Levels and in vitro functional effects of circulating anti-hinge antibodies in melanoma patients receiving the immune checkpoint inhibitor pembrolizumab.

The efficacy of PD-1 monoclonals such as pembrolizumab can be modulated by the signals delivered via their Fc region. Tumour/inflammation associated proteases can generate F(ab')2 fragments of therapeutic monoclonals, and subsequent recognition of F(ab')2 epitopes by circulating anti-hinge antibodies (AHA) can then, potentially, link F(ab')2 binding to the target antigen with novel Fc signalling. Although elevated in inflammatory diseases, AHA levels in cancer patients have not been investigated and functional studies utilising the full repertoire of AHA present in sera have been limited. AHA levels in pembrolizumab treated melanoma patients (n = 23) were therefore compared to those of normal donors and adalimumab treated patients. A subset of melanoma patients and the majority of adalimumab patients had elevated levels of AHA reactive with F(ab')2 fragments of IgG4 anti-PD-1 monoclonals (nivolumab, pembrolizumab) and IgG1 therapeutic monoclonals (rituximab, adalimumab). Survival analysis was restricted by the small patient numbers but those melanoma patients with the highest levels (>75% percentile, n = 5) of pembrolizumab-F(ab')2 reactive AHA had significantly better overall survival post pembrolizumab treatment (p = 0.039). In vitro functional studies demonstrated that the presence of AHA+ sera restored the neutrophil activating capacity of pembrolizumab to its F(ab')2 fragment. Neither pembrolizumab nor its F(ab')2 fragments can induce NK cell or complement dependent cytotoxicity (CDC). However, AHA+ sera in combination with pembrolizumab-F(ab')2 provided Fc regions that could activate NK cells. The ability of AHA+ sera to restore CDC activity was more restricted and observed using only one pembrolizumab and one adalimumab patient serum in combination with rituximab- F(ab')2. This study reports the presence of elevated AHA levels in pembrolizumab treated melanoma patients and highlight the potential for AHA to provide additional Fc signaling. The issue of whether tumour associated proteolysis of PD-1 mAbs and subsequent AHA recognition impacts on treatment efficacy requires further study.

Functional effects of immune complexes formed between pembrolizumab and patient-generated anti-drug antibodies.

The PD-1-targeting IgG4 antibody pembrolizumab has significant anti-tumor activity in a proportion of stage IV melanoma patients. A subset of patients develop anti-drug antibodies (ADA) which can form immune complexes (IC) with pembrolizumab. Although IC can induce powerful, Fc-mediated, immune-regulatory effects, their functional impact during pembrolizumab treatment is unclear. The functional effects of IC generated in vitro using pembrolizumab and patient-derived ADA was, therefore, investigated. Screening identified a patient whose trough serum samples from three treatment cycles contained both ADA with neutralizing activity and low levels of pembrolizumab. This patient responded well to therapy over 2 years and had ongoing, infusion-related, hypersensitivity reactions despite the later absence of detectable ADA. The components of IC were mimicked by forming a complex of pembrolizumab by absorption onto a solid phase with or without subsequent exposure to the ADA+ patient sera. Complexes comprised of pembrolizumab alone significantly inhibited TLR4 (LPS)-driven IL-10 production by PBMC and stimulated the generation of reactive oxygen species by granulocytes. In contrast, soluble and solid-phase F(ab´)2 fragments of pembrolizumab had no effect demonstrating the requirement for cross-linked Fc regions. IC containing pembrolizumab and ADA could additionally induce complement and NK activation. The results of this study demonstrate that, when oligomerized, the Fc region of pembrolizumab alone can provide immuno-regulatory signals. Furthermore, IC containing both pembrolizumab and patient-generated ADA can induce additional signals. These Fc-mediated signals may modulate both hypersensitivity reactions and anti-tumor responses associated with pembrolizumab therapy.

Long-Term Fine Motor Capability on the Staircase Test Correlates with the Absolute Number, but Not the Density, of DARPP-Positive Neurons in the Caudate-Putamen.

