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Interleukin-2 (IL-2) is a component of most protocols of adoptive cell transfer (ACT) therapy for cancer, but is limited by short exposure and high toxicities. NKTR-214 is a kinetically-engineered IL-2 receptor βγ (IL-2Rβγ)-biased agonist consisting of IL-2 conjugated to multiple releasable polyethylene glycol chains resulting in sustained signaling through IL-2Rβγ. We report that ACT supported by NKTR-214 increases the proliferation, homing and persistence of anti-tumor T cells compared to ACT with IL-2, resulting in superior antitumor activity in a B16-F10 murine melanoma model. The use of NKTR-214 increases the number of polyfunctional T cells in murine spleens and tumors compared to IL-2, and enhances the polyfunctionality of T and NK cells in the peripheral blood of patients receiving NKTR-214 in a phase 1 trial. In conclusion, NKTR-214 may have the potential to improve the antitumor activity of ACT in humans through increased in vivo expansion and polyfunctionality of the adoptively transferred T cells.

Purpose: Noninvasive and quantitative tracking of CD8+ T cells by PET has emerged as a potential technique to gauge response to immunotherapy. We apply an anti-CD8 cys-diabody, labeled with 64Cu, to assess the sensitivity of PET imaging of normal and diseased tissue.Experimental Design: Radiolabeling of an anti-CD8 cys-diabody (169cDb) with 64Cu was developed. The accumulation of 64Cu-169cDb was evaluated with PET/CT imaging (0, 5, and 24 hours) and biodistribution (24 hours) in wild-type mouse strains (n = 8/group studied with imaging and IHC or flow cytometry) after intravenous administration. Tumor-infiltrating CD8+ T cells in tumor-bearing mice treated with CpG and αPD-1 were quantified and mapped (n = 6-8/group studied with imaging and IHC or flow cytometry).Results: We demonstrate the ability of immunoPET to detect small differences in CD8+ T-cell distribution between mouse strains and across lymphoid tissues, including the intestinal tract of normal mice. In FVB mice bearing a syngeneic HER2-driven model of mammary adenocarcinoma (NDL), 64Cu-169cDb PET imaging accurately visualized and quantified changes in tumor-infiltrating CD8+ T cells in response to immunotherapy. A reduction in the circulation time of the imaging probe followed the development of treatment-related liver and splenic hypertrophy and provided an indication of off-target effects associated with immunotherapy protocols.Conclusions: 64Cu-169cDb imaging can spatially map the distribution of CD8+ T cells in normal organs and tumors. ImmunoPET imaging of tumor-infiltrating cytotoxic CD8+ T cells detected changes in T-cell density resulting from adjuvant and checkpoint immunotherapy protocols in our preclinical evaluation. Clin Cancer Res; 24(20); 4976-87. ©2018 AACR.

Inflammatory bowel diseases (IBDs) in humans are characterized in part by aberrant CD4-positive (CD4+) T-cell responses. Currently, identification of foci of inflammation within the gut requires invasive procedures such as colonoscopy and biopsy. Molecular imaging with antibody fragment probes could be used to noninvasively monitor cell subsets causing intestinal inflammation. Here, GK1.5 cys-diabody (cDb), an antimouse CD4 antibody fragment derived from the GK1.5 hybridoma, was used as a PET probe for CD4+ T cells in the dextran sulfate sodium (DSS) mouse model of IBD. Methods: The DSS mouse model of IBD was validated by assessing changes in CD4+ T cells in the spleen and mesenteric lymph nodes (MLNs) using flow cytometry. Furthermore, CD4+ T cell infiltration in the colons of colitic mice was evaluated using immunohistochemistry. 89Zr-labeled GK1.5 cDb was used to image distribution of CD4+ T cells in the abdominal region and lymphoid organs of mice with DSS-induced colitis. Region-of-interest analysis was performed on specific regions of the gut to quantify probe uptake. Colons, ceca, and MLNs were removed and imaged ex vivo by PET. Imaging results were confirmed by ex vivo biodistribution analysis. Results: An increased number of CD4+ T cells in the colons of colitic mice was confirmed by anti-CD4 immunohistochemistry. Increased uptake of 89Zr-maleimide-deferoxamine (malDFO)-GK1.5 cDb in the distal colon of colitic mice was visible in vivo in PET scans, and region-of-interest analysis of the distal colon confirmed increased activity in DSS mice. MLNs from colitic mice were enlarged and visible in PET images. Ex vivo scans and biodistribution confirmed higher uptake in DSS-treated colons (DSS, 1.8 ± 0.40; control, 0.45 ± 0.12 percentage injected dose [%ID] per organ, respectively), ceca (DSS, 1.1 ± 0.38; control, 0.35 ± 0.09 %ID per organ), and MLNs (DSS, 1.1 ± 0.58; control, 0.37 ± 0.25 %ID per organ). Conclusion:89Zr-malDFO-GK1.5 cDb detected CD4+ T cells in the colons, ceca, and MLNs of colitic mice and may prove useful for further investigations of CD4+ T cells in preclinical models of IBD, with potential to guide development of antibody-based imaging in human IBD.

