MEN1 mutations mediate clinical resistance to menin inhibition.

Chromatin-binding proteins are critical regulators of cell state in haematopoiesis1,2. Acute leukaemias driven by rearrangement of the mixed lineage leukaemia 1 gene (KMT2Ar) or mutation of the nucleophosmin gene (NPM1) require the chromatin adapter protein menin, encoded by the MEN1 gene, to sustain aberrant leukaemogenic gene expression programs3-5. In a phase 1 first-in-human clinical trial, the menin inhibitor revumenib, which is designed to disrupt the menin-MLL1 interaction, induced clinical responses in patients with leukaemia with KMT2Ar or mutated NPM1 (ref. 6). Here we identified somatic mutations in MEN1 at the revumenib-menin interface in patients with acquired resistance to menin inhibition. Consistent with the genetic data in patients, inhibitor-menin interface mutations represent a conserved mechanism of therapeutic resistance in xenograft models and in an unbiased base-editor screen. These mutants attenuate drug-target binding by generating structural perturbations that impact small-molecule binding but not the interaction with the natural ligand MLL1, and prevent inhibitor-induced eviction of menin and MLL1 from chromatin. To our knowledge, this study is the first to demonstrate that a chromatin-targeting therapeutic drug exerts sufficient selection pressure in patients to drive the evolution of escape mutants that lead to sustained chromatin occupancy, suggesting a common mechanism of therapeutic resistance.

BMP2/SMAD pathway activation in JAK2/p53-mutant megakaryocyte/erythroid progenitors promotes leukemic transformation.

Leukemic transformation (LT) of myeloproliferative neoplasm (MPN) has a dismal prognosis and is largely fatal. Mutational inactivation of TP53 is the most common somatic event in LT; however, the mechanisms by which TP53 mutations promote LT remain unresolved. Using an allelic series of mouse models of Jak2/Trp53 mutant MPN, we identify that only biallelic inactivation of Trp53 results in LT (to a pure erythroleukemia [PEL]). This PEL arises from the megakaryocyte-erythroid progenitor population. Importantly, the bone morphogenetic protein 2/SMAD pathway is aberrantly activated during LT and results in abnormal self-renewal of megakaryocyte-erythroid progenitors. Finally, we identify that Jak2/Trp53 mutant PEL is characterized by recurrent copy number alterations and DNA damage. Using a synthetic lethality strategy, by targeting active DNA repair pathways, we show that this PEL is highly sensitive to combination WEE1 and poly(ADP-ribose) polymerase inhibition. These observations yield new mechanistic insights into the process of p53 mutant LT and offer new, clinically translatable therapeutic approaches.

Plasmacytoid dendritic cell expansion defines a distinct subset of RUNX1-mutated acute myeloid leukemia.

Plasmacytoid dendritic cells (pDCs) are the principal natural type I interferon-producing dendritic cells. Neoplastic expansion of pDCs and pDC precursors leads to blastic plasmacytoid dendritic cell neoplasm (BPDCN), and clonal expansion of mature pDCs has been described in chronic myelomonocytic leukemia. The role of pDC expansion in acute myeloid leukemia (AML) is poorly studied. Here, we characterize patients with AML with pDC expansion (pDC-AML), which we observe in ∼5% of AML cases. pDC-AMLs often possess cross-lineage antigen expression and have adverse risk stratification with poor outcome. RUNX1 mutations are the most common somatic alterations in pDC-AML (>70%) and are much more common than in AML without pDC expansion and BPDCN. We demonstrate that pDCs are clonally related to, as well as originate from, leukemic blasts in pDC-AML. We further demonstrate that leukemic blasts from RUNX1-mutated AML upregulate a pDC transcriptional program, poising the cells toward pDC differentiation and expansion. Finally, tagraxofusp, a targeted therapy directed to CD123, reduces leukemic burden and eliminates pDCs in a patient-derived xenograft model. In conclusion, pDC-AML is characterized by a high frequency of RUNX1 mutations and increased expression of a pDC transcriptional program. CD123 targeting represents a potential treatment approach for pDC-AML.

Molecular predictors of immunophenotypic measurable residual disease clearance in acute myeloid leukemia.

