Hypercatabolism of normal IgG; an unexplained immunoglobulin abnormality in the connective tissue diseases

Physiology-based pharmacokinetic model with relative transcriptomics to evaluate tissue distribution and receptor occupancy of anifrolumab

Type I interferons contribute to the pathogenesis of several autoimmune disorders, including systemic lupus erythematosus (SLE), systemic sclerosis, cutaneous lupus erythematosus, and myositis. Anifrolumab is a monoclonal antibody that binds to subunit 1 of the type I interferon receptor (IFNAR1). Results of phase IIb and phase III trials led to the approval of intravenous anifrolumab 300 mg every 4 weeks (Q4W) alongside standard therapy in patients with moderate-to-severe SLE. Here, we built a population physiology-based pharmacokinetic (PBPK) model of anifrolumab by utilizing the physiochemical properties of anifrolumab, binding kinetics to the Fc gamma neonatal receptor, and target-mediated drug disposition properties. A novel relative transcriptomics approach was employed to determine IFNAR1 expression in tissues (blood, skin, gastrointestinal tract, lungs, and muscle) using mRNA abundances from bioinformatic databases. The IFNAR1 expression and PBPK model were validated by testing their ability to predict clinical pharmacokinetics over a large dose range from different clinical scenarios after subcutaneous and intravenous anifrolumab dosing. The validated PBPK model predicted high unbound local concentrations of anifrolumab in blood, skin, gastrointestinal tract, lungs, and muscle, which exceeded its IFNAR1 dissociation equilibrium constant values. The model also predicted high IFNAR1 occupancy with subcutaneous and intravenous anifrolumab dosing. The model predicted more sustained IFNAR1 occupancy ≥90% with subcutaneous anifrolumab 120 mg once-weekly dosing vs. intravenous 300 mg Q4W dosing. The results informed the dosing of phase III studies of anifrolumab in new indications and present a novel approach to PBPK modeling coupled with relative transcriptomics in simulating pharmacokinetics of therapeutic monoclonal antibodies.

A Novel Class of On-Treatment Cancer Immunotherapy Biomarker: Trough Levels of Antibody Therapeutics in Peripheral Blood

While immune checkpoint blockade has revolutionized cancer treatment, unfortunately most patients do not benefit from this treatment. Many pharmacodynamic (PD) studies have revealed essential requirements for successful cancer immunotherapy that may provide insight into how we can improve these agents. Despite enormous efforts focused on interrogating the immune system using different biospecimens (e.g. blood, primary tumor, metastatic tumor, microbiome samples), a variety of technologies (e.g. flow cytometry, bulk and single-cell RNA-sequencing, immunohistochemistry), and wide-ranging disciplines (e.g. pathology, genomics, bioinformatics, immunology, cancer biology, metabolomics, bacteriology), discovery of consistent biomarkers of response have remained elusive. Pharmacokinetics (PK) studies, however, not only provide critical information regarding safe dosing but may also reveal useful biomarkers. For example, recent studies found that trough levels of therapeutic monoclonal antibodies (mAbs) or clearance (CL) of them were associated with clinical outcome, which suggests that trough levels of mAbs may represent a new class of on-treatment cancer immunotherapy biomarker. In this review, we summarize the potential utility of trough levels of mAbs, the mechanism of varying PK, consideration for therapeutic drug monitoring, and assay attributes that will facilitate wider utilization of PK information in conjunction with PD assessments.

Population Pharmacokinetic Modelling of Intravenous Immunoglobulin Treatment in Patients with Guillain-Barré Syndrome

Background and Objective

Intravenous immunoglobulin (IVIg) at a standard dosage is the treatment of choice for Guillain–Barré syndrome. The pharmacokinetics, however, is highly variable between patients, and a rapid clearance of IVIg is associated with poor recovery. We aimed to develop a model to predict the pharmacokinetics of a standard 5-day IVIg course (0.4 g/kg/day) in patients with Guillain–Barré syndrome.

Methods

Non-linear mixed-effects modelling software (NONMEM^®) was used to construct a pharmacokinetic model based on a model-building cohort of 177 patients with Guillain–Barré syndrome, with a total of 589 sequential serum samples tested for total immunoglobulin G (IgG) levels, and evaluated on an independent validation cohort that consisted of 177 patients with Guillain–Barré syndrome with 689 sequential serum samples.