Measurement of long-term functional and anatomical outcomes in the same animal is considered a powerful strategy for correlating structure with function. In a neonatal animal model of hypoxic-ischemic brain injury that is relevant to cerebral palsy, long-term functional deficits on the staircase test and long-term anatomical deficits in the absolute number of medium-spiny projection neurons in the caudate-putamen were reported in different animals due to logistical constraints. Here, we investigated if these functional and anatomical measures were correlated when measured in the same animals. The medium-spiny projection neurons were investigated because (1) they comprise the vast majority (>97%) of all neurons in the caudate-putamen and (2) motor deficits observed during staircase testing are likely to involve these striatal medium-spiny projection neurons through their connections. We found that long-term skilled forepaw capability on the staircase test was correlated with the absolute number of DARPP-32-positive medium-spiny projection neurons in the caudate-putamen. Specifically, deficits in skilled forepaw ability for the number of sugar pellets eaten and retrieved, and for the maximum staircase level reached, were significantly correlated with a lower absolute neuronal number. We also found that skilled forepaw ability on the staircase test was not correlated with the neuronal density (i.e., number per unit volume) of DARPP-32-positive medium-spiny projection neurons. Since neuronal density is an indirect measure of neuronal survival that is used in the literature, and absolute neuronal number is a direct measure, the results also highlight the scientific value of measuring absolute neuronal number. Anat Rec, 302:2040-2048, 2019. © 2019 American Association for Anatomy.

Discrimination of Anti-drug Antibodies With Neutralizing Capacity in Infliximab- and Adalimumab-Treated Patients: Comparison of the Homogeneous Mobility Shift Assay and the Affinity Capture and Elution Assay.

BACKGROUND: The measurement of anti-drug antibody (ADA) levels in adalimumab (ADAL)-treated and infliximab (IFX)-treated patients is critical for guiding therapeutic strategies. The homogeneous mobility shift assay (HMSA) and affinity capture elution (ACE) assay provide effective, drug-tolerant formats for measuring total ADA levels. However, their ability to discriminate between ADA from samples with or without neutralizing capacity is unclear and therefore was analyzed in this study. METHODS: Sera from ADAL and IFX patients with low drug levels (<1 mcg/mL) were analyzed by ACE, HMSA, and bridging assay. Neutralizing capacity was determined by competitive ligand-binding assay. RESULTS: HMSA and ACE detected high ADA levels in all ADAL (19/42) and IFX (27/64) samples with neutralizing capacity. ADA was also detected in most of the samples without neutralizing capacity, but levels were significantly lower (P < 0.0001). Receiver operator characteristic curve analysis demonstrated that for both assays, ADA levels were a strong discriminatory marker of neutralizing ADA (area under the curve > 0.9, P < 0.0001). Using a signal >8× background as a cut-point, neutralizing ADA could be identified with high specificity (HMSA > 95%, ACE > 85%) and sensitivity (HMSA > 70%, ACE > 80%). The detection of multimeric drug-ADA complexes after HMSA was also a highly specific marker (specificity > 95%) of neutralizing ADA in both ADAL and IFX patients. Results using ACE and HMSA were highly correlated. CONCLUSIONS: Results obtained after HMSA and ACE analysis are strongly correlated, and in both assays, high ADA levels are a specific marker of neutralizing capacity. The detection of multimeric complexes by HMSA also selectively identifies sera with neutralizing capacity. These data support the use of these assays as quantitative rather than simple qualitative measures of ADA.

Marked differences in the number and type of synapses innervating the somata and primary dendrites of midbrain dopaminergic neurons, striatal cholinergic interneurons, and striatal spiny projection neurons in the rat.

Elucidating the link between cellular activity and goal-directed behavior requires a fuller understanding of the mechanisms underlying burst firing in midbrain dopaminergic neurons and those that suppress activity during aversive or non-rewarding events. We have characterized the afferent synaptic connections onto these neurons in the rat substantia nigra pars compacta (SNpc) and ventral tegmental area (VTA), and compared these findings with cholinergic interneurons and spiny projection neurons in the striatum. We found that the average absolute number of synapses was three to three and one-half times greater onto the somata of dorsal striatal spiny projection neurons than onto the somata of dopaminergic neurons in the SNpc or dorsal striatal cholinergic interneurons. A similar comparison between populations of dopamine neurons revealed a two times greater number of somatic synapses on VTA dopaminergic neurons than SNpc dopaminergic neurons. The percentage of symmetrical, presumably inhibitory, synaptic inputs on somata was significantly higher on spiny projection neurons and cholinergic interneurons compared with SNpc dopaminergic neurons. Synaptic data on the primary dendrites yielded similar significant differences for the percentage of symmetrical synapses for VTA dopaminergic vs. striatal neurons. No differences in the absolute number or type of somatic synapses were evident for dopaminergic neurons in the SNpc of Wistar vs. Sprague-Dawley rat strains. These data from identified neurons are pivotal for interpreting their electrophysiological responses to afferent activity and for generating realistic computer models of neuronal networks of striatal and midbrain dopaminergic function.

