pre-B Cell ALL Research Articles

Identification of Cell Surface Proteins as Potential Immunotherapy Targets in 12 Pediatric Cancers

Technological advances now allow us to rapidly produce CARs and other antibody-derived therapeutics targeting cell surface receptors. To maximize the potential of these new technologies, relevant extracellular targets must be identified. The Pediatric Oncology Branch of the NCI curates a freely accessible database of gene expression data for both pediatric cancers and normal tissues, through which we have defined discrete sets of over-expressed transcripts in 12 pediatric cancer subtypes as compared to normal tissues. We coupled gene expression profiles to current annotation databases (i.e., Affymetrix, Gene Ontology, Entrez Gene), in order to categorize transcripts by their sub-cellular location. In this manner we generated a list of potential immune targets expressed on the cell surface, ranked by their difference from normal tissue. Global differences from normal between each of the pediatric tumor types studied varied, indicating that some malignancies expressed transcript sets that were more highly diverged from normal tissues than others. The validity of our approach is seen by our findings for pre-B cell ALL, where targets currently in clinical trials were top-ranked hits (CD19, CD22). For some cancers, reagents already in development could potentially be applied to a new disease class, as exemplified by CD30 expression on sarcomas. Moreover, several potential new targets shared among several pediatric solid tumors are herein identified, such as MCAM (MUC18), metadherin (MTDH), and glypican-2 (GPC2). These targets have been identified at the mRNA level and are yet to be validated at the protein level. The safety of targeting these antigens has yet to be demonstrated and therefore the identified transcripts should be considered preliminary candidates for new CAR and therapeutic antibody targets. Prospective candidate targets will be evaluated by proteomic analysis including Westerns and immunohistochemistry of normal and tumor tissues.

Isolated Hepatic Recurrence of Pre-B Cell ALL Masquerading as Veno-Occlusive Liver Disease

Isolated Hepatic Recurrence of Pre-B Cell ALL Masquerading as Veno-Occlusive Liver Disease

Adoptive Transfer of Primed CD62L+ T Cells Mediate Selective GVL In a Murine Model of Pediatric ALL

AbstractAbstract 2535 Background:While current upfront therapy will cure over 80% of patients with pediatric ALL, treating recurrence remains a major challenge. Blood or marrow transplantation (BMT) offers a curative option but approximately 50% of patients undergoing BMT will relapse. Donor lymphocyte infusions (DLIs) have demonstrated efficacy in myeloid leukemia but are much less effective for ALL. Strategies to improve the potency of DLI can result in GVHD and may compromise outcome. Thus, we explored strategies to improve on the potency and specificity of the graft versus leukemia response in a murine model of pediatric ALL. Methods:A transplantable cell line was generated from E2a-PBX1 transgenic mice (that express a recurring translocation t(1;19) present in approximately 5% of all pediatric ALL). Lethally irradiated C57Bl/6 (H2b) mice received T-cell-depleted C3H.SW (H2b, minor histocompatibility antigen miHA mismatch allogeneic) or C57Bl/6 (syngeneic) bone marrow followed by E2aPBX1 IV on day +6. A purified T cell DLI was given on day +7. DLI donors were primed with irradiated cells as indicated intraperitoneally 14 days prior to harvest. In some experiments T cell subsets were purified using magnetic beads. Results:E2a-PBX1 is a pre-B cell ALL that expresses B220, BP-1, CD43 and the alpha chain of the IL-7 receptor. The distribution of leukemia is similar to that observed in humans with bone marrow, lymph node, liver, spleen and central nervous system involvement confirmed by necropsy and imaging following injection of luciferase-expressing cells. Administration of naive T cells (6×106) following syngeneic or allogeneic BMT was not effective at treating E2a-PBX1 indicating that the presence of miHA did not increase the efficacy of naïve T cells consistent with the poor response rate to DLI in patients with ALL. However, primed T cell DLI (6×10ee6) from a donor immunized by irradiated E2a-PBX1 resulted in a statistically significant prolongation of survival in syngeneic (and cure in allogeneic BMT models suggesting the presence of tumor-specific antigens as well as a contribution from miHA. However, mice receiving sufficient primed allogeneic T cells for cure developed GVHD-associated weight loss and 40% late mortality (after 30 days). While purified, primed CD4 or CD8 T cells prevented GVHD associated mortality, 40–60% of mice developed leukemia. Remarkably, mice receiving magnetic-bead purified CD62L+ T cells from primed allogeneic donors were cured of leukemia with no GVHD-associated weight loss or mortality. Conclusion:Naïve T cells (analogous to DLI given post-relapse in the clinic) were ineffective at treating ALL our model. However, priming of allogeneic DLI donors with whole tumor cells results in cure but with the development of GVHD. CD62L+ expressing T cells from primed donors mediate curative GVL without GVHD. Disclosures:No relevant conflicts of interest to declare.

