Optimal T Cell Activation and B Cell Antibody Responses In Vivo Require the Interaction between Leukocyte Function–Associated Antigen-1 and Kindlin-3
Abstract Mutual interactions of the neoplastic clone with the non-neoplastic immune system may influence immune function and the clinical behaviour of lymphoma. Individuals with immunodeficiency or autoimmune diseases have an increased risk for lymphoma development. The immune microenvironment appears to have a major influence on the prognosis of indolent lymphomas. Conversely, leukemic lymphomas may also cause immunodeficiency: In CLL, direct lymphoma-T cell interactions, which may occur ubiquitously, induce defects in T cell functions (Görgün et al., 2005). We demonstrate here a systemic perturbance of cellular immunity in a prospective study in patients with untreated de novo, limited-stage, non-leukemic indolent B cell lymphomas. Calibrated, quantitative flow cytometry showed a significant reduction of circulating T helper (TH) cells in follicular (FL; n=11; p<0.005) and extranodal marginal zone (eMZL; n=7; p<0.05) lymphomas compared to age-matched healthy persons. Naive TH cells were strongest reduced to 51% (p=0.002) in FL and 24% (p=0.002) in eMZL. Regulatory T cells (CD4loCD25hi; CD4+FoxP3+) were affected less (p=0.04). T cell receptor excision circles within CD4+ cells as assessed by quantitative PCR were not altered in lymphoma patients, indicating neither increased increased thymic output nor homeostatic T cell proliferation to compensate the contracted pool of naive T cells. The TH memory compartments, the global numbers and subsets of CD8+ T (TC) cells, NK, and NKT cells were normal. The peripheral lymphocyte composition was altered differently in early CLL (stage Binet A; leukocyte counts < 28/nl; n=9) with increased TH (p=0.04) and TC (p=0.0002) cells. No significant changes in lymphocyte subsets were noted in monoclonal gammopathy of unknown significance (MGUS; n=6). The functional T cell phenotype in vivo was altered in eMZL as indicated by four- and twofold increased HLA-DR+ TH (p<0.02) and TC (p=0.05) cells. This T cell activation may also explain an increased fraction of terminally differentiated (CD45RA+CD27−) TC cells (p<0.05). Qualitatively similar abnormalities were seen in FL, where activated TH cells were more frequent (p<0.005), and in CLL, where activated TC cells were increased (p=0.04), but not in MGUS. Finally, an increased T cell activation may effect senescence, which was evident by elevated fractions of CD57+ and CD28− cells within the TC compartment of FL/eMZL (p<0.05) and CLL (p<0.005) patients. The activated T cell phenotype was paralleled by increased upregulation of activation markers (CD25, OX40, CD95, p<0.005 for each) and proliferation (p<0.005) by purified CD4 cells from FL/eMZL patients in a standardized anti-CD3/anti-CD28 stimulation culture. None of these parameters was significantly aberrant in CLL. Expression of the activation marker CD69, which is downregulated rapidly after T cell activation, was markedly reduced both in vivo and after in vitro stimulation in FL/eMZL. Collectively, these data demonstrate a global, “preactivated” and presenescent state of peripheral T cells in non-leukemic, indolent T cell lymphomas. Finally, a shift towards TH2 cells was evident in FL/eMZL TH stimulation cultures by increased secretion of IL-4 and IL-5 (p=0.01), but not of IL-2, IFNg, IL-10, and TNFa. This cytokine pattern was absent in CLL and MGUS. The TH2 shift, and the qualitative difference in the immune status in FL/eMZL versus CLL was validated by gene expression profiling of stimulated TH cells with Affymetrix U133 arrays. KEGG annotation revealed decreased expression of proximal TCR signalling molecules and TCR/CD28 transduction pathways with the exception of NFAT in FL/eMZL and CLL. Extensive correlative analyses between gene expression profiles and functional data indicated at least two distinct immune dysregulation patterns: A hyperreactivity/TH2 pattern which is operational even in early disease; and a B cell burden-dependent impairment of TCR signalling. The latter pattern predominates in CLL, which has a comparatively high B cell burden in early disease. These data are clinically relevant since we demonstrate in a prospective trial that untreated FL/eMZL patients fail to respond to protective hepatitis B vaccination (p<0.005). Precise definition of functional T cell defects will permit to study the causes, the prognostic influence, and potential reversibility of immune dysregulation patterns in indolent B cell lymphomas.
