Design and Efficacy of a Monovalent Bispecific PD-1/CTLA4 Antibody That Enhances CTLA4 Blockade on PD-1+ Activated T Cells.

The clinical benefit of PD-1 blockade can be improved by combination with CTLA4 inhibition but is commensurate with significant immune-related adverse events suboptimally limiting the doses of anti-CTLA4 mAb that can be used. MEDI5752 is a monovalent bispecific antibody designed to suppress the PD-1 pathway and provide modulated CTLA4 inhibition favoring enhanced blockade on PD-1+ activated T cells. We show that MEDI5752 preferentially saturates CTLA4 on PD-1+ T cells versus PD-1- T cells, reducing the dose required to elicit IL2 secretion. Unlike conventional PD-1/CTLA4 mAbs, MEDI5752 leads to the rapid internalization and degradation of PD-1. Moreover, we show that MEDI5752 preferentially localizes and accumulates in tumors providing enhanced activity when compared with a combination of mAbs targeting PD-1 and CTLA4 in vivo. Following treatment with MEDI5752, robust partial responses were observed in two patients with advanced solid tumors. MEDI5752 represents a novel immunotherapy engineered to preferentially inhibit CTLA4 on PD-1+ T cells. SIGNIFICANCE: The unique characteristics of MEDI5752 represent a novel immunotherapy engineered to direct CTLA4 inhibition to PD-1+ T cells with the potential for differentiated activity when compared with current conventional mAb combination strategies targeting PD-1 and CTLA4. This molecule therefore represents a step forward in the rational design of cancer immunotherapy.See related commentary by Burton and Tawbi, p. 1008.This article is highlighted in the In This Issue feature, p. 995.

Preclinical Characterization of an Antibody-Drug Conjugate Targeting CS-1 and the Identification of Uncharacterized Populations of CS-1-Positive Cells.

Multiple myeloma is a hematologic cancer that disrupts normal bone marrow function and has multiple lines of therapeutic options, but is incurable as patients ultimately relapse. We developed a novel antibody-drug conjugate (ADC) targeting CS-1, a protein that is highly expressed on multiple myeloma tumor cells. The anti-CS-1 mAb specifically bound to cells expressing CS-1 and, when conjugated to a cytotoxic pyrrolobenzodiazepine payload, reduced the viability of multiple myeloma cell lines in vitro In mouse models of multiple myeloma, a single administration of the CS-1 ADC caused durable regressions in disseminated models and complete regression in a subcutaneous model. In an exploratory study in cynomolgus monkeys, the CS-1 ADC demonstrated a half-life of 3 to 6 days; however, no highest nonseverely toxic dose was achieved, as bone marrow toxicity was dose limiting. Bone marrow from dosed monkeys showed reductions in progenitor cells as compared with normal marrow. In vitro cell killing assays demonstrated that the CS-1 ADC substantially reduced the number of progenitor cells in healthy bone marrow, leading us to identify previously unreported CS-1 expression on a small population of progenitor cells in the myeloid-erythroid lineage. This finding suggests that bone marrow toxicity is the result of both on-target and off-target killing by the ADC.

HER2 antibody-drug conjugate controls growth of breast cancer brain metastases in hematogenous xenograft models, with heterogeneous blood-tumor barrier penetration unlinked to a passive marker.

