Long-term follow-up of CD19 chimeric antigen receptor T-cell therapy for relapsed/refractory acute lymphoblastic leukemia after allogeneic hematopoietic stem cell transplantation

Background aimsThe efficacy of CD19-targeted chimeric antigen receptor T (CAR T) cells for treatment of relapsed B-cell malignancies after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and the long-term outcomes of these patients remain inconclusive.MethodsThe authors focused on the survival of 35 patients with B-cell acute lymphoblastic leukemia who relapsed after allo-HSCT and received CAR T cells.ResultsOf the 34 eligible patients, 30 achieved minimal residual disease-negative complete remission (CR), with a total CR rate of 85.7% (79.8–91.6%). There were 14 patients who received various forms of additional therapy after achieving CR. After a median follow-up of 20.7 months, it was noted that 17 patients had relapsed at a median of 4.5 months (2–34 months). The cumulative recurrence rate (RR) at 18 months was 68.3% (57.6–79.0%). Additional treatment did not reduce the RR but seemed to delay the time to relapse (mean: 5.9 months vs 13.1 months; P = 0.046). Patients with a lower tumor burden (≤10%) had a lower RR (25.0% vs 78.6% at 12 months; P = 0.006). The overall survival (OS) rate for the CR patients was 30.0% (20.3–29.7%) at 18 months, with a median OS of 12.7 months.ConclusionsThe authors’ study indicated that for patients who relapsed after HSCT, although a high CR rate was achieved after CAR T therapy, the long-term efficacy was unsatisfactory. It is necessary to optimize additional treatment, including a second HSCT, to further improve long-term efficacy after CAR T infusion.     

Add-back of allodepleted donor T cells to improve immune reconstitution after haplo-identical stem cell transplantation

Poor immune reconstitution after haplo-identical stem cell transplantation results in high mortality from viral infections and relapse. One approach to overcome this problem is to deplete alloreactive cells selectively by deleting T cells activated by recipient stimulators, using an immunotoxin directed against the activation marker CD25. However, the degree of depletion of alloreactive cells is variable following stimulation with recipient PBMC, and this can result in GvHD. We have shown that using recipient EBV-transformed LCL as stimulators to activate donor alloreactive T cells results in more consistent depletion of in vitro alloreactivity while preserving T-cell responses to viral and potential myeloid tumor Ag. Based on these data, we have embarked on a phase I clinical dose escalation study of add-back of allo-LCL-depleted donor T cells in the haplo-identical setting, to determine if the allodepletion we achieve to allow infusion of sufficient T cells to restore useful antiviral/anti-leukemic responses without causing GvHD. Fifteen patients have so far been treated. The incidence of significant acute or chronic GvHD has been low (2/15), as has mortality from infection (1/15). Preliminary data show accelerated immune reconstitution in dose level 2 patients. Infused allodepleted donor T cells appear able to expand significantly in the face of viral reactivations, and doses as low as 3 x 10(5)/kg may be sufficient to confer useful antiviral immunity in this setting. At a median follow-up of 19.5 months, nine of 15 patients are alive and disease-free. Five patients have relapsed, all of whom have died.     

Inhibition of interleukin-2 receptor (CD25) expression induced on T cells from children with acute lymphoblastic leukemia

 Peripheral blood lymphocytes obtained from children with acute lymphoblastic leukemia (ALL) at onset were studied for the expression of interleukin-2 (IL-2) receptor α-chain (CD25) by two-color flow-cytometric analysis. Stimulated with anti-CD3 monoclonal antibody (mAb) alone, CD25 expression was significantly suppressed in CD4⁺ T cells from 27 of 48 (56.3%) cases and in CD8⁺ T cells from 29 of 48 (60.4%) cases. When stimulated with anti-CD3 mAb plus phorbol 12-myristate 13-acetate (PMA), CD25 expression was clearly restored in certain cases of ALL. When PMA plus ionomycin were used for stimulation of T cells, CD25 was inducible in a majority of cases. Interestingly CD25 expression upon anti-CD3 mAb stimulation was recovered after complete remission had been achieved. These observations suggest the presence in ALL children at onset of an in vitro defect in the signal transduction pathway of the T-cell-receptor/CD3 complex, resulting in inefficient CD25 expression. However, immune-staining analysis indicated that protein kinase C was normally translocated from the cytosol fraction to the cell membrane fraction. The mobilization of cytoplasmic free calcium is also normal. Received: 27 March 1996 / Accepted: 23 December 1996     