Abstract Immunotherapies targeting B-lineage-specific surface marker CD19 had demonstrated promising clinical results. Two CD19 CAR-T therapies (Kymriah® and Yescarta®) have been approved by FDA to treat patients with B cell malignancies, however, the complicated manufacturing process and low throughput limit its accessibility to more patients, especially in developing countries. The first CD3-activating bi-specific antibody targeting CD19, Blincyto, or CD19 BiTE, was approved to treat relapsed and refractory acute lymphoblastic lymphoma (r/r ALL). The relatively short half-life of Blincyto requires continuous IV infusion for weeks to maintain a steady levels of drug exposure, not to mention the high risk of developing severe cytokine release syndrome in patients. We had established a bispecific antibody platform ITabTM (immunotherapy antibody) for the generation of CD3-activating bi-specific antibodies that could potentially overcome the shortcomings of BiTEs. A CH1 domain was introduced into the ITabTM construct design with the intent to increase the molecular weight thus led to extend the serum half-life of the bispecific antibody. A novel CD3-activating and monkey cross-reactive antibody was generated with a less degree of T cell activation and cytokine release compared to BiTEs. A bi-valent binding to tumor associated antigen (TAA) format was established to target tumor cells and/or stem cells expressing very low levels of TAA. We report here the biological properties of the mono-valent/bi-valent binding of CD19 bi-specific antibody with CD3-activating activity (A-319/A-329). A series of studies were conducted to evaluate the bioactivities of A-319/A-329 in vitro and in vivo including binding to CD3 and CD19 antigens, T-cell and B-cell binding activities, T cell activation and proliferation and B cell killing activities in vitro as well as in vivo efficacy using human PBMC engrafted mouse xenograft models. The in vitro data showed that the mono-valent and bi-valent CD19 binding had little effect on the CD3-associated activities including CD3 antigen binding affinity, T cell binding and T cell activation. In contrast, the bi-valent binding format A-329 showed better potency compared to the mono-valent format A-319 in CD19 binding (KD 0.89 nM vs 19.4 nM); B cell binding (EC50 at 2.3 pM vs 462 pM); in vitro human B cell killing (EC50 0.2 pM vs 3.4 pM). Both A-319 and A-329 were capable of mediating tumor cell lysis with EC50 at 0.03~4 pM. A-329 demonstrated a greater killing activity on Pfeiffer, a human diffuse large B-cell lymphoma (DLBCL) cell line with a low expression of CD19 antigen. In human PBMC engrafted NOG mouse xenograft model, a dose-dependent tumor growth inhibition was observed at 0.5~100 µg/kg in both A-319 and A-329. In monkey studies, when A-319 and A-329 was dosed at 3, 10, 30 µg/kg, twice or three times weekly via IV infusion for A-329 or A-319. Dose-dependent elimination of peripheral blood B cells were observed with both ITabTM. The CD19 bi-valent format of A-329 revealed more complete B cell killing in monkeys. No significant difference of cytokine induction or liver injuries were observed between A-319 and A-329. These results demonstrated that both A-319 and A-329 may benefit patients with B cell malignancies with less dosing frequency and lower cytokine inductions especially, A-329 may have the potential to targeting the low CD19 expressing tumor stem cells. Disclosures No relevant conflicts of interest to declare.