Hypercvad+Bortezomib Is a Well Tolerated Salvage Regimen for Relapsed/Refractory Adult Acute Lymphoblastic Leukemia

AbstractAbstract 4345We report the excellent tolerability of a regimen of HyperCVAD+Bortezomib for relapsed/refractory ALL in adults. The regimen consisted of addition of two doses of Bortezomib 2 mg(1mg/m2) on day 1 and day 4 of the HyperCVAD regimen(arm A). The doses of bortezomib were given an hour after the second dose of cyclophosphamide on day 1 and on day 4. GCSF 10 mcg/kg was used from nadir to recovery of ANC > 500. Two patients, one with relapsed ALL and the second with primary induction failure were treated with this regimen after informed consent. The first patient was a 38 year male who was diagnosed with Ph+ ALL four years ago and had relapsed three years later on maintenance treatment. He was subsequently treated with Adriamycin, Etoposide and Cyclophosphamide with minimal response. Last bone marrow showed 35–40% blasts. The second patient was 40 year female with CALLA + Pre-B cell ALL with primary induction failure with a BFM regimen. Both patient reached nadir counts by day 10–11 and recovered the absolute neutrophil counts > 500 by day 16. There was minimal blood product requirement and minimal episodes of neutropenic fever which were treated as per institutional protocol. All cultures were negative. Isolation was not required. Strict aseptic precautions were maintained. Minimal grade I mucositis occurred in the first patient. Minimal diarrhea with nausea and vomiting occurred in the second patient on day 15. No neuropathy was noted. On day +21, the first patient, who was resistant to multiple chemo agents still has 40% blasts in the marrow but also shows recovery of the normal marrow elements. The second patient, who had primary induction failure is in complete remission in the marrow. One report of a phase I trial by Messinger et al from Minnesota showed the feasibility and tolerability of Bortezomib added to VXLD in pediatric ALL. Horton et al from a COG phase I study did not find any objective responses to single agent Bortezomib in resistant leukemia even though it suppressed NfKB activity. This is the first report to our knowledge on the use of salvage bortezomib based regimen in relapsed/refractory adult ALL. We used low dose bortezomib(1 mg/m2) after the administration of chemotherapy on day 1 and day 4. The timing of bortezomib just after chemotherapy is probably important. One ASH abstract #949(2007) by Lonial et al suggested that Bortezomib following high dose melphalan in multiple myeloma results in increased apoptosis of MM cells than if Bortezomib precedes melphalan. We plan to proceed to a phase II trial to test this regimen in relapsed/refractory ALL. Disclosures:Off Label Use: Bortezomib as chemosensitizer with Hyper CVAD in ALL.

Romedepsin (RM), A Hdaci, Significantly Increases The Expression Of NKG2D Ligands, MIC A/B, In Leukemia/Lymphoma Cells (LL), In Part Through The Glycogen Synthase Kinase-3 (GSK-3) Pathway, Resulting In Enhanced NK Cytotoxicity: Translational Approach For Adoptive NK Cell Immunotherapy

