Rapid anti-myeloma activity by T cells expressing an anti-BCMA CAR with a human heavy-chain-only antigen-binding domain.

Multiple myeloma (MM) is a rarely curable malignancy of plasma cells. MM expresses B cell maturation antigen (BCMA). We developed a fully human anti-BCMA chimeric antigen receptor (CAR) with a heavy-chain-only antigen-recognition domain, a 4-1BB domain, and a CD3ζ domain. The CAR was designated FHVH33-CD8BBZ. We conducted the first-in-humans clinical trial of T cells expressing FHVH33-CD8BBZ (FHVH-T). Twenty-five patients with relapsed MM were treated. The stringent complete response rate (sCR) was 52%. Median progression-free survival (PFS) was 78 weeks. Of 24 evaluable patients, 6 (25%) had a maximum cytokine-release syndrome (CRS) grade of 3; no patients had CRS of greater than grade 3. Most anti-MM activity occurred within 2-4 weeks of FHVH-T infusion as shown by decreases in the rapidly changing MM markers serum free light chains, urine light chains, and bone marrow plasma cells. Blood CAR+ cell levels peaked during the time that MM elimination was occurring, between 7 and 15 days after FHVH-T infusion. C-C chemokine receptor type 7 (CCR7) expression on infusion CD4+ FHVH-T correlated with peak blood FHVH-T levels. Single-cell RNA sequencing revealed a shift toward more differentiated FHVH-T after infusion. Anti-CAR antibody responses were detected in 4 of 12 patients assessed. FHVH-T has powerful, rapid, and durable anti-MM activity.

CD19/22 CAR T cells in children and young adults with B-ALL: phase 1 results and development of a novel bicistronic CAR.

Remission durability following single-antigen targeted chimeric antigen receptor (CAR) T-cells is limited by antigen modulation, which may be overcome with combinatorial targeting. Building upon our experiences targeting CD19 and CD22 in B-cell acute lymphoblastic leukemia (B-ALL), we report on our phase 1 dose-escalation study of a novel murine stem cell virus (MSCV)-CD19/CD22-4-1BB bivalent CAR T-cell (CD19.22.BBζ) for children and young adults (CAYA) with B-cell malignancies. Primary objectives included toxicity and dose finding. Secondary objectives included response rates and relapse-free survival (RFS). Biologic correlatives included laboratory investigations, CAR T-cell expansion and cytokine profiling. Twenty patients, ages 5.4 to 34.6 years, with B-ALL received CD19.22.BBζ. The complete response (CR) rate was 60% (12 of 20) in the full cohort and 71.4% (10 of 14) in CAR-naïve patients. Ten (50%) developed cytokine release syndrome (CRS), with 3 (15%) having ≥ grade 3 CRS and only 1 experiencing neurotoxicity (grade 3). The 6- and 12-month RFS in those achieving CR was 80.8% (95% confidence interval [CI]: 42.4%-94.9%) and 57.7% (95% CI: 22.1%-81.9%), respectively. Limited CAR T-cell expansion and persistence of MSCV-CD19.22.BBζ compared with EF1α-CD22.BBζ prompted laboratory investigations comparing EF1α vs MSCV promoters, which did not reveal major differences. Limited CD22 targeting with CD19.22.BBζ, as evaluated by ex vivo cytokine secretion and leukemia eradication in humanized mice, led to development of a novel bicistronic CD19.28ζ/CD22.BBζ construct with enhanced cytokine production against CD22. With demonstrated safety and efficacy of CD19.22.BBζ in a heavily pretreated CAYA B-ALL cohort, further optimization of combinatorial antigen targeting serves to overcome identified limitations (www.clinicaltrials.gov #NCT03448393).

Treatment strategies for progressive immune effector cell-associated hemophagocytic lymphohistiocytosis-like syndrome: case series.

Not available.

A novel approach for characterization of KSHV-associated multicentric Castleman disease from effusions.