Results

The final two-compartment model accurately described the daily increment in serum IgG levels during a standard IVIg course; the initial rapid fall and then a gradual decline to steady-state levels thereafter. The covariates that increased IgG clearance were a more severe disease (as indicated by the Guillain–Barré syndrome disability score) and concomitant methylprednisolone treatment. When the current dosing regimen was simulated, the percentage of patients who reached a target ∆IgG > 7.3 g/L at 2 weeks decreased from 74% in mildly affected patients to only 33% in the most severely affected and mechanically ventilated patients (Guillain–Barré syndrome disability score of 5).

Conclusions

This is the first population-pharmacokinetic model for standard IVIg treatment in Guillain–Barré syndrome. The model provides a new tool to predict the pharmacokinetics of alternative regimens of IVIg in Guillain–Barré syndrome to design future trials and personalise treatment.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40262-022-01136-z.

Trough levels of ipilimumab in serum as a potential biomarker of clinical outcomes for patients with advanced melanoma after treatment with ipilimumab

Background

Immune checkpoint blockade (ICB) using anti-CTLA-4 and anti-PD-1/PD-L1 has revolutionized the treatment of advanced cancer. However, ICB is effective for only a small fraction of patients, and biomarkers such as expression of PD-L1 in tumor or serum levels of CXCL11 have suboptimal sensitivity and specificity. Exposure–response (E-R) relationships have been observed with other therapeutic monoclonal antibodies. There are many factors influencing E-R relationships, yet several studies have shown that trough levels of anti-PD-1/PD-L1 correlated with clinical outcomes. However, the potential utility of anti-CTLA-4 levels as a biomarker remains unknown.

Methods

Serum was obtained at trough levels at weeks 7 and 12 (after doses 2 and 4) from patients with advanced melanoma who received ipilimumab alone (3 mg/kg every 3 weeks for four treatments) via an expanded access program (NCT00495066). We have successfully established a proteomics assay to measure the concentration of ipilimumab in serum using an liquid chromatography with tandem mass spectrometry-based nanosurface and molecular-orientation limited proteolysis (nSMOL) approach. Serum samples from 38 patients were assessed for trough levels of ipilimumab by the nSMOL assay.

Results

We found that trough levels of ipilimumab were higher in patients who developed immune-related adverse events but did not differ based on the presence or absence of disease progression. We found that patients with higher trough levels of ipilimumab had better overall survival when grouped based on ipilimumab trough levels. Trough levels of ipilimumab were inversely associated with pretreatment serum levels of CXCL11, a predictive biomarker we previously identified, and soluble CD25 (sCD25), a prognostic biomarker for advanced melanoma, as well as C reactive protein (CRP) and interleukin (IL)-6 levels at week 7.

Conclusions

Our results suggest that trough levels of ipilimumab may be a useful biomarker for the long-term survival of patients with advanced melanoma treated with ipilimumab. The association of ipilimumab trough levels with pretreatment serum levels of CXCL11 and sCD25 is suggestive of a baseline-driven E-R relationship, and the association of ipilimumab trough levels with on-treatment levels of CRP and IL-6 is suggestive of response-driven E-R relationship. Our findings highlight the potential utility of trough levels of ipilimumab as a biomarker.

Trial registration number

NCT00495066.

In vivo trafficking of a tumor-targeting IgE antibody: molecular imaging demonstrates rapid hepatobiliary clearance compared to IgG counterpart

