A CD38-directed, single-chain T-cell engager targets leukemia stem cells through IFN-γ-induced CD38 expression.

ABSTRACT: Treatment resistance of leukemia stem cells (LSCs) and suppression of the autologous immune system represent major challenges to achieve a cure in acute myeloid leukemia (AML). Although AML blasts generally retain high levels of surface CD38 (CD38pos), LSCs are frequently enriched in the CD34posCD38neg blast fraction. Here, we report that interferon gamma (IFN-γ) reduces LSCs clonogenic activity and induces CD38 upregulation in both CD38pos and CD38neg LSC-enriched blasts. IFN-γ-induced CD38 upregulation depends on interferon regulatory factor 1 transcriptional activation of the CD38 promoter. To leverage this observation, we created a novel compact, single-chain CD38-CD3 T-cell engager (BN-CD38) designed to promote an effective immunological synapse between CD38pos AML cells and both CD8pos and CD4pos T cells. We demonstrate that BN-CD38 engages autologous CD4pos and CD8pos T cells and CD38pos AML blasts, leading to T-cell activation and expansion and to the elimination of leukemia cells in an autologous setting. Importantly, BN-CD38 engagement induces the release of high levels of IFN-γ, driving the expression of CD38 on CD34posCD38neg LSC-enriched blasts and their subsequent elimination. Critically, although BN-CD38 showed significant in vivo efficacy across multiple disseminated AML cell lines and patient-derived xenograft models, it did not affect normal hematopoietic stem cell clonogenicity and the development of multilineage human immune cells in CD34pos humanized mice. Taken together, this study provides important insights to target and eliminate AML LSCs.

Copper 64-labeled daratumumab as a PET/CT imaging tracer for multiple myeloma.

As a growing number of patients with multiple myeloma (MM) respond to upfront therapies while eventually relapsing in a time frame that is often unpredictable, attention has increasingly focused on developing novel diagnostic criteria to also account for disease dissemination. Positron emission tomography/computed tomography (PET/CT) is often used as a noninvasive monitoring strategy to assess cancer cell dissemination, but because the uptake of the currently used radiotracer 18fluorodeoxyglucose (18F-FDG) is a function of the metabolic activity of both malignant and nonmalignant cells, the results frequently lack sufficient specificity. Radiolabeled antibodies targeting MM tissue may detect disease irrespective of cell metabolism. Hence, we conjugated the clinically significant CD38-directed human antibody daratumumab (Darzalex [Dara]) to the DOTA chelator and labeled it with the positron-emitting radionuclide copper 64 (64Cu; 64Cu-DOTA-Dara). Here, we show that 64Cu-DOTA-Dara can efficiently bind CD38 on the surface of MM cells and was mainly detected in the bones associated with tumor in a MM murine model. We also show that PET/CT based on 64Cu-DOTA-Dara displays a higher resolution and specificity to detect MM cell dissemination than does 18F-FDG PET/CT and was even more sensitive than were bioluminescence signals. We therefore have supporting evidence for using 64Cu-DOTA-Dara as a novel imaging agent for MM.

Outcomes of Haploidentical Transplantation in Patients with Relapsed Multiple Myeloma: An EBMT/CIBMTR Report.