Natural killer (NK) cells recognize malignant cells through the tumor-associated expression of NKG2D-ligands, including MIC A/B. However, tumor cells may shed MIC A/B and escape immuno- surveillance. Glycogen synthase kinase-3 (GSK-3), a constitutively active serine-threonine kinase with numerous functions including regulation of cellular differentiation, stress and apoptosis, also an important regulatory enzyme in the expression of MIC A/B in response to RM (Skov et al, Cancer Res, 2005). To determine the expression of MIC A/B in response to RM in various leukemia and lymphoma cells (LL), its influence on NK cell mediated cytotoxicity and to investigate the role of the GSK-3 pathway in the regulation of expression of MIC A/B in response to RM. LL cells (106/ml, RS 4:11 [MLL-ALL], REH [pre-B cell ALL], Jurkat [T-cell ALL], Toledo [DLBCL], Ramos [Burkitt's Lymphoma]) were exposed to RM (10 ng/mL) for 24 hours, followed by FACS staining with PE-conjugated anti-MIC A/B. Peripheral blood NK cells were isolated via magnetic separation followed by IL-2 activation. Cytotoxicity assays (europium assay) were performed at effector:target (E:T) ratio of 5-10:1. LL cells were also pre-treated for 1 hour with 100 mM lithium chloride (LiCl), a potent inhibitor of GSK-3 activity. Blocking studies were also performed with anti-NKG2D antibodies. MIC A/B expression significantly increased in LL cells in response to RM ([RS4:11 0.2% vs 82%, p< 0.0001], [REH 0.2% vs 46%, p= 0.0003], [Jurkat 1.12% vs 85%, p< 0.0001], [Toledo 0.5% vs 15.8%, p=0.0001], [Ramos 0.57% vs 67%, p=0.0003]). Enhanced expression of MIC A/B in response to RM was inhibited when LL cells are pre-treated with LiCl (Jurkat [RM vs RM+LiCl] 85% vs 18%, p<0.0001; RS 4:11 [RM vs RM+LiCl] 82% vs 5%, p<0.0001; Ramos [RM vs RM+LiCl] 67% vs 35%, p<0.0001). Cytotoxicity assays revealed significant increases in-vitro cytotoxicty in RS 4:11, Ramos and REH cells at E:T ratio of 5-10:1 (Table-1). NKG2D receptor-blocking resulted in significant decrease in NK cell mediated cytotoxicity in REH (p<0.03) and Ramos cells (p<0.001). In-vivo experiments are underway. Expression of MICA/B in LL cells is significantly increased by RM leading to enhanced susceptibility for NKG2D- MIC A/B mediated cytotoxicity by NK cells. Furthermore, up-regulation of MICA/B in LL cells secondary to RM exposure is in part regulated by the GSK-3 signal transduction pathway.Tabled 1Cell LineCondition RM - 10 ng/mlMean % Specific Release±SEM-E:T-5:1Mean % Specific Release±SEM-E:T-10:1P-valueRS4;11+NK(A)3.2%±2%10%±3%5:1-AvsC; BvsD - P<0.01; 10:1-AvsC; BvsD-p<0.05+NK+IL2(B)11%±3.3%12±4%+NK+IRM(C)78±42%108%±47%+NK_IL2+RM(D)123±48%145%±Ramos+NK(A)0.3%±0.3%7.6%±7.6%10:1-AvsC; BvsD - p<0.05+NK+IL2(B)16.3%±8.6%35.3%±13%+NK+IRM(C)62.6%±14%79.6%±15%+NK_IL2+RM(D)78.3%±26%90%±22%Jurkat+NK(A)22.2%±8%63.7%±22%5:1-AvsC; BvsD - p<0.01+NK+IL2(B)51%±11%102%±21%+NK+IRM(C)130%±14%174%±39%+NK_IL2+RM(D)174%±27%208%±34% Open table in a new tab

Romedepsin (RM), a HDACi, Significantly Increases the Expression of NKG2D Ligands, MIC A/B, in Leukemia/Lymphoma Cells (LL), in Part through the Glycogen Synthase Kinase-3 (GSK-3) Pathway, Resulting in Enhanced NK Cytotoxicity.