While chemotherapy delivery by nanocarriers has modestly improved the survival prospects of pancreatic ductal adenocarcinoma (PDAC), additional engagement of the immune response could be game changing. We demonstrate a nano-enabled approach for accomplishing robust anti-PDAC immunity in syngeneic mice through the induction of immunogenic cell death (ICD) as well as interfering in the immunosuppressive indoleamine 2,3-dioxygenase (IDO) pathway. This is accomplished by conjugating the IDO inhibitor, indoximod (IND), to a phospholipid that allows prodrug self-assembly into nanovesicles or incorporation into a lipid bilayer that encapsulates mesoporous silica nanoparticles (MSNP). The porous MSNP interior allows contemporaneous delivery of the ICD-inducing chemotherapeutic agent, oxaliplatin (OX). The nanovesicles plus free OX or OX/IND-MSNP induce effective innate and adaptive anti-PDAC immunity when used in a vaccination approach, direct tumor injection or intravenous biodistribution to an orthotopic PDAC site. Significant tumor reduction or eradication is accomplishable by recruiting cytotoxic T lymphocytes, concomitant with downregulation of Foxp3+ T cells.

The rapidly advancing field of cancer immunotherapy is currently limited by the scarcity of noninvasive and quantitative technologies capable of monitoring the presence and abundance of CD8(+) T cells and other immune cell subsets. In this study, we describe the generation of (89)Zr-desferrioxamine-labeled anti-CD8 cys-diabody ((89)Zr-malDFO-169 cDb) for noninvasive immuno-PET tracking of endogenous CD8(+) T cells. We demonstrate that anti-CD8 immuno-PET is a sensitive tool for detecting changes in systemic and tumor-infiltrating CD8 expression in preclinical syngeneic tumor immunotherapy models including antigen-specific adoptive T-cell transfer, agonistic antibody therapy (anti-CD137/4-1BB), and checkpoint blockade antibody therapy (anti-PD-L1). The ability of anti-CD8 immuno-PET to provide whole body information regarding therapy-induced alterations of this dynamic T-cell population provides new opportunities to evaluate antitumor immune responses of immunotherapies currently being evaluated in the clinic.

UnlabelledThe proliferation and trafficking of T lymphocytes in immune responses are crucial events in determining inflammatory responses. To study whole-body T lymphocyte dynamics noninvasively in vivo, we generated anti-CD4 and -CD8 cys-diabodies (cDbs) derived from the parental antibody hybridomas GK1.5 and 2.43, respectively, for (89)Zr-immuno-PET detection of helper and cytotoxic T cell populations.MethodsAnti-CD4 and -CD8 cDbs were engineered, produced via mammalian expression, purified using immobilized metal affinity chromatography, and characterized for T cell binding. The cDbs were site-specifically conjugated to maleimide-desferrioxamine for (89)Zr radiolabeling and subsequent small-animal PET/CT acquisition and ex vivo biodistribution in both wild-type mice and a model of hematopoietic stem cell (HSC) transplantation.ResultsImmuno-PET and biodistribution studies demonstrate targeting and visualization of CD4 and CD8 T cell populations in vivo in the spleen and lymph nodes of wild-type mice, with specificity confirmed through in vivo blocking and depletion studies. Subsequently, a murine model of HSC transplantation demonstrated successful in vivo detection of T cell repopulation at 2, 4, and 8 wk after HSC transplantation using the (89)Zr-radiolabeled anti-CD4 and -CD8 cDbs.ConclusionThese newly developed anti-CD4 and -CD8 immuno-PET reagents represent a powerful resource to monitor T cell expansion, localization, and novel engraftment protocols. Future potential applications of T cell-targeted immuno-PET include monitoring immune cell subsets in response to immunotherapy, autoimmunity, and lymphoproliferative disorders, contributing overall to preclinical immune cell monitoring.

