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Acute myeloid leukemia (AML) is a hematological malignancy derived from neoplastic myeloid progenitor cells characterized by abnormal clonal proliferation and differentiation. Although novel therapeutic strategies have recently been introduced, the prognosis of AML is still unsatisfactory. So far, the efficacy of chimeric antigen receptor (CAR)-T-cell therapy in AML has been hampered by several factors, including the poor accumulation of the blood-injected cells in the leukemia bone marrow (BM) niche in which chemotherapy-resistant leukemic stem cells reside. Thus, we hypothesized that overexpression of CXCR4, whose ligand CXCL12 is highly expressed by BM stromal cells within this niche, could improve T-cell homing to the BM and consequently enhance their intimate contact with BM-resident AML cells, facilitating disease eradication. Specifically, we engineered conventional CD33.CAR-cytokine-induced killer cells (CIKs) with the wild-type (wt) CXCR4 and the variant CXCR4R334X, responsible for leukocyte sequestration in the BM of patients with warts, hypogammaglobulinemia, immunodeficiency, and myelokathexis syndrome. Overexpression of both CXCR4wt and CXCR4mut in CD33.CAR-CIKs resulted in significant improvement of chemotaxis toward recombinant CXCL12 or BM stromal cell-conditioned medium, with no observed impairment of cytotoxic potential in vitro. Moreover, CXCR4-overexpressing CD33.CAR-CIKs showed enhanced in vivo BM homing, associated with a prolonged retention for the CXCR4R334X variant. However, only CD33.CAR-CIKs coexpressing CXCR4wt but not CXCR4mut exerted a more sustained in vivo antileukemic activity and extended animal survival, suggesting a noncanonical role for CXCR4 in modulating CAR-CIK functions independent of BM homing. Taken together, these data suggest that arming CAR-CIKs with CXCR4 may represent a promising strategy for increasing their therapeutic potential for AML., (© 2023 by The American Society of Hematology. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.)

The adoptive transfer of T-lymphocytes modified to express chimeric antigen receptors (CAR-Ts) has produced impressive clinical responses among patients with B-cell malignancies. This has led to a rapid expansion in the number of clinical trials over the past several years. Although CD19-specific CAR-Ts are the most extensively evaluated, CAR-Ts specific for other B-cell-associated targets have also shown promise. However, despite this success, toxicities associated with CAR-T administration remain a significant concern. There continues to be substantial heterogeneity among CAR-T products, and differences in both CAR designs and CAR-T production strategies can substantially affect clinical outcomes. Ongoing clinical studies will further elucidate these differences and many other innovative approaches are being evaluated at the preclinical level. In this review, we will discuss the background and rationale for the use of CAR-Ts, provide an overview of advances in the field, and examine the application of CAR-Ts to the treatment of B-cell malignancies, including a summary of clinical trials published to date., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Background Aims: The PR1 peptide, derived from the leukemia-associated antigens proteinase 3 and neutrophil elastase, is overexpressed on HLA-A2 in acute myeloid leukemia (AML). We developed a T-cell receptor (TCR)-like monoclonal antibody (8F4) that binds the PR1/HLA-A2 complex on the surface of AML cells, efficiently killing them in vitro and eliminating them in preclinical models. Humanized 8F4 (h8F4) with high affinity for the PR1/HLA-A2 epitope was used to construct an h8F4- chimeric antigen receptor (CAR) that was transduced into T cells to mediate anti-leukemia activity., Methods: Human T cells were transduced to express the PR1/HLA-A2-specific CAR (h8F4-CAR-T cells) containing the scFv of h8F4 fused to the intracellular signaling endo-domain of CD3 zeta chain through the transmembrane and intracellular costimulatory domain of CD28., Results: Adult human normal peripheral blood (PB) T cells were efficiently transduced with the h8F4-CAR construct and predominantly displayed an effector memory phenotype with a minor population (12%) of central memory cells in vitro. Umbilical cord blood (UCB) T cells could also be efficiently transduced with the h8F4-CAR. The PB and UCB-derived h8F4-CAR-T cells specifically recognized the PR1/HLA-A2 complex and were capable of killing leukemia cell lines and primary AML blasts in an HLA-A2-dependent manner., Conclusions: Human adult PB and UCB-derived T cells expressing a CAR derived from the TCR-like 8F4 antibody rapidly and efficiently kill AML in vitro. Our data could lead to a new treatment paradigm for AML in which targeting leukemia stem cells could transfer long-term immunity to protect against relapse., (Copyright © 2016 International Society for Cellular Therapy. Published by Elsevier Inc. All rights reserved.)

Hematologic malignancies provide a suitable testing environment for cell-based immunotherapies, which were pioneered by the development of allogeneic hematopoietic stem cell transplant. All types of cell-based therapies, from donor lymphocyte infusion to dendritic cell vaccines, and adoptive transfer of tumor-specific cytotoxic T cells and natural killer cells, have been clinically translated for hematologic malignancies. The recent success of chimeric antigen receptor-modified T lymphocytes in B-cell malignancies has stimulated the development of this approach toward other hematologic tumors. Similarly, the remarkable activity of checkpoint inhibitors as single agents has created enthusiasm for potential combinations with other cell-based immune therapies. However, tumor cells continuously develop various strategies to evade their immune-mediated elimination. Meanwhile, the recruitment of immunosuppressive cells and the release of inhibitory factors contribute to the development of a tumor microenvironment that hampers the initiation of effective immune responses or blocks the functions of immune effector cells. Understanding how tumor cells escape from immune attack and favor immunosuppression is essential for the improvement of immune cell-based therapies and the development of rational combination approaches., (© 2016 by The American Society of Hematology.)

To test the feasibility of a single T-cell manipulation to eliminate alloreactivity while sparing antiviral and antitumor T cells, we infused 12 haploidentical hematopoietic stem cell transplant patients with increasing numbers of alloreplete haploidentical T cells expressing the inducible caspase 9 suicide gene (iC9-T cells). We determined whether the iC9-T cells produced immune reconstitution and if any resultant graft-versus-host disease (GVHD) could be controlled by administration of a chemical inducer of dimerization (CID; AP1903/Rimiducid). All patients receiving >10(4) alloreplete iC9-T lymphocytes per kilogram achieved rapid reconstitution of immune responses toward 5 major pathogenic viruses and concomitant control of active infections. Four patients received a single AP1903 dose. CID infusion eliminated 85% to 95% of circulating CD3(+)CD19(+) T cells within 30 minutes, with no recurrence of GVHD within 90 days. In one patient, symptoms and signs of GVHD-associated cytokine release syndrome (CRS-hyperpyrexia, high levels of proinflammatory cytokines, and rash) resolved within 2 hours of AP1903 infusion. One patient with varicella zoster virus meningitis and acute GVHD had iC9-T cells present in the cerebrospinal fluid, which were reduced by >90% after CID. Notably, virus-specific T cells recovered even after AP1903 administration and continued to protect against infection. Hence, alloreplete iC9-T cells can reconstitute immunity posttransplant and administration of CID can eliminate them from both peripheral blood and the central nervous system (CNS), leading to rapid resolution of GVHD and CRS. The approach may therefore be useful for the rapid and effective treatment of toxicities associated with infusion of engineered T lymphocytes. This trial was registered at www.clinicaltrials.gov as #NCT01494103., (© 2015 by The American Society of Hematology.)

