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

What is the clinical significance of infusing hematopoietic cell grafts contaminated with bacteria?

Although hematopoietic stem cell (HSC) products are routinely cultured for sterility, bacterial contamination of these products is rarely observed and little is known about the clinical consequences of infusing contaminated grafts. We retrieved the sterility cultures of bone marrow and peripheral HSC grafts from 938 patients transplanted at our center from January 1990 to July 2005. Fever, septicemia and other adverse events were assessed for up to 14 days following infusion of the graft. Out of the 1502 grafts collected during this 15-year period, 15 (1.0%) had a positive sterility culture (11 Gram-positive cocci, 2 Gram-positive bacilli and 2 Gram-negative bacilli). No correlation was observed between the graft contamination rate and the extent of graft manipulation or the patient's underlying condition. Thirteen recipients were transplanted with contaminated grafts. Five patients were treated with specific pre-emptive antibiotics. Only one episode of Staphylococcus epidermidis bacteremia possibly related to a contaminated graft was observed on day +5. As the infusion of contaminated grafts with Gram-positive skin contaminants rarely results in unfavorable clinical outcomes, close patient monitoring without the use of specific pre-emptive antibiotics could be appropriate and could avoid antibiotic-associated adverse events.

Hematopoietic stem cell transplantation after first marrow relapse of non-T, non-B acute lymphoblastic leukemia: a pediatric oncology group pilot feasibility study

BACKGROUND

Relapsed acute lymphoblastic leukemia (ALL) in children is associated with a poor outcome, especially for those patients whose relapse occurs during the first 36 months after diagnosis. The best therapy for these patients is not known. This study was designed to evaluate the feasibility of enrolling children with recurrent ALL in a standardized treatment protocol that included receipt of a hematopoietic stem cell transplant (HSCT).

PROCEDURE

Eligible patients with a bone marrow relapse of non-T, non-B ALL underwent a common induction and consolidation followed by receipt of either an allogeneic HSCT from a human leukocyte antigen (HLA)-identical sibling or an autologous HSCT purged with B-4 blocked ricin. A common conditioning regimen was used for all patients.

RESULTS

Twenty-eight patients from eight institutions were enrolled. Fourteen patients did not receive a transplant during the study, because of toxicity (4), relapse (1), inadequate purging (1), and parental or physician preference for an alternative donor transplant (8). Six patients received allogeneic HSCTs. Five of them have remained in remission for a median of 78 months. Eight patients received autologous HSCTs purged with B4-blocked ricin. Four have remained in remission for a median of 94 months. Of the nine patients who received alternative donor transplants, only two remain in remission.

CONCLUSION

We conclude that well designed and controlled prospective studies are necessary to define the role of HSCTs in children with recurrent ALL. In order to be successful, such studies must have the full support of participating centers. Autologous HSC transplantation may have a role in the treatment of relapsed ALL, but further studies are needed.

Development and application of CD19-specific T cells for adoptive immunotherapy of B cell malignancies

The graft-versus-leukemia (GVL)-effect achieved by donor-derived T cells arising from transplanted allogeneic hematopoietic stem cells or given as donor-leukocyte infusions (DLI) after allogeneic transplant, demonstrates that donor-derived T cells can eradicate B-lineage malignancies. However, graft-versus-host-disease (GVHD) occurring after allogeneic hematopoietic stem-cell transplant (HSCT) or polyclonal DLI can limit the efficacy of these interventions. This toxicity can be avoided by using autologous T cells and/or tumor-specific cytotoxic T lymphocytes (CTLs). To generate antigen-specific T cells that can be derived from the allogeneic donor or the patient, we have genetically manipulated T cells to express a CD19-specific chimeric immunoreceptor. This renders T cells specific for CD19, a cell surface molecule found on B-lineage leukemia and lymphoma. This review will demonstrate the redirected specificity of CD19-specific T cells and implementation of clinical trials using these cellular agents.

