Combined CD44- and CD25-Targeted Near-Infrared Photoimmunotherapy Selectively Kills Cancer and Regulatory T Cells in Syngeneic Mouse Cancer Models.

Near-infrared photoimmunotherapy (NIR-PIT) is a newly developed and selective cancer treatment that induces necrotic and immunogenic cell death and utilizes a mAb conjugated to a photo-absorber dye, IR700DX, activated by NIR light. Although CD44 is a surface cancer marker associated with drug resistance, anti-CD44-IR700 NIR-PIT results in inhibited cell growth and prolonged survival in multiple tumor types. Meanwhile, CD25-targeted NIR-PIT has been reported to achieve selective and local depletion of FOXP3+CD25+CD4+ regulatory T cells (Treg), which are primary immunosuppressive cells in the tumor microenvironment (TME), resulting in activation of local antitumor immunity. Combined NIR-PIT with CD44- and CD25-targeted agents has the potential to directly eliminate tumor cells and also amplify the immune response by removing FOXP3+CD25+CD4+ Tregs from the TME. We investigated the difference in therapeutic effects of CD44-targeted NIR-PIT alone, CD25-targeted NIR-PIT alone, and the combination of CD44- and CD25-targeted NIR-PIT in several syngeneic tumor models, including MC38-luc, LL/2, and MOC1. The combined NIR-PIT showed significant tumor growth inhibition and prolonged survival compared with CD44-targeted NIR-PIT alone in all tumor models and showed prolonged survival compared with CD25-targeted NIR-PIT alone in MC38-luc and LL/2 tumors. Combined CD44- and CD25-targeted NIR-PIT also resulted in some complete remissions. Therefore, combined NIR-PIT simultaneously targeting cancer antigens and immunosuppressive cells in the TME may be more effective than either type of NIR-PIT alone and may have potential to induce prolonged immune responses in treated tumors.

ADCT-301, a Pyrrolobenzodiazepine (PBD) Dimer-Containing Antibody-Drug Conjugate (ADC) Targeting CD25-Expressing Hematological Malignancies.

Despite the many advances in the treatment of hematologic malignancies over the past decade, outcomes in refractory lymphomas remain poor. One potential strategy in this patient population is the specific targeting of IL2R-α (CD25), which is overexpressed on many lymphoma and leukemic cells, using antibody-drug conjugates (ADC). ADCT-301 is an ADC composed of human IgG1 HuMax-TAC against CD25, stochastically conjugated through a dipeptide cleavable linker to a pyrrolobenzodiazepine (PBD) dimer warhead with a drug-antibody ratio (DAR) of 2.3. ADCT-301 binds human CD25 with picomolar affinity. ADCT-301 has highly potent and selective cytotoxicity against a panel of CD25-expressing human lymphoma cell lines. Once internalized, the released warhead binds in the DNA minor groove and exerts its potent cytotoxic action via the formation of DNA interstrand cross-links. A strong correlation between loss of viability and DNA cross-link formation is demonstrated. DNA damage persists, resulting in phosphorylation of histone H2AX, cell-cycle arrest in G2-M, and apoptosis. Bystander killing of CD25-negative cells by ADCT-301 is also observed. In vivo, a single dose of ADCT-301 results in dose-dependent and targeted antitumor activity against both subcutaneous and disseminated CD25-positive lymphoma models. In xenografts of Karpas 299, which expressed both CD25 and CD30, marked superiority over brentuximab vedotin (Adcetris) is observed. Dose-dependent increases in DNA cross-linking, γ-H2AX, and PBD payload staining were observed in tumors in vivo indicating a role as relevant pharmacodynamic assays. Together, these data support the clinical testing of this novel ADC in patients with CD25-expressing tumors. Mol Cancer Ther; 15(11); 2709-21. ©2016 AACR.

Icaritin inhibits T cell activation and prolongs skin allograft survival in mice.

Icaritin is a native compound from Epimedium Genus, a traditional Chinese herbal medicine which is effective in treating asthma, autoimmune diseases and viral infections. In the present paper, the immunosuppressive effects of icaritin were found through in vitro and in vivo studies. Icaritin could dose-dependently inhibit murine CD4(+) T cells proliferation stimulated with mitogens or specific antigen ovabumin (OVA). Icaritin at 0.25-25µM could down-regulate T cell activation marker CD25 expression and inhibit IL-2 production. It could also reduce the Th1 cytokine IFN-γ production significantly if the T cells were activated by ConA or anti-CD3; while the inhibition of IL-4 secretion was only seen on anti-CD3 activated T cells treated with low concentrations of icaritin. In vivo study showed that treatment of icaritin at 10mg/kg/day on mice could suppress the immune response with prolonged allograft skin survival. Further study demonstrated that it reduced the alloantigen-induced splenocytes proliferation and Th1/Th2 cytokines. It could also increase NF-AT luciferase activity in Jurkat-NF-AT-luc T cells. The above results suggested that icaritin might be used to treat Th1 dominated immune diseases by interfering T cells activation with mechanism different to CsA.

Monoclonal antibody blockade of IL-2 receptor α during lymphopenia selectively depletes regulatory T cells in mice and humans.

Lymphodepletion augments adoptive cell transfer during antitumor immunotherapy, producing dramatic clinical responses in patients with malignant melanoma. We report that the lymphopenia induced by the chemotherapeutic agent temozolomide (TMZ) enhances vaccine-driven immune responses and significantly reduces malignant growth in an established model of murine tumorigenesis. Unexpectedly, despite the improved antitumor efficacy engendered by TMZ-induced lymphopenia, there was a treatment related increase in the frequency of immunosuppressive regulatory T cells (T(Regs); P = .0006). Monoclonal antibody (mAb)-mediated inhibition of the high-affinity IL-2 receptor α (IL-2Rα/CD25) during immunotherapy in normal mice depleted T(Regs) (73% reduction; P = .0154) but also abolished vaccine-induced immune responses. However, during lymphodepletion, IL-2Rα blockade decreased T(Regs) (93% reduction; P = .0001) without impairing effector T-cell responses, to augment therapeutic antitumor efficacy (66% reduction in tumor growth; P = .0024). Of clinical relevance, we also demonstrate that anti-IL-2Rα mAb administration during recovery from lymphodepletive TMZ in patients with glioblastoma reduced T(Reg) frequency (48% reduction; P = .0061) while permitting vaccine-stimulated antitumor effector cell expansion. To our knowledge, this is the first report of systemic antibody-mediated T(Reg) depletion during lymphopenia and the consequent synergistic enhancement of vaccine-driven cellular responses, as well as the first demonstration that anti-IL-2Rα mAbs function differentially in nonlymphopenic versus lymphopenic contexts.