IgE antibodies elicit powerful immune responses, recruiting effector cells to tumors more efficiently and with greater cytotoxicity than IgG antibodies. Consequently, IgE antibodies are a promising alternative to conventional IgG-based therapies in oncology (AllergoOncology). As the pharmacokinetics of IgE antibodies are less well understood, we used molecular imaging in mice to compare the distribution and elimination of IgE and IgG antibodies targeting the human tumor-associated antigen chondroitin sulfate proteoglycan 4 (CSPG4). Anti-CSPG4 IgE and IgG1 antibodies with human Fc domains were radiolabeled with 111In. CSPG4-expressing A375 human melanoma xenografts implanted in NOD-scid IL2rg-/- mice were also engrafted with human immune cells by intravenous administration. 111In-anti-CSPG4 antibodies were administered intravenously. Their distribution was determined by single-photon emission computed tomography (SPECT) and ex vivo gamma-counting over 120 h. SPECT imaging was conducted from 0 to 60 min after antibody administration to precisely measure the early phase of IgE distribution. 111In-labeled anti-CSPG4 IgG and IgE showed serum stability in vitro of >92% after 5 days. In A375 xenograft-bearing mice, anti-CSPG4 IgE showed much faster blood clearance and higher accumulation in the liver compared to anti-CSPG4 IgG. However, tumor-to-blood and tumor-to-muscle ratios were similar between the antibody isotypes and higher compared with a non-tumor-targeting isotype control IgE. IgE excretion was much faster than IgG. In non-tumor-bearing animals, early SPECT imaging revealed a blood clearance half-life of 10 min for IgE. Using image-based quantification, we demonstrated that the blood clearance of IgE is much faster than that of IgG while the two isotypes showed comparable tumor-to-blood ratios.

Understanding Inter-Individual Variability in Monoclonal Antibody Disposition

Monoclonal antibodies (mAbs) are currently the largest and most dominant class of therapeutic proteins. Inter-individual variability has been observed for several mAbs; however, an understanding of the underlying mechanisms and factors contributing to inter-subject differences in mAb disposition is still lacking. In this review, we analyze the mechanisms of antibody disposition and the putative mechanistic determinants of inter-individual variability. Results from in vitro, preclinical, and clinical studies were reviewed evaluate the role of the neonatal Fc receptor and Fc gamma receptors (expression and polymorphism), target properties (expression, shedding, turnover, internalization, heterogeneity, polymorphism), and the influence of anti-drug antibodies. Particular attention is given to the influence of co-administered drugs and disease, and to the physiological relevance of covariates identified by population pharmacokinetic modeling, as determinants of variability in mAb pharmacokinetics.

Hypercatabolism of IgG in mice with lupus-like syndrome

The metabolism of radioiodinated mouse IgG was studied in mice with lupus-like syndrome before and after the onset of the disease. Before the onset of the disease, the pharmacokinetic parameters of IgG in MLR-lpr and Pristane-primed Balb/c mice were within the normal range of values. After the onset of the disease a considerable increase in the catabolic rate of IgG was recorded abbreviating its half life to less than one third of the normal value. The increased catabolism of IgG could not be related to the concentration-catabolism effect or to the presence of rheumatoid factor and autoantibody or to the IgG loss through the kidney and gastrointestinal tract. The hypercatabolism of IgG was explained by disease-induced impairment of the function of the receptor FcRn, which regulates the homeostasis of IgG.

Therapeutic Drug Monitoring of Anti-tumor Necrosis Factor Agents in Patients with Inflammatory Bowel Diseases

Anti-tumor necrosis factor (TNF) agents have radically changed the treatment of inflammatory bowel diseases. Although a significant amount of patients respond to therapy, others experience only a partial response or do not benefit at all. Although, in some cases, the mechanistic action of the anti-TNF therapy may explain such findings, we have now learned that many patients may instead suffer from inadequate dosing and drug exposure. Such heterogeneity in how patients respond to therapy may be explained by multiple pharmacodynamic variables, such as factors that alter drug clearance, including the level of systemic inflammation, the presence of antidrug antibodies, and concomitant use of immunomodulators. Multiple studies have found that low-serum anti-TNF levels are associated with active disease and that adjusting the dose in these cases may offer a therapeutic benefit. In this review, we discuss the most recent evidence on therapeutic drug monitoring in patients with inflammatory bowel disease receiving anti-TNF biological therapies.

