Nilotinib and donor lymphocyte infusion in the treatment of Philadelphia-positive acute lymphoblastic leukemia (Ph+ ALL) relapsing after allogeneic stem cell transplantation and resistant to imatinib

A critical review of management of allogeneic transplant-eligible adults with Ph+ acute lymphoblastic leukaemia

Acute lymphoblastic leukaemia (ALL) in 20%-30% of adult patients contains the Philadelphia (Ph+) chromosome. Historically, Ph+ ALL denoted a markedly inferior outcome and long-term survival in the absence of an allograft was uncommon. However, the advent of targeted therapy directed against the BCR::ABL1 fusion protein with various tyrosine kinase inhibitors (TKIs) has markedly improved the prognosis, resulting in a number of treatment controversies in allograft-eligible patients. Which is the best TKI to use in induction? What is the clinical relevance of the subdivision of Ph+ ALL into multilineage vs lymphoid types? Do all patients in first morphological complete remission (CR1) after induction and consolidation with chemotherapy/TKI require an allograft? If not, what risk factors predict a poor outcome without an allograft? Can chemotherapy-free approaches, such as blinatumomab in conjunction with more potent TKIs, obviate the need for an allograft in high-risk patients? What is the best strategy to deal with persistent or emerging minimal residual disease both pre- and post-transplant? Is maintenance TKI indicated in all patients post allograft? Can salvage therapy and a subsequent allograft cure patients who relapse after not being transplanted in CR1? This manuscript reviews the latest data influencing contemporary management and discusses these controversies.

20-Year Steady Increase in Survival of Adult Patients with Relapsed Philadelphia-Positive Acute Lymphoblastic Leukemia Post Allogeneic Hematopoietic Cell Transplantation

PURPOSE

Relapse after allogeneic hematopoietic cell transplantation (allo-HCT) remains the first cause of transplant failure in patients with Philadelphia-positive (Ph+) acute lymphoblastic leukemia (ALL). In other hematologic malignancies, therapeutic advances resulted in significant improvement over time in survival of patients relapsing after transplant.

EXPERIMENTAL DESIGN

We compared outcomes at European Society for Blood and Marrow Transplantation (EBMT) participating centers of 899 adult patients with Ph+ ALL who relapsed between 2000 and 2019 after allo-HCT performed in first complete remission. Median follow-up for alive patients was 56 months.

RESULTS

Overall, 116 patients relapsed between 2000 and 2004, 225 between 2005 and 2009, 294 between 2010 and 2014, and 264 between 2015 and 2019. Patient and transplant characteristics were similar over the four time periods except for a progressive increase in unrelated donors, peripheral blood stem cells, reduced intensity conditioning, and in vivo T-cell depletion and a progressive decrease in total body irradiation. The 2-year overall survival (OS) after relapse increased from 27.8% for patients relapsing between 2000 and 2004 to 54.8% for 2015 and 2019 (P = 0.001). A second allo-HCT within 2 years after relapse was performed in 13.9% of patients resulting in a 2-year OS of 35.9%. In multivariate analysis, OS from relapse was positively affected by a longer time from transplant to relapse and the year of relapse.

CONCLUSIONS

We observed a major progressive improvement in OS from posttransplant relapse for patients with Ph+ ALL over the years, likely multifactorial including transplant-related factors, posttransplant salvage, and improvement in supportive care. These large-scale real-world data can serve as a benchmark for future studies in this setting. See related commentary by Gale, p. 813.

Acute Lymphoblastic Leukemia, Version 2.2021, NCCN Clinical Practice Guidelines in Oncology

The NCCN Guidelines for Acute Lymphoblastic Leukemia (ALL) focus on the classification of ALL subtypes based on immunophenotype and cytogenetic/molecular markers; risk assessment and stratification for risk-adapted therapy; treatment strategies for Philadelphia chromosome (Ph)-positive and Ph-negative ALL for both adolescent and young adult and adult patients; and supportive care considerations. Given the complexity of ALL treatment regimens and the required supportive care measures, the NCCN ALL Panel recommends that patients be treated at a specialized cancer center with expertise in the management of ALL This portion of the Guidelines focuses on the management of Ph-positive and Ph-negative ALL in adolescents and young adults, and management in relapsed settings.