PurposeProstate stem cell antigen (PSCA) is highly expressed in local prostate cancers and prostate cancer bone metastases and its expression correlates with androgen receptor activation and a poor prognosis. In this study, we investigate the potential clinical applications of immunoPET with the anti-PSCA A11 minibody, an antibody fragment optimized for use as an imaging agent. We compare A11 minibody immunoPET to (18)F-Fluoride PET bone scans for detecting prostate cancer bone tumors and evaluate the ability of the A11 minibody to image tumor response to androgen deprivation.Experimental designOsteoblastic, PSCA-expressing, LAPC-9 intratibial xenografts were imaged with serial (124)I-anti-PSCA A11 minibody immunoPET and (18)F-Fluoride bone scans. Mice bearing LAPC-9 subcutaneous xenografts were treated with either vehicle or MDV-3100 and imaged with A11 minibody immunoPET/CT scans pre- and posttreatment. Ex vivo flow cytometry measured the change in PSCA expression in response to androgen deprivation.ResultsA11 minibody demonstrated improved sensitivity and specificity over (18)F-Fluoride bone scans for detecting LAPC-9 intratibial xenografts at all time points. LAPC-9 subcutaneous xenografts showed downregulation of PSCA when treated with MDV-3100 which A11 minibody immunoPET was able to detect in vivo.ConclusionsA11 minibody immunoPET has the potential to improve the sensitivity and specificity of clinical prostate cancer metastasis detection over bone scans, which are the current clinical standard-of-care. A11 minibody immunoPET additionally has the potential to image the activity of the androgen signaling axis in vivo which may help evaluate the clinical response to androgen deprivation and the development of castration resistance.

PurposeIntact antibodies have a long serum persistence resulting in high background signal that inhibits their direct translation as imaging agents. Engineering of antibody fragments through the introduction of mutations in the fragment crystallizable (Fc) region can dramatically reduce serum persistence. We sought to develop a Fc-mutated, anti-CA19-9 antibody fragment (anti-CA 19-9 scFv-Fc H310A) to provide micro-positron emission tomography (microPET) imaging of pancreatic cancer xenografts.ProceduresThe anti-CA19-9 scFv-Fc H310A was successfully expressed and purified. Biochemical characterization included size exclusion chromatography, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), Western blot, and flow cytometry. The antibody fragment was labeled with iodine-124 ((124)I) and injected into mice containing human pancreatic cancer xenografts. MicroPET/CT images were then obtained. Blood, organ, and tumor radioactivity was measured and expressed as the percent of injected dose per gram of tissue (%ID/g).ResultsBiochemical characterization was consistent with the creation of a 105 kD dimer containing a human Fc region. Flow cytometry demonstrated antigen-specific binding, and cell-based ELISA further established a dissociation constant (K D) of 10.7 nM. (124)I-labeled scFv-Fc H310A localized to the antigen-positive tumor xenografts as detected by microPET. Objective confirmation of targeting was demonstrated by higher %ID/g in the antigen-positive tumor compared to the blood, antigen-negative tumor, and liver.ConclusionsWe successfully engineered and produced an anti-CA19-9 scFv-Fc H310A antibody fragment that retains similar affinity when compared to the parental intact murine antibody. Additionally, our engineered and mutated fragment exhibited antigen-specific microPET imaging of both subcutaneous and orthotopic pancreatic cancer xenografts at early time points secondary to decreased serum half-life.