Abstract 3027Poster Board II-1003 IntroductionNatural killer (NK) cells recognize malignant cells through the tumor-associated expression of NKG2D-ligands, including MIC A/B, which are known to be expressed on epithelial tumors, resulting in tumor cytotoxicity (Ayello/Cairo et al, BBMT, 2006). The expression of MIC A/B on these tumors can be induced by in vitro exposure of these cells to HDACi, specifically Romedepsin (RM) (Skov et al, Cancer Res, 2005). Glycogen synthase kinase-3 (GSK-3), a constitutively active serine-threonine kinase with numerous functions including regulation of cellular differentiation, stress and apoptosis, has also been shown to be an important regulatory enzyme in the expression of MIC A/B in response to RM (Doble et al, J cell Sci 2003; Frame et al, Biochem J 2001; Skov et al, Cancer Res, 2005). ObjectiveWe sought to determine of the expression of MIC A/B in response to RM in various leukemia and lymphoma cells (LL), its influence on NK cell mediated cytotoxicity and to investigate the role of the GSK-3 pathway in the regulation of expression of MIC A/B in response to RM. MethodsLL cells (106/ml, RS 4:11 [MLL-ALL], REH [pre-B cell ALL], Jurkat [T-cell ALL], Toledo [DLBCL], Ramos [Burkitt's Lymphoma]) were exposed to RM (10 ng/mL) for 24 hours, followed by FACS staining with PE-conjugated anti-MIC A/B antibody to determine surface expression of MIC A/B. Peripheral blood NK cells (CD3-/56+) were isolated via magnetic separation followed by IL-2 activation (3000IU/ml, 18 hrs). LL cells exposed to RM (generously supplied by Gloucester Pharmaceuticals) were subjected to NK cell mediated cytotoxicity assays (using an europium assay) at effector:target (E:T) ratio of 10:1, as we had previously described (Ayello/Cairo et al, BBMT 2006). LL cells were also pre-treated for 1 hour with 100mM lithium chloride (LiCl), a potent inhibitor of GSK-3 activity (Davies et al, Biochem J, 2000), to determine the role of this regulatory enzyme in the RM mediated expression of MIC A/B in these LL cells. Finally, blocking studies were also performed with anti-NKG2D receptor blockers to determine the specific role of NKG2D signal transduction pathway in NK cell mediated cytotoxicity. ResultsMIC A/B expression significantly increased in LL cells in response to RM ([RS4:11 0.2% vs 19.2%, p< 0.0001], [REH 0.2% vs 46%, p= 0.0003], [Jurkat 1.12% vs 44.7%, p< 0.0001], [Toledo 0.5% vs 15.8%, p=0.0001], [Ramos 0.57% vs 33.6%, p=0.0003]). In addition, the expression of MIC A/B in response to RM was inhibited when LL cells are pre-treated with LiCl (Jurkat [RM vs RM+LiCl] 85% vs 18%, p<0.0001; RS 4:11 [RM vs RM+LiCl] 82% vs 5%, p<0.0001; Ramos [RM vs RM+LiCl] 67% vs 35%, p<0.0001). Cytotoxicity assays revealed significant increases in-vitro cytotoxicty in RS 4:11, Ramos and REH cells at E:T ratio of 10:1. Mean specific release (MSR)(±SEM) was measured for four conditions in the assay: NK cells (A) vs NK cells with 10 ng/ml RM (C) vs IL-2 activated NK cells (B) IL-2 activated NK cells +10 ng/ml of RM (D). MSR for RS 4:11 10%±3.6% vs 108%±47% and 12%±4% vs 145%±45% p<0.05(A vs C, B vs D) for RS 4;11. MSR for REH was 13.2%±14.4% vs 50%±17.6% and 22%±18% vs 132%±29% p<0.01(A vs C, B vs D). MSR for Ramos was 7.6%±7.6% vs 79%±15.6% and 35%±13% vs 90%±22% p<0.05(A vs C, B vs D). NKG2D receptor-blocking experiments resulted in significant decrease in NK cell mediated cytotoxicity in REH (p<0.03) and Ramos cells (p<0.001). ConclusionOur data suggests that the surface expression of MICA/B in LL cells is significantly increased by RM leading to enhanced susceptibility for NKG2D-mediated cytotoxicity by NK cells. Furthermore, up-regulation of MICA/B in LL cells secondary to RM exposure is in part regulated by the GSK-3 signal transduction pathway. DisclosuresNo relevant conflicts of interest to declare.

Adipocytes Secrete Factors That Cause Leukemia Drug Resistance.