A new pre-emptive TKIs strategy for preventing relapse based on BCR/ABL monitoring for Ph+ALL undergoing allo-HCT: a prospective clinical cohort study

Relapse is a major cause of treatment failure in Philadelphia-chromosome-positive acute lymphoblastic leukemia (Ph+ALL) undergoing allogeneic hematopoietic cell transplantation (allo-HCT). This study aimed to evaluate the effect of a new pre-emptive tyrosine kinase inhibitors (TKIs) strategy on relapse in Ph+ALL patients with complete remission undergoing allo-HCT. Pre-emptive TKIs initiation was based on BCR/ABL molecular monitoring. TKIs choice was based on BCR/ABL mutations. Donor lymphocyte infusion was recommended in those with poor response to TKIs. Prophylactic TKIs from historical data were as control. The primary endpoint was relapse. One hundred and sixty-seven Ph+ALL patients were enrolled in this study, including 103 in the pre-emptive group and 64 in the prophylactic group. The 3-year cumulative incidence of relapse was 11% and 31% in the pre-emptive and prophylactic groups (P = 0.001), respectively. The 3-year overall survival (OS) was 87% and 66% (P = 0.001), and leukemia-free survival (LFS) was 83% and 61% (P = 0.000), respectively, in the pre-emptive and prophylactic groups. Multivariate analysis showed that the pre-emptive strategy was the protective factor for relapse, OS, and LFS (P = 0.005, P = 0.005, and P = 0.003, respectively). Our data suggest that this new pre-emptive TKIs strategy based on BCR/ABL molecular monitoring might reduce relapse and improve survival for Ph+ALL patients undergoing allo-HCT. ClinicalTrials.Gov Identifier (NCT01883219).

Second- and third-generation tyrosine kinase inhibitors for Philadelphia-positive adult acute lymphoblastic leukemia relapsing post allogeneic stem cell transplantation-a registry study on behalf of the EBMT Acute Leukemia Working Party

Second- and third-generation tyrosine kinase inhibitors (TKI) play an important role in the treatment of Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph + ALL). However, data on feasibility and efficacy of using these drugs for persisting or relapsed Ph + ALL after allogeneic stem cell transplantation (alloSCT) are scarce. Based on the EBMT Acute Leukemia Working Party registry, we evaluated the use of second-/third-generation TKI in 140 patients with Ph + ALL, suffering from measurable residual disease (MRD, n = 6), molecular relapse (MRel, n = 23), or hematological relapse (HRel, n = 111) following alloSCT. Treatment included dasatinib in 104, nilotinib in 18, or ponatinib in 18 patients. Forty-nine patients received TKI monotherapy, while 91 received additional treatment. Toxicity of second-/third-generation TKI post alloSCT was comparable to pretransplant use and could be managed with dose reduction or temporary discontinuation. Response rates were 71% (overall) and 61% (following TKI monotherapy). For the entire cohort, 2- and 5-year overall survival (OS) was 49% and 33%, respectively. OS was comparable among patients treated for persisting MRD/MRel and HRel. Among patients treated with TKI monotherapy, 2- and 5-year OS was 38% and 33%, respectively. The data underscore that second-/third-generation TKI are important compounds for the management of active Ph + ALL post alloSCT.