Measurable residual disease (MRD) is a powerful prognostic factor in acute myeloid leukemia (AML). However, pre-treatment molecular predictors of immunophenotypic MRD clearance remain unclear. We analyzed a dataset of 211 patients with pre-treatment next-generation sequencing who received induction chemotherapy and had MRD assessed by serial immunophenotypic monitoring after induction, subsequent therapy, and allogeneic stem cell transplant (allo-SCT). Induction chemotherapy led to MRD- remission, MRD+ remission, and persistent disease in 35%, 27%, and 38% of patients, respectively. With subsequent therapy, 34% of patients with MRD+ and 26% of patients with persistent disease converted to MRD-. Mutations in CEBPA, NRAS, KRAS, and NPM1 predicted high rates of MRD- remission, while mutations in TP53, SF3B1, ASXL1, and RUNX1 and karyotypic abnormalities including inv (3), monosomy 5 or 7 predicted low rates of MRD- remission. Patients with fewer individual clones were more likely to achieve MRD- remission. Among 132 patients who underwent allo-SCT, outcomes were favorable whether patients achieved early MRD- after induction or later MRD- after subsequent therapy prior to allo-SCT. As MRD conversion with chemotherapy prior to allo-SCT is rarely achieved in patients with specific baseline mutational patterns and high clone numbers, upfront inclusion of these patients into clinical trials should be considered.

Drugging Chromatin in Cancer: Recent Advances and Novel Approaches.

Chromatin regulatory mechanisms play a major role in the control of gene expression programs during normal development and are disrupted in specific disease states, particularly in cancer. Important mediators of chromatin regulatory processes can broadly be classified into writers, erasers, and readers of covalent chromatin modifications that modulate eukaryotic gene transcription and maintain the integrity of the genome. The reversibility and disease-specific nature of these chromatin states make these regulators attractive therapeutic targets. As such, there is an ever-increasing number of candidate therapies aimed at targeting cancer-associated chromatin states that are in various stages of preclinical and clinical development. In this review, we discuss recent advances that have been made in the rational therapeutic targeting of chromatin regulatory mechanisms and highlight certain cancers where there is a specific rationale to assess these therapeutic approaches.

LSD1 inhibition exerts its antileukemic effect by recommissioning PU.1- and C/EBPα-dependent enhancers in AML.

Epigenetic regulators are recurrently mutated and aberrantly expressed in acute myeloid leukemia (AML). Targeted therapies designed to inhibit these chromatin-modifying enzymes, such as the histone demethylase lysine-specific demethylase 1 (LSD1) and the histone methyltransferase DOT1L, have been developed as novel treatment modalities for these often refractory diseases. A common feature of many of these targeted agents is their ability to induce myeloid differentiation, suggesting that multiple paths toward a myeloid gene expression program can be engaged to relieve the differentiation blockade that is uniformly seen in AML. We performed a comparative assessment of chromatin dynamics during the treatment of mixed lineage leukemia (MLL)-AF9-driven murine leukemias and MLL-rearranged patient-derived xenografts using 2 distinct but effective differentiation-inducing targeted epigenetic therapies, the LSD1 inhibitor GSK-LSD1 and the DOT1L inhibitor EPZ4777. Intriguingly, GSK-LSD1 treatment caused global gains in chromatin accessibility, whereas treatment with EPZ4777 caused global losses in accessibility. We captured PU.1 and C/EBPα motif signatures at LSD1 inhibitor-induced dynamic sites and chromatin immunoprecipitation coupled with high-throughput sequencing revealed co-occupancy of these myeloid transcription factors at these sites. Functionally, we confirmed that diminished expression of PU.1 or genetic deletion of C/EBPα in MLL-AF9 cells generates resistance of these leukemias to LSD1 inhibition. These findings reveal that pharmacologic inhibition of LSD1 represents a unique path to overcome the differentiation block in AML for therapeutic benefit.

Loss of plasmacytoid dendritic cell differentiation is highly predictive for post-induction measurable residual disease and inferior outcomes in acute myeloid leukemia.