Delayed post-treatment with bone marrow-derived mesenchymal stem cells is neurorestorative of striatal medium-spiny projection neurons and improves motor function after neonatal rat hypoxia-ischemia.

Perinatal hypoxia-ischemia is a major cause of striatal injury and may lead to cerebral palsy. This study investigated whether delayed administration of bone marrow-derived mesenchymal stem cells (MSCs), at one week after neonatal rat hypoxia-ischemia, was neurorestorative of striatal medium-spiny projection neurons and improved motor function. The effect of a subcutaneous injection of a high-dose, or a low-dose, of MSCs was investigated in stereological studies. Postnatal day (PN) 7 pups were subjected to hypoxia-ischemia. At PN14, pups received treatment with either MSCs or diluent. A subset of high-dose pups, and their diluent control pups, were also injected intraperitoneally with bromodeoxyuridine (BrdU), every 24h, on PN15, PN16 and PN17. This permitted tracking of the migration and survival of neuroblasts originating from the subventricular zone into the adjacent injured striatum. Pups were euthanized on PN21 and the absolute number of striatal medium-spiny projection neurons was measured after immunostaining for DARPP-32 (dopamine- and cAMP-regulated phosphoprotein-32), double immunostaining for BrdU and DARPP-32, and after cresyl violet staining alone. The absolute number of striatal immunostained calretinin interneurons was also measured. There was a statistically significant increase in the absolute number of DARPP-32-positive, BrdU/DARPP-32-positive, and cresyl violet-stained striatal medium-spiny projection neurons, and fewer striatal calretinin interneurons, in the high-dose mesenchymal stem cell (MSC) group compared to their diluent counterparts. A high-dose of MSCs restored the absolute number of these neurons to normal uninjured levels, when compared with previous stereological data on the absolute number of cresyl violet-stained striatal medium-spiny projection neurons in the normal uninjured brain. For the low-dose experiment, in which cresyl violet-stained striatal medium-spiny neurons alone were measured, there was a lower statistically significant increase in their absolute number in the MSC group compared to their diluent controls. Investigation of behavior in another cohort of animals showed that delayed administration of a high-dose of bone marrow-derived MSCs, at one week after neonatal rat hypoxia-ischemia, improved motor function on the cylinder test. Thus, delayed therapy with a high- or low-dose of adult MSCs, at one week after injury, is effective in restoring the loss of striatal medium-spiny projection neurons after neonatal rat hypoxia-ischemia and a high-dose of MSCs improved motor function.

Spectrum of short- and long-term brain pathology and long-term behavioral deficits in male repeated hypoxic rats closely resembling human extreme prematurity.

Brain injury in the premature infant is associated with a high risk of neurodevelopmental disability. Previous small-animal models of brain injury attributable to extreme prematurity typically fail to generate a spectrum of pathology and behavior that closely resembles that observed in humans, although they provide initial answers to numerous cellular, molecular, and therapeutic questions. We tested the hypothesis that exposure of rats to repeated hypoxia from postnatal day 1 (P1) to P3 models the characteristic white matter neuropathological injury, gray matter volume loss, and memory deficits seen in children born extremely prematurely. Male Sprague Dawley rats were exposed to repeated hypoxia or repeated normoxia from P1 to P3. The absolute number of pre-oligodendrocytes and mature oligodendrocytes, the surface area and g-ratio of myelin, the absolute volume of cerebral white and gray matter, and the absolute number of cerebral neurons were quantified stereologically. Spatial memory was investigated on a radial arm maze. Rats exposed to repeated hypoxia had a significant loss of (1) pre-oligodendrocytes at P4, (2) cerebral white matter volume and myelin at P14, (3) cerebral cortical and striatal gray matter volume without neuronal loss at P14, and (4) cerebral myelin and memory deficits in adulthood. Decreased myelin was correlated with increased attention deficit hyperactivity disorder-like hyperactivity. This new small-animal model of extreme prematurity generates a spectrum of short- and long-term pathology and behavior that closely resembles that observed in humans. This new rat model provides a clinically relevant tool to investigate numerous cellular, molecular, and therapeutic questions on brain injury attributable to extreme prematurity.