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Background: Patients with relapsed/refractory (R/R) diffuse large B-cell lymphoma (DLBCL) often have a poor prognosis despite therapies using second-line chemoimmunotherapy (CIT). Achievement of complete response (CR) with second-line therapy is associated with improved long-term outcomes. Unfortunately, only 25-35% of patients achieve CR with standard CIT regimens alone. The addition of novel targeted agents such as Bruton Tyrosine Kinase inhibitors (BTKi) to second-line therapy may offer improved treatment responses given the importance of B-cell receptor (BCR) signaling in DLBCL. BTK has been shown to be essential for BCR-mediated activation of the NF- κB/Rel family of transcription factors and BCR signaling has been recognized as a key pathway in the pathogenesis of DLBCL. Moreover, NF-κB activity relies upon chronic active BCR signaling in activated B-cell-like DLBCL, which can be potentially blocked by kinase inhibitors targeting BTK. In this study we examine the feasibility and efficacy of adding the BTKi, acalabrutinib (A), to standard second-line therapy to improve disease response in patients with R/R DLBCL. Here we present initial safety and tolerability data for the ongoing study. Study Design and Methods: This is an open-label, prospective phase II trial (NCT03736616). Cohort A is open to R/R DLBCL patients eligible for autologous hematopoietic transplantation (HCT). Cohort B is open to R/R DLBCL patients considered ineligible for autologous HCT. The primary endpoint for cohort A is to estimate the confirmed CR rate (RECIL 2017 criteria) prior to autologous HCT in patients undergoing second-line CIT. The primary endpoint for cohort B is defined as the estimate of one-year progression-free survival in patients undergoing second-line induction and maintenance acalabrutinib therapy. Cohort A receive 2 cycles of standard RICE salvage CIT in combination with acalabrutinib, 100mg BID days 1-21 of a 21-day cycle (RICE+A). After 2 cycles of therapy, patients undergo autologous stem cell mobilization and collection. Patients then receive a 3 rd cycle of RICE in combination with acalabrutinib. PET-CT (PET3) is to be performed on day 15 of cycle 3 to assess response. Patients with CR or partial response (PR) after PET3 proceed to autologous HCT with BEAM conditioning within 28-42 days of PET3. Post-HCT CR patients receive acalabrutinib 100mg BID as maintenance therapy for 12 additional months. Protocol amendment in May 2021 allows for PET assessment (C2D15) prior to autologous stem cell collection (after cycle 3). Cohort B receive 3 cycles of RICE+A in 21-day cycles followed by PET-CT (PET3) on day 15 of cycle 3. Patients without progressive disease at PET3 continue with acalabrutinib maintenance up to 12 additional cycles until disease progression or unacceptable toxicity. Patients demonstrating progressive disease are withdrawn from study treatment but followed for outcomes. Results: Here we report initial safety and tolerability data for the ongoing study with data cutoff July 28, 2021. Twenty-two patients have been screened and 20 patients have received at least 1 cycle of RICE+A. Patient characteristics are shown in Table 1. Fifteen patients (79%) have completed 3 cycles of RICE+A. One patient (5%) discontinued due to an adverse event (AE; recurrent appendicitis), 3 patients (16%) discontinued due to progressive disease, and 1 patient is receiving ongoing RICE+A as of data cutoff. Hematologic AE have been observed in 17 patients (89%) with 74% being Grade 3/4. Amongst these, neutropenia was the most common AE occurring in 47% with all being Grade 3/4, and thrombocytopenia occurring in 32% with all being Grade 3/4. All hematologic AE recovered to baseline or grade 1 in median 7 days. Amongst non-hematologic AE, diarrhea occurred in 21% and 0% were Grade 3/4, nausea 16% with 0% Grade 3/4, and headache in 16% with 0% Grade 3/4. Discontinuation of therapy due to AE occurred in 1 patient (recurrent appendicitis) and dose reduction occurred in 1 patient (Gr 4 neutropenia). Temporary (per protocol) dose holds of A occurred in 9 patients (45%), primarily for cytopenias during concurrent RICE+A. Median duration for dose holds of A was 5.5 days. Conclusion: RICE+A is feasible with manageable primarily hematologic AEs similar to those reported for RICE alone. Enrollment and follow up is ongoing for efficacy endpoints and further toxicity assessment. Figure 1 Figure 1. Disclosures Bensinger: BMS, Janssen, Poseida, Regeneron, Trillium: Research Funding; Amgen, BMS, Janssen, Sanofi: Speakers Bureau. Glennie: Pharmacyclics/Janssen: Speakers Bureau. Pagel: Pharmacyclics/AbbVie: Consultancy; Incyte/MorphoSys: Consultancy; MEI Pharma: Consultancy; Gilead: Consultancy; Actinium Pharmaceuticals: Consultancy; AstraZeneca: Consultancy; BeiGene: Consultancy; Kite, a Gilead Company: Consultancy; Epizyme: Consultancy. Patel: Bristol Myers Squibb: Consultancy, Speakers Bureau; Janssen: Consultancy; Genentech: Consultancy; BeiGene: Consultancy; TG Therapeutics: Consultancy, Speakers Bureau; Abbvie: Consultancy; Pharmacyclics: Consultancy; Morphosys: Consultancy; Kite Pharma: Consultancy, Speakers Bureau; AstraZeneca: Consultancy, Research Funding, Speakers Bureau; MEI Pharma: Consultancy; ADC Therapeutics: Consultancy; Lilly: Consultancy. OffLabel Disclosure: Acalabrutinib is not FDA approved for treatment of DLBCL and is discussed in the context of an ongoing clinical trial only.