Allogeneic hematopoietic cell transplantation (allo-HCT) using siblings and matched donors has the potential for long-term disease control in a subset of high-risk patients with multiple myeloma (MM); however, the data on using haploidentical donors in this disease are limited. We conducted a retrospective analysis to examine the outcomes of patients with MM who underwent haploidentical allo-HCT within European Society for Blood and Marrow Transplantation/Center for International Blood and Marrow Transplant Research centers. A total of 96 patients underwent haploidentical allo-HCT between 2008 and 2016. With a median follow-up of 24.0 months (range, 13.2 to 24.9 months), 97% (95% confidence interval [CI], 93% to 100%) of patients had neutrophil engraftment by day 28, and 75% (95% CI, 66% to 84%) achieved platelet recovery by day 60. Two-year progression-free survival (PFS) was 17% (95% CI, 8% to 26%), and overall survival (OS) was 48% (95% CI, 36% to 59%). At 2 years, the cumulative risk of relapse/progression was 56% (95% CI, 45% to 67%), and 1-year nonrelapse mortality (NRM) was 21% (95% CI, 13% to 29%). The incidences of acute graft-versus-host-disease (GVHD) grades II-IV by 100 days and chronic GVHD at 2 years were 39% (95% CI, 28% to 49%) and 46% (95% CI, 34% to 59%), respectively. On univariate analysis, use of post-transplantation cyclophosphamide (PT-Cy) (54% [95% CI, 41% to 68%] versus 25% [95% CI, 1% to 48%]; P =.009) and use of bone marrow as source of stem cells (72% [95% CI, 55% to 89%] versus 31% [95% CI, 17% to 46%]; P = .001) were associated with improved OS at 2 years. Disease status, patient sex, intensity of conditioning regimen, recipient/donor sex mismatch, and cytomegalovirus serostatus had no impact on OS, PFS, or NRM. Haploidentical transplantation is feasible for patients with multiply relapsed or high-risk MM, with an encouraging 2-year OS of 48% and an NRM of 21% at 1 year, supporting further investigation of haploidentical allo-HCT in suitable candidates with MM.

Optimization of IL13Rα2-Targeted Chimeric Antigen Receptor T Cells for Improved Anti-tumor Efficacy against Glioblastoma.

T cell immunotherapy is emerging as a powerful strategy to treat cancer and may improve outcomes for patients with glioblastoma (GBM). We have developed a chimeric antigen receptor (CAR) T cell immunotherapy targeting IL-13 receptor α2 (IL13Rα2) for the treatment of GBM. Here, we describe the optimization of IL13Rα2-targeted CAR T cells, including the design of a 4-1BB (CD137) co-stimulatory CAR (IL13BBζ) and a manufacturing platform using enriched central memory T cells. Utilizing orthotopic human GBM models with patient-derived tumor sphere lines in NSG mice, we found that IL13BBζ-CAR T cells improved anti-tumor activity and T cell persistence as compared to first-generation IL13ζ-CAR CD8+ T cells that had shown evidence for bioactivity in patients. Investigating the impact of corticosteroids, given their frequent use in the clinical management of GBM, we demonstrate that low-dose dexamethasone does not diminish CAR T cell anti-tumor activity in vivo. Furthermore, we found that local intracranial delivery of CAR T cells elicits superior anti-tumor efficacy as compared to intravenous administration, with intraventricular infusions exhibiting possible benefit over intracranial tumor infusions in a multifocal disease model. Overall, these findings help define parameters for the clinical translation of CAR T cell therapy for the treatment of brain tumors.

Incidence of Second Primary Malignancies after Autologous Transplantation for Multiple Myeloma in the Era of Novel Agents.

The advent of novel agents for multiple myeloma (MM) is cause for a re-examination of the incidence of second primary malignancies (SPMs). We examined the SPM rate in MM patients who were enrolled in the prospective observational CALM (Collaboration to Collect Autologous Transplant outcome in Lymphoma and Myeloma) study. Between 2008 and 2012, 3204 patients with MM underwent a first autologous hematopoietic stem cell transplantation. Plerixafor was used as a mobilizing agent for patients with poor (or potentially poor) stem cell mobilization as defined by the respective centers. A total of 135 patients developed SPMs, with a cumulative incidence of 5.3% (95% confidence interval, 4.4 to 6.3) at 72 months. Ninety-four patients developed solid tumors, 30 developed hematologic malignancies, and 11 developed an SPM of an unknown type. The cumulative incidence of known hematologic and solid malignancies were 1.4% and 3.6%, respectively, at 72 months. In a univariate analysis, use of radiotherapy, type of induction regimen, hematopoietic stem cell dose, poor mobilizer status, plerixafor use, and sex did not influence the cumulative incidence of SPMs. Only age over 65 years was statistically associated with an increased incidence. Overall, the incidence of SPMs was comparable to earlier estimations of SPMs in MM.