CD26 and DPP IV expression in T acute lymphoblastic leukemia cells: immunocytochemistry and enzyme cytochemistry

Recent studies have revealed the dipeptidyl peptidase IV (DPP IV) enzymatic activity of CD26 antigen. In this paper, the possible identity of DPP IV and CD26 expression in phenotypically defined T-ALL has been examined. The combination of enzyme cytochemistry and immunocytochemistry was used. The correlation between the CD26 antigen expression and DPP IV positivity in the vast majority of T lymphoblasts in T-ALL patients was observed. No CD26 was expressed on DPP IV negative T cells. The variable CD4 and/or CD8 antigen expression, frequent CD7 positivity and absence of membrane CD3 antigen expression were the characteristic immunophenotypic features of CD26/DPP IV positive T cells. CD26/DPP IV activity strongly paralleled the CD71 antigen (transferrin receptor, T cell activation/proliferation antigen) expression. The phenotypic features of CD26/DPP IV positive T cells are characteristic for the relative immature cell population. Noteworthy was the slight disassociation between the very high CD26 antigen J expression and moderate DPP IV activity in cells of some T-ALL patients. The possible existence of enzymatically inactive structures of CD26 antigen or inactive precursors of DPP IV detectable only by immunocytochemistry was discussed. Our study indicates that CD26 antigen expression is tended to identify cells with DPP IV enzymatic activity in T-ALL patients. The results provide information of CD26 antigen possible involvement in the pathology of leukemic cells via its DPP IV enzyme activity.     

Philadelphia chromosome-positive leukemia stem cells in acute lymphoblastic leukemia and tyrosine kinase inhibitor therapy

Leukemia stem cells(LSCs),which constitute a minority of the tumor bulk,are functionally defined on the basis of their ability to transfer leukemia into an immunodeficient recipient animal.The presence of LSCs has been demonstrated in acute lymphoblastic leukemia(ALL),of which ALL with Philadelphia chromosome-positive(Ph+).The use of imatinib,a tyrosine kinase inhibitor(TKI),as part of front-line treatment and in combination with cytotoxic agents,has greatly improved the proportions of complete response and molecular remission and the overall outcome in adults with newly diagnosed Ph+ ALL.New challenges have emerged with respect to induction of resistance to imatinib via Abelson tyrosine kinase mutations.An important recent addition to the arsenal against Ph+ leukemias in general was the development of novel TKIs,such as nilotinib and dasatinib.However,in vitro experiments have suggested that TKIs have an antiproliferative but not an antiapoptotic or cytotoxic effect on the most primitive ALL stem cells.None of the TKIs in clinical use target the LSC.Second generation TKI dasatinib has been shown to have a more profound effect on the stem cell compartment but the drug was still unable to kill the most primitive LSCs.Allogeneic stem cell transplantation(SCT) remains the only curative treatment available for these patients.Several mechanisms were proposed to explain the resistance of LSCs to TKIs in addition to mutations.Hence,TKIs may be used as a bridge to SCT rather than monotherapy or combination with standard chemotherapy.Better understanding the biology of Ph+ ALL will open new avenues for effective management.In this review,we highlight recent findings relating to the question of LSCs in Ph+ ALL.     

Malignant stem cells in childhood acute lymphoblastic leukemia: The stem cell concept revisited

We have recently shown that in childhood acute lymphoblastic leukemia (ALL) blasts at different stages of immunophenotypic maturation possess stem cell properties. Here, we discuss our results in the context of previous investigations of ALL stem cells and recent studies highlighting specific limitations of the xenotransplantation models for human hematopoietic cells. Leukemia-propagating stem cells in ALL may be more frequent than previously thought!     