Familial hypercatabolic hypoproteinemia. A disorder of endogenous catabolism of albumin and immunoglobulin

The metabolism of albumin and IgG was investigated in two siblings, products of a first-cousin marriage, a female aged 34 yr and a male aged 17, who had a marked reduction in their respective serum concentrations of IgG (1.3 and 3.1 mg/ml) and albumin (19 and 21 mg/ml). The metabolism of radioiodinated IgG and albumin was studied in the two patients. The total circulating and body pools of IgG were less than 28% of normal. The IgG synthetic rates were within the normal range. However, the IgG survival was short, with their respective fractional catabolic rates increased fivefold to 31% and 36% of the intravenous pool per day (normal, 6.7 +/- 2%/d). Furthermore, the patients had reduced total body pools, normal synthetic rates, and increased fractional catabolic rates for albumin. There was no proteinuria or abnormality of renal or liver function. In addition, the patients did not have circulating antibodies directed toward IgG, IgA, or albumin. Furthermore, both patients had normal fecal 51Cr-labeled albumin tests, thus excluding excessive gastrointestinal protein loss. We propose that these siblings have a previously unrecognized familial disorder characterized by reduced serum concentrations of IgG and albumin caused by a defect in endogenous catabolism, leading to a short survival of these proteins that is associated in this family with chemical diabetes and a skeletal deformity.

Clearance of cryoglobulins in man

From the foregoing it is evident that the defective clearance of immune complexes may contribute to tissue damage seen in patients with cryoglobulins. Hypocomplementaemia, decreased erythrocyte CR1, and the nature of the immune complexes may all contribute to decreased binding of immune complexes to erythrocytes with the potential consequence of increased availability for deposition and decreased processing of immune complexes. In addition, in type II cryoglobulinaemia the nature of the immune complex namely IgM RF/IgG complexes, has been shown in some circumstances to fix C3 and C4 inefficiently in spite of detectable fluid phase complement activation. The poor C3 fixation results not only in decreased transport by erythrocytes to the RES but also in inefficient removal of immune complexes by phagocytic cells, since the Fc receptor on these cells would be acting alone without the synergy of occupied complement receptors. Persistence of immune complexes in tissues in these circumstances has two potential consequences. First, the multivalency of IgM may contribute to enlargement of these immune complexes in situ by successive trapping of antigen and antibody complexes; this process may be aided by local factors such as low temperature at the peripheries and increased protein concentration in glomerular capillary loops, which favour "cryo" precipitation. The higher avidity of RF for IgG that is surface bound rather than monomeric would also favor immune complex formation in these circumstances. Second, although there is no opsonization of the immune complex complement activation results in bystander fixation of C4 and C3 to the surrounding tissues resulting in tissue injury.

Polyvalent immunoglobulins for prophylaxis of bacterial infections in patients following multiple trauma. A randomized, placebo-controlled study

One hundred and fifty severely injured patients requiring long-term artificial ventilation were evaluated in a prospective, randomized, double blind study comparing the prophylactic effect of an intravenous immunoglobulin (Sandoglobulin; IGIV) against nosocomial infections with a placebo preparation. The groups were comparable in age, sex, injury pattern, and severity of the trauma. Seventy-six patients received 12 g of Sandoglobulin as a 3% solution on day 0, day 5 and day 12, i.e. a total of 36 g. Sandoglobulin significantly reduced the incidence of pneumonia (28 cases in the IGIV group, 43 cases in the placebo group, p = 0.0111). This resulted in a reduced therapeutic use of antibiotics. For the occurrence of sepsis (IGIV: 14 cases; placebo 19 cases) and other infections (IGIV: 11 cases; placebo: 10 cases) no significant differences were found. No side effects of the administration of IGIV were observed. IGIV prophylaxis neither reduced the overall death rate nor those deaths caused by infection. On day 5 after administration of the first 12 g of IGIV, the IgG serum concentrations were significantly higher in the Sandoglobulin group (8.41 +/- 1.96 mg/ml and 7.42 +/- 2.25 mg/ml respectively, p less than 0.001) whereas later serum samples showed no significant differences.