Measurable residual disease is associated with inferior outcomes in patients with acute myeloid leukemia (AML). Measurable residual disease monitoring enhances risk stratification and may guide therapeutic intervention. The European LeukemiaNet working party recently came to a consensus recommendation incorporating leukemia associated immunophenotype-based different from normal approach by multi-color flow cytometry for measurable residual disease evaluation. However, the analytical approach is highly expertise-dependent and difficult to standardize. Here we demonstrate that loss of plasmacytoid dendritic cell differentiation after 7+3 induction in AML is highly specific for measurable residual disease positivity (specificity 97.4%) in a uniformly treated patient cohort. Moreover, loss of plasmacytoid dendritic cell differentiation as determined by a blast-to-plasmacytoid dendritic cell ratio >10 was strongly associated with inferior overall and relapse-free survival (RFS) [Hazard ratio 2.79, 95% confidence interval (95%CI): 0.98-7.97; P=0.077) and 3.83 (95%CI: 1.51-9.74; P=0.007), respectively), which is similar in magnitude to measurable residual disease positivity. Importantly, measurable residual disease positive patients who reconstituted plasmacytoid dendritic cell differentiation (blast/ plasmacytoid dendritic cell ratio <10) showed a higher rate of measurable residual disease clearance at later pre-transplant time points compared to patients with loss of plasmacytoid dendritic cell differentiation (blast/ plasmacytoid dendritic cell ratio <10) (6 of 12, 50% vs 2 of 18, 11%; P=0.03). Furthermore pre-transplant plasmacytoid dendritic cell recovery was associated with superior outcome in measurable residual disease positive patients. Our study provides a novel, simple, broadly applicable, and quantitative multi-color flow cytometry approach to risk stratification in AML.

CRISPR Dependency Screens in Primary Hematopoietic Stem Cells Identify KDM3B as a Genotype Specific Vulnerability in IDH2- and TET2-Mutant Cells.

Clonal hematopoiesis (CH) is a common premalignant state in the blood and confers an increased risk of blood cancers and all-cause mortality. Identification of therapeutic targets in CH has been hindered by the lack of an ex vivo platform amenable for studying primary hematopoietic stem and progenitor cells (HSPCs). Here, we utilize an ex vivo co-culture system of HSPCs with bone marrow endothelial cells to perform CRISPR/Cas9 screens in mutant HSPCs. Our data reveal that loss of the histone demethylase family members Kdm3b and Jmjd1c specifically reduces the fitness of Idh2- and Tet2-mutant HSPCs. Kdm3b loss in mutant cells leads to decreased expression of critical cytokine receptors including Mpl, rendering mutant HSPCs preferentially susceptible to inhibition of downstream JAK2 signaling. Our study nominates an epigenetic regulator and an epigenetically regulated receptor signaling pathway as genotype-specific therapeutic targets and provides a scalable platform to identify genetic dependencies in mutant HSPCs.

A study to assess the efficacy of enasidenib and risk-adapted addition of azacitidine in newly diagnosed IDH2-mutant AML.

ABSTRACT: Enasidenib (ENA) is an inhibitor of isocitrate dehydrogenase 2 (IDH2) approved for the treatment of patients with IDH2-mutant relapsed/refractory acute myeloid leukemia (AML). In this phase 2/1b Beat AML substudy, we applied a risk-adapted approach to assess the efficacy of ENA monotherapy for patients aged ≥60 years with newly diagnosed IDH2-mutant AML in whom genomic profiling demonstrated that mutant IDH2 was in the dominant leukemic clone. Patients for whom ENA monotherapy did not induce a complete remission (CR) or CR with incomplete blood count recovery (CRi) enrolled in a phase 1b cohort with the addition of azacitidine. The phase 2 portion assessing the overall response to ENA alone demonstrated efficacy, with a composite complete response (cCR) rate (CR/CRi) of 46% in 60 evaluable patients. Seventeen patients subsequently transitioned to phase 1b combination therapy, with a cCR rate of 41% and 1 dose-limiting toxicity. Correlative studies highlight mechanisms of clonal elimination with differentiation therapy as well as therapeutic resistance. This study demonstrates both efficacy of ENA monotherapy in the upfront setting and feasibility and applicability of a risk-adapted approach to the upfront treatment of IDH2-mutant AML. This trial is registered at www.clinicaltrials.gov as #NCT03013998.

Jak2V617F Reversible Activation Shows Its Essential Requirement in Myeloproliferative Neoplasms.

