Interleukin-15 (IL-15) is a powerful immunostimulatory cytokine with a broad range of biological activities that was co-discovered in the Metabolism Branch, NCI. In contrast to IL-2, IL-15 inhibits the activation-induced cell death (AICD) of T cells and is not involved in the maintenance of CD4+CD25+ regulatory T cells that act as inhibitory checkpoints on the immune response. IL-15 is involved in the proliferation, differentiation and activation of CD8+ T cells and NK cells and the maintenance of long-term central memory CD8+ T cells. In preclinical studies, vaccines expressing IL-15 induced long-lasting, high-avidity CD8+ cytotoxic T lymphocyte (CTL)-mediated immunity, whereas the immunity mediated by IL-2-expressing vaccines was short lived. IL-15 can overcome that lack of CD4+ T-help to induce both CD8+ CTL and humoral immune responses. IL-15 was shown to be highly active against a number of syngeneic mouse tumor models and it is also effective in augmenting the activity of natural killer (NK) cells and CD8+ T cells in rhesus macaques, indicating that it may be active against human cancers. A phase I study of intravenous recombinant human interleukin-15 (rhIL-15) in adults with refractory metastatic malignant melanoma and metastatic renal cell cancer has been approved to begin patient accrual. The primary objectives of this trial are to determine the: 1) safety, 2) toxicity profile, 3) dose-limiting toxicity, and 4) maximum tolerated dose of rhIL-15 administered as a single daily intravenous infusion for 12 consecutive days in subjects with metastatic malignant melanoma and renal cell carcinoma. A clinical trial to evaluate the T-cell receptor gamma alternate reading frame protein (TARP), a novel protein that is expressed in patients with prostate cancer and breast cancer, has been approved for patient accrual. TARP, a 58-amino acid protein, was identified using the NCBI Expressed Sequence Tags database. TARP is expressed both by normal and malignant prostate cancer tissue and more than 90 percent of prostate cancer specimens are positive for TARP expression. An alternative method of vaccination is also being evaluated in patients with lung cancer. Through a CRADA with NewLink Genetics (Ames, IA), a clinical vaccine trial was initiated using allogeneic lung cancer cells that have been genetically altered with a Moloney murine retrovirus vector to express alpha (1,3) galactosyl transferase (alpha-GT) for patients with advanced non-small cell lung cancer. This trial has completed phase I and II components. In phase I, cohorts of patients received intradermal injections totaling 3, 10, 30, or 100 x 10E+6 vaccine cells every 4-weeks x 4;or 500 x 10E+6 vaccine cells followed by 300 x 10E+6 vaccine cells every 2-weeks x 7. In Phase II, eligible patients received injections totaling 300 x 10E+6 vaccine cells every 2 weeks for 8 doses. Adverse events were assessed using CTC v3.0 and response was determined using modified RECIST criteria. Serum anti-AGal antibody titers were monitored and ELISPOT assays for the induction of interferon gamma and interleukin-5 by PBMC were examined pre- and post-vaccination. Vaccine site biopsies were performed. Seventeen patients were treated in phase I. No vaccine-related serious adverse events (AE) were observed. Related AEs were less than or equal to CTC grade 2 and included injection site pain/discomfort, local hyperpigmentation, skin reactions, local urticaria, arthralgias/myalgias, dyspnea, fatigue, herpes zoster, hypertension, lymphopenia and mild serum transaminitis. Six patients experienced stable disease (SD) for greater than or equal to 4.0 months (median 8.0, range, 6.0-63.1 months). In phase II, 23 patients were treated, 16 patients received one and 5 patients received two prior treatment regimens and 2 patients had no prior treatment (one of those had surgery only). Seven patients demonstrated an SD greater than or equal to 4.0 months. Median survival for the entire group was 11.0 months (range, 2.1-35.7 months) and 23.7 months (range, 11.0-35.7 months) for patients that achieved SD. Vaccine sites demonstrated infiltration of lymphocytes, granulocytes and eosinophils. Anti-AGal titers increased in all patients, and release of interferon gamma and interleukin-5 during co-culture with vaccine parental and an unrelated NSCLC cell line was detected in some patients. Increases in anti-CEA antibodies were also detected. Antitumor vaccination using genetically altered human lung cancer cells expressing alphaGT is safe and feasible. A number of patients had prolonged SD and the median survival of vaccinated patients compared favorably to that reported in patients receiving second-line chemotherapy for relapsed or progressive advanced non-small cell lung cancer (NSCLC). Although peptide immunization with epitope-enhanced peptides reproducibly generates T cell responses in patients, tumor regression is infrequent. In addition, immune therapies in general produce long-lasting tumor regressions in only a small minority of patients. These observations suggest that there are immune mechanisms that prevent the induced immune response from producing tumor regression. A number of checkpoint controls in immune regulation can be targeted, including transforming growth factor-beta (TGF-beta), CTLA-4, PD1 and the CD4+, CD25+ T cell regulatory population. A clinical trial using an antibody that binds to and inhibits TGF-beta has been completed. Responses have been observed in patients with melanoma and toxicity has been minimal. We are currently evaluating the activity of MDX-010, a fully human antibody that binds to CTLA-4, to eliminate this checkpoint in regulation of T cell expansion. Responses have been observed in 5 of 20 patients with follicular lymphoma and tumor regression has been observed in 2 patients with refractory Hodgkins lymphoma. In a phase I trial (06-C-0200) we have been studying the safety, toxicity and antitumor activity of GC1008, a human monoclonal antibody targeting TGF-beta in patients with metastatic malignant melanoma and renal cell carcinoma. TGF-beta is a pleiotrophic cytokine that normally helps to maintains cellular homeostasis;however, in cancers TGF-beta promotes tumor cell proliferation, migration, metastasis, neoangiogenesis and suppressesion of the host antitumor immune response. Patient cohorts were treated with GC1008 doses ranging from 0.3 to 15 mg/kg. No maximum tolerated dose was determined;however, extensive eruptive keratoacanthomas were observed in 2 patients and a squamous cell carcinoma of the skin in a third patient. There was one very good partial response in a patient with extensive cutaneous melanoma, two mixed responses were seen and two patients with stable disease were observed. This trial has been extended at the highest dose (15 mg/kg) in an effort to achieve a better estimate of the incidence of keratoacanthomas and other skin events associated with this agent. No additional cases were noted. Future clinical studies are planned using GC1008 in melanoma. This study will evaluate two different dose levels of the agent to determine the optimal dose for melanoma treatment.
