Cutting edge: CD4+ T cell control of CD8+ T cell reactivity to a model tumor antigen

Abstract

Neoantigens resulting from the inherent genomic instability of tumor cells generally do not trigger immune recognition. Similarly, transfection of tumors with model Ags often fails to elicit CD8+ T cell responses or alter a tumor's growth rate or lethality. We report here that the adoptive transfer of activated Th1-type CD4+ T cells specific for a model tumor Ag results in the de novo generation of CD8+ T cells with specificity to that Ag and concomitant tumor destruction. The anti-tumor effects of the CD4+ T cells required the presence of both MHC class I and class II on host cells, as evidenced by experiments in knockout mice, suggesting that CD4+ T cells enhanced the ability of host APC to activate endogenous CD8+ T cells. These results indicate that the apparent inability of tumor cells expressing highly immunogenic epitopes to activate tumor-specific CD8+ T cells can be altered by activated CD4+ T cells.

FIGURE 1

Generation of a I-A^b-restricted, β-gal-specific, CD4⁺, Th1-type clone. A, Clones obtained by limiting dilution of a β-gal-specific, CD4⁺ bulk line were assayed for release of IL-4 (top) or IL-2 (bottom) when cocultured in the presence of splenocytes pulsed with OVA or β-gal protein. B, The B12 clone was confirmed to be CD4⁺ by FACS analysis. C, β-gal-specific IL-2 secretion by the B12 clone was CD4 dependent and I-A^b restricted as evidenced by blocking experiments.

FIGURE 2

Adoptive transfer of the B12 clone results in eradication of pulmonary nodules established for 3 days. Mice were given 3 × 10⁵ B12 clone 3 days after i.v. injection of tumor. Pulmonary nodules were enumerated in a coded, blinded fashion 14–16 days later in repeated experiments. Representative experiments are shown. The ability of the B12 clone to mediate tumor regression was assessed in wild-type mice (A) and in mice that were depleted of CD8⁺ cells (B). Ag specificity was determined by treatment of mice bearing either the WP4.WT (C) or the WP4.β-gal tumor (D–F). Identically treated β₂m KO mice and MHC class II KO mice are shown in E and F, respectively (*, p₂ = 0.007 in A and p₂ = 0.008 in D, no treatment vs treatment with B12, as assessed by the Kruskal-Wallis test).

FIGURE 3

De novo generation of β-gal-reactive CD8⁺ T cells occurs only in mice treated by adoptive transfer of B12 clone. A, Spleens from mice bearing WP4.WT or WP4.β-gal tumor and treated with 3 × 10⁵ B12 clone or with nothing were removed 12 days after treatment and restimulated for 6 days with the MHC class I-restricted β-gal_96–103 peptide or control peptide. Splenocytes were then cultured for 24 h with β-gal_96–103 or control peptide. Stimulation index was calculated by dividing the amount of Ag-specific IFN-γ released by nonspecific release. B, Mice receiving WP4.β-gal tumor were treated with B12 clone or an OVA-reactive clone. Twelve days later, spleens were removed, restimulated, and assayed as above. C, Class II KO or wild-type mice bearing WP4.β-gal were treated with B12 clone or with nothing. Spleens were removed, restimulated, and assayed as above. The results shown are the averages from three independently performed experiments in A and C and two independently performed experiments in B.