Phase II Study of Yttrium-90 Ibritumomab Tiuxetan Plus High-Dose BCNU, Etoposide, Cytarabine, and Melphalan for Non-Hodgkin Lymphoma: The Role of Histology.

Standard-dose 90yttrium-ibritumomab tiuxetan (.4 mci/kg) together with high-dose BEAM (BCNU, etoposide, cytarabine, and melphalan) (Z-BEAM) has been shown to be a well-tolerated autologous hematopoietic stem cell transplantation preparative regimen for non-Hodgkin lymphoma. We report the outcomes of a single-center, single-arm phase II trial of Z-BEAM conditioning in high-risk CD20+ non-Hodgkin lymphoma histologic strata: diffuse large B cell (DLBCL), mantle cell, follicular, and transformed. Robust overall survival and notably low nonrelapse mortality rates (.9% at day +100 for the entire cohort), with few short- and long-term toxicities, confirm the safety and tolerability of the regimen. In addition, despite a high proportion of induction failure patients (46%), the promising response and progression-free survival (PFS) rates seen in DLBCL (3-year PFS: 71%; 95% confidence interval, 55 to 82%), support the premise that the Z-BEAM regimen is particularly effective in this histologic subtype. The role of Z-BEAM in other strata is less clear in the context of the emergence of novel agents.

Hyperfractionated Cyclophosphamide, Vincristine, Doxorubicin, and Dexamethasone Chemotherapy in Mantle Cell Lymphoma Patients Is Associated with Higher Rates of Hematopoietic Progenitor Cell Mobilization Failure despite Plerixafor Rescue.

Induction regimens for mantle cell lymphoma (MCL) can be categorized into highly intensive regimens containing cytarabine and less intense regimens, such as rituximab, cyclophosphamide, hydroxydaunorubicin, vincristine, and prednisone (R-CHOP) or rituximab with bendamustine (R-bendamustine). Prior publications have shown rituximab and hyperfractionated cyclophosphamide, vincristine, doxorubicin, and dexamethasone (R-hyperCVAD) can be associated with stem cell mobilization failures. However, those studies did not include the use of plerixafor as rescue for stem cell mobilization failure. We examined our database of 181 consecutive MCL patients who received upfront therapy from 2005 to 2015 with either R-hyperCVAD or less intense chemotherapy (R-bendamustine and R-CHOP only) regimens to assess impact of frontline chemotherapy on collection of hematopoietic cell progenitors before autologous stem cell transplantation (ASCT). In the preplerixafor era (before August 16, 2009), a significant difference in peripheral blood stem cell (PBSC) collection failure between the R-hyperCVAD (12%) and other chemotherapy (11%) groups was not established. However, in the postplerixafor era, use of R-hyperCVAD chemotherapy was associated with significantly higher rates of hematopoietic progenitor cell collection failures (17%) compared with that observed in the other chemotherapy group (4%; P = .04). The rates of mobilization failure declined to 4% in the postplerixafor era from 11% in the preplerixafor era for patients receiving less intensive chemotherapy. Conversely, the rate of mobilization failure increased in the R-hyperCVAD group from 12% in the preplerixafor era to 17% in the postplerixafor era. Plerixafor does not overcome the negative impact of R-hyperCVAD on PBSC mobilization, and caution is warranted in using R-hyperCVAD in patients with newly diagnosed MCL who are candidates for ASCT.

Phase I Trial of Total Marrow and Lymphoid Irradiation Transplantation Conditioning in Patients with Relapsed/Refractory Acute Leukemia.