Long-Term Remission Achieved by Ponatinib and Donor Lymphocytes Infusion in a Ph+ Acute Lymphoblastic Leukemia Patient in Molecular Relapse After Allogenic Stem Cell Transplant and Dasatinib: A Case Report

Currently, the prognosis of Ph+ acute lymphoblastic leukemia (Ph+ ALL) patients relapsing after an allogenic hematopoietic stem cell transplantation (allo-SCT) remains poor, with few therapeutic options available. Here we present the case of a 32 years old patient with dasatinib-resistant post-transplant molecular relapse of ALL, who received, as second-line therapy, the combination of ponatinib and donor lymphocyte infusion (DLI). The therapy was safe and the patient achieved a sustained minimal residual disease negative disease, still ongoing after 22 months, which was accompanied by several changes in the immune populations distribution within the bone marrow (i.e., the increase in the CD8/CD4 lymphocytes ratio). Our report provides evidence of the efficacy of the third generation TKI inhibitor ponatinib in combination with DLI as second line therapy for Ph+ ALL relapsing after an allo-SCT.

Outcome of donor lymphocyte infusion for fall in chimerism after hematopoietic stem cell transplant

Achievement of complete donor chimerism after an allogeneic hematopoietic stem cell transplant is necessary for elimination of underlying malignant disease. A decline in donor chimerism may herald an impending relapse and therefore, early recognition and intervention plays an important role in such cases. A 32 year old male patient diagnosed as a case of Philadelphia positive mixed phenotypic acute leukaemia underwent peripheral blood hematopoietic stem cell transplant (HSCT) with his sibling as donor. During follow-up, a fall in donor chimerism was observed from 91.86% on day +37 to 88.83% on day +57 and 85.34% on day +77. Donor Lymphocyte Infusion (DLI) was harvested via apheresis. A dose of 1 × 10⁶ per kg was infused and the rest was cryopreserved in aliquots of escalating doses. On day +102, he presented with biopsy proven acute mucocutaneous GVHD grade 2 which was managed conservatively and donor chimerism of 57.99%. On day +126, a repeat donor chimerism was performed which showed 100% chimerism. He continues to do well at day +161. Timely use of DLI can improve donor chimerism in patients with Philadelphia positive acute leukaemia who tend to relapse after HSCT.

Additional Cytogenetic Abnormalities with Philadelphia Chromosome-Positive Acute Lymphoblastic Leukemia on Allogeneic Stem Cell Transplantation in the Tyrosine Kinase Inhibitor Era

Cytogenetic abnormalities are well known and powerful independent prognostic factors for various hematologic disorders. Although the combination of chemotherapy with tyrosine kinase inhibitor (TKI) is now considered the standard of care in patients with Philadelphia chromosome-positive acute lymphoblastic leukemia, little is known about the impact of additional cytogenetic abnormalities (ACAs). Therefore, we retrospectively evaluated 1375 adult patients who underwent their first allogeneic hematopoietic stem cell transplantation in the TKI era. In this study, 224 patients had ACAs (16.3%). The ACAs that were seen in more than 20 cases (1.5%) were as follows: -7, der(22), der(9), +8, and +X. Overall survival at 4 years was 56.9% (95% confidence interval [CI], 49.4% to 63.7%) in the group with ACAs and 60.5% (95% CI, 57.3% to 63.5%) in the group without ACAs (P = .266). The cumulative incidence of relapse at 4 years was 28.9% (95% CI, 22.6% to 35.6%) in the group with ACAs and 21.9% (95% CI, 19.4% to 24.6%) in the group with Ph alone (P = .051). In multivariate analyses there were no statistically significant differences in the risk of overall mortality or risk of relapse between the groups with and without ACAs. In the subgroup analyses of specific ACAs, although the presence of +8 was associated with a higher relapse rate in univariate and multivariate analyses, no specific ACA was associated with poor overall survival. Further studies will be needed to verify the impact of specific ACAs on transplantation outcomes.