T-cell clones can be rendered specific for CD19: toward the selective augmentation of the graft-versus-B-lineage leukemia effect

Relapse of B-lineage acute lymphoblastic leukemia (B-ALL) after allogeneic hematopoietic stem cell transplantation (HSCT) commonly results from the failure of a graft-versus-leukemia (GVL) effect to eradicate minimal residual disease. Augmenting the GVL effect by the adoptive transfer of donor-derived B-ALL-specific T-cell clones is a conceptually attractive strategy to decrease relapse rates without exacerbating graft-versus-host disease (GVHD). Toward this end, we investigated whether a genetic engineering approach could render CD8(+) cytotoxic T lymphocytes (CTLs) specific for tumor cells that express the B-cell lineage cell surface molecule CD19. This was accomplished by the genetic modification of CTLs to express a chimeric immunoreceptor composed of a CD19-specific single-chain immunoglobulin extracellular targeting domain fused to a CD3-zeta intracellular signaling domain. CD19-redirected CTL clones display potent CD19-specific lytic activity and chimeric immunoreceptor-regulated cytokine production and proliferation. Because B-ALL cells can evade T-cell/natural killer- cell recognition by down-regulation of cell surface accessory molecules that participate in the formation of a functional immunologic synapse, we compared the CD19-specific effector function of genetically modified CD8(+) CTLs toward CD19(+) cells with disparate levels of intercellular adhesion molecule 1 (ICAM-1), leukocyte function-associated antigen 1 (LFA-1), and LFA-3. We observed that recognition of B-lineage tumor lines by CD19-specific CTLs was not impaired by low levels of ICAM-1, LFA-1, and LFA-3 cell surface expression, a functional attribute that is likely a consequence of our high-affinity CD19-specific chimeric immunoreceptor. Furthermore, the CD19-specific CTLs could lyse primary B-ALL blasts. These preclinical observations form the basis for implementing clinical trials using donor-derived CD19-specific T-cell clones to treat or prevent relapse of B-ALL after allogeneic HSCT.

Immunotoxins for targeted cancer therapy

Immunotoxins constitute a new modality for the treatment of cancer, since they target cells displaying specific surface-receptors or antigens. Immunotoxins contain a ligand such as a growth factor, monoclonal antibody, or fragment of an antibody which is connected to a protein toxin. After the ligand subunit binds to the surface of the target cell, the molecule internalizes and the toxin kills the cell. Bacterial toxins which have been targeted to cancer cells include Pseudomonas exotoxin and diphtheria toxin, which are well suited to forming recombinant single-chain or double-chain fusion toxins. Plant toxins include ricin, abrin, pokeweed antiviral protein, saporin and gelonin, and have generally been connected to ligands by disulfide-bond chemistry. Immunotoxins have been produced to target hematologic malignancies and solid tumors via a wide variety of growth factor receptors and antigens. Challenges facing the clinical application of immunotoxins are discussed.

Lymphoma Cell Burden in Progenitor Cell Grafts Measured by Competitive Polymerase Chain Reaction: Less Than One Log Difference Between Bone Marrow and Peripheral Blood Sources

