Comparative activities of rabbit complements of different ages using an in-vitro marrow purging model

Eradication of multiple myeloma and breast cancer cells by TH9402-mediated photodynamic therapy: implication for clinical ex vivo purging of autologous stem cell transplants

High-dose chemotherapy combined with autologous transplantation using bone marrow or peripheral blood-derived stem cells (PBSC) is now widely used in the treatment of hematologic malignancies as well as some solid tumors like breast cancer (BC). However, some controversial results were recently obtained in the latter case. The presence of malignant cells in the autograft has been associated with the recurrence of the disease, and purging procedures are needed to eliminate this risk. The aim of this study was to evaluate the potential of the photosensitizer 4,5-dibromorhodamine methyl ester (TH9402), a dibrominated rhodamine derivative, to eradicate multiple myeloma (MM) and BC cell lines, while sparing more than 50% of normal pluripotential blood stem cells from healthy volunteers. The human BC MCF-7 and T-47D and MM RPMI 8226 and NCI-H929 cell lines were used to optimize the photodynamic purging process. Cell concentration and the cell suspension thickness as well as the dye and light doses were varied in order to eventually treat 1-2 L of apheresis. The light source consisted of two fluorescent scanning tubes emitting green light centered about 515 nm. The cellular uptake of TH9402 was measured during the incubation and washout periods and after photodynamic treatment (PDT) using spectrofluorometric analysis. The limiting dilution assay showed that an eradication rate of more than 5 logs is obtained when using a 40 min incubation with 5-10 microM dye followed by a 90 min washout period and a light dose of 5-10 J/cm2 (2.8 mW/cm2) in all cell lines. Agitating the 2 cm thick cell suspension containing 20 x 10(6) cells/mL during PDT was essential for maximal photoinactivation. Experiments on mobilized PBSC obtained from healthy volunteers showed that even more drastic purging conditions than those found optimal for maximal eradication of the malignant cell lines were compatible with a good recovery of hematopoietic progenitors cells. The absence of significant toxicity towards normal hematopoietic stem cells, combined with the 5 logs eradication of cancer cell lines induced by this procedure suggests that TH9402 offers an excellent potential as an ex vivo photodynamic purging agent for autologous transplantation in MM and BC treatment.

Elimination of B-lineage leukemia and lymphoma cells from bone marrow grafts using anti-B4-blocked-ricin immunotoxin

Bone marrow is the primary site of disease in patients with acute lymphoblastic leukemia (ALL) and is frequently involved in patients with non-Hodgkin's lymphoma (NHL). At the time of autologous bone marrow transplantation, marrow grafts from patients with leukemia and lymphoma are often still contaminated by malignant cells, even when such patients achieve complete clinical remission. In this study, we evaluated the potential of anti-B4-blocked-ricin (anti-B4-bR) immunotoxin to eliminate residual ALL and NHL cells from bone marrow. Anti-B4-bR binds to the CD19 antigen, which is B-lineage specific, and, at concentrations of 5 x 10(-9) M or greater, could eliminate more than 3 logs of CD19+ Nalm-6 or Namalwa cells in a 20-fold excess of normal irradiated bone marrow after only 5 hr of incubation. This activity was abrogated by the addition of anti-B4 but not by the presence of galactose, which is the natural ligand for native ricin. Also, when used at these high concentrations, anti-B4-bR showed little nonspecific toxicity against normal hematopoietic progenitors. In conclusion, a single short exposure to anti-B4-bR is capable of inducing high levels of depletion of CD19+ leukemia and lymphoma cells without significant nonspecific toxicity against normal marrow progenitors. Therefore, anti-B4-bR offers an interesting approach to the elimination of B-lineage malignant cells prior to autologous bone marrow transplantation.