Activated leukocyte cell adhesion molecule (ALCAM) is an immunoglobulin superfamily cell adhesion molecule that is aberrantly expressed in a wide variety of human tumors, including melanoma, prostate cancer, breast cancer, colorectal carcinoma, bladder cancer and pancreatic adenocarcinoma. This wide spectrum of human malignancies makes ALCAM a prospective pan-cancer immunoPET target to aid in detection and diagnosis in multiple malignancies. In this study, we assess site-specific versus non-site-specific conjugation strategies for (64)Cu-DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) immunoPET imaging of a fully human ALCAM cys-diabody (cDb) with a reduced linker length that retains its bivalent binding ability. ALCAM constructs with linker lengths of eight, five and three amino acids were produced to make true non-covalent site-specifically modified cDbs. Characterization by gel electrophoresis, size exclusion chromatography, flow cytometry and mass spectrometry of the various constructs was performed. To demonstrate the increased utility of targeting multiple malignancies expressing ALCAM, we compare the targeting of the site-specific versus non-site-specific conjugated cDbs to the human colorectal cancer xenograft LS174T. Interestingly, the conjugation strategy not only affects tumor targeting but also hepatic and renal uptake/clearance.

The noninvasive detection and quantification of CD8(+) T cells in vivo are important for both the detection and staging of CD8(+) lymphomas and for the monitoring of successful cancer immunotherapies, such as adoptive cell transfer and antibody-based immunotherapeutics. Here, antibody fragments are constructed to target murine CD8 to obtain rapid, high-contrast immuno-positron emission tomography (immuno-PET) images for the detection of CD8 expression in vivo. The variable regions of two anti-murine CD8-depleting antibodies (clones 2.43 and YTS169.4.2.1) were sequenced and reformatted into minibody (Mb) fragments (scFv-CH3). After production and purification, the Mbs retained their antigen specificity and bound primary CD8(+) T cells from the thymus, spleen, lymph nodes, and peripheral blood. Importantly, engineering of the parental antibodies into Mbs abolished the ability to deplete CD8(+) T cells in vivo. The Mbs were subsequently conjugated to S-2-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid for (64)Cu radiolabeling. The radiotracers were injected i.v. into antigen-positive, antigen-negative, immunodeficient, antigen-blocked, and antigen-depleted mice to evaluate specificity of uptake in lymphoid tissues by immuno-PET imaging and ex vivo biodistribution. Both (64)Cu-radiolabeled Mbs produced high-contrast immuno-PET images 4 h postinjection and showed specific uptake in the spleen and lymph nodes of antigen-positive mice.

PurposeProstate stem cell antigen (PSCA), a cell surface glycoprotein expressed in normal human prostate and bladder, is over-expressed in the majority of localized prostate cancer and most bone metastases. We have previously shown that the hu1G8 minibody, a humanized anti-PSCA antibody fragment (single-chain Fv-C(H)3 dimer, 80 kDa), can localize specifically and image PSCA-expressing xenografts at 21 h post-injection. However, the humanization and antibody fragment reformatting decreased its apparent affinity. Here, we sought to evaluate PET imaging contrast with affinity matured minibodies.MethodsYeast scFv display, involving four rounds of selection, was used to generate the three affinity matured antibody fragments (A2, A11, and C5) that were reformatted into minibodies. These three affinity matured anti-PSCA minibodies were characterized in vitro, and following radiolabeling with (124)I were evaluated in vivo for microPET imaging of PSCA-expressing tumors.ResultsThe A2, A11, and C5 minibody variants all demonstrated improved affinity compared to the parental (P) minibody and were ranked as follows: A2 > A11 > C5 > P. The (124)I-labeled A11 minibody demonstrated higher immunoreactivity than the parental minibody and also achieved the best microPET imaging contrast in two xenograft models, LAPC-9 (prostate cancer) and Capan-1 (pancreatic cancer), when evaluated in vivo.ConclusionOf the affinity variant minibodies tested, the A11 minibody that ranked second in affinity was selected as the best immunoPET tracer to image PSCA-expressing xenografts. This candidate is currently under development for evaluation in a pilot clinical imaging study.

To assess potential effects of human DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane] exposure, we evaluated the reproductive history of 2,033 workers in the antimalaria campaign of Mexico. Data on occupational exposure to DDT and [...]