We have previously shown that obesity is an independent predictor of leukemia relapse in children. We have also shown that obese mice transplanted with syngeneic leukemia cells have poorer survival after chemotherapy, even when they are dosed proportional to body weight. Since interactions between leukemia cells and cells of the bone marrow niche are considered important for chemotherapy resistance and relapse, and adipocytes can comprise ~50% of the bone marrow niche, we developed in vivo and in vitro models to investigate the role of adipocytes in the leukemia microenvironment.Obese C57Bl/6J mice were transplanted with GFP+ murine preB cell ALL (“8093”) cells and then treated with vincristine (0.5 mg/kg/week × 3 weeks). At the time of relapse, we found that GFP+ leukemia cells persisted in the fat pads of the mice. We then developed an in vitro co-culture system in which human or murine leukemia cells were cultured together with adipocytes (differentiated 3T3-L1s). Undifferentiated 3T3-L1 cells, which are fibroblastic in nature, were used as a control. In this model, adipocytes severely diminished the anti-leukemic effect of all chemotherapeutics tested against murine 8093 cells, including vincristine, dexamethasone, nilotinib, daunorubicin, and L-asparaginase. Adipocytes also protected murine T-cell ALL and human SD-1, RCH-ACV, and BV173 cells from vincristine and daunorubicin. Adipocyte protection of leukemia cells occurred independent of cell contact.Further experiments demonstrated that media conditioned by adipocytes was able to protect 8093 cells from a 3-day exposure to 25 nM dexamethasone (viable cells were at 40±12% of their plated value in regular media, 66±17% in fibroblast-conditioned media, and 109±24% in adipocyte-conditioned media, p<0.05). Surprisingly, adipocyte-conditioned media did not protect leukemia cells from daunorubicin. However, media conditioned by the presence of both adipocytes and leukemia cells simultaneously conferred a high degree of resistance to the leukemia cells (n=3, p<0.05 compared to all other media types).In summary, adipose tissue is a reservoir for relapsed leukemia cells in vivo. Adipocytes engender protection from multiple chemotherapies in murine and human leukemia cell lines. Adipocytes secrete factor(s) that confer dexamethasone and daunorubicin resistance to leukemia cells, though for the latter drug it appears that a two-way communication between leukemia and adipocytes may be necessary for this protection. [Display omitted]

Expression of CD66c and CD25 in acute lymphoblastic leukemia as a predictor of the presence of BCR/ABL rearrangement

Expression of myeloid or T cell lymphoid in precursor B cell acute lymphoblastic leukemia (pre-B cell ALL), which is referred to as aberrant expression, is quite a common phenomenon. CD66c is a myeloid marker which has aberrant expression in pre-B cell ALL, with strong correlation with non-random genetic changes (BCR/ABL rearrangement). Another leukemia associated marker (CD25) is frequently expressed in pre-B cell ALL. The frequency of CD25-expressing lymphoblasts has been found to be significantly higher in BCR/ABL-positive vs. BCR/ABL-negative patients. In a cohort of 103 patients diagnosed with pre-B cell ALL or biphenotypic leukemia and studied for expression of CD66c and CD25 at presentation, we evaluated the frequency of expression of either or both in BCR/ABL positive cases. Surface CD66c was expressed by 70 cases (68%) and CD25 was expressed by 33 cases (32%) while both were expressed together on 29 cases (28%). BCR/ABL was positive in 18/103 patients. All BCR/ABL positive cases were positive for surface CD66c and CD25. Positivity for both leukemia-associated antigens CD66c and CD25 in combination can predict the presence of BCR/ABL rearrangement in pre-B cell ALL. While this finding does not replace the detection of BCR/ABL abnormality by cytogenetic or molecular techniques, it does provide an early and handy tool for prediction and management of high-risk cases of pre-B cell ALL, especially in centers with limited laboratory facilities.

Ondansetron-associated Hypokalemia in a 2-year-old With Pre–B-cell ALL

Ondansetron is a commonly used medication in the treatment of nausea and vomiting arising from many etiologies, including chemotherapy. Although it is a highly safe drug, ondansetron use has been associated, rarely, with hypokalemia. However, it is unknown whether hypokalemia is due to the medication itself or to an underlying potassium disturbance caused by prior metabolic derangements, including vomiting. We relate a patient who presents with hypokalemia of unknown etiology, with evidence suggesting a possible relationship to ondansetron. We also present a proposed mechanism for this phenomenon.

Man with blurry vision

A 35 year-old Caucasian man with Pre-B cell ALL on day 197 post allogenic stem cell transplant and with a chest tube for pneumothorax post VATS was admitted for pain at his chest tube site. Sixteen days into his admission he developed acute onset of blurry vision. The patient first noticed some difficulty reading a wall clock when he woke up in the morning followed by a subsequent worsening of his visual acuity over the next eight hours. By late afternoon he could only detect light. Review of systems was significant only for an intermittent headache over the preceding week.

Outcome of Adults with Precursor B-Cell and Mature B-Cell (Burkitt-Cell) ALL/Lymphoma in a Large Inner City Hospital.