A biopsy of lymphoid tissue is currently required to diagnose Kaposi sarcoma-associated herpesvirus (KSHV)-associated multicentric Castleman disease (KSHV-MCD). Patients showing clinical manifestations of KSHV-MCD but no pathological changes of KSHV-MCD are diagnosed as KSHV inflammatory cytokine syndrome. However, a lymph node biopsy is not always feasible to make the distinction. A pathognomonic feature of lymph nodes in KSHV-MCD is the expansion of KSHV-infected, lambda-restricted but polyclonal plasmablasts. To investigate whether these cells also reside in extra-nodal sites, effusion from 11 patients with KSHV-MCD and 19 with KSHV inflammatory cytokine syndrome was analysed by multiparametric flow cytometry. A distinct, lambda-restricted plasmablastic population (LRP) with highly consistent immunophenotype was detected in effusions in 8/11 patients with KSHV-MCD. The same population was also observed in 7/19 patients with KSHV inflammatory cytokine syndrome. The detection of LRP stratified KSHV inflammatory cytokine syndrome into two clinically distinct subgroups; those with detectable LRP closely resembled KSHV-MCD, showing similar KSHV viral load, comparable severity of thrombocytopenia and hypoalbuminaemia, and similar incidences of hepatosplenomegaly. Collectively, the detection of LRP by flow cytometry can serve as a valuable tool in diagnosing KSHV-MCD. KSHV inflammatory cytokine syndrome with LRP in effusions may represent a liquid-form of KSHV-MCD.

Characterization of HLH-like manifestations as a CRS variant in patients receiving CD22 CAR T cells.

Chimeric antigen receptor (CAR) T-cell toxicities resembling hemophagocytic lymphohistiocytosis (HLH) occur in a subset of patients with cytokine release syndrome (CRS). As a variant of conventional CRS, a comprehensive characterization of CAR T-cell-associated HLH (carHLH) and investigations into associated risk factors are lacking. In the context of 59 patients infused with CD22 CAR T cells where a substantial proportion developed carHLH, we comprehensively describe the manifestations and timing of carHLH as a CRS variant and explore factors associated with this clinical profile. Among 52 subjects with CRS, 21 (40.4%) developed carHLH. Clinical features of carHLH included hyperferritinemia, hypertriglyceridemia, hypofibrinogenemia, coagulopathy, hepatic transaminitis, hyperbilirubinemia, severe neutropenia, elevated lactate dehydrogenase, and occasionally hemophagocytosis. Development of carHLH was associated with preinfusion natural killer(NK) cell lymphopenia and higher bone marrow T-cell:NK cell ratio, which was further amplified with CAR T-cell expansion. Following CRS, more robust CAR T-cell and CD8 T-cell expansion in concert with pronounced NK cell lymphopenia amplified preinfusion differences in those with carHLH without evidence for defects in NK cell mediated cytotoxicity. CarHLH was further characterized by persistent elevation of HLH-associated inflammatory cytokines, which contrasted with declining levels in those without carHLH. In the setting of CAR T-cell mediated expansion, clinical manifestations and immunophenotypic profiling in those with carHLH overlap with features of secondary HLH, prompting consideration of an alternative framework for identification and management of this toxicity profile to optimize outcomes following CAR T-cell infusion.

Clinical and biological implications of target occupancy in CLL treated with the BTK inhibitor acalabrutinib.

Inhibition of the B-cell receptor pathway, and specifically of Bruton tyrosine kinase (BTK), is a leading therapeutic strategy in B-cell malignancies, including chronic lymphocytic leukemia (CLL). Target occupancy is a measure of covalent binding to BTK and has been applied as a pharmacodynamic parameter in clinical studies of BTK inhibitors. However, the kinetics of de novo BTK synthesis, which determines occupancy, and the relationship between occupancy, pathway inhibition and clinical outcomes remain undefined. This randomized phase 2 study investigated the safety, efficacy, and pharmacodynamics of a selective BTK inhibitor acalabrutinib at 100 mg twice daily (BID) or 200 mg once daily (QD) in 48 patients with relapsed/refractory or high-risk treatment-naïve CLL. Acalabrutinib was well tolerated and yielded an overall response rate (ORR) of partial response or better of 95.8% (95% confidence interval [CI], 78.9-99.9) and an estimated progression-free survival (PFS) rate at 24 months of 91.5% (95% CI, 70.0-97.8) with BID dosing and an ORR of 79.2% (95% CI, 57.9-92.9) and an estimated PFS rate at 24 months of 87.2% (95% CI, 57.2-96.7) with QD dosing. BTK resynthesis was faster in patients with CLL than in healthy volunteers. BID dosing maintained higher BTK occupancy and achieved more potent pathway inhibition compared with QD dosing. Small increments in occupancy attained by BID dosing relative to QD dosing compounded over time to augment downstream biological effects. The impact of BTK occupancy on long-term clinical outcomes remains to be determined. This trial was registered at www.clinicaltrials.gov as #NCT02337829.