Abstract Introduction Along with CD20 and CD22, the restricted expression of CD19 to the B-cell lineage makes it an attractive target for the therapeutic treatment of B-cell malignancies. Many monoclonal antibodies and antibody drug conjugates specific to CD19 have been described, including bispecific T-cell redirecting antibodies (T-BsAbs). In addition, anti-CD19 chimeric antigen receptor T-cells (CAR-Ts) have been approved to treat leukemia. To date, toxicity from over-activation of T-cells and large-scale production of CAR-Ts still hinder this approach. Bispecific T-cell engaging antibodies redirecting T cells to CD19 circumvent the latter problem but to date have shown similar T-cell over-activation, as well as significant neurotoxicity. Utilizing TeneoSeek, a next generation sequencing (NGS)-based discovery pipeline that uses in silico analysis of heavy chain only/fixed light chain antibody (HCA/Flic, respectively) sequences to enrich for antigen specific antibodies, we made a high affinity αCD19 HCA and a library of αCD3 Flic antibodies that showed a >2 log range of EC50s for T cell activation in vitro. Of note, the library contained a selectively-activating αCD3 that induced potent T-cell dependent lysis of lymphoma cells (when paired with an αCD19 HCA) with minimal cytokine secretion. To characterize the relative efficacy and potential therapeutic window of this unique molecule, we compared the low-activating (and Fc-containing) CD19 x CD3 to two pan T-cell activating bispecific CD19 x CD3 antibodies (blinatumomab and another developed in-house) in vitro and in vivo for T-cell activation, efficacy in killing lymphoma cells, and toxicity. Methods T-cell activation was measured via flow cytometry (CD69 and CD25 expression) and cytokine ELISA (IL-2, IL-6, IL-10, INF-ɣ, and TNFα) in vitro. Lysis of B-cell tumor cell lines (Raji, Ramos, and Nalm6) was measured via calcein release in vitro. In vivo, NOG mice were engrafted with human peripheral blood mononuclear cells (huPBMC) and human lymphoma cell lines, and the mice treated with weekly injections of T-BsAbs. Tumor burden was evaluated via caliper measurement. Pharmacokinetic (PK) studies were performed in NOG mice using ELISA. Results EC50s for cytotoxicity were in the single-digit nanomolar range for the selective T cell activating T-BsAb and sub-nanomolar for the pan T-cell activating controls. The selective T cell activator showed markedly reduced cytokine release for all cytokines tested compared to the pan T-cell controls even at saturating concentrations. In vivo, established CD19 positive B-cell tumors were cleared in NOG mice in the presence of huPBMC. PK profiles of both molecules generated in-house (selective and pan T-cell activators) were consistent with those of an IgG in mice. No activation of T-cells was observed in vitro or in vivo in the absence of CD19 expressing target cells. Conclusions Both the selectively-activating and the pan T-cell activating control bispecific antibodies killed lymphoma cells in vitro and in vivo in a CD19-dependent manner. While the pan T-cell activating controls showed T-cell activation comparable to other CD3-engaging bispecifics, the selective activator induced significantly reduced cytokine secretion by T-cells and demonstrated a half-life consistent with other IgG antibodies. In summary, our selectively activating CD19 x CD3 T-BsAb shows promise as a lymphoma therapeutic differentiated from current T-cell targeted therapies currently in the clinic and in clinical trials. Disclosures Malik: Teneobio, Inc.: Employment. Buelow:Teneobio Inc.: Employment. Avanzino:Teneobio, Inc.: Employment. Balasubramani:Teneobio, Inc.: Employment. Boudreau:Teneobio, Inc.: Employment. Clarke:Teneobio, Inc.: Employment. Dang:Teneobio, Inc.: Employment. Davison:Teneobio, Inc.: Employment. Force Aldred:Teneobio Inc.: Employment. Harris:Teneobio, Inc.: Employment. Jorgensen:Teneobio, Inc.: Employment. Li:Teneobio, Inc.: Employment. Medlari:Teneobio, Inc.: Employment. Narayan:Teneobio, Inc.: Employment. Ogana:Teneobio, Inc.: Employment. Pham:Teneobio Inc.: Employment. Prabhakar:Teneobio, Inc.: Employment. Rangaswamy:Teneobio, Inc.: Employment. Sankaran:Teneobio, Inc.: Employment. Schellenberger:Teneobio, Inc.: Employment. Ugamraj:Teneobio, Inc.: Employment. Trinklein:Teneobio, Inc.: Employment. Van Schooten:Teneobio, Inc.: Employment.