Current conditioning regimens provide insufficient disease control in relapsed/refractory acute leukemia patients undergoing hematopoietic stem cell transplantation (HSCT) with active disease. Intensification of chemotherapy and/or total body irradiation (TBI) is not feasible because of excessive toxicity. Total marrow and lymphoid irradiation (TMLI) allows for precise delivery and increased intensity treatment via sculpting radiation to sites with high disease burden or high risk for disease involvement, while sparing normal tissue. We conducted a phase I trial in 51 patients (age range, 16 to 57 years) with relapsed/refractory acute leukemia undergoing HSCT (matched related, matched unrelated, or 1-allele mismatched unrelated) with active disease, combining escalating doses of TMLI (range, 1200 to 2000 cGy) with cyclophosphamide (CY) and etoposide (VP16). The maximum tolerated dose was declared at 2000 cGy, as TMLI simulation studies indicated that >2000 cGy might deliver doses toxic for normal organs at or exceeding those delivered by standard TBI. The post-transplantation nonrelapse mortality (NRM) rate was only 3.9% (95% confidence interval [CI], .7 to 12.0) at day +100 and 8.1% (95% CI, 2.5 to 18.0) at 1 year. The cumulative incidence of grades II to IV acute graft-versus-host disease (GVHD) was 43.1% (95% CI, 29.2 to 56.3) and for grade III and IV, it was 13.7% (95% CI, 6.9 to 27.3). The day +30 complete remission rate for all patients was 88% and was 100% for those treated at 2000 cGy. The overall 1-year survival was 55.5% (95% CI, 40.7 to 68.1). The TMLI/CY/VP16 conditioning regimen is well tolerated at TMLI doses up to 2000 cGy with a low 100-day and 1-year NRM rate and no increased risk of GVHD with higher doses of radiation.

Preclinical data support leveraging CS1 chimeric antigen receptor T-cell therapy for systemic light chain amyloidosis.

BACKGROUND AIMS: Light chain amyloidosis (AL) is a protein deposition disorder that is a result of a plasma cell dyscrasia, similar to multiple myeloma (MM). Immunotherapy is an attractive approach because of the low burden of disease, but the optimal target for AL is unclear. CS1 and B-cell maturation antigen (BCMA) are two potential targets because they are expressed on normal plasma cells and MM cells. METHODS: We performed a prospective study evaluating bone marrow specimens of 20 patients with plasma cell diseases, 10 with AL and 10 with MM. We evaluated the clonal population of plasma cells for BCMA and CS1 expression. We designed a second-generation CS1 chimeric antigen receptor (CAR) construct, comprising a CS1 antigen-specific scFv, shortened hinge region and CD28 costimulatory domain. Purified central memory T cells were activated and transduced with a lentiviral vector encoding the CS1 CAR. Cytotoxicity was evaluated using 51Cr release assays. Five days after tumor inoculation, NSG mice were injected intravenously with CS1 CAR T cells. RESULTS: Whereas CS1 is present on the plasma cells of AL patients, we found BCMA expression in AL to be markedly low. CS1 CAR T cells were cytotoxic against CS1 positive tumor cells and induced durable tumor regressions in mice. DISCUSSION: Our work represents a novel application of CS1-directed CAR T cells while revealing that BCMA would not be a suitable target. We expect AL to be particularly susceptible to CAR T-cell therapy because of the low tumor burden in the bone marrow.

Implications and Management of Central Nervous System Involvement before Allogeneic Hematopoietic Cell Transplantation in Acute Lymphoblastic Leukemia.