Although T cells expressing CD19-specific chimeric antigen receptors (CARs) are a promising new therapy for B-cell malignancies, objective responses are observed at lower frequencies in patients with lymphoma than in those with acute B-cell leukemia. We postulated that the tumor microenvironment suppresses CAR-expressing T cells (CARTs) through the activity of indoleamine 2,3-dioxygenase (IDO), an intracellular enzyme that converts tryptophan into metabolites that inhibit T -: cell activity. To investigate the effects of tumor IDO on CD19-CART therapy, we used a xenograft lymphoma model expressing IDO as a transgene. CD19-CARTs inhibited IDO-negative tumor growth but had no effect on IDO-positive tumors. An IDO inhibitor (1-methyl-tryptophan) restored IDO-positive tumor control. Moreover, tryptophan metabolites inhibited interleukin (IL)-2-, IL-7-, and IL-15-dependent expansion of CARTs; diminished their proliferation, cytotoxicity, and cytokine secretion in vitro in response to CD19 recognition; and increased their apoptosis. Inhibition of CD19-CARTs was not mitigated by the incorporation of costimulatory domains, such as 4-1BB, into the CD19-CAR. Finally, we found that fludarabine and cyclophosphamide, frequently used before CART administration, downregulated IDO expression in lymphoma cells and improved the antitumor activity of CD19-CART in vivo. Because tumor IDO inhibits CD19-CARTs, antagonizing this enzyme may benefit CD19-CART therapy., (© 2015 by The American Society of Hematology.)

Advances in the design of chimeric antigen receptors (CARs) have improved the antitumor efficacy of redirected T cells. However, functional heterogeneity of CAR T cells limits their therapeutic potential and is associated with toxicity. We proposed that CAR expression in Vα24-invariant natural killer T (NKT) cells can build on the natural antitumor properties of these cells while their restriction by monomorphic CD1d limits toxicity. Primary human NKT cells were engineered to express a CAR against the GD2 ganglioside (CAR.GD2), which is highly expressed by neuroblastoma (NB). We compared CAR.GD2 constructs that encoded the CD3ζ chain alone, with CD28, 4-1BB, or CD28 and 4-1BB costimulatory endodomains. CAR.GD2 expression rendered NKT cells highly cytotoxic against NB cells without affecting their CD1d-dependent reactivity. We observed a striking T helper 1-like polarization of NKT cells by 4-1BB-containing CARs. Importantly, expression of both CD28 and 4-1BB endodomains in the CAR.GD2 enhanced in vivo persistence of NKT cells. These CAR.GD2 NKT cells effectively localized to the tumor site had potent antitumor activity, and repeat injections significantly improved the long-term survival of mice with metastatic NB. Unlike T cells, CAR.GD2 NKT cells did not induce graft-versus-host disease. These results establish the potential of NKT cells to serve as a safe and effective platform for CAR-directed cancer immunotherapy., (© 2014 by The American Society of Hematology.)

Adoptive transfer of donor-derived T lymphocytes expressing a safety switch may promote immune reconstitution in patients undergoing haploidentical hematopoietic stem cell transplant (haplo-HSCT) without the risk for uncontrolled graft versus host disease (GvHD). Thus, patients who develop GvHD after infusion of allodepleted donor-derived T cells expressing an inducible human caspase 9 (iC9) had their disease effectively controlled by a single administration of a small-molecule drug (AP1903) that dimerizes and activates the iC9 transgene. We now report the long-term follow-up of 10 patients infused with such safety switch-modified T cells. We find long-term persistence of iC9-modified (iC9-T) T cells in vivo in the absence of emerging oligoclonality and a robust immunologic benefit, mediated initially by the infused cells themselves and subsequently by an apparently accelerated reconstitution of endogenous naive T lymphocytes. As a consequence, these patients have immediate and sustained protection from major pathogens, including cytomegalovirus, adenovirus, BK virus, and Epstein-Barr virus in the absence of acute or chronic GvHD, supporting the beneficial effects of this approach to immune reconstitution after haplo-HSCT. This study was registered at www.clinicaltrials.gov as #NCT00710892., (© 2014 by The American Society of Hematology.)

Adoptive transfer of T lymphocytes expressing a CD19-specific chimeric antigen receptor (CAR.CD19) induces complete tumor regression in patients with lymphoid malignancies. Although in vivo persistence of CAR-T cells correlates with clinical responses, it remains unknown whether specific cell subsets within the CAR-T-cell product correlate with their subsequent in vivo expansion and persistence. We analyzed 14 patients with B-cell malignancies infused with autologous CAR.CD19-redirected T cells expanded ex vivo using IL-2, and found that their in vivo expansion only correlated with the frequency within the infused product of a CD8(+)CD45RA(+)CCR7(+) subset, whose phenotype is closest to "T-memory stem cells." Preclinical models showed that increasing the frequency of CD8(+)CD45RA(+)CCR7(+) CAR-T cells in the infused line by culturing the cells with IL-7 and IL-15 produced greater antitumor activity of CAR-T cells mediated by increased resistance to cell death, following repetitive encounters with the antigen, while preserving their migration to secondary lymphoid organs. This trial was registered at www.clinicaltrials.gov as #NCT00586391 and #NCT00709033., (© 2014 by The American Society of Hematology.)

Background Aims: Advantages associated with the use of cord blood (CB) transplantation include the availability of cryopreserved units, ethnic diversity and lower incidence of graft-versus-host disease compared with bone marrow or mobilized peripheral blood. However, poor engraftment remains a major obstacle. We and others have found that ex vivo fucosylation can enhance engraftment in murine models, and now ex vivo treatment of CB with fucosyltransferase (FT) VI before transplantation is under clinical evaluation (NCT01471067). However, FTVII appears to be more relevant to hematopoietic cells and may alter acceptor substrate diversity. The present study compared the ability of FTVI and FTVII to improve the rapidity, magnitude, multi-lineage and multi-tissue engraftment of human CB hematopoietic stem and progenitor cells (HSPCs) in vivo., Methods: CD34-selected CB HSPCs were treated with recombinant FTVI, FTVII or mock control and then injected into immunodeficient mice and monitored for multi-lineage and multi-tissue engraftment., Results: Both FTVI and FTVII fucosylated CB CD34⁺ cells in vitro, and both led to enhanced rates and magnitudes of engraftment compared with untreated CB CD34⁺ cells in vivo. Engraftment after treatment with either FT was robust at multiple time points and in multiple tissues with similar multi-lineage potential. In contrast, only FTVII was able to fucosylate T and B lymphocytes., Conclusions: Although FTVI and FTVII were found to be similarly able to fucosylate and enhance the engraftment of CB CD34⁺ cells, differences in their ability to fucosylate lymphocytes may modulate graft-versus-tumor or graft-versus-host effects and may allow further optimization of CB transplantation., (Copyright © 2014 International Society for Cellular Therapy. Published by Elsevier Inc. All rights reserved.)