CD40 stimulation induces differentiation of acute lymphoblastic leukemia cells into dendritic cells

Despite the very high percentage of long-term remissions in acute lymphoblastic leukemia (ALL) in children, some of them suffer from recurrence of the disease. New treatment modalities, e.g. effective geno- and immunotherapy are needed. The use of neoplasmatic cells to present tumor antigens is one of the approaches in cancer vaccines. ALL cells lack the expression of costimulatory molecules and are poor antigen presenting cells (APCs) for T-cell activation. CD40/40L interaction stimulates B-cells to proliferate, differentiate, upregulate costimulatory molecules and increase antigen presentation. The aim of the study was to test the hypothesis that ALL cells can be turned into professional APCs by CD40L activation. Children with B-cell precursor ALL were enrolled into the study. Mononuclear cells from bone marrow or peripheral blood were stimulated with CD40L and interleukin 4. Results: 1) after culture we noted upregulation of all assessed costimulatory, adhesion and activatory molecules i.e. CD1a, CD11c, CD40, CD54, CD80, CD83, CD86, CD123, HLA class I and II; 2) CD40L activated ALL cells induced proliferation of allogeneic T-cells (measured by [(3)H]thymidine incorporation). These results confirm the possibility of enhancing the immunogenicity of ALL cells with the CD40L system and indicate that this approach can be used in immunotherapeutic trials.     

Rearrangements of the T cell receptor delta gene in T acute lymphoblastic leukemia cells are distinct from those occurring in B lineage acute lymphoblastic leukemia and preferentially involve one V delta gene segment

Rearrangement of the TCR-delta gene was studied using J delta, C delta, and V delta probes in 61 cases of acute lymphoblastic leukemia (ALL) and several cases of chronic lymphoid neoplasms to define the specificity and the diversity of rearrangements occurring at the delta locus. TCR-delta rearrangements or deletions were found in all T (33 cases) and B lineage (28 cases) ALL but not in any case of B cell chronic proliferations (13 cases). The restriction patterns of rearrangement were clearly distinct between T and B ALL and use of one V delta probe showed that rearrangement of the V delta IDP2 gene segment which is also productively rearranged in the Peer cell line, occurred frequently in T-ALL but never in B lineage ALL. Studies of WT31 and delta TCS1 antibody reactivity showed that at least 4 of 13 CD3+ T-ALL cases expressed the delta protein. CD4 and/or CD8 Ag expression were observed in some of the gamma delta expressing T-ALL. These data show that particular TCR-delta gene rearrangements occur in neoplastic early B cells and that the combinatorial diversity of TCR-delta rearrangements in T cells is higher than initially expected. In addition this study shows that an important proportion of CD3 positive T-ALL cases express the gamma delta heterodimer.     

CD90 and CD110 correlate with cancer stem cell potentials in human T-acute lymphoblastic leukemia cells

Although cancer stem cells (CSCs) have been recently identified in myeloid leukemia, published data on lymphoid malignancy have been sparse. T-acute lymphoblastic leukemia (T-ALL) is characterized by the abnormal proliferation of T-cell precursors and is generally aggressive. As CD34 is the only positive-selection marker for CSCs in T-ALL, we performed extensive analysis of CD markers in T-ALL cell lines. We found that some of the tested lines consisted of heterogeneous populations of cells with various levels of surface marker expression. In particular, a small subpopulation of CD90 (Thy-1) and CD110 (c-Mpl) were shown to correlate with stem cell properties both in vitro and in transplantation experiments. As these markers are expressed on hematopoietic stem cells, our results suggest that stem cell-like population are enriched in CD90+/CD110+ fraction and they are useful positive-selection markers for the isolation of CSCs in some cases of T-ALL.     

CD9 correlates with cancer stem cell potentials in human B-acute lymphoblastic leukemia cells

Cancer stem cell (CSC) theory suggests that only a small subpopulation of cells having stem cell-like potentials can initiate tumor development. While recent data on acute lymphoblastic leukemia (ALL) are conflicting, some studies have demonstrated the existence of such cells following CD34-targeted isolation of primary samples. Although CD34 is a useful marker for the isolation of CSCs in leukemias, the identification of other specific markers besides CD34 has been relatively unsuccessful. To identify new markers, we first performed extensive analysis of surface markers on several B-ALL cell lines. Our data demonstrated that every B-ALL cell line tested did not express CD34 but certain lines contained cell populations with marked heterogeneity in marker expression. Moreover, the CD9⁺ cell population possessed stem cell characteristics within the clone, as demonstrated by in vitro and transplantation experiments. These results suggest that CD9 is a useful positive-selection marker for the identification of CSCs in B-ALL.     

