Phase I/II Study of Ipilimumab (MDX-010), an Anti-CTLA-4 Monoclonal Antibody, in Patients with Follicular Non-Hodgkin Lymphoma.

Background: Follicular lymphoma is a B-cell malignancy in which tumor-immune system interactions have the potential to profoundly influence malignant cell growth. Cytotoxic T lymphocyte antigen 4 (CTLA-4) is a negative regulator of T cell activation that can serve to dampen anti-tumor immune responses. Administration of blocking anti-CTLA-4 monoclonal antibodies has been shown to improve host resistance to immunogenic tumors and amplify the anti-tumor effects of cancer vaccines in a variety of mouse tumor models. Recently, the anti-CTLA-4 antibody ipilimumab (MDX-010) has been shown to have significant clinical activity against melanoma, prostate, and ovarian cancers, with clinical responses associated with autoimmune events.

Methods: We have therefore initiated a phase I/II trial of ipilimumab, a blocking fully human monoclonal antibody to CTLA-4, in patients with relapsed or refractory follicular lymphoma (grade 1 or 2). Enrollment is stratified into 2 cohorts, with half of patients required to be previously treated with a lymphoma vaccine (idiotype or other). It is hypothesized that previously vaccinated subjects are more likely to have anti-lymphoma T cells amenable to activation by an anti-CTLA-4 antibody. Study objectives include characterization of drug safety, immunologic activity and potential clinical efficacy. Treatment consists of MDX-010 at 3 mg/kg, then monthly at 1 mg/kg x 3, with plans to escalate to 3 mg/kg monthly x 4 if tolerated.

Results: To date, 12 patients have been treated and accrual to the first dose level has been completed. All patients were previously treated and the median number of prior treatment regimens was 2 (range 1–4). Eight patients had previously received rituximab and 6 patients had received prior anti-idiotype vaccines. Nine patients have completed therapy with ipilimumab and 3 patients are still receiving treatment. Ipilimumab was generally well tolerated and the most common adverse events attributed to ipilimumab in the first 9 patients include diarrhea (grade 3–3 patients, grade 1–1 patient), abdominal pain (grade 2–4, grade 1–2), anorexia (grade 2-1, grade 1 – 2), fatigue (grade 2 -2, grade 1–3, and neutropenia (grade 3-1, grade 1– 2). Among 9 patients evaluable for clinical response, 1 previously vaccinated patient had partial regression of multiple abdominal nodes, ongoing at 10+ months. T cell proliferative responses to the recall antigens tetanus toxoid and keyhole limpet hemocycanin (in idiotype-vaccinated cases) were measured pre- and post-ipilimumab. In 3 of 5 cases tested, including the patient with a clinical response, T cell proliferation to KLH and/or tetanus was significantly increased (>2-fold) one month after initiation of ipilimumab, implying expansion and/or activation of the memory T cell pool.

Conclusions: Blockade of CTLA-4 signaling using ipilimumab is well tolerated at the dose used thus far in this ongoing study and has anti-tumor activity in patients with follicular B-cell lymphoma. Further evaluation of the efficacy of ipilimumab at this and higher doses is therefore warranted.