BACKGROUND: Brain metastases of HER2+ breast cancer persist as a clinical challenge. Many therapeutics directed at human epidermal growth factor receptor 2 (HER2) are antibodies or antibody-drug conjugates (ADCs), and their permeability through the blood-tumor barrier (BTB) is poorly understood. We investigated the efficacy of a biparatopic anti-HER2 antibody-tubulysin conjugate (bHER2-ATC) in preclinical models of brain metastases. METHODS: The compound was evaluated in 2 hematogenous HER2+ brain metastasis mouse models, SUM190-BR and JIMT-1-BR. Endpoints included metastasis count, compound brain penetration, cancer cell proliferation, and apoptosis. RESULTS: Biparatopic HER2-ATC 3 mg/kg prevented metastasis outgrowth in the JIMT-1-BR model. At 1 mg/kg bHER2-ATC, a 70% and 92% reduction in large and micrometastases was observed. For the SUM190-BR model, an 85% and 53% reduction, respectively, in large and micrometastases was observed at 3 mg/kg, without statistical significance. Proliferation was reduced in both models at the highest dose. At the endpoint, bHER2-ATC uptake covered a median of 4-6% and 7-17% of metastasis area in the JIMT-1-BR and SUM190-BR models, respectively. Maximal compound uptake in the models was 19% and 86% in JIMT-1-BR and SUM190-BR, respectively. Multiple lesions in both models demonstrated ADC uptake in the absence or low diffusion of Texas Red Dextran, a marker of paracellular permeability. Using in vitro BTB assays, the ADC was endocytosed into brain endothelial cells, identifying a potentially new mechanism of antibody permeability. CONCLUSIONS: Biparatopic HER2-ATC significantly prevented JIMT-1-BR brain metastasis outgrowth and showed activity in the SUM190-BR model. The bHER2-ATC penetration into metastases that are impermeable to fluorescent dye suggested an endocytic mechanism of brain penetration.

Imaging CD4 T Cell Interstitial Migration in the Inflamed Dermis.

The ability of CD4 T cells to carry out effector functions is dependent upon the rapid and efficient migration of these cells in inflamed peripheral tissues through an as-yet undefined mechanism. The application of multiphoton microscopy to the study of the immune system provides a tool to measure the dynamics of immune responses within intact tissues. Here we present a protocol for non-invasive intravital multiphoton imaging of CD4 T cells in the inflamed mouse ear dermis. Use of a custom imaging platform and a venous catheter allows for the visualization of CD4 T cell dynamics in the dermal interstitium, with the ability to interrogate these cells in real-time via the addition of blocking antibodies to key molecular components involved in motility. This system provides advantages over both in vitro models and surgically invasive imaging procedures. Understanding the pathways used by CD4 T cells for motility may ultimately provide insight into the basic function of CD4 T cells as well as the pathogenesis of both autoimmune diseases and pathology from chronic infections.

Inflammation-induced interstitial migration of effector CD4⁺ T cells is dependent on integrin αV.

Leukocytes must traverse inflamed tissues to effectively control local infection. Although motility in dense tissues seems to be integrin independent and based on actomyosin-mediated protrusion and contraction, during inflammation, changes to the extracellular matrix (ECM) may necessitate distinct motility requirements. Indeed, we found that the interstitial motility of T cells was critically dependent on Arg-Gly-Asp (RGD)-binding integrins in the inflamed dermis. Inflammation-induced deposition of fibronectin was functionally linked to higher expression of integrin αV on effector CD4⁺ T cells. By intravital multiphoton imaging, we found that the motility of CD4⁺ T cells was dependent on αV expression. Selective blockade or knockdown of αV arrested T helper type 1 (TH1) cells in the inflamed tissue and attenuated local effector function. Our data demonstrate context-dependent specificity of lymphocyte movement in inflamed tissues that is essential for protective immunity.

Uropod elongation is a common final step in leukocyte extravasation through inflamed vessels.

The efficient trafficking of immune cells into peripheral nonlymphoid tissues is key to enact their protective functions. Despite considerable advances in our understanding of cell migration in secondary lymphoid organs, real-time leukocyte recruitment into inflamed tissues is not well characterized. The conventional multistep paradigm of leukocyte extravasation depends on CD18 integrin-mediated events such as rapid arrest and crawling on the surface of the endothelium and transmigration through the endothelial layer. Using enhanced three-dimensional detection of fluorescent CD18 fusion proteins in a newly developed knockin mouse, we report that extravasating leukocytes (neutrophils, monocytes, and T cells) show delayed uropod detachment and become extremely elongated before complete transmigration across the endothelium. Additionally, these cells deposit CD18(+) microparticles at the subendothelial layer before retracting the stretched uropod. Experiments with knockout mice and blocking antibodies reveal that the uropod elongation and microparticle formation are the result of LFA-1-mediated adhesion and VLA-3-mediated cell migration through the vascular basement membrane. These findings suggest that uropod elongation is a final step in the leukocyte extravasation cascade, which may be important for precise regulation of leukocyte recruitment into inflamed tissues.