Avelumab, a PD-L1 Inhibitor, in Combination with Hypofractionated Radiotherapy and the Abscopal Effect in Relapsed Refractory Multiple Myeloma.

LESSONS LEARNED: Despite the initial optimism for using immune checkpoint inhibition in the treatment of multiple myeloma, subsequent clinical studies have been disappointing. Preclinical studies have suggested that priming the immune system with various modalities in addition to checkpoint inhibition may overcome the relative T-cell exhaustion or senescence; however, in this small data set, radiotherapy with checkpoint inhibition did not appear to activate the antitumor immune response. BACKGROUND: Extramedullary disease (EMD) is recognized as an aggressive subentity of multiple myeloma (MM) with a need for novel therapeutic approaches. We therefore designed a proof-of-principle pilot study to evaluate the synergy between the combination of the anti-PD-L1, avelumab, and concomitant hypofractionated radiotherapy. METHODS: This was a single-arm phase II Simon two-stage single center study that was prematurely terminated because of the COVID-19 pandemic after enrolling four patients. Key eligibility included patients with relapsed/refractory multiple myeloma (RRMM) who had exhausted or were not candidates for standard therapy and had at least one lesion amenable to radiotherapy. Patients received avelumab until progression or intolerable toxicity and hypofractionated radiotherapy to a focal lesion in cycle 2. Radiotherapy was delayed until cycle 2 to allow the avelumab to reach a study state, given the important observation from previous studies that concomitant therapy is needed for the abscopal effect. RESULTS: At a median potential follow-up of 10.5 months, there were no objective responses, one minimal response, and two stable disease as best response. The median progression-free survival (PFS) was 5.3 months (95% confidence interval [CI]: 2.5-7.1 months), and no deaths occurred. There were no grade ≥3 and five grade 1-2 treatment-related adverse events. CONCLUSION: Avelumab in combination with radiotherapy for patients with RRMM and EMD was associated with very modest systemic clinical benefit; however, patients did benefit as usual from local radiotherapy. Furthermore, the combination was very well tolerated compared with historical RRMM treatment regimens.

Depth and durability of response to ibrutinib in CLL: 5-year follow-up of a phase 2 study.

The safety and efficacy of ibrutinib (420 mg) in chronic lymphocytic leukemia (CLL) were evaluated in a phase 2 study; 51 patients had TP53 aberration (TP53 cohort) and 35 were enrolled because of age 65 years or older (elderly cohort). Both cohorts included patients with treatment-naive (TN) and relapsed/refractory (RR) CLL. With the median follow-up of 4.8 years, 49 (57.0%) of 86 patients remain on study. Treatment was discontinued for progressive disease in 20 (23.3%) patients and for adverse events in 5 (5.8%). Atrial fibrillation occurred in 18 (20.9%) patients for a rate of 6.4 per 100 patient-years. No serious bleeding occurred. The overall response rate at 6 months, the primary study endpoint, was 95.8% for the TP53 cohort (95% confidence interval, 85.7%-99.5%) and 93.9% for the elderly cohort (95% confidence interval, 79.8%-99.3%). Depth of response improved with time: at best response, 14 (29.2%) of 48 patients in the TP53 cohort and 9 (27.3%) of 33 in the elderly cohort achieved a complete response. Median minimal residual disease (MRD) in peripheral blood was 3.8 × 10-2 at 4 years, with MRD-negative (<10-4) remissions in 5 (10.2%) patients. In the TP53 cohort, the estimated 5-year progression-free survival (PFS) was 74.4% in TN-CLL compared with 19.4% in RR-CLL (P = .0002), and overall survival (OS) was 85.3% vs 53.7%, respectively (P = .023). In the elderly cohort, the estimated 5-year PFS and OS in RR-CLL were 64.8% and 71.6%, respectively, and no event occurred in TN-CLL. Long-term administration of ibrutinib was well tolerated and provided durable disease control for most patients. This trial was registered at www.clinicaltrials.gov as #NCT01500733.