Determination of treatment response to immunotherapy in glioblastoma multiforme (GBM) is a process which can take months. Detection of CD8+ T cell recruitment to the tumor with a noninvasive imaging modality such as positron emission tomography (PET) may allow for tumor characterization and early evaluation of therapeutic response to immunotherapy. In this study, we utilized 89Zr-labeled anti-CD8 cys-diabody-PET to provide proof-of-concept to detect CD8+ T cell immune response to oncolytic herpes simplex virus (oHSV) M002 immunotherapy in a syngeneic GBM model. Immunocompetent mice (n = 16) were implanted intracranially with GSC005 GBM tumors, and treated with intratumoral injection of oHSV M002 or saline control. An additional non-tumor bearing cohort (n = 4) receiving oHSV M002 treatment was also evaluated. Mice were injected with 89Zr-labeled anti-CD8 cys-diabody seven days post oHSV administration and imaged with a preclinical PET scanner. Standardized uptake value (SUV) was quantified. Ex vivo tissue analyses included autoradiography and immunohistochemistry. PET imaging showed significantly higher SUV in tumors which had been treated with M002 compared to those without M002 treatment (p = 0.0207) and the non-tumor bearing M002 treated group (p = 0.0021). Accumulation in target areas, especially the spleen, was significantly reduced by blocking with the non-labeled diabody (p < 0.001). Radioactive probe accumulation in brains was consistent with CD8+ cell trafficking patterns after oHSV treatment. This PET imaging strategy could aid in distinguishing responders from non-responders during immunotherapy of GBM. [ABSTRACT FROM AUTHOR]

While chemotherapy delivery by nanocarriers has modestly improved the survival prospects of pancreatic ductal adenocarcinoma (PDAC), additional engagement of the immune response could be game changing. We demonstrate a nano-enabled approach for accomplishing robust anti-PDAC immunity in syngeneic mice through the induction of immunogenic cell death (ICD) as well as interfering in the immunosuppressive indoleamine 2,3-dioxygenase (IDO) pathway. This is accomplished by conjugating the IDO inhibitor, indoximod (IND), to a phospholipid that allows prodrug self-assembly into nanovesicles or incorporation into a lipid bilayer that encapsulates mesoporous silica nanoparticles (MSNP). The porous MSNP interior allows contemporaneous delivery of the ICD-inducing chemotherapeutic agent, oxaliplatin (OX). The nanovesicles plus free OX or OX/IND-MSNP induce effective innate and adaptive anti-PDAC immunity when used in a vaccination approach, direct tumor injection or intravenous biodistribution to an orthotopic PDAC site. Significant tumor reduction or eradication is accomplishable by recruiting cytotoxic T lymphocytes, concomitant with downregulation of Foxp3+ T cells. [ABSTRACT FROM AUTHOR]

The noninvasive detection and quantification of CD8+ T cells in vivo are important for both the detection and staging of CD8+ lymphomas and for the monitoring of successful cancer immunotherapies, such as adoptive cell transfer and antibody-based immunotherapeutics. Here, antibody fragments are constructed to target murine CD8 to obtain rapid, high-contrast immuno-positron emission tomography (immuno-PET) images for the detection of CD8 expression in vivo. The variable regions of two anti-murine CD8-depleting antibodies (clones 2.43 and YTS169.4.2.1) were sequenced and reformatted into minibody (Mb) fragments (scFv-CH3). After production and purification, the Mbs retained their antigen specificity and bound primary CD8+ T cells from the thymus, spleen, lymph nodes, and peripheral blood. Importantly, engineering of the parental antibodies into Mbs abolished the ability to deplete CD8+ T cells in vivo. The Mbs were subsequently conjugated to S-2-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid for 64Cu radiolabeling. The radiotracers were injected i.v. into antigen-positive, antigen-negative, immunodeficient, antigen-blocked, and antigen-depleted mice to evaluate specificity of uptake in lymphoid tissues by immuno-PET imaging and ex vivo biodistribution. Both 64Cu-radiolabeled Mbs produced high-contrast immuno-PET images 4 h postinjection and showed specific uptake in the spleen and lymph nodes of antigen-positive mice. [ABSTRACT FROM AUTHOR]