Patients with Philadelphia-positive leukemia with BCR-ABL kinase mutations before allogeneic transplantation predominantly relapse with the same mutation

Despite the successes of tyrosine kinase inhibitors (TKIs) in improving outcomes in patients with chronic myeloid leukemia (CML) and Philadelphia-positive acute lymphoblastic leukemia (Ph + ALL), allogeneic hematopoietic stem cell transplantation (HSCT) continues to be an important and potentially curative option for selected patients with either disease. After HSCT, TKIs are increasingly being used to treat or prevent disease relapse, and practice patterns suggest that these TKIs are often chosen empirically without regard to pre-HSCT mutation status. We investigated whether ABL kinase domain mutations persist after transplantation and, thus, whether pre-HSCT mutation status should inform the selection of post-HSCT TKIs in these patients. We retrospectively analyzed adults who underwent allogeneic HSCT for CML and Ph + ALL at our institution between 2000 and 2010, and we identified subjects who had detectable BCR-ABL transcripts by polymerase chain reaction (PCR), as well as available RNA for Sanger sequencing of the ABL kinase domain, in both the pre- and post-HSCT settings. In total, 95 CML and 20 Ph + ALL patients with positive PCR transcripts were identified, of which 10 (10.5%) and 4 (20.0%), respectively, were found to have pre-HSCT ABL kinase mutations known to confer TKI resistance. In 9 (64.2%) of these 14 patients, the same kinase mutation was also detectable at an average time of 191 days after HSCT. Seven (50.0%) of the 14 harboring mutations had relapsed/refractory disease by last follow-up, of which, in retrospect, 6 had received a predictably ineffective TKI within the first 100 days after transplantation based on our mutation analysis. These data support the idea that pre-existing mutations in the ABL kinase domain, frequently associated with resistance to TKIs and prevalent in a transplantation population, are persistently detectable in the majority of patients after transplantation. We propose that such resistance patterns should be considered when selecting TKIs in the post-HSCT setting, including clinical trials of post-HSCT TKI prophylaxis.

Efficacy and pharmacologic data of second-generation tyrosine kinase inhibitor nilotinib in BCR-ABL-positive leukemia patients with central nervous system relapse after allogeneic stem cell transplantation

Central nervous system (CNS) involvement is a severe complication of BCR-ABL-positive leukemia after allogenic stem cell transplantation (alloSCT) associated with fatal outcome. Although second-generation tyrosine-kinase inhibitors (TKI) such as nilotinib have shown activity in systemic BCR-ABL⁺ disease, little data exists on their penetration and efficacy within the CNS. Four patients (3 male, 1 female; age 15–49) with meningeal relapse after alloSCT and subsequent treatment with nilotinib were identified. A total of 17 cerebrospinal fluid (csf) and serum samples were assessed for nilotinib concentration and patient outcome was recorded. Nilotinib concentrations showed a low median csf/plasma ratio of 0.53% (range 0.23–1.5%), yet pronounced clinical efficacy was observed with long-lasting responses (>1 year) in three patients. Comparison with historical data showed a trend towards superior efficacy of nilotinib versus imatinib. Despite poor csf penetration, nilotinib showed significant clinical activity in CNS relapse of BCR-ABL⁺ leukemias. As nilotinib has a high protein-binding affinity, the low-protein concentration in csf could translate into a relatively higher amount of free and therefore active nilotinib in csf as compared to blood, possibly explaining the observed efficacy. Thus, treatment with a 2nd generation TKI warrants further investigation and should be considered in cases of CNS relapse of BCR-ABL-positive leukemia after alloSCT.

Cellular therapy following allogeneic stem-cell transplantation

Allogeneic hematopoietic stem-cell transplantation (HSCT) is the most effective approach for many patients with hematologic malignancies. Unfortunately, relapse remains the most common cause of death after allogeneic HSCT, and the prognosis of relapsed disease is poor for most patients. Induction of a graft-versus-leukemia (GVL), or graft-versus-tumor, effect through the use of donor leukocyte infusion (DLI), or donor lymphocyte infusion, has been remarkably successful for relapsed chronic myelogenous leukemia. Unfortunately, response to DLI in other hematologic malignancies is much less common and depends on many factors including histology, pace and extent of relapse, and time from HSCT to relapse. Furthermore, graft-versus-host disease (GVHD) is common after DLI and often limits successful immunotherapy. Ultimately, manipulations to minimize GVHD while preserving or enhancing GVL are necessary to improve outcomes for relapse after allogeneic HSCT.

