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Therapeutic monoclonal antibodies (mAb), directed toward either tumor antigens or inhibitory checkpoints on immune cells, are effective in cancer therapy. Increasing evidence suggests that the therapeutic efficacy of these tumor antigen–targeting mAbs is mediated—at least partially—by myeloid effector cells, which are controlled by the innate immune-checkpoint interaction between CD47 and SIRPα. We and others have previously demonstrated that inhibiting CD47–SIRPα interactions can substantially potentiate antibody-dependent cellular phagocytosis and cytotoxicity of tumor cells by IgG antibodies both in vivo and in vitro. IgA antibodies are superior in killing cancer cells by neutrophils compared with IgG antibodies with the same variable regions, but the impact of CD47–SIRPα on IgA-mediated killing has not been investigated. Here, we show that checkpoint inhibition of CD47–SIRPα interactions further enhances destruction of IgA antibody–opsonized cancer cells by human neutrophils. This was shown for multiple tumor types and IgA antibodies against different antigens, i.e., HER2/neu and EGFR. Consequently, combining IgA antibodies against HER2/neu or EGFR with SIRPα inhibition proved to be effective in eradicating cancer cells in vivo. In a syngeneic in vivo model, the eradication of cancer cells was predominantly mediated by granulocytes, which were actively recruited to the tumor site by SIRPα blockade. We conclude that IgA-mediated tumor cell destruction can be further enhanced by CD47–SIRPα checkpoint inhibition. These findings provide a basis for targeting CD47–SIRPα interactions in combination with IgA therapeutic antibodies to improve their potential clinical efficacy in tumor patients.

Supplementary Materials and Methods

Supplementary Figures

Three FDA-approved epidermal growth factor receptor (EGFR) antibodies (cetuximab, panitumumab, necitumumab) are clinically available to treat patients with different types of cancers. Interestingly, panitumumab is of human IgG2 isotype, which is often considered to have limited immune effector functions. Unexpectedly, our studies unraveled that human IgG2 antibodies against EGFR mediated effective CDC when combined with another noncross-blocking EGFR antibody. This second antibody could be of human IgG1 or IgG2 isotype. Furthermore, EGFR antibodies of human IgG2 isotype were highly potent in recruiting myeloid effector cells such as M1 macrophages and PMN for tumor cell killing by ADCC. Tumor cell killing by PMN was more effective with IgG2 than with IgG1 antibodies if tumor cells expressed lower levels of EGFR. Additionally, lower expression levels of the “don′t eat me” molecule CD47 on tumor cells enabled ADCC also by M2 macrophages, and improved PMN and macrophage-mediated ADCC. A TCGA enquiry revealed broadly varying CD47 expression levels across different solid tumor types. Together, these results demonstrate that human IgG2 antibodies against EGFR can promote significant Fc-mediated effector functions, which may contribute to their clinical efficacy. The future challenge will be to identify clinical situations in which myeloid effector cells can optimally contribute to antibody efficacy.

The Figure S1 shows: A) Maximal EGFR binding of different EGFR antibodies B) Complement factor binding and deposition by combinations of EGFR IgG1/IgG1, IgG1/IgG2 and IgG2/IgG2 antibodies C) EGFR expression of A431 ctrl and A431 CD47 Ko cells D) Target antigen binding and growth inhibition induced by different Matuzumab variants