Acute lymphoblastic leukemia is the most common acute leukemia in children, but accounts for only about 20% of adult acute leukemias. In children overall survival at 5 years is about 70% as a result of intensive treatment regimens. Application of such treatment regimens to adults has improved the 5 year survival to about 30–35% in large studies. We report here a retrospective analysis of all 18 cases which presented to our hospital during the last 2 1/2 years. All patients were treated with intensive chemotherapy regimens (primarily Hyper CVAD alternating with MTX/AraC) including maintenance therapy for patients with precursor B-cell ALL. The mean age of all patients was 39.6 ± 15.2 years., 11 patients were male and 7 female. Thirteen patients presented with precursor B-cell ALL (8 male/5 female); the mean age of these patients was 36.3 ± 16.1 years. Five patients presented with Burkitt-cell leukemia (3 male/2 female), the mean age of these patients was 48 ± 8.9 years; 4 patients were HIV positive. Overall, 7 of 18 patients are alive, 5 are in remission, 1 did not achieve remission and is being evaluated for stem cell transplant, and 1 is completing the first cycle of chemotherapy. The 7 surviving patients include 5 with precursor B-cell ALL (4 male/1 female) and 2 Burkitt-cell patients (both female, both HIV+, both with CD4 count > 400). An analysis of high risk features in pre B-cell ALL patients showed only one patient older than 60, 1 with adverse cytogenetics (9:22 translocation), one with WBC count >50,000/ml at presentation, and 2 who required more than 1 course to achieve CR. Positivity for CD20 has been reported by some to be an adverse prognostic factor in pre B ALL. In our study 8 of 13 pre B ALL patients were CD20 positive, 3 of these patients survive as compared to 2 of 5 CD20 negative patients. Women with pre B ALL had significantly poorer outcomes than men with only 1 of 5 surviving; all women with CD20 positive disease succumbed. Among the Burkitt-cell patients, the 2 survivors were HIV positive women with the highest CD4 counts. Three of 18 patients (16.6%) died during induction; 1 presented to our hospital in first relapse 3 years after first CR, 1 developed overwhelming fungal infection, and 1 suffered probable anaphylactic reaction. More than 75% of patients with pre B ALL were Hispanic, and while 3 are still living, only one has completed induction and consolidation and is still in remission. The reasons behind the poor survival of the Hispanic subgroup are not clear, however, it should be noted that all patients who were CD20 positive in this group have either died or failed to achieve remission. In this series 27% of patients had mature B-cell disease, which is much higher than the 5% estimated incidence in adults overall. Despite the preponderance of HIV positive patients, the survival of these patients compares favorably with that reported in the literature.

Translocation (2;8)(p12;q24) associated with a cryptic t(12;21)(p13;q22) TEL/AML1 gene rearrangement in a child with acute lymphoblastic leukemia

We report a case of childhood acute lymphoblastic leukemia with the simultaneous occurrence of a t(2;8)(p12;q24) typically associated with mature B cell or Burkitt leukemia, and a t(12;21)(p13;q22) exclusively associated with pre-B cell ALL. The lymphoblasts were characterized as L2 morphology by the French–American–British classification. However, there were atypical morphologic findings for L2 ALL, including vacuolization in some cells. The lymphoblasts were periodic acid-Schiff positive and myeloperoxidase negative. Immunophenotypic analysis revealed that the majority of lymphoblasts were TdT+, CD10+, CD19+, CD20−, and cytoplasmic μ+. These features were consistent with an immature pre-B cell leukemia phenotype with some characteristics of a mature B-cell leukemia. A t(2;8)(p12;q24)(p12;q24), characteristic of mature B-cell leukemia or Burkitt type leukemia, was detected by conventional cytogenetics with no other cytogenetic abnormalities. However, diagnostic peripheral blood and bone marrow specimens demonstrated simultaneous occurrence of a cryptic t(12;21)(p13;q22) by both FISH and RT-PCR. The simultaneous occurrence of these translocations in a pediatric patient have implications for the pathogenesis of leukemias with t(2;8)(p12;q24) as well as t(12;21)(p12;q22). Analysis of additional cases of leukemia with translocations involving the MYC locus on 8q24 will be required to determine the frequency of association with the cryptic t(12;21)(p13;22), and the prognostic significance of the simultaneous occurrence of the translocations.