Disease detection methodologies in relapsed B-cell acute lymphoblastic leukemia: Opportunities for improvement.

BACKGROUND: Accurate disease detection is integral to risk stratification in B-cell acute lymphoblastic leukemia (ALL). The gold standard used to evaluate response in the United States includes morphologic evaluation and minimal residual disease (MRD) testing of aspirated bone marrow (BM) by flow cytometry (FC). This MRD assessment is usually made on a single aspirate sample that is subject to variability in collection techniques and sampling error. Additionally, central nervous system (CNS) assessments for ALL include evaluations of cytopathology and cell counts, which can miss subclinical involvement. PROCEDURE: We retrospectively compared BM biopsy, aspirate, and FC samples obtained from children and young adults with relapsed/refractory ALL to identify the frequency and degree of disease discrepancies in this population. We also compared CNS FC and cytopathology techniques. RESULTS: Sixty of 410 (14.6%) BM samples had discrepant results, 41 (10%) of which were clinically relevant as they resulted in a change in the assignment of marrow status. Discrepant BM results were found in 28 of 89 (31.5%) patients evaluated. Additionally, cerebrospinal fluid (CSF) FC identified disease in 9.7% of cases where cytopathology was negative. CONCLUSIONS: These results support further investigation of the role of concurrent BM biopsy, with aspirate and FC evaluations, and the addition of FC to CSF evaluations, to fully assess disease status and response, particularly in patients with relapsed/refractory ALL. Prospective studies incorporating more comprehensive analysis to evaluate the impact on clinical outcomes are warranted.

Activation of Th1 Immunity within the Tumor Microenvironment Is Associated with Clinical Response to Lenalidomide in Chronic Lymphocytic Leukemia.

Immune stimulation contributes to lenalidomide's antitumor activity. Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of mature, autoreactive B cells in secondary lymphoid tissues, blood, and bone marrow and progressive immune dysfunction. Previous studies in CLL indicated that lenalidomide can repair defective T cell function in vitro. Whether T cell activation is required for clinical response to lenalidomide remains unclear. In this study, we report changes in the immune microenvironment in patients with CLL treated with single-agent lenalidomide and associate the immunologic effects of lenalidomide with antitumor response. Within days of starting lenalidomide, T cells increased in the tumor microenvironment and showed Th1-type polarization. Gene expression profiling of pretreatment and on-treatment lymph node biopsy specimens revealed upregulation of IFN-γ and many of its target genes in response to lenalidomide. The IFN-γ-mediated Th1 response was limited to patients achieving a clinical response defined by a reduction in lymphadenopathy. Deep sequencing of TCR genes revealed decreasing diversity of the T cell repertoire and an expansion of select clonotypes in responders. To validate our observations, we stimulated T cells and CLL cells with lenalidomide in culture and detected lenalidomide-dependent increases in T cell proliferation. Taken together, our data demonstrate that lenalidomide induced Th1 immunity in the lymph node that is associated with clinical response.

Clonal evolution leading to ibrutinib resistance in chronic lymphocytic leukemia.