Precursor B-cell acute lymphoblastic leukemia (B-ALL) is an aggressive hematopoietic neoplasm characterized by recurrent genetic lesions resulting in B-cell maturation arrest and malignant transformation. Even with the addition of targeted therapies to conventional treatment regimens, prognosis for adults with high risk disease remains poor, particularly for those patients with relapsed or refractory disease. Despite an arrest in B cell maturation, we previously showed that human B-ALL blasts retain the capacity for reprogramming to the myeloid lineage (McClellan et al, PNAS 2015). While the concept of forced differentiation was proposed several decades ago, no differentiation therapies have been effective in the treatment of B-ALL. Thus, we sought to investigate the therapeutic implications of myeloid lineage reprogramming of B-ALL cells. We speculated that myeloid-reprogramming of B-ALL cells into antigen presenting cells (APCs) could induce tumor-specific T cell responses through effective presentation of aberrant tumor-associated self-peptides. To test this hypothesis, we generated murine models of B-ALL capable of reprogramming to the myeloid lineage through the inducible expression of two transcription factors, CEBPα and PU.1. Ectopic expression of these factors efficiently reprogrammed B-ALL cells into myeloid-lineage APCs, expressing myeloid markers (CD11b, CD14, CD115, and Ly6C). Reprogramming ablated the tumorigenicity of these cells as they acquired APC characteristics, including phagocytic activity and expression of antigen presentation and co-stimulation molecules: MHC-I (3.13-fold, p=0.0018), MHC-II (8.6-fold, p<0.0001), CD80 (62.1-fold, p<0.0001), CD86 (107.6-fold, p<0.0001), and CD40 (92-fold, p<0.0001). Using chicken ovalbumin as a model antigen and DO11.10 transgenic CD4+ T cells, we demonstrated that reprogrammed B-ALL cells, but not parental blasts, can process and present both endogenous and exogenous peptides for antigen-specific T cell activation. To explore the therapeutic potential of B-ALL reprogramming, we engrafted immunodeficient (NSG) and immunocompetent syngeneic (BALB/c) mice with our B-ALL model and induced myeloid reprogramming in vivo. While B-ALL reprogramming in immunodeficient mice led to a three day extension in median survival (p=0.0016, n= 5 per group), all of the mice succumbed to their disease. Strikingly, B-ALL reprogramming in immunocompetent mice led to complete tumor regression and survival of the entire cohort 100 days post treatment (p<0.0001, n=10 per group), suggesting that reprogramming induced immune-mediated tumor eradication. Importantly, these animals were not susceptible to subsequent B-ALL re-challenge, demonstrating successful generation of durable, systemic, and protective immunity. In order to investigate the mechanism underlying tumor eradication, we depleted BALB/c mice of CD4+ or CD8+ T cells. Depletion of either T cell population abrogated the therapeutic benefit of B-ALL reprogramming, indicating that reprogrammed B-ALL cells stimulate T cell activation in vivo. Further analysis of the CD8 T cell repertoire by TCRVb chain usage revealed significant 10.3-fold (p=0.0109, n=5 per group) expansion of a single TCRVb chain family in response to B-ALL reprogramming, consistent with an oligoclonal T cell response. Following reprogramming, a 4.01-fold increase in the frequency of infiltrating T cells is observed in the bone marrow (p=0.0028), including both activated (CD25+/CD69+) (1.62-fold, p=0.018) and effector memory (CD44+CD62L-) (1.99-fold, p=0.0097) T cells. Finally, using a dual tumor model, we demonstrated that myeloid reprogramming-dependent T cell activation eradicates malignant cells systemically, as demonstrated by regression of contralateral tumors lacking reprogramming. Together, our data suggests that (1) B-ALL cells reprogrammed to the myeloid lineage can operate as potent APCs capable of presenting both endogenous and exogenous tumor-associated antigens, (2) in vivo B-ALL reprogramming elicits robust immune activation, dependent on both CD4+ and CD8+ T cells, and (3) B-ALL reprogramming-induced immune activation is potent, durable, tumor-eradicating, and systemic. Thus, reprogramming of B-ALL cells into APCs represents a novel immunotherapeutic strategy with potential clinical benefit for the management of B-ALL disease progression. Disclosures Majeti: Forty Seven Inc.: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties; BioMarin: Consultancy.
