Immunoglobulins A, G, and M in serum and in some secretions of monkeys (Macaca fascicularis syn. irus)

An Fc variant with two mutations confers prolonged serum half-life and enhanced effector functions on IgG antibodies

The pH-selective interaction between the immunoglobulin G (IgG) fragment crystallizable region (Fc region) and the neonatal Fc receptor (FcRn) is critical for prolonging the circulating half-lives of IgG molecules through intracellular trafficking and recycling. By using directed evolution, we successfully identified Fc mutations that improve the pH-dependent binding of human FcRn and prolong the serum persistence of a model IgG antibody and an Fc-fusion protein. Strikingly, trastuzumab-PFc29 and aflibercept-PFc29, a model therapeutic IgG antibody and an Fc-fusion protein, respectively, when combined with our engineered Fc (Q311R/M428L), both exhibited significantly higher serum half-lives in human FcRn transgenic mice than their counterparts with wild-type Fc. Moreover, in a cynomolgus monkey model, trastuzumab-PFc29 displayed a superior pharmacokinetic profile to that of both trastuzumab-YTE and trastuzumab-LS, which contain the well-validated serum half-life extension Fcs YTE (M252Y/S254T/T256E) and LS (M428L/N434S), respectively. Furthermore, the introduction of two identified mutations of PFc29 (Q311R/M428L) into the model antibodies enhanced both complement-dependent cytotoxicity and antibody-dependent cell-mediated cytotoxicity activity, which are triggered by the association between IgG Fc and Fc binding ligands and are critical for clearing cancer cells. In addition, the effector functions could be turned off by combining the two mutations of PFc29 with effector function-silencing mutations, but the antibodies maintained their excellent pH-dependent human FcRn binding profile. We expect our Fc variants to be an excellent tool for enhancing the pharmacokinetic profiles and potencies of various therapeutic antibodies and Fc-fusion proteins.

Lymphocyte subsets and immunoglobulin levels in peripheral blood from cynomolgus monkeys (Macaca fascicularis) of different age groups

Immunotoxicity assessment is an important part of non-clinical safety evaluation of biotechnology-derived pharmaceuticals. The reference ranges of evaluated parameters, which depend on the sex, age and geographical origin of animals, play a significant role in interpreting the study results. The aim of this study was to determine the reference ranges of parameters commonly used for non-clinical immunotoxicity studies in cynomolgus monkeys (Macaca fascicularis) of different ages. The percentages of CD3⁺, CD4⁺, CD8⁺, CD20⁺, CD16/56⁺ lymphocytes, and the serum levels of immunoglobulins A, M, G and E in clinically healthy cynomolgus monkeys of both sexes and different ages (37-104 months) were analysed. The lymphocyte subsets were assessed by flow cytometry and serum immunoglobulin levels were determined by enzyme-linked immunosorbent assay. Statistical analysis showed a weak rank correlation of CD3⁺, CD20⁺ lymphocyte levels with the ages of female and male cynomolgus monkeys, and no significant correlation with age for the combined data of both sexes. The serum levels of immunoglobulins A, M, G and E did not have a significant rank correlation with age for the combined data of both sexes, whereas IgA levels in females and IgG levels in males were weakly correlated with age. Overall, these results justify the use of animals aged three to eight years for non-clinical immunotoxicity evaluation of biotechnology-derived pharmaceuticals. It is important to avoid the formation of animal groups with extreme ages (three years or eight years) in one group during randomization.

Elimination of plasma soluble antigen in cynomolgus monkeys by combining pH-dependent antigen binding and novel Fc engineering

A conventional antibody targeting a soluble antigen in circulation typically requires a huge dosage and frequent intravenous administration to neutralize the antigen. This is because antigen degradation is reduced by the formation of antigen–antibody immune complexes, which escape from lysosomal degradation using neonatal Fc receptor (FcRn)-mediated recycling. To address this, we developed an antigen-sweeping antibody that combines pH-dependent antigen binding and Fc engineering to enhance Fc receptor binding. The sweeping antibody actively eliminates the plasma antigens by increasing the cellular uptake of the immune complex and dissociating the antigens in the acidic endosome for degradation. Strong antigen sweeping can reduce the dosage, potentially achieve higher efficacy, and expand the scope of antigen space available for targeting by antibodies. In this study, to further improve the sweeping efficacy, we developed a novel antibody Fc variant by enhancing Fcγ receptor IIb (FcγRIIb) binding and modulating charge characteristics for increased cellular uptake of the immune complex, together with enhancing FcRn binding for efficient salvage of the antigen-free antibodies. Our Fc variant achieved strong antigen sweeping in cynomolgus monkeys with antibody pharmacokinetics comparable to a wild-type human IgG₁ antibody. The positive-charge substitutions enhanced uptake of the immune complex by FcγRIIb-expressing cells in vitro, which was completely inhibited by an anti-FcγRIIb antibody. This suggests that the strong in vivo sweeping efficacy improved by the charge engineering is more likely achieved by FcγRIIb-dependent uptake of the immune complex rather than nonspecific uptake. We expect this novel Fc engineering can maximize the antigen sweeping efficacy even in humans and create novel therapeutic antibodies that meet unmet medical needs for patients.