Background : Central line associated blood stream infections (CLABSI) have been the costliest of all healthcare associated infections. The average CLABSI cost is approximately $46,000 (Haddadin & Regunath, 2019). Most cases may be preventable with utilization of aseptic techniques, surveillance, and management through local protocols. The majority of CLABSI occur more than five days after central vascular access (CVA); therefore, there has been a growing focus on central line handling and maintenance techniques. CLABSI prevention data has been largely focused on the intensive care unit (ICU) patient population where an average of about half of patients have CVA. There have been few studies exploring the rates of CLABSI in the adult hematology population, a population with unique risk factors due to their immunosuppressing treatments and prolonged immunocompromised states. There has been emerging data that suggests the use of new technology in addition to existing central line maintenance recommendations by the Center for Disease Control may further reduce the rate of CLABSI occurrences in high-risk patient populations. Aim: To determine the efficacy of passive valve antimicrobial swab caps on the reduction of CLABSI in an inpatient hematology patient population when compared to current existing local practices. Outcomes of reported incidents of CLABSI have been evaluated against pre-interventional data for this setting. Methods : Retrospective analysis of medical records from January 2016 - September 2019 identified the existing rate of CLABSI occurrence among inpatient hematology patients at a single institution. We utilized the intervention of antimicrobial swab caps for 10 months and tracked the rate of CLABSI during this time. The nursing staff were educated on the quality improvement project, the use of the new equipment, and expectations that existing standard practices per local policy for CLABSI prevention bundles would be adhered to prior to the start of the intervention. To evaluate the impact of the antimicrobial swab caps on the rate of CLABSI we compared the number of infections pre- and post-intervention. Randomized audits, including chart reviews for compliance with existing standard CLABSI bundle practices were performed during the initial 3 months of the intervention. Results : Prior to the introduction of the passive valve antimicrobial swab cap to the existing CLABSI prevention protocol, CLABSI rates on the hematology unit exceeded the standardized infection ratio 75th percentile on 9 of the previous 15 calendar quarters. The intervention was observed for 6,674 central line days. The CLABSI rate during the intervention was 0.4495 per 1,000 central line days. The CLABSIs identified were due to nosocomial opportunistic infection in setting of immunosuppressed status (66%) and gastrointestinal translocation (33%). The common diagnosis in setting of CLABSI was refractory/relapse diffuse large B-cell lymphoma (66%) and active acute myeloid leukemia (33%). The two patients who were diagnosed with CLABSI were neutropenic with an absolute neutrophil count of 0 at time of CLABSI diagnosis. The organisms identified at time of CLABSI diagnosis were Clostridium ramosom, Enterococcus faecium, Staphylococcus epidermisis, and Candida parapsilosis. When considering the cost of a CLABSI to be about $46,000 per event and the annual cost for the inpatient hematology unit's use of the caps of approximately $19,710, the implementation of the antimicrobial swab cap reduced the cost associated with CLASBI in the hematology unit by approximately $26,290 annually. Conclusions : The introduction of the passive valve antimicrobial swab caps appears to demonstrate potential for reduced costs due to CLABSI when implemented into current CLABSI prevention bundles. This resulted in a 25% reduction in rates of CLABSI in the adult hematology patient population when compared to the previous year. The prevention of CLABSI in hematology patients with central vascular access remains challenging, however, standardized protocols for CLABSI prevention and use of antimicrobial swab caps may help further reduce the rate of CLABSI in hematology patients. Disclosures: No relevant conflicts of interest to declare. Disclosures Glennie: Pharmacyclics: Speakers Bureau; Janssen: Speakers Bureau. Bensinger:BMS: Consultancy, Honoraria, Research Funding, Speakers Bureau; Sanofi: Consultancy, Honoraria, Research Funding, Speakers Bureau; Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Amgen: Consultancy, Honoraria, Research Funding, Speakers Bureau; GSK: Consultancy, Honoraria, Research Funding, Speakers Bureau; Regeneron: Consultancy, Honoraria, Research Funding, Speakers Bureau. Patel:Celgene/BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Speakers Bureau; AstraZeneca: Consultancy, Research Funding, Speakers Bureau; BeiGene: Consultancy; Adaptive Biotechnologies: Consultancy; Genentech: Consultancy, Speakers Bureau; Kite: Consultancy; Pharmacyclics: Consultancy, Speakers Bureau.