Abstract Abstract 3721 Background: CD19 is expressed from early B cell development through differentiation into plasma cells, and is an attractive alternative to CD20 as a target for the development of therapeutic antibodies to treat B cell malignancies. T cells are potent tumor-killing effector cells that cannot be recruited by native antibodies. The CD3 RECRUIT-TandAb AFM11, a humanized bispecific tetravalent antibody with two binding sites for both CD3 and CD19, is a novel therapeutic for the treatment of NHL that harnesses the cytotoxic nature of T cells. Methods: We engineered a bispecific anti-CD19/anti-CD3e tetravalent TandAb with humanized and affinity-matured variable domains. The TandAb's binding properties, T cell-mediated cytotoxic activity, and target-mediated T cell activation were characterized in a panel of in vitro assays. In vivo efficacy was evaluated in a murine NOD/scid xenograft model reconstituted with human PBMC. Results: AFM11 mediates highly potent CD19+ tumor cell lysis in cytotoxicity assays performed on a panel of cell lines (JOK-1, Raji, Nalm-6, MEC-1, VAL, Daudi) and primary B-CLL tumors: EC50 values are in the low- to sub-picomolar range and do not correlate with the expression density of CD19 on the target cell lines. The cytotoxic activity of tetravalent AFM11 is superior to that of alternative bivalent antibody formats possessing only a single binding site for both CD19 and CD3. High affinity binding of AFM11 to CD19 and to CD3 is essential for efficacious T cell recruitment. Both CD8+ and CD4+ T cells mediate cytotoxicity however the former exhibit much faster killing. We observe that AFM11 displays similar cytotoxic efficacy at different effector to target ratios (from 5:1 to 1:5) in cytotoxicity assays; this suggests that T cells are engaged in the serial killing of CD19+ target cells. In the absence of CD19+ target cells in vitro, AFM11 does not elicit T cell activation as manifested by cytokine release (from a panel of ten cytokines associated with T cell activation), their proliferation, or their expression of activation markers. AFM11 activates T cells exclusively in the presence of its targets and mediates lysis of CD19+ cells while sparing antigen-negative bystanders. In the absence of CD19+ target cells, AFM11 concentrations in excess of 500-fold over EC50 induce down-modulation of the CD3/TCR complex. Yet, AFM11-treated T cells can be re-engaged for target cell lysis. All of these features of AFM11-induced T cell activation may contribute additional safety without compromising its efficacy. In vivo AFM11 demonstrates a robust dose-dependent inhibition of subcutaneous Raji tumors in mice. At 5 mg/kg AFM11 demonstrates a complete suppression of tumor growth, and even at 5 ug/kg tumor growth is reduced by 60%. Moreover, we observe that a single administration of AFM11 produces inhibition of tumor growth similar to that of 5 consecutive administrations. Conclusions: In summary, our in vitro and in vivo experiments with AFM11 demonstrate the high potency and efficacy of its anti-tumor cytotoxicity. Thus, AFM11 is a novel highly efficacious drug candidate for the treatment of B cell malignancies with an advantageous safety profile. Disclosures: Zhukovsky: Affimed Therapeutics AG: Employment, Equity Ownership. Reusch:Affimed Therapeutics AG: Employment. Burkhardt:Affimed Therapeutics AG: Employment. Knackmuss:Affimed Therapeutics AG: Employment. Fucek:Affimed Therapeutics AG: Employment. Eser:Affimed Therapeutics AG: Employment. McAleese:Affimed Therapeutics AG: Employment. Ellwanger:Affimed Therapeutics AG: Employment.
Immunoglobulin (Ig) class switch recombination is associated with the production and splicing of germline IgCH messenger RNA transcripts. Levels of gamma 1 transcripts in mouse spleen sections were assessed by semiquantitative analysis of reverse transcriptase polymerase chain reaction (PCR) products during primary and secondary antibody responses to chicken gamma globulin (CGG). This was correlated with the appearance of CGG-specific B cells and their growth and differentiation to plasma cells. After primary immunization with CGG, gamma 1 switch transcripts appeared after 4 d, peaked at a median of six times starting levels between 10 and 18 d after immunization, and returned to background levels before secondary immunization at 5 wk. By contrast, after secondary challenge with CGG, a sevenfold increase in transcripts occurs during the first d. The level again doubles by day 3, when it is six times that which is seen at the peak of the primary response. After day 4, there was a gradual decline over the next 2-3 wk. Within 12 h of secondary immunization, antigen-specific memory B cells appeared in the outer I zone and by 24 h entered S phase, presumably as a result of cognate interaction with primed T cells. Over the next few hours, they migrated to the edge of the red pulp, where they grew exponentially until the fourth day, when they synchronously differentiated to become plasma cells. The same pattern was seen for the migration, growth, and differentiation of virgin hapten-specific B cells when CGG-primed mice were challenged with hapten protein. The continued production of transcripts after day 3 indicates that switching also occurs in germinal centers, but in a relatively small proportion of their B cells. The impressive early production of switch transcripts during T cell-dependent antibody responses occurs in cells that are about to undergo massive clonal expansion. It is argued that Ig class switching at this time, which is associated with cognate T cell-B cell interaction in the T zone, has a major impact on the class and subclasses of Ig produced during the response.
