Administration of low-dose combination anti-CTLA4, anti-CD137, and anti-OX40 into murine tumor or proximal to the tumor draining lymph node induces systemic tumor regression.

The delivery of immunomodulators directly into the tumor potentially harnesses the existing antigen, tumor-specific infiltrating lymphocytes, and antigen presenting cells. This can confer specificity and generate a potent systemic anti-tumor immune response with lower doses and less toxicity compared to systemic administration, in effect an in situ vaccine. Here, we test this concept using the novel combination of immunomodulators anti-CTLA4, -CD137, and -OX40. The triple combination administered intratumorally at low doses to one tumor of a dual tumor mouse model had dramatic local and systemic anti-tumor efficacy in lymphoma (A20) and solid tumor (MC38) models, consistent with an abscopal effect. The minimal effective dose was 10 µg each. The effect was dependent on CD8 T-cells. Intratumoral administration resulted in superior local and distant tumor control compared to systemic routes, supporting the in situ vaccine concept. In a single tumor A20 model, injection close to the tDLN resulted in similar efficacy as intratumoral and significantly better than targeting a non-tDLN, supporting the role of the tDLN as a viable immunotherapy target in addition to the tumor itself. Distribution studies confirmed expected concentration of antibodies in tumor and tDLN, in keeping with the anti-tumor results. Overall intratumoral or peri-tDLN administration of the novel combination of anti-CTLA4, anti-CD137, and anti-OX40, all agents in the clinic or clinical trials, demonstrates potent systemic anti-tumor effects. This immunotherapeutic combination is promising for future clinical development via both these safe and highly efficacious routes of administration.

Targets, Toxins, and T Cells--a Review of New Monoclonal Antibodies in the Treatment of Peripheral T Cell Lymphomas.

The peripheral T cell lymphomas (PTCLs) are a heterogeneous group of neoplasms for which standardized treatment approaches remain elusive. A number of new therapeutic agents have become available, of which monoclonal antibodies (MAbs) represent a powerful tool for targeted treatment of PTCLs. Therapeutic MAbs vary in their structure, targets, and mechanisms of action. Common mechanisms of action include antibody-dependent cell-mediated cytotoxicity, complement-dependent cytotoxicity, direct apoptosis, blocking of receptors or signaling pathways, delivery of cytotoxic agents to tumor cells, and binding to and blocking biologically active molecules. This review will focus on recent published evidence for the various MAbs used in the treatment of PTCLs. The results overall have been very promising, and the future will see more trials with these antibodies alone and in various therapy combinations, as well as newer ones with novel modifications, conjugates, and targets.

Targeting CD137 enhances the efficacy of cetuximab.

Treatment with cetuximab, an EGFR-targeting IgG1 mAb, results in beneficial, yet limited, clinical improvement for patients with head and neck (HN) cancer as well as colorectal cancer (CRC) patients with WT KRAS tumors. Antibody-dependent cell-mediated cytotoxicity (ADCC) by NK cells contributes to the efficacy of cetuximab. The costimulatory molecule CD137 (4-1BB) is expressed following NK and memory T cell activation. We found that isolated human NK cells substantially increased expression of CD137 when exposed to cetuximab-coated, EGFR-expressing HN and CRC cell lines. Furthermore, activation of CD137 with an agonistic mAb enhanced NK cell degranulation and cytotoxicity. In multiple murine xenograft models, including EGFR-expressing cancer cells, HN cells, and KRAS-WT and KRAS-mutant CRC, combined cetuximab and anti-CD137 mAb administration was synergistic and led to complete tumor resolution and prolonged survival, which was dependent on the presence of NK cells. In patients receiving cetuximab, the level of CD137 on circulating and intratumoral NK cells was dependent on postcetuximab time and host FcyRIIIa polymorphism. Interestingly, the increase in CD137-expressing NK cells directly correlated to an increase in EGFR-specific CD8+ T cells. These results support development of a sequential antibody approach against EGFR-expressing malignancies that first targets the tumor and then the host immune system.

A phase I study of imatinib mesylate in combination with chlorambucil in previously treated chronic lymphocytic leukemia patients.

PURPOSE: The tyrosine kinase inhibitor, imatinib, has the potential to indirectly inhibit DNA repair. This mechanism of action has been shown to mediate sensitization to chlorambucil in chronic lymphocytic leukemia (CLL). To evaluate this effect in vivo, we performed a phase I study of chlorambucil combined with imatinib in relapsed CLL patients. METHODS: The three dose levels studied included imatinib at 300, 400, or 600 mg/day. Imatinib was given on days 1-10, and chlorambucil (8 mg/m(2) daily) was given on days 3-7 of a 28-day cycle (up to 6 cycles). RESULTS: Eleven patients participated in this study. Low-grade gastrointestinal toxicities were observed in a dose-dependent manner. Forty-five percent of patients responded (two unconfirmed CRs and three PRs). Two responding patients were fludarabine refractory. The in vitro IC(50) of chlorambucil alone or in the presence of 5 µM imatinib in CLL lymphocytes correlated with the decrease in lymphocyte counts on day 15. Imatinib plasma concentrations achieved in patients were in the range of those effective in in vitro sensitization studies. CONCLUSION: The combination of chlorambucil and imatinib in patients with previously treated CLL was well tolerated and showed evidence of clinical efficacy. Based on our results, we recommend the 400 mg daily dose of imatinib on days 1-10 with 8 mg/m(3) chlorambucil on days 3-7 every 28 days as the phase II dose. This represents the first clinical trial examining the potential synergy between a tyrosine kinase inhibitor and a conventional alkylating agent for the treatment of CLL.