD38 IT used alone. However, when anti-CD19 IT was given in combination with CD38 antibody, a significant prolongation of survival ensued over that obtained with anti-CD19 IT alone, though this was not as significantly pronounced as that obtained when both ITs were used in combination and was only as good as the survival obtained with OKT10 antibody used alone. CD19 and CD38 are expressed on the surface of the vast majority of B-cell lymphoma and common acute lymphoblastic leukaemia cells, and our findings provide a sound rationale for a combination immunotoxin trial in these diseases directed against both these target molecules.

Therapy of human T-cell acute lymphoblastic leukaemia in severe combined immunodeficient mice with two different anti-CD7-saporin immunotoxins containing hindered or non-hindered disulphide cross-linkers.

A SCID mouse model of human T-ALL has been used to determine the in vivo therapeutic efficacy of two anti-CD7-saporin immunotoxins constructed with either a hindered (HB2-SMPT-Sap) or non-hindered (HB2-SPDP-Sap) disulphide bond between antibody and saporin. Groups of 10 SCID mice were injected intravenously (i.v.) with 2 x 10(6) human T-ALL HSB-2 cells followed seven days later by i.v. injection with either a single dose or with 3 doses of HB2-SPDP-Sap or HB2-SMPT-Sap given on alternate days. Control groups received equivalent sham injections of PBS or molar equivalent amounts of unconjugated HB2 antibody+saporin. Animals receiving a single dose of HB2-SMPT-Sap showed better survival than animals receiving a single dose of HB2-SPDP-Sap but the difference was not shown to be significant by log-rank analysis. When given as a triple dose both immunotoxins performed similarly. Comparison of single-dose with triple-dose IT therapy revealed that the therapeutic effect of a triple dose of HB2-SPDP-Sap was significantly better than that of single dose, but this was not the case with HB2-SMPT-Sap. Pharmacokinetic studies of HB2-SPDP-Sap and HB2-SMPT-Sap in normal and HSB-2 leukaemia bearing SCID mice failed to reveal any difference in clearance rates for these two IT's. We conclude from these studies that there is no therapeutic advantage to be gained from constructing the HB2-Sap IT with a hindered disulphide bond in this particular model of human T-ALL.

Effectiveness of HB2 (anti-CD7)--saporin immunotoxin in an in vivo model of human T-cell leukaemia developed in severe combined immunodeficient mice.

The transplantation of the human T-cell acute lymphoblastic leukaemia (T-ALL) cell line HSB-2 into severe combined immunodeficient (SCID) mice was found to produce a disseminated pattern of leukaemia similar to that seen in man. The intravenous injection of 10(7) HSB-2 cells was associated with a universally fatal leukaemia. Histopathological examination of animals revealed the spread of leukaemia initially from bone marrow to involve all major organs including the meninges. An immunotoxin (HB2-Sap) was constructed by conjugating the anti-CD7 MAb HB2 to the ribosome-inactivating protein saporin. An in vitro protein synthesis inhibition assay revealed specific delivery of HB2-Sap immunotoxin (IT) to CD7+ HSB-2 target cells with an IC50 of 4.5 pM. When SCID mice were injected with 10(6) HSB-2 cells and then treated 8 days later with a single intravenous dose of 10 micrograms of immunotoxin there was a significant therapeutic effect evidenced by the numbers of animals surviving in the therapy group compared with untreated controls (chi 2 = 5.348, P = 0.021). These results demonstrate the useful application of human leukaemia xenografts in SCID mice and the potential therapeutic effect of an anti-CD7 immunotoxin in human T-ALL.

Immunotoxin studies in a model of human T-cell acute lymphoblastic leukemia developed in severe combined immune-deficient mice.