Disease progression in patients with chronic lymphocytic leukemia (CLL) treated with ibrutinib has been attributed to histologic transformation or acquired mutations in BTK and PLCG2. The rate of resistance and clonal composition of PD are incompletely characterized. We report on CLL patients treated with single-agent ibrutinib on an investigator-initiated phase 2 trial. With median follow-up of 34 months, 15 of 84 evaluable patients (17.9%) progressed. Relapsed/refractory disease at study entry, TP53 aberration, advanced Rai stage, and high ß-2 microglobulin were independently associated with inferior progression-free survival (P < .05 for all tests). Histologic transformation occurred in 5 patients (6.0%) and was limited to the first 15 months on ibrutinib. In contrast, progression due to CLL in 10 patients (11.9%) occurred later, diagnosed at a median 38 months on study. At progression, mutations in BTK (Cys481) and/or PLCG2 (within the autoinhibitory domain) were found in 9 patients (10.7%), in 8 of 10 patients with progressive CLL, and in 1 patient with prolymphocytic transformation. Applying high-sensitivity testing (detection limit ∼1 in 1000 cells) to stored samples, we detected mutations up to 15 months before manifestation of clinical progression (range, 2.9-15.4 months). In 5 patients (6.0%), multiple subclones carrying different mutations arose independently, leading to subclonal heterogeneity of resistant disease. For a seamless transition to alternative targeted agents, patients progressing with CLL were continued on ibrutinib for up to 3 months, with 19.8 months median survival from the time of progression. This trial was registered at www.clinicaltrials.gov as #NCT01500733.

Partial reconstitution of humoral immunity and fewer infections in patients with chronic lymphocytic leukemia treated with ibrutinib.

Chronic lymphocytic leukemia (CLL) is characterized by immune dysregulation, often including hypogammaglobulinemia, which contributes to a high rate of infections and morbidity. Ibrutinib, a covalent inhibitor of Bruton tyrosine kinase (BTK), inhibits B-cell receptor signaling and is an effective, US Food and Drug Administration (FDA)-approved treatment of CLL. Inactivating germline mutations in BTK cause a severe B-cell defect and agammaglobulinemia. Therefore, we assessed the impact of ibrutinib on immunoglobulin levels, normal B cells, and infection rate in patients with CLL treated with single-agent ibrutinib on a phase 2 investigator-initiated trial. Consistent with previous reports, immunoglobulin G (IgG) levels remained stable during the first 6 months on treatment, but decreased thereafter. In contrast, there were a transient increase in IgM and a sustained increase in IgA (median increase 45% at 12 months, P < .0001). To distinguish the effects on clonal B cells from normal B cells, we measured serum free light chains (FLCs). In κ-clonal CLL cases, clonal (κ) FLCs were elevated at baseline and normalized by 6 months. Nonclonal (λ) FLCs, which were often depressed at baseline, increased, suggesting the recovery of normal B cells. Consistently, we observed normal B-cell precursors in the bone marrow and an increase in normal B-cell numbers in the peripheral blood. Patients with superior immune reconstitution, as defined by an increase in serum IgA of ≥50% from baseline to 12 months, had a significantly lower rate of infections (P = .03). These data indicate that ibrutinib allows for a clinically meaningful recovery of humoral immune function in patients with CLL. This trial was registered at www.clinicaltrials.gov as #NCT015007330.

T cells expressing CD19 chimeric antigen receptors for acute lymphoblastic leukaemia in children and young adults: a phase 1 dose-escalation trial.

