Interaction with Fc gamma RIIB Is Critical for the Agonistic Activity of Anti-CD40 Monoclonal Antibody

Division of Cancer Sciences, Faculty of Medicine, University of Southampton, Southampton SO16 6YD, United Kingdom.
The Journal of Immunology (Impact Factor: 4.92). 08/2011; 187(4):1754-63. DOI: 10.4049/jimmunol.1101135
Source: PubMed


A high activatory/inhibitory FcγR binding ratio is critical for the activity of mAb such as rituximab and alemtuzumab that attack cancer cells directly and eliminate them by recruiting immune effectors. Optimal FcγR binding profiles of other anti-cancer mAb, such as immunostimulatory mAb that stimulate or block immune receptors, are less clear. In this study, we analyzed the importance of isotype and FcγR interactions in controlling the agonistic activity of the anti-mouse CD40 mAb 3/23. Mouse IgG1 (m1) and IgG2a (m2a) variants of the parental 3/23 (rat IgG2a) were engineered and used to promote humoral and cellular responses against OVA. The mouse IgG1 3/23 was highly agonistic and outperformed the parental Ab when promoting Ab (10-100-fold) and T cell (OTI and OTII) responses (2- to >10-fold). In contrast, m2a was almost completely inactive. Studies in FcγR knockout mice demonstrated a critical role for the inhibitory FcγRIIB in 3/23 activity, whereas activatory FcγR (FcγRI, -III, and -IV) was dispensable. In vitro experiments established that the stimulatory effect of FcγRIIB was mediated through Ab cross-linking delivered in trans between neighboring cells and did not require intracellular signaling. Intriguingly, activatory FcγR provided effective cross-linking of 3/23 m2a in vitro, suggesting the critical role of FcγRIIB in vivo reflects its cellular distribution and bioavailability as much as its affinity for a particular Ab isotype. In conclusion, we demonstrate an essential cross-linking role for the inhibitory FcγRIIB in anti-CD40 immunostimulatory activity and suggest that isotype will be an important issue when optimizing reagents for clinical use.

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    • "For instance, CD40-signaling induced by soluble CD40L (sCD40L) was potentiated ~10-fold upon secondary cross-linking of CD40L into higher order multimers [15-17]. In line with this, CD40 signaling induced by anti-CD40 antibodies critically depends on the presence of Fc-receptor positive cells [18]. Based on these crosslinking requirements for CD40/CD40L signaling, CD40L has also been evaluated in a proof-of-concept study with a fibroblast activation protein (FAP)-targeted scFv:CD40L fusion protein. "
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    • "In contrast to these activating FcγRs that function as immunostimulatory receptors, inhibitory FcγRIIb is reported to function as an immunomodulatory receptor (Li and Ravetch, 2011; White et al., 2011). The inhibitory receptor FcγRIIb is the only IgG Fc receptor expressed on B-cells and plays a critical role in regulating B-cell homeostasis (Heyman, 2003; Nimmerjahn and Ravetch, 2008). "
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