Genetically targeted T cells promise to solve the feasibility and efficacy hurdles of adoptive T-cell therapy for cancer. Selecting a target expressed in multiple-tumor types and that is required for tumor growth would widen disease indications and prevent immune escape caused by the emergence of antigen-loss variants. The adhesive receptor CD44 is broadly expressed in hematologic and epithelial tumors, where it contributes to the cancer stem/initiating phenotype. In this study, silencing of its isoform variant 6 (CD44v6) prevented engraftment of human acute myeloid leukemia (AML) and multiple myeloma (MM) cells in immunocompromised mice. Accordingly, T cells targeted to CD44v6 by means of a chimeric antigen receptor containing a CD28 signaling domain mediated potent antitumor effects against primary AML and MM while sparing normal hematopoietic stem cells and CD44v6-expressing keratinocytes. Importantly, in vitro activation with CD3/CD28 beads and interleukin (IL)-7/IL-15 was required for antitumor efficacy in vivo. Finally, coexpressing a suicide gene enabled fast and efficient pharmacologic ablation of CD44v6-targeted T cells and complete rescue from hyperacute xenogeneic graft-versus-host disease modeling early and generalized toxicity. These results warrant the clinical investigation of suicidal CD44v6-targeted T cells in AML and MM.

Autologous T cells expressing a CD19-specific chimeric antigen receptor (CD19.CAR) are active against B-cell malignancies, but it is unknown whether allogeneic CD19.CAR T cells are safe or effective. After allogeneic hematopoietic stem cell transplantation (HSCT), infused donor-derived virus-specific T cells (VSTs) expand in vivo, persist long term, and display antiviral activity without inducing graft-vs-host disease; therefore, we determined whether donor VSTs, engineered to express CD19.CAR, retained the characteristics of nonmanipulated allogeneic VSTs while gaining antitumor activity. We treated 8 patients with allogeneic (donor-derived) CD19.CAR-VSTs 3 months to 13 years after HSCT. There were no infusion-related toxicities. VSTs persisted for a median of 8 weeks in blood and up to 9 weeks at disease sites. Objective antitumor activity was evident in 2 of 6 patients with relapsed disease during the period of CD19.CAR-VST persistence, whereas 2 patients who received cells while in remission remain disease free. In 2 of 3 patients with viral reactivation, donor CD19.CAR-VSTs expanded concomitantly with VSTs. Hence CD19.CAR-VSTs display antitumor activity and, because their number may be increased in the presence of viral stimuli, earlier treatment post-HSCT (when lymphodepletion is greater and the incidence of viral infection is higher) or planned vaccination with viral antigens may enhance disease control.

We generated MHC-independent chimeric antigen receptors (CARs) directed to the GD2 antigen expressed by neuroblastoma tumor cells and treated patients with this disease. Two distinguishable forms of this CAR were expressed in EBV-specific cytotoxic T lymphocytes (EBV-CTLs) and activated T cells (ATCs). We have previously shown that EBV-CTLs expressing GD2-CARs (CAR-CTLs) circulated at higher levels than GD2-CAR ATCs (CAR-ATCs) early after infusion, but by 6 weeks, both subsets became low or undetectable. We now report the long-term clinical and immunologic consequences of infusions in 19 patients with high-risk neuroblastoma: 8 in remission at infusion and 11 with active disease. Three of 11 patients with active disease achieved complete remission, and persistence of either CAR-ATCs or CAR-CTLs beyond 6 weeks was associated with superior clinical outcome. We observed persistence for up to 192 weeks for CAR-ATCs and 96 weeks for CAR-CTLs, and duration of persistence was highly concordant with the percentage of CD4(+) cells and central memory cells (CD45RO(+)CD62L(+)) in the infused product. In conclusion, GD2-CAR T cells can induce complete tumor responses in patients with active neuroblastoma; these CAR T cells may have extended, low-level persistence in patients, and such persistence was associated with longer survival. This study is registered at www.clinialtrials.gov as #NCT00085930.

Background Aims: Several studies have demonstrated that the immunogenicity of chronic lymphocytic leukemia (CLL) cells can be increased by manipulation of the CD40/CD40-ligand (CD40L) pathway. Although immunologic, and perhaps clinical, benefits have been obtained with an autologous CLL tumor vaccine obtained by transgenic expression of CD40L and interleukin (IL)-2, there is little information about the optimal gene transfer strategies., Methods: We compared two different CLL vaccines prepared by adenoviral gene transfer and plasmid electroporation, analyzing their phenotype and immunostimulatory activity., Results: We found that higher expression of transgenic CD40L was mediated by adenoviral gene transfer than by plasmid transduction, and that adenoviral transfer of CD40L was associated with up-regulation of the co-stimulatory molecules CD80 and CD86 and adhesion molecule CD54. In contrast, transgenic IL-2 secretion was greater following plasmid transduction. These phenotypic differences in the vaccines were associated with different functionality, both ex vivo and following administration to patients. Thus adenoviral vaccines induced greater activation of leukemia-reactive T cells ex vivo than plasmid vaccines. In treated patients, specific T-cell (T helper 1 (Th1) and T helper 2 (Th2)) and humoral anti-leukemia responses were detected following administration of the adenoviral vaccine (n = 15), while recipients of the plasmid vaccine (n = 9) manifested only a low-level Th2 response. Progression-free survival at 2 years was 46.7% in the adenoviral vaccine recipients, versus 11.1 % in those receiving plasmid vaccine., Conclusions: CLL vaccines expressing the same transgenes but produced by distinct methods of gene transfer may differ in the polarity of the immune response they induce in patients.

Chronic lymphocytic leukemia (CLL) is characterized by an accumulation of mature CD19(+)CD5(+)CD20(dim) B lymphocytes that typically express the B-cell activation marker CD23. In the present study, we cloned and expressed in T lymphocytes a novel chimeric antigen receptor (CAR) targeting the CD23 antigen (CD23.CAR). CD23.CAR(+) T cells showed specific cytotoxic activity against CD23(+) tumor cell lines (average lysis 42%) and primary CD23(+) CLL cells (average lysis 58%). This effect was obtained without significant toxicity against normal B lymphocytes, in contrast to CARs targeting CD19 or CD20 antigens, which are also expressed physiologically by normal B lymphocytes. Moreover, CLL-derived CD23.CAR(+) T cells released inflammatory cytokines (1445-fold more TNF-β, 20-fold more TNF-α, and 4-fold more IFN-γ). IL-2 was also produced (average release 2681 pg/mL) and sustained the antigen-dependent proliferation of CD23.CAR(+) T cells. Redirected T cells were also effective in vivo in a CLL Rag2(-/-)γ(c)(-/-) xenograft mouse model. Compared with mice treated with control T cells, the infusion of CD23.CAR(+) T cells resulted in a significant delay in the growth of the MEC-1 CLL cell line. These data suggest that CD23.CAR(+) T cells represent a selective immunotherapy for the elimination of CD23(+) leukemic cells in patients with CLL.