Intracellular cytokine profile of T cells from children with acute lymphoblastic leukemia

Purpose: During an ongoing immune response, cytokines produced by T helper types 1 (Th1) and 2 (Th2) together with T cytotoxic types 1 (Tc1) and 2 (Tc2) are critical to the effectiveness of that response. Dysregulated expansion of one or the other subset may contribute to the impaired function of the T-cell-mediated immune system in cancer patients. In the present study we have investigated whether such dysregulation might exist in children with acute lymphoblastic leukemia (ALL). Methods: We analyzed 61 blood samples from 45 children with B cell precursor ALL and 16 healthy children. Interleukin(IL)-2, IL-4, and interferon γ (IFNγ) production of their respective purified CD4⁺ and CD8⁺ T cells were assessed at the single-cell level by intracellular-cytokine-staining flow cytometry. Results: At the time of diagnosis, IL-2-producing cell populations in CD4⁺ and CD8⁺ T cells were reduced below the normal range in 31 of 44 (70.5%) and 23 of 38 (60.5%) cases respectively. Similarly, IFNγ-producing cell populations in CD4⁺ and CD8⁺ T cells decreased in 17 of 44 (38.6%) and 18 of 38 (47.4%) cases respectively. Conversely cell populations capable of IL-4 production in CD4⁺ and CD8⁺ T cell subsets were increased in 13 of 30 (43.3%) and 15 of 30 (50.0%) cases respectively. Therefore, the Th1-to-Th2 and Tc1-to-Tc2 ratios (1.6 ± 2.2 and 7.7 ± 6.7 respectively) were significantly lower in peripheral blood T cells of ALL patients (n = 30) than those (6.0 ± 2.9 and 20.1 ± 10.3 respectively) in 15 healthy controls (P < 0.0001). Although both CD45RA⁺/CD4⁺ and CD45RA⁺/CD8⁺ cells significantly increased in 43 ALL patients (P < 0.05), there existed no apparent correlation between CD45 isoform expression and cytokine (IL-2 and IFNγ) production. Interestingly, the ability to produce both IL-2 and IFNγ was recovered in 8 cases examined, after complete remission had been achieved. Conclusion: These observations suggest that, in both CD4⁺ and CD8⁺ T cells of ALL patients, there is a dysregulation in the functionality of Th1 (Tc1) and Th2 (Tc2) cells with a gross reduction of Th1 (Tc1) cell populations and an expansion in Th2 (Tc2). Received: 12 November 1999 / Accepted: 2 January 2000     

Cytometric evaluation of transferrin receptor 1 (CD71) in childhood acute lymphoblastic leukemia

Transferrin receptor 1 (CD71) is a transmembrane glycoprotein responsible for cellular iron uptake. Higher expression of CD71 has been identified as a negative prognostic marker for numerous solid tumor types and for some lymphomas. The aim of this study was to evaluate CD71 expression on acute lymphoblastic leukemia (ALL) cells and to follow its possible clinical correlations. Sixty one patients, aged 1-17 years and diagnosed with ALL, were enrolled in the study. CD71 expression was analyzed on the bone marrow blastic cells by flow cytometry. CD71 expression on the leukemic blasts was diversified; in most patients, all blastic cells showed expression of CD71, but levels of expression varied. CD71 expression was statistically higher on T-lineage leukemias. Within the B lineage ALL, a significant difference in CD71 expression existed between precursor B ALL and mature B-ALL, which showed higher CD71 expression. CD71 expression positively correlated with Hgb concentration at diagnosis. Initial risk group assessment and therapy response were not correlated with CD71 expression, although disease free and overall survival times tended to be shorter in patients with B-lineage leukemias with initial high CD71 expression.     

Adoptive transfer of T cells transduced with a chimeric antigen receptor to treat relapsed or refractory acute leukemia: efficacy and feasibility of immunotherapy approaches