Anti-CD6-blocked ricin: an anti-pan T-cell immunotoxin

We report the development of a potent anti-pan T-cell immunotoxin capable of killing cells in an antigen dependent manner. The immunotoxin is composed of a high affinity anti-CD6 antibody (IgG2a, Kd = 1.3 x 10(-11) M) conjugated to blocked ricin that is a chemically modified ricin molecule wherein the lectin binding sites of the B-chain have been blocked by covalent attachment of affinity ligands. Conjugation of blocked ricin to the antibody has minimal effect on the apparent affinity of the antibody and no effect on the ribosome-inactivating activity of the ricin A-chain moiety. Anti-CD6-blocked ricin is a specific and highly toxic immunoconjugate killing the antigen-positive Molt-4 cell line with an IC37 of 4 x 10(-12) M after a 24 h exposure of cells to the immunotoxin. Nonspecific cytotoxicity of anti-CD6-blocked ricin for the antigen-negative Namalwa cell line was more than 750-fold lower with an IC37 > 3 x 10(-9) M. The cytotoxicity of anti-CD6-blocked ricin is dependent on the length of the incubation of cells with the conjugate ranging from an IC37 of 1.5 x 10(-11) M leaving a surviving fraction of Molt-4 cells of 0.03 after a 2.5 h exposure to an IC37 of 5 x 10(-13) M and leaving a surviving fraction of 3 x 10(-6) after a continuous (3 weeks) exposure. Anti-CD6-blocked ricin is also capable of killing CD6 positive cells in human peripheral blood lymphocyte populations. Systemic toxicity of anti-CD6-blocked ricin in mice is similar to the toxicity of other immunotoxins containing blocked ricin that were found to be tolerated well by patients. An application of this immunoconjugate for the prevention and treatment of graft versus host disease or tissue graft rejection is suggested.

Bone marrow purging for autologous bone marrow transplantation

High dose therapy with the resulting myeloablation rescued by infusion of autologous bone marrow (ABMT) has become a major treatment option for an increasing number of patients with hematologic and solid tumors. ABMT has several potential advantages over allogeneic transplantation. However, the major obstacle to the use of ABMT is that the infusion of occult tumor cells harbored within the harvested marrow would result in more rapid relapse of disease. To minimize the effects of the infusion of significant numbers of malignant cells, marrow for ABMT is obtained when the patient is either in complete remission or when there is no histologic evidence of bone marrow infiltration of disease. There is increasing evidence that minimal numbers of malignant cells can be detected within the remission marrow of these patients, particularly when assessed by sensitive clonogenic assays or polymerase chain reaction amplification. A variety of methods, pharmacologic and immunologic have been developed to "purge" malignant cells from the marrow. The aim of purging is to eliminate any contaminating malignant cells and leave intact the hematopoietic stem cells that are necessary for engraftment. Although the rationale for removing any contaminating cells from the autologous marrow appears compelling, the issue of purging remains highly controversial. Intense argument persists as to whether attempts to remove residual tumor cells from the harvested bone marrow have contributed to improving disease-free survival in these patients. To date there have been no clinical trials testing the efficacy of purging by comparison of infusion of purged versus unpurged autologous bone marrow. This is due primarily to the large number of patients that would be required for such studies.

In vitro purging of clonogenic leukemic cells from human bone marrow by heat: simulation experiments for autologous bone marrow transplantation

In order to apply a simple purging method by heat to autologous bone marrow transplantation (ABMT), we have revaluated the ability to purge clonogenic leukemic cells from the simulated marrow mixture of normal marrow cells and leukemic cell lines (HL-60, Molt-3 and HEL) in vitro by heat, using two different clonogenic assays for normal granulocyte-macrophage progenitors (CFU-GM) and leukemic cell lines. It appeared that in vitro hyperthermia (42 degrees C for 120 min) is able to selectively remove clonogenic leukemic cells from simulated tumor cell-normal marrow mixtures even when leukemic cell concentrations are increased up to 3 x 10(6) cells/ml in vitro, and results in a 4-6 log destruction of clonogenic leukemic cells/ml according to a limiting dilution assay, while leaving half of normal CFU-GM surviving. The hyperthermic purging of clonogenic leukemic cells was not affected in the presence of normal marrow cells in vitro. This high level of clonogenic leukemic cell depletion by heat correlated with that of immunologic and pharmacologic studies. These results suggest that in vitro hyperthermia could be applied effectively and safely for the elimination of residual clonogenic leukemic cells in autologous marrow grafts before ABMT.