T-cell therapy with genetically modified T cells targeting CD19 or CD20 holds promise for the immunotherapy of hematologic malignancies. These targets, however, are only present on B cell-derived malignancies, and because they are broadly expressed in the hematopoietic system, their targeting may have unwanted consequences. To expand T-cell therapies to hematologic malignancies that are not B cell-derived, we determined whether T cells can be redirected to CD70, an antigen expressed by limited subsets of normal lymphocytes and dendritic cells, but aberrantly expressed by a broad range of hematologic malignancies and some solid tumors. To generate CD70-specific T cells, we constructed a chimeric antigen receptor (CAR) consisting of the CD70 receptor (CD27) fused to the CD3-ζ chain. Stimulation of T cells expressing CD70-specific CARs resulted in CD27 costimulation and recognition of CD70-positive tumor cell lines and primary tumor cells, as shown by IFN-γ and IL-2 secretion and by tumor cell killing. Adoptively transferred CD70-specific T cells induced sustained regression of established murine xenografts. Therefore, CD70-specific T cells may be a promising immunotherapeutic approach for CD70-positive malignancies.

The cancer testis antigen (CTA) preferentially expressed antigen of melanoma (PRAME) is overexpressed by many hematologic malignancies, but is absent on normal tissues, including hematopoietic progenitor cells, and may therefore be an appropriate candidate for T cell-mediated immunotherapy. Because it is likely that an effective antitumor response will require high-avidity, PRAME-specific cytotoxic T lymphocytes (CTLs), we attempted to generate such CTLs using professional and artificial antigen-presenting cells loaded with a peptide library spanning the entire PRAME protein and consisting of 125 synthetic pentadecapeptides overlapping by 11 amino acids. We successfully generated polyclonal, PRAME-specific CTL lines and elicited high-avidity CTLs, with a high proportion of cells recognizing a previously uninvestigated HLA-A*02-restricted epitope, P435-9mer (NLTHVLYPV). These PRAME-CTLs could be generated both from normal donors and from subjects with PRAME(+) hematologic malignancies. The cytotoxic activity of our PRAME-specific CTLs was directed not only against leukemic blasts, but also against leukemic progenitor cells as assessed by colony-forming-inhibition assays, which have been implicated in leukemia relapse. These PRAME-directed CTLs did not affect normal hematopoietic progenitors, indicating that this approach may be of value for immunotherapy of PRAME(+) hematologic malignancies.

Background Aims: The Food and Drug Administration (FDA) currently recommends at least 4 h of recipient monitoring after T cell infusions to detect early infusion reactions. Recent catastrophic reactions to 'first-in-man' biologic agents have emphasized the importance of this rule for initial studies of new products. The value of such monitoring for better established agents is less obvious., Methods: We reviewed infusion-related adverse events (AE) following administration of ex vivo-expanded T cell products (antigen-specific cytotoxic T lymphocytes, allodepleted T cells, and genetically modified T cells) on investigational new drug (IND) studies in our center., Results: From 1998 to 2008, we infused 381 T cell products to 180 recipients, enrolled on 18 studies, receiving T cells targeting malignancies or post-transplant viral infections. There were no grade 3-4 infusion reactions during initial monitoring or 24-h follow-up. Twenty-four mild (grade 1-2) AE occurred in 21 infusions either during or immediately following infusion (up to 6 h), most commonly nausea and vomiting (10/24, 41.6%), probably because of the dimethyl sulfoxide cryoprotectant, and hypotension (20.8%), attributable to diphenhydramine pre-medication. Twenty-two additional non-severe events were reported within 24 h of infusion, most commonly culture-negative fever, chills and nausea. An increased risk of adverse events was associated with age [incidence rate ratio (IRR) 0.98; 95% confidence interval (CI) 0.96-1.00, P = 0.05], while an increased risk of immediate infusion-related events was higher in patients reporting allergies (IRR 2.72, 95% CI 1.00-7.40, P = 0.05); sex, disease type and T cell source (allogeneic or autologous) had no effect on frequency of adverse events., Conclusions: Infusion of these T cell products was safe in the outpatient setting and associated with no severe reactions, so monitoring for 1 h after infusion is probably sufficient. As many of the AE were attributable to diphenhydramine premedication, a lower dose (0.25 mg/kg) should be selected.

Infusions of antigen-specific T cells have yielded therapeutic responses in patients with pathogens and tumors. To broaden the clinical application of adoptive immunotherapy against malignancies, investigators have developed robust systems for the genetic modification and characterization of T cells expressing introduced chimeric antigen receptors (CARs) to redirect specificity. Human trials are under way in patients with aggressive malignancies to test the hypothesis that manipulating the recipient and reprogramming T cells before adoptive transfer may improve their therapeutic effect. These examples of personalized medicine infuse T cells designed to meet patients' needs by redirecting their specificity to target molecular determinants on the underlying malignancy. The generation of clinical grade CAR(+) T cells is an example of bench-to-bedside translational science that has been accomplished using investigator-initiated trials operating largely without industry support. The next-generation trials will deliver designer T cells with improved homing, CAR-mediated signaling, and replicative potential, as investigators move from the bedside to the bench and back again.

Viral infections and leukemic relapse account for the majority of treatment failures in patients with B-cell acute lymphoblastic leukemia (B-ALL) receiving allogeneic hematopoietic stem cell (HSC) or cord blood (CB) transplants. Adoptive transfer of virus-specific cytotoxic T lymphocytes (CTLs) provides protection against common viruses causing serious infections after HSC transplantation without concomitant graft-versus-host disease. We have now generated CTL lines from peripheral blood (PB) or CB units that recognize multiple common viruses and provide antileukemic activity by transgenic expression of a chimeric antigen receptor (CAR) targeting CD19 expressed on B-ALL. PB-derived CAR(+) CTLs produced interferon-gamma (IFNgamma) in response to cytomegalovirus-pp65, adenovirus-hexon, and Epstein-Barr virus pepmixes (from 205 +/- 104 to 1034 +/- 304 spot-forming cells [SFCs]/10(5) T cells) and lysed primary B-ALL blasts in (51)Cr-release assays (mean, 66% +/- 5% specific lysis; effector-target [E/T] ratio, 40:1) and the CD19(+) Raji cell line (mean, 78% +/- 17%) in contrast to nontransduced controls (8% +/- 8% and 3% +/- 2%). CB-derived CAR(+) CTLs showed similar antiviral and antitumor function and both PB and CB CAR(+) CTLs completely eliminated B-ALL blasts over 5 days of coculture. This approach may prove beneficial for patients with high-risk B-ALL who have recently received an HSC or CB transplant and are at risk of infection and relapse.

