Abstract LB-136: IL-21-derived melanoma-reactive CTL combined with anti-CTLA4 persist, acquire central memory characteristics, and mediate tumor regression in patients with metastatic melanoma

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Adoptive transfer of melanoma-reactive CD8+ T Cells (CTL) has demonstrated antitumor activity that may be enhanced by prolonging survival of transferred T cells in vivo. CTLA4 is up-regulated on activated T cells and when engaged to its B7-ligand, delivers inhibitory signals that impede TCR signaling, IL-2 transcription, and T cell proliferation. Human anti-CTLA4 monotherapy benefits about 25% of patients (pts), but most pts likely lack a sufficiently high frequency of pre-existing melanoma-reactive T cells susceptible to CTLA4 blockade and fail to respond. We propose a combined biologic strategy involving the adoptive transfer of melanoma-reactive CTL with concurrent administration of anti-CTLA4 as a means of enhancing the in vivo CTL survival and anti-tumor effect. Autologous polyclonal CTL were generated by multimer sorting and expanding melanoma-specific CTL lines to increase the probability of infusing cells derived from central memory (Tcm), as such cells were shown to exhibit prolonged persistence and superior replicative potential in murine and non-human primate models. Ex-vivo cultures were supplemented with the γc-chain cytokine Interleukin-21 (IL-21), which has been demonstrated to promote effector CTL helper-independence and to arrest differentiation at a Tcm stage. To date, 6 pts with bulky, therapy-resistant progressive melanoma were infused with 1010/m2 polyclonal IL-21-derived CTL targeting MART1. The infusions were preceded by intravenous cyclophosphamide 300mg/m2 and followed by low-dose subcutaneous IL-2 (250,000 IU/m2 BID) x 14 days. Anti CTLA4 (ipilimumab) 3mg/kg was started on the day after the CTL infusion. Side effects included fevers and chills starting 1-2 hours post-CTL infusion and moderately erythematous maculo-papular skin rashes in all 6 patients. No unexpected or serious (grade ≥3) toxicity was observed. Persistence of the infused CTL to frequencies >2x baseline levels was documented at 6 weeks (5/5 evaluable pts) and 12 weeks (4/4 pts). 3/5 and 2/3 evaluable pts experienced stable disease by RECIST 1.1 criteria at 6 and 12 weeks respectively. One patient had a delayed response with 25% reduction in tumor mass at 12 weeks after having failed previous ipilimumab monotherapy and prior CTL therapy without CTLA4 blockade. Tracking of infused multimer+ CTL in vivo revealed acquisition of both phenotypic (CD27, CD28, CD127, CD62L and CCR7) and functional (secretion of IL-2 in response to cognate antigen) characteristics of Tcm within 12 weeks. Our preliminary results suggest polyclonal IL-21-stimulated CTL targeting melanoma in combination with Ipilmumab is safe and promotes persistent anti-tumor responses such that CTL are poised for enhanced therapeutic activity in vivo. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-136. doi:1538-7445.AM2012-LB-136