Treatment outcomes of acute leukemia(AL) have not improved over the past several decades and relapse rates remain high despite the availability of aggressive therapies. Conventional relapsed leukemia treatment includes second allogeneic hematopoietic stem cell transplantation(allo-HSCT) and donor lymphocyte infusion(DLI), which in most cases mediate, at best, a modest graft-versus-leukemia effect, although their clinical efficacy is still limited. Although allo-HSCT following myeloablative conditioning is a curative treatment option for younger patients with acute myeloid leukemia(AML) in a first complete remission(CR), allo-HSCT as a clinical treatment is usually limited because of treatment-related toxicity. The overall DLI remission rate is only 15%–42% and 2-year overall survival(OS) is approximately 15%–20%, with a high(40%–60%) incidence of DLI-related graft-versus-host disease(GVHD). Therefore, development of new, targeted treatment strategies for relapsed and refractory AL patients is ongoing. Adoptive transfer of T cells with genetically engineered chimeric antigen receptors(CARs) is an encouraging approach for treating hematological malignancies. These T cells are capable of selectively recognizing tumor-associated antigens and may overcome many limitations of conventional therapies, inducing remission in patients with chemotherapy-refractory or relapsed AL. In this review, we aimed to highlight the current understanding of this promising treatment modality, discussing its adverse effects and efficacy.     

Bortezomib enhances cytotoxicity of ex vivo-expanded gamma delta T cells against acute myeloid leukemia and T-cell acute lymphoblastic leukemia

Engagement between the natural killer group 2, member D (NKG2D) receptor and its ligands is one of the main mechanisms used by immune cells to target stressed cells for cell death. NKG2D ligands are known markers of cellular stress and are often upregulated on tumor cells. Certain drugs can further increase NKG2D ligand levels, thereby making tumor cells more susceptible to immune cell detection and destruction. However, the effectiveness of this approach appears to be limited with drug treatment alone, possibly due to immune dysregulation in the setting of malignancies. We hypothesized that a more effective approach would be a combination of NKG2D ligand-inducing drugs, such as the proteasome inhibitor bortezomib, and ex vivo-expanded peripheral blood γδ T cells (i.e., Vγ9Vδ2 T cells). Acute myeloid leukemia (AML) is a high-risk hematologic malignancy, and treatment has shown limited benefit with the addition of bortezomib to standard chemotherapy regimens. Two AML cells lines, Nomo-1 and Kasumi-1, were treated with increasing concentrations of bortezomib, and changes in NKG2D ligand expression were measured. Bortezomib treatment significantly increased expression of the NKG2D ligand UL16 binding protein (ULBP) 2/5/6 in both cell lines. Vγ9Vδ2 T cells were expanded and isolated from peripheral blood of healthy donors to generate a final cellular product with a mean of 96% CD3⁺/γδ T-cell receptor-positive cells. Combination treatment of the AML cell lines with γδ T cells and bortezomib resulted in significantly greater cytotoxicity than γδ T cells alone, even at lower effector-to-target ratios. Based on the positive results against AML and the generalizable mechanism of this combination approach, it was also tested against T-cell acute lymphoblastic leukemia (T-ALL), another high-risk leukemia. Similarly, bortezomib increased ULBP 2/5/6 expression in T-ALL cell lines, Jurkat and MOLT-4 and improved the cytotoxicity of γδ T cells against each line. Collectively, these results show that bortezomib enhances γδ T-cell-mediated killing of both AML and T-ALL cells in part through increased NKG2D ligand-receptor interaction. Furthermore, proof-of-concept for the combination of ex vivo-expanded γδ T cells with stress ligand-inducing drugs as a therapeutic platform for high-risk leukemias is demonstrated.     

Characterization of an acute T lymphoblastic leukemia expressing the gamma/delta T-cell receptor

Leukemic cells of a 20 year old patient, suffering from acute lymphoblastic leukemia, were characterized by surface marker and functional analysis. A significant cell population within this type of leukemia expresses concomitantly the CD4 and CD8 antigen on the same cell and might represent a new differentiation stage of T-cells with the gamma/delta receptor. The leukemic cells show a distinct pattern of growth response to mitogens and lymphokines, which might correlate to their differentiation stage. Moreover, a "natural killer"-like activity can be induced in these cells by IL-2.     

The clinical outcomes of fresh versus cryopreserved CD19-directed chimeric antigen receptor T cells in non-Hodgkin lymphoma patients