Randomized comparison of prophylactic and minimal residual disease-triggered imatinib after allogeneic stem cell transplantation for BCR-ABL1-positive acute lymphoblastic leukemia

Minimal residual disease (MRD) after allogeneic stem cell transplantation (SCT) for Ph+ acute lymphoblastic leukemia (ALL) is predictive of relapse. Imatinib administration subsequent to SCT may prevent relapse, but the role of scheduling and its impact on outcome are not known. In a prospective, randomized multicenter trial, we compared the tolerability and efficacy of post-transplant imatinib administered either prophylactically (arm A; n=26) or following detection of MRD (arm B; n=29). Prophylactic imatinib significantly reduced the incidence of molecular recurrence after SCT compared with MRD-triggered imatinib (40% vs 69%; P=0.046). Median duration of PCR negativity was 26.5 and 6.8 months, respectively (P=0.065). Five-year survival in both interventional groups was high (80 and 74.5%), despite premature discontinuation of imatinib in the majority of patients because of poor tolerability. Relapse probability was significantly higher in patients who became MRD positive (P=0.017). In conclusion, post-transplant imatinib results in a low relapse rate, durable remissions and excellent long-term outcome in patients with BCR-ABL1-positive ALL irrespective of whether it is given prophylactically or MRD-triggered. Reappearance of BCR-ABL1 transcripts early after SCT or at higher levels identifies a small subset of patients who do not benefit sufficiently from imatinib, and in whom alternative approaches should be explored.

Persistent complete molecular remission after nilotinib and graft-versus-leukemia effect in an acute lymphoblastic leukemia patient with cytogenetic relapse after allogeneic stem cell transplantation

We report the successful treatment and sustained molecular remission using single agent nilotinib in a relapsed Philadelphia chromosome positive (Ph+) acute lymphoblastic leukemia patient after allogeneic hematopoietic stem cell transplantation. Compared to previously published studies, this is the first report where a patient did not receive additional chemotherapy after relapse, nor did she receive donor lymphocyte infusions. With nilotinib, the patient reverted back to normal blood counts and 100% donor reconstitution by single tandem repeat (STR) chimerism analysis in the bone marrow and in peripheral blood, granulocytes, T and B-lymphocytes. This report also highlights the use of nilotinib in combination with extracorporeal photopheresis (ECP) for concomitant graft-versus-host disease. Our data suggests that ECP, together with nilotinib, did not adversely affect the overall Graft-versus-leukemia (GVL) effect.

BCR-ABL regulates death receptor expression for TNF-related apoptosis-inducing ligand (TRAIL) in Philadelphia chromosome-positive leukemia

Allogeneic stem cell transplantation (allo-SCT) is a potentially curative therapy for chronic myeloid leukemia and Philadelphia chromosome-positive (Ph(+)) acute lymphoblastic leukemia, and the graft-vs-leukemia (GVL) effect can eradicate residual leukemia after allo-SCT. Ph(+) leukemia cells frequently express death-inducing receptors (DR4 and DR5) for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), which is one of the cytotoxic ligands expressed on cytotoxic T cells and natural killer cells mediating the GVL effect. Here we demonstrate that imatinib specifically downregulated DR4 and DR5 expression in cell lines and clinical samples of Ph(+) leukemia. Second-generation tyrosine kinase inhibitors (dasatinib and nilotinib) and short hairpin RNA against bcr-abl also downregulated DR4 and DR5 expression in Ph(+) leukemia cells, and transfection of bcr-abl into a Ph(-) leukemia cell line induced DR4 and DR5 expression, which was abrogated by imatinib treatment. Accordingly, Ph(+) leukemia cells that had been pretreated with imatinib showed resistance to the pro-apoptotic activity of recombinant human soluble TRAIL. These observations demonstrate that BCR-ABL is critically involved in the leukemia-specific expression of DR4 and DR5 and in the susceptibility of Ph(+) leukemia to TRAIL-mediated anti-leukemic activity, providing new insight into the mechanisms of the tumor-specific cytotoxic activities of TRAIL.

