Figure 3. CD4 cells are required for maximal tumor elimination and immunologic memory after the treatment with anti-OX40 and anti–PD-1.

(A, H, J) Schedule of tumor implantation and injection of antibodies for cell depletion in mice receiving treatment only (A), in mice rechallenged after treatment (H), and in mice monitored for the baseline immunogenicity of KPC-Luc tumor (J).

(B–E) Depletion of CD4 (CD4-D) (C), CD8 (CD8-D) (D), or double depletion of CD4 and CD8 (CD4+8-D) (E) was confirmed by flow cytometry, and no cells were depleted after control immunoglobulin G (IgG) antibody injection (B).

(F–G) The antitumor effect was completely abolished after depletion of CD4 cells with or without depletion of CD8 cells; however, the antitumor effect was only partially reduced by depletion of CD8 cells. IVIS bioluminescence images of tumor size in mice are shown on the right in the setting of anti-OX40 monotherapy (F) and combination therapy with anti-OX40 and anti–PD-1 (G).

(I) In mice previously cured by combination therapy with anti-OX40 and anti–PD-1, the immunologic memory effect was completely abolished after depletion of CD4 cells; however, the immunologic memory effect was intact after depletion of CD8 cells.

(K) KPC-Luc tumor exhibited similar growth curves in Rag2 knockout, CD4- and/or CD8-depleted, and immunocompetent control mice.