C3d regulates immune checkpoint blockade and enhances antitumor immunity
Jeffrey L. Platt, … , Michael C. Carroll, Marilia Cascalho
Jeffrey L. Platt, … , Michael C. Carroll, Marilia Cascalho
Published May 4, 2017
Citation Information: JCI Insight. 2017;2(9):e90201. https://doi.org/10.1172/jci.insight.90201.
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Research Article Immunology

C3d regulates immune checkpoint blockade and enhances antitumor immunity

Abstract

Despite expression of immunogenic polypeptides, tumors escape immune surveillance by engaging T cell checkpoint regulators and expanding Tregs, among other mechanisms. What orchestrates these controls is unknown. We report that free C3d, a fragment of the third component of complement, inside tumor cells — or associated with irradiated tumor cells and unattached to antigen — recruits, accelerates, and amplifies antitumor T cell responses, allowing immunity to reverse or even to prevent tumor growth. C3d enhances antitumor immunity independently of B cells, NK cells, or antibodies, but it does so by increasing tumor infiltrating CD8+ lymphocytes, by depleting Tregs, and by suppressing expression of programmed cell death protein 1 (PD-1) by T cells. These properties of C3d appear specific for the tumor and dependent on complement receptor 2, and they incur no obvious systemic toxicity. The heretofore unrecognized properties of free C3d suggest that protein might determine the effectiveness of immune surveillance and that increasing availability of the protein might prove advantageous in the treatment or prevention of cancer and premalignant conditions.

Authors

Jeffrey L. Platt, Inês Silva, Samuel J. Balin, Adam R. Lefferts, Evan Farkash, Ted M. Ross, Michael C. Carroll, Marilia Cascalho

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Figure 5

C3d modifies antitumor T cell functions.

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C3d modifies antitumor T cell functions. (A) CR2 and PD-1 expression mea...
(A) CR2 and PD-1 expression measured by qPCR on Tregs. Expression of CR2 and PD-1 were relative to that of GAPDH. (B) Flow cytometry analysis of lymphocytes obtained from the spleen of mice 10 days after injection of 5 × 103 lymphoma cells. Figure shows reciprocal expression of CD21 and PD-1 by Tregs (CD4+, Foxp3+). (C and D) Figure shows the percent (%) of CD4+ (C) or CD8+ (D) T cells isolated from the spleen of recipients of C3d+ or C3d– tumors that express perforin, TNFα, and IFNγ, 3.5 hours after culture on anti-CD3– and anti-CD2–coated plates. Boxes in graphs represent distribution of data between the 25th and the 75th percentiles. The mean is indicated by a horizontal line, and whiskers represent maximum and minimum values. Statistical analysis was by the Mann Whitney 2-tailed test. (E) Impact of anti-CR2 antibodies on survival of mice given C3d+ or C3d– lymphoma cells. Anti-CD21/CD35 (7G6) antibodies were administered at the same time as tumor cells. Figure represents Kaplan-Meier plots obtained with at least 5 mice per condition, and differences between curves were analyzed by the log rank Mantel-Cox test. Note, the C3d-positive tumor and C3d-negative tumor groups in (E) are the same data as presented in Figure 1A. The data were not collected contemporaneously as the other groups in (E), but are shown here for reference.