BACKGROUND: Chimeric antigen receptor (CAR) modified T cells targeting CD19 have shown activity in case series of patients with acute and chronic lymphocytic leukaemia and B-cell lymphomas, but feasibility, toxicity, and response rates of consecutively enrolled patients treated with a consistent regimen and assessed on an intention-to-treat basis have not been reported. We aimed to define feasibility, toxicity, maximum tolerated dose, response rate, and biological correlates of response in children and young adults with refractory B-cell malignancies treated with CD19-CAR T cells. METHODS: This phase 1, dose-escalation trial consecutively enrolled children and young adults (aged 1-30 years) with relapsed or refractory acute lymphoblastic leukaemia or non-Hodgkin lymphoma. Autologous T cells were engineered via an 11-day manufacturing process to express a CD19-CAR incorporating an anti-CD19 single-chain variable fragment plus TCR zeta and CD28 signalling domains. All patients received fludarabine and cyclophosphamide before a single infusion of CD19-CAR T cells. Using a standard 3 + 3 design to establish the maximum tolerated dose, patients received either 1 × 10(6) CAR-transduced T cells per kg (dose 1), 3 × 10(6) CAR-transduced T cells per kg (dose 2), or the entire CAR T-cell product if sufficient numbers of cells to meet the assigned dose were not generated. After the dose-escalation phase, an expansion cohort was treated at the maximum tolerated dose. The trial is registered with ClinicalTrials.gov, number NCT01593696. FINDINGS: Between July 2, 2012, and June 20, 2014, 21 patients (including eight who had previously undergone allogeneic haematopoietic stem-cell transplantation) were enrolled and infused with CD19-CAR T cells. 19 received the prescribed dose of CD19-CAR T cells, whereas the assigned dose concentration could not be generated for two patients (90% feasible). All patients enrolled were assessed for response. The maximum tolerated dose was defined as 1 × 10(6) CD19-CAR T cells per kg. All toxicities were fully reversible, with the most severe being grade 4 cytokine release syndrome that occurred in three (14%) of 21 patients (95% CI 3·0-36·3). The most common non-haematological grade 3 adverse events were fever (nine [43%] of 21 patients), hypokalaemia (nine [43%] of 21 patients), fever and neutropenia (eight [38%] of 21 patients), and cytokine release syndrome (three [14%) of 21 patients). INTERPRETATION: CD19-CAR T cell therapy is feasible, safe, and mediates potent anti-leukaemic activity in children and young adults with chemotherapy-resistant B-precursor acute lymphoblastic leukaemia. All toxicities were reversible and prolonged B-cell aplasia did not occur. FUNDING: National Institutes of Health Intramural funds and St Baldrick's Foundation.

Ibrutinib for previously untreated and relapsed or refractory chronic lymphocytic leukaemia with TP53 aberrations: a phase 2, single-arm trial.

BACKGROUND: Patients with chronic lymphocytic leukaemia (CLL) with TP53 aberrations respond poorly to first-line chemoimmunotherapy, resulting in early relapse and short survival. We investigated the safety and activity of ibrutinib in previously untreated and relapsed or refractory CLL with TP53 aberrations. METHODS: In this investigator-initiated, single-arm phase 2 study, we enrolled eligible adult patients with active CLL with TP53 aberrations at the National Institutes of Health Clinical Center (Bethesda, MD, USA). Patients received 28-day cycles of ibrutinib 420 mg orally once daily until disease progression or the occurrence of limiting toxicities. The primary endpoint was overall response to treatment at 24 weeks in all evaluable patients. This study is registered with ClinicalTrials.gov, number NCT01500733, and is fully enrolled. FINDINGS: Between Dec 22, 2011, and Jan 2, 2014, we enrolled 51 patients; 47 had CLL with deletion 17p13.1 and four carried a TP53 mutation in the absence of deletion 17p13.1. All patients had active disease requiring therapy. 35 enrolled patients had previously untreated CLL and 16 had relapsed or refractory disease. Median follow-up was 24 months (IQR 12.9-27.0). 33 previously untreated patients and 15 patients with relapsed or refractory CLL were evaluable for response at 24 weeks. 32 (97%; 95% CI 86-100) of 33 previously untreated patients achieved an objective response, including partial response in 18 patients (55%) and partial response with lymphocytosis in 14 (42%). One patient had progressive disease at 0.4 months. 12 (80%; 95% CI 52-96) of the 15 patients with relapsed or refractory CLL had an objective response: six (40%) achieved a partial response and six (40%) a partial response with lymphocytosis; the remaining three (20%) patients had stable disease. Grade 3 or worse treatment-related adverse events were neutropenia in 12 (24%) patients (grade 4 in one [2%] patient), anaemia in seven (14%) patients, and thrombocytopenia in five (10%) patients (grade 4 in one [2%] patient). Grade 3 pneumonia occurred in three (6%) patients, and grade 3 rash in one (2%) patient. INTERPRETATION: The activity and safety profile of single-agent ibrutinib in CLL with TP53 aberrations is encouraging and supports its consideration as a novel treatment option for patients with this high-risk disease in both first-line and second-line settings. FUNDING: Intramural Research Program of the National Heart, Lung, and Blood Institute and the National Cancer Institute, Danish Cancer Society, Novo Nordisk Foundation, National Institutes of Health Medical Research Scholars Program, and Pharmacyclics Inc.

Anti-CD22-chimeric antigen receptors targeting B-cell precursor acute lymphoblastic leukemia.

