Nonclinical Evaluation of GMA161—An Antihuman CD16 (FcγRIII) Monoclonal Antibody for Treatment of Autoimmune Disorders in CD16 Transgenic Mice

Abstract

Fc receptors are a critical component of the innate immune system responsible for the recognition of cross-linked antibodies and the subsequent clearance of pathogens. However, in autoimmune diseases, these receptors play a role in the deleterious action of self-directed antibodies and as such are candidate targets for treatment. GMA161 is an aglycosyl, humanized version of the murine antibody 3G8 that targets the human low-affinity Fcγ receptor III (CD16). As CD16 expression and sequence have high species specificity, preclinical assessments were conducted in mice transgenic for both isoforms of human CD16, CD16A, and CD16B. This transgenic mouse model was useful in transitioning into phase I clinical trials, as it generated positive efficacy data in a relevant disease model and an acceptable single-dose safety profile. However, when GMA161 or its murine parent 3G8 were dosed repeatedly in transgenic mice having both human CD16 isoforms, severe reactions were observed that were not associated with significant cytokine release, nor were they alleviated by antihistamine administration. Prophylactic dosing with an inhibitor of platelet-activating factor (PAF), however, completely eliminated all signs of hypersensitivity. These findings suggest that (1) GMA161 elicits a reaction that is target dependent, (2) immunogenicity and similar adverse reactions were observed with a murine version of the antibody, and (3) the reaction is driven by the atypical hypersensitivity pathway mediated by PAF.

Monovalent Fc receptor blockade by an anti–Fcγ receptor/albumin fusion protein ameliorates murine ITP with abrogated toxicity

“…Based on this theory, a second-generation anti-huFcgRIIIA antibody, GMA161, engineered to lack Fc-mediated FcgR engagement, had been developed. 15 However, GMA161 failed to arrest the adverse events in refractory ITP patients, pointing out the genesis of these adverse events by some other attribute of the therapeutic antibody. We have speculated in the current work that this adverse event profile might be contributed to by the bivalent antigen-binding domain of anti-FcgR antibodies.…”

“…A deglycosylated version of 3G8 (called GMA161), known to have abrogated Fc function, 14 had thus been developed by Fc engineering. 15 In a humanized mouse model, GMA161 was able to ameliorate ITP, but unfortunately, rapidly depleted granulocytes. 15 Consistent with the humanized mouse model, GMA161 improved platelet counts in refractory patients but failed to reverse adverse events exhibited by its parent 3G8.…”

“…15 In a humanized mouse model, GMA161 was able to ameliorate ITP, but unfortunately, rapidly depleted granulocytes. 15 Consistent with the humanized mouse model, GMA161 improved platelet counts in refractory patients but failed to reverse adverse events exhibited by its parent 3G8. 10,11 The outcome of the pilot trial of GMA161 suggested to us that the bivalent Fab domain likely triggers the adverse events.…”

State of the art – how I manage immune thrombocytopenia

“…Novel targets include: the spleen tyrosine kinase (Syk) inhibitor fostamatinib, which has shown promise for refractory patients (8 of 16 patients responded to treatment) (Podolanczuk et al , ) and is in phase 3 trials. Other agents targeting T cell co‐stimulation – toralizumab (IDEC‐151) (Kuwana et al , ) and ruplizumab (hu5c8) (Patel et al , ), or FcR binding and signalling – GMA161 (Flaherty et al , ) are in study. Newer TPO‐RAs are also in trial – avatrombopag, 23A11 and amifostine.…”

Advantages and Limitations of Commonly Used Nonhuman Primate Species in Research and Development of Biopharmaceuticals

“…In NHPs there is only one CD16 gene, homologous to the human CD16A, which is restricted to NK cells and monocytes [53]. This difference necessitated the testing of an antihuman CD16 (FcγRIIIA and FcγRIIIB)-specific mAb in human CD16 transgenic mice to assess the impact on neutrophils [54]. Even greater differences in Fc receptor expression, distribution, and internalization profiles between humans and mice also are observed [55].…”