Pre-B acute lymphoblastic leukemia cells may induce T-cell anergy to alloantigen

Abstract Even if neoplastic cells express tumor associated antigens they still may fail to function as antigen presenting cells (APC) if they lack expression of one or more molecules critical for the induction of productive immunity. These cellular defects can be repaired by physiologic activation, transfection, or fusion of tumor cells with professional APC. Although such defects can be repaired, antitumor specific T cells may still fail to respond in vivo if they may have been tolerized. Here, human pre-B cell acute lymphoblastic leukemia (pre-B ALL) was used as a model to determine if primary human tumor cells can function as alloantigen presenting cells (alloAPC) or alternatively whether they induce anergy. In the present report, we show that pre-B cell ALL express alloantigen and adhesion molecules but uniformly lack B7–1 (CD80) and only a subset express B7–2 (CD86). Pre-B ALL cells are inefficient or ineffective alloAPC and those cases that lack expression of B7–1 and B7–2 also induce alloantigen specific T- cell unresponsiveness. Under these circumstances, T-cell unresponsiveness could be prevented by physiologic activation of tumor cells via CD40, cross-linking CD28, or signaling through the common gamma chain of the interleukin-2 receptor on T cells. Taken together, these results suggest that pre-B ALL may be incapable of inducing clinically significant T-cell-mediated antileukemia responses. This defect may be not only due to their inability to function as APC, but also due to their potential to induce tolerance. Attempts to induce clinically significant antitumor immune responses may then require not only mechanisms to repair the antigen presenting capacity of the tumor cells, but also reversal of tolerance.

Pre-B acute lymphoblastic leukemia cells may induce T-cell anergy to alloantigen

Even if neoplastic cells express tumor associated antigens they still may fail to function as antigen presenting cells (APC) if they lack expression of one or more molecules critical for the induction of productive immunity. These cellular defects can be repaired by physiologic activation, transfection, or fusion of tumor cells with professional APC. Although such defects can be repaired, antitumor specific T cells may still fail to respond in vivo if they may have been tolerized. Here, human pre-B cell acute lymphoblastic leukemia (pre-B ALL) was used as a model to determine if primary human tumor cells can function as alloantigen presenting cells (alloAPC) or alternatively whether they induce anergy. In the present report, we show that pre-B cell ALL express alloantigen and adhesion molecules but uniformly lack B7-1 (CD80) and only a subset express B7-2 (CD86). Pre-B ALL cells are inefficient or ineffective alloAPC and those cases that lack expression of B7-1 and B7-2 also induce alloantigen specific T-cell unresponsiveness. Under these circumstances, T-cell unresponsiveness could be prevented by physiologic activation of tumor cells via CD40, cross-linking CD28, or signaling through the common gamma chain of the interleukin-2 receptor on T cells. Taken together, these results suggest that pre-B ALL may be incapable of inducing clinically significant T-cell-mediated antileukemia responses. This defect may be not only due to their inability to function as APC, but also due to their potential to induce tolerance. Attempts to induce clinically significant antitumor immune responses may then require not only mechanisms to repair the antigen presenting capacity of the tumor cells, but also reversal of tolerance.

Identification of a novel human B cell activation antigen involved in B cell growth factor-dependent proliferation.

The B6.4 mAb we present here identifies a novel activation Ag of B cell lineage. The B6.4 mAb was generated by immunizing mice with B cell growth factor (BCGF)-responding BA3 cells, and selected by its capability to block BCGF-induced proliferation of BA3 cells. The inhibitory effect of this antibody on BCGF-dependent proliferation was further confirmed by using normal activated B cells in the presence of exogenous BCGF derived from T cells or B cells. Furthermore, it did not affect IL-2-dependent proliferation of B cells. The expression of the B6.4 Ag, as analyzed by FACS, is restricted to in vitro activated B cells, and remains undetectable on resting B or T cells, PHA-activated T cells, and monocytes. The B6.4 Ag is also expressed on some lymphoblastoid B cell lines and most of the lymphomas and CLL of B cell origin; however, it did not express on pre-B cell ALL and plasma cell leukemias. The B6.4 Ag has a Mr of 35,000 Da, as determined by SDS-PAGE of radiolabeled immunoprecipitates from activated B cells. The B6.4 Ag is detectable on B cells as early as 8 h after activation, and precedes that of the IL-2R or transferrin R. All of these results suggest that the B6.4 Ag is an early activation Ag of B cells and is functionally related to a receptor of BCGF, but not IL-2.