Adoptive transfer of autologous Epstein-Barr virus-specific cytotoxic T lymphocytes (EBV-CTLs) to solid organ transplant (SOT) recipients has been shown safe and effective for the treatment of EBV-associated posttransplantation lymphoproliferative disorders (PTLDs). SOT recipients, however, require the continuous administration of immunosuppressive drugs to prevent graft rejection, and these agents may significantly limit the long-term persistence of transferred EBV-CTLs, precluding their use as prophylaxis. Tacrolimus (FK506) is one of the most widely used immunosuppressive agents in SOT recipients, and its immunosuppressive effects are largely dependent on its interaction with the 12-kDa FK506-binding protein (FKBP12). We have knocked down the expression of FKBP12 in EBV-CTLs using a specific small interfering RNA (siRNA) stably expressed from a retroviral vector and found that FKBP12-silenced EBV-CTLs are FK506 resistant. These cells continue to expand in the presence of the drug without measurable impairment of their antigen specificity or cytotoxic activity. We confirmed their FK506 resistance and anti-PTLD activity in vivo using a xenogenic mouse model, suggesting that the proposed strategy may be of value to enhance EBV-specific immune surveillance in patients at high risk of PTLD after transplantation.

The naive phenotype of cord blood (CB) T cells may reduce graft-versus-host disease after umbilical cord blood transplantation, but this naivety and their low absolute numbers also delays immune reconstitution, producing higher infection-related mortality that is predominantly related to CMV, adenovirus (Adv), and EBV. Adoptive immunotherapy with peripheral blood-derived virus-specific cytotoxic T lymphocytes (CTLs) can effectively prevent viral disease after conventional stem cell transplantation, and we now describe the generation of single cultures of CTLs from CB that are specific for multiple viruses. Using EBV-infected B cells transduced with a clinical-grade Ad5f35CMVpp65 adenoviral vector as sources of EBV, Adv, and CMV antigens, we expanded virus-specific T cells even from CB T cells with a naive phenotype. After expansion, each CTL culture contained both CD8(+) and CD4(+) T-cell subsets, predominantly of effector memory phenotype. Each CTL culture also had HLA-restricted virus-specific cytotoxic effector function against EBV, CMV, and Adv targets. The CB CTLs recognized multiple viral epitopes, including CD4-restricted Adv-hexon epitopes and immunosubdominant CD4- and CD8-restricted CMVpp65 epitopes. Notwithstanding their naive phenotype, it is therefore possible to generate trivirus-specific CTLs in a single culture of CB, which may be of value to prevent or treat viral disease in CB transplant recipients. This study is registered at www.clinicaltrials.gov as NCT00078533.

The PD-1 pathway is emerging as an important tumor-evasion mechanism. In this issue of Blood, 3 independent groups report that PD-1 is highly expressed by tumor-specific cytotoxic T lymphocytes in hematologic and nonhematologic malignancies, and is associated with impaired T-cell function.

For the adoptive transfer of tumor-directed T lymphocytes to prove effective, there will probably need to be a match between the chemokines the tumor produces and the chemokine receptors the effector T cells express. The Reed-Stemberg cells of Hodgkin lymphoma (HL) predominantly produce thymus- and activation-regulated chemokine/CC chemokine ligand 17 (TARC/CCL17) and macrophage-derived chemokine (MDC/CCL22), which preferentially attract type 2 T helper (Th2) cells and regulatory T cells (Tregs) that express the TARC/MDC-specific chemokine receptor CCR4, thus generating an immunosuppressed tumor environment. By contrast, effector CD8(+) T cells lack CCR4, are nonresponsive to these chemokines and are rarely detected at the tumor site. We now show that forced expression of CCR4 by effector T cells enhances their migration to HL cells. Furthermore, T lymphocytes expressing both CCR4 and a chimeric antigen receptor directed to the HL associated antigen CD30 sustain their cytotoxic function and cytokine secretion in vitro, and produce enhanced tumor control when infused intravenously in mice engrafted with human HL. This approach may be of value in patients affected by HL.

The cancer testis antigen (CTA) preferentially expressed antigen of melanoma (PRAME) is overexpressed in many hematologic malignancies, including chronic myeloid leukemia (CML). The sensitivity of CML to donor lymphocyte infusion after allogeneic stem cell transplantation suggests this tumor can be highly susceptible to cellular immunotherapy targeted to tumor associated antigens. We therefore tested whether functional PRAME-specific cytotoxic T lymphocytes (PRAME CTLs) could be generated and expanded from healthy donors and CML patients, or whether the limited immunogenicity of this CTA coupled with tumor-associated anergy would preclude this approach. Using optimized culture conditions and HLA-A*02-restricted PRAME-peptides, we have consistently generated PRAME CTLs from 8/9 healthy donors and 5/6 CML patients. These CTLs released IFNgamma in response to PRAME peptides (between 113 +/- 8 and 795 +/- 23 spot forming cells/10(5) T cells) and lysed PRAME peptide-loaded cells (45 +/- 19% at an effector:target [E:T] ratio of 20:1) in a MHC-restricted fashion. Importantly, these CTLs recognized and had cytotoxic activity against HLA-A*02(+)/PRAME(+) tumor cell lines, and could recognize and respond to primary CML cells. PRAME CTLs were generated almost exclusively from the naive T-cell compartment, and clonal analysis showed these cells could have high alphabetaTCR-peptide avidity. PRAME CTLs or vaccines may thus be of value for patients with CML.

Immunotherapy for B-cell chronic lymphocytic leukaemia (B-CLL) and other haematological malignancies may consist of passive antibody, active immunization or adoptive T-cell transfer. This chapter will focus on T-lymphocyte immunotherapy; an approach supported by earlier observations that the beneficial effects of allogeneic stem cell transplantation depend, in part, on the graft-versus-leukaemia effects mediated by these cells. One promising strategy consists of the genetic manipulation of effector T lymphocytes to express tumour-specific T-cell receptors or chimeric antigen receptors directed against surface antigens on the B-CLL cells. This methodology is now being integrated with the concept that tumour recurrence may be due to the persistence of a reservoir of more primitive and chemoresistant tumour cells, dubbed 'cancer stem cells', with self-renewal capacity. Identification and characterization of these cancer stem cells in B-CLL is crucial for the development of new anti-tumour agents, and for the identification of target antigens for cellular immunotherapy. This chapter will describe how immunotherapy may be directed to a more primitive side population of B-CLL cells.

The antitumor effect of adoptively transferred tumor-specific cytotoxic T lymphocytes (CTLs) is impaired by the limited capacity of these cells to expand within the tumor microenvironment. Administration of interleukin 2 (IL-2) has been used to overcome this limitation, but the systemic toxicity and the expansion of unwanted cells, including regulatory T cells, limit the clinical value of this strategy. To discover whether transgenic expression of lymphokines by the CTLs themselves might overcome these limitations, we evaluated the effects of transgenic expression of IL-2 and IL-15 in our model of Epstein Barr Virus-specific CTLs (EBV-CTLs). We found that transgenic expression of IL-2 or IL-15 increased the expansion of EBV-CTLs both in vitro and in vivo in a severe combined immunodeficiency disease (SCID) mouse model and enhanced antitumor activity. Although the proliferation of these cytokine genes transduced CTLs remained strictly antigen dependent, clinical application of this approach likely requires the inclusion of a suicide gene to deal with the potential development of T-cell mutants with autonomous growth. We found that the incorporation of an inducible caspase-9 suicide gene allowed efficient elimination of transgenic CTLs after exposure to a chemical inducer of dimerization, thereby increasing the safety and feasibility of the approach.

