Synergistic Activation of Macrophages via CD40 and TLR9 Results in T Cell Independent Antitumor Effects

Abstract

We have previously shown that macrophages (Mφ) can be activated by CD40 ligation to become cytotoxic against tumor cells in vitro. Here we show that treatment of mice with agonistic anti-CD40 mAb (anti-CD40) induced up-regulation of intracellular TLR9 in Mφ and primed them to respond to CpG-containing oligodeoxynucleotides (CpG), resulting in synergistic activation. The synergy between anti-CD40 and CpG was evidenced by increased production of IFN-γ, IL-12, TNF-α, and NO by Mφ, as well as by augmented apoptogenic effects of Mφ against tumor cells in vitro. The activation of cytotoxic Mφ after anti-CD40 plus CpG treatment was dependent on IFN-γ but not TNF-α or NO, and did not require T cells and NK cells. Anti-CD40 and CpG also synergized in vivo in retardation of tumor growth in both immunocompetent and immunodeficient mice. Inactivation of Mφ in SCID/beige mice by silica treatment abrogated the antitumor effect. Taken together, our results show that Mφ can be activated via CD40/TLR9 ligation to kill tumor cells in vitro and inhibit tumor growth in vivo even in immunocompromised tumor-bearing hosts, indicating that this Mφ-based immunotherapeutic strategy may be appropriate for clinical testing.

Intratumoral immunocytokine treatment results in enhanced antitumor effects

“…In the same way that combination with chemotherapy seems to augment the efficacy of IV IC [16], we hypothesize that combination therapy using IT IC will be more effective than IT IC alone against aggressive or more established tumors. On-going murine studies are attempting to augment the antitumor effect of IT IC with chemotherapeutic agents or antitumor immune stimulants such as αCD40 or CpG [2,3,26]. In addition, since IV IC has been shown to have significant antimetastatic effects, combinatorial IT and IV IC therapy is a clinical possibility.…”

Development of TLR9 agonists for cancer therapy

“…To induce rejection of larger or poorly immunogenic tumors, the CpG ODN generally needs to be combined with either a tumor vaccine (reviewed in ref. 71) or with other effective antitumor strategies, such as monoclonal antibody therapy (72)(73)(74)(75)(76)(77)(78), other immune therapies (including in combination with ligands for TLR3 or TLR5) (79)(80)(81)(82)(83)(84), angiogenesis inhibitors (85), radiation therapy (86), surgery (87,88), cryotherapy (89), and chemotherapy (87,(90)(91)(92)(93)(94)(95) (Table 4). In humans also, monotherapy with the TLR9 agonist CPG 7909 (now called PF-3512676 when used in oncology without a vaccine) or another B-class CpG ODN, 1018 ISS, activates NK cells and induces a Th1 cytokine response in humans with B cell lymphomas (37,96).…”

Confirming the RNAi-mediated mechanism of action of siRNA-based cancer therapeutics in mice

“…These types of response are known to elicit antitumor effects, primarily through the actions of IFNs and inflammatory cytokines that exert antiangiogenic, proapoptotic, and adjuvant effects that enhance cellular immunity (7,8). Many of these mechanisms remain active in the immunodeficient mouse strains typically used as hosts for human tumor xenografts, including SCID/beige mice, which lack functional lymphocyte and NK cell populations (9,10). Induction of the innate immune response by nucleic acids can also have significant toxicologic consequences (reviewed in ref.…”