The transplantation of the human T-cell acute lymphoblastic leukemia (T-ALL) cell line HSB-2 into severe combined immune-deficient (SCID) mice was found to produce a disseminated pattern of leukemia similar to that seen in humans. The iv injection of 10(7) HSB-2 cells was associated with a universally fatal leukemia. Histopathological examination of animals revealed the spread of leukemia initially from bone marrow to involve all major organs including the meninges. An immunotoxin (HB2-Sap) was constructed by conjugating the anti-CD7 monoclonal antibody (MAb) HB2 to the ribosome inactivating protein (RIP) saporin. An in vitro protein synthesis inhibition assay revealed specific delivery of HB2-Sap immunotoxin (IT) to CD7+ HSB-2 target cells with an IC50 of 4.5 pM. In an in vivo study, the IT was shown to significantly prolong the survival of SCID mice injected with HSB-2 cells compared to untreated control animals. This therapeutic effect was seen both with a single injection of 10 micrograms of IT given 7 d after the injection of HSB-2 cells, and was even more effective when IT was administered as three daily injections of 10 micrograms on d 7, 8, and 9. These results demonstrate the useful application of human leukemia xenografts in SCID mice and the potential therapeutic effect of an anti-CD7 IT in human T-ALL.

Localisation of granulocyte macrophage colony-stimulating factor in human long-term bone marrow cultures. Biological and immunocytochemical characterisation.

The distribution of granulocyte macrophage colony-stimulating factor (GM-CSF) in human long-term bone marrow cultures (HLTBMC) was examined using two monoclonal antibodies raised using purified recombinant GM-CSF and a third commercially available GM-CSF antibody. The antibodies were able to bind to purified recombinant GM-CSF and showed inhibition of GM-CFC colonies in the presence of both recombinant and native protein. All antibodies displayed similar patterns of distribution in both permeabilised and non-permeabilised stromal cell preparations. Fibroblasts were labelled at their periphery in early cultures and both endothelial cells and fibroblasts showed cytoplasmic labelling with anti-GM-CSF. The fact that GM-CSF appears to be sequestered by cells of the bone marrow stroma raises the possibility that it is synthesized by these cells and may regulate activity of the progenitor cells in the haemopoietic foci. In contrast, early progenitor cells within the foci did not stain with any of the anti-GM-CSF antibodies. Adipocytes, which differentiate from fibroblasts in these cultures, showed a diffuse staining pattern. Two types of macrophage staining were observed in the non-permeabilised cells; those exhibiting only autofluorescence and those that bound the antibody. Intracellular staining was apparent in a small sub-population. Generally, the staining persisted up to eight weeks of culture and thereafter declined, becoming virtually undetectable after 12 weeks. This correlates with the pattern of GM-CFC production in long-term bone marrow cultures.

Effectiveness of combinations of bispecific antibodies for delivering saporin to human acute T-cell lymphoblastic leukaemia cell lines via CD7 and CD38 as cellular target molecules.

We have investigated the effectiveness of three different F(ab' gamma)2 bispecific antibodies (BsAb) for delivering the ribosome inactivating protein (RIP) saporin via the CD7 or CD38 cell surface molecules to the human T-ALL cell lines HSB-2 and HPB-ALL. Inhibition of 3H-leucine uptake by target cells was used as the parameter of cellular cytotoxicity. Used singly against HSB-2 cells in the presence of varied concentrations of saporin, an anti-CD7 BsAb, (HB2 x DB7-18) and an anti-CD38 BsAb (OKT10 x RabSap), gave 435- and 286-fold increases in saporin toxicity, respectively. For HPB-ALL cells the anti-CD7 BsAb performed poorly giving only an eight-fold increase in toxicity whilst on the same cell line the anti-CD38 BsAb was highly potent giving an 80,000-fold increase in saporin toxicity. A combination of both BsAb used together against HSB-2 cells was ten times more effective, than the best single BsAb HB2 x DB7-18 used alone. Kinetic studies conducted with HSB-2 cells revealed that the BsAb combination also gave an increased rate of protein synthesis inactivation in comparison to either BsAb used alone. These investigations clearly demonstrate a synergistic action when both BsAb are used in combination to target saporin against CD7 and CD38 expressed on the surface of the HSB-2 cell line.