Abstract Abstract 3935 Rituximab, a chimeric anti-C20 monoclonal antibody, has been extensively used over the last decade for the therapy of B cell malignancies. Recent clinical data suggest that rituximab may affect T cell function, increasing the risk of T cell dependent infections in heavily-treated patients. The current study was designed to investigate the effect of rituximab on T cell activation and assess T cell function following the addition of rituximab to purified T cells. The T cell activation profile, dependent on rituximab administration, was evaluated in vivo and in vitro. Peripheral blood mononuclear cells (PBMCs) generated from B-cell non-Hodgkin lymphoma (NHL) patients prior and immediately after the administration of 375 mg/m2 rituximab, were examined for the expression of inflammatory cytokines. The in vitro studies were performed by using CD25 depleted PBMCs or B cell depleted T cells (CD3+CD25-CD19-). The obtained cells were stimulated with allogeneic dendritic cells (DCs), in the absence or presence or 2 mg/ml rituximab. T cell activation was evaluated using immunophenotypic markers, cytokine profile and T cell proliferation assay. Eight NHL patients participated in the study. The level of T cells expressing inflammatory cytokines was significantly decreased following the administration of a single dose of rituximab. T cells expressing IL-2 declined from a mean level of 26.5% to 11.5% and the level of IFN- γ decreased from 22% to 4.2%. Further administration of rituximab, up to 4 weekly doses, resulted in an additional decline in the amount of inflammatory cytokine producing T cells to a level of 1.4% for IL-2 and 3.5% for IFN-g. However, repeated evaluation, performed at 4 months after completing rituximab, showed restoration of the inflammatory population. In accord with this inhibitory effect, in vitro stimulation of T cells with allogeneic DCs, in the presence of rituximab, resulted in a significant decrease in activation markers (CD25, GITR and CTLA-4) (Table 1). These changes were accompanied by a marked reduction in inflammatory cytokine production and proliferative capacity. Of interest, these inhibitory effects were also obtained whilst using B cell depleted T cells (CD3+CD25-CD19-). In conclusion, rituximab administration results in a transient T cell inactivation, demonstrated through the reduction in inflammatory cytokine production and T cell proliferation capacity. This effect appears to be non-B cell dependent, being obtained in the absence of B cell in the culture, and may account for clinical observations in ameliorating T-cell dependent disorders, such as graft-versus-host disease. Table 1. Activation profile depending on rituximab (in vitro) Without rituximab With rituximab *Activation marker (%) CD25 27 9 GITR 15.6 4.7 CTLA4 17.7 7 *Cytokines expression (%) IL-2 22 2 IL12 16 4 IFN-gamma 21 1.8 T cells proliferation (O.D.) DC stimulation 1.528 0.580 CMV stimulation 1.563 0.570 anti CD3/CD28 stimulation 0.705 0.407 * Gated out of lymphocytes Disclosures: No relevant conflicts of interest to declare.
AbstractMigration and adhesion play critical roles in B cells, regulating recirculation between lymphoid organs, migration within lymphoid tissue and interaction with CD4+ T cells. However, there is limited knowledge of how B cells integrate chemokine receptor and integrin signaling with B cell activation to generate efficient humoral responses. Here we show that the WNK1 kinase, a regulator of migration and adhesion, is essential in B cells for T-dependent antibody responses. We demonstrate that WNK1 transduces signals from the BCR, CXCR5 and CD40, and using intravital imaging we show that WNK1 regulates migration of naive and activated B cells, and their interactions with T cells. Unexpectedly, we show that WNK1 is required for BCR- and CD40-induced proliferation, acting through the OXSR1 and STK39 kinases, and for efficient B cell-T cell collaboration in vivo. Thus, WNK1 is critical for humoral immune responses, by regulating B cell migration, adhesion and T cell-dependent activation.SummaryThe WNK1 kinase is essential in B cells for T-dependent antibody responses because it is activated by signaling from BCR, CXCR5 and CD40 and regulates B cell migration, adhesion, T-dependent activation, and differentiation into germinal center B cells and plasma cells.