Metabolism of IgG in type II mixed essential cryoglobulinaemia--autologous cryoprecipitated and normal homologous IgG are incorporated into complexes and metabolized in vivo at similar rates

The metabolism of autologous cryoprecipitated and normal homologous IgG was studied in four patients with type II mixed essential cryoglobulinaemia. 131I-autologous IgG purified from each patient's cryoglobulin (Cryo-IgG), and 125I-pooled normal homologous IgG (N-IgG) were studied simultaneously to compare the extent of their incorporation into complexes with IgM in vitro and in vivo, and their turnover in vivo. A proportion of each preparation of IgG was incorporated into macromolecular complexes in vitro and in vivo in all patients, the Cryo-IgG only slightly more so than N-IgG. Results of the turnover studies were heterogeneous, but the common finding was the absence of any significant difference in the metabolism of Cryo-IgG and N-IgG. In two patients the fractional catabolic rates (FCR) of Cryo-IgG and N-IgG were increased and in one they were normal. The fourth patient was also hypogammaglobulinaemic (IgG 0.52 mg/ml) and it was shown that in vivo virtually all his IgG was combined with IgM; despite this the FCR of both types of IgG was reduced. These results suggest (1) that the IgG component of the cryoglobulins in these patients is unlikely to differ significantly from normal IgG and (2) that, contrary to expectation, complexed IgG is not necessarily rapidly eliminated from the circulation.

In vivo behaviour of gamma globulin preparations

Metabolic properties of standard gamma globulin (St-GG) and of several gamma globulin (GG) preparations for intravenous use were analyzed in radioactive tracer studies. The in vivo behaviour of St-GG was investigated in 16 probands and found to be comparable to that of normal IgG. The kinetics of the resorption of St-GG from intramuscular deposits, its elimination from the intravascular compartment and from the body were studied in 2 probands. Metabolic properties of GG preparations for intravenous use were compared with those of St-GG in 3-4 probands after simultaneous injection of 125I- and 131I-labelled tracer doses. Important differences in the half-times of intravascular survival, in the rates of catabolism and in the distribution in the body were noticed for most of the preparations for intravenous use except for an improved acid-treated (pH 4) GG, the in vivo behaviour of which was similar to that of St-GG.

Metabolism of autologous and homologous IgG in rheumatoid arthritis

The metabolism of radioiodinated IgG was studied in 20 patients with rheumatoid arthritis and 11 normal controls using autologous IgG and homologous IgG pooled from normal donors. Fractional catabolic rates in the controls were 4.44% of the autologous- and 4.29% of the homologous-labeled protein per day. The corresponding rates in the rheumatoid patients were 9.67% of the autologous- and 8.64% of the homologous-labeled protein per day. Extravascular catabolism occurred only in the rheumatoid group and accounted essentially for the entire increased catabolism of IgG observed in these patients. 10 patients were especially hypercatabolic, with fractional catabolic rates for autologous IgG greater than 10%. Moreover, they catabolized their autologous IgG significantly faster than the homologous IgG (12.6 vs. 9.9%). The increment of catabolism of autologous over homologous IgG also occurred in the extravascular compartment. These highly hypercatabolic patients had a significantly increased number of manifestations of extra-articular disease. The hypercatabolism of IgG could not be correlated with age, weight, sex, duration of disease, joint erosions, corticosteroid therapy, erythrocyte sedimentation rate, rheumatoid factor titer, serum IgG concentration, or circulating immune complexes as measured by the Raji cell radioimmunoassay. Conceivable sites of extravascular catabolism and possible causes of faster catabolism of autologous (rheumatoid) than of homologous (normal) IgG are discussed.

Measurement of DNA-binding immunoglobulins in systemic lupus erythematosus

A radioimmunoadsorbant assay for quantitating DNA antibody in the IgM, IgG, and IgA classes is described. The method was standardized allowing expression of results in absolute terms. Effects of rheumatoid factor on the results were investigated. The new assay was found to correlate well with the Farr assay for DNA antibody. Serum levels of DNA antibody in all three immunoglobulin classes reflected the degree of clinical activity of SLE.

Immunoglobulin synthesis by peripheral blood cells in systemic lupus erythematosus

A study of the immunoglobulin (Ig) synthesis by peripheral blood cells of patients with systemic lupus erythematosus (SLE), rheumatoid arthritis, and controls was carried out. Synthesis was markedly elevated in patients with active SLE, whereas patients with the active SLE or RA showed normal values. Treatment of 3 patients with active SLE resulted in a reduction of Ig synthesis that correlated well with the disappearance of disease activity. There results indicate that the abnormal immune process in active SLE, characterized by intense B-lymphocyte stimulation, is associated with the appearance of more highly differentiated B cells in the blood.