High-dose mitoxantrone and etoposide conditioning in autologous bone marrow transplantation for relapsed Hodgkin's disease.

We administered high-dose mitoxantrone in combination with etoposide to 6 patients with relapsed Hodgkin's disease as the conditioning regimen for autologous bone marrow transplantation. This regimen was well tolerated and no significant cardiotoxicity was observed. Responses of the Hodgkin's disease to this therapy were favourable but short-lived. Serial measurements of the serum levels of mitoxantrone suggested an open 3-compartment model of drug distribution. The rapid early phase of drug distribution was followed by an intermediate phase and a slow terminal drug-elimination phase. However, mitoxantrone was still detected in the serum of all patients 7 days after the last dose of mitoxantrone and on the day of bone marrow re-infusion. The clinical significance of such findings is unclear but they may suggest a need for the use of other anthracycline-related cytotoxic agents for the conditioning in autologous bone marrow transplantation.

Characteristics and performance of a bispecific F (ab'gamma)2 antibody for delivering saporin to a CD7+ human acute T-cell leukaemia cell line.

We have investigated the efficacy of a F(ab'gamma)2 bispecific antibody (BsAb) with dual specificity for the CD7 molecule in one Fab arm and for the ribosome inactivating protein (rip) saporin in the other arm, for delivering saporin to the acute T-cell leukaemia cell line HSB-2. Saporin titration experiments revealed that BsAb increased the toxicity of saporin 435-fold for HSB-2 cells, reducing the IC50 for saporin alone from 0.1 mumol to 0.23 nmol when BsAb was included. The rate of protein synthesis inactivation brought about by BsAb-mediated toxin delivery to HSB-2 cells was very similar to that described for conventional immunotoxins (IT's) with a t10 (time taken for a one log inhibition of protein synthesis compared with controls) of 46 h obtained at a saporin concentration of 1 nmol and 226 h at 0.1 nmol. BsAb titration studies demonstrated a clear dose response effect of BsAb concentration on target cell protein synthesis inhibition and cell proliferation. The absolute specificity of toxin delivery was unequivocally demonstrated by a failure of BsAb to deliver an effective dose of saporin to the CD7- cell line HL60 and by the blocking of BsAb-mediated delivery of saporin to HSB-2 cells with an excess of F(ab)2 fragments of the anti-CD7 antibody, HB2. These studies have clearly demonstrated the effectiveness of this BsAb for delivering saporin to a T-ALL cell line utilising CD7 as the target molecule on the cell surface. BsAb's would therefore appear to offer a realistic alternative to IT's for toxin delivery to tumour cells and may even offer certain advantages over conventional IT's for clinical use.

The anti-mitozantrone monoclonal antibody NO-1, protects acute leukaemia cell lines from the cytotoxic effects of mitozantrone.

The monoclonal antibody NO-1 was raised against the potent anti-cancer drug mitozantrone by immunization of a BALB/c mouse with a mitozantrone-keyhole limpet haemocyanin conjugate in Freund's complete adjuvant. This antibody was shown to be highly effective in vitro at neutralizing the cytotoxic effects of mitozantrone for the acute leukaemia cell lines ALL-1 and MOLT4. In order to achieve complete protection, a drug to antibody molar ratio of 1.5:1 was required. The neutralizing effect was specific for mitozantrone, as NO-1 antibody offered no protection of the MOLT4 cell line to the cytotoxic effects of the anthracycline drug daunorubicin when used at a near identical molar ratio. NO-1 antibody has already proven a highly successful monoclonal reagent for use in a competitive enzyme-linked immunosorbent assay for the accurate and sensitive quantitation of mitozantrone in serum. The neutralizing properties of NO-1 suggest other possible applications for this antibody. These could include a use in the rapid clearance of pharmacologically active mitozantrone from the circulation following very high dose administration prior to bone marrow transplantation and for the construction of bispecific antibodies for targeting mitozantrone to tumour cell populations.