Abstract The anti-CD20/CD3 T-cell recruiting bispecific antibody (CD20-TDB) is a full-length, fully humanized IgG1 molecule currently under clinical investigation in B-cell malignancies. Previously we have shown that CD20-TDB is highly active in killing CD20-expressing B cells, including primary patient leukemia and lymphoma cells both in vitro and in vivo (Sun et.al. STM 2015). The current standard therapy in B-cell malignancies often contains anti-CD20 based monoclonal antibody and various chemo reagents such as the R-CHOP regimen in Non-Hodgkin's' Lymphoma. Previously we have shown that CD20-TDB can be potentially combined with rituximab as very low level of antigen expression or antigen receptor occupancy is needed for CD20-TDB activity. As many chemo reagents have non-targeted, anti-proliferative activity or immune suppressive activity such as glucocorticoids, it's conceivable that they could potentially interfere with T-cell activation and the subsequent T-cell proliferation and therefore negatively affect CD20-TDB activity. In addition, as a T-cell recruiting bispecific reagent, cell killing activity of CD20-TDB is dependent on T-cell activation which can be subject to negative regulation posed by checkpoint molecules such as PD-1/PD-L1. Here in an effort to better understand the clinical applicability and to improve upon single-agent activity of CD20-TDB, we evaluated the combinability of CD20-TDB with standard-of-care chemo reagents as well as potential synergy of CD20-TDB with PD-1/PD-L1 blockade in vitro and in vivo. B-cell killing activity of CD20-TDB was not significantly impacted by high concentration of chemo reagents including cyclophosphamide, hydroxydaunorubicin, vincristine, and dexamethasone individually in vitro. In vivo in human CD20/CD3 double transgenic mice, no apparent inhibitory effect on CD20-TDB activity in T-cell activation and B-cell depletion was observed with cyclophosphamide, hydroxydaunorubicin, vincristine, and prednisone either individually or in combination. In vitro, PD-1 and PD-L1 expression appeared to be upregulated on T-cells and B-cells respectively upon CD20-TDB treatment, though the expression of PD-1/PD-L1 didn't appear to inhibit the B-cell killing activity of CD20-TDB significantly. The in vivo anti-tumor activity of the combination of CD20-TDB and anti-PD-L1, as well as CD20-TDB and anti-PD-1, was evaluated in an A20-human CD20 syngeneic mouse lymphoma model. In the A20-human CD20 mouse B-lymphoma tumor model, where the target B lymphoma cells uniformly express high level of PD-L1, single-agent CD20-TDB did not significantly inhibit tumor growth. Treatment with single-agent anti-PD-L1 inhibited tumor growth and resulted in three partial responses (tumor regression of more than 50% but less than 100% of the starting tumor volume) out of nine treated animals. The combination of CD20-TDB and anti-PD-L1 resulted in substantially greater tumor growth inhibition compared to either agent alone and resulted in tumor regression in the majority of the nine animals tested, achieving eight partial responses and one complete response (100% tumor regression, no measurable tumor). Similar results were observed with the combination of CD20-TDB and anti-PD-1. Together, these results suggest that CD20-TDB can have broad clinical applicability, either combining with chemo reagents to enable flexible treatment strategies to incorporate CD20-TDB into current standard of therapy for B cell malignancies or with immune checkpoint inhibitors such as anti-PD-L1/PD-1 to improve upon single-agent efficacy. Disclosures Sun: Genentech Inc.: Employment. Wang:Genentech Inc.: Employment. Clark:Genentech Inc.: Employment. Hristopoulos:Genentech Inc.: Employment. Ellerman:Genentech Inc.: Employment. Mathieu:Genentech Inc.: Employment. Chu:Genentech Inc.: Employment. Wang:Genentech Inc.: Employment. Totpal:Genentech Inc.: Employment. Ebens:NGM: Employment. Polson:Genentech Inc.: Employment. Gould:Genentech Inc.: Employment.