Background: Patients with relapsed/refractory (R/R) diffuse large B-cell lymphoma (DLBCL) often have a poor prognosis despite therapies using second-line chemoimmunotherapy. Achievement of CR with second-line therapy is associated with improved long-term outcomes. Unfortunately, only 25-35% of patients achieve complete response (CR) with RICE chemotherapy alone. The addition of novel targeted agents such as Bruton Tyrosine Kinase inhibitors (BTKi) to second-line therapy may offer improved treatment responses given the importance of B-cell receptor (BCR) signaling in DLBCL. BTK has been shown to be essential for BCR-mediated activation of the NF- κB/Rel family of transcription factors and BCR signaling has been recognized as a key pathway in the pathogenesis of DLBCL. Moreover, NF-κB activity relies upon chronic active BCR signaling in activated B-cell-like DLBCL, which can be potentially blocked by kinase inhibitors targeting BTK. The goal of this study is to examine the feasibility and efficacy of adding the BTKi, acalabrutinib, to standard second-line therapy as a means to improve disease response. Establishing the feasibility of combining acalabrutinib with RICE chemotherapy in autologous hematopoietic cell transplantation (HCT) eligible and HCT ineligible patients with R/R DLBCL may provide the foundation for a larger study of efficacy and long-term outcomes of the combination therapy for patients with R/R DLBCL. Study Design and Methods: The primary objective of this phase 2 trial is to evaluate the tolerability, feasibility, and efficacy of combining acalabrutinib with RICE as second line therapy in R/R DLBCL patients. There are two study cohorts. Cohort A is open to R/R DLBCL patients who are eligible for autologous HCT. Cohort B is open to R/R DLBCL patients who are considered medically ineligible for autologous HCT. The primary endpoint for cohort A is to estimate the confirmed CR rate (RECIL 2017 criteria) prior to HCT in patients undergoing second-line therapy. The primary endpoint for cohort B is defined as the estimate of one-year progression-free survival in patients undergoing second-line induction and maintenance acalabrutinib therapy. Secondary endpoints include assessment of the proportion of patients completing 3 cycles of acalabrutinib with RICE and proceeding with HCT or 2 additional cycles of maintenance acalabrutinib for HCT ineligible patients, overall response rate, incidence of Grade 3/4 adverse events, and incidence of SAEs. Patients in cohort A receive 2 cycles of standard RICE salvage chemoimmunotherapy in combination with acalabrutinib, 100mg BID day 1-21 of a 21 day cycle. After 2 cycles of therapy, patients in cohort A undergo autologous stem cell mobilization and collection. Patients then receive a 3rd cycle of RICE in combination with acalabrutinib. PET-CT (PET3) is performed 14-21 days after day 1 of cycle 3 to assess response. Those patients with CR or partial response (PR) after PET3 proceed to autologous HCT with BEAM conditioning within 28-42 days of PET3. After adequate hematopoietic recovery, patients restart acalabrutinib 100mg BID as maintenance therapy for a period of 12 additional months. Patients in cohort B receive 3 cycles of RICE salvage chemoimmunotherapy in combination with acalabrutinib 100mg BID day 1-21 of a 21-day cycle followed by PET-CT (PET3) 14-21 days after start of Cycle 3. Patients without progressive disease at PET3 continue with acalabrutinib maintenance up to 12 additional cycles until disease progression or unacceptable toxicity. Patients demonstrating progressive disease are withdrawn from study treatment but their outcomes continue to be recorded and will be included in the final data analysis. Historical outcomes from completed, published prospective clinical trials using RICE chemoimmunotherapy serve as a reference for statistical calculations. This trial is currently ongoing and additional information can be found on clinicaltrials.gov NCT listing NCT03736616 Disclosures Bensinger: BMS: Consultancy, Honoraria, Research Funding, Speakers Bureau; Sanofi: Consultancy, Honoraria, Research Funding, Speakers Bureau; Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Amgen: Consultancy, Honoraria, Research Funding, Speakers Bureau; GSK: Consultancy, Honoraria, Research Funding, Speakers Bureau; Regeneron: Consultancy, Honoraria, Research Funding, Speakers Bureau. Mawad:Abbvie: Speakers Bureau; Adaptive Biotechnologies: Speakers Bureau. Glennie:Pharmacyclics: Speakers Bureau; Janssen: Speakers Bureau. Patel:Pharmacyclics: Consultancy, Speakers Bureau; Janssen: Consultancy, Speakers Bureau; Kite: Consultancy; AstraZeneca: Consultancy, Research Funding, Speakers Bureau; Adaptive Biotechnologies: Consultancy; Genentech: Consultancy, Speakers Bureau; Celgene/BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees; BeiGene: Consultancy. OffLabel Disclosure: Acalabrutinib is used an investigational agent for DLBCL in this study.

The anti-CD28 superagonist antibody TGN1412 caused life-threatening cytokine release syndrome (CRS) in healthy volunteers, which had not been predicted by preclinical testing. T cells in fresh peripheral blood mononuclear cells (PBMCs) do not respond to soluble TGN1412 but do respond following high-density (HD) preculture. We show for the first time that this response is dependent on crystallizable fragment gamma receptor IIb (FcγRIIb) expression on monocytes. This was unexpected because, unlike B cells, circulating monocytes express little or no FcγRIIb. However, FcγRIIb expression is logarithmically increased on monocytes during HD preculture, and this upregulation is necessary and sufficient to explain TGN1412 potency after HD preculture. B-cell FcγRIIb expression is unchanged by HD preculture, but B cells can support TGN1412-mediated T-cell proliferation when added at a frequency higher than that in PBMCs. Although low-density (LD) precultured PBMCs do not respond to TGN1412, T cells from LD preculture are fully responsive when cocultured with FcγRIIb-expressing monocytes from HD preculture, which shows that they are fully able to respond to TGN1412-mediated activation. Our novel findings demonstrate that cross-linking by FcγRIIb is critical for the superagonist activity of TGN1412 after HD preculture, and this may contribute to CRS in humans because of the close association of FcγRIIb-bearing cells with T cells in lymphoid tissues.

