Ad-ISF35 is a replication-defective adenovirus (Ad) vector that encodes ISF35, which is a potent immuno-stimulatory CD40 binding protein designed to maximize stable, high-level cell-surface expression of this molecule. ISF35 can induce expression of costimulatory and death receptor molecules on chronic lymphocytic leukemia (CLL) cells in vitro and in vivo.
Ad-ISF35 has shown to be safe and to have potential activity in two clinical studies in CLL patients, one using infusions of autologous CLL cells trasduced ex-vivo with Ad-ISF35 and the second one using a single intranodal injection of Ad-ISF35. From this second study we have observed that the maximum tolerated intranodal dose (MTD) was 3.3 × 1010 viral particles (vp) due to development of asymptomatic and transient hypophosphatemia, SGOT/AST elevation and neutropenia in some patients treated with higher doses.
Using this MTD dose (3.3 × 1010 vp), we designed a clinical study to evaluate the toxicity and efficacy of repeat doses of intranodal Ad-ISF35 administration in CLL patients. Ten patients with median age of 66 years (range 56–74, 80% male and 20% female), with progressive CLL (Rai stage III and IV) and median leukemia-cell doubling times of 6 months participated in this repeat dose intranodal administration study involving up to six biweekly injections with a fixed dose of 3.3 ×1010 vp. Intranodal Ad-ISF35 injections were done into pathologically enlarged lymph nodes accessible by palpation using ultrasound guidance.
Repeat dose intranodal administration of Ad-ISF35 was well tolerated by the majority of patients. The median number of injections was 5. One patient developed transient and asymptomatic Grade III hyponatremia after injection #4 considered to be a dose-limiting toxicity (DLT). No dose adjustments were required in any of the patients and we have not observed cumulative dose effect or long-term toxicities after a median follow up of 14 months. Other adverse events included erythema, swelling and/or pain at the site of injection and “flu-like symptoms”, which occurred primarily during the first 24 hours after each injection and were self-limited.
The majority of patients experienced >50% reduction in leukemia cell counts (70% of patients), lymphadenopathy (80% of patients) and/or splenomegaly (70% of patients) during the course of treatment. Response assessment based on IW-CLL-08 criteria showed and overall response rate of 30% with 3 patients achieving a partial response, 4 patients with stable disease and 3 patients with disease progression.
Although we have no evidence of Ad-ISF35 vector expression beyond the injected lymph node, we observed upregulation of death receptors, immune costimulatory molecules, and pro-apoptotic proteins in the circulating, non-transduced CLL cells of the treated patients suggesting a bystander effect. Cytokine expression analysis in the sera of treated patients showed increased levels of interferon-gamma and interleukin-6 beginning 8 hours after injection. In addition, we observed evidence of antibody production against Ad-ISF35 with the ability in some cases to neutralize vector transduction in vitro. However, we did not see antibody formation against human CD154.
In summary, we found that repeat dose Ad-ISF35 intranodal administration via direct injection in patients with CLL was well tolerated and had systemic biologic and clinical activity that appears to be mediated by the effect of non-transduced bystander cells. These data suggest that intranodal administration of Ad-ISF35 may be safe and potentially effective in the treatment of patients with CLL or other B-cell lymphomas.
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