The long circulation persistence of human serum albumin (HSA) is enabled by its domain III (DIII) interaction with the neonatal Fc receptor (FcRn). A protein scaffold based on HSA DIII was designed. To modify the serum half life of the scaffold, residues H535, H510, and H464 were individually mutated to alanine. HSA DIII wild type (WT) and variants were fused to the anti-carcinoembryonic antigen (CEA) T84.66 diabody (Db), radiolabeled with 124I and injected into xenografted athymic mice for serial PET/CT imaging. All proteins targeted the CEA-positive tumor. The mean residence times (MRT) of the proteins, calculated by quantifying blood activity from the PET images, were: Db-DIII WT (56.7 h), H535A (25 h), H510A (20 h), H464A (17 h), compared with Db (2.9 h). Biodistribution confirmed the order of blood clearance from slow to fast: Db-DIII WT > H535A > H510A > H464A > Db with 4.0, 2.0, 1.8, 1.6 and 0.08 %ID/g of remaining blood activity at 51 h, respectively. This study demonstrates that attenuating the DIII-FcRn interaction provides a way of controlling the pharmacokinetics of the entire Db-DIII fusion protein without compromising tumor targeting. H464 appears to be most crucial for FcRn binding (greatest reduction in MRT), followed by H510 and H535. By mutating the DIII scaffold, we can dial serum kinetics for imaging or therapy applications. [ABSTRACT FROM AUTHOR]

An abstract of the article "Short Hairpin RNA Interference Expressed from a Gene-Deleted Adenoviral Vector Results in Reduction of Hepatits B Surface Antigen Levels In Vitro and in a Small Animal Model for Hepatitis B Infection," by Anja Ehrhardt and colleagues is presented.

Antibody-mediated tumor delivery of cytokines can overcome limitations of systemic administration (toxicity, short half-lives). Previous work showed improved antitumor potency of anti-CD20-IFNα fusion proteins in preclinical mouse models of B-cell lymphoma. Although tumor targeting is mediated by the antibody part of the fusion protein, the cytokine component might strongly influence biodistribution and pharmacokinetics, as a result of its affinity, size, valency, and receptor distribution. Here, we used immunoPET to study the in vivo biodistribution and tumor targeting of the anti-CD20 rituximab-murine IFNα1 fusion protein (Rit-mIFNα) and compared it with the parental mAb (rituximab, Rit). Rit-mIFNα and Rit were radiolabeled with zirconium-89 (89Zr, t1/2 78.4 hours) and injected into C3H mice bearing syngeneic B-cell lymphomas (38C13-hCD20). Dynamic [(2 hours post injection (p.i.)] and static (4, 24, and 72 hours) PET scans were acquired. Ex vivo biodistribution was performed after the final scan. Both 89Zr-Rit-mIFNα and 89Zr-Rit specifically target hCD20-expressing B-cell lymphoma in vivo. 89Zr-Rit-mIFNα showed specific uptake in tumors (7.6 ± 1.0 %ID/g at 75 hours p.i.), which was significantly lower than 89Zr-Rit (38.4 ± 9.9 %ID/g, P < 0.0001). ImmunoPET studies also revealed differences in the biodistribution, 89Zr-Rit-mIFNα showed rapid blood clearance and high accumulation in the liver compared with 89Zr-Rit. Importantly, immunoPET clearly revealed a therapeutic effect of the single 89Zr-Rit-mIFNα dose, resulting in smaller tumors and fewer lymph node metastases compared with mice receiving 89Zr-Rit. Mice receiving 89Zr-Rit-mIFNα had enlarged spleens, suggesting that systemic immune activation contributes to therapeutic efficacy in addition to the direct antitumoral activity of IFNα. In conclusion, immunoPET allows the noninvasive tracking and quantification of the antibody-cytokine fusion protein and helps understand the in vivo behavior and therapeutic efficacy., (©2022 American Association for Cancer Research.)