Immunoglobulin A and nutrients in milk from great apes throughout lactation

Differences in macronutrients between human and ape milks appear relatively small, but variation in other components such as immunoglobulins (Ig) may be greater. This study characterized the macronutrient and secretory (sIgA) profiles in milk from gorillas and orangutans throughout lactation. Fifty-three milk samples from four gorillas and three orangutans were collected throughout 48 and 22 months postpartum (MPP), respectively. Samples were grouped in five stages of lactation (0 to 6 months, more than 6 months to 12 months, more than 12 months to 18 months, more than 18 months to 36 months, and more than 36 months to 48 months). Data were analyzed as a complete randomized design. Concentration of sIgA did not change due to species or its interaction with MPP. Crude protein, regardless of MPP, was greater for gorillas compared with orangutans (1.27 vs. 0.85%). Fat, sugar, and gross energy were affected by the interaction of species × MPP. For gorilla milk, concentrations of sIgA were 43 mg/L at 6 MPP increasing to 79 mg/L at 48 MPP. Protein was highest at 48 MPP. Sugar was lowest at 48 MPP. Values for fat and gross energy were the highest 36 MPP. For orangutan milk, concentrations of sIgA were highest at 6 MPP. Sugar decreased with MPP. Protein, dry matter, or fat were unaffected by MPP. Gross energy content was steady during the first 18 MPP but it tended to decrease by 36 MPP. The results indicate that macronutrients are similar between human, published data, and great ape milk, though gorilla milk has higher protein and human milk higher fat (published data). Concentrations of sIgA in ape milk were about 10-fold lower than human values from the literature. Differences between human and ape milk may lie more in bioactive/immune molecules than nutrients.

RESEARCH HIGHLIGHTS

Milk macronutrients from great apes differed throughout lactation. Milk macronutrients but not IgA from non-human great apes and humans were quite similar. Milk protein was greater in Gorilla compared with Orangutan.

Generation of monoclonal antibodies to Macaca mulatta (rhesus) IgA

One IgG1 and five IgM murine monoclonal antibodies (mAb) specific for rhesus (Rh) IgA were generated. These mAbs bound to Rh IgA but not IgG or IgM when tested by enzyme-linked immunosorbent assay. Immunoblotting revealed that the mAbs reacted with the alpha heavy chain of Rh but not human IgA. The IgG1 anti-Rh IgA mAb detected IgA-producing cells in sections of monkey gut examined by immunofluorescent staining. These mAbs should be useful for characterizing IgA responses in the Rh monkey.

Measurement of squirrel monkey serum IgG levels by a two-site sandwich radioimmunoassay with monoclonal antibodies

Monoclonal antibodies against the squirrel monkey Saimiri sciureus IgG have been produced for a more specific analysis of the antibody-related immunological aspects in experimental human or monkey malaria. Two monoclonal antibodies, 3D8/D5 and 3F11/G10, out of 64 reacted with distinct epitopes on the IgG present throughout the complete population without interfering with each other. The 2 monoclonal antibodies were used to develop a highly specific, reliable and sensitive two-site sandwich radioimmunoassay for the measurement of the serum IgG levels in 83 animals. The antibodies also allowed us to produce by a simple immunoabsorbent technique a highly purified IgG standard easy to calibrate and store. The assay permits the detection of IgG levels as low as 0.48 ng/ml. The standard curve is linear between 3.9 and 125 ng protein/ml and allows by a simple mathematical equation an accurate measurement of the serum IgG levels.

Chromatographic fractionation of rhesus monkey (Macaca mulatta) IgG subclasses using deae cellulose and protein A-sepharose

Rhesus monkey serum was applied to a protein A-Sepharose column at pH 7.3. IgG was not detectable in the unbound effluent. Bound protein was eluted with a pH gradient of citrate-phosphate buffer. Two major elution peaks reproducibly resulted at pH 4.85-4.9 and pH 4.35-4.43, respectively, with only slight variability among individuals. Since the immunoelectrophoretic mobility of IgG in the peak at pH 4.85-4.9 was slower than that of the peak at pH 4.35-4.43, serum was first fractionated by ion exchange chromatography into 2 fractions: the first did not bind to DEAE cellulose in 0.01 M phosphate buffer pH 7.8, the second did bind and was eluted by an NaCl gradient. Each DEAE fraction was then further fractionated on protein A-Sepharose. IgG in the first DEAE fraction bound to protein A at pH 7.3 and eluted in a single peak at pH 4.72-5.0. IgG in the second DEAE fraction also bound to protein A, but eluted in 2 peaks at pH 4.65-5.1, and 4.25-4.6, respectively. All 3 IgG fractions eluted in the same position from an A5m column, had immunodiffusion reactions of identity with anti-human gamma chain and were composed of similar heavy and light chains judged by SDS polyacrylamide gel electrophoresis. However, IgG eluting from protein A at the low pH (4.25-4.6) had a reaction of partial identity with other IgG fractions when tested by immunodiffusion against rabbit anti-rhesus gamma chain, suggestive of an antigenically different subclass. Analysis of rabbit antisera prepared against the 3 IgG fractions confirmed the occurrence of at least 3 antigenically distinct rhesus monkey IgG subclasses. These 3 subclasses have been provisionally designated IgG I, IgG II and IgG III.