The effect of azathioprine on gammaglobulin synthesis in man

The effect of azathioprine therapy on gammaglobulin synthesis was evaluated in nine patients with rheumatic disorders. The rates of synthesis of IgG and IgM were calculated before and after 4 months of azathioprine treatment using turnover studies of radioiodinated gammaglobulins. The synthesis of IgG decreased 33.4% of the initial IgG synthetic rate. Seven of nine patients showed reductions of IgG synthesis ranging from 16.8 to 74.1%. IgM production decreased from 24.5 to 74.2% in eight of nine patients with a mean reduction of 40.9%. Studies before and after a control period of 4 months of placebo in six patients revealed a mean increase in IgG and IgM synthesis. Serum immunoglobulin concentrations after 4 months of azathioprine treatment were not consistently reduced and did not parallel changes in immunoglobulin synthesis. Reduced gammaglobulin synthesis may play a role in the therapeutic action of this and other "immunosuppressive" drugs.

Metabolism of radio-iodinated IgG in patients with abnormal serum IgG levels. II. Hypogamma-globulinaemia

The metabolism of radio-iodinated IgG was studied in seven patients with IgG deficiency (<600 mg/100 ml). The group comprised two patients with primary hypogamma-globulinaemia, one with primary hypogamma-globulinaemia and nodular lymphoid hyperplasia, and one each with chronic lymphatic leukaemia (CLL), γG multiple myeloma, renal homotransplantation and the nephrotic syndrome.

All patients had markedly reduced plasma and total body pools of normal IgG with normal distribution (intravascular and extravascular pools). An increase in the initial urinary excretion of free isotope in one patient was attributed to a degree of protein denaturation. Compared to the normal range of 20–60 mg/kg/day for IgG synthesis, the patients with primary deficiency and the patient with CLL all had markedly reduced synthesis of normal IgG (2, 5, 4 and 7 mg/kg/day respectively). These patients also had a prolonged or normal plasma T½ and a normal or decreased fractional turnover rate (FTR).

The patients with deficiency of normal IgG secondary to multiple myeloma, renal homotransplant or nephrotic syndrome all had an IgG synthesis rate at the lower limit of the normal range with values of 19, 21 and 19 mg/kg/day respectively. They had increased catabolism with a short plasma T½ and increased FTR.

An assessment of the factors controlling the metabolism of normal IgG is important in the individual patient as regards the management of their recurrent infections with therapeutic human γ-globulin.

Metabolism of radio-iodinated IgG in patients with abnormal IgG levels. I. Hypergamma-globulinaemia

Metabolic turnover studies were performed with radio-iodinated IgG in twelve patients with a serum IgG level greater than 1600 mg/100 ml (six with monoclonal gammopathy and six with a polyclonal increase in IgG associated with liver disease). The six patients with an IgG monoclonal protein comprised four multiple myeloma, one benign monoclonal gammopathy and one biclonal gammopathy presenting as Waldenström's macroglobulinaemia. The six patients with liver disease comprised two patients with cirrhosis, two with infective hepatitis and two with chronic active hepatitis. The injected IgG was either autologous normal IgG (five cases), autologous monoclonal IgG (five cases), homologous normal IgG (one case) or therapeutic intravenous HGG (two cases).

The plasma volume was increased in six patients; the plasma IgG pool in nine; and the total body IgG pool in seven. The plasma T½ was normal in one patient with monoclonal and one patient with polyclonal gammopathy but shortened in the other ten studies with mean values of 11·3 and 11·0 days in monoclonal and polyclonal gammopathy respectively. The fractional turnover rate was normal in two studies in polyclonal gammopathy and increased in the other ten with mean values of 13·6% per day in both groups of patients. The IgG synthesis rate was significantly increased in all studies except for a reduced synthesis of normal IgG in one patient with multiple myeloma. The mean synthesis rates in monoclonal and polyclonal gammopathy were respectively 6·7 and 4·1 times the mean synthesis rate in normal controls.

The pattern of increased synthesis and increased catabolism in such patients confirms published reports in some diseases and demonstrates a similar pattern in chronic active hepatitis. The findings are consistent with the `concentration-catabolism' effect.