Adoptive transfer of Epstein Barr virus (EBV)-specific cytotoxic T-lymphocytes (EBV-CTLs) has shown that these cells persist in patients with EBV(+) Hodgkin lymphoma (HD) to produce complete tumor responses. Treatment failure, however, occurs if a subpopulation of malignant cells in the tumor lacks or loses expression of EBV antigens. We have therefore determined whether we could prepare EBV-CTLs that retained the antitumor activity conferred by their native receptor while expressing a chimeric antigen receptor (CAR) specific for CD30, a molecule highly and consistently expressed on malignant Hodgkin Reed-Sternberg cells. We made a CD30CAR and were able to express it on 26% (+/- 11%) and 22% (+/- 5%) of EBV-CTLs generated from healthy donors and HD patients, respectively. These CD30CAR(+) CTLs killed both autologous EBV(+) cells through their native receptor and EBV(-)/CD30(+) targets through their major histocompatibility complex (MHC)-unrestricted CAR. A subpopulation of activated T cells also express CD30, but the CD30CAR(+) CTLs did not impair cellular immune responses, probably because normal T cells express lower levels of the target antigen. In a xenograft model, CD30CAR(+) EBV-CTLs could be costimulated by EBV-infected cells and produce antitumor effects even against EBV(-)/CD30(+) tumors. EBV-CTLs expressing both a native and a chimeric antigen receptor may therefore have added value for treatment of HD.

There has been interest in generating T cells expressing chimeric artificial receptors (CARs) targeting CD19/CD20 antigens to treat B-cell lymphomas. If successful, however, this approach would likely impair humoral immunity because T cells may persist long-term. Most low-grade lymphoma and chronic lymphocytic leukemia (B-CLL) cells express monoclonal immunoglobulins carrying either kappa or lambda light chains. We, therefore, explored whether T lymphocytes could be genetically modified to target the tumor-associated light chain, sparing B lymphocytes expressing the reciprocal light chain, and consequently reduce impairment of humoral immunity. We found that T lymphocytes expressing the anti-kappa light chain CAR showed cytotoxic activity against Igkappa(+) tumor cell lines and B-CLL cells both in vitro and in vivo. We also found that the incorporation of the CD28 endodomain within the CAR enhanced the in vitro and in vivo expansion of transgenic T cells after tumor-associated antigen stimulation. Free Igkappa(+) did not compromise the ability of redirected T lymphocytes to eliminate Igkappa(+) tumors because these free immunoglobulins served to sustain proliferation of CAR-CD28 transgenic T cells. Thus, adoptive transfer of T lymphocytes targeting the appropriate light chain could be a useful immunotherapy approach to treat B-lymphocyte malignancies that clonally express immunoglobulin without entirely compromising humoral immunity.

Effector-memory T cells expressing Fas (Apo-1/CD95) are switched to an apoptotic program by cross-linking with Fas-ligand (FasL). Consequently, tumors that express FasL can induce apoptosis of infiltrating Fas-positive T lymphocytes and subdue any antitumor host immune response. Since Epstein-Barr virus (EBV)-associated tumors such as Hodgkin lymphoma (HL) and nasopharyngeal carcinoma (NPC) express FasL, we determined whether EBV-specific cytotoxic T lymphocytes (EBV-CTLs) could be modified to resist this evasion strategy. We show that long-term down-modulation of Fas can be achieved in EBV-CTLs by transduction with small interfering RNA (siRNA) encoded in a retrovirus. Modified T cells resisted Fas/FasL-mediated apoptosis compared with control cells and showed minimal cleavage of the caspase3 substrate poly(ADP-ribose) polymerase (PARP) protein after Fas engagement. Prolonged Fas stimulation selected a uniformly Fas(low) and FasL resistant population. Removal of responsiveness to this single death signal had no other discernible effects on EBV-CTLs. In particular, it did not lead to their autonomous growth since the modified EBV-CTLs remained polyclonal, and their survival and proliferation retained dependence on antigen-specific stimulation and on the presence of other physiologic growth signals. EBV-CTLs with knocked down Fas should have a selective functional and survival advantage over unmodified EBV-CTLs in the presence of tumors expressing FasL and may be of value for adoptive cellular therapy.

The efficacy of adoptive T-cell therapy as treatment for malignancies may be enhanced by genetic modification of infused cells. However, oncogenic events due to vector/transgene integration, and toxicities due to the infused cells themselves, have tempered enthusiasm. A safe and efficient means of removing aberrant cells in vivo would ameliorate these concerns. We describe a "safety switch" that can be stably and efficiently expressed in human T cells without impairing phenotype, function, or antigen specificity. This reagent is based on a modified human caspase 9 fused to a human FK506 binding protein (FKBP) to allow conditional dimerization using a small molecule pharmaceutical. A single 10-nM dose of synthetic dimerizer drug induces apoptosis in 99% of transduced cells selected for high transgene expression in vitro and in vivo. This system has several advantages over currently available suicide genes. First, it consists of human gene products with low potential immunogenicity. Second, administration of dimerizer drug has no effects other than the selective elimination of transduced T cells. Third, inducible caspase 9 maintains function in T cells overexpressing antiapoptotic molecules. These characteristics favor incorporation of inducible caspase 9 as a safety feature in human T-cell therapies.

Clinical benefits from monoclonal antibody therapy for B-chronic lymphocytic leukemia (B-CLL) have increased interest in developing additional immunotherapies for the disease. CD40 ligand is an accessory signal for T-cell activation and can overcome T-cell anergy. The OX40-OX40 ligand pathway is involved in the subsequent expansion of memory antigen-specific T cells. We expressed both CD40L and OX40L on B-CLL cells by exploiting the phenomenon of molecular transfer from fibroblasts overexpressing these ligands. We analyzed the effects of the modified B-CLL cells on the number, phenotype, and cytotoxic function of autologous T cells in 7 B-CLL patients. Transfer of CD40L and OX40L was observed in all and was followed by the up-regulation of B7-1 and B7-2. The culture of CD40L/OX40L-expressing B-CLL cells with autologous T cells generated CD4+/CD8+ cytotoxic T-cell lines, which secreted interferon-gamma (IFN-gamma) and granzyme-B/perforin in response to autologous, but not to allogeneic, B-CLL cells or to autologous T-cell blasts. CD40L or OX40L alone was insufficient to expand tumor-reactive T cells. The combination of CD40L and OX40L on B-CLL cells may allow the generation of therapeutic immune responses to B-CLL, either by active immunization with modified tumor cells or by adoptive immunotherapy with tumor-reactive autologous T cells.