Relapse after allogeneic stem cell transplantation

Since allogeneic stem cell transplantation (SCT) represents an intensive curative treatment for high-risk malignancies, its failure to prevent relapse leaves few options for successful salvage treatment. While many patients have a high early mortality from relapse, some respond and have sustained remissions, and a minority has a second chance of cure with appropriate therapy. The prognosis for relapsed hematological malignancies after SCT depends on four factors: the time elapsed from SCT to relapse (with relapses occurring within 6 months having the worst prognosis), the disease type (with chronic leukemias and some lymphomas having a second possibility of cure with further treatment), the disease burden and site of relapse (with better treatment success if disease is treated early), and the conditions of the first transplant (with superior outcome for patients where there is an opportunity to increase either the alloimmune effect, the specificity of the antileukemia effect with targeted agents or the intensity of the conditioning in a second transplant). These features direct treatments toward either modified second transplants, chemotherapy, targeted antileukemia therapy, immunotherapy or palliative care.

Approaches to relapse after allogeneic stem cell transplantation

PURPOSE OF REVIEW

Relapse has become the leading cause of death following allogeneic hematopoietic stem cell transplantation (HSCT). Despite improved understanding of the biology that underlies the graft-versus-leukemia/tumor effect the relapse rate did not decrease over the past 20 years. In general, prognosis is poor for patients who relapsed to an allograft since effective treatment options are limited. Here, we review the available and upcoming treatment approaches for relapse.

RECENT FINDINGS

Treatment of relapse after allogeneic HSCT has been rarely investigated systematically and results differ substantially from diseases. Withdrawal of immunosuppressive medication, donor lymphocyte infusions with or without chemotherapy and/or second allogeneic HSCT are the most used options. New specific cellular approaches such as disease-specific T-cells, alloreactive natural killer cells or vaccination strategies are under investigation. Novel agents such as tyrosine-kinase inhibitors, hypomethylating agents, monoclonal antibodies, immunomodulating drugs, or proteasome-inhibitors either alone or in combination with adoptive immunotherapy are upcoming promising options, but valid data are lacking so far.

SUMMARY

With some exceptions (chronic myeloid leukemia), treatment options for patients who relapse are limited. The results are poor and the majority of patients ultimately die of their disease. More effort and research is needed to prevent and treat relapse after allogeneic HSCT.

Allogeneic immunotherapy to optimize the graft-versus-tumor effect: concepts and controversies

Allogeneic stem cell transplantation (SCT) can be considered the most successful method of adoptive immunotherapy of cancer. It is successful in part because of the potent graft-versus-tumor (GVT) effects of the donor graft, which are independent of the conditioning regimen. This potent GVT reaction can be harnessed in some cases to treat patients who relapse after allogeneic SCT with the use of donor leukocyte infusions (DLIs). This has led to the rapid development of reduced-intensity conditioning (RIC) regimens for allogeneic SCT, an approach that relies primarily on GVT activity. However, the effects of GVT have clear disease specificity and remain associated with significant GVHD. Optimization of GVT induction will require a better understanding of the important target antigens and effector cells, as well as the development of methods that enhance GVT reactivity without excessive GVHD. The appropriate clinical setting and timing for GVT induction need to be defined more clearly, but ultimately, the immunologic control of cancer through allogeneic adoptive immunotherapy represents one of the most potent and promising therapeutic strategies for patients with hematologic malignancies.