Leishmania induces survival, proliferation and elevated cellular dNTP levels in human monocytes promoting acceleration of HIV co-infection.

Leishmaniasis is a parasitic disease that is widely prevalent in many tropical and sub-tropical regions of the world. Infection with Leishmania has been recognized to induce a striking acceleration of Human Immunodeficiency Virus Type 1 (HIV-1) infection in coinfected individuals through as yet incompletely understood mechanisms. Cells of the monocyte/macrophage lineage are the predominant cell types coinfected by both pathogens. Monocytes and macrophages contain extremely low levels of deoxynucleoside triphosphates (dNTPs) due to their lack of cell cycling and S phase, where dNTP biosynthesis is specifically activated. Lentiviruses, such as HIV-1, are unique among retroviruses in their ability to replicate in these non-dividing cells due, at least in part, to their highly efficient reverse transcriptase (RT). Nonetheless, viral replication progresses more efficiently in the setting of higher intracellular dNTP concentrations related to enhanced enzyme kinetics of the viral RT. In the present study, in vitro infection of CD14+ peripheral blood-derived human monocytes with Leishmania major was found to induce differentiation, marked elevation of cellular p53R2 ribonucleotide reductase subunit and R2 subunit expression. The R2 subunit is restricted to the S phase of the cell cycle. Our dNTP assay demonstrated significant elevation of intracellular monocyte-derived macrophages (MDMs) dNTP concentrations in Leishmania-infected cell populations as compared to control cells. Infection of Leishmania-maturated MDMs with a pseudotyped GFP expressing HIV-1 resulted in increased numbers of GFP+ cells in the Leishmania-maturated MDMs as compared to control cells. Interestingly, a sub-population of Leishmania-maturated MDMs was found to have re-entered the cell cycle, as demonstrated by BrdU labeling. In conclusion, Leishmania infection of primary human monocytes promotes the induction of an S phase environment and elevated dNTP levels with notable elevation of HIV-1 expression in the setting of coinfection.

CD4+ T cells modulate expansion and survival but not functional properties of effector and memory CD8+ T cells induced by malaria sporozoites.

CD4(+) helper T cells are critical orchestrators of immune responses to infection and vaccination. During primary responses, naïve CD8(+) T cells may need "CD4 help" for optimal development of memory populations. The immunological factors attributed to CD4 help depend on the context of immunization and vary depending on the priming system. In response to immunization with radiation-attenuated Plasmodium yoelii sporozoites, CD8(+) T cells in BALB/c mice fail to generate large numbers of effector cells without help from CD4(+) T cells--a defect not observed in most systems. Given this unique early dependence on CD4 help, we evaluated the effects of CD4(+) cells on the development of functional properties of CD8(+) T cells and on their ability to abolish infection. First, we determined that this effect was not mediated by CD4(+) non-T cells and did not involve CD1d-restricted NKT cells. We found that CD8(+) T cells induced by sporozoites without CD4 help formed memory populations severely reduced in magnitude that could not limit parasite development in the liver. The inability of these "helpless" memory T cells to protect is not a result of defects in effector function, as their capacity to produce cytokines and undergo cytotoxic degranulation was indistinguishable from control memory T cells. These data indicate that CD4(+) T help may not be necessary to develop the functional attributes of CD8(+) T cells; however they are crucial to ensure the survival of effector and memory cells induced in primary responses.

Adenovirus particles that display the Plasmodium falciparum circumsporozoite protein NANP repeat induce sporozoite-neutralizing antibodies in mice.