The evaluation of long-term cellular immunity to EBV in pediatric orthotopic liver transplant (OLT) recipients after treatment with the humanized anti-CD20 monoclonal antibody (Rituximab) has not yet been explored. At our institution, one child with EBV-related mononucleosis-like syndrome and five children with polymorphic-EBV-PTLD occurring 6-88 months after OLT were treated with Rituximab. Treatment was well tolerated. All children achieved complete remission. After Rituximab, B-lymphocytes were undetectable in the peripheral blood and EBV-load, monitored with real-time PCR, decreased to undetectable levels in all children from >4000 copies/microg DNA at diagnosis. Four to eight months after Rituximab, EBV-load increased (>4000 copies/microg DNA) in four children, and PTLD recurred in three. Their frequency of EBV-specific T-cell precursors, measured by Elispot analysis, remained lower than in healthy controls. Rituximab effectively induced regression of PTLD in OLT recipients. However, EBV-specific T-cell immunocompetence, which may be crucial for the long-term control of EBV-mediated proliferation, did not improve.

Clinical studies of adoptive immunotherapy with T cells have shown activity directed at hematologic and solid malignancies and viral infections. Genetic modification of infused T cells offers the prospect of improving such therapies and has already been used to track infused T cells, insert suicide genes and redirect the immune response towards specific Ag. Pre-clinical studies are evaluating novel approaches to genetically modify T cells to confer resistance to tumor evasion mechanisms. There is also increasing interest in developing suicide gene strategies as a failsafe mechanism to eradicate genetically modified cells should adverse effects occur.

Graft-versus-host disease (GVHD) represents one of the major complications of allogeneic hematopoietic stem cell transplantation. Techniques to prevent GVHD have included ex vivo T-cell depletion of the graft or prolonged in vivo immunosuppression. Both reduce the frequency and severity of GVHD but also reduce T-cell-mediated graft-versus-malignancy effect, and increase the risk of infection. A major goal in transplantation is to prevent alloreactivity while preserving activity against tumors and infectious agents. We have used activation of the Notch pathway to try to generate T cells able to specifically regulate alloantigen responses. We used allogeneic Epstein-Barr virus lymphoblastoid B cells (EBV-LCLs) as stimulator cells. Such LCLs are excellent (allo) antigen-presenting cells and can be obtained in large numbers even from donors who have received extensive chemo/radiotherapy. We overexpressed a Notch ligand, Jagged-1, in these cells by adenoviral vector transduction. Stimulation of CD45RA+ naive T cells by Jagged-1 EBV-LCL reduces production of interferon-gamma, interleukin-2, and interleukin-5, but up-regulates transforming growth factor-beta 1 synthesis, consistent with induction of a regulatory T-cell phenotype. Transfer of these T cells to fresh lymphocyte cultures inhibits proliferative and cytotoxic immune responses to the priming alloantigens while sparing responses to third-party stimulator cells. Notch activation in the presence of alloantigen-presenting cells may therefore be a means of inducing specific regulatory T cells while preserving other T-cell functionality.

Posttransplantation lymphoproliferative disorders (PTLDs) represent a serious complication of solid organ transplantation. This study assessed the molecular histogenesis of 52 B-cell monoclonal PTLDs, including 12 polymorphic PTLDs (P-PTLDs), 36 diffuse large B-cell lymphomas (DLBCLs), and 4 Burkitt/Burkitt-like lymphomas (BL/BLLs). Somatic hypermutation (SHM) of immunoglobulin variable (IgV) genes documented that most monoclonal B-cell PTLDs (75% P-PTLDs, 91.3% DLBCLs, 100% BL/BLLs) derive from germinal center (GC)-experienced B cells. B-cell lymphoma 6 (BCL6) mutations occurred in 25% P-PTLDs, 60.6% DLBCLs, and 75.0% BL/BLLs. A first histogenetic category of PTLDs (31.2% DLBCLs) express the BCL6+/multiple myeloma oncogene-1 protein (MUM1-/+)/CD138- profile and mimic B cells experiencing the GC reaction, as also suggested by ongoing SHM in a fraction of these cases. A second subset of PTLDs (66.7% P-PTLDs and 31.2% DLBCLs) display the BCL6-/MUM1+/CD138- phenotype and mimic B cells that have concluded the GC reaction. A third histogenetic category of PTLDs (25.0% P-PTLDs and 31.2% DLBCLs) shows the BCL6-/MUM1+/CD138+ profile, consistent with preterminally differentiated post-GC B cells. Crippling mutations of IgV heavy chain (IgVH) and/or IgV light chain (IgVL) genes, leading to sterile rearrangements and normally preventing cell survival, occur in 4 DLBCLs and 1 BL/BLL that may have been rescued from apoptosis through expression of Epstein-Barr virus (EBV)-encoded latent membrane protein 1 (LMP1). Overall, the histogenetic diversity of monoclonal B-cell PTLDs may help define biologically homogeneous categories of the disease.

Recent advances have made haploidentical transplantation for leukemia feasible, but the rigorous T-cell depletion used contributes to the high relapse rates observed. We have attempted to improve the graft-versus-leukemia (GVL) effect by generating allorestricted cytotoxic T lymphocytes (CTLs) directed against human CD45. Such CTLs should recognize patient hematopoietic cells including leukemia, enhancing donor cell engraftment and improving the GVL effect, but they should not recognize host nonhematopoietic tissues or donor cells from the graft. Using the T2 binding assay, 4 CD45-derived peptides were found to bind HLA-A2 molecules. These peptides were used to generate cytotoxic T-cell lines from HLA-A2(-) donors by sequential stimulation with peptide-pulsed HLA-A2(+) stimulators, and the lines obtained were screened for peptide-specific cytotoxicity. Using one of these peptides (P1218), it was possible to generate peptide-specific, allorestricted CTLs in 3 of 7 responders. P1218-specific CTL lines show potent cytotoxicity against hematopoietic cell lines coexpressing HLA-A2 and CD45 but not CD45 loss variants. Studies with stable transfectants of 293 cells demonstrated recognition by P1218-specific CTLs of endogenously expressed CD45. Likewise P1218-specific CTLs recognized peripheral blood mononuclear cells (PBMCs) from HLA-A2(+) patients with chronic myeloid leukemia (CML) and leukemic blasts in HLA-A2(+) patients with acute myeloid leukemia (AML), but they were unable to lyse HLA-A2(+) fibroblasts or HLA-A2(-) normal PBMCs. Coculture of CD34(+) PBMCs and bone marrow mononuclear cells (BMMCs) with P1218-specific CTL significantly inhibited colony-forming unit-granulocyte macrophage (CFU-GM) formation in HLA-A2(+) healthy controls and CML patients but resulted in no significant inhibition in HLA-A2(-) healthy controls. These studies demonstrate that P1218-specific cytotoxic T lymphocytes (CTLs) have potent activity against leukemic progenitors and suggest that adoptive immunotherapy with allorestricted CTLs directed against CD45 epitopes may be useful in restoring the GVL effect after HLA-A2-mismatched haploidentical transplantation. Further, because P1218-specific CTLs also recognize healthy HLA-A2(+) progenitors, such CTLs could also contribute to host myeloablation and enhance donor cell engraftment.