Gain-of-function mutations activating JAK/STAT signaling are seen in the majority of patients with myeloproliferative neoplasms (MPN), most commonly JAK2V617F. Although clinically approved JAK inhibitors improve symptoms and outcomes in MPNs, remissions are rare, and mutant allele burden does not substantively change with chronic therapy. We hypothesized this is due to limitations of current JAK inhibitors to potently and specifically abrogate mutant JAK2 signaling. We therefore developed a conditionally inducible mouse model allowing for sequential activation, and then inactivation, of Jak2V617F from its endogenous locus using a combined Dre-rox/Cre-lox dual-recombinase system. Jak2V617F deletion abrogates MPN features, induces depletion of mutant-specific hematopoietic stem/progenitor cells, and extends overall survival to an extent not observed with pharmacologic JAK inhibition, including when cooccurring with somatic Tet2 loss. Our data suggest JAK2V617F represents the best therapeutic target in MPNs and demonstrate the therapeutic relevance of a dual-recombinase system to assess mutant-specific oncogenic dependencies in vivo. SIGNIFICANCE: Current JAK inhibitors to treat myeloproliferative neoplasms are ineffective at eradicating mutant cells. We developed an endogenously expressed Jak2V617F dual-recombinase knock-in/knock-out model to investigate Jak2V617F oncogenic reversion in vivo. Jak2V617F deletion abrogates MPN features and depletes disease-sustaining MPN stem cells, suggesting improved Jak2V617F targeting offers the potential for greater therapeutic efficacy. See related commentary by Celik and Challen, p. 701. This article is featured in Selected Articles from This Issue, p. 695.

Single-cell genotypic and phenotypic analysis of measurable residual disease in acute myeloid leukemia.

Measurable residual disease (MRD), defined as the population of cancer cells that persist following therapy, serves as the critical reservoir for disease relapse in acute myeloid leukemia and other malignancies. Understanding the biology enabling MRD clones to resist therapy is necessary to guide the development of more effective curative treatments. Discriminating between residual leukemic clones, preleukemic clones, and normal precursors remains a challenge with current MRD tools. Here, we developed a single-cell MRD (scMRD) assay by combining flow cytometric enrichment of the targeted precursor/blast population with integrated single-cell DNA sequencing and immunophenotyping. Our scMRD assay shows high sensitivity of approximately 0.01%, deconvolutes clonal architecture, and provides clone-specific immunophenotypic data. In summary, our scMRD assay enhances MRD detection and simultaneously illuminates the clonal architecture of clonal hematopoiesis/preleukemic and leukemic cells surviving acute myeloid leukemia therapy.

Disabling Uncompetitive Inhibition of Oncogenic IDH Mutations Drives Acquired Resistance.

Mutations in IDH genes occur frequently in acute myeloid leukemia (AML) and other human cancers to generate the oncometabolite R-2HG. Allosteric inhibition of mutant IDH suppresses R-2HG production in a subset of patients with AML; however, acquired resistance emerges as a new challenge, and the underlying mechanisms remain incompletely understood. Here we establish isogenic leukemia cells containing common IDH oncogenic mutations by CRISPR base editing. By mutational scanning of IDH single amino acid variants in base-edited cells, we describe a repertoire of IDH second-site mutations responsible for therapy resistance through disabling uncompetitive enzyme inhibition. Recurrent mutations at NADPH binding sites within IDH heterodimers act in cis or trans to prevent the formation of stable enzyme-inhibitor complexes, restore R-2HG production in the presence of inhibitors, and drive therapy resistance in IDH-mutant AML cells and patients. We therefore uncover a new class of pathogenic mutations and mechanisms for acquired resistance to targeted cancer therapies. SIGNIFICANCE: Comprehensive scanning of IDH single amino acid variants in base-edited leukemia cells uncovers recurrent mutations conferring resistance to IDH inhibition through disabling NADPH-dependent uncompetitive inhibition. Together with targeted sequencing, structural, and functional studies, we identify a new class of pathogenic mutations and mechanisms for acquired resistance to IDH-targeting cancer therapies. This article is highlighted in the In This Issue feature, p. 1.

Interaction between myelodysplasia-related gene mutations and ontogeny in acute myeloid leukemia.