Adenovirus particles can be engineered to display exogenous peptides on their surfaces by modification of viral capsid proteins, and particles that display pathogen-derived peptides can induce protective immunity. We constructed viable recombinant adenoviruses that display B-cell epitopes from the Plasmodium falciparum circumsporozoite protein (PfCSP) in the major adenovirus capsid protein, hexon. Recombinants induced high-titer antibodies against CSP when injected intraperitoneally into mice. Serum obtained from immunized mice recognized both recombinant PfCSP protein and P. falciparum sporozoites, and neutralized P. falciparum sporozoites in vitro. Replicating adenovirus vaccines have provided economical protection against adenovirus disease for over three decades. The recombinants described here may provide a path to an affordable malaria vaccine in the developing world.

Prolonged antigen presentation is required for optimal CD8+ T cell responses against malaria liver stage parasites.

Immunization with irradiated sporozoites is currently the most effective vaccination strategy against liver stages of malaria parasites, yet the mechanisms underpinning the success of this approach are unknown. Here we show that the complete development of protective CD8+ T cell responses requires prolonged antigen presentation. Using TCR transgenic cells specific for the malaria circumsporozoite protein, a leading vaccine candidate, we found that sporozoite antigen persists for over 8 weeks after immunization--a remarkable finding since irradiated sporozoites are incapable of replication and do not differentiate beyond early liver stages. Persisting antigen was detected in lymphoid organs and depends on the presence of CD11c+ cells. Prolonged antigen presentation enhanced the magnitude of the CD8+ T cell response in a number of ways. Firstly, reducing the time primed CD8+ T cells were exposed to antigen in vivo severely reduced the final size of the developing memory population. Secondly, fully developed memory cells expanded in previously immunized mice but not when transferred to naïve animals. Finally, persisting antigen was able to prime naïve cells, including recent thymic emigrants, to become functional effector cells capable of eliminating parasites in the liver. Together these data show that the optimal development of protective CD8+ T cell immunity against malaria liver stages is dependent upon the prolonged presentation of sporozoite-derived antigen.

CpG-enhanced CD8+ T-cell responses to peptide immunization are severely inhibited by B cells.

Synthetic peptides encoding protective pathogen-derived epitopes represent--in principle--an ideal approach to T-cell vaccination. Empirically, however, these strategies have not been successful. In the current study, we profiled the early activation of CD8+ T cells by MHC class I-restricted peptide immunization to better understand the biology of this response. We found that CD8+ T cells proliferated robustly in response to low doses of short synthetic peptides in PBS, but failed to acquire effector function or form memory populations in the absence of the TLR ligand CpG. CpG was unique among TLR ligands in its ability to enhance the response to peptide and its adjuvant effects had strict temporal requirements. Interestingly, CpG treatment modulated T-cell expression of the surface receptors PD-1 and CD25, providing insight into its possible adjuvant mechanism. The effects of CpG on peptide immunization were dramatically enhanced in the absence of B cells, demonstrating a unique system of regulation of T-cell responses by these lymphocytes. The results reported here provide insight into the complex response to a simple vaccination regimen, as well as a framework for a rational peptide-based vaccine design to both exploit and overcome targeted aspects of the immune response.

Effector CD8+ T lymphocytes against liver stages of Plasmodium yoelii do not require gamma interferon for antiparasite activity.

The protective immune response against liver stages of the malaria parasite critically requires CD8(+) T cells. Although the nature of the effector mechanism utilized by these cells to repress parasite development remains unclear, a critical role for gamma interferon (IFN-gamma) has been widely assumed based on circumstantial evidence. However, the requirement for CD8(+) T-cell-mediated IFN-gamma production in protective immunity to this pathogen has not been directly tested. In this report, we use an adoptive transfer strategy with circumsporozoite (CS) protein-specific transgenic T cells to examine the role of CD8(+) T-cell-derived IFN-gamma production in Plasmodium yoelii-infected mice. We show that despite a marginal reduction in the expansion of naive IFN-gamma-deficient CS-specific transgenic T cells, their antiparasite activity remains intact. Further, adoptively transferred IFN-gamma-deficient CD8(+) T cells were as efficient as their wild-type counterparts in limiting parasite growth in naive mice. Taken together, these studies demonstrate that IFN-gamma secretion by CS-specific CD8(+) T cells is not essential to protect mice against live sporozoite challenge.