Because tumor-specific antigens have been identified in multiple myeloma (MM), immunotherapy might provide an additional treatment modality for the disease. Expression of CD40 ligand (CD40L) proximate to the MM cells might serve this purpose, either by increasing their capacity to present self-antigens by activation through their CD40 receptor or by the recruitment of professional antigen-presenting cells (APCs) able to take up and present tumor-associated antigens. To distinguish between these possibilities and predict whether human CD40(-) myeloma might respond to this approach, we examined 3 murine plasmacytoma cell lines, 2 (MPC-11 and S107) expressing the CD40 molecule and 1 (X-24) lacking such expression. Syngeneic BALB/CBYJ mice were inoculated subcutaneously with tumor cells mixed with CL7.1 fibroblasts, retrovirally transduced to express either the mCD40L or the neo gene. For all 3 plasmacytoma cell lines, coinjection with CL7.1/mCD40L significantly reduced local tumor growth compared with controls. This effect was mediated by a systemic antitumor immune response, since mice immunized with tumor and CL7.1/mCD40L were resistant to subsequent challenge with tumor, and tumor growth inhibition was abolished when CD8(+) or CD4(+) lymphocytes were depleted. Because expression of CD40L gave equivalent protection from CD40(+) and CD40(-) tumors and transgenic-CD40L failed to up-regulate costimulatory molecules in either tumor, the protective effects of CD40L probably resulted from recruitment/activation of professional APCs rather than from CD40 activation of plasmacytoma cells. As further support of this concept, we found that mice were also well protected if CL7.1 and CD40L were injected together with apoptotic plasmacytoma cells from these tumors. Hence, transgenic CD40L expression may produce an antimyeloma immune response against either CD40(+) or CD40(-) tumors and may be of therapeutic value for both types of myeloma in humans.

A major obstacle in purifying either autologous or allogeneic hematopoietic stem cells from granulocyte colony-stimulating factor (G-CSF) mobilized circulating progenitor cells (CPC) is represented by the huge cellularity present in each apheretic product. To obtain a significant debulking of unwanted cells from the leukapheresis, we developed a modified protocol of immune rosetting whereby human ABO-Rh- compatible red blood cells (RBCs) are treated with chromium chloride and then coated with murine monoclonal antibodies (MoAbs) against leukocyte antigens. When experiments were performed with leukaphereses obtained from normal donors or from T-cell acute lymphoblastic leukemia (T-ALL) patients, RBCs were coated with murine MoAbs against human mature myeloid cells (CD11b) and T cells (CD6); whereas, in the case of patients with B-precursor ALL, B-cell non-Hodgkin's lymphoma (B-NHL), or multiple myeloma (MM), RBCs were coated with anti-CD11b only. After incubation with CPC, rosetting cells (myeloid precursor cells, granulocytes, monocytes, and T cells) were removed by Ficoll-Hypaque density gradient centrifugation with a blood cell processor apparatus, COBE (Lakewood, CO) 2991. After this step, a significant reduction of the initial cellularity was consistently obtained (range, 72% to 97%), whereas the median absolute recovery of the CD34+ cells was above 85% (range, 64 to 100), with a 10-fold relative enrichment ranging from 3% to 41%. In a second step, CPC can be further purged of contaminating T or B cells by incubation with lymphoid-specific magnetic microbeads (anti-CD2 and -CD7 to remove T cells; anti-CD19 to remove B cells) and elution through a type-D depletion column (composed of ferromagnetic fiber) inserted within a SuperMACS separator device (Miltenyi Biotech, Bergisch-Gladbach, Germany). By this approach, a highly effective (three to four logs) T-cell depletion was achieved in all experiments performed with normal donors or T-ALL patients (median loss of CD3+ cells: 99.8% [range 99.2 to 100]) and an equally efficient B-cell depletion was obtained from B-precursor ALL, B-NHL, or MM patients. At the end of the procedure the T- or B-cell depleted fraction retained a high proportion of the initial hematopoietic CD34+ stem cells, with a median recovery above 70% (range 48% to 100%) and an unmodified clonogenic potential. In five patients (two follicular NHL and three ALL) the purified fraction of stem cells was found disease free at the molecular level as assessed by polymerase chain reaction (PCR) analysis of the t(14;18) chromosome translocation or clono-specific DNA sequences of IgH or T-cell receptor gamma and delta chain genes. Purified autologous and allogeneic CPCs were transplanted in three and six patients, respectively, who showed a prompt and sustained hematologic engraftment. In conclusion, this method represents a simple and reproducible two-step procedure to obtain a highly efficient purging of T or B cells from G-CSF expanded and mobilized CPCs. This approach might lead to the eradication of the neoplastic clone in the autologous stem cell inoculum as well as for T-cell depletion during allogeneic transplantation.

Chronic myelogenous leukemia (CML) is a clonal disorder of the hematopoietic stem cell characterized by a chimeric BCR/ABL gene giving rise to a 210-kD fusion protein with dysregulated tyrosine kinase activity. We investigated the effect of genistein, a protein tyrosine kinase inhibitor, on the in vitro growth of CML and normal marrow-derived multi-potent (colony-forming unit-mix [CFU-Mix]), erythroid (burst-forming unit-erythroid [BFU-E]), and granulocyte-macrophage (colony-forming unit-granulocyte-macrophage [CFU-GM]) hematopoietic progenitors. Continuous exposure of CML and normal marrow to genistein induced a statistically significant and dose-dependent suppression of colony formation. Genistein doses causing 50% inhibition of CML and normal progenitors were not significantly different for CFU-Mix (27 mumol/L v 23 mumol/L), BFU-E (31 mumol/L v 29 mumol/L), and CFU-GM (40 mumol/L v 32 mumol/L v 32 mumol/L). Preincubation of CML and normal marrow with genistein (200 mumol/ L for 1 to 18 hours) induced a time-dependent suppression of progenitor cell growth, while sparing a substantial proportion of long-term culture-initiating cells (LTC-IC) from CML (range, 91% +/- 9% to 32% +/- 3%) and normal marrow (range, 85% +/- 8% to 38% +/- 9%). Analysis of individual CML colonies for the presence of the hybrid BCR/ABL mRNA by reverse transcription-polymerase chain reaction (RT-PCR) showed that genistein treatment significantly reduced the mean +/- SD percentage of marrow BCR/ABL+ progenitors both by continuous exposure (76% +/- 18% v 24% +/- 12%, P < or = .004) or preincubation (75% +/- 16% v 21% +/- 10%, P < or = .002) experiments. Preincubation with genistein reduced the percentage of leukemic LTC-IC from 87% +/- 12% to 37% +/- 12% (P < or = .003). Analysis of individual colonies by cytogenetics and RT-PCR confirmed that genistein-induced increase in the percentage of nonleukemic progenitors was not due to suppression of BCR/ABL transcription. Analysis of nuclear DNA fragmentation by DNA gel electrophoresis and terminal deoxynucleotidyl transferase assay showed that preincubation of CML mononuclear and CD34+ cells with genistein induced significant evidence of apoptosis. These observations show that genistein is capable of (1) exerting a strong antiproliferative effect on CFU-Mix, BFU-E, and CFU-GM while sparing the more primitive LTC-IC and (2) selecting benign hematopoietic progenitors from CML marrow, probably through an apoptotic mechanism.