Immune targeting of B-cell malignancies using chimeric antigen receptors (CARs) is a promising new approach, but critical factors impacting CAR efficacy remain unclear. To test the suitability of targeting CD22 on precursor B-cell acute lymphoblastic leukemia (BCP-ALL), lymphoblasts from 111 patients with BCP-ALL were assayed for CD22 expression and all were found to be CD22-positive, with median CD22 expression levels of 3500 sites/cell. Three distinct binding domains targeting CD22 were fused to various TCR signaling domains ± an IgG heavy chain constant domain (CH2CH3) to create a series of vector constructs suitable to delineate optimal CAR configuration. CARs derived from the m971 anti-CD22 mAb, which targets a proximal CD22 epitope demonstrated superior antileukemic activity compared with those incorporating other binding domains, and addition of a 4-1BB signaling domain to CD28.CD3 constructs diminished potency, whereas increasing affinity of the anti-CD22 binding motif, and extending the CD22 binding domain away from the membrane via CH2CH3 had no effect. We conclude that second-generation m971 mAb-derived anti-CD22 CARs are promising novel therapeutics that should be tested in BCP-ALL.

Characterization of CD22 expression in acute lymphoblastic leukemia.

BACKGROUND: CD22 is a B-lineage differentiation antigen that has emerged as a leading therapeutic target in acute lymphoblastic leukemia (ALL). PROCEDURE: Properties of CD22 expression relevant to therapeutic targeting were characterized in primary samples obtained from children and young adults with relapsed and chemotherapy refractory B-precursor (pre-B) ALL. RESULTS: CD22 expression was demonstrated in all subjects (n = 163) with detection on at least 90% of blasts in 155 cases. Median antigen site density of surface CD22 was 3,470 sites/cell (range 349-19,653, n = 160). Blasts from patients with known 11q23 (MLL) rearrangement had lower site density (median 1,590 sites/cell, range 349-3,624, n = 20 versus 3,853 sites/cell, range 451-19,653, n = 140; P = <0.0001) and 6 of 21 cases had sub-populations of blasts lacking CD22 expression (22%-82% CD22 +). CD22 expression was maintained in serial studies of 73 subjects, including those treated with anti-CD22 targeted therapy. The levels of soluble CD22 in blood and marrow by ELISA were low and not expected to influence the pharmacokinetics of anti-CD22 directed agents. CONCLUSIONS: These characteristics make CD22 an excellent potential therapeutic target in patients with relapsed and chemotherapy-refractory ALL, although cases with MLL rearrangement require close study to exclude the presence of a CD22-negative blast population.

Standardization of flow cytometric detection of antigen expression.

Since response to antigen-based immunotherapy relies upon the level of tumor antigen expression we developed an antigen quantification assay using ABC values. Antigen quantification as a clinical assay requires methods for quality control and for interlaboratory and inter-cytometer platform standardization. A single lot of Cytotrol™ Lyophilized Control Cells (Beckman Coulter) used for all studies. The variability in antigen quantification across 4 different instrument platforms in 2 separate laboratories was evaluated. The effect of the antibody clone utilized, importance of custom 1:1 molar ratio (fluorophore to protein, F/P) verses off-the-shelf antibodies, and QuantiBrite PE calibration verses linearity calibration combined with a single point scale transformation with CD4 as reference were determined. Use of single lot control cells allowed validation of reproducibility between flow cytometer platforms and laboratories and allowed assessment of different antibody lots, cocktail preparation, and different antibody clones. Off the shelf antibody preparations provide reproducible estimates of antigen density, however custom 1:1 unimolar antibody preparations should be utilized for definitive measurement of antigen expression.Geometric Mean fluorescent Intensity (GeoMFI) was not comparable across instruments and inter-laboratory. The use of CD4 as the reference marker can minimize variability in ABC values. Comparable antigen quantification is vital in managing patients receiving antigen-based immunotherapy. If this assay is to be utilized in a clinical setting, quality control methods have to be instituted to assure reproducibility and allow validation across laboratories. We have demonstrated that use of a lyophilized cell control is highly valuable in achieveing these goals.