17beta-estradiol alters the activity of conventional and IFN-producing killer dendritic cells.

Estrogens increase aspects of innate immunity and contribute to sex differences in the prevalence of autoimmune diseases and in response to infection. The goal of the present study was to assess whether exposure to 17beta-estradiol (E2) affects the development and function of bone marrow-derived dendritic cells and to determine whether similar changes are observed in CD11c(+) splenocytes exposed to E2 in vivo. E2 facilitated the differentiation of BM precursor cells into functional CD11c(+)CD11b(+)MHC class II(+) dendritic cells (DCs) with increased expression of the costimulatory molecules CD40 and CD86. Exposure of bone marrow-derived dendritic cells to E2 also enhanced production of IL-12 in response to the TLR ligands, CpG and LPS. In contrast, CD11c(+) cells isolated from the spleens of female C57BL/6 mice that were intact, ovariectomized, or ovariectomized with E2 replacement exhibited no differences in the number or activity of CD11c(+)CD11b(+)MHC class II(+) DCs. The presence of E2 in vivo, however, increased the number of CD11c(+)CD49b(+)NK1.1(low) cells and reduced numbers of CD11c(+)CD49b(+)NK1.1(high) cells, a surface phenotype for IFN-producing killer DCs (IKDCs). Ultrastructural analysis demonstrated that CD11c(+)NK1.1(+) populations were comprised of cells that had the appearance of both DCs and IKDCs. CD11c(+) splenocytes isolated from animals with supplemental E2 produced more IFN-gamma in response to IL-12 and IL-18. These data illustrate that E2 has differential effects on the development and function of DCs and IKDCs and provide evidence that E2 may strengthen innate immunity by enhancing IFN-gamma production by CD11c(+) cells.

Memory CD8+ T cell responses expand when antigen presentation overcomes T cell self-regulation.

Antimicrobial memory CD8+ T cell responses are not readily expanded by either repeated infections or immunizations. This is a major obstacle to the development of T cell vaccines. Prime-boost immunization with heterologous microbes sharing the same CD8+ epitope can induce a large expansion of the CD8+ response; however, different vectors vary greatly in their ability to boost for reasons that are poorly understood. To investigate how efficient memory T cell expansion can occur, we evaluated immune regulatory events and Ag presentation after secondary immunization with strong and weak boosting vectors. We found that dendritic cells were essential for T cell boosting and that Ag presentation by these cells was regulated by cognate memory CD8+ T cells. When weak boosting vectors were used for secondary immunization, pre-established CD8+ T cells were able to effectively curtail Ag presentation, resulting in limited CD8+ T cell expansion. In contrast, a strong boosting vector, vaccinia virus, induced highly efficient Ag presentation that overcame regulation by cognate T cells and induced large numbers of memory CD8+ T cells to expand. Thus, efficient targeting of Ag to dendritic cells in the face of cognate immunity is an important requirement for T cell expansion.

CD8+ T lymphocytes protective against malaria liver stages are primed in skin-draining lymph nodes.

The success of immunization with irradiated sporozoites is unparalleled among the current vaccination approaches against malaria, but its mechanistic underpinnings have yet to be fully elucidated. Using a model mimicking natural infection by Plasmodium yoelii, we delineated early events governing the development of protective CD8(+) T-cell responses to the circumsporozoite protein. We demonstrate that dendritic cells in cutaneous lymph nodes prime the first cohort of CD8(+) T cells after an infectious mosquito bite. Ablation of these lymphoid sites greatly impairs subsequent development of protective immunity. Activated CD8(+) T cells then travel to systemic sites, including the liver, in a sphingosine-1-phosphate (S1P)-dependent fashion. These effector cells, however, no longer require bone marrow-derived antigen-presenting cells for protection; instead, they recognize antigen on parenchymal cells-presumably parasitized hepatocytes. Therefore, we report an unexpected dichotomy in the tissue restriction of host responses during the development and execution of protective immunity to Plasmodium.