Acute lymphoblastic leukemia (ALL) with a history of central nervous system (CNS) involvement, either at diagnosis or relapse, poses challenges when the decision is made to proceed with allogeneic hematopoietic cell transplantation (alloHCT), as there is no evidence-based consensus on the best peri-transplantation approach to reduce subsequent CNS relapse risk. Here, we retrospectively analyzed outcomes of 87 patients with ALL and a history of CNS involvement who later underwent alloHCT. Patients with pretransplantation CNS involvement had higher risk of CNS relapse after transplantation (2-year CNS relapse: 9.6% versus 1.4%, P < .0001), inferior event-free survival (EFS) (hazard ratio [HR], 1.52; P = .003), and worse overall survival (OS) (HR, 1.55; P = .003) compared with patients without pretransplantation CNS involvement (n = 543). There was no difference in post-transplantation CNS relapse, EFS, or OS among patients presenting with CNS involvement at diagnosis, those with isolated CNS relapse, and those with combined bone marrow and CNS relapse before HCT. Interestingly, neither pretransplantation cranial irradiation, use of total body irradiation-based conditioning, nor post-transplantation prophylactic intrathecal chemotherapy were associated with a reduction of CNS relapse risk after transplantation. Thus, among the patients in the cohort studied, there was no clear benefit of CNS-directed therapy in the peri-transplantation period among patients who had prior CNS involvement and underwent subsequent alloHCT.

Inhibition of Tau aggregation by three Aspergillus nidulans secondary metabolites: 2,ω-dihydroxyemodin, asperthecin, and asperbenzaldehyde.

The aggregation of the microtubule-associated protein tau is a significant event in many neurodegenerative diseases including Alzheimer's disease. The inhibition or reversal of tau aggregation is therefore a potential therapeutic strategy for these diseases. Fungal natural products have proven to be a rich source of useful compounds having wide varieties of biological activity. We have screened Aspergillus nidulans secondary metabolites containing aromatic ring structures for their ability to inhibit tau aggregation in vitro using an arachidonic acid polymerization protocol and the previously identified aggregation inhibitor emodin as a positive control. While several compounds showed some activity, 2,ω-dihydroxyemodin, asperthecin, and asperbenzaldehyde were potent aggregation inhibitors as determined by both a filter trap assay and electron microscopy. In this study, these three compounds were stronger inhibitors than emodin, which has been shown in a prior study to inhibit the heparin induction of tau aggregation with an IC50 of 1-5 µM. Additionally, 2,ω-dihydroxyemodin, asperthecin, and asperbenzaldehyde reduced, but did not block, tau stabilization of microtubules. 2,ω-Dihydroxyemodin and asperthecin have similar structures to previously identified tau aggregation inhibitors, while asperbenzaldehyde represents a new class of compounds with tau aggregation inhibitor activity. Asperbenzaldehyde can be readily modified into compounds with strong lipoxygenase inhibitor activity, suggesting that compounds derived from asperbenzaldehyde could have dual activity. Together, our data demonstrates the potential of 2,ω-dihydroxyemodin, asperthecin, and asperbenzaldehyde as lead compounds for further development as therapeutics to inhibit tau aggregation in Alzheimer's disease and neurodegenerative tauopathies.

Biosynthetic pathway for the epipolythiodioxopiperazine acetylaranotin in Aspergillus terreus revealed by genome-based deletion analysis.

Epipolythiodioxopiperazines (ETPs) are a class of fungal secondary metabolites derived from diketopiperazines. Acetylaranotin belongs to one structural subgroup of ETPs characterized by the presence of a seven-membered 4,5-dihydrooxepine ring. Defining the genes involved in acetylaranotin biosynthesis should provide a means to increase the production of these compounds and facilitate the engineering of second-generation molecules. The filamentous fungus Aspergillus terreus produces acetylaranotin and related natural products. Using targeted gene deletions, we have identified a cluster of nine genes (including one nonribosomal peptide synthetase gene, ataP) that is required for acetylaranotin biosynthesis. Chemical analysis of the wild-type and mutant strains enabled us to isolate 17 natural products from the acetylaranotin biosynthesis pathway. Nine of the compounds identified in this study are natural products that have not been reported previously. Our data have allowed us to propose a biosynthetic pathway for acetylaranotin and related natural products.

Reprogramming of PD-1+ M2-like tumor-associated macrophages with anti-PD-L1 and lenalidomide in cutaneous T cell lymphoma.