Accurate classification and risk stratification are critical for clinical decision making in patients with acute myeloid leukemia (AML). In the newly proposed World Health Organization and International Consensus classifications of hematolymphoid neoplasms, the presence of myelodysplasia-related (MR) gene mutations is included as 1 of the diagnostic criteria for AML, AML-MR, based largely on the assumption that these mutations are specific for AML with an antecedent myelodysplastic syndrome. ICC also prioritizes MR gene mutations over ontogeny (as defined in the clinical history). Furthermore, European LeukemiaNet (ELN) 2022 stratifies these MR gene mutations into the adverse-risk group. By thoroughly annotating a cohort of 344 newly diagnosed patients with AML treated at the Memorial Sloan Kettering Cancer Center, we show that ontogeny assignments based on the database registry lack accuracy. MR gene mutations are frequently observed in de novo AML. Among the MR gene mutations, only EZH2 and SF3B1 were associated with an inferior outcome in the univariate analysis. In a multivariate analysis, AML ontogeny had independent prognostic values even after adjusting for age, treatment, allo-transplant and genomic classes or ELN risks. Ontogeny also helped stratify the outcome of AML with MR gene mutations. Finally, de novo AML with MR gene mutations did not show an adverse outcome. In summary, our study emphasizes the importance of accurate ontogeny designation in clinical studies, demonstrates the independent prognostic value of AML ontogeny, and questions the current classification and risk stratification of AML with MR gene mutations.

Granzyme B is not required for regulatory T cell-mediated suppression of graft-versus-host disease.

Regulatory T (T(reg)) cells can suppress a wide variety of immune responses, including antitumor and alloimmune responses. The mechanisms by which T(reg) cells mediate their suppressive effects depend on the context of their activation. We previously reported that granzyme B is important for T(reg) cell-mediated suppression of antitumor immune responses. We therefore hypothesized that granzyme B may likewise be important for suppression of graft-versus-host disease (GVHD). We found that allogeneic mismatch induces the expression of granzyme B in mixed lymphocyte reactions and in a model of graft-versus-host disease (GVHD). However, wild-type and granzyme B-deficient T(reg) cells were equally able to suppress effector T (T(eff)) cell proliferation driven by multiple stimuli, including allogeneicantigen-presenting cells. Surprisingly, adoptive transfer of granzyme B-deficient T(reg) cells prevented GVHD lethality, suppressed serum cytokine production in vivo, and prevented target organ damage. These data contrast strikingly with our previous study, which demonstrated that granzyme B plays a nonredundant role in T(reg) cell-mediated suppression of antitumor responses. Taken together, these findings suggest that targeting specific T(reg) cell-suppressive mechanisms, such as granzyme B, may be therapeutically beneficial for segregating GVHD and graft-versus-tumor immune responses.

Targeting Lysine-Specific Demethylase 1 Rescues Major Histocompatibility Complex Class I Antigen Presentation and Overcomes Programmed Death-Ligand 1 Blockade Resistance in SCLC.

INTRODUCTION: SCLC is a highly aggressive neuroendocrine tumor that is characterized by early acquired therapeutic resistance and modest benefit from immune checkpoint blockade (ICB). Repression of the major histocompatibility complex class I (MHC-I) represents a key mechanism driving resistance to T cell-based immunotherapies. METHODS: We evaluated the role of the lysine-specific demethylase 1 (LSD1) as a determinant of MHC-I expression, functional antigen presentation, and immune activation in SCLC in vitro and in vivo through evaluation of both human SCLC cell lines and immunocompetent mouse models. RESULTS: We found that targeted inhibition of LSD1 in SCLC restores MHC-I cell surface expression and transcriptionally activates genes encoding the antigen presentation pathway. LSD1 inhibition further activates interferon signaling, induces tumor-intrinsic immunogenicity, and sensitizes SCLC cells to MHC-I-restricted T cell cytolysis. Combination of LSD1 inhibitor with ICB augments the antitumor immune response in refractory SCLC models. Together, these data define a role for LSD1 as a potent regulator of MHC-I antigen presentation and provide rationale for combinatory use of LSD1 inhibitors with ICB to improve therapeutic response in SCLC. CONCLUSIONS: Epigenetic silencing of MHC-I in SCLC contributes to its poor response to ICB. Our study identifies a previously uncharacterized role for LSD1 as a regulator of MHC-I antigen presentation in SCLC. LSD1 inhibition enables MHC-I-restricted T cell cytolysis, induces immune activation, and augments the antitumor immune response to ICB in SCLC.

Differential expression of granzyme B and C in murine cytotoxic lymphocytes.