The anti-CD20 mAb rituximab is central to the treatment of B-cell malignancies, but resistance remains a significant problem. We recently reported that resistance could be explained, in part, by internalization of rituximab (type I anti-CD20) from the surface of certain B-cell malignancies, thus limiting engagement of natural effectors and increasing mAb consumption. Internalization of rituximab was most evident in chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL), but the extent of internalization was heterogeneous within each disease. Here, we show that the inhibitory FcγRIIb on target B cells promotes this process and is largely responsible for the observed heterogeneity across a range of B-cell malignancies. Internalization correlated strongly with FcγRIIb expression on normal and malignant B cells, and resulted in reduced macrophage phagocytosis of mAb-coated targets. Furthermore, transfection of FcγRIIb into FcγRIIb negative Ramos cells increased internalization of rituximab in a dose-dependent manner. Target-cell FcγRIIb promoted rituximab internalization in a cis fashion and was independent of FcγRIIb on neighboring cells. It became phosphorylated and internalized along with CD20:anti-CD20 complexes before lysosomal degradation. In MCL patients, high FcγRIIb expression predicted less durable responses after rituximab-containing regimens. Therefore, target-cell FcγRIIb provides a potential biomarker of response to type I anti-CD20 mAb.

Rituximab, a monoclonal antibody that targets CD20 on B cells, is now central to the treatment of a variety of malignant and autoimmune disorders. Despite this success, a substantial proportion of B-cell lymphomas are unresponsive or develop resistance, hence more potent anti-CD20 monoclonal antibodies (mAbs) are continuously being sought. Here we demonstrate that type II (tositumomab-like) anti-CD20 mAbs are 5 times more potent than type I (rituximab-like) reagents in depleting human CD20 Tg B cells, despite both operating exclusively via activatory Fcγ receptor–expressing macrophages. Much of this disparity in performance is attributable to type I mAb-mediated internalization of CD20 by B cells, leading to reduced macrophage recruitment and the degradation of CD20/mAb complexes, shortening mAb half-life. Importantly, human B cells from healthy donors and most cases of chronic lymphatic leukemia and mantle cell lymphoma, showed rapid CD20 internalization that paralleled that seen in the Tg mouse B cells, whereas most follicular lymphoma and diffuse large B-cell lymphoma cells were far more resistant to CD20 loss. We postulate that differences in CD20 modulation may play a central role in determining the relative efficacy of rituximab in treating these diseases and strengthen the case for focusing on type II anti-CD20 mAb in the clinic.

Microarray gene expression profiling studies have demonstrated immune response gene signatures that appear predictive of outcome in follicular lymphoma (FL). However, measurement of these marker genes in routine practice remains difficult. We have therefore investigated the immune response in FL using real-time polymerase chain reaction (PCR) to measure expression levels of 35 candidate Indicator genes, selected from microarray studies, to polyA cDNAs prepared from 60 archived human frozen lymph nodes, in parallel with immunohistochemical analysis for CD3, CD4, CD7, CD8, CD10, CD20, CD21, and CD68. High levels of CCR1, a marker of monocyte activation, were associated with a shorter survival interval, and high levels of CD3 with better survival, while immunohistochemistry demonstrated association of high numbers of CD68+ macrophages with a shorter survival interval and of high numbers of CD7+ T cells with a longer survival interval. The results confirm the role of the host immune response in outcome in FL and identify CCR1 as a prognostic indicator and marker of an immune switch between macrophages and a T cell–dominant response. They demonstrate the utility of polyA DNA and real-time PCR for measurement of gene signatures and the applicability of using this type of “molecular block” in clinical practice.

Growing evidence points to the potential of agonistic anti-CD40 mAbs as adjuvants for vaccination against cancer. These appear to act by maturing dendritic cells (DCs) and allowing them to prime CD8 cytotoxic T lymphocytes (CTLs). Although it is well established that optimal T-cell priming requires costimulation via B7:CD28, recent studies emphasize the contribution of TNF receptors to this process. To understand how anti-CD40 mAbs trigger effective antitumor immunity, we investigated the role of TNFR superfamily members CD27 and 4-1BB in the generation of this immunity and showed that, although partially dependent on 4-1BB:4-1BBL engagement, it is completely reliant on CD27:CD70 interactions. Importantly, blocking CD70, and to some extent 4-1BBL, during anti-CD40 treatment prevented accumulation of tumor-reactive T cells and subsequent tumor protection. However, it did not influence changes in DC number, phenotype, nor the activity of CTLs once immunity was established. We conclude that CD27:CD70 and 4-1BB:4-1BBL interactions are needed for DC-driven accumulation of antitumor CTLs following anti-CD40 mAb treatment. Finally, in support of the critical role for CD70:CD27, we show for the first time that agonistic anti-CD27 mAbs given without a DC maturation signal completely protect tumor-bearing mice and provide a highly potent reagent for boosting antitumor T-cell immunity.

Recent microarray gene expression profiling studies have identified gene signatures predictive of outcome, so-called “indicator” genes, for diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma (FL). However, measurement of these genes in routine practice remains difficult. We applied real-time polymerase chain reaction (PCR) to polyA cDNAs prepared from 106 archived human frozen lymph nodes (63 of FL, 25 of DLBCL, 10 reactive lymph nodes, and cases with paired samples of FL [4] and subsequent DLBCL [4]). Reverse transcription and polyA reverse transcriptase (RT)–PCR was performed, and resultant cDNA was probed by real-time PCR for 36 candidate indicator genes, selected from microarray studies. Nine genes showed statistically significant different expression between FL and DLBCL, including cyclin B, COL3A1, NPM3, H731, PRKCB1, OVGL, ZFPC150, HLA-DQ-a, and XPB. Of these, cyclin B, NPM3, and COL3A1 were higher in DLBCL. Six genes showed statistically significant higher expression in the neoplastic nodes compared with reactive nodes, namely PRKCB1, BCL-6, EAR2, ZFX, cyclin B, YY1. High levels of YY.1 were associated with a shorter survival interval in both FL and DLBCL. The method is simple, sensitive, and robust, facilitating routine use and may be used as a platform for clinical measurement of prognostic gene signatures.