NCI First International Workshop on the Biology, Prevention, and Treatment of Relapse after Allogeneic Hematopoietic Stem Cell Transplantation: Report from the Committee on Treatment of Relapse after Allogeneic Hematopoietic Stem Cell Transplantation

Relapse is a major cause of treatment failure after allogeneic hematopoietic stem cell transplantation (alloHSCT). Treatment options for relapse have been inadequate, and the majority of patients ultimately die of their disease. There is no standard approach to treating relapse after alloHSCT. Withdrawal of immune suppression and donor lymphocyte infusions are commonly used for all diseases; although these interventions are remarkably effective for relapsed chronic myelogenous leukemia, they have limited efficacy in other hematologic malignancies. Conventional and novel chemotherapy, monoclonal antibody therapy, targeted therapies, and second transplants have been utilized in a variety of relapsed diseases, but reports on these therapies are generally anecdotal and retrospective. As such, there is an immediate need for well-designed, disease-specific trials for treatment of relapse after alloHSCT. This report summarizes current treatment options under investigation for relapse after alloHSCT in a disease-specific manner. In addition, recommendations are provided for specific areas of research necessary in the treatment of relapse after alloHSCT.

Donor lymphocyte infusion for leukemia relapse after hematopoietic stem cell transplantation

Leukemia relapse is a serious therapeutic challenge following hematopoietic stem cell transplantation (HSCT). In this retrospective study, 23 patients [15 (65.2%) AML, 8 (34.8%) ALL] who received DLI+/-reinduction chemotherapy for post-transplant relapse were reviewed. The overall response rate of DLI was 66.7% for AML and 50% for ALL. A total of 15 patients (65.2%) developed acute graft versus host disease (GVHD). Response rates were higher in patients with GVHD (80% versus 25%; p=0.01; OR: 12.0). The probability of OS was better in patients who respond to DLI (p=0.04). Further strategies are required to improve the anti-tumor properties of alloreactive donor lymphocytes and to obtain durable responses with DLI in patients with relapsed acute leukemia after allogeneic HSCT.

Immunotherapy in acute leukemia

Recent advances in immunotherapy of cancer may represent a successful example in translational research, in which progress in knowledge and technology in immunology has led to new strategies of immunotherapy, and even past failures in many clinical trials have led to a better understanding of basic cancer immunobiology. This article reviews the latest concepts in antitumor immunology and its application in the treatment of cancer, with particular focus on acute leukemia.

Management of Philadelphia chromosome–positive acute lymphoblastic leukemia (Ph+ ALL)

The tyrosine kinase inhibitor (TKI) imatinib has become an integral part of front-line therapy for Ph+ ALL, with remission rates exceeding 90% irrespective of whether imatinib is given alone or combined with chemotherapy. Treatment outcome with imatinib-based regimens has improved compared with historic controls, but most patients who do not undergo allogeneic stem cell transplantation (SCT) eventually relapse. Acquired resistance on TKI treatment is associated with mutations in the bcr-abl tyrosine kinase domain in the majority of patients, and may be detected at low frequency prior to TKI treatment in a subset of patients. Second generation TKIs, eg, dasatinib and nilotinib, show activity against most of the bcr-abl tyrosine kinase domain (TKD) mutations involved in acquired imatinib resistance, but clinical benefit is generally short-lived. Accordingly, SCT in first complete remission (CR) is considered to be the best curative option. Molecular monitoring of minimal residual disease levels appears to have prognostic relevance and should be used to guide treatment. International standardization and quality control efforts are ongoing to ensure comparability of results. Mutation analysis during treatment relies increasingly on highly sensitive PCR techniques or denaturing HPLC and may assist in treatment decisions, eg, in case of molecular relapse. Results from current studies of second-generation TKI as front-line treatment for Ph+ ALL are promising and show high molecular response rates, but follow-up is still too short to determine their impact on remission duration and long-term survival. Strategies to improve outcome after SCT include the pre-emptive use of imatinib, which appears to reduce the relapse rate. In patients ineligible for transplantation, novel concepts for maintenance therapy are needed. These could involve novel immunotherapeutic interventions and combinations of TKI.