A simple elimination of clonogenic tumor cells from human bone marrow in vitro by heat: its application to autologous bone marrow transplantation for B-cell lymphoma

The application of hyperthermia to the treatment of neoplastic disease has focused on solid tumors. Since the hyperthermic sensitivity of human B-cell lymphoma cells is not known, we have examined the effect of hyperthermia on the growth of B-cell lymphoma cell lines (Raji and Daudi) in vitro to evaluate the ability to purge tumor cells from normal bone marrow by heat, utilizing a limiting-dilution assay to measure log depletion of tumor cells in a 20-fold excess of normal bone marrow. When exposed at 42 degrees C and 43 degrees C for 120 min, both clonogenic Raji and Daudi cells were dramatically decreased (a 4- to 6-log reduction) with exposure time, while leaving over half of the normal granulocyte-macrophage progenitor cells surviving at 42 degrees C and 10% at 43 degrees C. This high level of lymphoma-cell depletion by heat correlated with that obtained in immunologic and pharmacologic studies. These results suggest that in vitro hyperthermia might be applied effectively for the elimination of residual lymphoma cells in autologous marrow grafts before autologous bone marrow transplantation in B-cell non-Hodgkin's lymphoma.

Blocked ricin-conjugated T cell immunotoxins: effect of anti-CD6-blocked ricin on normal T cell function

The biological properties of an immunotoxin composed of an anti-CD6 monoclonal antibody conjugated to whole ricin, which had been modified so that the galactose-binding sites of the B chain were blocked ("blocked ricin"), were examined. Treatment of peripheral blood lymphocytes with anti-CD6-blocked ricin for a 24-h period prevented T cell proliferation induced by phytohemagglutinin in a dose-dependent manner with concentrations causing 50% inhibition (IC50) ranging from 5 pM to 30 pM. In contrast, treatment with either blocked ricin alone or with a control immunotoxin prepared with a B-cell-lineage-restricted monoclonal antibody gave IC50 values of approximately 2 nM. Although shortening the duration of the anti-CD6-blocked ricin treatment to as little as 3 h had little significant effect on the observed inhibition, T cell viability experiments demonstrated that the magnitude of immunotoxin-induced killing after a given time period is significantly higher when the target cells become activated. Thus, from the initial concentration of cells treated with anti-CD6-blocked ricin placed in culture, 40%-45% viable cells remained after 2 days yet only 3%-9% remained if phorbol ester and Ca2+ ionophore were added; activation of T cells after mock treatment using blocked ricin plus nonconjugated anti-CD6 demonstrated that this effect was not the result of activation alone. The toxicity of anti-CD6-blocked ricin was also measured by inhibition of PHA-induced clonogenic growth of normal T cells. Continuous treatment of the cells using anti-CD6-blocked ricin at 0.1 nM resulted in a surviving fraction of about 3.5 x 10(-3); when immunotoxin treatment was for 24 h or less, the surviving fraction was only about 10(-1). As an indication of the unique specificity of anti-CD6-blocked ricin, immunotoxin pretreatment of potential responder cells prevented the generation of allogeneic cytolytic T lymphocytes in mixed lymphocyte cultures yet had little effect on the generation of interleukin-2-induced lymphokine-activated killer cell activity. We conclude that anti-CD6-blocked ricin demonstrates a cellular specificity and potency that make it a highly promising anti-T cell reagent.

Immunologic purging of marrow assessed by PCR before autologous bone marrow transplantation for B-cell lymphoma

BACKGROUND

The use of autologous bone marrow transplantation is increasing in the management of advanced cancers. Many investigators have attempted to "purge" autologous marrow of residual tumor cells because of concern that reinfused tumor cells might contribute to relapse. The efficacy of purging remains unproved.

METHODS

We performed clonogenic assays in a tumor cell line in culture to determine the efficiency of immunologic purging. Amplification by the polymerase chain reaction (PCR) was used to detect residual lymphoma cells before and after purging of bone marrow from 114 patients with B-cell non-Hodgkin's lymphoma in whom a translocation (t(14;18] that could be amplified by PCR was detected at the time of their initial evaluation.

RESULTS

Immunologic purging in vitro resulted in a 3-to-6-log destruction of cells in the tumor cell line. Residual lymphoma cells were detected by PCR in the bone marrow of all patients before purging. No lymphoma cells could be detected in the marrow of 57 patients after purging. Disease-free survival was increased in these 57 patients as compared with those whose marrow contained detectable residual lymphoma (P less than 0.00001). The ability to purge residual lymphoma cells was not associated with the degree of bone marrow involvement (P = 0.4494) or the previous response to therapy (P = 0.1298).

CONCLUSIONS

The inability to purge residual lymphoma cells was the most important prognostic indicator in predicting relapse. These results provide evidence of the clinical usefulness of ex vivo purging of autologous bone marrow in the treatment of patients with lymphoma and suggest that the reinfusion of malignant cells in autologous marrow contributes to relapse