Monoclonal antibody (mAb) therapeutics are revolutionizing cancer treatment; however, not all tumors respond, and agent optimization is essential to improve outcome. It has become clear over recent years that isotype choice is vital to therapeutic success with agents that work through different mechanisms, direct tumor targeting, agonistic receptor engagement, or receptor-ligand blockade, having contrasting requirements. Here we summarize how isotype dictates mAb activity and discuss ways in which this information can be used for the development of enhanced therapeutics.

Despite the rapid and widespread integration of chimeric CD20 monoclonal antibody (mAb), rituximab, into the management of non-Hodgkin lymphoma, its efficacy remains variable and often modest when used as a single agent. To develop more potent reagents, human immunoglobulin transgenic mice were used to generate a panel of immunoglobulin G1kappa (IgG1kappa) CD20 mAbs. All reagents bound strongly to CD20(+) cells and recruited mononuclear cells for the lysis of malignant B cells. However, 2 mAbs, 2F2 and 7D8, were exceptionally active in complement-dependent cytotoxicity (CDC), being able to lyse a range of rituximab-resistant targets, such as CD20-low chronic lymphocytic leukemia (CLL), in the presence of human plasma or unfractionated blood. Further analysis showed that 2F2 and 7D8, like rituximab, redistributed CD20 into Triton X-100-insoluble regions of the plasma membrane, but that they had markedly slower off-rates. To determine whether off-rate influenced CDC, a non-complement activating F(ab')(2) antihuman kappa reagent was used. This reagent markedly slowed the off-rate of rituximab and increased its CDC activity to that of 2F2 and 7D8. Thus, with increasing evidence that mAb therapeutic activity in vivo depends on complement activation, these new CD20 reagents with their slow off-rates and increased potency in CDC hold considerable promise for improved clinical activity.

Despite the success of anti-CD20 monoclonal antibody (mAb) in the treatment of lymphoma, there remains considerable uncertainty about their mechanism(s) of action. Here, we show that certain of these reagents (rituximab and 1F5), which redistribute CD20 into membrane rafts, are bound efficiently by C1q, deposit C3b, and result in complement-dependent cytotoxicity (CDC). This activity is important in vivo, because complement depletion using cobra venom factor (CVF) markedly reduced the efficacy of rituximab and 1F5 in 2 lymphoma xenograft models. However, complement depletion had no effect on the potent therapeutic activity of B1, a mAb that does not redistribute CD20 into membrane rafts, bind C1q, or cause efficient CDC. Equivalent immunotherapy also occurred in the presence or absence of natural killer (NK) cells. Perhaps most surprising was the observation that F(ab′)2 fragments of B1 but not 1F5 were able to provide substantial immunotherapy, indicating that non-Fc-dependent mechanisms are involved with B1. In accordance with this, B1 was shown to induce much higher levels of apoptosis than rituximab and 1F5. Thus, although complement is important for the action of rituximab and 1F5, this is not so for B1, which more likely functions through its ability to signal apoptosis. (Blood. 2004;103:2738-2743)

The mechanisms of interaction between anti-CD40 monoclonal antibody (mAb) therapy and external beam irradiation were investigated in 2 syngeneic B-cell lymphoma models. We have established doses of anti-CD40 mAb and irradiation which, although ineffective when given singly, were capable of providing long-term protection when used in combination. Furthermore, such treatment was not only critically dependent on the dose of mAb and irradiation but also on tumor load, with greater efficacy only occurring at higher tumor burden. Using blocking antibody, the potency of treatment was shown to be totally dependent on CD8+ T cells, with protective levels of CD8+ cells occurring only in mice receiving the combination of anti-CD40 and irradiation. Interestingly, the ratio of T cells (CD8+) to tumor cells in mice receiving combination treatment was between 10 and 15 times that seen in animals given anti-CD40 or irradiation alone. In vivo tracking experiments revealed a 2-phase decrease in tumor burden, the first resulting directly from the external irradiation and the second, occurring 5 days later, concomitant with the rise in tumor-specific CD8+ cells. We suggest that the external irradiation induced an initial kill of lymphoma cells, probably by apoptosis, which releases tumor antigens and slows the progression of the malignancy to allow generation of a curative cytotoxic T lymphocyte (CTL) response promoted by the anti-CD40 mAb. Combining irradiation with immunomodulatory mAb as described here appears to provide a powerful new approach to the management of cancer.

The B-cell receptor (BCR) for antigen is composed of surface immunoglobulin (sIg), which provides antigen specificity, and a noncovalently associated signaling unit, the CD79a/b heterodimer. Defects in CD79 can influence both BCR expression and signaling and may explain why cells from certain malignancies, such as B-chronic lymphocytic leukemia (B-CLL), often express diminished and inactive BCR. Recently, an alternative transcript of CD79b (ΔCD79b) has been reported that is up-regulated in B-CLL and may explain this diminished BCR expression. Here we assess the expression of ΔCD79b in B-CLL and other lymphoid malignancies and investigate its function. High relative expression of ΔCD79b was confirmed in most cases of B-CLL and found in 6 of 6 cases of splenic lymphomas with villous lymphocytes (SLVLs) and hairy cell leukemia. In a range of Burkitt lymphoma cell lines, expression of ΔCD79b was relatively low but correlated inversely with the ability of the BCR to signal apoptosis when cross-linked by antibody (Ab). Interestingly, when Ramos-EHRB cells, which express low ΔCD79b, were transfected with this transcript, they were transformed from being sensitive to anti-Fcμ–induced apoptosis to being highly resistant. Although ΔCD79b was expressed as protein, its overexpression did not reduce the level of cell surface BCR. Finally, we showed that the inhibitory activity of ΔCD79b depended on an intact leader sequence to ensure endoplasmic reticulum (ER) trafficking and a functional signaling immunoreceptor tyrosine-based activation motif (ITAM) in its cytoplasmic tail. These results point to ΔCD79b being a powerful modulator of BCR signaling that may play an important role in normal and malignant B cells.