Abstract CD19 targeted 2nd generation chimeric antigen receptor T (CAR T) cells have been successful against relapsed and/or refractory B cell malignancies. The pending FDA-approval of 2 separate CD19 targeted CAR T products highlight the need to understand the biology behind this novel therapy. CAR design includes a single-chain variable fragment, which encodes antigen-binding, fused to a transmembrane domain, co-stimulatory domain, and CD3ζ activation domain. The two CARs likely to be approved as standard of care include a 41BB or CD28 co-stimulatory domain. CD28 is a critical co-stimulatory receptor required for full T cell activation and persistence, while 4-1BB is a member of the tumor necrosis factor receptor family and also a critical T cell co-stimulatory factor. Early evaluation of the co-stimulatory domains role in CAR design confirmed that they are required to enhance T cell function, but lacked insight regarding their mechanism for this enhancement. Furthermore, clinical outcomes suggest that the co-stimulatory domains in CARs support different T cell functions in patients. For example, while overall outcomes are similar between 41BB (19BBz) and CD28-containing CARs (1928z), 19BBz CAR T cells can persist for years in patients, but functional 1928z CAR T cells rarely persist longer than a month. Recent studies are providing insight to these differences and have demonstrated that 4-1BB-containing CARs reduce T cell exhaustion, enhance persistence, and increase central memory differentiation and mitochondrial biogenesis, while CD28-containing CARs support robust T cell activation and exhaustion, and are associated with effector-like differentiation. However, these studies have been performed mostly in vitro or in immune deficient mice, which limits their ability to model complex immune biology. Therefore, we evaluated murine CD19-targeting CARs with a 4-1BB (m19BBz) or CD28- (m1928z) co-stimulatory domain in relevant animal models of immunity. We directly compared m19BBz and m1928z CAR T cell immune phenotype, cytotoxicity, cytokine production, gene expression, intracellular signaling, and in vivo persistence, expansion, and B cell acute lymphoblastic leukemia (B-ALL) eradication. In vitro assays revealed that m1928z CAR T cells had enhanced cytotoxicity and cytokine production compared to m19BBz CAR T cells. Also, evaluation of m1928z and m19BBz CAR T cells displayed similar immune phenotypes, but markedly different gene expression with m1928z CAR T cells upregulating genes related to effector function and exhaustion, while m19BBz CAR upregulated genes critical for NFkB regulation, T cell quiescence and memory. In vivo, both m1928z and m19BBz CAR T cells supported equivalent protection against B-ALL. Similar to patients, in our mouse models there are functional differences between the mouse CD19-targeted CAR T cells. At 1 week post-infusion m19BBz CAR T cells are present in the blood of mice at significantly greater levels than m1928z CAR T cells. Furthermore, m19BBz CAR T cells enhance proliferation and/or anti-apoptosis protein expression to enhance B cell killing, which is evidenced by our observation that irradiation significantly weakens the in vivo efficacy of m19BBz but not m1928z CAR T cells. Our results suggest that B cell killing by m1928z CAR T cells is not impacted by irradiation because of their efficacious cytotoxicity of B cells. In contrast, m19BBz CAR T cells have enhanced viability and anti-apoptosis protein expression, which allows them to compensate for reduced effector function. We investigated potential mechanisms for the enhanced viability and anti-apoptosis of m19BBz CAR T cells and determined that NFkB signaling is upregulated much greater by m19BBz than m1928z. We have observed this difference in both a reporter cell line and primary mouse T cells. We are now dissecting what cellular components mediate increased NFkB signaling by the m19BBz CAR. Our animal models recapitulate equivalent anti-leukemia efficacy of CD19-targeted CAR T cells regardless of co-stimulatory domain, but underscore that anti-leukemia killing is mediated by different methods depending on the co-stimulatory domain. Our work sheds light on how 4-1BB mechanistically regulates and impacts CAR T function and has implications for future CAR design and evaluation. Disclosures No relevant conflicts of interest to declare.