CD19-directed chimeric antigen receptor T (CAR-T) cells have been widely reported in the therapy of relapsed/refractory non-Hodgkin lymphoma (NHL). Both cryopreserved and fresh formulations of CAR-T have been used in previous studies. However, quite a few studies investigated the effects of cryopreservation on the clinical outcomes of CAR-T cells. Here we retrospectively analyzed a phase I/II clinical trial of CD19-directed CAR-T cells in NHL patients, and compared the safety and efficacy of cryopreserved and fresh CAR-T products. All CAR-T cells were prepared using the same manufacturing process except the formulation step. Fifteen patients were infused with cryopreserved/thawed CAR-T cells, and 8 patients were treated with fresh CAR-T cells. Comparative overall response rates and in vivo expansion kinetics of CAR-T cells were observed between the cryopreserved cohort and fresh cohort. The occurrence rates of cytokine release syndrome and neurotoxicity were also similar in both groups. Patients in the fresh cohort showed higher incidence of acute hematological toxicity including anemia, hypoleukemia, and thrombocytopenia. This study demonstrated that cryopreservation showed negligible effects on the efficacy of CD19-directed CAR-T cells, but endowed CAR-T cells with higher safety in NHL patients, supporting the application of cryopreserved CAR-T products for NHL therapy.     

Stimulation of the beta-subunit of the IL-2 receptor induces MHC-unrestricted cytotoxicity in T acute lymphoblastic leukemia cells and normal thymocytes

Recently, several laboratories have identified a novel protein(s) of 70,000 to 75,000 Da (IL-2R beta-subunit) that, when expressed with the p55 Tac protein (alpha-subunit), imparts high affinity IL-2 binding. Expression of the beta-subunit mediates acquisition of MHC-unrestricted cytotoxicity in large granular lymphocytes. We report that thymocytes and T acute lymphoblastic leukemia cells express the beta-subunit of the IL-2R in the absence of detectable alpha-subunit expression and that IL-2 induces acquisition of MHC-unrestricted cytotoxic activity in these cells through stimulation of the beta-subunit.     

Requirement for NK cells in CD40 ligand-mediated rejection of Philadelphia chromosome-positive acute lymphoblastic leukemia cells.

We have previously developed a murine model of Philadelphia chromosome-positive acute lymphoblastic leukemia by i.v. injection of a pre-B ALL cell line (BM185) derived from Bcr-Abl-transformed BALB/c bone marrow. We are studying the potential to elicit autologous antileukemic immune responses by introducing genes encoding immunomodulators (CD40 ligand (CD40L), CD80, and GM-CSF) into leukemia cells. BM185 cells expressing CD40L or CD80 alone, when injected into BALB/c mice, were rejected in approximately 25% of mice, whereas cohorts receiving BM185 cells expressing two or more immunomodulator genes rejected challenge 50-76% of the time. The greatest protection was conferred in mice receiving BM185 cells expressing all three immunomodulators. Addition of murine rIL-12 treatments in conjunction with BM185/CD80/CD40L/GM-CSF vaccination allowed rejection of preestablished leukemia. BM185 cell lines expressing CD40L were rejected in BALB/c nu/nu (nude) mice, in contrast to cell lines expressing CD80 and/or GM-CSF. Nude mice depleted of NK cells were no longer protected when challenged with BM185/CD40L, demonstrating a requirement for NK cells. Similarly, NK cell depletion in immunocompetent BALB/c mice resulted in a loss of protection when challenged with BM185/CD40L, confirming the data seen in nude mice. The ability of CD40L to act in a T cell-independent manner may be important for clinical applications in patients with depressed cellular immunity following chemotherapy.     

Closed-system manufacturing of CD19 and dual-targeted CD20/19 chimeric antigen receptor T cells using the CliniMACS Prodigy device at an academic medical center

Background aims

Multiple steps are required to produce chimeric antigen receptor (CAR)-T cells, involving subset enrichment or depletion, activation, gene transduction and expansion. Open processing steps that increase risk of contamination and production failure are required. This complex process requires skilled personnel and costly clean-room facilities and infrastructure. Simplified, reproducible CAR-T-cell manufacturing with reduced labor intensity within a closed-system is highly desirable for increased availability for patients.

Efficacy of low dose clofarabine in refractory precursor T- acute lymphoblastic leukemia

Refractory T-lymphoblastic leukemia in adults has a poor prognosis in patients who relapse after allogeneic stem cell transplantation, and relatively few new agents have demonstrated activity. Clofarabine is a novel nucleoside analog that has been associated with significant clinical activity in relapsed pediatric B-ALL. We used low dose clofarabine and induced a remission in a patient who relapsed in the skin and marrow after allogeneic transplant and was refractory to nelarabine and report a near complete response, suggesting significant activity for low intermittent dose clofarabine in patients with relapsed T-cell leukemias.