CD64 (FcγRI) receptors represent highly potent trigger molecules for activated polymorphonuclear cells (PMN) and mediate lysis of a range of tumors in the presence of appropriate monoclonal antibodies. An huCD64 transgenic mouse model designed to analyze the therapeutic activity of a panel of bispecific F(ab')2(BsAb) in retargeting granulocyte–colony-stimulating factor (G-CSF)–activated PMN against syngeneic B-cell lymphomas is reported. This model allows careful analysis of the individual elements of the therapeutic process. BsAb were directed against immunoglobulin-idiotype (Id), major histocompatibility class II (MHC II), or CD19 on the tumors and huCD64 on the effectors. In vitro cytotoxicity assays and in vivo tumor tracking showed that, provided effectors were activated with G-CSF, all 3 derivatives destroyed and cleared lymphoma cells, with (huCD64 × MHC II) proving by far the most cytotoxic in vitro. However, though all derivatives delivered some survival advantage, only the [huCD64 × Id] BsAb provided long-term protection to tumor-bearing animals. These results demonstrate that CD64-recruited cytotoxic effectors operate in vivo but that the (huCD64 × Id) conferred an additional anti-tumor function essential for long-term protection. T-cell depletion studies demonstrated that this extra therapeutic activity with [huCD64 × Id] was totally dependent on CD4 and CD8 T cells and that mice, once “cured” with BsAb, were resistant to tumor rechallenge. These findings indicate that CD64 is an effective trigger molecule for delivering cytokine-activated PMN against tumor in vivo and that, provided tumor targets are selected appropriately, CD64-based BsAb can establish long-term T-cell immunity.

We report the radioimmunotherapy of mouse B-cell lymphoma, BCL1, using a panel of anti–B-cell monoclonal antibodies (MoAb) (anti-CD19, anti-CD22, anti-major histocompatibility complex (MHC) II, and anti-idiotype (Id) radiolabeled with 131-iodine. When administered early in disease (day 4), the 131I–anti-MHCII MoAb cured tumors as a result of targeted irradiation alone, the unlabeled MoAb being nontherapeutic. In contrast,131I–anti-Id, despite targeting irradiation and having therapeutic activity as an unconjugated antibody, protected mice for only 30 days; 131I–anti-CD19 and anti-CD22 were therapeutically inactive. Binding and biodistribution studies showed that the anti-Id, unlike anti-MHCII, MoAb was cleared from target cells in vivo and delivered 4 times less irradiation to splenic tumor. Treating later in the disease (day 14) increased tumor load and produced the expected reduction in therapeutic activity with the anti-MHCII, but surprisingly, allowed 131I–anti-Id to cure most mice. This unexpected potency of 131I–anti-Id late in the disease appeared to result from the direct cytotoxicity of the anti-Id MoAb, which was more active in established disease, in combination with targeted irradiation. We believe the ability of targeted irradiation and certain cytotoxic MoAb to work cooperatively against tumor in this way has important implications for the selection of reagents in radioimmunotherapy of B-cell lymphoma.

A major feature that distinguishes type I from type II anti-CD20 monoclonal antibodies (mAbs) and reduces their therapeutic efficacy is the tendency to internalize from the cell surface. We have shown previously that the extent of internalization correlates with the capacity of type I mAb to simultaneously engage both CD20 and the inhibitory Fcγ receptor, FcγRIIb, in a bipolar configuration. Here, we investigated whether mAbs directed at other B-cell surface receptors also engaged FcγRIIb and whether this interaction promoted internalization. Most mAbs engaged and activated FcγRIIb, with the strength of activation related to the level of mAb bound to the cell surface. However, engagement did not affect internalization of most mAb-ligated receptors, either in cell lines or primary chronic lymphocytic leukemia cells with the exception of CD19 and CD38. Furthermore, at high cell concentrations/density both cis and trans interactions between cell-surface bound mAb and FcγRIIb were evident, but trans interactions did not inhibit type I anti-CD20 mAb-mediated internalization. These data identify that FcγRIIb is engaged by many mAbs in both cis and trans configurations, triggering its activation, but that internalization via FcγRIIb occurs for only a select subset. These findings have implications when designing new antibody-based therapeutics.

