Fc receptors are required in passive and active immunity to melanoma

Abstract

Effective tumor immunity requires recognition of tumor cells coupled with the activation of host effector responses. Fc receptor (FcR) gamma-/- mice, which lack the activating Fc gamma R types I and III, did not demonstrate protective tumor immunity in models of passive and active immunization against a relevant tumor differentiation antigen, the brown locus protein gp75. In wild-type mice, passive immunization with mAb against gp75 or active immunization against gp75 prevented the development of lung metastases. This protective response was completely abolished in FcR gamma-deficient mice. Immune responses were intact in gamma-/- mice because IgG titers against gp75 develop normally in gamma-/- mice immunized with gp75. However, uncoupling of the Fc gamma R effector pathway from antibody recognition of tumor antigens resulted in a loss of protection against tumor challenge. These data demonstrate an unexpected and critical role for FcRs in mediating tumor cytotoxicity in vivo and suggest that enhancement of Fc gamma R-mediated antibody-dependent cellular cytotoxicity by inflammatory cells is a key step in the development of effective tumor immunotherapeutics.

Figure 1

Passive protection from melanoma metastases requires FcRs. (A) Representative lungs from wt and γ^−/− mice injected i.v. with 10⁵ B16 melanoma cells. Mice were injected with either anti-gp75 (TA99) or control isotype antibody (UPC10). Six mice were present in each group. (B) Data are the mean ± SEM. P values of significant differences (Fisher exact test) are noted.

Figure 2

Anti-gp75-induced depigmentation occurs normally in FcγR-deficient mice. γ^−/− and wt mice were immunized with Sf9-gp75 (gray mice) or with control Sf9 extract (black mice).

Figure 3

Active protection from melanoma metastases requires FcRs. (A) Representative lungs from wt and γ^−/− mice injected i.v. with 10⁵ B16 melanoma cells. Mice were immunized with either anti-gp75 (Sf9-gp75) or control extract (Sf9). Six mice were present in each group. (B) Data are the mean ± SEM. P values of significant differences (Fisher exact test) are noted.

Figure 4

Anti-gp75 titers in Sf9-gp75-immunized γ^+/+ and γ^−/− mice are indistinguishable. Immunoprecipitations of diluted serum samples from Sf9-immunized (negative control) and Sf9-gp75-immunized mice. Diluted TA99 anti-gp75 mAb is used as a positive control.

Figure 5

Macrophage ADCC of tumor target cells requires FcγR γ chain. Bacillus Calmette–Guérin-elicited peritoneal γ^+/+ and γ^−/− macrophages were cultured with chromium-labeled TNP-opsonized HSB-2 target cells at an effector/target ratio of 10:1. Data are expressed as the mean ± SEM of triplicate samples assayed in the presence or absence of subagglutinating quantities of IgG1, IgG2a, or IgG2b anti-dinitrophenyl antibody.