Cutaneous T cell lymphoma (CTCL) is a disfiguring and incurable disease characterized by skin-homing malignant T cells surrounded by immune cells that promote CTCL growth through an immunosuppressive tumor microenvironment (TME). Preliminary data from our phase I clinical trial of anti-programmed cell death ligand 1 (anti-PD-L1) combined with lenalidomide in patients with relapsed/refractory CTCL demonstrated promising clinical efficacy. In the current study, we analyzed the CTCL TME, which revealed a predominant PD-1+ M2-like tumor-associated macrophage (TAM) subtype with upregulated NF-κB and JAK/STAT signaling pathways and an aberrant cytokine and chemokine profile. Our in vitro studies investigated the effects of anti-PD-L1 and lenalidomide on PD-1+ M2-like TAMs. The combinatorial treatment synergistically induced functional transformation of PD-1+ M2-like TAMs toward a proinflammatory M1-like phenotype that gained phagocytic activity upon NF-κB and JAK/STAT inhibition, altered their migration through chemokine receptor alterations, and stimulated effector T cell proliferation. Lenalidomide was more effective than anti-PD-L1 in downregulation of the immunosuppressive IL-10, leading to decreased expression of both PD-1 and PD-L1. Overall, PD-1+ M2-like TAMs play an immunosuppressive role in CTCL. Anti-PD-L1 combined with lenalidomide provides a therapeutic strategy to enhance antitumor immunity by targeting PD-1+ M2-like TAMs in the CTCL TME.

Leflunomide Confers Rapid Recovery from COVID-19 and is Coupled with Temporal Immunologic Changes.

Background: Vaccines for SARS-CoV-2 have been considerably effective in reducing rates of infection and severe COVID-19. However, many patients, especially those who are immunocompromised due to cancer or other factors, as well as individuals who are unable to receive vaccines or are in resource-poor countries, will continue to be at risk for COVID-19. We describe clinical, therapeutic, and immunologic correlatives in two patients with cancer and severe COVID-19 who were treated with leflunomide after failing to respond to standard-of-care comprising remdesivir and dexamethasone. Both patients had breast cancer and were on therapy for the malignancy. Methods: The protocol is designed with the primary objective to assess the safety and tolerability of leflunomide in treating severe COVID-19 in patients with cancer. Leflunomide dosing consisted of a loading dose of 100 mg daily for the first three days, followed by daily dosing, at the assigned dose level (Dose Level 1: 40 mg, Dose Level -1, 20 mg; Dose Level 2, 60 mg), for an additional 11 days. At defined intervals, serial monitoring of blood samples for toxicity, pharmacokinetics, and immunologic correlative studies were performed, as well as nasopharyngeal swabs for PCR analysis of SARS-CoV-2. Results: Preclinically, leflunomide impaired viral RNA replication, and clinically, it led to a rapid improvement in the two patients discussed herein. Both patients completely recovered, with minimal toxicities; all adverse events experienced were considered unrelated to leflunomide. Single-cell mass-cytometry analysis showed that leflunomide increased levels of CD8+ cytotoxic and terminal effector T cells and decreased naïve and memory B cells. Conclusions: With ongoing COVID-19 transmission and occurrence of breakthrough infections in vaccinated individuals, including patients with cancer, therapeutic agents that target both the virus and host inflammatory response would be helpful despite the availability of currently approved anti-viral agents. Furthermore, from an access to care perspective, especially in resource-limited areas, an inexpensive, readily available, effective drug with existing safety data in humans is relevant in the real-world setting.

Leveraging IFNγ/CD38 regulation to unmask and target leukemia stem cells in acute myelogenous leukemia.