Cytotoxic lymphocytes use the granule exocytosis pathway to kill pathogen-infected cells and tumor cells. Although many genes in this pathway have been extensively characterized (e.g., perforin, granzymes A and B), the role of granzyme C is less clear. We therefore developed a granzyme C-specific mAb and used flow cytometry to examine the expression of granzyme B and C in the lymphocyte compartments of wild-type and mutant GzmB(-/-) cre mice, which have a small deletion in the granzyme B gene. We detected granzyme B and C expression in CD4(+) and CD8(+) T cells activated with CD3/CD28 beads or MLRs. Stimulation of NK cells in vitro with IL-15 also induced expression of both granzymes. Granzyme C up-regulation was delayed relative to granzyme B in wild-type lymphocytes, whereas GzmB(-/-) cre cells expressed granzyme C earlier and more abundantly on a per-cell basis, suggesting that the deleted 350-bp region in the granzyme B gene is important for the regulation of both granzymes B and C. Quantitative RT-PCR revealed that granzyme C protein levels were regulated by mRNA abundance. In vivo, a population of wild-type CD8alphaalpha(+) intraepithelial lymphocytes constitutively expressed granzyme B and GzmB(-/-) cre intraepithelial lymphocytes likewise expressed granzyme C. Using a model of a persistent murine CMV infection, we detected delayed expression of granzyme C in NK cells from infected hosts. Taken together, these findings suggest that granzyme C is activated with persistent antigenic stimulation, providing nonredundant backup protection for the host when granzyme B fails.

Clinical and molecular predictors of response and survival following venetoclax therapy in relapsed/refractory AML.

Azacitidine + venetoclax, decitabine + venetoclax, and low-dose cytarabine + venetoclax are now standard treatments for newly diagnosed older or unfit patients with acute myeloid leukemia (AML). Although these combinations are also commonly used in relapsed or refractory AML (RR-AML), clinical and molecular predictors of response and survival in RR-AML are incompletely understood. We retrospectively analyzed clinical and molecular characteristics and outcomes for 86 patients with RR-AML who were treated with venetoclax combinations. The complete remission (CR) or CR with incomplete hematologic recovery (CRi) rate was 24%, and the overall response rate was 31% with the inclusion of a morphologic leukemia-free state. Azacitidine + venetoclax resulted in higher response rates compared with low-dose cytarabine + venetoclax (49% vs 15%; P = .008). Median overall survival (OS) was 6.1 months, but it was significantly longer with azacitidine + venetoclax compared with low-dose cytarabine + venetoclax (25 vs 3.9 months; P = .003). This survival advantage of azacitidine + venetoclax over low-dose cytarabine + venetoclax persisted when patients were censored for subsequent allogeneic stem cell transplantation (8.1 vs 3.9 months; P = .035). Mutations in NPM1 were associated with higher response rates, whereas adverse cytogenetics and mutations in TP53, KRAS/NRAS, and SF3B1 were associated with worse OS. Relapse was driven by diverse mechanisms, including acquisition of novel mutations and an increase in cytogenetic complexity. Venetoclax combination therapy is effective in many patients with RR-AML, and pretreatment molecular characteristics may predict outcomes. Trials that evaluate novel agents in combination with venetoclax therapy in patients with RR-AML that have adverse risk genomic features are warranted.

Venetoclax-based combinations in AML and high-risk MDS prior to and following allogeneic hematopoietic cell transplant.

The role of allogeneic hematopoietic cell transplant (allo-HCT) as consolidation after initial venetoclax therapy and the efficacy of venetoclax salvage therapy for relapse after allo-HCT in patients with acute myeloid leukemia (AML) are unclear. We conducted a retrospective study of patients with AML or myelodysplastic syndrome (MDS) who received venetoclax either before or after allo-HCT at Memorial Sloan Kettering Cancer Center and Yale University from 11 August 2016 to 16 November 2020. Among 39 heavily pretreated patients who received venetoclax before allo-HCT, median OS from allo-HCT was not reached after a median follow up of 12.5 months resulting in a 12-month OS estimate of 79.0%. In 37 patients who had received venetoclax-based combinations as salvage therapy after allo-HCT, the overall response rate was 32% with a median OS of 4.7 months (12-month OS estimate: 43.4%). Four patients underwent a second allo-HCT following venetoclax-based salvage therapy suggesting it as a potential salvage treatment option.