In this issue of Blood , Albanesi et al have added weight to the contention that neutrophils are an important effector population in monoclonal antibody (mAb)-mediated tumor cell clearance. Their data, obtained using subcutaneous tumor models and an extensive panel of genetically modified mice

We read with interest the paper from Jilani et al[1][1] in which rituximab treatment appeared to down-modulate CD20 expression through a combination of internalization and RNA regulation. The result is unexpected because previous studies had shown that CD20 is not modulated by monoclonal antibody (

Direct-targeting monoclonal antibodies (mAb) such as anti-CD20 mAb are thought to elicit their anti-tumor function through antibody-dependent cellular phagocytosis (ADCP) mediated by myeloid cells (monocytes and macrophages), with little involvement of T cells. In contrast, immunomodulatory mAbs to TNFR superfamily members, CD27, OX40 and CD137, function by augmenting T-cell responses. We examined the therapeutic potential of combining anti-CD20 mAb with a panel of immunomodulatory mAbs (OX40, CD137, CD27, TIGIT, GITR, CTLA4, PD-1). In the syngeneic BCL1 B-cell lymphoma mouse model only an agonistic mAb to CD27, provided a synergistic effect when combined with anti-CD20. Anti-CD20 and anti-CD27 mAb individually provided modest therapeutic benefit (median survival 33 days and 62 days, respectively), but mice treated with the combination survived beyond 100 days. Similar synergistic survival benefit was observed in another B-cell lymphoma model, A31, and in BCL1-bearing human CD27 transgenic mice, when anti-CD20 was combined with varlilumab, an anti-human CD27 mAb currently under clinical investigation. We observed that in mice treated with anti-CD27, there was an early and substantial increase in intra-tumoral monocyte, neutrophil and macrophage infiltration. CD27 is expressed constitutively on T and NK cells but not myeloid cells or the tumor itself. To investigate whether CD27 agonism promotes intra-tumoral myeloid cell infiltration through T cells, we depleted T cells in the BCL1model. Surprisingly, CD4 or CD8 T-cell depletion had no effect on the survival of anti-CD20 and anti-CD27-treated mice, suggesting that the remaining CD27+ immune effector cells, NK cells, are required. To further probe the relative importance of these two sub-sets, we performed experiments in γ chain knockout mice, where activatory FcγR are not expressed. Here, anti-CD27 mediated T-cell activation can still occur via crosslinking from the inhibitory FcγRII, but effector function through NK cells, mediated through activatory FcγR, is abrogated. In this model, the therapeutic benefit of anti-CD27 was completely abolished, thereby supporting the requirement for NK cells. We hypothesize that anti-CD27 stimulates CD27+ NK cells to release chemokines that draw myeloid cells into the tumor, where they subsequently perform augmented anti-CD20 mediated ADCP. These data demonstrate the clear therapeutic potential of combining direct targeting and immunomodulatory mAb but that the therapeutic mechanism of action may differ to that expected; here involving a previously unheralded effect of anti-CD27 on myeloid infiltration. Based upon these data, we have implemented a phase II clinical trial examining rituximab and varlilumab in B-cell lymphoma, which will commence recruitment shortly. Disclosures Keler: Celldex Therapeutics: Employment, Equity Ownership. Johnson:Celldex Therapeutics: Research Funding. Al-Shamkhani:Celldex Therapeutics: Patents & Royalties: On therapeutic use of antibodies targeting anti-CD27 and another applied for anti-CD20/anti-CD27 use, Research Funding. Glennie:Celldex Therapeutics: Patents & Royalties: Patent on therapeutics use of antibodies targeting human CD27 and patent for anti-CD20+anti-CD27 applied. Cragg:Baxalta: Consultancy; Gilead Sciences: Research Funding; GSK: Research Funding; Roche: Consultancy, Research Funding; Bioinvent International: Consultancy, Research Funding. Lim:Celldex Therapeutics: Patents & Royalties: Patent for anti-CD20+anti-CD27 applied, Research Funding.

The anti-CD20 mAb rituximab has substantially improved the clinical outcome of patients with a wide range of B-cell malignancies. However, many patients relapse or fail to respond to rituximab, and thus there is intense investigation into the development of novel anti-CD20 mAbs with improved therapeutic efficacy. Although Fc-FcγR interactions appear to underlie much of the therapeutic success with rituximab, certain type II anti-CD20 mAbs efficiently induce programmed cell death (PCD), whereas rituximab-like type I anti-CD20 mAbs do not. Here, we show that the humanized, glycoengineered anti-CD20 mAb GA101 and derivatives harboring non-glycoengineered Fc regions are type II mAb that trigger nonapoptotic PCD in a range of B-lymphoma cell lines and primary B-cell malignancies. We demonstrate that GA101-induced cell death is dependent on actin reorganization, can be abrogated by inhibitors of actin polymerization, and is independent of BCL-2 overexpression and caspase activation. GA101-induced PCD is executed by lysosomes which disperse their contents into the cytoplasm and surrounding environment. Taken together, these findings reveal that GA101 is able to potently elicit actin-dependent, lysosomal cell death, which may potentially lead to improved clearance of B-cell malignancies in vivo.

The importance of T cells in the generation of antigen-specific B-cell immunity has been extensively described, but the role B cells play in shaping T-cell memory is uncertain. In healthy controls, exposure to Neisseria meningitidis in the upper respiratory tract is associated with the generation of memory T cells in the mucosal and systemic compartments. However, we demonstrate that in B cell–deficient subjects with X-linked agammaglobulinemia (XLA), naturally acquired T-cell memory responses to meningococcal antigens are reduced compared with healthy control patients. This difference is not found in T-cell memory to an obligate respiratory pathogen, influenza virus. Accordingly, we show that meningococcal antigens up-regulate major histocompatibility complex (MHC) class II, CD40, CD86/80 expression on mucosal and systemic associated B cells and that antigen presentation stimulates T-cell proliferation. A similar reduction in N meningitidis but not influenza antigen–specific T-cell memory was observed in subjects with X-linked hyper IgM syndrome (X-HIM), implicating the interaction of CD40-CD40L in this process. Together, these data implicate B cells in the induction and maintenance of T-cell memory to mucosal colonizing bacteria such as N meningitidis and highlight the importance of B cells beyond antibody production but as a target for immune reconstitution.