A controversy persists in autologous transplantation as to which source of progenitor cells, bone marrow (BM) or peripheral blood (PB), contains the lowest number of contaminating lymphoma cells, and how mobilization procedures affect these numbers. To accurately measure the number of non-Hodgkin's lymphoma (NHL) cells harboring the bcl-2/immunoglobulin H (IgH) rearrangement in progenitor cell grafts, we developed a nested quantitative competitive polymerase chain reaction assay (QC-PCR). DNA from lymph nodes of four patients with NHL were cloned into the pSK(+) vectors to generate four internal controls (ICs) (two with major breakpoint region [MBR] and two with minor cluster region [mcr] rearrangements). The kinetics of amplification of ICs paralleled those of bcl-2/IgH rearranged genomic DNA. When used in a QC-PCR assay, these ICs were accurate at a 0.2-log level and provided reproducible results, as shown by low intrarun and interrun variability. An excellent correlation between predicted and observed lymphoma cell content (r = .99) was observed over a range of at least 5 logs of rearranged cells. This approach was used to measure involvement by NHL cells at the time of progenitor cell harvest in 37 autologous transplant patients. The number of bcl-2/IgH rearranged cells in BM, PB, and mobilized PB (mPB) was found to vary from 1 to 1.1 × 105 per million cells. The number of lymphoma cells present in BM was significantly higher than in PB (P = .0001), with a median difference in lymphoma cell content between BM and PB of 0.48 log of cells (range, −0.7 to 5 logs). In contrast, we found no difference in the concentration of bcl-2/IgH rearranged cells present in BM versus PB progenitor cells mobilized with cyclophosphamide and granulocyte colony-stimulating factor (G-CSF) (mPB) (P = .57). In conclusion, the QC-PCR assay described in this study could measure accurately and reproducibly the number of bcl-2/IgH rearranged cells among normal cells. Differences in levels of contamination by lymphoma cells between BM and PB were of less than one log (10-fold), and no differences in lymphoma cell concentrations were observed between BM and mobilized PB. As more cells are usually infused with mPB than with BM grafts, mPB progenitor cell grafts may actually be associated with higher levels of contamination by lymphoma cells. Furthermore, this QC-PCR assay should provide an important tool to assess the prognostic impact of lymphoma cell burden both in progenitor cell grafts and in vivo.

Lymphoma Cell Burden in Progenitor Cell Grafts Measured by Competitive Polymerase Chain Reaction: Less Than One Log Difference Between Bone Marrow and Peripheral Blood Sources

A controversy persists in autologous transplantation as to which source of progenitor cells, bone marrow (BM) or peripheral blood (PB), contains the lowest number of contaminating lymphoma cells, and how mobilization procedures affect these numbers. To accurately measure the number of non-Hodgkin's lymphoma (NHL) cells harboring the bcl-2/immunoglobulin H (IgH) rearrangement in progenitor cell grafts, we developed a nested quantitative competitive polymerase chain reaction assay (QC-PCR). DNA from lymph nodes of four patients with NHL were cloned into the pSK(+) vectors to generate four internal controls (ICs) (two with major breakpoint region [MBR] and two with minor cluster region [mcr] rearrangements). The kinetics of amplification of ICs paralleled those of bcl-2/IgH rearranged genomic DNA. When used in a QC-PCR assay, these ICs were accurate at a 0.2-log level and provided reproducible results, as shown by low intrarun and interrun variability. An excellent correlation between predicted and observed lymphoma cell content (r = .99) was observed over a range of at least 5 logs of rearranged cells. This approach was used to measure involvement by NHL cells at the time of progenitor cell harvest in 37 autologous transplant patients. The number of bcl-2/IgH rearranged cells in BM, PB, and mobilized PB (mPB) was found to vary from 1 to 1.1 × 105 per million cells. The number of lymphoma cells present in BM was significantly higher than in PB (P = .0001), with a median difference in lymphoma cell content between BM and PB of 0.48 log of cells (range, −0.7 to 5 logs). In contrast, we found no difference in the concentration of bcl-2/IgH rearranged cells present in BM versus PB progenitor cells mobilized with cyclophosphamide and granulocyte colony-stimulating factor (G-CSF) (mPB) (P = .57). In conclusion, the QC-PCR assay described in this study could measure accurately and reproducibly the number of bcl-2/IgH rearranged cells among normal cells. Differences in levels of contamination by lymphoma cells between BM and PB were of less than one log (10-fold), and no differences in lymphoma cell concentrations were observed between BM and mobilized PB. As more cells are usually infused with mPB than with BM grafts, mPB progenitor cell grafts may actually be associated with higher levels of contamination by lymphoma cells. Furthermore, this QC-PCR assay should provide an important tool to assess the prognostic impact of lymphoma cell burden both in progenitor cell grafts and in vivo.

