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 NK cells and CD8+ T-cells in rhesus macaques indicating that it may be active against human cancers. A protocol entitled, 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 reviewed and 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) the 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. Secondary objectives include determination of (1) rhIL-15 pharmacokinetics;(2) rhIL-15 immunogenicity;(3) characterization of the effects of rhIL-15 on the fractions and absolute numbers of circulating NK cells and CD45RO+CD8+ T cells;(4) determination of rhIL-15 effects on the plasma levels of pro-inflammatory cytokines such as IL-6 and TNF;and (5) to estimate the antitumor activity of rhIL-15 in patients with metastatic malignant melanoma and renal cell carcinoma. Once this trial is completed, we anticipate proceeding with phase II studies of rhIL-15 as single agent or as part of a combination therapy. Attractive study diseases for rhIL-15 include melanoma and renal cell carcinoma because these tumors have a component of immunological responsiveness as evidence by spontaneous regressions and sensitivity to agents such as IL-2, interferon and immune checkpoint modulation (e.g., anti-CTLA-4, anti-TGF-, etc). Studies in the Waldmann laboratory have demonstrated that the antitumor activity of IL-15 is enhanced by the co-expression of IL-15Rand trans-presentation of IL-15. Another potential target disease based on enhanced trans-presentation may be lung cancer or pulmonary metastatic disease because of the constitutive expression of IL-15Rin lung tissue. As another approach to exploiting the enhanced activity of IL-15, combinations of rhIL-15 and interferon, CD40, or agonist anti-CD40 antibodies may be a way to increase expression of IL-15Rand enhance the antitumor activity of IL-15.67-69 An ultimate goal will be to combine rhIL-15 as part of a vaccine strategy against tumor antigens or HIV based on our preclinical results vaccinating against tumor antigens such as neu. 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, with more than 90% of prostate cancer specimens positive for TARP expression. An alternative method of vaccination is also undergoing evaluation in patients with lung cancer. Through a CRADA collaboration 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 testing and the phase II component has been initiated. Phase I has been completed with no serious or dose-limiting toxicity observed, and Phase II has accrued 19 patients to date. Approximately a quarter of patients have demonstrated prolonged stable disease of their lung cancers. A more than 8-fold increase in serum anti-alpha-gal antibody titers has been demonstrated in all patients (phase I). Patients have shown interferon-gamma ELISPOT responses to the unmodified parental cell lines used in the vaccine. More importantly ELISPOT responses observed against non-small cell lung cancer cell lines not used as part of the vaccine suggest the ability of this approach to generate a more generalized anti-lung cancer immune response. 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 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 observed in two 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 transforming growth factor-beta (TGF-) 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. Cohorts of patient 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) to 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 combination with chemotherapy and antitumor vaccines in melanoma, breast and prostate cancer.