Elimination of drug-resistant leukemia stem cells (LSCs) represents a major challenge to achieve a cure in acute myeloid leukemia (AML). Although AML blasts generally retain high levels of surface CD38 (CD38pos), the presence of CD34 and lack of CD38 expression (CD34posCD38neg) are immunophenotypic features of both LSC-enriched AML blasts and normal hematopoietic stem cells (HSCs). We report that IFN-γ induces CD38 upregulation in LSC-enriched CD34posCD38neg AML blasts, but not in CD34posCD38neg HSCs. To leverage the IFN-γ mediated CD38 up-regulation in LSCs for clinical application, we created a compact, single-chain CD38-CD3-T cell engager (CD38-BIONIC) able to direct T cells against CD38pos blasts. Activated CD4pos and CD8pos T cells not only kill AML blasts but also produce IFNγ, which leads to CD38 expression on CD34posCD38neg LSC-enriched blasts. These cells then become CD38-BIONIC targets. The net result is an immune-mediated killing of both CD38neg and CD38pos AML blasts, which culminates in LSC depletion.

Illuminating the diversity of aromatic polyketide synthases in Aspergillus nidulans.

Genome sequencing has revealed that fungi have the ability to synthesize many more natural products (NPs) than are currently known, but methods for obtaining suitable expression of NPs have been inadequate. We have developed a successful strategy that bypasses normal regulatory mechanisms. By efficient gene targeting, we have replaced, en masse, the promoters of nonreducing polyketide synthase (NR-PKS) genes, key genes in NP biosynthetic pathways, and other genes necessary for NR-PKS product formation or release. This has allowed us to determine the products of eight NR-PKSs of Aspergillus nidulans, including seven novel compounds, as well as the NR-PKS genes required for the synthesis of the toxins alternariol (8) and cichorine (19).

Advances in Aspergillus secondary metabolite research in the post-genomic era.

This review studies the impact of whole genome sequencing on Aspergillus secondary metabolite research. There has been a proliferation of many new, intriguing discoveries since sequencing data became widely available. What is more, the genomes disclosed the surprising finding that there are many more secondary metabolite biosynthetic pathways than laboratory research had suggested. Activating these pathways has been met with some success, but many more dormant genes remain to be awakened.

Longitudinal Preclinical Imaging Characterizes Extracellular Drug Accumulation After Radiation Therapy in the Healthy and Leukemic Bone Marrow Vascular Microenvironment.

PURPOSE: Recent initial findings suggest that radiation therapy improves blood perfusion and cellular chemotherapy uptake in mice with leukemia. However, the ability of radiation therapy to influence drug accumulation in the extracellular bone marrow tissue is unknown, due in part to a lack of methodology. This study developed longitudinal quantitative multiphoton microscopy (L-QMPM) to characterize the bone marrow vasculature (BMV) and drug accumulation in the extracellular bone marrow tissue before and after radiation therapy in mice bearing leukemia. METHODS AND MATERIALS: We developed a longitudinal window implant for L-QMPM imaging of the calvarium BMV before, 2 days after, and 5 days after total body irradiation (TBI). Live time-lapsed images of a fluorescent drug surrogate were used to obtain measurements, including tissue wash-in slope (WIStissue) to measure extracellular drug accumulation. We performed L-QMPM imaging on healthy C57BL/6 (WT) mice, as well as mice bearing acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML). RESULTS: Implants had no effects on calvarium dose, and parameters for wild-type untreated mice were stable during imaging. We observed decreased vessel diameter, vessel blood flow, and WIStissue with the onset of AML and ALL. Two to 10 Gy TBI increased WIStissue and vessel diameter 2 days after radiation therapy in all 3 groups of mice and increased single-vessel blood flow in mice bearing ALL and AML. Increased WIStissue was observed 5 days after 10 Gy TBI or 4 Gy split-dose TBI (2 treatments of 2 Gy spaced 3 days apart). CONCLUSIONS: L-QMPM provides stable functional assessments of the BMV. Nonmyeloablative and myeloablative TBI increases extracellular drug accumulation in the leukemic bone marrow 2 to 5 days posttreatment, likely through improved blood perfusion and drug exchange from the BMV to the extravascular tissue. Our data show that neo-adjuvant TBI at doses from 2 Gy to 10 Gy conditions the BMV to improve drug transport to the bone marrow.