Conjugation of Blocked Ricin to an Anti-CD19 Monoclonal Antibody Increases Antibody-Induced Cell Calcium Mobilization and CD19 Internalization

CD19 (B4) is a signal transduction molecule restricted to the B-cell lineage and the target of the immunotoxin anti-B4–blocked ricin (anti-B4–bR), which is composed of the monoclonal antibody (MoAb) anti-B4 and the modified plant toxin blocked ricin. To explore the influence of conjugation of blocked ricin to anti-B4 on functional activation of CD19, we investigated the effects of anti-B4–bR, and that of unconjugated anti-B4, on intracellular calcium mobilization and ligand/receptor internalization. The data showed that anti-B4–bR was more potent than anti-B4 in triggering cell calcium mobilization. Two other immunotoxins that bind to the B-cell surface, anti-CD20–bR and anti-CD38–bR, were devoid of the calcium increasing effect of anti-B4–bR. Furthermore, anti-B4 conjugated to ricin A-chain was also without effect in Namalwa cells, indicating that the ricin B-chain component was required for anti-B4–bR effect. Anti-B4–bR-induced calcium mobilization was inhibited in the presence of lactose, yet the calcium response induced by cross-linking anti-B4–bR with a second step antibody was not affected. The extent of CD19 modulation induced by anti-B4–bR was higher than that induced by anti-B4, and lactose dampened the effect of the immunotoxin down to that of the MoAb. Moreover, the number of internalized immunotoxin molecules was higher than that of unconjugated MoAb. Although a mechanism involving dimerization of the immunotoxin cannot be excluded, our findings suggest that the residual binding activity of the blocked ricin B-chain to cell surface molecules plays an important role in the greater calcium fluxes and greater internalization rate of anti-B4–bR, and is of functional significance in the mechanism of intoxication of cells by the immunotoxin.

Conjugation of Blocked Ricin to an Anti-CD19 Monoclonal Antibody Increases Antibody-Induced Cell Calcium Mobilization and CD19 Internalization

CD19 (B4) is a signal transduction molecule restricted to the B-cell lineage and the target of the immunotoxin anti-B4–blocked ricin (anti-B4–bR), which is composed of the monoclonal antibody (MoAb) anti-B4 and the modified plant toxin blocked ricin. To explore the influence of conjugation of blocked ricin to anti-B4 on functional activation of CD19, we investigated the effects of anti-B4–bR, and that of unconjugated anti-B4, on intracellular calcium mobilization and ligand/receptor internalization. The data showed that anti-B4–bR was more potent than anti-B4 in triggering cell calcium mobilization. Two other immunotoxins that bind to the B-cell surface, anti-CD20–bR and anti-CD38–bR, were devoid of the calcium increasing effect of anti-B4–bR. Furthermore, anti-B4 conjugated to ricin A-chain was also without effect in Namalwa cells, indicating that the ricin B-chain component was required for anti-B4–bR effect. Anti-B4–bR-induced calcium mobilization was inhibited in the presence of lactose, yet the calcium response induced by cross-linking anti-B4–bR with a second step antibody was not affected. The extent of CD19 modulation induced by anti-B4–bR was higher than that induced by anti-B4, and lactose dampened the effect of the immunotoxin down to that of the MoAb. Moreover, the number of internalized immunotoxin molecules was higher than that of unconjugated MoAb. Although a mechanism involving dimerization of the immunotoxin cannot be excluded, our findings suggest that the residual binding activity of the blocked ricin B-chain to cell surface molecules plays an important role in the greater calcium fluxes and greater internalization rate of anti-B4–bR, and is of functional significance in the mechanism of intoxication of cells by the immunotoxin.