The effect of induction therapy with multiple doses of rituximab on the subsequent efficacy and toxicity of anti-CD20 radioimmunotherapy is unknown. We evaluated a novel protocol using 4 weekly infusions of 375 mg/m2 rituximab followed by 2 fractions of 131I-rituximab, preceded by a 100-mg/m2 predose of rituximab, in relapsed indolent B-cell lymphoma. Induction therapy with rituximab significantly increased the effective half-life of 131I-rituximab (P = .003) and high serum levels of rituximab after induction therapy correlated with increased effective half-life of the radioimmunoconjugate (P = .009). Patients with large tumor burdens experienced significant increases in the effective half-life of 131I-rituximab between delivery of the first and second fractions (P = .007). Induction therapy with multiple doses of rituximab did not appear to compromise the clinical efficacy or increase toxicity of subsequent 131I-rituximab radioimmunotherapy. The overall response rate was 94%, with complete response rate 50%. The median time to progression was 20 months, significantly longer than for the last qualifying chemotherapy (P = .001). Fractionation of 131I-rituximab allowed cumulative whole-body doses of more than 120 cGy, approximately 60% greater than those previously achieved with a single administration of a murine radioimmunconjugate, to be delivered without significant hematologic toxicity.

Anti-CD20 monoclonal antibodies (mAbs) are classified into type I (rituximab-like) or type II (tositumomab-like) based on their ability to redistribute CD20 molecules in the plasma membrane and activate various effector functions. To compare type I and II mAbs directly in vivo and maximize Fc effector function, we selected and engineered mAbs with the same mouse IgG2a isotype and assessed their B-cell depleting activity in human CD20 transgenic mice. Despite being the same isotype, having similar affinity, opsonizing activity for phagocytosis, and in vivo half-life, the type II mAb tositumomab (B1) provided substantially longer depletion of B cells from the peripheral blood compared with the type I mAb rituximab (Rit m2a), and 1F5. This difference was also evident within the secondary lymphoid organs, in particular, the spleen. Failure to engage complement did not explain the efficacy of the type II reagents because type I mAbs mutated in the Fc domain (K322A) to prevent C1q binding still did not display equivalent efficacy. These results give support for the use of type II CD20 mAbs in human B-cell diseases.

It has been shown that mesenchymal stem cells (MSCs) induce T cells to become unresponsive. We characterized the phenotype of these T cells by dissecting the effect of MSCs on T-cell activation, proliferation, and effector function. For this purpose, an in vitro murine model was used in which T-cell responses were generated against the male HY minor histocompatibility antigen. In the presence of MSCs, the expression of early activation markers CD25 and CD69 was unaffected but interferon-γ (IFN-γ) production was reduced. The inhibitory effect of MSCs was directed mainly at the level of cell proliferation. Analysis of the cell cycle showed that T cells, stimulated in the presence of MSCs, were arrested at the G1 phase. At the molecular level, cyclin D2 expression was profoundly inhibited, whereas p27kip1 was up-regulated. When MSCs were removed from the cultures and restimulated with the cognate peptide, T cells produced IFN-γ but failed to proliferate. The addition of exogenous interleukin-2 (IL-2) did not restore proliferation. MSCs did not preferentially target any T-cell subset, and the inhibition was also extended to B cells. MSC-mediated inhibition induces an unresponsive T-cell profile that is fully consistent with that observed in division arrest anergy.

The chimeric anti-CD20 monoclonal antibody (mAb), rituximab, is an established part of the management of many non-Hodgkin lymphomas. The in vivo action of rituximab remains elusive, and this partially reflects a lack of highly specific reagents to detect rituximab binding at the cell surface. Here we report a new high-affinity mAb (MB2A4) with fine specificity for the idiotype of rituximab. It is able to detect rituximab in vitro, in the presence of high levels of human immunoglobulin G (IgG), in the serum of patients receiving rituximab therapy, and, surprisingly, when rituximab is bound to CD20 on the cell surface. We propose that the anti–idiotype (Id) binds to rituximab molecules bound univalently at the cell surface, facilitated by the relatively high off-rate of rituximab. This reagent provides new insights into the binding of rituximab at the cell surface and demonstrates a mode of binding that could be exploited for the surface detection of other mAbs with clinical and biologic applications.

Radioimmunotherapy (RIT) has emerged as an effective treatment for lymphoma, however the underlying mechanisms are poorly understood. We therefore investigated the relative contributions of antibody and targeted radiation to the clearance of tumor in vivo, using 2 different syngeneic murine B-cell lymphoma models. Although RIT with 131I–anti–major histocompatibility complex class II (MHCII) was effective in targeting radiation to tumor, no improvement in survival was seen by escalating the radiation dose alone and there were no long-term survivors. In contrast, using the combination of 131I anti-MHCII in the presence of unlabeled anti-idiotype (anti-Id), 100% prolonged disease-free survival was seen in both B-cell lymphoma models at the higher radiation dose. Using in vivo tracking we show that treatment with radiation plus anti-Id monoclonal antibody (mAb) results in a substantially greater reduction of splenic tumor cells than with either treatment alone. Prolonged survival could also be achieved using 131I anti-MHCII plus the signaling anti-CD19 mAb. Furthermore, the ability of these anti–B-cell mAbs to improve survival with targeted radiotherapy appeared to correlate with their ability to initiate intracellular signal transduction. Together these data illustrate that using 1 mAb to target radiation to tumor and a second to induce cell signaling is an effective new strategy in RIT.