Purpose: Noninvasive and quantitative tracking of CD8 + T cells by PET has emerged as a potential technique to gauge response to immunotherapy. We apply an anti-CD8 cys-diabody, labeled with 64 Cu, to assess the sensitivity of PET imaging of normal and diseased tissue. Experimental Design: Radiolabeling of an anti-CD8 cys-diabody (169cDb) with 64 Cu was developed. The accumulation of 64 Cu-169cDb was evaluated with PET/CT imaging (0, 5, and 24 hours) and biodistribution (24 hours) in wild-type mouse strains ( n = 8/group studied with imaging and IHC or flow cytometry) after intravenous administration. Tumor-infiltrating CD8 + T cells in tumor-bearing mice treated with CpG and αPD-1 were quantified and mapped ( n = 6-8/group studied with imaging and IHC or flow cytometry). Results: We demonstrate the ability of immunoPET to detect small differences in CD8 + T-cell distribution between mouse strains and across lymphoid tissues, including the intestinal tract of normal mice. In FVB mice bearing a syngeneic HER2 -driven model of mammary adenocarcinoma (NDL), 64 Cu-169cDb PET imaging accurately visualized and quantified changes in tumor-infiltrating CD8 + T cells in response to immunotherapy. A reduction in the circulation time of the imaging probe followed the development of treatment-related liver and splenic hypertrophy and provided an indication of off-target effects associated with immunotherapy protocols. Conclusions: 64 Cu-169cDb imaging can spatially map the distribution of CD8 + T cells in normal organs and tumors. ImmunoPET imaging of tumor-infiltrating cytotoxic CD8 + T cells detected changes in T-cell density resulting from adjuvant and checkpoint immunotherapy protocols in our preclinical evaluation. Clin Cancer Res; 24(20); 4976-87. ©2018 AACR ., (©2018 American Association for Cancer Research.)

Activated leukocyte cell adhesion molecule (ALCAM) is an immunoglobulin superfamily cell adhesion molecule that is aberrantly expressed in a wide variety of human tumors, including melanoma, prostate cancer, breast cancer, colorectal carcinoma, bladder cancer and pancreatic adenocarcinoma. This wide spectrum of human malignancies makes ALCAM a prospective pan-cancer immunoPET target to aid in detection and diagnosis in multiple malignancies. In this study, we assess site-specific versus non-site-specific conjugation strategies for (64)Cu-DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) immunoPET imaging of a fully human ALCAM cys-diabody (cDb) with a reduced linker length that retains its bivalent binding ability. ALCAM constructs with linker lengths of eight, five and three amino acids were produced to make true non-covalent site-specifically modified cDbs. Characterization by gel electrophoresis, size exclusion chromatography, flow cytometry and mass spectrometry of the various constructs was performed. To demonstrate the increased utility of targeting multiple malignancies expressing ALCAM, we compare the targeting of the site-specific versus non-site-specific conjugated cDbs to the human colorectal cancer xenograft LS174T. Interestingly, the conjugation strategy not only affects tumor targeting but also hepatic and renal uptake/clearance., (© The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

The long circulation persistence of human serum albumin (HSA) is enabled by its domain III (DIII) interaction with the neonatal Fc receptor (FcRn). A protein scaffold based on HSA DIII was designed. To modify the serum half life of the scaffold, residues H535, H510, and H464 were individually mutated to alanine. HSA DIII wild type (WT) and variants were fused to the anti-carcinoembryonic antigen (CEA) T84.66 diabody (Db), radiolabeled with (124)I and injected into xenografted athymic mice for serial PET/CT imaging. All proteins targeted the CEA-positive tumor. The mean residence times (MRT) of the proteins, calculated by quantifying blood activity from the PET images, were: Db-DIII WT (56.7 h), H535A (25 h), H510A (20 h), H464A (17 h), compared with Db (2.9 h). Biodistribution confirmed the order of blood clearance from slow to fast: Db-DIII WT > H535A > H510A > H464A > Db with 4.0, 2.0, 1.8, 1.6 and 0.08 %ID/g of remaining blood activity at 51 h, respectively. This study demonstrates that attenuating the DIII-FcRn interaction provides a way of controlling the pharmacokinetics of the entire Db-DIII fusion protein without compromising tumor targeting. H464 appears to be most crucial for FcRn binding (greatest reduction in MRT), followed by H510 and H535. By mutating the DIII scaffold, we can dial serum kinetics for imaging or therapy applications.